全文获取类型
收费全文 | 93256篇 |
免费 | 17284篇 |
国内免费 | 8596篇 |
专业分类
化学 | 79674篇 |
晶体学 | 1049篇 |
力学 | 4025篇 |
综合类 | 477篇 |
数学 | 8729篇 |
物理学 | 25182篇 |
出版年
2024年 | 199篇 |
2023年 | 1219篇 |
2022年 | 2286篇 |
2021年 | 2553篇 |
2020年 | 3589篇 |
2019年 | 4632篇 |
2018年 | 2952篇 |
2017年 | 2581篇 |
2016年 | 6001篇 |
2015年 | 6197篇 |
2014年 | 6653篇 |
2013年 | 8193篇 |
2012年 | 8148篇 |
2011年 | 7389篇 |
2010年 | 6421篇 |
2009年 | 6212篇 |
2008年 | 6076篇 |
2007年 | 5067篇 |
2006年 | 4430篇 |
2005年 | 4122篇 |
2004年 | 3389篇 |
2003年 | 2863篇 |
2002年 | 3589篇 |
2001年 | 2642篇 |
2000年 | 2379篇 |
1999年 | 1564篇 |
1998年 | 1036篇 |
1997年 | 930篇 |
1996年 | 915篇 |
1995年 | 820篇 |
1994年 | 694篇 |
1993年 | 596篇 |
1992年 | 477篇 |
1991年 | 438篇 |
1990年 | 356篇 |
1989年 | 261篇 |
1988年 | 199篇 |
1987年 | 181篇 |
1986年 | 171篇 |
1985年 | 152篇 |
1984年 | 96篇 |
1983年 | 104篇 |
1982年 | 58篇 |
1981年 | 47篇 |
1980年 | 32篇 |
1979年 | 27篇 |
1977年 | 20篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1972年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
XiangGuoSHI DaFangZHONG YuMingSUN YuFengZHANG 《中国化学快报》2004,15(4):431-434
A sensitive analytical method to identify active metabolites of bitespiramycin in rat urine and bile was developed by liquid chromatography-electrospray ionization tandem mass spectrometry(LC/ESI-MS^n).Bitespiramycin and its major active metabolites in rat urine and bile were isolated and identified as M1 serial(spiramycin Ⅰ,Ⅱ,Ⅲ),M2 serial(platenomycin A1,josamycin and leucomycin A1) and M3 serial(deisovalerylplatenomycin A1,deisovaleryljosamycin,deisovalerylleucomycin A1). 相似文献
82.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products. 相似文献
83.
DongXiangLI WanGuoHOU ShuPingLI MingTuHAO GaoYongZHANG 《中国化学快报》2004,15(2):224-227
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations. 相似文献
84.
Ming Zhao WANG Guan Liang CAI Ling XIA Jun Jian YAO Hong Yan CHEN Zhao Xing MENG Bo Li LIUDepartment of Chemistry Beijing Normal University Beijing Chemical Defense Institute PLA Beijing 《中国化学快报》2004,15(4):495-497
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents. 相似文献
85.
Yang Woo Shin 《Operations Research Letters》2004,32(4):364-373
We consider a single server queue with disasters where the arrivals of customers and disasters are correlated. When a disaster occurs, it removes all the customers in the system and there requires repair time for the system to be operated normally. The stationary queue length distribution at the embedded points and at an arbitrary time are presented. 相似文献
86.
Mari Grobbelaar‐Van Dalsen 《Mathematical Methods in the Applied Sciences》2004,27(11):1301-1315
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
87.
Continuous dependence on a modelling parameter is established for solutions of a problem for a complex Ginzburg–Landau equation. A homogenizing boundary condition is also used to discuss the continuous dependence results. We derive a priori estimates that indicate that solutions depend continuously on a parameter in the governing differential equation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
88.
LiAlO2 single crvstals doped with Ti at concentration 0.2at.% are grown by the Czochralskl technique with dimensions φ42×55mm. Ti ions in the crystal are quadrivalence proven by comparing the absorption and fluorescence spectra of pure LiAlO2 and Ti: LiAlO2. After air and Li-rich atmosphere annealing, the absorption peaks in the range of 600-800nm disappear. We conclude that 682 and 756nm absorption peaks are attributed to the VLi and Vo absorptions, respectively: The peaks at 716nm and 798nm may stem from the VLi^+ and absorptions. The colour-centre model can be applied to explain the experimental phenomena. Ti^4+-doping produces more lithium vacancies in the LiAlO2 crystal. The intensities of [LiO4] and the associated bonds remain unchanged, which improves the anti-hydrolyzation and thermal stability of LiAlO2 crystals. 相似文献
89.
90.
Let f be a smooth map between unit spheres of possibly different dimensions. We prove the global existence and convergence of the mean curvature flow of the graph of f under various conditions. A corollary is that any area‐decreasing map between unit spheres (of possibly different dimensions) is isotopic to a constant map. © 2004 Wiley Periodicals, Inc. 相似文献