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   699515篇
  免费   6082篇
  国内免费   2002篇
化学   340190篇
晶体学   9882篇
力学   38238篇
综合类   27篇
数学   112839篇
物理学   206423篇
  2021年   5828篇
  2020年   6288篇
  2019年   7173篇
  2018年   19330篇
  2017年   19181篇
  2016年   19144篇
  2015年   8030篇
  2014年   12576篇
  2013年   28165篇
  2012年   24989篇
  2011年   35205篇
  2010年   24501篇
  2009年   24893篇
  2008年   30261篇
  2007年   31955篇
  2006年   22049篇
  2005年   20677篇
  2004年   19666篇
  2003年   18313篇
  2002年   17240篇
  2001年   17696篇
  2000年   13700篇
  1999年   10553篇
  1998年   9122篇
  1997年   9007篇
  1996年   8509篇
  1995年   7576篇
  1994年   7617篇
  1993年   7358篇
  1992年   7877篇
  1991年   8278篇
  1990年   7991篇
  1989年   7910篇
  1988年   7704篇
  1987年   7437篇
  1986年   7165篇
  1985年   9152篇
  1984年   9566篇
  1983年   7994篇
  1982年   8228篇
  1981年   7787篇
  1980年   7368篇
  1979年   7997篇
  1978年   8218篇
  1977年   8181篇
  1976年   8157篇
  1975年   7789篇
  1974年   7579篇
  1973年   7955篇
  1972年   5850篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
A 1.5-μm eye-safe, 3-D scanning, and compact Mie LIght Detection and Ranging (LIDAR) is presented. The transmitter of the LIDAR is based on a KTA optical parameter oscillator (OPO) resonator. For detecting return signals, an InGaAs APD is used. The all solid-state OPO laser transmitter has the feature of small volume and lightweight, which allows a 165-lb compact eye-safe scanning LIDAR to be constructed. A system simulation using our own model was conducted to direct the system development. A method to solve the problem with small active area APD detectors was developed and described. The preliminary field-test measurement results indicated that the LIDAR has the capability to detect aerosols and clouds in lower atmospheres up to three dimensions.  相似文献   
154.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  相似文献   
155.
Methods for phase stabilization of ammonium nitrate were sought for in order to considerably expand the application area of this oxidizing agent in various-purpose self-combustible formulations, including that in a new generation of gas-generating formulations for automobile air bags. New methods for stabilization of ammonium nitrate were studied and, in particular, a search was made for organic compounds that can stabilize ammonium nitrate even at their low content. The mechanism of phase state stabilization of ammonium nitrate by compounds of this kind was examined.  相似文献   
156.
    
The reaction of [{(η5-C5Me5)M(μ-Cl)Cl}2] {where M = Rh (1), Ir (2)} with functionalized phosphine viz., diphenyl-2-pyridylphosphine (PPh2Py) in dichloromethane solvent yield neutral ϰ1-P-coordinated rhodium and iridium complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3 and [(η5-C5Me5) IrCl21-P-PPh2Py)]4. Reaction of complexes 1 and 2 with the ligand PPh2Py in methanol under reflux give bis-substituted complexes such as [(η5-C5Me5)RhCl(ϰ1-P-PPh2Py)2]+ 5 and [(η5-C5Me5)IrCl(ϰ1-P-PPh2Py)2]+ 6, whereas stirring in methanol at room temperature gives P-, N-chelating complexes of the type [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5)IrCl(ϰ2-P-N-PPh2Py)]+ 8. Neutral ϰ1-P-coordinated complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3 and [(η5-C5Me5)IrCl21-P-PPh2Py)]4 easily undergo conversion to the cationic P-, N-chelating complexes [(η5-C5Me5)RhCl(ϰ2-P-N-PPh2Py)]+ 7 and [(η5-C5Me5) IrCl(ϰ2-P, N-PPh2Py)]+ 8 on stirring in methanol at room temperature. These complexes are characterized by FT-IR and FT-NMR spectroscopy as well as analytical methods. The molecular structures of the representative complexes [(η5-C5Me5)RhCl21-P-PPh2Py)]3, [(η5-C5Me5)IrCl21-P-PPh2Py)]4 and hexafluorophosphate salt of complex [(η5-C5Me5)IrCl(ϰ2-P-PPh2Py)2]+ 6 are established by single-crystal X-ray diffraction methods  相似文献   
157.
The European Physical Journal E - The isothermal gas adsorption of two hexane isomers (n-hexane and cyclohexane) in the mesopores of MCM-41 silica have been investigated by small angle neutron...  相似文献   
158.
159.
160.
A combination of 1,3-dihalo-5,5-dimethylhydantoin (X = Br, Cl) and sodium nitrite in the presence of wet SiO2 was used as an effective nitrosating agent for the nitrosation of N,N-dialkyl amines to their corresponding nitroso derivatives under mild and heterogeneous conditions in good to excellent yields.  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