全文获取类型
收费全文 | 49550篇 |
免费 | 8482篇 |
国内免费 | 1440篇 |
专业分类
化学 | 51522篇 |
晶体学 | 390篇 |
力学 | 643篇 |
数学 | 3633篇 |
物理学 | 3284篇 |
出版年
2023年 | 123篇 |
2022年 | 489篇 |
2021年 | 686篇 |
2020年 | 1522篇 |
2019年 | 2884篇 |
2018年 | 1259篇 |
2017年 | 870篇 |
2016年 | 3785篇 |
2015年 | 3908篇 |
2014年 | 3819篇 |
2013年 | 4831篇 |
2012年 | 3758篇 |
2011年 | 3105篇 |
2010年 | 3402篇 |
2009年 | 3346篇 |
2008年 | 3151篇 |
2007年 | 2528篇 |
2006年 | 2132篇 |
2005年 | 2238篇 |
2004年 | 1941篇 |
2003年 | 1742篇 |
2002年 | 2412篇 |
2001年 | 1504篇 |
2000年 | 1383篇 |
1999年 | 458篇 |
1998年 | 156篇 |
1997年 | 130篇 |
1996年 | 149篇 |
1995年 | 106篇 |
1994年 | 97篇 |
1993年 | 87篇 |
1992年 | 73篇 |
1991年 | 88篇 |
1990年 | 61篇 |
1989年 | 80篇 |
1988年 | 70篇 |
1987年 | 52篇 |
1986年 | 55篇 |
1985年 | 67篇 |
1984年 | 88篇 |
1983年 | 55篇 |
1982年 | 72篇 |
1981年 | 65篇 |
1980年 | 62篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 40篇 |
1976年 | 37篇 |
1975年 | 25篇 |
1958年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
Helmut Schmidhammer Eva Scherb-Bukowiecki Thomas A. Mayer Peter Schnholzer 《Helvetica chimica acta》1994,77(6):1590-1594
The synthesis of benzazepine analogues of the opium alkaloid noscapine ( 1 ) is described. The benzazepines 2 and 3 were prepared starting from nornarceine ethyl ester ( 4 ; readily available from 1 ) in several steps. X-Ray analysis of compound 2 revealed that it is not a diastereosisomer mixture but a racemate of the threo-form and thus has the same configuration as 1 . 相似文献
4.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
5.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
6.
Eva Lesanska 《Applications of Mathematics》2002,47(5):411-426
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model. 相似文献
7.
Josep Maria Izquierdo 《TOP》2006,14(2):375-398
The paper introduces a refinement of the notion of population monotonic allocation scheme, called regular population monotonic
allocation scheme (regularpmas). This refinement is based on economic situations in which players may have to select new partners from a set of potential
players and in which there exist certain capacity constraints. A sufficient condition for the existence of a regularpmas is given. For the class of games with regularpmas, we prove that the core coincides with the Davis and Maschler and the Mas-Colell bargaining sets. 相似文献
8.
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
9.
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