首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13304篇
  免费   2265篇
  国内免费   779篇
化学   1694篇
晶体学   145篇
力学   2325篇
综合类   164篇
数学   5238篇
物理学   4145篇
无线电   2637篇
  2024年   28篇
  2023年   125篇
  2022年   197篇
  2021年   228篇
  2020年   324篇
  2019年   285篇
  2018年   263篇
  2017年   400篇
  2016年   445篇
  2015年   362篇
  2014年   595篇
  2013年   876篇
  2012年   752篇
  2011年   691篇
  2010年   638篇
  2009年   713篇
  2008年   817篇
  2007年   917篇
  2006年   837篇
  2005年   840篇
  2004年   703篇
  2003年   738篇
  2002年   626篇
  2001年   559篇
  2000年   512篇
  1999年   444篇
  1998年   353篇
  1997年   333篇
  1996年   231篇
  1995年   202篇
  1994年   163篇
  1993年   170篇
  1992年   131篇
  1991年   111篇
  1990年   95篇
  1989年   56篇
  1988年   62篇
  1987年   55篇
  1986年   47篇
  1985年   63篇
  1984年   53篇
  1983年   31篇
  1982年   37篇
  1981年   49篇
  1980年   27篇
  1979年   34篇
  1978年   43篇
  1977年   32篇
  1976年   20篇
  1971年   9篇
排序方式: 共有10000条查询结果,搜索用时 813 毫秒
981.
982.
In this paper, we prove that a class of parabolic equations involving a second order fully nonlinear uniformly elliptic operator has a Fujita type exponent. These exponents are related with an eigenvalue problem in all RN and play the same role in blow-up theorems as the classical p?=1+2/N introduced by Fujita for the Laplacian. We also obtain some associated existence results.  相似文献   
983.
The purpose of this paper is by using the generalized projection approach to introduce an iterative scheme for finding a solution to a system of generalized nonlinear variational inequality problem. Under suitable conditions, some existence and strong convergence theorems are established in uniformly smooth and strictly convex Banach spaces. The results presented in the paper improve and extend some recent results.  相似文献   
984.
A number of novel acid-sensitive Schiff bases derived from p-aminobenzyl alcohol and various benzaldehyde derivatives were synthesized and were subsequently shown to trigger benzyl elimination reactions. The kinetics of acid-catalyzed hydrolysis at pH 5.0 as well as stability at pH 7.4 were studied using fluorogenic model compounds. Two fluoro-substituted Schiff bases showed efficient hydrolysis at pH 5.0 combined with a long-term stability at pH 7.4 and are considered suitable candidates for the development of anticancer prodrugs.  相似文献   
985.
根据对数型非线性介质中高斯光束的束宽和波阵面曲率变化所满足的耦合方程,采用数值计算对高斯光束的传输特性进行了详细的分析。结合相图分析了高斯光束在不同初始条件下束宽与波阵面的变化情况。利用力学类比,讨论了高斯光束在传输过程中形成的对称呼吸模式与不对称呼吸模式的空间孤子。  相似文献   
986.
直线加速器中束团的非线性空间电荷效应是引起发射度增长的重要原因之一.根据计算在屏蔽筒中非均匀分布京团的空间电荷效应的普遍方法,推导了直线加速器圆波导中几种非均匀分布束团的非线性场能公式,并给出数值计算结果.讨论了由非线性所引起发射度增长.  相似文献   
987.
Service providers often offer tariff structures with several two-part tariffs that consist of a fixed fee and a usage price, such that consumers may pick the tariff they prefer. Prices of tariffs have significant impacts on service providers’ profit, because they simultaneously influence consumers’ tariff choices and their usage. The number of tariffs also plays an important role, because more tariffs segment the market better but also increase the administrative burden and require more marketing effort. This article presents a mixed-integer nonlinear programming optimization problem to determine profit-maximizing tariffs; compares several heuristic search methods, in particular, the gradient method, stochastic search, and simulated annealing, to solve this problem; analyses the profitability of different tariff structures; and outlines the factors that drive differences in profitability across various tariff structures. The results show that especially for large samples of more than 100 consumers, simulated annealing performs best and deviates only 0.2% from the optimum. Structures with fewer two-part tariffs are generally sufficient, because additional two-part tariffs only negligibly increase service providers’ profit.  相似文献   
988.
In this paper, we prove a Hadamard property and Liouville type theorems for viscosity solutions of fully nonlinear elliptic partial differential equations with a gradient term, both in the whole space and in an exterior domain.  相似文献   
989.
Psychophysical tasks requiring stimulus discrimination frequently report underconfidence; subjects think they are doing less accurately at discrimination or identification than is the case, measured in terms of probabilities of correct performance. An investigation to see if underconfidence is predictable from the intrinsic nonlinearities of the psychophysics, without assuming that confidence itself is a subjective analogue of a frequentist probability of correct identification, is explored using the algebra of cascaded nonlinear psychophysics previously developed.  相似文献   
990.
Two interior-point algorithms using a wide neighborhood of the central path are proposed to solve nonlinear P *-complementarity problems. The proof of the polynomial complexity of the first method requires the problem to satisfy a scaled Lipschitz condition. When specialized to monotone complementarity problems, the results of the first method are similar to those in Ref. 1. The second method is quite different from the first in that the global convergence proof does not require the scaled Lipschitz assumption. However, at each step of this algorithm, one has to compute an approximate solution of a nonlinear system such that a certain accuracy requirement is satisfied.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号