全文获取类型
收费全文 | 33131篇 |
免费 | 759篇 |
国内免费 | 967篇 |
专业分类
化学 | 13732篇 |
晶体学 | 303篇 |
力学 | 1759篇 |
综合类 | 41篇 |
数学 | 9398篇 |
物理学 | 9624篇 |
出版年
2023年 | 95篇 |
2022年 | 179篇 |
2021年 | 213篇 |
2020年 | 218篇 |
2019年 | 203篇 |
2018年 | 1340篇 |
2017年 | 1600篇 |
2016年 | 883篇 |
2015年 | 730篇 |
2014年 | 678篇 |
2013年 | 962篇 |
2012年 | 3478篇 |
2011年 | 2683篇 |
2010年 | 2055篇 |
2009年 | 1758篇 |
2008年 | 820篇 |
2007年 | 813篇 |
2006年 | 808篇 |
2005年 | 4627篇 |
2004年 | 4053篇 |
2003年 | 2448篇 |
2002年 | 630篇 |
2001年 | 420篇 |
2000年 | 206篇 |
1999年 | 302篇 |
1998年 | 193篇 |
1997年 | 148篇 |
1996年 | 127篇 |
1995年 | 111篇 |
1994年 | 93篇 |
1993年 | 84篇 |
1992年 | 216篇 |
1991年 | 202篇 |
1990年 | 175篇 |
1989年 | 142篇 |
1988年 | 120篇 |
1987年 | 74篇 |
1986年 | 58篇 |
1985年 | 54篇 |
1984年 | 41篇 |
1983年 | 39篇 |
1976年 | 87篇 |
1975年 | 43篇 |
1974年 | 42篇 |
1973年 | 55篇 |
1972年 | 44篇 |
1970年 | 38篇 |
1969年 | 37篇 |
1968年 | 35篇 |
1966年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 50 毫秒
1.
2.
3.
In this research article, we describe the synthesis and characterization of mononuclear and dinuclear Cu complexes bound by a family of tridentate redox-active ligands with tunable H-bonding donors. The mononuclear Cu-anion complexes were oxidized to the corresponding “high-valent” intermediates by oxidation of the redox-active ligand. These species were capable of oxidizing phenols with weak O−H bonds via H-atom abstraction. Thermodynamic analysis of the H-atom abstractions, which included reduction potential measurements, pKa determination and kinetic studies, revealed that modification of the anion coordinated to the Cu and changes in the H-bonding donor did not lead to major differences in the reactivity of the “high-valent” CuY complexes (Y: hydroxide, phenolate and acetate), which indicated that the tridentate ligand scaffold acts as the H+ and e− acceptor. 相似文献
4.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 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.
L. Tong Y. Tian Q. Y. Wang Y. S. Ling 《International Journal of Infrared and Millimeter Waves》2006,27(9):1307-1314
The paper introduces a special system calibration technology in s-parameters measurement of microwave and millimeter wave
devices. The 8-term errors module is built by analyzing the signals flowing in the measurement system. Then the calibration
technology using non-standard kits is designed on the base. Finally, the experiment using the calibration technology is introduced. 相似文献
7.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
8.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
9.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
10.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献