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   436057篇
  免费   4846篇
  国内免费   1231篇
化学   233775篇
晶体学   6489篇
力学   18764篇
综合类   13篇
数学   49930篇
物理学   133163篇
  2021年   3768篇
  2020年   4186篇
  2019年   4518篇
  2018年   5853篇
  2017年   5744篇
  2016年   8831篇
  2015年   5561篇
  2014年   8542篇
  2013年   20183篇
  2012年   15648篇
  2011年   19261篇
  2010年   13497篇
  2009年   13350篇
  2008年   17647篇
  2007年   17541篇
  2006年   16252篇
  2005年   14550篇
  2004年   13525篇
  2003年   11892篇
  2002年   11728篇
  2001年   13429篇
  2000年   10086篇
  1999年   7916篇
  1998年   6569篇
  1997年   6315篇
  1996年   6082篇
  1995年   5470篇
  1994年   5392篇
  1993年   5198篇
  1992年   5828篇
  1991年   5924篇
  1990年   5665篇
  1989年   5472篇
  1988年   5493篇
  1987年   5374篇
  1986年   5091篇
  1985年   6560篇
  1984年   6695篇
  1983年   5301篇
  1982年   5387篇
  1981年   5367篇
  1980年   4955篇
  1979年   5352篇
  1978年   5491篇
  1977年   5385篇
  1976年   5329篇
  1975年   4914篇
  1974年   4886篇
  1973年   4881篇
  1972年   3455篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
995.
It was demonstrated that some foreign metal monolayers formed by underpotential deposition have pronounced catalytic effects on the oxidation of formic acid on platinum. The explanation of these effects was sought within the framewor of existing data on the formic acid oxidation and the underpotential deposition. It was found that the catalytic effect of foreign metal monolayers originates in the decrease of hydrogen adsorption thus preventing the formation of the main poisoning species COH. At the same time these experiments confirm the previously postulated mechanism of formation of the poisoning species involving adsorbed hydrogen.  相似文献   
996.
Summary INAA was applied for searching more effective biosorbents for U and Ag among 9 and 47 strains of actinomyces, respectively. Biomasses of strains were tested for the Ag and U sorption capacity from model solution, containing 50 mg/l Ag ions and from technological solution of U-production, containing 7.11 mg/l U ions. The U and Ag samples were irradiated for 5 hours and 20 hours, respectively, at a neutron flux density of 5.3 . 1013 n . cm-2 . s-1. The Ag content was calculated from the gamma-line of radionuclide 110mAg (T1/2 = 250.4d, Eγ= 657.7keV). The U content was calculated from the gamma-lines (228.2 keV, 277.8 keV) of radionuclide 239Np (T1/2 = 2.35 d). The error of U and Ag determination (relative standard deviation) was 2-3%.  相似文献   
997.
The structures of dioxaphosphepane (I) and dioxaphosphecane (II) salts prepared by hydrolysis of the corresponding bicyclophosphates have been compared. In both cases, hydrolysis occurs with breaking of the P–O bond of the fragment at the secondary carbon atom of bicyclophosphate. In phosphocycles I and II, the endocyclic bond angles O–P–O are 104.2 and 104.9°, and the exocyclic ones are 117.7 and 118.6°, respectively. Conformations of the anions in I and II differ substantially: for I it is a twist conformationC1TC4, and for II a distorted armchair. The data obtained are compared with those found earlier for similar molecules.Moscow State Pedagogical University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 154–160, July–August, 1993.Translated by T. Yudanova  相似文献   
998.
999.
1000.
The 17″×14″ X-ray film, gels, and blots are widely used in DNA research. However, DNA laser scanners are costly and unaffordable for the majority of surveyed biotech scientists who need it. The high-tech breakthrough analytical personal scanner (PS) presented in this report is an inexpensive 1 lb hand-held scanner priced at 2–4% of the bulky and costly 30–95 lb conventional laser scanners. This PS scanner is affordable from an operation budget and biotechnologists, who originate most science breakthroughs, can acquire it to enhance their speed, accuracy, and productivity. Compared to conventional laser scanners that are currently available only through hard-to-get capital-equipment budgets, the new PS scanner offers improved spatial resolution of 20 μm, higher speed (scan up to 17″×14″ molecular X-ray film in 48 s), 1–32,768 gray levels (16-bits), student routines, versatility, and, most important affordability. Its programs image the film, read DNA sequences automatically, and detect gene mutation. In parallel to the wide laboratory use of PC computers instead of mainframes, this PS scanner might become an integral part of a PC-PS powerful and cost-effective system where the PS performs the digital imaging and the PC acts on the data.  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