全文获取类型
收费全文 | 83498篇 |
免费 | 6760篇 |
国内免费 | 6974篇 |
专业分类
化学 | 26210篇 |
晶体学 | 286篇 |
力学 | 6452篇 |
综合类 | 1225篇 |
数学 | 25005篇 |
物理学 | 21119篇 |
无线电 | 16935篇 |
出版年
2024年 | 140篇 |
2023年 | 826篇 |
2022年 | 1361篇 |
2021年 | 1647篇 |
2020年 | 1737篇 |
2019年 | 1872篇 |
2018年 | 1579篇 |
2017年 | 1934篇 |
2016年 | 2246篇 |
2015年 | 2201篇 |
2014年 | 3393篇 |
2013年 | 5214篇 |
2012年 | 3784篇 |
2011年 | 4062篇 |
2010年 | 3402篇 |
2009年 | 4427篇 |
2008年 | 4940篇 |
2007年 | 5294篇 |
2006年 | 5000篇 |
2005年 | 4257篇 |
2004年 | 3877篇 |
2003年 | 3931篇 |
2002年 | 3480篇 |
2001年 | 2927篇 |
2000年 | 2834篇 |
1999年 | 2488篇 |
1998年 | 2263篇 |
1997年 | 1891篇 |
1996年 | 1757篇 |
1995年 | 1546篇 |
1994年 | 1412篇 |
1993年 | 1230篇 |
1992年 | 1167篇 |
1991年 | 918篇 |
1990年 | 761篇 |
1989年 | 642篇 |
1988年 | 565篇 |
1987年 | 432篇 |
1986年 | 364篇 |
1985年 | 436篇 |
1984年 | 434篇 |
1983年 | 215篇 |
1982年 | 342篇 |
1981年 | 403篇 |
1980年 | 305篇 |
1979年 | 293篇 |
1978年 | 221篇 |
1977年 | 206篇 |
1976年 | 155篇 |
1974年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
301.
Benxin Wu 《Applied Surface Science》2007,253(8):4079-4084
The ultra-short laser metal ablation is a very complex process, the complete simulation of which requires applications of complicated hydrodynamics or molecular dynamics models, which, however, are often time-consuming and difficult to apply. For many practical applications, where the laser ablation depth is the main concern, a simplified model that is easy to apply but at the same time can also provide reasonably accurate predictions of ablation depth is very desirable. Such a model has been developed and presented in this paper, which has been found to be applicable for laser pulse duration up to 10 ps based on comparisons of model predictions with experimental measurements. 相似文献
302.
首先通过集代数得到了Stone代数的表示定理,然后证明了每一个Stone代数均嵌入到某个集合X上的一个Stone映射类S中. 相似文献
303.
基于约束优化的联想记忆模型学习算法 总被引:1,自引:1,他引:0
本文提出了一种对称互连神经元网络的学习策略,利用全局约束优化方法确定连接权。优化过程采用了梯度下降技术。这种学习算法可以保证训练样本成为系统的稳定吸引子,并且具有优化意义上的最大吸引域。本文讨论了网络的存储容量,训练样本的渐近稳定性和吸引域大小。计算机实验结果说明了学习算法的优越性。 相似文献
304.
By Hückel molecular orbital (HMO) theory, the calculation of the total energy of all π-electrons in conjugated hydrocarbons can be reduced to that of E(G)=|λ1|+|λ2|+?+|λn|, where λi are the eigenvalues of the corresponding graph G. Denote by Ψn the set of all fully-angular polyhex chains with n hexagons. In this paper, we show that Hn has the minimum total π-electron energy among chains in Ψn, where Hn is the helicene chain. 相似文献
305.
306.
Veli B. Shakhmurov 《Journal of Mathematical Analysis and Applications》2007,327(2):1182-1201
The nonlocal boundary value problems for anisotropic partial differential-operator equations with a dependent coefficients are studied. The principal parts of the appropriate generated differential operators are nonself-adjoint. Several conditions for the maximal regularity and the fredholmness in Banach-valued Lp-spaces of these problems are given. These results permit us to establish that the inverse of corresponding differential operators belongs to Schatten q-class. Some spectral properties of the operators are investigated. In applications, the nonlocal BVP's for quasielliptic partial differential equations and for systems of quasielliptic equations on cylindrical domain are studied. 相似文献
307.
R. Uribe-Vargas 《Functional Analysis and Its Applications》2003,37(3):236-240
On a smooth surface in Euclidean 3-space, we consider vanishing curves whose projections on a given plane are small circles centered at the origin. The bifurcations diagram of a parameter-dependent surface is the set of parameters and radii of the circles corresponding to curves with degenerate flattening points. Solving a problem due to Arnold, we find a normal form of the first nontrivial example of a flattening bifurcation diagram, which contains one continuous invariant. 相似文献
308.
For one‐dimensional simple symmetric random walk, the Hausdorff and packing dimensions of sets of sample paths with prescribed rate of returns to the origin are determined. This gives a multifractal decomposition of the underlying sample space. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
309.
By introducing an imaginary space transform curvature ρs, a complex space called Riemannian space is constructed, in which the light propagating in free space has the trajectory
of straight line while propagating. Moreover, this curvature couples with that of the wave front of the paraxial beam ρw, and therefore a complex curvature ρc is constructed, which can be employed to investigate the behavior of the light transmission and to generalize the ABCD law.
Project supported by the National Hi-Tech Inertial Confinement Fusion Committee, the Guangdong Natural Science Foundation
the Postdoctoral Foundation of Guangdong and National Postdoctoral Foundation of China. 相似文献
310.
An extremum problem is embedded in a parametric scheme which contains, as a particular case, the classic perturbation function. The introduction of the image of the embedded problem allows one to derive a generalized duality and, in particular, Lagrangian and Fenchel duality. 相似文献