首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   63篇
  免费   1篇
  国内免费   28篇
教育   44篇
科学研究   38篇
各国文化   3篇
体育   2篇
信息传播   5篇
  2021年   2篇
  2020年   6篇
  2019年   2篇
  2018年   3篇
  2017年   1篇
  2016年   4篇
  2015年   2篇
  2014年   3篇
  2013年   6篇
  2012年   2篇
  2011年   5篇
  2010年   2篇
  2009年   4篇
  2007年   2篇
  2006年   4篇
  2005年   5篇
  2004年   3篇
  2003年   2篇
  2001年   1篇
  2000年   1篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   2篇
  1993年   2篇
  1992年   1篇
  1991年   2篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   2篇
  1985年   1篇
  1984年   3篇
  1983年   1篇
  1982年   1篇
  1981年   2篇
  1979年   3篇
  1978年   2篇
  1966年   1篇
排序方式: 共有92条查询结果,搜索用时 31 毫秒
71.
After having examined all specimens of the genus Prenanthes L. of Compositae in the Herbarium of Institute of Botany, Academia Sinica, I find that the classic concept on the genus Prenanthes established by G. Bentham in 1873 has not been held exactly by some of Euro- pean, American, Japanese and Chinese botanists. For example, W. B. Hemsley, S. T. Dunn, A. Franchet, S. Kitamura and C. C. Chang placed plants from China which belong to other groups into the genus; I also find that the classic concept of the genus is not clear.  The present paper makes a revision not only on the classic concept of the genus, but also on its concept assumed by the above-mentionded botanists.      With the combination of numerous (25-35), white or yellow ligular florets, numerous ribs of achenes, Prenanthes alba L. (Nabalus albus (L.) Shih, comb. nov.) is distinctly different from Prenanthes purpurea L., which has the combination of purple, few (5-15) ligular flo- rests and few ribs of achenes.  Nabalus Cass., as a genus established early (1825) by H. Cassini, should be restored.  It is not reasonable to treat Nabalus as a subgenus (E. B. Babcock et al. 1947) or a section (S. Kitamura, 1956) or as a synonym (G. Bentham, 1983) of the genus Preanathes L.       The present author recognizes seven species in the new revised genus  Prenanthes L.  in China, 4 of which are described as new.  In the genus Nabalus Cass.  only one species, N. ochroleuca Maxim., is distributed in Northeast China.       As Lactuca melanantha Franch. (1895), Prenanthes henryi Dunn (1903), P. glandulosa Dunn (1903), Lactuca triflora Hemsl. (1888) (it was transferred to Prenanthes L. by C. C. Chang in 1934), Prenanthes formosana Kitam. (1934) and P. wilsoni Chang (1934) all have campanulate involucres, purple phyllaries, purple dorsi-ventrally compressed achenes, longitu- dinal rids 6-9 on each side of achene truncate and beakless at its apex and pilose tubes of co- rollae, they should be placed neither into the genus Prenanthes with obtusely tri-or pentagonous, subterete achenes and glabrous tubes of corollae, nor into the genus Lactuca with beak achenes. Besides the above-mentioned species misnamed by some of foreign and Chinese botanists, 6 other species also have the same structure in achenes and corollae.  Evidently, they fall into a new genus with the name Notoseris Shih.       The new genus Notoseris Shih of the tribe Lactuceae of Compositae seems to be more re- miniscent of Lactuca L. than of Prenanthes L. emend.       All the 12 species of the genus Notoseris Shih are endemic to China and distributed in the area of south of Yantze River. Of them 6 are new combinations and 6 are described as new.  相似文献   
72.
本文是对中国-喜马拉雅地区的原莴苣属植物提出的分类订正。是笔者前一篇文章《莴苣属订正 及亚洲大陆菊科植物二新属》的续篇。文中建立了两个新属,即毛鳞菊属Chaetoseris Shih和细莴苣属Stenoseris Shih;文末及文中提供了本文所涉及的一些属种的分属和分种检索表。  相似文献   
73.
