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   270篇
  免费   15篇
  国内免费   3篇
化学   124篇
力学   27篇
数学   52篇
物理学   85篇
  2024年   10篇
  2023年   1篇
  2022年   14篇
  2021年   11篇
  2020年   10篇
  2019年   11篇
  2018年   16篇
  2017年   8篇
  2016年   12篇
  2015年   5篇
  2014年   11篇
  2013年   19篇
  2012年   22篇
  2011年   21篇
  2010年   10篇
  2009年   15篇
  2008年   20篇
  2007年   13篇
  2006年   12篇
  2005年   7篇
  2004年   8篇
  2003年   1篇
  2002年   4篇
  2000年   2篇
  1998年   1篇
  1997年   2篇
  1995年   2篇
  1994年   1篇
  1993年   1篇
  1992年   3篇
  1991年   1篇
  1988年   1篇
  1987年   1篇
  1986年   2篇
  1985年   3篇
  1984年   2篇
  1983年   4篇
  1982年   1篇
排序方式: 共有288条查询结果,搜索用时 15 毫秒
51.
    
As generalizations of annihilators and associated primes, we introduce the notions of weak annihilators and weak associated primes, respectively. We first study the properties of the weak annihilator of a subset X in a ring R. We next investigate how the weak associated primes of a ring R behave under passage to the skew monoid ring R*M. Let R be a semicommutative ring, and M an ordered monoid and φ: M → Aut(R) a compatible monoid homomorphism. Then we can describe all weak associated primes of the skew monoid ring R*M in terms of the weak associated primes of R in a very straightforward way.  相似文献   
52.
    
We prove that in the nonextreme Kerr‐Newman black hole geometry, the Dirac equation has no normalizable, time‐periodic solutions. A key tool is Chan‐drasekhar's separation of the Dirac equation in this geometry. A similar nonexistence theorem is established in a more general class of stationary, axisymmetric metrics in which the Dirac equation is known to be separable. These results indicate that, in contrast to the classical situation of massive particle orbits, a quantum mechanical Dirac particle must either disappear into the black hole or escape to infinity. © 2000 John Wiley & Sons, Inc.  相似文献   
53.
54.
    
Heterocyclic skeleton building blocks to afford dihydropyrimidinones and dihydropyridines based on neat adducts of diketene,alcohols and aldehydes via silica sulfuric acid(SSA) catalyzed ring opening of diketene in four-component Biginelli-type and Hantzsch-type reactions are presented.  相似文献   
55.
Using the most recent differential cross section data for ep quasi-elastic scattering, the charged pion formation and its form factor Fπ is calculated in the energy range of 2.4 ~ 4 GeV at Q2 = 0.6 ~ 1.6 (GeV/c)2. The functional dependence of the charged pion form factor to the separated cross section σL is investigated and compared to the previously determined result.  相似文献   
56.
    
Stable and non-hygroscopic silica gel supported aluminium chloride(SiO2-AlCl3),which is prepared easily from cheap and commercially available compounds was found to be an environmentally friendly heterogeneous catalyst for the condensation of indole with aldehydes and ketones to afford bis-indolylmethanes at room temperature under solvent-free conditions.The catalyst can be reused up to five times after simple washing with ether.  相似文献   
57.
    
Using perturbative QCD in conjunction with CVC and standard electroweak theory, it is shown that at large Q2, F1n/F1P = F2n/F1P = -0.69. The comparison with other results on form factor ratios from QCD sum rules and/or PQCD is carried out.  相似文献   
58.
59.
The unsteady flow of an incompressible generalized Oldroyd-B fluid induced by a constantly accelerating plate between two side walls perpendicular to the plate has been studied using Fourier sine and Laplace transforms. The obtained solutions for the velocity field and shear stresses, written in terms of the generalized G and R functions, are presented as sum of the similar Newtonian solutions and the corresponding non-Newtonian contributions. For α = β = 1 and λr → λ these solutions are going to the corresponding Newtonian solutions. Furthermore, the solutions for generalized Maxwell fluids as well as those for ordinary Oldroyd-B and Maxwell fluids, performing the same motion, are also obtained as limiting cases of our general solutions. In the absence of the side walls, namely when the distance between the two walls tends to infinity, the solutions corresponding to the motion over an infinite constantly accelerating plate are recovered. For λr → 0 and β → 1, these solutions reduce to the known solutions from the literature. Finally, the effect of the material parameters on the velocity profile is spotlighted by means of the graphical illustrations.  相似文献   
60.
    
Honey bee venom (HBV) is a valuable bee product famous for its therapeutic efficacy. HBV has a complex matrix containing several compounds, of which melittin is identified as the major component and can be considered an indicator compound. According to the numerous pharmacological effects of HBV, it can be a great candidate as an efficient active pharmaceutical ingredient (API). Despite the widespread analysis of crude HBV, not enough evaluations have been conducted on HBV pharmaceutical products, which is crucial in quality control procedures. Following the importance of APIs assay, we aimed to develop a feasible and valid HBV extraction method from cosmeceutical creams using precipitation techniques, and an analysis method was developed and validated based on high-performance liquid chromatography.  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