全文获取类型
收费全文 | 289857篇 |
免费 | 3048篇 |
国内免费 | 1267篇 |
专业分类
化学 | 150299篇 |
晶体学 | 4046篇 |
力学 | 12148篇 |
综合类 | 14篇 |
数学 | 39703篇 |
物理学 | 87962篇 |
出版年
2021年 | 1870篇 |
2020年 | 2141篇 |
2019年 | 2377篇 |
2018年 | 4535篇 |
2017年 | 4694篇 |
2016年 | 5252篇 |
2015年 | 3661篇 |
2014年 | 4898篇 |
2013年 | 12616篇 |
2012年 | 12269篇 |
2011年 | 13454篇 |
2010年 | 8751篇 |
2009年 | 8442篇 |
2008年 | 10361篇 |
2007年 | 10510篇 |
2006年 | 9731篇 |
2005年 | 14234篇 |
2004年 | 12906篇 |
2003年 | 9698篇 |
2002年 | 7047篇 |
2001年 | 7563篇 |
2000年 | 5570篇 |
1999年 | 4500篇 |
1998年 | 3736篇 |
1997年 | 3741篇 |
1996年 | 3473篇 |
1995年 | 3256篇 |
1994年 | 3078篇 |
1993年 | 3118篇 |
1992年 | 3500篇 |
1991年 | 3547篇 |
1990年 | 3306篇 |
1989年 | 3239篇 |
1988年 | 3305篇 |
1987年 | 3142篇 |
1986年 | 3018篇 |
1985年 | 4105篇 |
1984年 | 4267篇 |
1983年 | 3474篇 |
1982年 | 3867篇 |
1981年 | 3764篇 |
1980年 | 3615篇 |
1979年 | 3646篇 |
1978年 | 3895篇 |
1977年 | 3705篇 |
1976年 | 3948篇 |
1975年 | 3484篇 |
1974年 | 3609篇 |
1973年 | 3917篇 |
1972年 | 2379篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
23.
24.
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
25.
26.
27.
R. J. Vanderbei 《Mathematical Programming》1989,43(1-3):31-44
The affine-scaling modification of Karmarkar's algorithm is extended to solve problems with free variables. This extended primal algorithm is used to prove two important results. First the geometrically elegant feasibility algorithm proposed by Chandru and Kochar is the same algorithm as the one obtained by appending a single column of residuals to the constraint matrix. Second the dual algorithm as first described by Adler et al., is the same as the extended primal algorithm applied to the dual. 相似文献
28.
A new geometrical method to determine the surface damage threshold for ultrashort pulses is presented. It consists in the formation of a surface damage profile by a movement of the sample across the laser beam focus. A single measurement of the maximum transversal dimension of this damage profile, which depends solely on the laser beam power, is used to calculate the local damage threshold intensity. It is also theoretically shown that the damage in the transverse dimension can be controlled under the diffraction-limited spot. 相似文献
29.
Aidan Mooney John G. Keating Daniel M. Heffernan 《Chaos, solitons, and fractals》2006,30(5):1088-1097
A digital watermark is a visible, or preferably invisible, identification code that is permanently embedded in digital media, to prove owner authentication and provide protection for documents. Given the interest in watermark generation using chaotic functions a detailed study of one chaotic function for this purpose is performed. In this paper, we present an approach for the generation of watermarks using the logistic map. Using this function, in conjunction with seed management, it is possible to generate chaotic sequences that may be used to create highpass or lowpass digital watermarks. In this paper we provide a detailed study on the generation of optically detectable watermarks and we provide some guidelines on successful chaotic watermark generation using the logistic map, and show using a recently published scheme, how care must be taken in the selection of the function seed. 相似文献
30.
R. J. Hinde 《Few-Body Systems》2006,38(2-4):187-191
We compute the vibrational coupling between two H2 molecules from ab initio quantum chemical calculations of the H2-H2 potential carried out at the full configuration interaction level of theory using the atom-centered aug-cc-pVTZ basis set
for hydrogen. We compare the full configuration interaction results with those obtained using two variants of coupled cluster
theory and find that a fully iterative treatment of connected triples may be required to estimate the H2-H2 vibrational coupling accurately using coupled cluster theory. 相似文献