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   193834篇
  免费   1010篇
  国内免费   275篇
化学   89573篇
晶体学   2635篇
力学   9377篇
综合类   7篇
数学   20912篇
物理学   58127篇
无线电   14488篇
  2020年   2050篇
  2019年   2566篇
  2018年   3690篇
  2017年   3799篇
  2016年   4485篇
  2015年   1951篇
  2014年   3864篇
  2013年   7453篇
  2012年   5856篇
  2011年   6979篇
  2010年   5892篇
  2009年   6144篇
  2008年   6917篇
  2007年   6993篇
  2006年   6232篇
  2005年   5566篇
  2004年   5401篇
  2003年   4938篇
  2002年   5068篇
  2001年   5508篇
  2000年   4243篇
  1999年   3305篇
  1998年   3050篇
  1997年   2874篇
  1996年   2566篇
  1995年   2347篇
  1994年   2328篇
  1993年   2333篇
  1992年   2329篇
  1991年   2625篇
  1990年   2620篇
  1989年   2638篇
  1988年   2509篇
  1987年   2438篇
  1986年   2282篇
  1985年   2802篇
  1984年   2797篇
  1983年   2424篇
  1982年   2447篇
  1981年   2355篇
  1980年   2142篇
  1979年   2455篇
  1978年   2598篇
  1977年   2687篇
  1976年   2780篇
  1975年   2592篇
  1974年   2514篇
  1973年   2682篇
  1972年   2186篇
  1971年   2004篇
排序方式: 共有10000条查询结果,搜索用时 541 毫秒
81.
Russian Journal of General Chemistry - Highly dispersed CaO has been synthesized by heating an aqueous solution of calcium nitrate and D-glucose up to 800°C. Calcium oxide is formed with an...  相似文献   
82.

A procedure was suggested for preparing brominated polyols of reduced viscosity for the synthesis of foamed polyurethanes of reduced flammability. The flame-retarding action of the synthesized polyol tetrabromophthalate in polyurethane was studied in comparison with that of other widely used flame retardants. Evaluation of the effect exerted on the flammability of the polurethane compound by the polyol tetrabromophthalate synthesized, melamine, and aluminum hydroxide shows that all the samples containing flame retardants are self-extinguishing. The shortest combustion time was observed for the sample containing 6% polyol tetrabromophthalate synthesized. The sample containing as a flame retardant additive solely the synthesized polyole tetrabromophthalate also exhibits the highest performance as a heat-insulating material from the viewpoint of thermal conductivity.

  相似文献   
83.
Shanin  A. V.  Korolkov  A. I.  Kniazeva  K. S. 《Acoustical Physics》2022,68(4):316-325
Acoustical Physics - The problem of pulsed excitation of an acoustic waveguide with a constant cross section is considered. Absorption is ignored. As the most general model of such a waveguide,...  相似文献   
84.
Crystallography Reports - The specific features of the formation of concentration inhomogeneities in crystals grown by the Czochralski method (GaSb:Te, Ge:Ga) and by the Bridgman method...  相似文献   
85.
Physics of Atomic Nuclei - The paper presents a comparison of three neutrons identifying methods in scintillators based on ZnS with 6Li and 10B: charge integration method, pulse gradient analysis,...  相似文献   
86.
Journal of Applied Spectroscopy - Aqueous solutions of human hemoglobin have been studied by the multi-angle static light scattering method. The tendency of sickle-shaped erythrocytes to aggregate...  相似文献   
87.
Kamashev  A. A.  Garifullin  I. A. 《JETP Letters》2021,113(3):194-206
JETP Letters - We have demonstrated that with increasing the exchange splitting of the conduction band of a ferromagnet and, respectively, of the degree of the spin polarization, the probability of...  相似文献   
88.
Crystallography Reports - Nd1 – yEuyF3 – y crystals (y is the molar fraction of EuF2; 0 ≤ y ≤ 0.15) with a tysonite (LaF3) structure have...  相似文献   
89.
A new derivative of dioxouranium(VI) salen complex, [UO2(L)(pyridine)], where [L = N,N′-Bis(2-hydroxybenzylidene)-2,2-dimethyl-1,3-propanediamine] is synthesized and characterized by elemental analysis (C, H, N), FT-IR, ESI-MS spectrometry, UV/Vis, fluorescence, 1H and 13C NMR spectroscopy and thermal gravimetric (TG) study. Furthermore, the single crystal X-ray diffraction measurements of the complex were carried out at 100 and 273 K. The crystal structure measurements revealed that the complex has distorted pentagonal bipyramidal geometry with uranium atom located at the centre and bonded to two phenoxy oxygen and two azomethine nitrogen in tetradenate fashion and one nitrogen from pyridine making it seven coordinated. In addition, the photoluminescence property of the complex was also recorded.  相似文献   
90.
Russian Journal of Organic Chemistry - A procedure has been proposed for the synthesis of a series of substituted N-(1,3-thiazol-2-yl)-pyrimidin-2-amines and N-(pyrimidin-2-yl)thioureas by...  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