全文获取类型
收费全文 | 54930篇 |
免费 | 10458篇 |
国内免费 | 3468篇 |
专业分类
化学 | 53981篇 |
晶体学 | 623篇 |
力学 | 1446篇 |
综合类 | 187篇 |
数学 | 3817篇 |
物理学 | 8802篇 |
出版年
2024年 | 40篇 |
2023年 | 290篇 |
2022年 | 612篇 |
2021年 | 795篇 |
2020年 | 1826篇 |
2019年 | 3099篇 |
2018年 | 1501篇 |
2017年 | 1162篇 |
2016年 | 4096篇 |
2015年 | 4180篇 |
2014年 | 4314篇 |
2013年 | 5307篇 |
2012年 | 4615篇 |
2011年 | 3866篇 |
2010年 | 3972篇 |
2009年 | 3809篇 |
2008年 | 3545篇 |
2007年 | 2779篇 |
2006年 | 2481篇 |
2005年 | 2532篇 |
2004年 | 2198篇 |
2003年 | 1976篇 |
2002年 | 2704篇 |
2001年 | 1823篇 |
2000年 | 1718篇 |
1999年 | 764篇 |
1998年 | 352篇 |
1997年 | 311篇 |
1996年 | 294篇 |
1995年 | 273篇 |
1994年 | 211篇 |
1993年 | 200篇 |
1992年 | 205篇 |
1991年 | 161篇 |
1990年 | 131篇 |
1989年 | 115篇 |
1988年 | 96篇 |
1987年 | 72篇 |
1986年 | 74篇 |
1985年 | 83篇 |
1984年 | 41篇 |
1983年 | 40篇 |
1982年 | 29篇 |
1981年 | 35篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1974年 | 18篇 |
1973年 | 10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.
K. C. Shin 《Communications in Mathematical Physics》2002,229(3):543-564
We study the eigenvalue problem with the boundary conditions that decays to zero as z tends to infinity along the rays , where is a real polynomial and . We prove that if for some we have for all , then the eigenvalues are all positive real. We then sharpen this to a larger class of polynomial potentials.
In particular, this implies that the eigenvalues are all positive real for the potentials when with , and with the boundary conditions that decays to zero as z tends to infinity along the positive and negative real axes. This verifies a conjecture of Bessis and Zinn-Justin.
Received: 16 January 2002 / Accepted: 1 May 2002 Published online: 6 August 2002 相似文献
6.
Guofen Yu Yuanci Gao Shenggang Liu Wenxiang Wang Jin Wu 《International Journal of Infrared and Millimeter Waves》2002,23(8):1261-1269
Analysis of the field distributions in a single biological cell under electromagnetic wave is given. With Debye approximation, the dielectric relaxation of each part of the cell, including the extracellular and cellular media, the cell membrane and the nuclear membrane, was taken into account. Making use of some typical parameters for a cell, the voltage across nuclear and cytoplasma membranes under electromagnetic waves are calculated up to millimeter wave frequency range. The calculated result indicates that it is unlikely to generate electroporation by present available millimeter wave sources. 相似文献
7.
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
8.
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
9.
Syntheses, structures, and properties of novel molybdenum and tungsten complexes of fullerenes 总被引:1,自引:0,他引:1
The synthesis and characterization of several fullerene-based organometallic complexes containing Mo and W is reported. 相似文献
10.
Time-domain numerical computation of noise reduction by diffraction and finite impedance of barriers
Chang Woo Lim 《Journal of sound and vibration》2003,268(2):385-401
A new time-domain numerical method is presented for the estimation of noise reduction by the diffraction and finite impedance of barriers. High order finite difference schemes conventionally used for computational aeroacoustics, and time-domain impedance boundary conditions are utilized for the development of the time-domain method. Compared with other methods, this method can be applied more easily to the problems related to nonlinear noise propagation such as impulsive noise and broadband noise. Linearized Euler equations in Cartesian co-ordinates are considered and solved numerically. Straight and T-shaped barriers with and without surface admittance are calculated. In order to assess the accuracy of this time-domain method, comparison with the results of SYSNOISE software (Ver. 5.3) are made. There are very good agreements between the results of the present time-domain numerical method and the boundary element method of the SYSNOISE software. 相似文献