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   733篇
  免费   8篇
  国内免费   1篇
化学   467篇
晶体学   6篇
力学   9篇
数学   61篇
物理学   166篇
无线电   33篇
  2022年   10篇
  2020年   11篇
  2019年   20篇
  2018年   16篇
  2017年   18篇
  2016年   17篇
  2015年   6篇
  2014年   22篇
  2013年   27篇
  2012年   34篇
  2011年   26篇
  2010年   42篇
  2009年   45篇
  2008年   27篇
  2007年   34篇
  2006年   21篇
  2005年   24篇
  2004年   33篇
  2003年   14篇
  2002年   15篇
  2001年   13篇
  2000年   14篇
  1999年   11篇
  1998年   8篇
  1996年   7篇
  1995年   8篇
  1994年   16篇
  1993年   8篇
  1992年   13篇
  1991年   16篇
  1990年   9篇
  1989年   6篇
  1988年   8篇
  1987年   7篇
  1986年   7篇
  1985年   10篇
  1984年   5篇
  1982年   8篇
  1981年   15篇
  1980年   6篇
  1979年   9篇
  1978年   6篇
  1977年   9篇
  1976年   5篇
  1975年   5篇
  1974年   5篇
  1972年   5篇
  1968年   8篇
  1966年   4篇
  1959年   4篇
排序方式: 共有742条查询结果,搜索用时 46 毫秒
11.
It is established that the -chloroepoxide methyl 2-chloro-3-(3-nitrophenyl)-2, 3-epoxypropionate, in contrast to its a-chloroketone isomer methyl 3-(3-nitrophenyl-3-chloro-2-oxopropionate, forms 2-(3-nitrophenyl-3methoxycarbonylquinoxaline in reaction with 1,2-phenylene diamine, whereas the condensation of the achloroketone with 1,2 phenylene diamine gives 3-(-chloro-3-nitrophenyl)-2-oxo-1,2-dihydroquinoxaline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1105-1108, August, 1994.  相似文献   
12.
The reaction of p-xylene with epichlorohydrin in the presence of aluminum chloride gave 1,4-dimethyl-2,5-bis(1-chloro-2-hydroxypropyl)benzene, which serves as the starting compound for the synthesis of the corresponding symmetrical dithiirane.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1319–1321, October, 1985.  相似文献   
13.
1.  The reaction of esters of 3-phenyl-3-chloro-2-ketopropionic acid with sodium alcoholates in alcohol (methanol or ethanol) at reflux leads to the formation of an ester of 2,5-diketo-3,4-diphenyl-3-methoxyhexanedioic or 2,5-diketo-3,4-diphenyl-3-ethoxyhexanedioic acid.
2.  The reactions of esters of 3-phenyl-3-chloro-2-ketopropionic acid with the corresponding sodium alcoholates in dilute solution at 0C give the product of the substitution of chlorine by an alkoxy group in quantitative yield.
Translated from Izvestiya Akadamii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 962–964, April, 1989.  相似文献   
14.
The combined use of 2D NMR correlation methods and ab initio chemical shift calculations is efficient and, in some cases, virtually the only way to determine the structures of new organic compounds. This approach enabled us to establish the structure of the major unusual product of the three-component reaction of imidazo[1,5-a]quinoxalin-4-one, bis(2-chloroethyl)amine hydrochloride, and potassium carbonate in DMF. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2172–2179, December, 2006. Dedicated to Professor A. V. Il’yasov on the occasion of his 70th birthday.  相似文献   
15.
16.
The electrochemical properties of membranes based on dibenzo-crown ethers bearing hydroxyl and chloromethyl groups in polyether rings were studied. These substances were tested as membrane ionophores for ion-selective electrodes (ISEs) reversible to potassium ion. The developed ISEs were used for determining potassium in blood plasma samples. The generalized results of determining potassium in the blood of different patients with cardiovascular diseases revealed quantitative regularities that allowed the diseases to be diagnosed early.  相似文献   
17.
Glasses and melts in the system (NaPO3)(1-x)(Al(PO3)3)x were studied with the aim of obtaining information about the structure on the next larger scale beyond the PO4 group. Magic angle spinning NMR was applied to the pure NaPO3 glass and Raman scattering to systems with x = 0.00, 0.03, 0.06, 0.15, and 0.60 in the temperature range T = 300-1100 K. Comparison of the 31P chemical shift between glass and crystalline forms revealed that polymerization of the metaphosphate into tricyclophosphatelike (PO3)3(3-) rings is the dominant structure, ca. 80%, formed by the twofold vertex-joined PO4 groups in the glass. In the Raman study we focused on the prominent polarized band at ca. 1170 cm(-1) which is due to the symmetric breathing mode of the tetrahedral PO4 group. This band was decomposed into a few Gaussian lines. These component lines could be identified using the NMR results: two narrow components are due to PO4 groups in the tricyclophosphatelike rings, which have either a Na or an Al counterion and a third broad component is due to chain-polymerized (PO3(-))n. The variations of the component lines (peak positions, widths, and intensities) with respect to x and T are presented. We derive the shifts of the symmetric breathing mode frequency which are caused by Na or Al counterions, by ring closure, by x > 0, etc. The relative intensities of the narrow and broad components in the 1170-cm(-1) band of the Raman spectra are discussed. The amount of ring-to-chain transformation on addition of Al3+, and as functions of T and x, is derived. Indications for ordering on a next larger scale, derivable from Raman, NMR, and thermodynamics, are compared.  相似文献   
18.
Addition of aliphatic diols to bicyclo[2.2.1]hept-2-ene and its 5-alkyl-substituted derivatives in the presence of naphthalene-1,5-disulfonic acid leads to the formation of the corresponding bicyclo[2.2.1]hept-2-yl monoethers in high yields.  相似文献   
19.
Substituted anilides of 1,4-dithiene- and oxathienecarboxylic acids were synthesized. It was shown that the reaction of 3-phenyl-1,4-dithi-2-ene-2-carboxyl chloride with 2-aminopyridines, depending on the base used and the reaction conditions, leads to the formation of N-[3-phenyl-2-(1,4-dithi-2-en)ylcarbonyl]2-amino-pyridine and/or N,N-bis[3-phenyl-2-(1,4-dithi-2-en)-ylcarbonyl]pyridonimine. The data of IR, UV, and PME spectroscopy were used to confirm the structure of the synthesized compounds.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Science Center, Russian Academy of Sciences. Kazan 420083. Translated fro, Khimiya Geterotskiklicheskikh Soedinenii, No. 9, pp. 1191–1196, September, 1994. Original article submitted May 10, 1994.  相似文献   
20.
By the use of complete orthonormal sets of -exponential-type orbitals, where ( = 1, 0, –1, –2,...) the multicenter electronic attraction (EA), electric field (EF) and electric field gradient (EFG) integrals of nonscreened and Yukawa-like screened Coulomb potentials are expressed through the two-center overlap integrals with the same screening constants and the auxiliary functions introduced in our previous paper (I.I. Guseinov, J. Phys. B, 3 (1970) 1399). The recurrence relations for auxiliary functions are useful for the calculation of multicenter EA, EF and EFG integrals for arbitrary integer and noninteger values of principal quantum numbers, screening constants, and location of slater-type orbitals. The convergence of the series is tested by calculating concrete cases.  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