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   12020篇
  免费   1706篇
  国内免费   1409篇
化学   8222篇
晶体学   147篇
力学   858篇
综合类   97篇
数学   1424篇
物理学   4387篇
  2024年   21篇
  2023年   172篇
  2022年   257篇
  2021年   298篇
  2020年   389篇
  2019年   345篇
  2018年   309篇
  2017年   295篇
  2016年   457篇
  2015年   431篇
  2014年   567篇
  2013年   809篇
  2012年   889篇
  2011年   973篇
  2010年   652篇
  2009年   721篇
  2008年   760篇
  2007年   727篇
  2006年   685篇
  2005年   634篇
  2004年   494篇
  2003年   394篇
  2002年   347篇
  2001年   327篇
  2000年   287篇
  1999年   318篇
  1998年   330篇
  1997年   266篇
  1996年   266篇
  1995年   227篇
  1994年   244篇
  1993年   161篇
  1992年   151篇
  1991年   133篇
  1990年   139篇
  1989年   86篇
  1988年   80篇
  1987年   87篇
  1986年   82篇
  1985年   71篇
  1984年   49篇
  1983年   33篇
  1982年   35篇
  1981年   27篇
  1980年   20篇
  1979年   15篇
  1978年   14篇
  1977年   8篇
  1976年   8篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 82 毫秒
971.
The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.  相似文献   
972.
Chen F  Wang XL  Wang KM  Lu QM  Shen DY 《Optics letters》2002,27(13):1111-1113
We report for what is believed to be the first time planar waveguide formation and propagation mode reduction in Nd:YVO(4) crystal, which were achieved by 3.0-MeV silicon-ion implantation followed by annealing under specific conditions. After the implantation, an enhanced refractive-index region was formed with a width of ~2microm beneath the sample surface to act as a waveguide structure. We found that there were four propagation modes for the as-implanted Nd:YVO(4) waveguide, whereas after annealing at 240-360 degrees C for several hours the number of modes could be reduced to three, two, and one. After annealing at 400 degrees C for 1 h the monomode waveguide was destroyed completely, and no mode was observed in the sample.  相似文献   
973.
Zhao J  Shen J  Hu C 《Optics letters》2002,27(20):1755-1757
A diffraction theory of continuous-wave photothermal deflection (PD) spectroscopy with fundamental and harmonic responses is presented. The displacement of the probe beam centroid is found to be a rigorous measurement of PD effect, which leads to a set of analytical solutions to the fundamental and the second-order harmonics. Harmonics are caused by the diffraction of the probe beam in the mirage region, which could not be handled by geometric-optics theory. This theory can be used to study bulk materials, thin films, and layered-structure samples. Experimental results are in good agreement with the theory.  相似文献   
974.
Poly (3-alkylthiophenes) (P3ATs) have made up of a family of conductive polymerswhich are soluble, fusible and processable, since the introduction of flexible alkyl sidechains"'. It is generally accepted that P3ATs can form similar layered structures. inwhich the thiophene rings possess planarity and the side chains act as spacers'-'. Whenthe number. of 'carbon atoms of alkyl side chains is more than 10, some orderlyarrangements will occur for side chains betWeen the' layers'. It has been w…  相似文献   
975.
976.
Low tropospheric wind measurement with Mie Doppler Lidar   总被引:3,自引:0,他引:3  
A double edge Mie Doppler lidar at 1064 nm was developed in Hefei, China in 2005 for low tropospheric wind measurement. Intercomparison experiments with a wind profiler and a wiresonde were held. Intercomparisons of concurrent lidar and other instrument observations show good agreement with expected measurement accuracy. The examples of validated lidar wind profiles obtained during these experiments as well as an example of continuous wind observations are presented. The instrument has demonstrated the capability of atmospheric wind field measurement from 0.2 to 5 km altitude, achieving below 2 m/s accuracy with 1 min averaging and 21.2 m vertical resolution.  相似文献   
977.
Capillary electrophoresis using diol-bonded fused-silica capillaries   总被引:1,自引:0,他引:1  
In this paper, 3-glycidoxypropyltrimethoxysilane was used to produce diol-bonded capillaries at room temperature for capillary electrophoresis (CE). A variety of standard reference compounds and authentic biological samples including ribonucleotides, peptides and proteins were used to test the columns. It was found that greatly suppressed electroosmotic flow was measured over a pH range of 3–10. Lower than 1.6% relative standard deviation (>10 runs) in migration time was observed for the analysis of test proteins. For real samples of ribonucleotides in tumor cell extracts, 1 million theoretical plates and excellent peak shapes were obtained. The high column efficiency and symmetrical peaks allowed the separation of samples with only 0.6% maximum difference in migration times. The diol-bonded fused-silica capillary columns were stable when used in a pH range of 2–8 under typical CE conditions. The column preparation method involved a simple dynamic coating procedure at room temperature, greatly simplifying the more typical static coating methods that require vacuum pumps and ovens.  相似文献   
978.
An existence and uniqueness result concerned with the Diriehlet boundary value prob-lem u“ cu‘ g(t,u)=e(t),u(0)=u(π)=0 is offered.  相似文献   
979.
Headspace solid phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS) has been applied to the determination of the volatile compounds of a common traditional Chinese medicine , Flos Chrysanthemi indici. Twenty-six compounds were identified by the present method, which are similar to the results from steam distillation. Difference in analysis from ten growing areas was found to be in their relative content and total concentrations. Four active compounds (cineole, 3-thujanone, borneol and bornyl acetate) were applied to the evaluation of the quality of Flos Chrysanthemi indici from different areas. By comparing their peak areas, it was found that Flos Chrysanthemi indici with the best quality was from Hangzhou in China. These results show that HS-SPME-GC-MS is a simple, rapid and solvent-free method for the analysis of the volatile compounds in this material and a potential tool for its quality assurance.  相似文献   
980.
J Shen  J Kirschner 《Surface science》2002,500(1-3):300-322
The current standard of electronic devices and data storage media has reached a level such that magnetic materials have to be fabricated on a nanometer scale. In particular, the emerging concept of spintronics, which is based on fact that current carriers have not only charge but also spin, requires the assembling of nanometer-sized magnetic structures with desired magnetic properties. It is this background that motivates scientists and engineers to attempt to grow and characterize magnetic objects at smaller and smaller length scales, from 2D films and multilayers to 1D wires and eventually to 0D dots. In this article, some of the most significant progress in recent years in the effort of growing artificially structured magnetic materials are reviewed. The new structural and magnetic properties of these materials are discussed, with an emphasis on the correlation between structure and magnetism, which also serves as guidance for improving their magnetic properties. The emerging emphasis is on converting the existing knowledge into growing and studying low-dimensional complex materials, which promise to have considerably higher “tuning” ability for desired properties.  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