全文获取类型
收费全文 | 137600篇 |
免费 | 20272篇 |
国内免费 | 15671篇 |
专业分类
化学 | 73959篇 |
晶体学 | 1168篇 |
力学 | 5951篇 |
综合类 | 700篇 |
数学 | 13033篇 |
物理学 | 38977篇 |
无线电 | 39755篇 |
出版年
2024年 | 355篇 |
2023年 | 3148篇 |
2022年 | 3666篇 |
2021年 | 5038篇 |
2020年 | 5250篇 |
2019年 | 4725篇 |
2018年 | 4398篇 |
2017年 | 4121篇 |
2016年 | 5846篇 |
2015年 | 6163篇 |
2014年 | 7544篇 |
2013年 | 9766篇 |
2012年 | 11504篇 |
2011年 | 11869篇 |
2010年 | 8816篇 |
2009年 | 8743篇 |
2008年 | 9041篇 |
2007年 | 8183篇 |
2006年 | 7781篇 |
2005年 | 6817篇 |
2004年 | 5012篇 |
2003年 | 4176篇 |
2002年 | 3776篇 |
2001年 | 3236篇 |
2000年 | 2956篇 |
1999年 | 3055篇 |
1998年 | 2617篇 |
1997年 | 2263篇 |
1996年 | 2249篇 |
1995年 | 1974篇 |
1994年 | 1699篇 |
1993年 | 1397篇 |
1992年 | 1227篇 |
1991年 | 1031篇 |
1990年 | 871篇 |
1989年 | 612篇 |
1988年 | 486篇 |
1987年 | 400篇 |
1986年 | 401篇 |
1985年 | 313篇 |
1984年 | 236篇 |
1983年 | 197篇 |
1982年 | 148篇 |
1981年 | 95篇 |
1980年 | 72篇 |
1979年 | 28篇 |
1978年 | 30篇 |
1976年 | 24篇 |
1975年 | 24篇 |
1957年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 236 毫秒
911.
Fu-li Li Zhang-qi Yin 《量子光学学报》2006,12(B08):75-75
Two atomic clusters, which have NA and Ns two-level atoms, respectively, are placed in a cavity but separated spatially. There is no direct interaction between the atoms. All the atoms interact with a single-mode of the cavity field. Quantum entanglement between the two atomic clusters is investigated for various initial states of the two atomic clusters and the field. When the cavity field is initially in a Fock state, we find that the time evolution of entanglement quasi-periodically oscillates regardless of the initial states of atoms. The oscillation period increases as the initial photon number increases. When all the atoms in both of the atomic clusters are initially in the excited state, we show that there is no entanglement between the atomic clusters with NA = NB = 1 regardless the initial state of the cavity field. However, when either NA or NB is larger than one, we find that the entanglement always exists even for a strong thermal field. In cases with different initial states of the atomic clusters, we notice that the entanglement becomes stronger as number of the atoms increases. When all the atoms in both of the clusters in the ground state, we also find that the entanglement can be enhanced even by a thermal field. We also notice that a single qubit can be entangled with multi-atoms which are initially in the ground state by the cavity field initially being in vacuum, thermal, coherent, and squeezed states. 相似文献
912.
Successive column correction algorithms for solving sparse nonlinear systems of equations 总被引:1,自引:0,他引:1
Guangye Li 《Mathematical Programming》1989,43(1-3):187-207
This paper presents two algorithms for solving sparse nonlinear systems of equations: the CM-successive column correction algorithm and a modified CM-successive column correction algorithm. Aq-superlinear convergence theorem and anr-convergence order estimate are given for both algorithms. Some numerical results and the detailed comparisons with some previously established algorithms show that the new algorithms have some promise of being very effective in practice.This research was partially supported by contracts and grants: DOE DE-AS05-82ER1-13016, AFOSR 85-0243 at Rice University, Houston, U.S.A. and Natural Sciences and Engineering Research Council of Canada grant A-8639. 相似文献
913.
Some Results behind Dividend Problems 总被引:1,自引:0,他引:1
Ming Zhou Li Wei Jun-yi Guo 《应用数学学报(英文版)》2006,22(4):681-686
We consider the basic dividend problem of the compound Poisson model with constant barrierstrategy.Some results concealed behind the dividend problem are made explicit in the present work.Differentmethods and some of which are firstly given in this paper.All these results presented certain direct relationshipbetween some important actuary variables in classical risk theory is also revealed. 相似文献
914.
915.
916.
Buckling of sandwich wide columns 总被引:2,自引:0,他引:2
The paper deals with the theoretical prediction of buckling loads for sandwich columns with metallic and laminated facings and foam or honeycomb core. The loading is a uniform axial compression, applied statically (very slowly) and suddenly with constant magnitude and infinite duration (step loading). The effect of length and boundary conditions is assessed and results are presented for the following cases: for a cantilever column, a simply supported column and a clamped column, for several lengths. Several fiber materials are used in the laminated facings. Two types of core were examined: alloy-foam or hexagonal glass/phenolic honeycomb. The facings are Boron/Epoxy, Graphite/Epoxy and Kevlar/Epoxy laminates with 0° orientation with respect to the column axis and a metallic one made out of aluminum. These various materials are employed to provide comparative data that can be used in design. Results, for the static case are generated by computer codes as well as by the use of closed form theoretical solutions. For the dynamic case, results are generated by the DYNA3D code. 相似文献
917.
918.
919.
920.
等离子体氧化nc-Si/SiO_2多层膜的蓝光发射 总被引:1,自引:0,他引:1
报道了在等离子体增强化学气相沉积 (PECVD)系统中用交替淀积 a-Si对其进行原位等离子体氧化的方法制备了 a-Si∶H/ Si O2 多层膜。随着 a-Si∶H子层的厚度从 3 .8nm减小到 1 .5 nm,a-Si∶H/ Si O2 多层膜的光吸收边和光致发光 (PL )出现了蓝移。在晶化的 a-Si∶ H/ Si O2 多层膜中不仅观察到室温下的红光带 (80 0nm)的发光峰 ,而且还观察到蓝光发射 (4 2 5 nm) ,结合 Raman,TEM和 PL测试 ,对其原因作了简单的分析 相似文献