全文获取类型
收费全文 | 5668篇 |
免费 | 455篇 |
国内免费 | 462篇 |
专业分类
化学 | 1662篇 |
晶体学 | 85篇 |
力学 | 259篇 |
综合类 | 46篇 |
数学 | 1307篇 |
物理学 | 1416篇 |
无线电 | 1810篇 |
出版年
2024年 | 12篇 |
2023年 | 62篇 |
2022年 | 96篇 |
2021年 | 130篇 |
2020年 | 126篇 |
2019年 | 150篇 |
2018年 | 142篇 |
2017年 | 230篇 |
2016年 | 260篇 |
2015年 | 220篇 |
2014年 | 385篇 |
2013年 | 474篇 |
2012年 | 278篇 |
2011年 | 334篇 |
2010年 | 325篇 |
2009年 | 334篇 |
2008年 | 334篇 |
2007年 | 328篇 |
2006年 | 289篇 |
2005年 | 267篇 |
2004年 | 279篇 |
2003年 | 185篇 |
2002年 | 184篇 |
2001年 | 135篇 |
2000年 | 123篇 |
1999年 | 99篇 |
1998年 | 107篇 |
1997年 | 94篇 |
1996年 | 73篇 |
1995年 | 70篇 |
1994年 | 66篇 |
1993年 | 59篇 |
1992年 | 44篇 |
1991年 | 18篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 18篇 |
1986年 | 9篇 |
1985年 | 22篇 |
1984年 | 13篇 |
1983年 | 7篇 |
1982年 | 21篇 |
1981年 | 31篇 |
1980年 | 23篇 |
1979年 | 15篇 |
1978年 | 11篇 |
1977年 | 13篇 |
1976年 | 16篇 |
1975年 | 7篇 |
1973年 | 7篇 |
排序方式: 共有6585条查询结果,搜索用时 31 毫秒
91.
Ram Manohar & Rajen Kumar Sinha 《计算数学(英文版)》2022,40(2):147-176
This article studies a posteriori error analysis of fully discrete finite element approximations for semilinear parabolic optimal control problems. Based on elliptic reconstruction approach introduced earlier by Makridakis and Nochetto [25], a residual based a posteriori error estimators for the state, co-state and control variables are derived. The space discretization of the state and co-state variables is done by using the piecewise linear and continuous finite elements, whereas the piecewise constant functions are employed for the control variable. The temporal discretization is based on the backward Euler method. We derive a posteriori error estimates for the state, co-state and control variables in the $L^\infty(0,T;L^2(\Omega))$-norm. Finally, a numerical experiment is performed to illustrate the performance of the derived estimators. 相似文献
92.
In this paper we present and study a new algorithm for the Maximum Satisfiability (Max Sat) problem. The algorithm is based on the Method of Conditional Expectations (MOCE, also known as Johnson’s Algorithm) and applies a greedy variable ordering to MOCE. Thus, we name it Greedy Order MOCE (GO-MOCE). We also suggest a combination of GO-MOCE with CCLS, a state-of-the-art solver. We refer to this combined solver as GO-MOCE-CCLS.We conduct a comprehensive comparative evaluation of GO-MOCE versus MOCE on random instances and on public competition benchmark instances. We show that GO-MOCE reduces the number of unsatisfied clauses by tens of percents, while keeping the runtime almost the same. The worst case time complexity of GO-MOCE is linear. We also show that GO-MOCE-CCLS improves on CCLS consistently by up to about 80%.We study the asymptotic performance of GO-MOCE. To this end, we introduce three measures for evaluating the asymptotic performance of algorithms for Max Sat. We point out to further possible improvements of GO-MOCE, based on an empirical study of the main quantities managed by GO-MOCE during its execution. 相似文献
93.
Robert P. Apaya Baldo Lucchese Sarah L. Price J.G. Vinter 《Journal of computer-aided molecular design》1995,9(1):33-43
Summary Ligands which bind to a specific protein binding site are often expected to have a similar electrostatic environment which complements that of the binding site. One method of assessing molecular electrostatic similarity is to examine the possible overlay of the maxima and minima in the electrostatic potential outside the molecules and thereby match the regions where strong electrostatic interactions, including hydrogen bonds, with the residues of the binding site may be possible. This approach is validated with accurate calculations of the electrostatic potential, derived from a distributed multipole analysis of an ab initio charge density of the molecule, so that the effects of lone pair and -electron density are correctly included. We have applied this method to the phosphodiesterase (PDE) III substrate adenosine-3,5-cyclic monophosphate (cAMP) and a range of nonspecific and specific PDE III inhibitors. Despite the structural variation between cAMP and the inhibitors, it is possible to match three or four extrema to produce relative orientations in which the inhibitors are sufficiently sterically and electrostatically similar to the natural substrate to account for their affinity for PDE III. This matching of extrema is more apparent using the accurate electrostatic models than it was when this approach was first applied, using semiempirical point charge models. These results reinforce the hypothesis of electrostatic similarity and give weight to the technique of extrema matching as a useful tool in drug design. 相似文献
94.
Best possibility of the Furuta inequality 总被引:5,自引:0,他引:5
Let , and . Furuta (1987) proved that if bounded linear operators on a Hilbert space satisfy , then . In this paper, we prove that the range and is best possible with respect to the Furuta inequality, that is, if or , then there exist which satisfy but .
95.
A study on the ductile deformation domain of the brittle fault in the shallow level ofthe crust is a new probe field for the modern structural geology. Taking the southern Jiang-su Province area as an example the orientation measurement of quartz crystals, the com-positional texture observation of three pressure sensitive minerals and the rheological param-eter determination of dislocation densities, etc. have been demonstrated and analysed basedon typical samples in the present paper. In addition, their generation mechanisms arealso discussed from the cataclastic rheology, the dynamic differentiation and the simpleshearing, specially, from the Ode strength theory. Finally, a generative relationship betweenthe ductile deformation domain of the brittle fault system, in the regional layer--slip andthe formation of the stratabound ore deposit is shown as well. 相似文献
96.
The vertical ionization potentials of difluoramine are calculated by perturbation corrections to Koopmans' theorem. The calculation shows that difluoraimine has three overlapping bands between 15 and 16 eV. The calculated results compare well with the experimental values. The photoelectron spectrum of difluoramine is compared with that of OF2 and CH2F2. 相似文献
97.
98.
99.
100.