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   91751篇
  免费   16335篇
  国内免费   80篇
化学   82081篇
晶体学   297篇
力学   2816篇
综合类   2篇
数学   11652篇
物理学   11318篇
  2023年   4264篇
  2022年   1674篇
  2021年   2830篇
  2020年   5064篇
  2019年   2789篇
  2018年   3186篇
  2017年   1472篇
  2016年   7000篇
  2015年   6668篇
  2014年   6133篇
  2013年   8048篇
  2012年   5962篇
  2011年   3757篇
  2010年   5118篇
  2009年   4763篇
  2008年   3425篇
  2007年   2931篇
  2006年   2073篇
  2005年   2117篇
  2004年   1817篇
  2003年   1510篇
  2002年   1324篇
  2001年   1010篇
  2000年   1003篇
  1999年   709篇
  1998年   554篇
  1997年   540篇
  1996年   683篇
  1995年   577篇
  1994年   603篇
  1993年   681篇
  1992年   604篇
  1991年   480篇
  1990年   520篇
  1988年   496篇
  1985年   551篇
  1984年   521篇
  1982年   473篇
  1981年   509篇
  1980年   487篇
  1978年   470篇
  1977年   571篇
  1976年   651篇
  1975年   701篇
  1974年   730篇
  1973年   555篇
  1972年   516篇
  1970年   681篇
  1969年   580篇
  1968年   617篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A simple model including different processes important for the creation of APS signals formed by electrons is proposed. Mean probabilities of elastic and inelastic interactions of electrons with individual atom layers in the solid are introduced. The contribution of different layers to the DAPS and AEPS signals and the dependence of these signals on the interaction parameters are calculated.I am indebted to dr. J. Pavluch for valuable discussions.  相似文献   
52.
The paper describes the results of investigations of the solar wind ions, carried out on board the high apogee Prognoz 7 and Prognoz 8 Earth's satellites with the aid of an SKS instrument (USSR) and a Monitor instrument (USSR-SSR). Behaviour of proton and that of components on the front of Earth's bow and interplanetary shock waves were compared by means of the energoanalysis and energy-mass analysis techniques. In several long-term periods of observation the solar wind heavy ions — oxygen, silicon and iron were determined. It enabled us to estimate the solar corona chemical composition and electron temperature.Presented at the 5th General Assembly IAGA/IAMAP August 5–17, 1985, Prague, Czechoslovakia.  相似文献   
53.
54.
The main result of this paper is that ifV satisfies GCH andω 1<λ<μ are arbitrary regular cardinals, then in some cardinal preserving forcing extensionW ofV we have λ=λ=2 N 0,μ=2 λ and there are a hereditarily separableX ?2 λ with |X|= \(2^{\aleph _0 } \) =μ and a hereditarily LindelöfY ?2 μ withw(Y)= \(2^{2^\aleph 0} \) =μ. So far similar results have only been obtained under the assumption of CH.  相似文献   
55.
This paper shows the separation and determination of eight compounds containing the OH group (ethanol, pentanol, 3-methyl-1-butanol, hexanol, phenol, benzyl-alcohol, phenylethanol and geraniol) in synthetic wine by gas chromatography using UV-Vis molecular absorption spectrometry as detection system. All the parameters affecting the separation and determination were optimised using some methods of experiment design. The analytical characteristics of each compound were calculated and detection limits ranging from 2.3 to 74 mg l(-1) have been obtained.  相似文献   
56.
Summary Under steady state conditions the reduction in the diffusive flux into a sphere due the presence of a neighboring, identical sphere is calculated. Taking the flux into a sphere as 1 when the particles are at infinite separation, the flux decreases to a minimum value of 0.693 when the spheres are touching.
Zusammenfassung Unter stationären Bedingungen wird die Abnahme des Diffusionsflusses in eine Kugel, bedingt durch eine benachbarte identische Kugel, berechnet.Wird der Diffusionsfluß in eine Kugel gleich 1 gesetzt, wenn die Partikel unendlich weit voneinander entfernt sind, so nimmt der Diffusionsfluß auf einen Minimalwert von 0,693 ab, wenn sich die Kugeln berühren.


With 2 figures  相似文献   
57.
58.
The leaching rate of1 3 7Cs from bituminized products was studied by leach tests conducted for two years.  相似文献   
59.
A model has been developed for calculating the enthalpy, entropy and free energy change associated with the creation of cavities in a liquid the size of which corresponds to the volume occupied by a solvent molecule. The molar enthalpy change H cav equals the molar enthalpy of vaporization of the liquid, the free energy change G cav is given by G cav=–RT ln (V m ·p eq /RT) (V m =molar volume,p eq =equilibrium vapor pressure) and is related to the standard free energy of vaporization. This relationship provides an estimate of the free energy of cavity formation required to accomodate a substrate in the liquid. It has been shown, that the free energy of solvation of a substrate can be dissected into different contributions accounting for (1) the concentration dependence of partial molar free energy quantities, (2) the formation of holes in the solvent, (3) the existence of specific, short range solute-solvent interactions and (4) the dielectric polarization of the medium. Application of this concept leads to an equation of the general form G S G R =a(DN S –DN R )+b(AN S –AN R )+c(G vp oS G vp oR ), where G represents the free energy of reaction or activation,DN the donor number,AN the acceptor number and G vp o the standard free energy of vaporization of a solventS and a reference solventR, resp.

Mit 3 Abbildungen  相似文献   
60.
An efficient method was developed for the determination of nanogram levels of lithium in biological samples. Serum samples from human subjects from southeastern Spain, treated or not treated with lithium carbonate, were analyzed by electrothermal atomic absorption spectrometry. The samples were previously treated with a matrix modifier consisting of 0.1% Triton X-100 and injected through a graphite tube with L'vov platform. The Li concentrations measured by the procedure described for the 3 certified reference samples used were not significantly different (p > 0.05) than certified levels. Sample recoveries and variability during several days, with coefficients of variation from 4.00 to 14.8%, demonstrated the reliability and accuracy of this technique. Mean Li concentration determined in the serum of individuals with psychiatric disorders treated with Li (n = 117, 5.077 +/- 1.795 microg Li/mL) was significantly higher (p < 0.001) than that in individuals not treated with Li (n = 24, 1.902 +/- 2.054 ng Li/mL).  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