全文获取类型
收费全文 | 445047篇 |
免费 | 4089篇 |
国内免费 | 1806篇 |
专业分类
化学 | 220934篇 |
晶体学 | 6832篇 |
力学 | 21259篇 |
综合类 | 64篇 |
数学 | 64294篇 |
物理学 | 137559篇 |
出版年
2020年 | 2927篇 |
2019年 | 3227篇 |
2018年 | 11675篇 |
2017年 | 12480篇 |
2016年 | 9810篇 |
2015年 | 4761篇 |
2014年 | 6329篇 |
2013年 | 15623篇 |
2012年 | 15964篇 |
2011年 | 25334篇 |
2010年 | 16662篇 |
2009年 | 16602篇 |
2008年 | 23013篇 |
2007年 | 25921篇 |
2006年 | 13540篇 |
2005年 | 17545篇 |
2004年 | 13819篇 |
2003年 | 12663篇 |
2002年 | 10781篇 |
2001年 | 10978篇 |
2000年 | 8474篇 |
1999年 | 6154篇 |
1998年 | 5188篇 |
1997年 | 5050篇 |
1996年 | 5023篇 |
1995年 | 4492篇 |
1994年 | 4528篇 |
1993年 | 4334篇 |
1992年 | 4803篇 |
1991年 | 4831篇 |
1990年 | 4616篇 |
1989年 | 4487篇 |
1988年 | 4422篇 |
1987年 | 4355篇 |
1986年 | 4238篇 |
1985年 | 5567篇 |
1984年 | 5702篇 |
1983年 | 4896篇 |
1982年 | 5205篇 |
1981年 | 4851篇 |
1980年 | 4626篇 |
1979年 | 4934篇 |
1978年 | 5161篇 |
1977年 | 5051篇 |
1976年 | 5144篇 |
1975年 | 4796篇 |
1974年 | 4876篇 |
1973年 | 5111篇 |
1972年 | 3724篇 |
1971年 | 2989篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
(S)-2-[2-(p-Tolylsulfinyl)phenyl]acetaldehyde reacts with different O-silylated ketenethioacetals in the presence of Yb(OTf)3 yielding β-hydroxythioesters in high yields and diastereoselectivities. The obtained compounds were readily transformed into β-hydroxyacids and their corresponding diols. These Mukaiyama aldol reactions are a direct evidence of the ability of the sulfinyl group to control 1,5- and 1,6-asymmetric induction processes. 相似文献
72.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
73.
An overview of theoretical and experimental studies of the coherent type-B e
+
e-pair production by photons in aligned crystals performed at Nuclear Physics Institute at Tomsk Polytechnic University is given. 相似文献
74.
B. Dubrulle F. Hersant 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):379-386
We generalize an analogy between rotating and stratified shear flows. This analogy is summarized in Table 1. We use this analogy
in the unstable case (centrifugally unstable flow vs. convection) to compute the torque in Taylor-Couette configuration, as a function of the Reynolds number. At low Reynolds
numbers, when most of the dissipation comes from the mean flow, we predict that the non-dimensional torque G = T/ν2
L, where L is the cylinder length, scales with Reynolds number R and gap width η, G = 1.46η3/2(1 - η)-7/4
R
3/2. At larger Reynolds number, velocity fluctuations become non-negligible in the dissipation. In these regimes, there is no
exact power law dependence the torque versus Reynolds. Instead, we obtain logarithmic corrections to the classical ultra-hard (exponent 2) regimes: G = 0.50
. These predictions are found to be in excellent agreement with avail-able experimental data. Predictions for scaling of velocity
fluctuations are also provided.
Received 7 June 2001 and Received in final form 7 December 2001 相似文献
75.
Electrical resistivity of U3Tein4, U2Te3 (cubic) and UTe3 has been measured over temperature range 4.2–300 K. The two former compounds appear to be semimetallic conductors while the last one has semiconducting character. The results are discussed in the terms of available magnetic data. 相似文献
76.
77.
78.
79.
We analyze diffusion from a periodic array of hemispherical droplets through a membrane. We find that the multiple sources do not interact strongly, even when the droplets are closely spaced, so that the flux through the membrane appears nearly additive. 相似文献
80.