全文获取类型
收费全文 | 16379篇 |
免费 | 435篇 |
国内免费 | 137篇 |
专业分类
化学 | 11312篇 |
晶体学 | 134篇 |
力学 | 510篇 |
数学 | 2509篇 |
物理学 | 2486篇 |
出版年
2022年 | 134篇 |
2021年 | 152篇 |
2020年 | 218篇 |
2019年 | 200篇 |
2018年 | 185篇 |
2017年 | 149篇 |
2016年 | 313篇 |
2015年 | 269篇 |
2014年 | 311篇 |
2013年 | 780篇 |
2012年 | 760篇 |
2011年 | 1037篇 |
2010年 | 485篇 |
2009年 | 437篇 |
2008年 | 844篇 |
2007年 | 879篇 |
2006年 | 929篇 |
2005年 | 854篇 |
2004年 | 779篇 |
2003年 | 710篇 |
2002年 | 682篇 |
2001年 | 227篇 |
2000年 | 198篇 |
1999年 | 159篇 |
1998年 | 190篇 |
1997年 | 199篇 |
1996年 | 232篇 |
1995年 | 179篇 |
1994年 | 184篇 |
1993年 | 147篇 |
1992年 | 151篇 |
1991年 | 157篇 |
1990年 | 131篇 |
1989年 | 113篇 |
1988年 | 147篇 |
1987年 | 142篇 |
1986年 | 107篇 |
1985年 | 212篇 |
1984年 | 234篇 |
1983年 | 169篇 |
1982年 | 241篇 |
1981年 | 220篇 |
1980年 | 224篇 |
1979年 | 206篇 |
1978年 | 198篇 |
1977年 | 181篇 |
1976年 | 182篇 |
1975年 | 152篇 |
1974年 | 162篇 |
1973年 | 155篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
James V. Crivello Umut Bulut 《Journal of polymer science. Part A, Polymer chemistry》2005,43(21):5217-5231
Curcumin, a naturally occurring, intensely yellow dye extracted from the spice turmeric, is an efficient photosensitizer for diaryliodonium salt photoinitiators at wavelengths ranging from 340 to 535 nm. With curcumin as a photosensitizer, it is possible to carry out the cationic photopolymerization of a wide variety of epoxide, oxetane, and vinyl monomers with long‐wavelength UV and visible light. An example of the photopolymerization of an epoxide monomer with ambient solar irradiation is provided. Several other curcumin analogues were synthesized, and their use as photosensitizers is examined. With such photosensitizers, the range of spectral sensitivity can be extended well into the visible region of the electromagnetic spectrum. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5217–5231, 2005 相似文献
32.
33.
A solution to Einstein's field equations is presented that represents a Petrov type II electromagnetic null field with one Killing vector. This solution generalizes a vacuum solution previously discovered by Hoenselaers. The solution was found by the peculiar method of generalizing a member of this class inadvertently discovered by making a typing error when checking the vacuum solution with the computer algebra system SHEEP. 相似文献
34.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields. 相似文献
35.
4-Amino-3-arylisothiazole-5-carboxylate esters are converted to the corresponding desamino, chloro, bromo, and iodo esters by processes involving nonaqueous diazotization. These related procedures open up the possibility for the conversion of readily available heterocyclic ortho-amino esters and nitriles to related heterocyclic derivatives, which are not easily obtained by alternate routes. 相似文献
36.
Let E
n:y
2=x
3−n
2
x denote the family of congruent number elliptic curves. Feng and Xiong (2004) equate the nontriviality of the Selmer groups
associated with E
n
to the presence of certain types of partitions of graphs associated with the prime factorization of n. In this paper, we extend the ideas of Feng and Xiong in order to compute the Selmer groups of E
n.
2000 Mathematics Subject Classification Primary—11G05; Secondary—14H52, 14H25, 05C90 相似文献
37.
38.
By optimizing pump power ratio between 1st order backward pump and 2nd order forward pump on discrete Raman amplifier, we demonstrated over 2dB noise figure improvement without excessive non-linearity degradation. 相似文献
39.
Whereas glucose oxidase and related proteins are encapsulated readily in silica sol–gels, α-hydroxy enzymes such as lactate
oxidase (LOx), are reported to be damaged by electrostatic interaction with these matrices. Based on a previous report, poly(ethyleneimine),
PEI, was evaluated as a protecting compound under conditions suited to analytical measurements. With LOx and PEI co-encapsulated
in a silica sol–gel, the enzyme retained 62% of its initial activity after 20 days. In the absence of PEI, activity was lost
during the processing. Batch analytical measurements with enzyme-doped sol–gel yielded a linear response over the range 0.5–2.0 mM
lactate and a detection limit of 0.03 mM lactate. Both simple incorporation of LOx in a silica sol–gel and an alternative
protection method, blocking the ion-exchange sites on silica with La(III), failed. These negative results supported the hypothesis
that the efficacy of PEI was related to its formation of a protective sheath around the enzyme.
Author for correspondence. E-mail: coxja@muohio.edu
Received July 29, 2002; accepted December 15, 2002
Published online May 19, 2003 相似文献
40.
Douglas R. White Jason Owen-Smith James Moody Walter W. Powell 《Computational & Mathematical Organization Theory》2004,10(1):95-117
Social action is situated in fields that are simultaneously composed of interpersonal ties and relations among organizations, which are both usefully characterized as social networks. We introduce a novel approach to distinguishing different network macro-structures in terms of cohesive subsets and their overlaps. We develop a vocabulary that relates different forms of network cohesion to field properties as opposed to organizational constraints on ties and structures. We illustrate differences in probabilistic attachment processes in network evolution that link on the one hand to organizational constraints versus field properties and to cohesive network topologies on the other. This allows us to identify a set of important new micro-macro linkages between local behavior in networks and global network properties. The analytic strategy thus puts in place a methodology for Predictive Social Cohesion theory to be developed and tested in the context of informal and formal organizations and organizational fields. We also show how organizations and fields combine at different scales of cohesive depth and cohesive breadth. Operational measures and results are illustrated for three organizational examples, and analysis of these cases suggests that different structures of cohesive subsets and overlaps may be predictive in organizational contexts and similarly for the larger fields in which they are embedded. Useful predictions may also be based on feedback from level of cohesion in the larger field back to organizations, conditioned on the level of multiconnectivity to the field. 相似文献