全文获取类型
收费全文 | 84951篇 |
免费 | 16047篇 |
国内免费 | 7327篇 |
专业分类
化学 | 73327篇 |
晶体学 | 965篇 |
力学 | 3870篇 |
综合类 | 415篇 |
数学 | 7791篇 |
物理学 | 21957篇 |
出版年
2024年 | 157篇 |
2023年 | 1042篇 |
2022年 | 1867篇 |
2021年 | 2008篇 |
2020年 | 3182篇 |
2019年 | 4282篇 |
2018年 | 2636篇 |
2017年 | 2159篇 |
2016年 | 5482篇 |
2015年 | 5698篇 |
2014年 | 6028篇 |
2013年 | 7476篇 |
2012年 | 7491篇 |
2011年 | 6768篇 |
2010年 | 5941篇 |
2009年 | 5767篇 |
2008年 | 5606篇 |
2007年 | 4664篇 |
2006年 | 4195篇 |
2005年 | 3910篇 |
2004年 | 3097篇 |
2003年 | 2606篇 |
2002年 | 3278篇 |
2001年 | 2340篇 |
2000年 | 2210篇 |
1999年 | 1420篇 |
1998年 | 827篇 |
1997年 | 826篇 |
1996年 | 847篇 |
1995年 | 703篇 |
1994年 | 619篇 |
1993年 | 487篇 |
1992年 | 457篇 |
1991年 | 387篇 |
1990年 | 332篇 |
1989年 | 276篇 |
1988年 | 241篇 |
1987年 | 182篇 |
1986年 | 167篇 |
1985年 | 137篇 |
1984年 | 89篇 |
1983年 | 82篇 |
1982年 | 62篇 |
1981年 | 44篇 |
1980年 | 33篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1976年 | 16篇 |
1975年 | 16篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
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.
具Hardy-Sobolev临界指数的奇异椭圆方程多解的存在性 总被引:1,自引:0,他引:1
运用变分方法研究了下面问题-Δpu=μupx(s)s-2u f(x,u),x∈Ω,u=0,x∈Ω,多重解的存在性,其中Ω是一个具有光滑边界的有界区域. 相似文献
6.
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
7.
Yuxi Zheng 《Communications in Mathematical Physics》1991,135(3):581-594
We show that the weak-L
2 limit of a sequence of solutions of the two dimensional incompressible Euler equation is still a solution, provided that a (strong) concentration set for the reduced defect measure has locally finite one dimensional Hausdorff measure in space and time. 相似文献
8.
A design of diode-pumped high-efficiency Nd:YVO4/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM00 mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively. 相似文献
9.
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
10.
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