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   342780篇
  免费   2791篇
  国内免费   988篇
化学   186473篇
晶体学   4942篇
力学   14349篇
综合类   12篇
数学   37416篇
物理学   103367篇
  2020年   2876篇
  2019年   3223篇
  2018年   4370篇
  2017年   4278篇
  2016年   6299篇
  2015年   3674篇
  2014年   5804篇
  2013年   14649篇
  2012年   11031篇
  2011年   13628篇
  2010年   9614篇
  2009年   9524篇
  2008年   12840篇
  2007年   12981篇
  2006年   12098篇
  2005年   11010篇
  2004年   9770篇
  2003年   8799篇
  2002年   8733篇
  2001年   9459篇
  2000年   7433篇
  1999年   5598篇
  1998年   4881篇
  1997年   4874篇
  1996年   4505篇
  1995年   3942篇
  1994年   4005篇
  1993年   3919篇
  1992年   4269篇
  1991年   4470篇
  1990年   4180篇
  1989年   4166篇
  1988年   4037篇
  1987年   3925篇
  1986年   3751篇
  1985年   4960篇
  1984年   5165篇
  1983年   4180篇
  1982年   4617篇
  1981年   4359篇
  1980年   4114篇
  1979年   4462篇
  1978年   4705篇
  1977年   4620篇
  1976年   4658篇
  1975年   4413篇
  1974年   4457篇
  1973年   4573篇
  1972年   3066篇
  1967年   2774篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Conclusions Silver perchlorate catalyzes the decomposition of aqueous hydrogen peroxide solutions and, contrary to the literature data, does not form the salt AgClO5 in either ethanol medium or in diethyl ether medium. Silver perchlorate, the same as other perchlorates, does not form molecular compounds with hydrogen peroxide at 0°C.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2640–2641, November, 1974.  相似文献   
992.
ULTRAVIOLET-ENHANCED REACTIVATION OF HERPES VIRUS IN HUMAN TUMOR CELLS   总被引:2,自引:0,他引:2  
Abstract —Virus-host cell interactions may be investigated by study of the enhancement of infectivity of ultraviolet (UV)-irradiated virus obtained by UV-irradiating the host cell [ultraviolet reactivation (UVR)]. This phenomenon was studied with Herpes simplex virus and normal (embryonic lung) and malignant (HeLa) human cells. Although the lung cells displayed no UVR, both the HeLa cells and a Sendai-virus carrier culture of HeLa cells demonstrated UVR capabilities. This UVR persisted at equal or increased levels for at least 24 h. Since the lung cells and HeLa cells have similar host-cell-reactivation (HCR) abilities, the differences in UVR suggests that UVR and HCR may operate by different mechanisms.  相似文献   
993.
Crystal chemistry and phase relations for the bronze-forming region of the EuWO system have been investigated. A bronze EuxWO3 is stable up to 1000°C when x ? 0.125 and in the region 0.085 ? x ? 0.125 the symmetry is cubic. A tetragonal bronze exists at x = 0.05, and an orthorhombic bronze with a structure closely related to the orthorhombic form of WO3 exists below x = 0.01. Mössbauer spectra at room temperature and at 80 K indicate that in all these phases the europium is highly ionized as Eu(III) with no electron localization to give (EuII) even at low values for x. The decomposition products of the bronzes have been established, and the Mössbauer parameters for the highly nonstoichiometric tungstates EuxWO4 were determined. Both Eu(II) and Eu(III) resonances were obtained, and a cation vacancy model for EuxWO4 was found to fit the data best. In conformity with the foregoing data, a sample of composition “Eu2W2O7” was found not be be a pyrochlore but to comprise a mixture of Eu6WO12, EuxWO4, and W. The phase relationships for the europium bronze system EuxWO3 are compared with those of other ionic bronzes NaxWO3, LixWO3, and AlxWO3.  相似文献   
994.
The application of Ag(I) catalysis of S2O82? to the oxidation of organic carbon to CO2 for determination of dissolved organic carbon in aqueous samples is described. The resulting method combines to a significant degree the speed of high-temperature combustion methods and the sensitivity of wet chemical oxidation. For some samples, a higher oxidation efficiency has been observed than with an uncatalyzed wet chemical oxidation method.  相似文献   
995.
The preparation of η-C3H5V(CO)5 from allyl chloride and sodium hexacarbonylvanadate (–I) is reported. Composition, IR and NMR spectra are in accordance with a π-bonded C3H5-moiety; the preparation has been extended to give complexes with substituted allyl groups. Furthermore (1-3-η-2-butenyl)pentacarbonylvanadium can be obtained by the addition of butadiene to HV (CO)6.  相似文献   
996.
The thermodynamic treatment of double-pseudobinary solutions of the type (A xBy) r o(M uNv) s o presented in a preceding publication was extended to include the conditions defining the critical points for the asymmetric case (r os o) and approximations for the spinodal and binodal surface near the critical solution point.Closed solutions for the coordinates of the critical points were obtained only for systems with ideal mixing behavior, and the isothermal binodal and spinodal near the critical solution point in such systems are adequately approximated by circles and ellipses, respectively. An axes ratio of is nearly independent of the relative sublattice abundance and the major effect of changes in the ratios o/r o is a rotation of the binodal by an angle tg .The principal features of nonideal regular systems for temperatures close to the critical solution point are described by expressions derived from small term expansions of the conditional equations, but generalizations are not possible to the same extent as for the case with ideal boundary systems. The results are discussed and the application of the equations demonstrated on model examples.Mit 6 Abbildungen  相似文献   
997.
The photoelectronic spectra of cis-2-chloro, 4-tert-butylcyclohexanone and cis-2-methyl-2-chlorocyclohexanone have been analysed. These analyses have been used in an investigation into the nature of the orbital interactions in these molecules, and into the dependence of these interactions on the axial or equatorial position of the halogen atom. The preferential conformations of 2-chlorocyclohexanone and 4,4-dimethyl-2-chlorocyclo-hexanone have thus been obtained.  相似文献   
998.
The sulfur analogs of harmaline, 7-methoxy-3,4-dihydro-1-methyl[1]benzothieno[2,3-c]-pyridine (Ib), harmine, 7-methoxy-1-methyl[1]benzothieno[2,3- c ]pyridine (IIb), and corresponding 6-methoxy isomers (Ic and IIc) have been synthesized for pharmacological evaluation as monoamine oxidase inhibitors.  相似文献   
999.
The results of allowing tetrahydro-as-triazine-3(2H)-thiones to react with various α,β-diiunctional compounds, such as, α-bromoethyl p-toluenesulfonate, chloroacetaldehyde, α-bromophenylacet-uldehyde, phenaeyl bromide, chloroacetonitrile, α-bromophenylaeelonitrile, and α-cyanobenzyl p-toluenesulfonate are discussed. These condensations give either a 5H-thiazolo[3,2-b]-as-triazine or a 2H-thiazolo[2,3-c]-as-triazine.  相似文献   
1000.
Quantitative measurement of both bulk and localized oxygen concentrations is of importance in the study of oxidation kinetics. We describe the combined application of two nuclear techniques, fast neutron activation analysis and (d, p) nuclear microprobe, to the determination of oxygen concentrations and surface profiles for steam-oxidized Zircaloy-4 cladding specimens. Results of measurements using these techniques are presented. Work partially supported by Electric Power Research Institute Contract T.S.A. No. 20.  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