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   241篇
  免费   5篇
化学   126篇
晶体学   1篇
力学   15篇
数学   34篇
物理学   70篇
  2023年   2篇
  2022年   7篇
  2021年   9篇
  2020年   10篇
  2019年   15篇
  2018年   11篇
  2017年   2篇
  2016年   14篇
  2015年   9篇
  2014年   8篇
  2013年   16篇
  2012年   12篇
  2011年   17篇
  2010年   16篇
  2009年   8篇
  2008年   15篇
  2007年   18篇
  2006年   14篇
  2005年   6篇
  2004年   4篇
  2003年   3篇
  2002年   8篇
  2001年   2篇
  2000年   1篇
  1999年   2篇
  1998年   1篇
  1997年   2篇
  1996年   1篇
  1995年   1篇
  1993年   2篇
  1988年   1篇
  1981年   1篇
  1979年   1篇
  1976年   2篇
  1973年   1篇
  1971年   1篇
  1968年   2篇
  1966年   1篇
排序方式: 共有246条查询结果,搜索用时 15 毫秒
1.
The current paper deals with the development of a new biologically active food supplement (BAFS) aimed at treating atherosclerosis. Since atherosclerosis is considered to be a disease of aging, the composition of the supplement includes such essential minerals as magnesium and potassium, which are commonly used to prevent atherosclerosis, as well as vitamins C, E and the B-group vitamins in order to address the needs of the elderly. The authors outline the supplement-manufacturing technology and discuss the clinical trial undertaken by patients, aged about 60 years, with peripheral atherosclerosis. The research methodology focuses on studying the effectiveness of the developed supplement by assessing the influence of the active ingredients on treating metabolic disorders. To establish the efficacy of the supplement, blood tests, ultrasound and physical examinations were applied. The combination therapy resulted in improved metabolism and an overall better performance of the cardiovascular system; therefore, the BASF can be recommended as part of combination therapy to prevent and treat atherosclerotic and age-related changes in blood vessels.  相似文献   
2.
In this paper we analyze the Cauchy problem for the Einstein equation in the case of a non-characteristic initial hypersurface. To find the correct notions for the characteristic and Cauchy data we introduce a complex, which we call the Einstein complex. Then the Cauchy problem acquires correctness in terms of the associated spectral sequence. We define the Cauchy data in such way that they allow us to reconstruct a cohomologously unique formal solution.  相似文献   
3.
4.
The chemical dynamics of the elementary reaction of ground state atomic silicon (Si; 3P) with germane (GeH4; X1A1) were unraveled in the gas phase under single collision condition at a collision energy of 11.8±0.3 kJ mol−1 exploiting the crossed molecular beams technique contemplated with electronic structure calculations. The reaction follows indirect scattering dynamics and is initiated through an initial barrierless insertion of the silicon atom into one of the four chemically equivalent germanium-hydrogen bonds forming a triplet collision complex (HSiGeH3; 3 i1 ). This intermediate underwent facile intersystem crossing (ISC) to the singlet surface (HSiGeH3; 1 i1 ). The latter isomerized via at least three hydrogen atom migrations involving exotic, hydrogen bridged reaction intermediates eventually leading to the H3SiGeH isomer i5 . This intermediate could undergo unimolecular decomposition yielding the dibridged butterfly-structured isomer 1 p1 (Si(μ-H2)Ge) plus molecular hydrogen through a tight exit transition state. Alternatively, up to two subsequent hydrogen shifts to i6 and i7 , followed by fragmentation of each of these intermediates, could also form 1 p1 (Si(μ-H2)Ge) along with molecular hydrogen. The overall non-adiabatic reaction dynamics provide evidence on the existence of exotic dinuclear hydrides of main group XIV elements, whose carbon analog structures do not exist.  相似文献   
5.
We propose a fully ab initio approach to calculate electron-phonon scattering times for excited electrons interacting with short-wavelength (intervalley) phonons in semiconductors. Our approach is based on density functional perturbation theory and on the direct integration of electronic scattering probabilities over all possible final states with no ad hoc assumptions. We apply it to the deexcitation of hot electrons in GaAs, and calculate the lifetime of the direct exciton in GaP, both in excellent agreement with experiments. Matrix elements of the electron-phonon coupling, and their dependence on the wave vector of the final state and on the phonon modes, are shown to be crucial ingredients of the evaluation of electron-phonon scattering times.  相似文献   
6.
The results of experimental measurement and numerical simulation of 979 rates of threshold reactions in 142 samples of 209Bi, 197Au, 181Ta, 169Tm, 115In, 93Nb, 65Cu, 64Zn, 63Cu, 59Co, 27Al, 19F, and 12C placed inside and outside of a “thick” W-Na target irradiated with 0.8-GeV protons are reported. The reaction rates are measured by the method of γ spectrometry using Ge and GeLi semiconductor detectors. The numerical calculations were performed using the LAHET code package together with the EXFOR database and the evaluated data libraries MENDL2N, MENDL2P, and IEAF2001. The experimental and calculated results are compared and the most significant discrepancies are analyzed.  相似文献   
7.
A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing 233U from 232Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.  相似文献   
8.
The methylgermylene species (HGeCH3; X1A′) has been synthesized via the bimolecular gas phase reaction of ground state methylidyne radicals (CH) with germane (GeH4) under single collision conditions in crossed molecular beams experiments. Augmented by electronic structure calculations, this elementary reaction was found to proceed through barrierless insertion of the methylidyne radical in one of the four germanium-hydrogen bonds on the doublet potential energy surface yielding the germylmethyl (CH2GeH3; X2A′) collision complex. This insertion is followed by a hydrogen shift from germanium to carbon and unimolecular decomposition of the methylgermyl (GeH2CH3; X2A′) intermediate by atomic hydrogen elimination leading to singlet methylgermylene (HGeCH3; X1A′). Our investigation provides a glimpse at the largely unknown reaction dynamics and isomerization processes of the carbon-germanium system, which are quite distinct from those of the isovalent carbon system thus providing insights into the intriguing chemical bonding of organo germanium species on the most fundamental, microscopic level.  相似文献   
9.
In this paper we consider the we known method by E. Post of solving the problem of construction of recursively enumerable sets that have a degree intermediate between the degrees of recursive and complete sets with respect to a given reducibility. Post considered reducibilities ≤m, ≤btt, ≤tt and ≤T and solved the problem for al of them except ≤T. Here we extend Post's original method of construction of incomplete sets onto two wide classes of sub‐Turing reducibilities what were studying in [1, 2].  相似文献   
10.
We derive the existence conditions for relativistic shock waves propagating in a perfectly conducting fluid with a general equation of state that guarantees that the stationary wave has a continuous profile in the presence of weak viscosity. To this end we study the one-dimensional solutions of the magnetohydrodynamic equations with a relativistic viscosity tensor. We allow for anomalous regions of thermodynamic variables and do not use the well-known condition for the convexity of Poisson adiabats. The results lead to relationships among the velocities of magnetoacoustic, Alfvén, and shock waves in front of and behind the discontinuity that prove to be more stringent than the corollaries of the evolution conditions. In the nonrelativistic case and in parallel and perpendicular shock waves, any difference between the two conditions disappears. Zh. éksp. Teor. Fiz. 114, 881–891 (September 1998)  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