全文获取类型
收费全文 | 31528篇 |
免费 | 264篇 |
国内免费 | 283篇 |
专业分类
化学 | 12716篇 |
晶体学 | 303篇 |
力学 | 1439篇 |
综合类 | 12篇 |
数学 | 9260篇 |
物理学 | 8345篇 |
出版年
2021年 | 56篇 |
2020年 | 64篇 |
2019年 | 74篇 |
2018年 | 1227篇 |
2017年 | 1470篇 |
2016年 | 785篇 |
2015年 | 656篇 |
2014年 | 567篇 |
2013年 | 816篇 |
2012年 | 3323篇 |
2011年 | 2525篇 |
2010年 | 1899篇 |
2009年 | 1658篇 |
2008年 | 743篇 |
2007年 | 784篇 |
2006年 | 776篇 |
2005年 | 4579篇 |
2004年 | 4033篇 |
2003年 | 2400篇 |
2002年 | 601篇 |
2001年 | 333篇 |
2000年 | 119篇 |
1999年 | 211篇 |
1998年 | 130篇 |
1997年 | 97篇 |
1996年 | 81篇 |
1995年 | 69篇 |
1994年 | 68篇 |
1993年 | 42篇 |
1992年 | 191篇 |
1991年 | 173篇 |
1990年 | 155篇 |
1989年 | 124篇 |
1988年 | 111篇 |
1987年 | 71篇 |
1986年 | 60篇 |
1985年 | 53篇 |
1984年 | 42篇 |
1983年 | 41篇 |
1979年 | 41篇 |
1978年 | 34篇 |
1976年 | 88篇 |
1975年 | 43篇 |
1974年 | 48篇 |
1973年 | 52篇 |
1972年 | 42篇 |
1970年 | 39篇 |
1969年 | 37篇 |
1968年 | 36篇 |
1966年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 17 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.
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
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.
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
7.
Fundamental processes in long air gap discharges 总被引:2,自引:0,他引:2
I. Gallimberti G. Bacchiega Anne Bondiou-Clergerie Philippe Lalande 《Comptes Rendus Physique》2002,3(10):854
The development of atmospheric lightning is initiated and sustained by the formation in virgin air of ‘streamer corona’ and ‘leader’ discharges, very similar to those observed in laboratory long sparks. Therefore, the experimental and theoretical investigations of these laboratory discharges have become of large interest to improve the physical knowledge of the lightning process and to develop self-consistent models that could be applied to new protection concepts.In the present paper the fundamental processes of the subsequent phases of long air gap discharges are analyzed, from the first corona inception and development to the leader channel formation and propagation. For all these processes simulations models are discussed that have been essentially derived and simplified by the authors, in order to develop sequential time-dependent simulation of the laboratory breakdown, with both positive and negative voltages. The possibility of extending these models to the case of natural lightning is discussed in the companion paper, presented in this same volume. To cite this article: I. Gallimberti et al., C. R. Physique 3 (2002) 1335–1359. 相似文献
8.
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
9.
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