全文获取类型
收费全文 | 7208篇 |
免费 | 882篇 |
国内免费 | 611篇 |
专业分类
化学 | 234篇 |
晶体学 | 4篇 |
力学 | 812篇 |
综合类 | 170篇 |
数学 | 6162篇 |
物理学 | 1319篇 |
出版年
2024年 | 13篇 |
2023年 | 60篇 |
2022年 | 77篇 |
2021年 | 104篇 |
2020年 | 155篇 |
2019年 | 168篇 |
2018年 | 190篇 |
2017年 | 213篇 |
2016年 | 255篇 |
2015年 | 156篇 |
2014年 | 279篇 |
2013年 | 566篇 |
2012年 | 323篇 |
2011年 | 376篇 |
2010年 | 349篇 |
2009年 | 402篇 |
2008年 | 454篇 |
2007年 | 453篇 |
2006年 | 438篇 |
2005年 | 413篇 |
2004年 | 379篇 |
2003年 | 320篇 |
2002年 | 351篇 |
2001年 | 237篇 |
2000年 | 281篇 |
1999年 | 226篇 |
1998年 | 195篇 |
1997年 | 183篇 |
1996年 | 135篇 |
1995年 | 157篇 |
1994年 | 103篇 |
1993年 | 108篇 |
1992年 | 90篇 |
1991年 | 63篇 |
1990年 | 76篇 |
1989年 | 48篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 40篇 |
1985年 | 24篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 18篇 |
1974年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有8701条查询结果,搜索用时 15 毫秒
81.
基于爆轰波原理声源定位方法初探 总被引:5,自引:0,他引:5
基于弹丸发射时所发出的爆轰波,利用传感器接收时差信息,从而确定声源位置。本文建立了该声源定位反问题的物理和数学模型,并依据该模型寻求适当的数值解法,最后针对延拓-广义逆法声源定位问题进行了演算和简要分析。 相似文献
82.
The difference between the classical treatment offlexible body impact and the treatment of impact in flexiblemultibody dynamics is due to several fundamental reasons. Inthe classical impact theory, simple structures such as beamsand plates are used. Infinite dimensional models can bedeveloped for these simple structural elements to study theimpact dynamics and the wave propagation problem. Flexiblemultibody impact problems, on the other hand, involve bodieswith complex geometry that cannot be modeled using infinitenumber of degrees of freedom. Furthermore, the classicalimpact theory has been mainly concerned with the impactbetween a rigid mass that moves without constraints beforeit impacts a simple flexible structure. This is not amultibody simulation scenario in which the impact occursbetween kinematically constrained bodies that are subjectedto impulsive constraint forces in addition to the impactforces. These constraint forces can influence the motion ofthe two bodies immediately after impact, and as aconsequence, the simple classical theory scenario of impactdoes not apply. It is the objective of this paper to discussthe use of the restitution condition in flexible multibodyimpact problems and demonstrate that the use of thisapproach does not exclude the classical formulation.Nonetheless, the impulse momentum balance approach can serveas an effective and efficient procedure for solving theimpact problem in finite dimensional models that do not obeythe classical wave theory. Energy results of simplestructural elements are presented in order to demonstratethe consistency of using the impulse momentum balanceapproach in solving impact problems in finite dimensionalflexible body applications. 相似文献
83.
Jie-Fang Zhang 《Acta Mechanica Solida Sinica》1991,4(2):139-151
Based on D'Alembert's principle of a mechanical system relative to non-inertial frame and by introducing the concept of the generalized inertial potential, new forms of differential equations of motion of a mechanical system with holonomic and the non-holonomic constraints relative to the non-inertial frame are obtained. The merits and demerits between our method and the Newtonian dynamic method as well as the analytic dynamic method are discussed comparatively. Finally, two examples are given to illustrate the application of the motive differential equations in the new forms. 相似文献
84.
85.
Koen Thas 《Journal of Algebraic Combinatorics》2006,24(1):5-22
In this paper, we classify the finite generalized quadrangles of order (s,t), s,t > 1, which have a line L of elation points, with the additional property that there is a line M not meeting L for which {L, M} is regular. This is a first fundamental step towards the classification of those generalized quadrangles having a line of
elation points.
Mathematics Subject Classification (2000): 51E12, 51E20, 20B25, 20E42 相似文献
86.
在实自反Banach空间,用补偿方法研究单调和Fuzzy单调广义非线性变分不等式,得到了几个解的存在性定理.改进和推广了Browder,Pascali-Sburlan,Zhang等人的各种结果. 相似文献
87.
88.
89.
J. Kogan 《Journal of Optimization Theory and Applications》1989,63(2):225-260
In this paper, we study intersections of extremals in a linear-quadratic Bolza problem of optimal control. The structure of the inter-sections is described. We show that this structure implies the semipositive definiteness of the quadratic cost functional. In addition, we derive necessary and sufficient conditions for the existence of minimizers. 相似文献
90.
Wei Gang SU Huai Jie ZHONG 《数学学报(英文版)》2006,22(2):515-522
This paper introduces the concept of the generalized Riesz operators and the concept of the generalized West decomposition of a general operator which generalizes the definition of the West decomposition of Riesz operators, and proves that the following three statements are equivalent on a general Banach space:
(a) Every generalized Riesz operator has the generalized West decomposition;
(b) Every operator makes strong Stampfli theorem true; Every operator has Apostol's compact correction. 相似文献