全文获取类型
收费全文 | 12728篇 |
免费 | 137篇 |
国内免费 | 37篇 |
专业分类
教育 | 8685篇 |
科学研究 | 1609篇 |
各国文化 | 147篇 |
体育 | 855篇 |
综合类 | 74篇 |
文化理论 | 109篇 |
信息传播 | 1423篇 |
出版年
2021年 | 122篇 |
2020年 | 184篇 |
2019年 | 218篇 |
2018年 | 252篇 |
2017年 | 315篇 |
2016年 | 264篇 |
2015年 | 214篇 |
2014年 | 312篇 |
2013年 | 2427篇 |
2012年 | 289篇 |
2011年 | 290篇 |
2010年 | 266篇 |
2009年 | 253篇 |
2008年 | 296篇 |
2007年 | 278篇 |
2006年 | 257篇 |
2005年 | 210篇 |
2004年 | 200篇 |
2003年 | 178篇 |
2002年 | 164篇 |
2001年 | 162篇 |
2000年 | 181篇 |
1999年 | 150篇 |
1998年 | 104篇 |
1997年 | 99篇 |
1996年 | 108篇 |
1995年 | 89篇 |
1994年 | 118篇 |
1993年 | 126篇 |
1992年 | 153篇 |
1991年 | 160篇 |
1990年 | 157篇 |
1989年 | 166篇 |
1988年 | 131篇 |
1987年 | 154篇 |
1986年 | 152篇 |
1985年 | 173篇 |
1984年 | 163篇 |
1983年 | 159篇 |
1982年 | 126篇 |
1981年 | 136篇 |
1980年 | 112篇 |
1979年 | 158篇 |
1978年 | 158篇 |
1977年 | 114篇 |
1976年 | 116篇 |
1975年 | 103篇 |
1974年 | 88篇 |
1973年 | 104篇 |
1972年 | 87篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
961.
The decade of the 1970s heralded a major research effort into mariculture of economically important red and brown seaweeds. Limited and declining natural populations, lack of synthetic substitutes for the phycocolloids, and their upwardly spiralling costs have emphasized the need for more research in this area. Algal mariculture is now technically and scientifically feasible, but the economic realities are still undetermined. This article examines what is known about seaweed mariculture and discusses where future research efforts must go. 相似文献
962.
Contingency in innovation and the role of national systems: taxol and taxotère in the USA and France
A very rich collection of archival material is used to compare two anticancer drugs commercialised by multinationals collaborating with public sector research, one in the USA and one in France. The framework of national innovation systems is used to compare the innovative environments for each development (different institutional structures, research programmes, financing, industry-academic-government relationships, environmental concern, and intellectual property regimes). The empirical work was able to bring out the nuances and subtleties of each environment, the way in which innovation took place in practice, and some striking differences from what stereotypical accounts of innovation in each country would have suggested. 相似文献
963.
Technological transitions as evolutionary reconfiguration processes: a multi-level perspective and a case-study 总被引:6,自引:0,他引:6
This paper addresses the question of how technological transitions (TT) come about? Are there particular patterns and mechanisms in transition processes? TT are defined as major, long-term technological changes in the way societal functions are fulfilled. TT do not only involve changes in technology, but also changes in user practices, regulation, industrial networks, infrastructure, and symbolic meaning or culture. This paper practices ‘appreciative theory’ [R.R. Nelson, S.G. Winter, An Evolutionary Theory of Economic Change, Bellknap Press, Cambridge, MA, 1982] and brings together insights from evolutionary economics and technology studies. This results in a multi-level perspective on TT where two views of the evolution are combined: (i) evolution as a process of variation, selection and retention, (ii) evolution as a process of unfolding and reconfiguration. The perspective is empirically illustrated with a qualitative longitudinal case-study, the transition from sailing ships to steamships, 1780–1900. Three particular mechanisms in TT are described: niche-cumulation, technological add-on and hybridisation, riding along with market growth. 相似文献
964.
