全文获取类型
收费全文 | 31243篇 |
免费 | 189篇 |
国内免费 | 280篇 |
专业分类
化学 | 12442篇 |
晶体学 | 281篇 |
力学 | 1413篇 |
综合类 | 12篇 |
数学 | 8995篇 |
物理学 | 8569篇 |
出版年
2021年 | 52篇 |
2020年 | 50篇 |
2019年 | 60篇 |
2018年 | 1224篇 |
2017年 | 1467篇 |
2016年 | 753篇 |
2015年 | 592篇 |
2014年 | 512篇 |
2013年 | 742篇 |
2012年 | 3223篇 |
2011年 | 2456篇 |
2010年 | 1866篇 |
2009年 | 1608篇 |
2008年 | 725篇 |
2007年 | 762篇 |
2006年 | 763篇 |
2005年 | 4565篇 |
2004年 | 4032篇 |
2003年 | 2407篇 |
2002年 | 583篇 |
2001年 | 324篇 |
2000年 | 141篇 |
1999年 | 217篇 |
1998年 | 142篇 |
1997年 | 98篇 |
1996年 | 74篇 |
1995年 | 61篇 |
1994年 | 67篇 |
1993年 | 48篇 |
1992年 | 195篇 |
1991年 | 171篇 |
1990年 | 169篇 |
1989年 | 129篇 |
1988年 | 125篇 |
1987年 | 83篇 |
1986年 | 69篇 |
1985年 | 69篇 |
1984年 | 75篇 |
1983年 | 51篇 |
1982年 | 57篇 |
1981年 | 43篇 |
1979年 | 48篇 |
1976年 | 96篇 |
1975年 | 56篇 |
1974年 | 54篇 |
1973年 | 67篇 |
1972年 | 42篇 |
1969年 | 41篇 |
1968年 | 43篇 |
1966年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Mitsuki Yamashita Yuna Kawasumi Yuki Tachibana Dr. Shinnosuke Horiuchi Dr. Koji Yamamoto Prof. Tetsuro Murahashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(5):1212-1216
Although small cyclic- and open-chain unsaturated hydrocarbon anions such as cyclopentadienide and open-chain pentadienide are used as the strongly electron-donating auxiliary ligands for metal complexes, more extended π-conjugated unsaturated hydrocarbon anions have rarely been used in coordination chemistry, despite their potential ability to serve as the multiply bridging π-ligands for metal clusters. This work reports isolation of metal chain clusters bearing the multi-dentate, open-chain extended unsaturated hydrocarbon anion ligands. The extended open-chain π-conjugated polyenyl ligands could effectively stabilize oxidized palladium chains, including an unprecedented [Pd4]4+ chain. 相似文献
2.
Surface texturing has been recognized as an effective means to improve the tribological performances of sliding surfaces. Usually, generation additional hydrodynamic pressure to increase the load carrying capacity is regarded as the most significant effect of surface texture. In the case of silicon carbide sliding against identical material in water, the experimental results indicate that surface texture is also helpful to improve the running-in progress to smooth the contact surfaces, showing another reason to result in low friction. Based on the consideration of enhancing the generation of hydrodynamic pressure and improving running-in progress, a surface texture pattern, which was combined with large (circle, 350 μm in diameter) and small (rectangular, 40 μm in length) dimples, was designed to maximize the texture effect on the load carrying capacity of SiC surfaces sliding in water. The friction coefficient of such textured surface was evaluated and compared with that of untextured and those only with large or small dimples only. The friction reduction mechanisms of the patterns with different dimples in size are discussed. 相似文献
3.
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
4.
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
5.
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
6.
Three new cytotoxic polyacetylenes, PQ-1 (1), PQ-2 (2) and PQ-3 (3), have been isolated from Panax quinquefolium. The structures of these acetylenes were determined by analyses of their 1H-1H and 1H-13C COSY spectra. All these compounds exhibited strong cytotoxic activities against leukemia cells (L 1210) in tissue culture. 相似文献
7.
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
8.
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
9.
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
10.
J. Fujimoto T. Ishikawa M. Jimbo T. Kaneko T. Kon Y. Kurihara M. Kuroda Y. Shimizu Y. Yasui 《Pramana》2007,69(5):943-946
We report the recent development on the SUSY calculations with the help of GRACE system. GRACE/SUSY/1LOOP is the computer
code which can generate Feynman diagrams in the MSSM automatically and compute one-loop amplitudes in the numerical way. We
present new results of various two-body decay widths and chargino pair production at ILC (international linear collider) at
one-loop level.
相似文献