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   2987篇
  免费   105篇
化学   1578篇
晶体学   16篇
力学   56篇
数学   392篇
物理学   1050篇
  2021年   33篇
  2020年   33篇
  2019年   33篇
  2016年   112篇
  2015年   116篇
  2014年   152篇
  2013年   288篇
  2012年   106篇
  2011年   81篇
  2010年   84篇
  2009年   63篇
  2008年   63篇
  2007年   40篇
  2006年   86篇
  2005年   28篇
  2004年   31篇
  2003年   33篇
  2002年   48篇
  2001年   36篇
  2000年   59篇
  1999年   37篇
  1998年   43篇
  1997年   38篇
  1996年   39篇
  1995年   42篇
  1994年   37篇
  1993年   39篇
  1992年   31篇
  1991年   34篇
  1990年   35篇
  1989年   27篇
  1988年   51篇
  1987年   39篇
  1986年   35篇
  1985年   56篇
  1984年   55篇
  1983年   37篇
  1982年   32篇
  1981年   32篇
  1980年   41篇
  1979年   40篇
  1978年   39篇
  1977年   49篇
  1976年   48篇
  1975年   42篇
  1974年   56篇
  1973年   37篇
  1972年   29篇
  1969年   28篇
  1962年   27篇
排序方式: 共有3092条查询结果,搜索用时 15 毫秒
31.
An HPLC method was developed for studying the stability of [3H] stobadin stored in physiological saline or buffers at various pH. Optimum conditions for the separation of degradation products were elaborated. A high-performance liquid chromatograph equipped with a radioactivity detector was used.  相似文献   
32.
Static softening of AISI 321 steel after cold and hot deformation characterizing the industrial thermomechanical treatment was studied by means of tensile tests and TEM. The deformation temperature, the strain and the grain size were the main parameters determining the final softening. The results can be applied for optimization of the solution annealing.  相似文献   
33.
In the present paper we report the first experimental results on ac and dc conductivity and permittivity of adenine hemisulphate hydrate and adenine sulphate measured at atmospheric and high hydrostatic pressures. For both materials ac conductivity is of s type, where:s 1·1· Room temperature dc conductivity of adenine hemisulphate hydrate equals approximately 5×10–15 –1 cm–1 with an activation energy of 0·86 eV; dc conductivity of adenine sulphate is less than 10–16 cm–1. On the basis of these measurements and those carried out at high pressure, it is concluded that conductivity of adenine hemisulphate hydrate is of electronic type.The authors wish to thank Dr. J. Zachová for the preparation of adenine salts single crystals.  相似文献   
34.
We calculate the density of states for the nondegenerate Anderson model for various values ofu=U/ andn f using the perturbation theory withu as the expansion parameter. Summing all the -independent self-energy diagrams, we use the Friedel sum rule and Ward identities to express the physical quantities in terms of the remaining -dependent part of the self-energy, which we evaluate to the 2nd order. The results for the spin and charge susceptibilities obtained in such a way compare rather well with the Bethe-ansatz results. The density of states exhibits different features in different parts of the parameter space. In Kondo region (u>1,n f 1, i.e., – f ~U/2), we obtain a many-body resonance (half-width T K ) around the Fermi level and two broad peaks () at about f +n f U and f +U. In the VF region (u>1, and | f |) we obtain only two peaks (), one at about f and one between f +n f U and f +U. The consequences regarding the shape of the photoemission and inverse photoemission spectra of Ce intermetallics are discussed.  相似文献   
35.
Zusammenfassung Eine Reihe von Metallkomplexen des 2,5-Dibenzoyl-3,4-dihydroxy-selenophens wurden spektroskopisch untersucht. Das Verhalten des Wismutkomplexes und die Möglichkeiten einer spektrophotometrischen Wismutbestimmung auf diesem Wege wurden eingehend studiert.
Summary A spectroscopic examination was made of a series of metal complexes of 2,5-dibenzoyl-3,4-dihydroxyselenophen. The behavior of the bismuth complex and the possibilities of a spectrophotometric method of determining bismuth in this manner were studied thoroughly.


Herrn Univ.-Prof. Dr.Hans Lieb zum 80. Geburtstag gewidmet.  相似文献   
36.
A new photoionization detector for gas chromatography   总被引:1,自引:0,他引:1  
Summary A new photoionization detector for gas chromatography is discribed. The source of vacuum ultra-violet (VUV) radiation is separated from the ionization chamber by a window and thus the ionization chamber may be run at atmospheric pressure using an intense source of ionizing radiation. The operation consequently is improved and considerably simplified. Except for a ten times reduction in linearity, the performance characteristics of the detector are comparable to those of the flame ionization detector. Filtration of the VUV radiation allows the selectivity to be varied without affecting the dynamic properties of the detector.Z. ternberg, N. Ostoji, Yug. Pat. Appl.  相似文献   
37.
Zusammenfassung Die Reaktion von 2-Nitroso-1-naphthol mit Resorcin bzw. Orcin in Äther bei Anwesenheit von HNO3 liefert Benzo[c]phenoxazon-(9) (I), Benzo[c]phenoxazon-(9)-12-oxid (II), Methyl-benzo[c]phenoxazon-(9) (III) sowie 11-Methyl-benzo[c]phenoxazon-(9)-12-oxid (IV). Die Struktur der isolierten Substanzen wurde durch Reduktion mittels TiCl3 sowie durch die UV- und IR-Spektren gestützt.
The reaction of 2-nitroso-1-naphthol with resorcinol and orcinol in ether solution in the presence of nitric acid has been studied. From the reaction mixture the benzophenoxazones I–IV have been isolated. Structures were assigned on the grounds of UV and IR spectra and partly by using TiCl3 as a reducing agent.


Mit 1 Abbildung  相似文献   
38.
Influence of Coriolis coupling on excitation of some Nilsson states in155Gd,157Gd and167Er by inelastic scattering of 12·1 MeV deuterons is analysed. Expanded Nilsson potential with hexadecapolar deformation is used for the model calculations. Theoretical values of reduced transition probability,B(E2) are compared with experimental ones.  相似文献   
39.
An extended version of the noncollinear spin model bySawatzky et al. is developed to derive a dependence of the differential high field susceptibility on the degree of inversion of the ferrite MnFe2O4. Using the available data on the main molecular field coefficients it is shown that the present model imposes restrictions on values of. Determination of from the measurements of the field dependence of the saturated moments at low temperatures on samples with varying degrees of inversion reveals good quantitative agreement with the present model.  相似文献   
40.
We develop a theory of low energy electron loss spectroscopy of vibrational modes of molecules adsorbed on metal surfaces. Differential and total cross sections are calculated in the Distorted Wave Born Approximation, assuming i) strong elastic scattering on the metal surface, ii) direct electron-molecule interaction via the electric dipole field associated with the molecular vibration. The angular distributions are calculated and discussed for molecules adsorbed at various distances above the metal surface and for several electron energies and impact angles. The influence of electronic screening of dipolar oscillations is discussed and the consequences of the classical induced image dipoles are explored. It is shown that the metal surface selection rule known in IR spectroscopy is only approximately valid in electron scattering. Finally, we give numerical estimates of the inelastic scattering cross sections for the stretching vibrations of CO molecule adsorbed on transition metal surfaces, in reasonable agreement with experiments.  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