In this essay, I argue that popular entertainment can be understood in terms of Husserl’s concepts of epochē, reduction and constitution, and, conversely, that epochē, reduction and constitution can be explicated in terms of popular entertainment. To this end I use Husserl’s concepts to explicate and reflect upon the psychological and ethical effects of an exemplary instance of entertainment, the renowned Star Trek episode entitled “The Measure of a Man.” The importance of such an exercise is twofold: (1) to demonstrate, once again, the fecundity of the methodological procedures Husserl bequeathed to us; more than any other philosopher, he tapped into the fundamental manners in which we lose, make and remake the meanings of our lives; and (2) to demonstrate how popular entertainment, similarly, plays a central role in the making and remaking of the meanings of our lives. If my zig-zag procedure between Husserl’s philosophy and popular entertainment is productive and cogent, in addition to elucidating Husserl’s philosophy, it will demonstrate the reality-generating potency and the constitutive power of entertainment in the contemporary world. Entertainment, via ourselves, has become the primary producer of the meanings via which consciousness constitutes the world. 相似文献
965.
966.
A performance index consisting of a Chebyshev absolute maximum functional plus terminal and integral cost is applied to the optimal control of dynamical systems. First-order necessary conditions are derived for a large class of systems. Utilizing the necessary conditions, analytic examples are worked in demonstrating many of the properties of this class of systems. 相似文献
967.
Maddy and Mathematics: Naturalism or Not 总被引:1,自引:0,他引:1
Penelope Maddy advances a purportedly naturalistic account ofmathematical methodology which might be taken to answer thequestion `What justifies axioms of set theory?' I argue thather account fails both to adequately answer this question andto be naturalistic. Further, the way in which it fails to answerthe question deprives it of an analog to one of the chief attractionsof naturalism. Naturalism is attractive to naturalists andnonnaturalists alike because it explains the reliability ofscientific practice. Maddy's account, on the other hand, appearsto be unable to similarly explain the reliability of mathematicalpractice without violating one of its central tenets.
- 1 Introduction
- 2 Mathematical Naturalism
- 3 Desiderata and the attractionof naturalism
- 4 Assessment: Naturalism and names
- 4.1 Takingnaturalismseriously
- 4.2 Second philosophy (orwhat's in a name)
- 5 A way out?
- 6 Or out of the way?
- 2 Mathematical Naturalism
968.
Until comparatively recently the purification of sea or brackish water depended largely on some form of distillation. In recent years, however, a number of industrial concerns have directed increasing attention to processes depending on reverse osmosis. A number of large plants have been installed and this article reviews the present state of reverse osmosis technology and the factors determining its efficiency. Its advantages include its relatively low fuel consumption, and in this respect further substantial savings are in prospect. 相似文献
969.
Dara J. Glasser Kenneth W. Goodman Norman G. Einspruch 《Ethics and Information Technology》2007,9(2):101-109
Radio Frequency Identification (RFID) systems identify and track objects, animals and, in principle, people. The ability to
gather information obtained by tracking consumer goods, government documents, monetary transactions and human beings raises
a number of interesting and important privacy issues. Moreover, RFID systems pose an ensemble of other ethical challenges
related to appropriate uses and users of such systems. This paper reviews a number of RFID applications with the intention
of identifying the technology’s benefits and possible misuses. We offer an overview and discussion of the most important ethical
issues concerning RFID, and describes and examine some methods of protecting privacy.
Norman G. Einspruch serves as a consultant to several high-technology companies, one of which is in the RFID components and
systems business. 相似文献
970.
This article reports original research examining characteristics of the active followers of the American animal rights movement. Typical respondents were Caucasian, highly educated urban professional women approximately thirty years old with a median income of $33,000 (1989). Most activists think of themselves as Democrats or as Independents, and have moderate to liberal political views. They were often suspicious of science and made no distinction between basic and applied science, or public versus private animal-based research. The research suggests that animal rights activism is part of a symbolic manifestation of egalitarian social and political views concerning scientific and technological change. 相似文献