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   196263篇
  免费   16410篇
  国内免费   437篇
化学   134992篇
晶体学   2071篇
力学   8535篇
综合类   7篇
数学   17894篇
物理学   49611篇
  2023年   4224篇
  2022年   2139篇
  2021年   3351篇
  2020年   5532篇
  2019年   3386篇
  2018年   3679篇
  2017年   2018篇
  2016年   7803篇
  2015年   6825篇
  2014年   7170篇
  2013年   11221篇
  2012年   7981篇
  2011年   7243篇
  2010年   7546篇
  2009年   7481篇
  2008年   6657篇
  2007年   6472篇
  2006年   5500篇
  2005年   5062篇
  2004年   4459篇
  2003年   3892篇
  2002年   3913篇
  2001年   4373篇
  2000年   3337篇
  1999年   2599篇
  1998年   2261篇
  1997年   2261篇
  1996年   2059篇
  1995年   2030篇
  1994年   1971篇
  1993年   1924篇
  1992年   2079篇
  1991年   2185篇
  1990年   1970篇
  1989年   1987篇
  1988年   1965篇
  1987年   1849篇
  1985年   2285篇
  1984年   2419篇
  1983年   1991篇
  1982年   2197篇
  1981年   2114篇
  1980年   2073篇
  1979年   2209篇
  1978年   2385篇
  1977年   2375篇
  1976年   2464篇
  1975年   2457篇
  1974年   2513篇
  1973年   2338篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We have investigated the low-lying collective states and electromagnetic transitions in 94Mo within the framework of the interacting boson model. The influence of model parameters on the energy levels and electromagnetic properties has been investigated. The analysis of the obtained results and the parameter values predict that the 23+state is the lowest mixed symmetry state with pure F = Fmax - 1 in this nucleus. The calculated results predicate that the 25+ (two-Q-phonon) mixed symmetry state is closed to the J = 2+ at 2.870 MeV in the experimental data, and the 2.965 MeV state is the lowest mixed symmetry with J = 3+.  相似文献   
72.
Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 41, No. 8, pp. 1054–1058, August, 1989.  相似文献   
73.
74.
The low-temperature reaction of magnesium with fluorobenzene has been investigated. Joint condensation of magnesium and fluorobenzene vapours at low temperatures quantitatively gave phenylmagnesium fluoride in one stage.  相似文献   
75.
76.
77.
The possibility of usage of the spontaneous electrooptical (EO) effect in strontium barium niobate (SBN) crystals for the creation of controlled electroholographic elements is studied. It is found that unipolar EO properties of these crystals with respect to switching their spontaneous polarization make it possible to devise field-controlled holographic elements with reversible energy-independent memory for spatial position of an optical beam.  相似文献   
78.
79.
Cavity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A–X (0–1) band of NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of ±13%. NO absorption in the flame was completely masked using the A–X (0–0) band. Finally, the prompt-NO mole fraction formed in a methane/air flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques. Received: 12 October / Revised version: 1 February 2002 / Published online: 14 March 2002  相似文献   
80.
The liquid chromatographic analysis of drugs in urine through direct injection without any sample pretreatment was extended to micellar chromatography with nonionic surfactants, the Pinkerton ISRP column and the shielded hydrophobic phase (Hisep) column. The feasibility of using each was demonstrated through the determination of the diuretic, hydrochlorothiazide, in urine. Good separation, recovery, precision and linearity, and adequate limits of detection were obtained for this analysis with all three techniques. The advantages and limitations of the mobile phase approach of micellar chromatography and the two stationary phase approaches are discussed for the direct injection of urine as well as other biological fluids.  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