全文获取类型
收费全文 | 1576篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
化学 | 943篇 |
晶体学 | 8篇 |
力学 | 71篇 |
数学 | 269篇 |
物理学 | 358篇 |
出版年
2023年 | 18篇 |
2022年 | 66篇 |
2021年 | 69篇 |
2020年 | 46篇 |
2019年 | 56篇 |
2018年 | 45篇 |
2017年 | 36篇 |
2016年 | 77篇 |
2015年 | 67篇 |
2014年 | 50篇 |
2013年 | 102篇 |
2012年 | 121篇 |
2011年 | 126篇 |
2010年 | 65篇 |
2009年 | 42篇 |
2008年 | 81篇 |
2007年 | 76篇 |
2006年 | 84篇 |
2005年 | 60篇 |
2004年 | 56篇 |
2003年 | 56篇 |
2002年 | 34篇 |
2001年 | 21篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 8篇 |
1996年 | 7篇 |
1995年 | 11篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 5篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 9篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1971年 | 4篇 |
1912年 | 1篇 |
1903年 | 1篇 |
1877年 | 1篇 |
排序方式: 共有1649条查询结果,搜索用时 15 毫秒
1.
2.
Giorgia Scetta Jianzhu Ju Nathan Selles Patrick Heuillet Matteo Ciccotti Costantino Creton 《Journal of polymer science. Part A, Polymer chemistry》2021,59(8):685-696
We investigate the cyclic mechanical behavior in uniaxial tension of three different commercial thermoplastic polyurethane elastomers (TPU) often considered as a sustainable replacement for common filled elastomers. All TPU have similar hard segment contents and linear moduli but sensibly different large strain properties as shown by X-ray analysis. Despite these differences, we found a stiffening effect after conditioning in step cyclic loading which greatly differs from the common softening (also referred as Mullins effect) observed in chemically crosslinked filled rubbers. We propose that this self-reinforcement is related to the fragmentation of hard domains, naturally present in TPU, in smaller but more numerous sub-units that may act as new physical crosslinking points. The proposed stiffening mechanism is not dissimilar to the strain-induced crystallization observed in stretched natural rubber, but it presents a persistent nature. In particular, it may cause a local reinforcement where an inhomogeneous strain field is present, as is the case of a crack propagating in cyclic fatigue, providing a potential explanation for the well-known toughness and wear resistance of TPU. 相似文献
3.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques. 相似文献
4.
L. Villa P. D' Agati C. Mansueto C. Pellerito M. Scopelliti T. Fiore L. Nagy L. Pellerito 《应用有机金属化学》2003,17(2):106-112
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
5.
6.
Motivated by the work of Crapo and Rota [6] on the lifting of a projective complex, we introduce a class of invariant operations associated to integral-weighted graphs, which we call graphical operations. Such operations generalize the sixth harmonic of a quadranguler set on a projective line. We determine the expansion of the graphical operations in terms of multi-linear bracket polynomials in a Grassmann-Cayley algebra. Reducibility and compositions of such invariant operations are also investigated with a number of examples.Supported by Courant Instructorship, New York University. 相似文献
7.
8.
The one-loop vacuum energy is explicitly computed for a class of perturbative string vacua where supersymmetry is spontaneously broken by a T-duality invariant asymmetric Scherk–Schwarz deformation. The low-lying spectrum is tachyon-free for any value of the compactification radii and thus no Hagedorn-like phase-transition takes place. Indeed, the induced effective potential is free of divergence, and has a global anti-de Sitter minimum where geometric moduli are naturally stabilised. 相似文献
9.
Adler J Becker JJ Blaylock GT Bolton T Brient J Browder T Brown JS Bunnell KO Burchell M Burnett TH Cassell RE Coffman D Cook V Coward DH DeJongh F Dorfan DE Drinkard J Dubois GP Eigen G Einsweiler KF Eisenstein BI Freese T Gatto C Gladding G Grab C Hamilton RP Hauser J Heusch CA Hitlin DG Izen JM Kim PC Köpke L Li A Lockman WS Mallik U Matthews CG Mincer AI Mir R Mockett PM Mozley RF Nemati B Odian A Parrish L Partridge R Pitman D Plaetzer SA Richman JD Sadrozinski HF Scarlatella M Schalk TL 《Physical review letters》1989,62(16):1821-1824
10.
Benati L Bencivenni G Leardini R Minozzi M Nanni D Scialpi R Spagnolo P Zanardi G 《The Journal of organic chemistry》2005,70(8):3046-3053
Thermal reaction of various alpha-azido esters with Bu(3)SnH in refluxing benzene results in smooth production of 3-(tributylstannyl)-1-triazene adducts affording cyclized 1,2,3-triazol-4-ones in preference to reduced amines and thence provides a new useful method for the preparation of these triazole derivatives. In the presence of AIBN the occurrence of triazene products still remains important or even exclusive and, consequently, generation of the expected stannylaminyl radicals is seriously limited. With 2-azidomalonates and alpha-azido-beta-keto esters stannyltriazenes can similarly occur in the absence of the radical initiator, but in the latter cases the ensuing triazenes undergo preferential cyclization onto the ketone moiety to give reactive hydroxytriazolines. Contrary to alpha-azido esters, in the presence of AIBN alpha-azido-beta-keto esters as well as azidomalonates give rise only to the usual stannylaminyl radicals. A possible explanation for the different behavior of the mono- and dicarbonyl azides in the presence of AIBN is put forward. 相似文献