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   400篇
  免费   8篇
化学   218篇
晶体学   4篇
力学   10篇
数学   52篇
物理学   124篇
  2023年   3篇
  2022年   4篇
  2021年   8篇
  2020年   12篇
  2019年   13篇
  2018年   9篇
  2017年   7篇
  2016年   8篇
  2015年   10篇
  2014年   10篇
  2013年   29篇
  2012年   20篇
  2011年   30篇
  2010年   15篇
  2009年   11篇
  2008年   13篇
  2007年   14篇
  2006年   23篇
  2005年   9篇
  2004年   8篇
  2003年   8篇
  2002年   8篇
  2001年   5篇
  2000年   7篇
  1998年   3篇
  1996年   4篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1991年   4篇
  1990年   3篇
  1989年   3篇
  1988年   4篇
  1987年   2篇
  1986年   7篇
  1985年   7篇
  1984年   6篇
  1983年   5篇
  1982年   4篇
  1981年   5篇
  1980年   7篇
  1979年   14篇
  1978年   6篇
  1977年   8篇
  1976年   5篇
  1975年   5篇
  1974年   3篇
  1973年   4篇
  1972年   3篇
  1963年   1篇
排序方式: 共有408条查询结果,搜索用时 15 毫秒
141.
142.
Recently, there have been several new developments in discrepancy theory based on connections to semidefinite programming. This connection has been useful in several ways. It gives efficient polynomial time algorithms for several problems for which only non-constructive results were previously known. It also leads to several new structural results in discrepancy itself, such as tightness of the so-called determinant lower bound, improved bounds on the discrepancy of the union of set systems and so on. We will give a brief survey of these results, focussing on the main ideas and the techniques involved.  相似文献   
143.
A facile synthesis and studies on the stereochemistry and biochemical aspects of some organosilicon(IV), organotin(IV), and manganese(II) complexes derived from imine having NNO donor system is reported. The imine was prepared by the condensation of salicylanilide with sulphathiazole. This imine reacts with organosilicon(IV)chloride, organotin(IV)chloride, and hydrated manganese(II) chloride to yield compounds having M─O and M←N bonds. The structures of the compounds have been elucidated by physicochemical and spectral (IR, 1H NMR, 13C NMR, 29Si NMR, 119Sn NMR, and ESR) studies, which clearly point to a trigonal bipyramidal geometry around silicon(IV) and tin(IV), and tetrahedral geometry around manganese(II), as the active lone pair of the nitrogen is also included in the coordination sphere. In the search for better fungicides and bactericides, studies were conducted to assess the growth-inhibiting potential of the synthesized complexes against various pathogenic fungal and bacterial strains. These complexes are highly active against nematode (Meloidogyneincognita) and insect (Trogodermagranarium). The activity will be increased with increasing concentration. These studies demonstrate that the concentrations reached levels that are sufficient to inhibit and kill the pathogens. All compounds have also been found to act as sterilizing agents by reducing the production of sperm in male mice.  相似文献   
144.
Abstract

Heterophosphole3 derive from the classical nitrogen, oxygen or/and sulfur containing five-membered 6n-heterocycles by replacing a CH unit by two-coordinate phosphorus as a member of the ring. Formally 4 8 systems seem possible this way. Of 21 of them representatives have been prepared so far4.  相似文献   
145.
146.
A k-distribution model is presented for gas mixtures in thermodynamic nonequilibrium, containing strongly radiating atomic species N and O together with molecular species of N2, N2+, NO and O2. In the VUV range of the spectrum there is strong absorption of atomic radiation by bands of N2. For this spectral range, a multi-scale model is presented, where RTEs are solved separately for each emitting species and overlap with other species is treated in an approximate way. Methodology for splitting the gas mixture into scales and evaluation of the overlap parameter between different scales is presented. The accuracy of the new model is demonstrated by solving the radiative transfer equation along the stagnation line flow field of the Crew Exploration Vehicle (CEV).  相似文献   
147.
A study of events with missing transverse energy and an energetic jet is performed using pp collision data at a center-of-mass energy of 7 TeV. The data were collected by the CMS detector at the LHC, and correspond to an integrated luminosity of 36 pb(-1). An excess of these events over standard model contributions is a signature of new physics such as large extra dimensions and unparticles. The number of observed events is in good agreement with the prediction of the standard model, and significant extension of the current limits on parameters of new physics benchmark models is achieved.  相似文献   
148.
Fourteen N-[{(substituted-phenylthiazol-2-yl)-3-aryl-1H-pyrazol-4-yl}methylene]-5-substituted-thiazol-2-amine (5a-n) analogs were synthesized by the reaction of 3-aryl-1-(thiazol-2-yl)-1H-pyrazole-4-carbaldehyde and substituted thiazole amines. The structures of prepared compounds were delineated by elemental analysis, FT-IR and 1H NMR spectra. These analogs were scrutinized for in vitro anti-infective and cytotoxic activities. Some thaizole clubbed pyrazole derivatives were assessed for their cytological changes in germ cells of Capra hircus by using histomorphological analysis, fluorescence assay and apoptosis quantification. Compound 5l having 4-NO2 substituent induced the significant apoptosis in tested cells of Capra hircus. The results revealed that compounds 5c, 5e, 5k, and 5l have commendable antibacterial activity within MIC range of 62.5–250 μg/ml. Compound 5c emerged as a potent antimalarial compound by exhibiting IC50 value of 0.23 μg/ml and compound 5j induced paralysis of Pherentima posthuma at 8.6 ± 1.94 min and death at 20 ± 5.04 min, respectively. Compound 5j revealed an excellent cytotoxicity at IC50 value of 30.7 and < 10 μg/ml against MCF-7 and HeLa cells, respectively. Individually, compounds 5c, 5j and 5l could be considered as promising anti-infective and cytotoxic compounds.  相似文献   
149.
Muon spin relaxation (μSR) data taken at LAMPF on ac-axis oriented fine powder sample of YBa2Cu3O7−δ (YBCO) embedded in epoxy are analyzed for relaxation rate anisotropy. Clear differences beyond simple magnetic field penetration depth anisotropy are observed forBc andB c. The low-temperature anisotropy ratio is consistent with oriented ceramic data. Small crystallite size and anisotropic flux pinning characteristics are suggested as the fundamental cause of the additional effects.  相似文献   
150.
Geostatistics is used to study the heterogeneities of reservoir cores, as well as to observe the orientation of layers inside the cores. This information obtained from geostatistics could be very useful for coreflood simulation programs. In this paper, it has been shown how semivariograms can be drawn using local porosities obtained from magnetic resonance imaging (MRI). These semivariograms are then used to determine the correlation lengths of the porosity in the cores and to qualitatively estimate the degree of heterogeneity in the core samples.  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