全文获取类型
收费全文 | 17849篇 |
免费 | 1954篇 |
国内免费 | 1056篇 |
专业分类
化学 | 5815篇 |
晶体学 | 42篇 |
力学 | 1621篇 |
综合类 | 152篇 |
数学 | 9319篇 |
物理学 | 3910篇 |
出版年
2023年 | 193篇 |
2022年 | 198篇 |
2021年 | 293篇 |
2020年 | 543篇 |
2019年 | 422篇 |
2018年 | 389篇 |
2017年 | 392篇 |
2016年 | 641篇 |
2015年 | 615篇 |
2014年 | 830篇 |
2013年 | 1475篇 |
2012年 | 955篇 |
2011年 | 1034篇 |
2010年 | 756篇 |
2009年 | 1149篇 |
2008年 | 1110篇 |
2007年 | 1156篇 |
2006年 | 1061篇 |
2005年 | 812篇 |
2004年 | 749篇 |
2003年 | 715篇 |
2002年 | 631篇 |
2001年 | 592篇 |
2000年 | 538篇 |
1999年 | 492篇 |
1998年 | 469篇 |
1997年 | 357篇 |
1996年 | 360篇 |
1995年 | 236篇 |
1994年 | 204篇 |
1993年 | 186篇 |
1992年 | 129篇 |
1991年 | 122篇 |
1990年 | 106篇 |
1989年 | 83篇 |
1988年 | 98篇 |
1987年 | 65篇 |
1986年 | 76篇 |
1985年 | 68篇 |
1984年 | 85篇 |
1983年 | 37篇 |
1982年 | 55篇 |
1981年 | 51篇 |
1980年 | 38篇 |
1979年 | 48篇 |
1978年 | 52篇 |
1977年 | 54篇 |
1976年 | 48篇 |
1975年 | 18篇 |
1974年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
反对称正交对称矩阵反问题 总被引:6,自引:0,他引:6
本文讨论一类反对称正交对称矩阵反问题及其最佳逼近.研究了这类矩阵的一些性质,利用这些性质给出了反问题解存在的一些条件和解的一般表达式,不仅证明了最佳逼近解的存在唯一性,而且给出了此解的具体表达式. 相似文献
72.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
73.
Krzysztof Pawaowski 《K-Theory》1998,13(1):41-55
The paper presents a procedure for constructing smooth actions of finite perfect groups on spheres with fixed point sets having certain prescribed properties (Theorem A); in particular, having any prescribed configuration of Chern and Pontryagin numbers (Corollary C). The main ingredients used are equivariant thickening and equivariant surgery. 相似文献
74.
75.
This paper presents a unified analysis of decomposition algorithms for continuously differentiable optimization problems defined on Cartesian products of convex feasible sets. The decomposition algorithms are analyzed using the framework of cost approx imation algorithms. A convergence analysis is made for three decomposition algorithms: a sequential algorithm which extends the classical Gauss-Seidel scheme, a synchronized parallel algorithm which extends the Jacobi method, and a partially asynchronous parallel algorithm. The analysis validates inexact computations in both the subproblem and line search phases, and includes convergence rate results. The range of feasible step lengths within each algorithm is shown to have a direct correspondence to the increasing degree of parallelism and asynchronism, and the resulting usage of more outdated information in the algorithms. 相似文献
76.
The projective method for solving linear matrix inequalities 总被引:2,自引:0,他引:2
Numerous problems in control and systems theory can be formulated in terms of linear matrix inequalities (LMI). Since solving
an LMI amounts to a convex optimization problem, such formulations are known to be numerically tractable. However, the interest
in LMI-based design techniques has really surged with the introduction of efficient interior-point methods for solving LMIs
with a polynomial-time complexity. This paper describes one particular method called the Projective Method. Simple geometrical
arguments are used to clarify the strategy and convergence mechanism of the Projective algorithm. A complexity analysis is
provided, and applications to two generic LMI problems (feasibility and linear objective minimization) are discussed. 相似文献
77.
We present a numerical implementation of the parallel gradient distribution (PGD) method for the solution of large-scale unconstrained optimization problems. The proposed parallel algorithm is characterized by a parallel phase which exploits the portions of the gradient of the objective function assigned to each processor; then, a coordination phase follows which, by a synchronous interaction scheme, optimizes over the partial results obtained by the parallel phase. The parallel and coordination phases are implemented using a quasi-Newton limited-memory BFGS approach. The computational experiments, carried out on a network of UNIX workstations by using the parallel software tool PVM, show that parallelization efficiency was problem dependent and ranged between 0.15 and 8.75. For the 150 problems solved by PGD on more than one processor, 85 cases had parallelization efficiency below 1, while 65 cases had a parallelization efficiency above 1. 相似文献
78.
The number of trials that is required by an algorithm to produce a given fraction of the problem solutions with a specified level of confidence is analyzed. The analysis indicates that the number of trials required to find a large fraction of the solutions rapidly decreases as the number of solutions obtained on each trial by an algorithm increases. In applications where multiple solutions are sought, this decrease in the number of trials could potentially offset the additional computational cost of algorithms that produce multiple solutions on a single trial. The analysis framework presented is used to compare the efficiency of a homotopy algorithm to that of a Newton method by measuring both the number of trials and the number of calculations required to obtain a specified fraction of the solutions. 相似文献
79.
Wolfgang Kirmse 《Angewandte Chemie (International ed. in English)》1997,36(11):1164-1170
Alkenylidenes R2C?C: (= alkylidene carbenes) undergo regio- and stereoselective intramolecular C? H insertion reactions that are excellently suited for the synthesis of cyclopentenes. The 1, 2-shifts occurring with R?H and R?Ar are useful for the preparation of alkynes. Alkenylidenes are efficiently generated from carbonyl compounds by diazomethylation, from vinyl halides by α-elimination, from alkynyliodonium salts by addition of nucleophiles, and from alkynes by retro-1, 2-shifts. Specific applications of the various methods, particularly in the synthesis of natural products, are discussed. 相似文献
80.