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   12839篇
  免费   2468篇
  国内免费   1333篇
化学   8750篇
晶体学   133篇
力学   769篇
综合类   114篇
数学   1534篇
物理学   5340篇
  2024年   52篇
  2023年   314篇
  2022年   511篇
  2021年   518篇
  2020年   545篇
  2019年   578篇
  2018年   499篇
  2017年   431篇
  2016年   667篇
  2015年   649篇
  2014年   724篇
  2013年   970篇
  2012年   1148篇
  2011年   1186篇
  2010年   773篇
  2009年   818篇
  2008年   818篇
  2007年   693篇
  2006年   631篇
  2005年   517篇
  2004年   411篇
  2003年   345篇
  2002年   326篇
  2001年   258篇
  2000年   265篇
  1999年   229篇
  1998年   229篇
  1997年   200篇
  1996年   163篇
  1995年   206篇
  1994年   173篇
  1993年   134篇
  1992年   110篇
  1991年   92篇
  1990年   97篇
  1989年   70篇
  1988年   48篇
  1987年   42篇
  1986年   44篇
  1985年   26篇
  1984年   23篇
  1983年   26篇
  1982年   15篇
  1981年   9篇
  1980年   13篇
  1979年   8篇
  1978年   7篇
  1977年   5篇
  1976年   5篇
  1957年   4篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
993.
This paper provides a noval solution to optimize the characteristics of a miniature coarse wavelength division multiplexing (mini-CWDM) module by employing collimators with plano-convex rod lenses of different radii. The 8-channel modules before optimization show maximum loss of 0.77 dB and nonuniformity of 0.34 dB. After optimization, the maximum loss and nonuniformity are reduced to 0.50 dB and 0.11 dB, respectively.  相似文献   
994.
In order to retrieve from high spectral resolution measurements with high accuracy, it is necessary to be able to evaluate the transmittance precisely. However, the uncertainty of the spectroscopic parameters is one of the most important contributions that affect the accuracy of transmittance. HITRAN is a compilation of spectroscopic parameters which has been updated several times. The transmittance calculations using the line parameters from the HITRAN’2000 database and the HITRAN’2004 database have been compared over the near infrared range from 4200 to 10,000 cm?1. The differences between calculated transmittances over this spectral range are mainly caused by changes of the line parameters for H2O, CO2 and CH4. For the tropical atmosphere, the differences are very prominent. Transmittance calculations for the sub-arctic winter atmosphere are less sensitive to the changes in the HITRAN database than those for the tropical atmosphere; but, the changes of line parameters still can not be ignored when considering the relative differences. For example, the relative difference is ~35% at 5073.3 cm?1 with 0.2 cm?1 spectral resolution. The comparisons have shown that it is important to pay attention to the changes of line parameters of the HITRAN database or to use the latest edition so as to improve the accuracy of atmospheric sounding with high spectral resolution.  相似文献   
995.
We study the Bondi-Sachs rockets with nonzero cosmological constant. We observe that the acceleration of the systems arises naturally in the asymptotic symmetries of (anti-) de Sitter spacetimes. Assuming the validity of the concepts of energy and mass previously introduced in asymptotically flat spacetimes, we find that the emission of pure radiation energy balances the loss of the Bondi mass in certain special families of the Bondi-Sachs rockets, so in these there is no gravitational radiation.  相似文献   
996.
997.
A novel fluorine-contained random copolymer (2,3,4,5,6-pentafluorostyrene)-r-poly(4-vinyl benzocyclobutene) (P(PFSt-r-4-VBCB)) was synthesized, and then spin-coated onto Si substrates followed by thermal cross-linking to produce the copolymer ultra-thin films. Although the surface modification with the P(PFSt-r-4-VBCB) film was simple and did not rely on special surface chemical reactions, the film could decrease the surface energy significantly, more importantly; the film demonstrated excellent stability and corrosion resistance. This random copolymer film could find broad applications in modifying various solid surfaces to enhance the properties such as corrosion resistance and solvent resistance.  相似文献   
998.
999.
Received: 13 August 1998 / Published online: 10 February 1999  相似文献   
1000.
Gold-coated iron oxide nanoparticle Hepatitis B virus (HBV) DNA probes were prepared, and their application for HBV DNA measurement was studied. Gold-coated iron oxide nanoparticles were prepared by the citrate reduction of tetra-chloroauric acid in the presence of iron oxide nanoparticles which were added as seeds. With a fluorescence-based method, the maximal surface coverage of hexaethiol 30-mer oligonucleotides and the maximal percentage of hybridization strands on gold-coated iron oxide nanoparticles were (120 ± 8) oligonucleotides per nanoparticle, and (14 ± 2%), respectively, which were comparable with those of (132 ± 10) and (22 ± 3%) in Au nanoparticle groups. Large network aggregates were formed when gold-coated iron oxide nanoparticle HBV DNA gene probe was applied to detect HBV DNA molecules as evidenced by transmission electron microscopy and the high specificity was verified by blot hybridization. Our results further suggested that detecting DNA with iron oxide nanoparticles and magnetic separator was feasible and might be an alternative effective method.  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