全文获取类型
收费全文 | 160456篇 |
免费 | 28340篇 |
国内免费 | 32084篇 |
专业分类
化学 | 115155篇 |
晶体学 | 3750篇 |
力学 | 10123篇 |
综合类 | 2870篇 |
数学 | 22598篇 |
物理学 | 66384篇 |
出版年
2024年 | 382篇 |
2023年 | 2559篇 |
2022年 | 5157篇 |
2021年 | 5618篇 |
2020年 | 6123篇 |
2019年 | 5868篇 |
2018年 | 5415篇 |
2017年 | 5954篇 |
2016年 | 6908篇 |
2015年 | 7733篇 |
2014年 | 9539篇 |
2013年 | 12356篇 |
2012年 | 14039篇 |
2011年 | 14878篇 |
2010年 | 11893篇 |
2009年 | 11768篇 |
2008年 | 12756篇 |
2007年 | 11356篇 |
2006年 | 10915篇 |
2005年 | 9079篇 |
2004年 | 7019篇 |
2003年 | 5404篇 |
2002年 | 5118篇 |
2001年 | 4673篇 |
2000年 | 4471篇 |
1999年 | 3567篇 |
1998年 | 2551篇 |
1997年 | 2178篇 |
1996年 | 2138篇 |
1995年 | 1910篇 |
1994年 | 1792篇 |
1993年 | 1518篇 |
1992年 | 1405篇 |
1991年 | 1130篇 |
1990年 | 954篇 |
1989年 | 842篇 |
1988年 | 663篇 |
1987年 | 580篇 |
1986年 | 551篇 |
1985年 | 425篇 |
1984年 | 342篇 |
1983年 | 289篇 |
1982年 | 228篇 |
1981年 | 162篇 |
1980年 | 134篇 |
1979年 | 114篇 |
1978年 | 50篇 |
1977年 | 40篇 |
1976年 | 35篇 |
1965年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Tian Le LIN Bao Zhen YAN Gao Fei HU Mei WANG 《中国化学快报》2006,17(7):937-940
Complex formation between aluminium and quercetin(Q) in methanol was investigated by means of 27^Al solid-state, 13^C and 1^H NMR and MS(ESI), UV and IR spectra. Formation of the 1:2 complex was favored in methanol relative to all other solvent and the predominant species observed of Al(Ⅲ) has a 1:2 stoichiometry. The fine structure of 1:2 aluminum complex of quercetin was that the aluminum central atom chelated with two quereetin molecules and two methoxyl groups between two five membered rings, its coordination is six, the chelated site was 3-hydroxy-4-carbonyl. 相似文献
993.
掺杂Er^3+的TiO2的发射光谱研究 总被引:1,自引:1,他引:0
用无水乙醇、冰醋酸、钛酸丁酯凝胶法制备了掺杂Er^3+的TiO2粉末,测量了其在488m激发下的Stokes发射光谱和980nm激发下的上转换发光光谱。在可见光范围内,观察到了绿光和红光,绿光从500-570nm,对应Er^3+的^2H11/2,^4S3/2→^4I15/2,红光从650~690m,对应Er^3+的^4F9/2→^4I15/2的跃迁。由ln Ivis-In Iin曲线可知,绿光和红光均为双光子过程,光强正比于泵浦功率的二次方,即Iout ∝Iin。初步研究了此材料的上转换过程。 相似文献
994.
995.
载能离子穿过固体界面引起界面原子迁移使界面原子混合和物质成分变化,从而导致界面发生材料相变。简要介绍了载能离子辐照引起金属/绝缘体界面混合效应及相变现象的主要实验研究进展、低能离子和高能离子辐照引起金属/绝缘体界面现象差异,并对离子辐照引起界面混合及相变的机制进行了初步探讨。When penetrating an interface between two kind of solids, energetic ions can induce atomic diffusion at both sides of the interface and then result in intermixing, atom re-distribution or composition change, as well as phase transformation. Main progress on the study of intermixing and phase change at metal/insulator interface induced by energetic ion irradiations, the difference of phenomena occurred at metal/insulator interfaces induced by high-and low-energy ions were briefly reviewed. Furthermore, the possible mechanisms related to intermixing and phase change at metal/insulator interface produced by energetic ion irradiations were also discussed in short words. 相似文献
996.
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
997.
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
998.
一类带有有限维控制器的弹性系统的反馈控制 总被引:1,自引:0,他引:1
本文讨论一类弹性系统的反馈控制问题,它在工程上,特别是在大宇航飞行器设计中的应用是非常活跃的.我们的主要结果是:利用谱分析方法和无条件基理论证明了这类系统是严格耗散的分布参数系统,给出了该系统的降维模型可控可观的充分条件,从而设计一个有限维控制器对系统进行反馈控制,使得闭环系统具有更好的稳定性能,将文献[2,3]中的结果推广到非常一般的情形. 相似文献
999.
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
1000.