全文获取类型
收费全文 | 6082篇 |
免费 | 1002篇 |
国内免费 | 663篇 |
专业分类
化学 | 4330篇 |
晶体学 | 46篇 |
力学 | 341篇 |
综合类 | 50篇 |
数学 | 713篇 |
物理学 | 2267篇 |
出版年
2024年 | 20篇 |
2023年 | 146篇 |
2022年 | 197篇 |
2021年 | 253篇 |
2020年 | 276篇 |
2019年 | 258篇 |
2018年 | 215篇 |
2017年 | 175篇 |
2016年 | 262篇 |
2015年 | 277篇 |
2014年 | 290篇 |
2013年 | 418篇 |
2012年 | 483篇 |
2011年 | 501篇 |
2010年 | 363篇 |
2009年 | 322篇 |
2008年 | 379篇 |
2007年 | 311篇 |
2006年 | 317篇 |
2005年 | 298篇 |
2004年 | 248篇 |
2003年 | 175篇 |
2002年 | 182篇 |
2001年 | 159篇 |
2000年 | 149篇 |
1999年 | 130篇 |
1998年 | 116篇 |
1997年 | 104篇 |
1996年 | 101篇 |
1995年 | 75篇 |
1994年 | 85篇 |
1993年 | 58篇 |
1992年 | 63篇 |
1991年 | 44篇 |
1990年 | 54篇 |
1989年 | 32篇 |
1988年 | 28篇 |
1987年 | 36篇 |
1986年 | 24篇 |
1985年 | 26篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1969年 | 4篇 |
排序方式: 共有7747条查询结果,搜索用时 9 毫秒
81.
82.
We experimentally study the generation of a partially coherent non-diffractive beam by focusing a partially coherent vortex beam with an axicon. The investigation results show that when the partially coherent vortex beam is focused by the axicon, the beam is transferred into a partially coherent higher-order non-diffractive beam. In the non-diffractive zone, the transverse intensity distribution of the partially coherent higher-order non-diffractive beam is invariant during propagation. In addition, the range of the non-diffractive zone is related to the coherence of the partially coherent vortex beam. The poorer the coherence of the partially coherent vortex beam, the shorter the range of the non-diffractive zone. 相似文献
83.
Hongyan Mao Changzheng Zhang Haiyun Shi 《Journal of Physics and Chemistry of Solids》2011,72(11):1230-1238
Two lanthanide coordination complexes [Nd(NO3)3(CH3OH)2(4,4′-bipy)2] (1) (4,4′-bipy=4,4′-bipyridine) and [4,4′-Hbipy][La(NO3)4(H2O)2(4,4′-bipy)] (2), with a salt of cationic diprotonated 4,4′-bipy, [2(4,4′-H2bipy)][4(NO3)] (3), have been identified and isolated from a methanol solution of Ln(NO3)3·6H2O, 4,4′-bipyridine and pyrazine in 1:2:1 ratio. Their structures have been determined by single-crystal X-ray diffraction analyses, which reveal that 1 has an interesting three-dimensional supramolecular architecture containing 21 double-stranded helical chains through hydrogen bonding and π–π interactions, while 2 and 3 have well defined infinite chiral 3D open networks that undergo self-interpenetration. The electrospray ionization mass spectra (ESI-MS) indicate that the covalent complex has higher stability than the electrostatic bonding one. ESI-MS/MS of these ions reveal that the Ln–O bond forms a stronger coordinated bonding than that of Ln–N system and the nitrate anion remains bound to the lanthanide centers after complete dissociation in methanol solution. 相似文献
84.
The electrophoretic mobilities of chloro-, bromo- and iodo-complexes of Hg, Bi, Cd, Pb, and Cu, obtained by heavy current electrophoresis on filter paper, are presented in diagrams as a function of the logarithm of the concentrations of the halogen ions KC1, HCl, KUr, HBr and KJ, mainly in concentrations between 0.1N and 4N, were selected as complexing agents Straight lines were obtuned with characteristic slopes, breaks and parallelisms. Furthermore it can be seen from the diagiarns, that the tendency to form complexes increases on the one hand in the sequence chloro - bromo -iodo, and on the other for the chloro- and bromo-complexes in the sequence Cu - Pb - Cd - Bi -Hg In the case of the lodo-complexes the sequence is (Pb + Cd) - Hg - Cu.Figures that show the electrophoretie scpartion of a mixture of Hg - Bi - Cd - Pb - Cu in Voirious concentrations of KC1, KBr and HBr, are given. The separation of these metals in the form of halogeno-complexes can be most satisfactorily accomplished in 0.5N KBr or 0.5NHBr. 相似文献
85.
利用循环伏安法对我们新设计合成的两种二茂铁甲基二氧大环多胺化合物——1-二茂铁甲基-1,4,8,11-四氮杂环十三烷-5,7-二酮(简称FcCH2L1)和1-二茂铁甲基-1,4,7,11,14-五氮杂环十六烷-3,15-二酮(简称FcCH2L2)——的电化学性质进行了研究,包括酸碱度的影响以及它们对Zn2+,Ca2+,Cd2+,Cu2+,Ni2+,Co2+等金属离子的电化学响应情况.在乙醇和水的混合溶剂体系中化合物FcCH2L1对Ni2+具有选择性络合,而化合物FcCH2L2对高氧化态的Ni3+有稳定作用 相似文献
86.
多维正态分布均值在序约束下的假设检验 总被引:1,自引:0,他引:1
在序限制下的统计推断是统计分析中的一个重要领域,保序回归理论在这个领域中起着关键性的作用。多维保序回归是一维保序回归的推广,本文给出了k=2,p=2时多维保序回归的求解方法。令Xij,j=1,2…,n是来自总体为二维正态分布N(μi,Λ)的样本,这是μi是未知的,Λ是已知的,i=1,2。令μ=(μ1,μ2),-={(μ1,μ2)|μ1,μ∈R^2,}-0={(μ1,μ2)|μ1≤μ2,μ1,μ2∈R^2}。μ1≤μ2表示μ2-μ1的每一个分量为非负。本文也讨论了假设检验问题H0:μ∈-0,H1:μ∈-0=---0(H0是零假设)。 相似文献
87.
Mao Guangjun Li Zhuxia Zhuo Yizhong Han Yinlu Yu Ziqiang M. Sano 《Zeitschrift für Physik A Hadrons and Nuclei》1994,347(3):173-179
The collision term has been deduced based on the effective Lagrangian in addition to the mean-field. We propose the momentum- and density-dependent coupling strengths for scalar and vector fields. The saturation properties of nuclear matter, the experimental data of the energy-dependent optical potential and the mean free path in the nuclei can be reproduced simultaneously. The in-mediumn–n cross section has also been calculated for different densities and energies, our results are consistent with Dirac-Brueckner-Hartree-Fock calculations.Supported by National Natural Science Foundation of China 相似文献
88.
89.
90.
This study investigates the robust output tracking problem for a class of uncertain linear systems. The uncertainties are assumed to be time invariant and to satisfy the matching conditions. According to the selected nominal parameters, an optimal solution with a prescribed degree of stability is determined. Then, an auxiliary input via the use of an adapting factor, connected to the nominal optimal control, is introduced to guarantee the robustness and prescribed degree of stability for the output tracking control of the uncertain linear systems. This method is very simple and effective and can reject bounded uncertainties imposed on the states. A maglev vehicle model example is given to show its effectiveness. 相似文献