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   575292篇
  免费   7066篇
  国内免费   1708篇
化学   313527篇
晶体学   8817篇
力学   24632篇
综合类   17篇
数学   65121篇
物理学   171952篇
  2021年   4359篇
  2020年   4873篇
  2019年   5257篇
  2018年   6638篇
  2017年   6479篇
  2016年   10287篇
  2015年   6697篇
  2014年   10071篇
  2013年   25679篇
  2012年   19045篇
  2011年   23569篇
  2010年   16403篇
  2009年   16184篇
  2008年   21563篇
  2007年   21554篇
  2006年   20069篇
  2005年   18074篇
  2004年   16764篇
  2003年   14834篇
  2002年   14584篇
  2001年   16912篇
  2000年   12850篇
  1999年   10186篇
  1998年   8392篇
  1997年   8137篇
  1996年   8011篇
  1995年   7173篇
  1994年   7066篇
  1993年   6822篇
  1992年   7749篇
  1991年   7725篇
  1990年   7472篇
  1989年   7305篇
  1988年   7286篇
  1987年   7186篇
  1986年   6830篇
  1985年   8901篇
  1984年   9106篇
  1983年   7352篇
  1982年   7644篇
  1981年   7544篇
  1980年   7046篇
  1979年   7564篇
  1978年   7930篇
  1977年   7722篇
  1976年   7585篇
  1975年   7122篇
  1974年   7028篇
  1973年   7085篇
  1972年   4951篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
983.
Sensitivity-enhanced 2D IPAP experiments using the accordion principle for measuring one-bond 13C'-13Calpha and 1Halpha-13Calpha dipolar couplings in proteins are presented. The resolution of the resulting spectra is identical to that of the decoupled HSQC spectra and the sensitivity of the corresponding 1D acquisitions are only slightly lower than those obtained with 3D HNCO and 3D HN(COCA)HA pulse sequences due to an additional delay 2Delta. For cases of limited resolution in the 2D 15N-1HN HSQC spectrum the current pulse sequences can easily be modified into 3D versions by introducing a poorly digitized third dimension, if so desired. The experiments described here are a valuable addition to the suites available for determination of residual dipolar couplings in biological systems.  相似文献   
984.
985.
986.
On the basis of the method of equivalent linearization combined with the method of moments, laws of self-oscillation excitation are obtained that provide the modes with maximum intensity of resonance (or quasi-resonance) oscillations in one-dimensional systems with distributed parameters. A restriction of a general type is imposed on the law of excitation. In the particular case of an integral quadratic restriction, the law of excitation leads to the generation of purely harmonic self-oscillations. The use of an extended (multiplicatively stabilizing) control provides the uniqueness and stability of the quasi-optimal mode of self-oscillation.  相似文献   
987.
988.
New results concerning the topology of the fragmentation of relativistic nuclei 7Li and 10B are presented. A program is proposed for studying the cluster structure of stable and radioactive nuclei. The use of emulsions in the investigation of nuclear clustering in the fragmentation of light nuclei at energies are in excess of 1 GeV per nucleon is discussed.  相似文献   
989.
A series of electrogenerated selective electrophiles based on substituted benzoquinones has been characterized as tags for l-cysteine and cysteine residues in proteins. The electrophiles are generated electrochemically from the corresponding hydroquinones. It is shown from mass spectrometry analysis that the electrogenerated benzoquinone can tag the biomolecules. The rate constants pertaining to the addition of l-cysteine onto the electrogenerated benzoquinones have been determined using electrochemical techniques. The substitution patterns have been unraveled leading to the assessment of site-specific rate constants. It is shown that the rate constants are primarily dependent on the electronic nature of the substituents as expressed by the Hammett substitution constant. The apparent tagging yields observed for l-cysteine in nanospray mass spectrometry experiments do not correspond to the yields expected from the electrochemical study, as the ionisation efficiencies are highly dependent on the tag. Finally, the on-line tagging has been tested using β-lactoglobulin A and myoglobin. Based on these results, it is concluded that the tagging reaction is selective towards cysteine when it takes place in the nanospray interface. The results show that the methodology presented can be used for a rapid characterization and identification of reactive sites in biomolecules.  相似文献   
990.
Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO5 samples doped with CeO2 and co-doped with CeO2 and Sm2O3. On gamma-irradiation at room temperature, BO3 2–, O2 and O radicals were produced. It was seen that the O radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O radical ions results in transfer of recombination energy to the impurity centre Ce3+ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce3+ to Sm3+ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work.  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