全文获取类型
收费全文 | 6767篇 |
免费 | 703篇 |
国内免费 | 273篇 |
专业分类
化学 | 588篇 |
晶体学 | 12篇 |
力学 | 703篇 |
综合类 | 34篇 |
数学 | 3445篇 |
物理学 | 2961篇 |
出版年
2024年 | 12篇 |
2023年 | 42篇 |
2022年 | 86篇 |
2021年 | 108篇 |
2020年 | 183篇 |
2019年 | 181篇 |
2018年 | 159篇 |
2017年 | 151篇 |
2016年 | 155篇 |
2015年 | 191篇 |
2014年 | 305篇 |
2013年 | 798篇 |
2012年 | 323篇 |
2011年 | 435篇 |
2010年 | 362篇 |
2009年 | 441篇 |
2008年 | 476篇 |
2007年 | 485篇 |
2006年 | 388篇 |
2005年 | 249篇 |
2004年 | 231篇 |
2003年 | 211篇 |
2002年 | 235篇 |
2001年 | 190篇 |
2000年 | 181篇 |
1999年 | 143篇 |
1998年 | 136篇 |
1997年 | 110篇 |
1996年 | 94篇 |
1995年 | 102篇 |
1994年 | 80篇 |
1993年 | 88篇 |
1992年 | 51篇 |
1991年 | 50篇 |
1990年 | 52篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 20篇 |
1984年 | 27篇 |
1983年 | 7篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 9篇 |
1975年 | 4篇 |
排序方式: 共有7743条查询结果,搜索用时 15 毫秒
1.
2.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
3.
José E. Valdés 《Operations Research Letters》2006,34(1):49-52
Components C1 and C2 form a series system. Suppose we can allocate the spare R1 in parallel with C1 and the spare R2 in parallel with C2, or otherwise, allocate R1 with C2 and R2 with C1. In this paper, we compare these two options using hazard rate ordering. 相似文献
4.
Yu. M. Smirnov 《Journal of Applied Spectroscopy》2006,73(6):785-791
Dissociative excitation of the lead atom in e-PbI2 collisions has been studied experimentally. 27 excitation cross sections were measured for an energy of the exciting electrons
equal to 100 eV. Nine optical excitation functions were recorded with variation of the electron energy in the range 0–100
eV. The most probable reaction channels for low electron energies are discussed, as well as the ratio of the dissociative
excitation cross sections for the lead atom in e-PbI2 and e-PbCl2 collisions.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 701–706, November–December, 2006. 相似文献
5.
An Nd:YAG laser-pumped periodically poled RbTiOAsO4 (PPRTA) optical parametric oscillator (OPO) near degeneracy is reported. At a pump power of 3.7 W, a net conversion efficiency of 43% was obtained. These crystals were found to be phase-matchable for the higher order quasi-phase-matched second-harmonic generation (SHG) in the visible range. Detailed analyses of the phase-matching properties for these processes were made by using the published Sellmeier and thermo-optic dispersion formulas. 相似文献
6.
Optimization technologies and environmental applications 总被引:1,自引:0,他引:1
7.
A stochastic approximation algorithm for estimating multichannel coefficients is proposed, and the estimate is proved to converge to the true parameters a.s. up-to a constant scaling factor. The estimate is updated after receiving each new observation, so the output data need not be collected in advance. The input signal is allowed to be dependent and the observation is allowed to be corrupted by noise, but no noise statistics are used in the estimation algorithm. 相似文献
8.
Robust linear optimization under general norms 总被引:1,自引:0,他引:1
We explicitly characterize the robust counterpart of a linear programming problem with uncertainty set described by an arbitrary norm. Our approach encompasses several approaches from the literature and provides guarantees for constraint violation under probabilistic models that allow arbitrary dependencies in the distribution of the uncertain coefficients. 相似文献
9.
Yan Zhibin 《东北数学》1998,(2)
SomeNotesaboutTanaka'sEquationYanZhibin(严质彬)(DepartmentofMathematics,HarbinInstituteofTechnology,Harbin,150001)AbstractLet{Wt... 相似文献
10.
Y. Yavin 《Journal of Optimization Theory and Applications》1993,78(1):77-91
Stochastic optimal control techniques are applied to compare the performance of identical medium-range air-to-air missiles which have different thrust-mass profiles. The measure of the performance is the probability of reaching a lock-on-point with a favorable range of guidance and flight parameters, during a fixed time interval [0,t
f
], given that, during the flight, the trajectories of the missile are subjected to a variety of constraints including dynamic pressure constraints. 相似文献