全文获取类型
收费全文 | 118695篇 |
免费 | 10334篇 |
国内免费 | 10841篇 |
专业分类
化学 | 54792篇 |
晶体学 | 772篇 |
力学 | 9314篇 |
综合类 | 2009篇 |
数学 | 38046篇 |
物理学 | 34937篇 |
出版年
2023年 | 1041篇 |
2022年 | 1568篇 |
2021年 | 3133篇 |
2020年 | 2772篇 |
2019年 | 2811篇 |
2018年 | 2490篇 |
2017年 | 2881篇 |
2016年 | 3394篇 |
2015年 | 3074篇 |
2014年 | 4319篇 |
2013年 | 8110篇 |
2012年 | 5329篇 |
2011年 | 5849篇 |
2010年 | 5141篇 |
2009年 | 6788篇 |
2008年 | 7214篇 |
2007年 | 7570篇 |
2006年 | 6604篇 |
2005年 | 5393篇 |
2004年 | 5003篇 |
2003年 | 4882篇 |
2002年 | 6991篇 |
2001年 | 4184篇 |
2000年 | 3656篇 |
1999年 | 3263篇 |
1998年 | 3008篇 |
1997年 | 2371篇 |
1996年 | 2121篇 |
1995年 | 1997篇 |
1994年 | 1854篇 |
1993年 | 1622篇 |
1992年 | 1508篇 |
1991年 | 1230篇 |
1990年 | 998篇 |
1989年 | 850篇 |
1988年 | 810篇 |
1987年 | 635篇 |
1986年 | 601篇 |
1985年 | 746篇 |
1984年 | 657篇 |
1983年 | 340篇 |
1982年 | 604篇 |
1981年 | 826篇 |
1980年 | 694篇 |
1979年 | 670篇 |
1978年 | 544篇 |
1977年 | 459篇 |
1976年 | 376篇 |
1974年 | 175篇 |
1973年 | 248篇 |
排序方式: 共有10000条查询结果,搜索用时 28 毫秒
981.
982.
983.
Twin Paradox and the Logical Foundation of Relativity Theory 总被引:3,自引:0,他引:3
We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in Specrel. As it turns out, this is practically equivalent to asking whether Specrel is strong enough to “handle” (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to Specrel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of Specrel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that~the Twin Paradox becomes provable in AccRel, but it is not provable without IND. 相似文献
984.
本文讨论了一类Rosenbrock方法求解比例延迟微分方程,y′(t)=λy(t) μy(qt),λ,μ∈C,0 相似文献
985.
Flat-top interleavers with chromatic dispersion compensator based on phase dispersive free space Mach-Zehnder interferometer 总被引:2,自引:0,他引:2
In this paper, novel interleavers using circular cavities (CC) in a Mach-Zehnder interferometer (MZI) has been presented and demonstrated for the first time, in which CCs act as phase dispersive mirrors which exhibit a periodic dependence on the frequency of light. Three implementation schemes have been proposed and investigated. Theoretical analysis shows the spectral characteristics of each scheme in a 50-GHz channel spacing application. Furthermore, the chromatic dispersion (CD) of each output comb can be flattened within passband by appending an additional CC. The result shows that the proposed designs with novel interferometer technique can simultaneously provide flat top passbands, high isolation stopband and low CD value as well. 相似文献
986.
Debora Di Caprio 《Topology and its Applications》2006,153(14):2680-2702
We introduce and study some completeness properties for systems of open coverings of a given topological space. A Hausdorff space admitting a system of cardinality κ satisfying one of these properties is of type Gκ. Hence, we define several new variants of the ?ech number and use elementary submodels to determine further results. We introduce M-hulls and M-networks, for M elementary submodel. As an application, we give estimates for both the tightness and the Lindelöf number of a generic upper hyperspace. Two recent results of Costantini, Holá and Vitolo on the tightness of co-compact hyperspaces follow from ours as corollaries. 相似文献
987.
988.
989.
本文对几类B值小指标鞅空间建立了原子分解定理,利用原子分解讨论了它们之间的相互嵌入关系,其原子分解的存在性和它们之间的关系均与Banach空间的凸性和光滑性有密切联系. 相似文献
990.
In this paper, we are concerned with the problem of stabilization for autonomous dynamical systems. We use theories in Liapunov stability and Lasalle stability theory and show that system (H) is stabilizable. 相似文献