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   5094篇
  免费   252篇
  国内免费   49篇
化学   3746篇
晶体学   45篇
力学   112篇
综合类   1篇
数学   454篇
物理学   1037篇
  2023年   25篇
  2022年   53篇
  2021年   93篇
  2020年   81篇
  2019年   107篇
  2018年   81篇
  2017年   67篇
  2016年   171篇
  2015年   153篇
  2014年   188篇
  2013年   306篇
  2012年   341篇
  2011年   386篇
  2010年   256篇
  2009年   225篇
  2008年   316篇
  2007年   270篇
  2006年   272篇
  2005年   276篇
  2004年   218篇
  2003年   207篇
  2002年   184篇
  2001年   117篇
  2000年   107篇
  1999年   55篇
  1998年   43篇
  1997年   53篇
  1996年   66篇
  1995年   45篇
  1994年   42篇
  1993年   59篇
  1992年   46篇
  1991年   40篇
  1990年   40篇
  1989年   48篇
  1988年   28篇
  1987年   26篇
  1986年   30篇
  1985年   29篇
  1984年   20篇
  1983年   16篇
  1982年   17篇
  1981年   26篇
  1980年   15篇
  1979年   18篇
  1977年   19篇
  1976年   19篇
  1975年   11篇
  1974年   19篇
  1973年   11篇
排序方式: 共有5395条查询结果,搜索用时 11 毫秒
71.
72.
73.
The generalized logit model of nominal type with random regressors is studied for bootstrapping. We assess the accuracy of some estimators for our generalized logit model, using a Monte Carlo simulation. That is, we study the finite sample properties containing the consistency and asymptotic normality of the maximum likelihood estimators. Also, we compare Newton Raphson algorithm with BHHH algorithm.  相似文献   
74.
Ali JH  Wang WB  Ho PP  Alfano RR 《Optics letters》2000,25(17):1303-1305
The spectral and polarization properties of scattered light were used to image corrosion beneath the surface of a painted aluminum plate. The quality of imaging of the corrosion on the metal surface was significantly enhanced by the spectral polarization optical imaging technique. Depolarization scattered light was used to detect and image corrosion beneath the paint layer.  相似文献   
75.
76.
Insertion of aniline molecules and subsequent polymerization using FeCl3 as an oxidizing agent were examined in the layers of rutile-type HNbMoO6. Although the polyaniline/host ratio was variable depending on the amount of intercalated aniline before polymerization, the interlayer spacing was constant as 6.3 Å regardless of the ratios. Comparison of FT-IR and FT-Raman spectra for (PANI)yNbMoO6 (0.26≤y≤0.64) clearly showed that both quinoid and benzenoid forms exist in the galleries of inorganic host. IR and Raman active modes of extracted PANI from the matrix were quite similar to those of emeraldine salt.  相似文献   
77.
We investigate the generation of large-scale magnetic fields due to the breaking of the conformal invariance in the electromagnetic field through the CPT-even dimension-six Chern–Simons-like effective interaction with a fermion current by taking account of the dynamical Kalb–Ramond and scalar fields in inflationary cosmology. It is explicitly demonstrated that magnetic fields on 1 Mpc scale with the field strength of ∼10−9 G at the present time can be induced.  相似文献   
78.
79.
A scalable synthesis of magnetic core–shell nanocomposite particles, acting as a novel class of magnetic resonance (MR) contrast agents, has been developed. Each nanocomposite particle consists of a biocompatible chitosan shell and a poly(methyl methacrylate) (PMMA) core where multiple aggregated γ‐Fe2O3 nanoparticles are confined within the hydrophobic core. Properties of the nanocomposite particles including their chemical structure, particle size, size distribution, and morphology, as well as crystallinity of the magnetic nanoparticles and magnetic properties were systematically characterized. Their potential application as an MR contrast agent has been evaluated. Results show that the nanocomposite particles have good stability in biological media and very low cytotoxicity in both L929 mouse fibroblasts (normal cells) and HeLa cells (cervical cancer cells). They also exhibited excellent MR imaging performance with a T2 relaxivity of up to 364 mMFe?1 s?1. An in vivo MR test performed on a naked mouse bearing breast tumor indicates that the nanocomposite particles can localize in both normal liver and tumor tissues. These results suggest that the magnetic core–shell nanocomposite particles are an efficient, inexpensive and safe T2‐weighted MR contrast agent for both liver and tumor MR imaging in cancer therapy.  相似文献   
80.
We investigate the Painleve integrabiiity of nonautonomous nonlinear Schr6dinger (NLS) equations with both space-and time-dependent dispersion, nonlinearity, and external potentials. The Painleve analysis is carried out without using the Kruskal's simplification, which results in more generalized form of inhomogeneous equations. The obtained equations are shown to be reducible to the standard NLS equation by using a point transformation. We also construct the corresponding Lax pair and carry out its Kundu-type reduction to the standard Lax pair. Special cases of equations from choosing limited form of coefficients coincide with the equations from the previous Painleve analyses and/or become unknown new equations.  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