全文获取类型
收费全文 | 3301篇 |
免费 | 85篇 |
国内免费 | 15篇 |
专业分类
化学 | 2028篇 |
晶体学 | 10篇 |
力学 | 79篇 |
数学 | 484篇 |
物理学 | 800篇 |
出版年
2023年 | 29篇 |
2022年 | 34篇 |
2021年 | 57篇 |
2020年 | 55篇 |
2019年 | 60篇 |
2018年 | 25篇 |
2017年 | 37篇 |
2016年 | 86篇 |
2015年 | 67篇 |
2014年 | 86篇 |
2013年 | 168篇 |
2012年 | 164篇 |
2011年 | 187篇 |
2010年 | 93篇 |
2009年 | 86篇 |
2008年 | 129篇 |
2007年 | 154篇 |
2006年 | 122篇 |
2005年 | 157篇 |
2004年 | 112篇 |
2003年 | 103篇 |
2002年 | 88篇 |
2001年 | 74篇 |
2000年 | 59篇 |
1999年 | 50篇 |
1998年 | 33篇 |
1997年 | 49篇 |
1996年 | 46篇 |
1995年 | 57篇 |
1994年 | 50篇 |
1993年 | 49篇 |
1992年 | 48篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1988年 | 26篇 |
1987年 | 25篇 |
1986年 | 29篇 |
1985年 | 41篇 |
1984年 | 29篇 |
1982年 | 32篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 35篇 |
1978年 | 32篇 |
1977年 | 35篇 |
1976年 | 42篇 |
1975年 | 36篇 |
1974年 | 33篇 |
1973年 | 39篇 |
1972年 | 32篇 |
排序方式: 共有3401条查询结果,搜索用时 0 毫秒
1.
Olaf Hansen 《Mathematical Methods in the Applied Sciences》2002,25(12):1075-1090
In this article we study the radiosity operator along an edge between two adjacent half‐planes. First we show that the radiosity operator is invertible in a whole scale of anisotropic Sobolev spaces. In the absence of any shadows we are able to derive regularity properties of the solution, which depend only on the angle between the half‐planes, the reflectivity coefficients and the right‐hand side. This work can be considered as a supplement to the article of Rathsfeld (Mathematical Methods in the Applied Sciences 1999; 22 : 217–241). Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
Nis Halland Tore Hansen Karl Anker Jrgensen 《Angewandte Chemie (International ed. in English)》2003,42(40):4837-4837
3.
One of the successful transformations within the field of organocatalysis, the organocatalytic asymmetric addition of nitromethane to α,β‐unsaturated aldehydes and ketones, has been studied by quantum chemical modeling. The level of accuracy of the hybrid density functional theory method B3LYP/6‐31G(d) was compared to a high level ab initio benchmark for this reaction. It is concluded that B3LYP/6‐31G(d) performs very well for this reaction type, giving good estimates of critical energies. The reaction between acrolein and nitromethane was studied in detail. The reaction mechanism revealed an intermediate oxazolidin structure, which is currently unknown. Alkyl substitution in various positions on the amine catalyst or α,β‐unsaturated carbonyl compound influences the reactivity in a predictive fashion. The iminium ion, prop‐2‐en‐iminium, is less activated towards nucleophilic attack compared to protonated acrolein. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
4.
5.
6.
A E Abdel-Megied P Hansen E B Pedersen C M Nielsen 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1991,45(10):1060-1063
The 3'-iodonucleoside 4 and the 3'-O-methylsulfonylthymidine 9 have been synthesized by condensation of silylated uracils 2 with methyl 5-O-tert-butyldiphensilyl-2,3-dideoxy-3-iodo-D-threo-pentofuran oside (3) and methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-3-methylsulfonyl-D-erythro- pentofuranoside (8), respectively. The nucleoside 4 and 9 produced the corresponding 2',3'-didehydro-2',3'-dideoxynucleosides 5 in an elimination reaction on treatment with sodium methoxide. The compounds 5b showed no antiviral activity against HIV-1. 相似文献
7.
8.
9.
We study the electronic level density in spherical clusters. Due to the granularity of the ionic background the surface is irregular at the microscopical level. We show that this affects the shell structure and that the level statistics display from the bottom to the top of the spectrum a transition from a poissonian behaviour to one consistent with the predictions of random matrices theory. 相似文献
10.
A probe-corrected theory based on complex point sources is presented for computing the acoustic field of an arbitrary finite source from measurements of the near field on a cylindrical scanning surface. The complex point sources are used both as basis functions for the expansion of the field outside the scan cylinder and for the representation of the probe. The resulting probe-corrected formulas are considerably simpler than the standard probe-corrected formulas based on cylindrical waves. The new formulation makes simulations of near-field scanning systems much less computationally intensive than simulations based on standard theory. The complex point-source theory is validated through numerical examples involving a baffled circular piston transducer probe. 相似文献