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   146976篇
  免费   1453篇
  国内免费   397篇
化学   80295篇
晶体学   2389篇
力学   6064篇
综合类   3篇
数学   13569篇
物理学   46506篇
  2021年   1034篇
  2020年   1183篇
  2019年   1254篇
  2018年   1638篇
  2017年   1689篇
  2016年   2542篇
  2015年   1563篇
  2014年   2351篇
  2013年   6040篇
  2012年   4845篇
  2011年   5944篇
  2010年   4185篇
  2009年   4209篇
  2008年   5733篇
  2007年   5517篇
  2006年   5391篇
  2005年   4948篇
  2004年   4456篇
  2003年   4123篇
  2002年   4013篇
  2001年   5545篇
  2000年   3975篇
  1999年   3075篇
  1998年   2112篇
  1997年   2209篇
  1996年   2072篇
  1995年   1918篇
  1994年   1913篇
  1993年   1732篇
  1992年   2216篇
  1991年   2301篇
  1990年   2136篇
  1989年   2100篇
  1988年   2077篇
  1987年   2085篇
  1986年   1910篇
  1985年   2376篇
  1984年   2391篇
  1983年   1910篇
  1982年   1914篇
  1981年   1753篇
  1980年   1740篇
  1979年   2031篇
  1978年   2102篇
  1977年   2047篇
  1976年   1976篇
  1975年   1859篇
  1974年   1844篇
  1973年   1875篇
  1972年   1236篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
972.
Conclusions The complexes of Co, Ni, Fe, and Cu with dimethyl- and diphenylglyoxime inhibit the initiated oxidation of cumene by reacting with the peroxide radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1342–1344, June, 1971.  相似文献   
973.
974.
In this paper, the NO-to-NO 2 conversion in various gaseous mixtures is experimentally investigated. Streamer coronas are produced with a dc-superimposed high-frequency ac power supply (10–60 kHz). According to NO x removal experiments in N 2 +NO x and N 2 +O 2 +NO x gaseous mixtures, it is supposed that the reverse reaction NO 2 +ONO+O 2 may not only limit NO 2 production in N 2 +NO x mixtures, but also increase the energy cost for NO removal. Oxygen could significantly suppress reduction reactions and enhance oxidation processes. The reduction reactions, such as N+NON 2 +O, induce negligible NO removal provided the O 2 concentration is larger than 3.6%. With adding H 2 O into the reactor, the produced NO 2 per unit removed NO can be significantly reduced due to NO 2 oxidation. NH 3 injection could also significantly decrease the produced NO 2 via NH and NH 2 - related reduction reactions. Almost 100% of NO 2 can be removed in gaseous mixtures of N 2 +O 2 +H 2 O+NO 2 with negligible NO production.  相似文献   
975.
(±)-Biotin has been synthesized from a mixture of cis- and allo-trisubstituted dehydrothiophanes by a scheme providing for the easy elimination of the accompanying allo-substituted thiophane in the form of an intermediate and not as the final isomeric allo-biotin. The imidazoline ring of biotin is formed from a dialkoxy-carbonyldiaminothiophane under the conditions of partial hydrolysis of one of the protective groups with the elimination of phosgene from the scheme of synthesis.All-Union Scientific-Research Vitamin Institute, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 220–223, March–April, 1981.  相似文献   
976.
977.
978.
Kubo K  Ishige R  Sakurai T 《Talanta》1999,49(2):339-344
Photoinduced electron transfer (PET) fluoroionophores (1b, 2b) that consist of diazacrown and two 9-anthryl pendants show fluorescent enhancement with various guest salts. The diaza-12-crown-4 derivative (2b) exhibited Zn(2+) selectivity and in the presence of this cation the host fluorescence intensity was increased by a factor of 182. The guest cation-induced fluorescence enhancement of 2b was larger than the diaza-18-crown-6 derivative (1b).  相似文献   
979.
The present state of a long term program is reviewed. It was started to elaborate a remote controlled automated radiochemical processing system for the neutron activation analysis of biological materials. The system is based on wet ashing of the sample, followed by reactive desorption of some volatile components. The distillation residue is passed through a series of columns filled with selective ion screening materials to remove the matrix activity. The solution is thus “stripped” from the interfering radioions, and it is processed to single-elements through group separations using ion-exchange chromatographic techniques. Some special problems concerning this system are treated. (a) General aspects of the construction of a (semi)automated radiochemical processing system are discussed; (b) Comparison is made between various technical realizations of the same basic concept; (c) Some problems concerning the “reconstruction” of an already published processing system are outlined.  相似文献   
980.
Conclusions A convenient method of preparing organochlorohydridesilanes by selective chlorination of organohydridesilanes with stannic chloride was proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2114–2117, September, 1967.  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