全文获取类型
收费全文 | 49739篇 |
免费 | 8525篇 |
国内免费 | 6614篇 |
专业分类
化学 | 35096篇 |
晶体学 | 803篇 |
力学 | 3203篇 |
综合类 | 496篇 |
数学 | 6049篇 |
物理学 | 19231篇 |
出版年
2024年 | 102篇 |
2023年 | 902篇 |
2022年 | 1186篇 |
2021年 | 1551篇 |
2020年 | 1863篇 |
2019年 | 1837篇 |
2018年 | 1636篇 |
2017年 | 1593篇 |
2016年 | 2298篇 |
2015年 | 2305篇 |
2014年 | 2803篇 |
2013年 | 3560篇 |
2012年 | 4328篇 |
2011年 | 4541篇 |
2010年 | 3157篇 |
2009年 | 3216篇 |
2008年 | 3471篇 |
2007年 | 3143篇 |
2006年 | 3025篇 |
2005年 | 2347篇 |
2004年 | 1981篇 |
2003年 | 1661篇 |
2002年 | 1688篇 |
2001年 | 1413篇 |
2000年 | 1247篇 |
1999年 | 1119篇 |
1998年 | 923篇 |
1997年 | 804篇 |
1996年 | 803篇 |
1995年 | 709篇 |
1994年 | 621篇 |
1993年 | 510篇 |
1992年 | 473篇 |
1991年 | 368篇 |
1990年 | 342篇 |
1989年 | 274篇 |
1988年 | 222篇 |
1987年 | 191篇 |
1986年 | 170篇 |
1985年 | 167篇 |
1984年 | 109篇 |
1983年 | 74篇 |
1982年 | 62篇 |
1981年 | 39篇 |
1980年 | 18篇 |
1979年 | 12篇 |
1977年 | 2篇 |
1959年 | 1篇 |
1957年 | 3篇 |
1936年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
151.
The electronic structure and chemical bonding in a recently synthesized inorganic fullerene-like molecule, [CuCl]20[Cp*FeP5]12[Cu-(CH3CN) +
2Cl−]5 has been studied by a density functional approach. Geometrical optimization of the three basic structural units of the molecule
is performed with Amsterdam Density Functional Program. The results are in agreement with the experiment. Localized MO’s obtained
by Boys-Foster method give a clear picture of the chemical bonding in this molecule. The reason why CuCl can react with Cp*FeP5 in solvent CH3CN to form the fullerene-like molecule is explained in terms of the soft-hard Lewis acid base theory and a new concept of
covalence. 相似文献
152.
JianXinCAO YiFengWANG GuoFangLAI ShiDeLUO 《中国化学快报》2004,15(7):797-800
From the dried aerial part ofParepigynumfuningesis Tsiang et P. T. Li (Apocynaceae),a new cardiac glucoside, named parefuningoside (1) had been isolated. Its structure was determined by means of hydrolysis and spectral analysis. 相似文献
153.
WeiMinSHI JianWU YiFengWU KaiXianQIAN 《中国化学快报》2004,15(12):1427-1429
A mono-funtionalised tetraphenylporphyrin (TPP) bearing valine moiety at the phenyl ring was synthesized for photocytotoxicity examination in four steps, starting from regiospecific mono-nitration of TPP at the phenyl ring. The in vitro photocytotoxicitic effect against SPC-Al adenocarcinona cell line was tested. 相似文献
154.
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
155.
156.
157.
We observe enhanced terahertz (THz) radiation generated from a Si3N4 film-coated GaAs photoconductive dipole antenna. Compared to an uncoated antenna with identical electrode geometry and optical excitation power, the Si3N4 film-coated antenna has a higher effective DC resistance and larger breakdown voltage. As a result, the peak amplitude of generated THz radiation is significantly enhanced due to the Si3N4 film-coated layer. 相似文献
158.
159.
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
160.
The ρ-T curves in our single phase HgBa2Ca2Cu3O8+δ superconductor were measured as a function of temperature and magnetic field, ρ=ρ0exp(−Ueff/κBT). It can be transformed to another form d(lnρ)/d(1/T)=−Ueff+TdUeff/dT, then this becomes a plot of the activation energy Ueff as a function of temperature. Our data plotted in these ways show a clear crossover from high-temperature two-dimensional vortex-liquid to a critical region associated with the low-temperature three-dimensional vortex-glass phase transition. The critical exponents v(z−1)=3.9±1.9 in this system are little different with previous measurements in BSCCO and YBCO systems. 相似文献