全文获取类型
收费全文 | 43897篇 |
免费 | 10186篇 |
国内免费 | 2181篇 |
专业分类
化学 | 47286篇 |
晶体学 | 424篇 |
力学 | 713篇 |
综合类 | 66篇 |
数学 | 3548篇 |
物理学 | 4227篇 |
出版年
2024年 | 10篇 |
2023年 | 112篇 |
2022年 | 194篇 |
2021年 | 436篇 |
2020年 | 1514篇 |
2019年 | 2815篇 |
2018年 | 1246篇 |
2017年 | 878篇 |
2016年 | 3733篇 |
2015年 | 3848篇 |
2014年 | 3816篇 |
2013年 | 4635篇 |
2012年 | 3714篇 |
2011年 | 3016篇 |
2010年 | 3421篇 |
2009年 | 3305篇 |
2008年 | 3008篇 |
2007年 | 2406篇 |
2006年 | 2017篇 |
2005年 | 2089篇 |
2004年 | 1836篇 |
2003年 | 1546篇 |
2002年 | 2205篇 |
2001年 | 1475篇 |
2000年 | 1370篇 |
1999年 | 464篇 |
1998年 | 115篇 |
1997年 | 116篇 |
1996年 | 81篇 |
1995年 | 73篇 |
1994年 | 71篇 |
1993年 | 77篇 |
1992年 | 73篇 |
1991年 | 53篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 39篇 |
1986年 | 21篇 |
1985年 | 55篇 |
1984年 | 40篇 |
1983年 | 32篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 11篇 |
1975年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Steven D. Bull Simon W. Epstein Nadeam Mujtaba Edward D. Savory Juan A. Tamayo 《Tetrahedron》2006,62(33):7911-7925
Enolates of (S)-N,N′-bis-(p-methoxybenzyl)-3-iso-propylpiperazine-2,5-dione exhibit high levels of enantiodiscrimination in alkylations with (RS)-1-aryl-1-bromoethanes and (RS)-2-bromoesters, affording substituted diketopiperazines containing two new stereogenic centres in high de. Deprotection and hydrolysis of the resultant substituted diketopiperazines provides a route to the asymmetric synthesis of homochiral methyl 2-amino-3-aryl-butanoates and 3-methyl-aspartates in high de and ee. 相似文献
53.
Wen Zhang Hui Huang Yu Ding Margherita Gavagnin Ernesto Mollo Guido Cimino Yue‐Wei Guo 《Helvetica chimica acta》2006,89(4):813-820
Three new polyoxygenated steroids, muricesteroid ( 1 ), and menellsteroids A ( 2 ) and B ( 3 ), were isolated from two species of the South China Sea gorgonian Muricella flexuosa and Menella verrucosa Brundin , respectively. The structures of these new compounds were elucidated on the basis of extensive spectroscopic analysis, chemical methods and comparison with known related compounds. 相似文献
54.
It is proved that the variety of relevant disjunction lattices has the finite embeddability property. It follows that Avron's relevance logic RMI min has a strong form of the finite model property, so it has a solvable deducibility problem. This strengthens Avron's result that RMI min is decidable. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
55.
56.
57.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
58.
59.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献
60.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc. 相似文献