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   451213篇
  免费   3807篇
  国内免费   1338篇
化学   233969篇
晶体学   7328篇
力学   20977篇
综合类   9篇
数学   52228篇
物理学   141847篇
  2020年   3506篇
  2019年   3970篇
  2018年   5269篇
  2017年   5178篇
  2016年   7618篇
  2015年   4604篇
  2014年   7481篇
  2013年   18994篇
  2012年   14143篇
  2011年   17389篇
  2010年   12380篇
  2009年   12220篇
  2008年   16223篇
  2007年   16341篇
  2006年   15393篇
  2005年   13894篇
  2004年   12863篇
  2003年   11532篇
  2002年   11417篇
  2001年   12762篇
  2000年   9828篇
  1999年   7653篇
  1998年   6687篇
  1997年   6538篇
  1996年   6227篇
  1995年   5719篇
  1994年   5801篇
  1993年   5621篇
  1992年   6103篇
  1991年   6265篇
  1990年   5995篇
  1989年   5803篇
  1988年   5929篇
  1987年   5706篇
  1986年   5390篇
  1985年   7350篇
  1984年   7674篇
  1983年   6368篇
  1982年   6629篇
  1981年   6532篇
  1980年   6419篇
  1979年   6500篇
  1978年   6879篇
  1977年   6687篇
  1976年   6851篇
  1975年   6323篇
  1974年   6352篇
  1973年   6527篇
  1972年   4585篇
  1971年   3843篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
We discuss a mass change that has its origin in the action of forces on an object. This phenomenon, well-known in the context of quantum field theory (mass renormalization), can be discussed systematically in both classical and quantum mechanics in a framework given by Stückelberg. We employ this framework to resolve an interesting conflict of opinions between Schopenhauer and Hegel in the mid-19th century. We show that Hegel, Kant, and Schopenhauer demonstrated remarkable prescience in their views as seen from a modern perspective.  相似文献   
92.
The European Physical Journal E - The temperature-induced microphase separation of the binary liquid system iso-butyric acid+heavy water (iBA + D2O) in a mesoporous silica glass (CPG-10-75) of...  相似文献   
93.
Frank  A. I.  Nosov  V. G. 《JETP Letters》2004,79(7):313-315
JETP Letters - The problem of storing ultracold neutrons over a plane magnetic mirror in the presence of gravity is considered. For neutrons with a definite polarization, the sum of the magnetic...  相似文献   
94.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed.  相似文献   
95.
96.
    
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e).  相似文献   
97.
We extend the matrix version of Cochran's statistical theorem to outer inverses of a matrix. As applications, we investigate the Wishartness and independence of matrix quadratic forms for Kronecker product covariance structures.  相似文献   
98.
Radio Engineering and Electronics Institute, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1113–1124, September, 1989.  相似文献   
99.
100.
Summary Using a saturated non-boiling hydrocarbon mixture, the influence of two parameters on the results of field ionization mass spectrometry (FI-MS) measurements was studied: (a) the potential difference between the FI emitter and the counterelectrode; (b) the emitter temperature.Variation of the potential difference had only a minor effect on the average molecular mass measured and had no evident effect on the relative ring number distribution in the sample. In contrast, when the emitter temperature was increased, higher average molecular masses were recorded. Moreover, the average molecular masses shifted to higher ring numbers. In order to control the relationship between the described influences during mixture analysis, measuring instructions have been developed that enable the quantitative analysis of unknown saturated samples. However, average molecular mass of the mixture must be known.
Entwicklung einer quantitativen FI-MS-Methode zur Charakterisierung von gesättigten hoch- und nichtsiedenden Kohlenwasserstoffgemischen
  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