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   20590篇
  免费   157篇
  国内免费   90篇
化学   10472篇
晶体学   417篇
力学   603篇
综合类   7篇
数学   1719篇
物理学   7619篇
  2017年   156篇
  2016年   243篇
  2015年   168篇
  2014年   270篇
  2013年   841篇
  2012年   580篇
  2011年   640篇
  2010年   462篇
  2009年   476篇
  2008年   624篇
  2007年   676篇
  2006年   647篇
  2005年   586篇
  2004年   509篇
  2003年   477篇
  2002年   470篇
  2001年   695篇
  2000年   520篇
  1999年   433篇
  1998年   350篇
  1997年   336篇
  1996年   310篇
  1995年   386篇
  1994年   353篇
  1993年   320篇
  1992年   346篇
  1991年   390篇
  1990年   362篇
  1989年   364篇
  1988年   335篇
  1987年   334篇
  1986年   328篇
  1985年   407篇
  1984年   424篇
  1983年   318篇
  1982年   327篇
  1981年   350篇
  1980年   324篇
  1979年   336篇
  1978年   335篇
  1977年   314篇
  1976年   332篇
  1975年   290篇
  1974年   283篇
  1973年   299篇
  1972年   182篇
  1969年   159篇
  1968年   189篇
  1967年   334篇
  1966年   284篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
971.
In the last two decades, quantitative NMR (qNMR) has become increasingly important for the analysis of pharmaceuticals, chemicals, and natural products including dietary supplements. For the purpose of quality control and chemical standardization of a large variety of pharmaceutical, chemical, and medicinal products, qNMR has proven to be a valuable orthogonal quantification method and a compelling alternative to chromatographic techniques. This work reviews a fundamental component of the early development of qNMR, reflected in the pioneering work of the late George M. Hanna during the years between 1984 and 2006 at the US Food and Drug Administration (FDA). Because Hanna performed the majority of his groundbreaking work on a 90‐MHz instrument, his legacy output connects with recent progress in low‐field benchtop NMR instrumentation. Hanna gradually established the utility of qNMR for the routine quality control analyses practiced in pharmaceutical and related operations well ahead of his peers. His work has the potential to inspire new developments in qNMR applied to small molecules of biomedical importance.  相似文献   
972.
JPC – Journal of Planar Chromatography – Modern TLC - Commiphora mukul of the family Burseraceae, commonly known as guggul, is commonly used worldwide. The major phytoconstituents...  相似文献   
973.
974.
975.
We investigate the plasmonic response of gold nanospheres calculated using discrete dipole approximation validated against the results from other discretization methods, namely the finite-difference time-domain method and the finite-element methods. Comparisons are also made with calculations from analytical methods such as the Mie solution and the null-field method with discrete sources. We consider the nanoparticle interacting with the incident field both in free space and sitting on a planar substrate. In the latter case, discrete dipole approximation with surface interaction is used; this includes the interaction with the ‘image dipoles’ using Sommerfeld integration.  相似文献   
976.
ABSTRACT

RAPUNCL, a study course on Radionuclide Production with Cyclotrons, was organized in September 2017 in Mannheim. The intention was to test the feasibility of an educational program which is mainly driven by the input of the participating students. All aspects of target construction and operation have been covered in detail. Also the relevant aspects of Radiation Protection have been discussed. The students used intensively IAEA databases and MC simulation programs to model target design and operations. Topics for improvement have been identified and will be realized in the next course. Sources of funding have to be found to be able to organize the summer school in a sustainable way.  相似文献   
977.
We investigate the resonant production of color octet muons in order to explore the discovery potential of Future Circular Collider(FCC)-based μp colliders.It is shown that the search potentials of μp colliders essentially surpass the potential of the LHC and would exceed that of the FCC pp collider.  相似文献   
978.
979.
980.
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies.  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