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   677篇
  免费   20篇
  国内免费   8篇
化学   516篇
晶体学   6篇
力学   12篇
数学   36篇
物理学   135篇
  2023年   9篇
  2022年   13篇
  2021年   10篇
  2020年   7篇
  2019年   20篇
  2018年   18篇
  2017年   20篇
  2016年   20篇
  2015年   20篇
  2014年   29篇
  2013年   47篇
  2012年   42篇
  2011年   50篇
  2010年   47篇
  2009年   34篇
  2008年   52篇
  2007年   47篇
  2006年   37篇
  2005年   32篇
  2004年   22篇
  2003年   17篇
  2002年   14篇
  2001年   7篇
  2000年   6篇
  1999年   4篇
  1998年   5篇
  1997年   6篇
  1996年   2篇
  1995年   8篇
  1994年   4篇
  1993年   6篇
  1992年   3篇
  1991年   2篇
  1990年   1篇
  1989年   4篇
  1988年   5篇
  1987年   2篇
  1986年   5篇
  1985年   2篇
  1984年   5篇
  1983年   5篇
  1982年   2篇
  1980年   4篇
  1979年   2篇
  1977年   1篇
  1976年   4篇
  1974年   2篇
  1973年   1篇
排序方式: 共有705条查询结果,搜索用时 187 毫秒
61.
We report the results of our modified distorted wave Born approximation calculation of triple differential cross section in the coplanar symmetric single ionization of potassium atom. We have included correlation-polarization potential as a function of electron density parameter and also studied the effect of post-collision interaction. The present attempt significantly improves the agreement between theoretical and experimental results.  相似文献   
62.
A mild, eco‐friendly and efficient route for the synthesis of quinolines and polycyclic quinolines via Friedländer annulation using cyanuric chloride as a catalyst under aqueous conditions is described.  相似文献   
63.
A copper catalyzed Pummerer type reaction of α-thio aryl/heteroarylacetates is described for the first time. This transformation represents a new route to synthesize α-keto esters, which are important intermediates for pharmaceuticals and organic synthesis. The reaction proceeds via in situ generation of a thionium ion that undergoes hydrolysis to furnish α-keto esters in synthetically viable yields (up to 82%).  相似文献   
64.
Tannase from Aspergillus awamori MTCC 9299 was purified using ammonium sulfate precipitation followed by ion-exchange chromatography. A purification fold of 19.5 with 13.5% yield was obtained. Temperature of 30 °C and pH of 5.5 were found optimum for tannase activity. The effects of metals and organic solvents on the activity of tannase were also studied. Metal ions Mg+2, Mn+2, Ca+2, Na+, and K + stimulated the tannase activity, while Cu+2, Fe+3, and Co+2 acted as inhibitors of the enzyme. The addition of organic solvents like acetic acid, isoamylalcohol, chloroform, isopropyl alcohol, and ethanol completely inhibited the enzyme activity. However, butanol and benzene increased the enzyme activity.  相似文献   
65.
Mixtures of a hydrophobic triblock copolymer (L121, PEO5PPO68PEO5) and a hydrophobic anionic surfactant (AOT, Sodium bis(2-ethylhexyl)sulfosuccinate), each alone forming turbid vesicular solutions in water, aggregate to produce a thermodynamically stable, transparent and isotropic solution. Mixed AOT/L121 aggregates could be confirmed by fluorescence, surface tension, differential scanning calorimetry (DSC) and isothermal titration calorimetry (ITC). In an isotropic region, where mixed aggregates are formed, there is a synergistic interaction between monomers of AOT and L121 in the mixture. In addition, Small Angle Neutron Scattering (SANS) experiments provided evidence that mixed aggregates have the shape of either spheres (with a certain polydispersity) or very short ellipsoids (axial ratio below 2), confirming a transition from giant multilamellar vesicles to small aggregates upon mixing the two hydrophobic amphiphiles. Upon dilution, the morphology changes to disk-like. From an examination of the results of all the methods the peculiar behavior of the mixed AOT/L121 system is explained.  相似文献   
66.
Novel chromogenic thiourea based sensors 4,4′-bis-[3-(4-nitrophenyl) thiourea] diphenyl ether 1 and 4,4′-bis-[3-(4-nitrophenyl) thiourea] diphenyl methane 2 having nitrophenyl group as signaling unit have been synthesized and characterized by spectroscopic techniques and X-ray crystallography. The both sensors show visual detection, UV-vis and NMR spectral changes in presence of fluoride and cyanide anions in organic solvent as well as in aqueous medium. The absorption spectra indicated the formation of complex between host and guest is in 1:2 stoichiometric ratios.  相似文献   
67.
We give a phenomenological model of CPT violating neutrino oscillation above the GUT scale. In this paper, we consider the effect of Planck scale operators on neutrino mixing. We assume that the main part of neutrino masses and mixing arise through GUT scale operators The dispersion relation for the CPT violating neutrino and anti-neutrino oscillation are discussed.  相似文献   
68.
The optical absorption coefficients and changes in the refractive index in GaAs/AlGaAs, disk shaped quantum dots (DSQD) with simultaneously applied laser and magnetic field are studied in detail. The use of the density matrix formalism is made to study the variations in linear and non-linear polarizability with the frequency of the electric field. It is found that the absorption coefficient and the refractive index changes depend not only on the optical wave but also on the strength of the static magnetic field.  相似文献   
69.
Self-assembled Sm-Co nanoparticles in the form of spherical aggregates (referred as nanospheres) with diameter ranging from 50 to 180 nm were achieved by means of polyol technique. The size distribution of the Sm-Co nanospheres can be regulated close to ∼100 nm by controlling the molar ratio of Sm:Co precursor. The spherical aggregates exhibited Sm2Co7 phase as a major constituent; while the aggregates obtained at higher Co concentration showed co-existence of Co-phase with Sm2Co7 phase. Upon annealing, the biphasic nature of nanospheres (Sm2Co7/Co) transformed into Sm2Co17 structure. By varying the Sm:Co precursor ratio from 1:5 to 1:9, the coercivity (Hc) and magnetization (Ms) values of the as-synthesized nanospheres can be tuned from 336 to 140 Oe and from 63.7 to 108 emu/g, respectively, and these values significantly improved after annealing. Maximum values of Hc (1050 Oe) at the Sm:Co molar ratio of 1:5 and Ms of 184.6 emu/g at the Sm:Co molar ratio of 1:9 were achieved in the annealed samples.  相似文献   
70.
JPC – Journal of Planar Chromatography – Modern TLC - A densitometric HPTLC method has been established for simultaneous quantification of sennosides A and B and gallic acid in a...  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