全文获取类型
收费全文 | 18829篇 |
免费 | 1389篇 |
国内免费 | 1789篇 |
专业分类
化学 | 879篇 |
晶体学 | 16篇 |
力学 | 928篇 |
综合类 | 453篇 |
数学 | 17479篇 |
物理学 | 2252篇 |
出版年
2024年 | 20篇 |
2023年 | 175篇 |
2022年 | 185篇 |
2021年 | 270篇 |
2020年 | 355篇 |
2019年 | 400篇 |
2018年 | 379篇 |
2017年 | 463篇 |
2016年 | 494篇 |
2015年 | 365篇 |
2014年 | 791篇 |
2013年 | 1266篇 |
2012年 | 822篇 |
2011年 | 1066篇 |
2010年 | 932篇 |
2009年 | 1298篇 |
2008年 | 1281篇 |
2007年 | 1412篇 |
2006年 | 1154篇 |
2005年 | 1033篇 |
2004年 | 798篇 |
2003年 | 838篇 |
2002年 | 794篇 |
2001年 | 731篇 |
2000年 | 753篇 |
1999年 | 641篇 |
1998年 | 603篇 |
1997年 | 514篇 |
1996年 | 382篇 |
1995年 | 256篇 |
1994年 | 215篇 |
1993年 | 157篇 |
1992年 | 114篇 |
1991年 | 111篇 |
1990年 | 98篇 |
1989年 | 62篇 |
1988年 | 57篇 |
1987年 | 42篇 |
1986年 | 43篇 |
1985年 | 111篇 |
1984年 | 103篇 |
1983年 | 46篇 |
1982年 | 92篇 |
1981年 | 64篇 |
1980年 | 58篇 |
1979年 | 49篇 |
1978年 | 33篇 |
1977年 | 23篇 |
1976年 | 18篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
31.
32.
We consider some Sobolev-type spaces and obtain a necessary and sufficient condition for their embedding in a Lebesgue space. 相似文献
33.
In this paper we consider an initial boundary value problem for a reaction-diffusion equation under nonlinear and nonlocal Robin type boundary condition. Assuming the existence of an ordered pair of upper and lower solutions we establish a generalized quasilinearization method for the problem under consideration whose characteristic feature consists in the construction of monotone sequences converging to the unique solution within the interval of upper and lower solutions, and whose convergence rate is quadratic. Thus this method provides an efficient iteration technique that produces not only improved approximations due to the monotonicity of its iterates, but yields also a measure of the convergence rate. 相似文献
34.
This paper gives some global and uniform convergence estimates for a class of subspace correction (based on space decomposition) iterative methods applied to some unconstrained convex optimization problems. Some multigrid and domain decomposition methods are also discussed as special examples for solving some nonlinear elliptic boundary value problems.
35.
考虑约束最优化问题:minx∈Ωf(x)其中:f:R^n→R是连续可微函数,Ω是一闭凸集。本文研究了解决此问题的梯度投影方法,在步长的选取时采用了一种新的策略,在较弱的条件下,证明了梯度投影响方法的全局收敛性。 相似文献
36.
This paper investigates the large scale travelling ionospheric disturbances (LSTIDs) using the observation data of an HF Doppler array located in Central China. The data observed in a high solar activity year (year 1989) are analyzed to obtain the main propagation parameters of LSTIDs such as period, horizontal phase velocity and propagating direction. Results are outlined as follows: Most of the LSTIDs propagate southward; others tend to propagate northward, mostly in summer; dispersion of most LSTIDs is matched with that of Lamb pseudomode, while others have the dispersion of long period gravity wave mode. The horizontal phase velocities of these two modes are about 220 and 450 m/s respectively. The analysis shows that LSTIDs are strongly pertinent to solar activity and space magnetic storms; thus the results presented here are significant for the research of ionospheric weather in mid-low latitude region. 相似文献
37.
Dalila B. M. M. Fontes Eleni Hadjiconstantinou Nicos Christofides 《Journal of Global Optimization》2006,34(1):97-125
In this paper we obtain Lower Bounds (LBs) to concave cost network flow problems. The LBs are derived from state space relaxations
of a dynamic programming formulation, which involve the use of non-injective mapping functions guaranteing a reduction on
the cardinality of the state space. The general state space relaxation procedure is extended to address problems involving
transitions that go across several stages, as is the case of network flow problems. Applications for these LBs include: estimation
of the quality of heuristic solutions; local search methods that use information of the LB solution structure to find initial
solutions to restart the search (Fontes et al., 2003, Networks, 41, 221–228); and branch-and-bound (BB) methods having as
a bounding procedure a modified version of the LB algorithm developed here, (see Fontes et al., 2005a). These LBs are iteratively
improved by penalizing, in a Lagrangian fashion, customers not exactly satisfied or by performing state space modifications.
Both the penalties and the state space are updated by using the subgradient method. Additional constraints are developed to
improve further the LBs by reducing the searchable space. The computational results provided show that very good bounds can
be obtained for concave cost network flow problems, particularly for fixed-charge problems. 相似文献
38.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
39.
一阶形式系统K~*及其完备性 总被引:2,自引:0,他引:2
裴道武 《数学年刊A辑(中文版)》2002,(6)
模糊命题演算的形式系统L*已经在模糊逻辑与模糊推理的结合研究中得到了成功的应用.本文考虑与系统L*相应的一阶逻辑理论,建立了一阶形式系统K*,并证明了这个系统的完备性. 相似文献
40.
An admissible minimax estimator of a bounded scale-parameter in a subclass of the exponential family under scale-invariant squared-error loss 总被引:3,自引:0,他引:3
Mohammad Jafari Jozani Nader Nematollahi Khalil Shafie 《Statistics & probability letters》2002,60(4):437-444
A subclass of the scale-parameter exponential family is considered and for the rth power of the scale parameter, which is lower bounded, an admissible minimax estimator under scale-invariant squared-error loss is presented. Also, an admissible minimax estimator of a lower-bounded parameter in the family of transformed chi-square distributions is given. These estimators are the pointwise limits of a sequence of Bayes estimators. Some examples are given. 相似文献