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   21004篇
  免费   576篇
  国内免费   103篇
化学   13533篇
晶体学   96篇
力学   484篇
综合类   2篇
数学   3918篇
物理学   3650篇
  2023年   126篇
  2022年   300篇
  2021年   398篇
  2020年   373篇
  2019年   340篇
  2018年   742篇
  2017年   509篇
  2016年   615篇
  2015年   542篇
  2014年   555篇
  2013年   1160篇
  2012年   1229篇
  2011年   1311篇
  2010年   854篇
  2009年   758篇
  2008年   1222篇
  2007年   1169篇
  2006年   1082篇
  2005年   1012篇
  2004年   810篇
  2003年   754篇
  2002年   639篇
  2001年   374篇
  2000年   426篇
  1999年   251篇
  1998年   231篇
  1997年   211篇
  1996年   258篇
  1995年   164篇
  1994年   175篇
  1993年   161篇
  1992年   158篇
  1991年   136篇
  1990年   144篇
  1989年   123篇
  1988年   115篇
  1987年   100篇
  1986年   102篇
  1985年   138篇
  1984年   173篇
  1983年   107篇
  1982年   124篇
  1981年   127篇
  1980年   104篇
  1979年   81篇
  1978年   108篇
  1977年   90篇
  1976年   105篇
  1975年   83篇
  1973年   64篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
A rather recent interpretation of quantum mechanics, known under the various names of consistent histories, decohering histories, or logical interpretation, has brought interpretation into a standard deductive theory and is now investigated in many places. A key difference with the Copenhagen interpretation is the status of classical physics, now derived completely from quantum principles in both its dynamical and logical aspects. After describing briefly this new interpretation in its essentials, leaving aside technical details, it is shown how its consequences in epistemology differ drastically from the familiar outcomes of the Copenhagen interpretation, leading in particular to a well-defined theory of knowledge. Some more speculative philosophical consequences associated with the unsolved problem of actuality are also mentioned.  相似文献   
12.
13.
The reaction between thiocarbamate herbicides and 2,6-dichlorobenzoquinone-N-chloroimine or 2,6-dibromobenzoquinone-N-chloroimine is suitable for the detection of these herbicides on thin-layer plates with high sensitivity. The reactions were followed by infrared, nuclear magnetic resonance and mass spectrometry. We have established the formation of 2,6-dichlorobenzoquinone-S-alkyl sulphenylimines. In the case of the bromo-derivative, halogen exchange and substitution on the quinone ring took place simultaneously leading to the formation of mixed halogenated 2,6-dihalo- and, in addition, 2,3,6-trihalobenzoquinone-S-alkyl sulphenylimines. The final product of the detection reaction, i.e. 2,6-dichlorobenzoquinone-S-alkyl sulphenylimine was reacted with 2,6-dibromobenzoquinone-N-chloroimine where 2,6-dichloro-3-bromobenzoquinone-S-alkyl sulphenylimine formed as a consequence of the looser bromine-carbon linkage on the 2 and 6 positions of the quinone ring.  相似文献   
14.
Hegedüs  A. J.  Bereznai  T.  Horkay  Klara  Kiss  A. B.  Lakó  Martha 《Mikrochimica acta》1975,63(4):351-354
Microchimica Acta - Mit der turbidimetrischen Strychninnitrat-Methode für Phosphorspurenbestimmung nach der Version von Hegedüs und Dvorszky kann man nur dann ausgezeichnete...  相似文献   
15.
High-resolution X-ray diffraction and polarized neutron diffraction experiments have been performed on the Y-semiquinonate complex, Y(HBPz3)2(DTBSQ), in order to determine the charge and spin densities in the paramagnetic ground state, S = (1/2). The aim of these combined studies is to bring new insights to the antiferromagnetic coupling mechanism between the semiquinonate radical and the rare earth ion in the isomorphous Gd(HBPz3)2(DTBSQ) complex. The experimental charge density at 106 K yields detailed information about the bonding between the Y3+ ion and the semiquinonate ligand; the topological charge of the yttrium atom indicates a transfer of about 1.5 electrons from the radical toward the Y3+ ion in the complex, in agreement with DFT calculations. The electron density deformation map reveals well-resolved oxygen lone pairs with one lobe polarized toward the yttrium atom. The determination of the induced spin density at 1.9 K under an applied magnetic field of 9.5 T permits the visualization of the delocalized magnetic orbital of the radical throughout the entire molecule. The spin is mainly distributed on the oxygen atoms [O1 (0.12(1) mu B), O2(0.11(1) mu B)] and the carbon atoms [C21 (0.24(1) mu B), C22(0.20(1) mu B), C24(0.16(1) mu B), C25(0.12(1) mu B)] of the carbonyl ring. A significant spin delocalization on the yttrium site of 0.08(2) mu B is observed, proving that a direct overlap with the radical magnetic orbital can occur at the rare earth site and lead to antiferromagnetic coupling. The DFT calculations are in good quantitative agreement with the experimental charge density results, but they underestimate the spin delocalization of the oxygen toward the yttrium and the carbon atoms of the carbonyl ring.  相似文献   
16.
17.
Accreditation and Quality Assurance -  相似文献   
18.
The effect of the ethanol oxidation rate on the interaction between the phosphorylation state (the [ATP]/[ADP] X [HPO4]2- ratio) and the redox state (the free [NAD+]/[NADH] ratio) of the liver cytosol was studied in intact fed rats. The rate of ethanol oxidation was inhibited to different degrees with pyrazole. The ethanol oxidation rate had no influence on the liver lactate level but correlated significantly with the pyruvate level. Accordingly, a significant correlation was also found between the ethanol oxidation rate and the lactate/pyruvate ratio. The rate of ethanol oxidation correlated significantly with the liver 3-phosphoglycerate level. No change in the glyceraldehyde-3-phosphate level was found. No correlation was found between the ethanol oxidation rate and the glyceraldehyde-3-phosphate/3-phosphoglycerate redox couple. Ethanol administration slightly increased the liver ATP level, but the simultaneous administration of pyrazole eliminated this effect. Other adenine nucleotides and HPO4 2- were not changed. The changes in the rate of ethanol oxidation had no effect on the phosphorylation state in the fed liver. It is assumed that in the fed liver the phosphorylation state is so well stabilized that the redox level has no influence.  相似文献   
19.
The molecular energy of the complex (η5-C5H5)2TiCl2 has been calculated for experimental geometry and for several hypothetical forms by a semi-empirical CNDO/2 approach. The energy difference between experimental (quasi-tetrahedral) geometry and a planar geometry is ca. 20 kcal mol?1. This difference is sufficiently high to explain the difficulty of the inversion process.  相似文献   
20.
At pH 5 (AcOHAcONa) protonation of the enamine of 3,6,6-trimethylnorpinane 2-one (3-methylnopinone) yields the cis immonium ion 6 (X  OAc), which isomerizes to the thermodynamically more stable trans immonium ion 6′ (X  OAc). Under more strongly acid conditions (aqueous hydrochloric or perchloric acids), the enamonium salts 7 (X  Cl or ClO4) are formed; these isomerize, with a rate increasing with decreasing acidity to the cis immonium salts 6, stable under these conditions. Epimerization of the cis salt 6 (X  Cl), occurs in ethereal hydrogen chloride, the rate increasing also with decreasing acidity. At pH 5, hydrolysis of the enamine yields 3-methylnopinone, the proportion of the less thermodynamically stable trans isomer increasing with a rise in reaction temperature.  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