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   402686篇
  免费   3777篇
  国内免费   1256篇
化学   212312篇
晶体学   6903篇
力学   17728篇
综合类   12篇
数学   43182篇
物理学   127582篇
  2020年   3278篇
  2019年   3701篇
  2018年   4582篇
  2017年   4585篇
  2016年   6867篇
  2015年   4273篇
  2014年   6946篇
  2013年   17772篇
  2012年   13006篇
  2011年   16013篇
  2010年   11349篇
  2009年   11300篇
  2008年   14615篇
  2007年   14501篇
  2006年   13672篇
  2005年   12405篇
  2004年   11367篇
  2003年   10271篇
  2002年   10039篇
  2001年   12046篇
  2000年   9204篇
  1999年   7154篇
  1998年   5833篇
  1997年   5739篇
  1996年   5500篇
  1995年   5071篇
  1994年   4927篇
  1993年   4852篇
  1992年   5560篇
  1991年   5584篇
  1990年   5344篇
  1989年   5274篇
  1988年   5342篇
  1987年   5242篇
  1986年   4961篇
  1985年   6599篇
  1984年   6798篇
  1983年   5379篇
  1982年   5653篇
  1981年   5628篇
  1980年   5328篇
  1979年   5764篇
  1978年   5837篇
  1977年   5901篇
  1976年   5789篇
  1975年   5282篇
  1974年   5305篇
  1973年   5290篇
  1972年   3703篇
  1968年   3119篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
111.
In recent years there has emerged significant interest in low pressure radio frequency (rf) glow discharges which are used widely particulary in IC fabrication. Various parameters of the rf glow discharge have been found to be useful for its electrical characterization; however, there is no uniformity and agreement. Extensive experimental investigations on various discharge systems have shown, that the self-bias on the rf driven electrode, the complex conductivity and the breakdown characteristic are preferable parameters of rf discharges. Advantageously the self-bias and the complex conductivity should be presented in dependence on the pressure and the applied rf voltage. The discharge current cannot be measured quite accurately due to currents via leaky capacitors and the deviations from a sinusoidal form of the current due to nonlinearities.  相似文献   
112.
Summary High-purity indium was analysed by spark source mass spectrometry, using electrical and photoplate detection. For the calibration of the differences in elemental sensitivity, a standard sample was prepared in which 10 impurities were determined by graphite furnace atomic absorption spectrometry. In this way accuracies of less than 40% were obtained for relatively homogeneous elements at ppm and sub-ppm level. About 40 elements could be determined with detection limits of 10 to 30 ppb. Two pattern recognition methods, principal component analysis and clustering analysis, were applied to obtain information on trace element distribution, which indicated that a number of elements were strongly spatially correlated in the analysed sample.
Chemische Analyse und Verteilungsbestimmung von Spurenelementen in Indium-Matrix durch Funkenquellen-Massenspektrometrie

On leave from: Department of Chemistry, Nanjing Normal University, Nanjing, People's Republic of China  相似文献   
113.
The behavior of real disperse systems with organic impurities was examined under conditions of destabilization by inorganic coagulants. A number of physicochemical methods of analysis and a simulation method were used to identify the character and type of the complexes formed and to calculate their stability constants.  相似文献   
114.
C Dufour  K Dumesnil  P H Mangin 《Pramana》2006,67(1):173-190
Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.  相似文献   
115.
A standard model Lagrangian is constructed making the pseudo-Finsleroid generalization of the Yang-Mills field equation by the conformal method. The Higgs field potential is suggested that ensures generation of particle masses caused by the spontaneous symmetry breaking. After transition to the conformal coordinates, the expressions obtained assume the standard form that in many cases allows the results of pseudo-Euclidean theory to be used in calculations of the Feynman diagrams. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 44–51, April, 2006.  相似文献   
116.
117.
A method for suppressing self-modulation in backward-wave tubes is proposed. Additional delay is introduced into the feedback circuit, owing to which the output signal amplitude affects the electron beam current that enters into the interaction space. Numerical simulations demonstrate that the operating current in the single-frequency oscillation mode may be increased roughly twofold.  相似文献   
118.
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
119.
120.
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