全文获取类型
收费全文 | 31323篇 |
免费 | 130篇 |
国内免费 | 272篇 |
专业分类
化学 | 11692篇 |
晶体学 | 298篇 |
力学 | 1439篇 |
综合类 | 12篇 |
数学 | 9202篇 |
物理学 | 9082篇 |
出版年
2022年 | 86篇 |
2021年 | 100篇 |
2020年 | 72篇 |
2019年 | 74篇 |
2018年 | 1262篇 |
2017年 | 1524篇 |
2016年 | 844篇 |
2015年 | 651篇 |
2014年 | 572篇 |
2013年 | 816篇 |
2012年 | 3274篇 |
2011年 | 2457篇 |
2010年 | 1941篇 |
2009年 | 1694篇 |
2008年 | 714篇 |
2007年 | 763篇 |
2006年 | 747篇 |
2005年 | 4517篇 |
2004年 | 3972篇 |
2003年 | 2322篇 |
2002年 | 511篇 |
2001年 | 315篇 |
2000年 | 138篇 |
1999年 | 193篇 |
1998年 | 150篇 |
1997年 | 93篇 |
1996年 | 52篇 |
1995年 | 50篇 |
1994年 | 48篇 |
1992年 | 171篇 |
1991年 | 155篇 |
1990年 | 138篇 |
1989年 | 112篇 |
1988年 | 103篇 |
1987年 | 62篇 |
1986年 | 44篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 38篇 |
1979年 | 40篇 |
1976年 | 91篇 |
1975年 | 42篇 |
1974年 | 49篇 |
1973年 | 55篇 |
1972年 | 41篇 |
1970年 | 37篇 |
1969年 | 38篇 |
1968年 | 37篇 |
1967年 | 35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.
2.
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
3.
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
4.
The dynamics of multiphoton transitions in a two-level spin system excited by transverse microwave and longitudinal RF fields with the frequencies ωmw and ωrf, respectively, is analyzed. The effective time-independent Hamiltonian describing the “dressed” spin states of the “spin + bichromatic field” system is obtained by using the Krylov-Bogoliubov-Mitropolsky averaging method. The direct detection of the time behavior of the spin system by the method of nonstationary nutations makes it possible to identify the multiphoton transitions for resonances ω0 = ωmw + rωrf (ω0 is the central frequency of the EPR line, r = 1, 2), to measure the amplitudes of the effective fields of these transitions, and to determine the features generated by the inhomogeneous broadening of the EPR line. It is shown that the Bloch-Siegert shifts for multiphoton resonances at the inhomogeneous broadening of spectral lines reduce only the nutation amplitude but do not change their frequencies. 相似文献
5.
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
6.
7.
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
8.
The conditions for obtaining a high efficiency of energy exchange upon two-wave interactions in dynamic holograms are found by analysis and numerical simulation of a system of nonlinear equations. Use of an asymmetric scheme of beam interaction in a medium with two nonlinearities, one of which determines the amplitude and relaxation time of a grating and the other of which provides phase modulation of the interacting beams, is proposed. It is shown that such a scheme in combination with the specific properties of a medium makes it possible to radically reduce the requirements for the nonlinearity of a medium and the intensity of a light flux in limiting systems, as well as to significantly decrease the time of the transition process. As a result, it becomes possible to attain an efficiency of energy transfer higher than 90% and to increase the corresponding attenuation of a high-power beam by almost two orders of magnitude, which is of interest for optical limiting of intense light fluxes. 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.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献