全文获取类型
收费全文 | 242430篇 |
免费 | 8836篇 |
国内免费 | 6287篇 |
专业分类
化学 | 139768篇 |
晶体学 | 4241篇 |
力学 | 10419篇 |
综合类 | 406篇 |
数学 | 24134篇 |
物理学 | 78585篇 |
出版年
2022年 | 2491篇 |
2021年 | 2945篇 |
2020年 | 3275篇 |
2019年 | 3537篇 |
2018年 | 3639篇 |
2017年 | 3775篇 |
2016年 | 5425篇 |
2015年 | 4268篇 |
2014年 | 6063篇 |
2013年 | 12283篇 |
2012年 | 10191篇 |
2011年 | 11785篇 |
2010年 | 8484篇 |
2009年 | 8479篇 |
2008年 | 10279篇 |
2007年 | 9654篇 |
2006年 | 9106篇 |
2005年 | 8054篇 |
2004年 | 7053篇 |
2003年 | 6348篇 |
2002年 | 6137篇 |
2001年 | 7089篇 |
2000年 | 5404篇 |
1999年 | 4185篇 |
1998年 | 3235篇 |
1997年 | 3133篇 |
1996年 | 3009篇 |
1995年 | 2757篇 |
1994年 | 2650篇 |
1993年 | 2418篇 |
1992年 | 3028篇 |
1991年 | 2902篇 |
1990年 | 2823篇 |
1989年 | 2794篇 |
1988年 | 2805篇 |
1987年 | 2804篇 |
1986年 | 2680篇 |
1985年 | 3369篇 |
1984年 | 3358篇 |
1983年 | 2634篇 |
1982年 | 2753篇 |
1981年 | 2801篇 |
1980年 | 2552篇 |
1979年 | 2914篇 |
1978年 | 2898篇 |
1977年 | 3004篇 |
1976年 | 2845篇 |
1975年 | 2568篇 |
1974年 | 2528篇 |
1973年 | 2481篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
82.
83.
Inspired by the recent work [HHM03], we prove two stability results for compact Riemannian manifolds with nonzero parallel spinors. Our first result says that Ricci flat metrics which also admit nonzero parallel spinors are stable (in the direction of changes in conformal structures) as the critical points of the total scalar curvature functional. Our second result, which is a local version of the first one, shows that any metric of positive scalar curvature cannot lie too close to a metric with nonzero parallel spinor. We also prove a rigidity result for special holonomy metrics. In the case of SU(m) holonomy, the rigidity result implies that scalar flat deformations of Calabi-Yau metric must be Calabi-Yau. Finally we explore the connection with a positive mass theorem of [D03], which presents another approach to proving these stability and rigidity results. Dedicated to Jeff Cheeger for his sixtieth birthday 相似文献
84.
Andrei K. Lerner 《Archiv der Mathematik》2005,85(6):538-543
We show that the Hardy-Littlewood maximal operator and a class of Calderón-Zygmund singular integrals satisfy the strong type
modular inequality in variable Lp spaces if and only if the variable exponent p(x) ∼ const.
Received: 15 September 2004 相似文献
85.
86.
87.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc. 相似文献
88.
K. C. Kumara Swamy E. Balaraman M. Phani Pavan N. N. Bhuvan Kumar K. Praveen Kumar N. Satish Kumar 《Journal of Chemical Sciences》2006,118(6):495-501
The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated
acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature
of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction. 相似文献
89.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
90.
We study the relation between the cohomology of general linear and symmetric groups and their respective quantizations, using Schur algebras and standard homological techniques to build appropriate spectral sequences. As our methods fit inside a much more general context within the theory of finite-dimensional algebras, we develop our results first in that general setting, and then specialize to the above situations. From this we obtain new proofs of several known results in modular representation theory of symmetric groups. Moreover, we reduce certain questions about computing extensions for symmetric groups and Hecke algebras to questions about extensions for general linear groups and their quantizations. 相似文献