全文获取类型
收费全文 | 31819篇 |
免费 | 250篇 |
国内免费 | 296篇 |
专业分类
化学 | 12488篇 |
晶体学 | 282篇 |
力学 | 1549篇 |
综合类 | 12篇 |
数学 | 9474篇 |
物理学 | 8560篇 |
出版年
2021年 | 80篇 |
2020年 | 97篇 |
2019年 | 82篇 |
2018年 | 1233篇 |
2017年 | 1478篇 |
2016年 | 794篇 |
2015年 | 641篇 |
2014年 | 590篇 |
2013年 | 804篇 |
2012年 | 3364篇 |
2011年 | 2554篇 |
2010年 | 1958篇 |
2009年 | 1665篇 |
2008年 | 735篇 |
2007年 | 787篇 |
2006年 | 759篇 |
2005年 | 4561篇 |
2004年 | 4052篇 |
2003年 | 2420篇 |
2002年 | 628篇 |
2001年 | 336篇 |
2000年 | 135篇 |
1999年 | 206篇 |
1998年 | 123篇 |
1997年 | 100篇 |
1996年 | 79篇 |
1995年 | 62篇 |
1994年 | 65篇 |
1993年 | 44篇 |
1992年 | 195篇 |
1991年 | 170篇 |
1990年 | 143篇 |
1989年 | 123篇 |
1988年 | 109篇 |
1987年 | 72篇 |
1986年 | 56篇 |
1985年 | 61篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1979年 | 40篇 |
1976年 | 95篇 |
1975年 | 43篇 |
1974年 | 46篇 |
1973年 | 51篇 |
1972年 | 45篇 |
1969年 | 42篇 |
1968年 | 50篇 |
1967年 | 39篇 |
1966年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
1.
2.
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.
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
7.
Olivier Ley 《Comptes Rendus Mathematique》2002,335(5):469-473
We consider a finite horizon deterministic optimal control problem with reflection. The final cost is assumed to be merely a locally bounded function which leads to a discontinuous value function. We address the question of the characterization of the value function as the unique solution of an Hamilton–Jacobi equation with Neumann boundary conditions. We follow the discontinuous approach developed by Barles and Perthame for problems set in the whole space. We prove that the minimal and maximal discontinuous viscosity solutions of the associated Hamilton–Jacobi can be written in terms of value functions of control problems with reflection. Nethertheless, we construct a counter-example showing that the value function is not the unique solution of the equation. To cite this article: O. Ley, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 469–473. 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.
Olivier Penacchio 《Comptes Rendus Mathematique》2002,335(5):475-480
Let X be a smooth projective variety over an algebraically closed field of characteristic 0. We prove that the category of μ-semistable reflexive sheaves of slope μ equivariant for the action of some group on X is Abelian. The same claim for and a stronger semistability condition gives us a geometric proof of the fact that the category of mixed Hodge structures is Abelian. To cite this article: O. Penacchio, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 475–480. 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