Having mixed extremely various  patterns of achenes  for a  long time in the genus Lactuca L., especially showed in the classification of it on the mainland of Asia, Lactuca  L.,  the  primary  unnatural genus,  becomes more nuclear in its limit.   The present paper makes a revision to attempt providing a clear cline between Lactuca L. and its relative genera.      On my opinion, only plants, represented by Lactuca sativa L., which have ovoid capitu- lum during its fruiting, numerous (7-25), yellow ligular florets and longitudinal 1-10 ribs or striae on each side of achenes, acute into filiform beak at its apex, should be defined as Lactuca L.      In view of the present concept of Lactuca L.,   another group of plants, embodied by Lactuca indica L., having its broadening, thin winged-margin of, 1-3 striae on each side of achenes,  black, dorsi-ventral compressed, acute into thick and short beak at its apex, evident- ly, should not be placed into Lactuca L., but be regarded as genus, i.e. Pterocypsela Shih, gen. nov. Pterocypsela Shih distributes in Eastern and southern Asia, where Lactuca L. does   not occur.  In China there is all of species, seven species, of Pterocypsela Shih.  They are P.   raddeana (Maxim.) Shih, P. indica (L.) Shih, P. elata (Hemsl.) Shih P. lacciniata (Houtt.)   Shih, P. triangulata (Maxim.) Shih, P. sonchus (Lévl.)  Shih and P. formosana  (Maxim.)   Shih, But in Mediterranean regions and Middle and Western Asia mainly distributes Lactu-   ca L., in which there are only seven species from western China, Xijiang autonomic district.   They are L. dolichophylla Kitam., L. sativa L., L. altaica Fisch. et Mey., L. serriola Torner,   L. dissecta Don, L. auriculata DC. and L. undulata Ledb.          With the combination of violet-purple ligular florets  non-ovoid  capitulum  during  its   fruiting, a little thick achenes, acuminate into longer. or short beak at its apex and 4-6 ribs   on each side of it, Mulgedium tataricum (L.) DC. is evidently different from Lactuca sativa L.   with combination of ovoid capitulum during its fruiting, yellow ligular florets and compres-  sed achenes, acute into filiform beak at its apex.  There seems to be no point in refusing Mu-  lgedium Cass. as a genus.  Strictly speak, Mulgedium Cass. seems to be reminiscent of Para-  prenanthes Chang (see bellow) without beak at the apex of its achenes.  In Hengduan moun-  tains and mountain range of Himalayas M. tataricum  (L.)  DC. discoveries its relative par-  tners. They are M. bracteatum (Mook. f. ex. C. B. Clarke) Shih, M. lessertianum (Wall. ex  C. B. Clarke) DC., M. monocephalum (Chang) Shih, M. umbrosum (Dunn) Shih, M. meridi-  onale Shih and M. polypodifolium (Franch.) Shih.         Having broadering and thickening margin and 4-7 striae on each side of achenes, grey,  dorsi-ventral compressed, truncate and beakless at its apex, Lactuca sibirica (L.) Benth. ex  Maxim.  (Sonchus sibiricus L.) is not only different from Lactuca sativa L. with the combi-  nation of yellow ligular florets and filiform beak at apex of its achenes, but also from the  genus Mulgedium Cass. with beak at apex of its achenes.  Therefore, Lagedium Sojak, establi-  shed by J. Sojak (1961), should be restored.  It should be point out that Lagedium Sojak is  monotypic genus excluding Mulgedium tataricum (L.) DC. with beak at the apex of its ache-  nes, non-marginated.   Lagedium Sojak widely distributes  in temperate  and  frigid  zone  of  northern hemisphere.  In our country, Lagedium sibiricum (L.) Sojak, sole species of the ge- nus, restricts its northeast region.        Paraprenanthes Chang, the new genus, established by Ch. Ch. Chang (1950) based on La- ctuca sororia Miq. and Lactuca yunnanensis Franch.  seems to be a distinct genus.  This ge- nus is characterized by 4-6 ribs on each side of achenes, black, fusiform, a little thick and beakless at its apex.  Besides above-mentioned two species, assigned by Chang, in forest of tro- pic and subtropic zones on the mainland of Asia there are many species with same structure in achenes like L. sororia Miq. and L. yunnanensis Franch.  The genus Paraprenanthes Chang seems to be reminiscants of Mulgedium Cass. and Lagedium Sojak, but differs from the former in its beakless achenes, from the later in its non-marginated  achenes  and 4-6 ribs on  each side of it.  In our country, there are all species of the genus known in the tropic and sub- tropic zones on the mainland of Asia.  They are P. sororia (Miq.) Shih, P. yunnanensis (Fra- nch.) Shih, P. longiloba Ling et Shih, sp. nov., P. heptontha Shih et D. J. Liou, sp. nov., P. prenanthoides (Hemsl.) Shih, P. pilipes (Migo) Shih, P. thirionii (Lévl.) Shih, P. sylvicola Shih., sp. nov., P. multiformis Shih, sp. nov., P. auriculiformis Shih, sp. nov. and P. sagitti- formis Shih, sp. nov.  相似文献   
74.
本文是对菊科莴苣属Lactuca L. 的分类订正, 文中起用了乳苣属Mulgedium Cass.和山   莴苣属Lagedium Sojak两个较老的属名, 建立了二个新属,即翅果菊属Ptrocypsela Shih与假   福王草属Paraprenathes Chang. 文末提供了莴苣属及邻近属以及东亚地区的有关种类的分属分种检索表。  相似文献   
75.
中国菊科春黄菊族的一个新组合   总被引:1,自引:0,他引:1  
  相似文献   
76.
77.
78.
79.
This study presents a novel approach to decant supernatant on a centrifugal platform. By manipulating the centrifugally induced pressure and the elastic deformation of the plastic lids in the decanting chamber, fixed amounts of the supernatant can be decanted into the detection chamber at lower rotational speeds. The experimental results showed that decanted volume is affected by the volume of deformation and the operating parameters. Factors that influence the decanting ratio are also discussed. This approach has the advantages of simple design and low manufacturing cost; further, it has no need of surface modification. It has been applied to on-disk separation of plasma from whole blood, and the results showed good stability and repeatability.  相似文献   
80.
INTRODUCTION The conventional design of rails uses steel clipboards and bolts to link rails, and avoids bucklingcaused by thermal expansion effect by mountingexpansion joints to solve axial restraint generated byseasonal or day-and-night temperature changes. Butthe discontinuity at the rail joints brings discomfortand noise to passengers when the train has suddenlystops or starts, during which train speed cannot beeffectively increased, rails are more easily damaged,and the cost of mainte…  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号