全文获取类型
收费全文 | 180232篇 |
免费 | 10156篇 |
国内免费 | 11600篇 |
专业分类
化学 | 33984篇 |
晶体学 | 456篇 |
力学 | 7567篇 |
综合类 | 1388篇 |
数学 | 27497篇 |
物理学 | 29049篇 |
综合类 | 102047篇 |
出版年
2024年 | 268篇 |
2023年 | 1153篇 |
2022年 | 2179篇 |
2021年 | 2490篇 |
2020年 | 2766篇 |
2019年 | 2813篇 |
2018年 | 2473篇 |
2017年 | 3071篇 |
2016年 | 3522篇 |
2015年 | 3984篇 |
2014年 | 7035篇 |
2013年 | 8592篇 |
2012年 | 8664篇 |
2011年 | 9674篇 |
2010年 | 8131篇 |
2009年 | 9863篇 |
2008年 | 10511篇 |
2007年 | 12394篇 |
2006年 | 11835篇 |
2005年 | 10962篇 |
2004年 | 9457篇 |
2003年 | 8909篇 |
2002年 | 7730篇 |
2001年 | 6645篇 |
2000年 | 5957篇 |
1999年 | 5020篇 |
1998年 | 4372篇 |
1997年 | 3853篇 |
1996年 | 3545篇 |
1995年 | 3221篇 |
1994年 | 3034篇 |
1993年 | 2617篇 |
1992年 | 2459篇 |
1991年 | 2144篇 |
1990年 | 1911篇 |
1989年 | 1814篇 |
1988年 | 1554篇 |
1987年 | 984篇 |
1986年 | 678篇 |
1985年 | 537篇 |
1984年 | 484篇 |
1983年 | 221篇 |
1982年 | 366篇 |
1981年 | 421篇 |
1980年 | 314篇 |
1979年 | 299篇 |
1978年 | 237篇 |
1977年 | 210篇 |
1976年 | 157篇 |
1973年 | 118篇 |
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
981.
CsLiB6O10晶体光参量振荡器的线宽分析 总被引:1,自引:1,他引:0
采用355nm脉冲激光作为泵浦源,对影响CsLiB_6O_(10)晶体光参量振荡器的信号光线宽的各种物理机制进行了数值模拟计算和分析.结果表明,泵浦光的发散角和偏轴方向对信号光线宽的影响较大。 相似文献
982.
Paul Howard 《Mathematical Logic Quarterly》2007,53(3):247-254
Two theorems are proved: First that the statement “there exists a field F such that for every vector space over F, every generating set contains a basis” implies the axiom of choice. This generalizes theorems of Halpern, Blass, and Keremedis. Secondly, we prove that the assertion that every vector space over ?2 has a basis implies that every well‐ordered collection of two‐element sets has a choice function. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
983.
分析了几种相关结构函数(Copula)表示的相关结构模型,给出了用相关结构函数对金融资产间的相关结构进行建模的方法.结果表明混合Gumbel(M-Gumbel)相关结构函数能较全面地描述上海深圳两证券指数的相关结构,模拟计算VaR的结果支持了实证分析的结论. 相似文献
984.
We construct separation variables for the Kovalevskaya–Goryachev–Chaplygin gyrostat for arbitrary values of the parameters. We show that different separation variables can be constructed for the same integrable system if different integrals of motion are chosen. 相似文献
985.
Marta Gimnez-Pedrs Ali Aghmiz Carmen Claver Anna M. Masdeu-Bult Denis Sinou 《Journal of molecular catalysis. A, Chemical》2003,200(1-2):157-163
High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO4) as the surfactant or methanol as the co-solvent. 相似文献
986.
In this paper, we examine a class of convex problems of Bolza type, involving a time delay in the state. It encompasses a variety of time-delay problems arising in the calculus of variations and optimal control. A duality analysis is carried out which, among other things, leads to a characterization of minimizers in terms of the Euler-Lagrange inclusion. The results obtained improve in significant respects on what is achievable by techniques previously employed, based on elimination of the time delay by introduction of an infinite-dimensional state space or on the method of steps. 相似文献
987.
Markus Hegland Jochen Garcke Vivien Challis 《Linear algebra and its applications》2007,420(2-3):249-275
The combination technique has repeatedly been shown to be an effective tool for the approximation with sparse grid spaces. Little is known about the reasons of this effectiveness and in some cases the combination technique can even break down. It is known, however, that the combination technique produces an exact result in the case of a projection into a sparse grid space if the involved partial projections commute.
The performance of the combination technique is analysed using a projection framework and the C/S decomposition. Error bounds are given in terms of angles between the spanning subspaces or the projections onto these subspaces. Based on this analysis modified combination coefficients are derived which are optimal in a certain sense and which can substantially extend the applicability and performance of the combination technique. 相似文献
988.
Wing-Sum Cheung Patricia J.Y. Wong 《Journal of Mathematical Analysis and Applications》2007,329(2):851-869
We consider a system of focal boundary value problems where the nonlinearities may be singular in the independent variable and may also be singular in the dependent arguments. Using Schauder fixed point theorem, we establish criteria such that the system of boundary value problems has at least one fixed-sign solution. 相似文献
989.
Considering a plane hyperbolic system with time-periodic coefficients, we construct a version of the direct Lyapunov method with the condition on the derivative of the Lyapunov functional along the trajectories of the system which is weakened by use of periodicity of the coefficients. We exhibit an illustrative example. 相似文献
990.
Chang-jian Zhao 《中国科学A辑(英文版)》2007,50(9):1347-1360
In this paper, we first introduce a concept of L
p
-dual Quermassintegral sum function of convex bodies and establish the polar projection Minkowski inequality and the polar
projection Aleksandrov-Fenchel inequality for L
p
-dual Quermassintegral sums. Moreover, by using Lutwak’s width-integral of index i, we establish the L
p
-Brunn-Minkowski inequality for the polar mixed projection bodies. As applications, we prove some interrelated results.
This work was partially supported by the National Natural Science Foundation of China (Grant No. 10271071), Zhejiang Provincial
Natural Science Foundation of China (Grant No. Y605065) and Foundation of the Education Department of Zhejiang Province of
China (Grant No. 20050392) 相似文献