首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   53266篇
  免费   2035篇
  国内免费   73篇
化学   33832篇
晶体学   265篇
力学   1772篇
数学   8376篇
物理学   11129篇
  2023年   383篇
  2022年   322篇
  2021年   549篇
  2020年   722篇
  2019年   695篇
  2018年   1096篇
  2017年   898篇
  2016年   1636篇
  2015年   1482篇
  2014年   1492篇
  2013年   3113篇
  2012年   3607篇
  2011年   3737篇
  2010年   2260篇
  2009年   1886篇
  2008年   3145篇
  2007年   3188篇
  2006年   2794篇
  2005年   2710篇
  2004年   2316篇
  2003年   1887篇
  2002年   1628篇
  2001年   983篇
  2000年   824篇
  1999年   578篇
  1998年   451篇
  1997年   418篇
  1996年   513篇
  1995年   336篇
  1994年   386篇
  1993年   376篇
  1992年   422篇
  1991年   361篇
  1990年   338篇
  1989年   337篇
  1988年   277篇
  1987年   282篇
  1986年   248篇
  1985年   413篇
  1984年   379篇
  1983年   274篇
  1982年   355篇
  1981年   351篇
  1980年   299篇
  1979年   292篇
  1978年   281篇
  1976年   293篇
  1975年   267篇
  1974年   280篇
  1973年   272篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
In this paper we propose a general integration scheme for a Multi-Criteria Decision Making model of the Multi-Attribute Utility Theory in Constraint Programming. We introduce the Choquet integral as a general aggregation function for multi-criteria optimization problems and define the Choquet global constraint that propagates this function during the Branch-and-Bound search. Finally the benefits of the propagation of the Choquet constraint are evaluated on the examination timetabling problem.  相似文献   
132.
Low-lying energy states of the [Fe3S4]0 cluster have been calculated by taking into account the double exchange, superexchange and vibronic interaction. It was found that the adiabatic potential of the excited state withS=0 corresponds to the full delocalization of the “excess” charge. From the analysis of experimental data of Mössbauer spectroscopy and the temperature dependence of the magnetic susceptibility the double exchange parametert≥4000 cm?1 and the vibronic interaction parameter λ2/2k cm?1 have been estimated.  相似文献   
133.
JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of...  相似文献   
134.
The generation of harmonics of the voltage response is considered when an AC current is applied through a superconducting film above Tc. It is shown that almost at all temperatures the mechanism of the temperature oscillations created by the AC current and the temperature dependence of the resistance dominates over the isothermal nonlinear electric conductivity. Only in a narrow critical region close to Tc the latter is essential for the generation of the harmonics. A detailed investigation of harmonics generation provides an accurate method for measuring the thermal boundary conductance between the film and the insulating substrate. The critical behaviour of the third harmonic will give a new method for the determination of the lifetime of metastable Cooper pairs above Tc. The comparison of the calculated fifth harmonics of the voltage with the experiment is proposed as an important test for the applicability of the employed theoretical models. Received 8 September 2001  相似文献   
135.
We calculate the site occupation probabilities of one-dimensional lattice gas models within the canonical and grand canonical ensembles. The appearing differences do not vanish if we increase the system size keeping the site energies discrete. In this way one can explain the surprising numerical results of Barszczak and Kutner. This effect in the single-site occupation number disappears in higher dimensions.  相似文献   
136.
137.
This paper is devoted to the proof of almost global existence results for Klein‐Gordon equations on Zoll manifolds (e.g., spheres of arbitrary dimension) with Hamiltonian nonlinearities, when the Cauchy data are smooth and small. The proof relies on Birkhoff normal form methods and on the specific distribution of eigenvalues of the Laplacian perturbed by a potential on Zoll manifolds. © 2007 Wiley Periodicals, Inc.  相似文献   
138.
We introduce the concept of quotient in PN spaces and give some examples. We prove some theorems with regard to the completeness of a quotient.  相似文献   
139.
Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO2 electrodes were prepared from a colloidal solution of TiO2 nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355 nm) for the fabrication of dye-sensitized solar cells. The overall conversion efficiency of the cells based on the laser-sintered TiO2 electrodes was double that of the devices with non-laser-treated TiO2 electrodes. This enhancement is attributed to both the removal of organic additives and the improved inter-nanoparticle electrical contacts induced by the laser-sintering process, which led to an increase in porosity and dye-absorption sites in the TiO2 electrodes. PACS 61.80.Ba; 61.46.+w; 73.22.-f; 84.60.Jt  相似文献   
140.
The spectral dynamics of a mid-infrared multimode Cr(2+):ZnSe laser located in a vacuum sealed chamber containing acetylene at low pressure is analyzed by a stepping-mode high-resolution time-resolved Fourier transform interferometer. Doppler-limited absorption spectra of C(2)H(2) in natural isotopic abundance are recorded around 4000 cm(-1) with kilometric absorption path lengths and sensitivities better than 3 10(-8) cm(-1). Two cold bands are newly identified and assigned to the ν(1)+ν(4) (1) and ν(3)+ν(5) (1) transitions of (12)C(13)CH(2). The ν(1)+ν(5) (1) band of (12)C(2)HD and fourteen (12)C(2)H(2) bands are observed, among which for the first time ν(2)+2ν(4) (2)+ν(5) (-1).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号