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   2104篇
  免费   267篇
  国内免费   253篇
化学   1486篇
晶体学   21篇
力学   94篇
综合类   5篇
数学   340篇
物理学   678篇
  2024年   2篇
  2023年   51篇
  2022年   49篇
  2021年   82篇
  2020年   105篇
  2019年   78篇
  2018年   66篇
  2017年   70篇
  2016年   98篇
  2015年   92篇
  2014年   97篇
  2013年   150篇
  2012年   163篇
  2011年   182篇
  2010年   97篇
  2009年   119篇
  2008年   131篇
  2007年   129篇
  2006年   98篇
  2005年   99篇
  2004年   57篇
  2003年   44篇
  2002年   42篇
  2001年   44篇
  2000年   47篇
  1999年   40篇
  1998年   28篇
  1997年   30篇
  1996年   42篇
  1995年   35篇
  1994年   34篇
  1993年   29篇
  1992年   25篇
  1991年   33篇
  1990年   25篇
  1989年   14篇
  1988年   16篇
  1987年   15篇
  1986年   11篇
  1985年   11篇
  1984年   11篇
  1983年   4篇
  1982年   8篇
  1981年   5篇
  1980年   4篇
  1979年   5篇
  1977年   2篇
  1975年   2篇
  1968年   1篇
  1957年   1篇
排序方式: 共有2624条查询结果,搜索用时 203 毫秒
81.
This paper concerns the existence of positive stationary solutions for a diffusive variable-territory prey–predator model, and completely settles an open problem of Wang and Pang (2009). The main result closes a gap in an earlier result (2011) by the authors.  相似文献   
82.
An organic solvent-tolerant lipase from Serratia marcescens ECU1010 (rSML) was overproduced in Escherichia coli in an insoluble form. High concentrations of both biomass (50 g cell wet weight/L culture broth) and inclusion bodies (10.5 g/L) were obtained by applying a high-cell-density cultivation procedure. Activity assays indicated that the enzymatic activity of rSML reached 600 U/L. After treatment with isopropyl ether for 12 h, the maximum lipase activity reached 6,000 U/L. Scanning electron microscopy and Fourier transform infrared microspectroscopy revealed the activation mechanism of rSML in the presence of organic solvents. rSML was stable in broad ranges of temperatures and pH values, as well as in a series of organic solvents. Besides, rSML showed the best enantioselectivity for the kinetic resolution of (±)-trans-3-(4-methoxyphenyl)glycidic acid methyl ester. These features render the S. marcescens ECU1010 lipase attractive for biotechnological applications in the field of organic synthesis and pharmaceutical industry.  相似文献   
83.
84.
85.
86.
Yang  Jin Hua  Yang  Qi  Pang  Xue Cheng 《数学学报(英文版)》2019,35(12):1972-1978
In this paper, we continue to discuss the normality concerning omitted holomorphic function and get the following result. Let F be a family of meromorphic functions on a domain D, k ≥ 4 be a positive integer, and let a(z) and b(z) be two holomorphic functions on D, where a(z) 0 and f(z) ≠ ∞ whenever a(z)=0. If for any f ∈ F, f'(z) -a(z)fk(z) ≠ b(z), then F is normal on D.  相似文献   
87.
Nickel oxide (NiO) has emerged as one of the most promising transition-metal oxides (TMOs) for electrochemical capacitors, batteries, catalysis, and electrochromic films, owing to its cost-effectiveness, abundance, and well-defined electrochemical properties. Recent studies have identified that mixing NiO with graphene or graphene derivatives results in novel composites with synergistic effects and superior electrochemical performance. This review summarizes the latest advances in composites of NiO with graphene or graphene derivatives. The synthetic strategies, morphologies, and electrochemical performance of these composites are introduced, as well as their electrochemical applications in supercapacitors, batteries, sensors, catalysis, and so forth. Finally, tentative conclusions and assessments regarding the opportunities and challenges for the future development of these composites and other TMOs/graphene or graphene-derived composites are presented.  相似文献   
88.
In this paper, we study the normality of the family of meromorphic functions from the viewpoint of hyperbolic metric. Then, a new sufficient and necessary condition is obtained, which can determine a given family of meromorphic functions is normal or not.  相似文献   
89.
We report the discovery of a new noncentrosymmetric superconductor CaPtAs.It crystallizes in a tetragonal structure(space group I41md,No.109),featuring three dimensional honeycomb networks of Pt-As and a much elongated c-axis(a=b=4.18?,and c=43.70?).The superconductivity of CaPtAs with Tc=1.47 K was characterized by means of electrical resistivity,specific heat,and ac magnetic susceptibility.The electronic specific heat Ce(T)/T shows evidence for a deviation from the behavior of a conventional BCS superconductor,and can be reasonably fitted by a p-wave model.The upper critical fieldμ0Hc2 of CaPtAs exhibits a moderate anisotropy,with an in-plane value of around 204 mT and an out-of-plane value of 148 mT.Density functional theory calculations indicate that the Pt-5 d and As-4 p orbitals mainly contribute to the density of states near the Fermi level,showing that the Pt-As honeycomb networks may significantly influence the superconducting properties.  相似文献   
90.
A series of well‐defined thermoresponsive graft polymers with different lengths and graft densities, poly(glycidyl methacrylate)‐graft‐poly(N‐isopropylacrylate) (PGMA‐g‐PNIPAM), were successfully prepared by combination of controlled/living free radical polymerization and click chemistry. Effects of grafting length and density on the thermoresponsive behavior, aggregating mean diameter, and self‐assembly morphology are systematically investigated. The thermosensitive characteristics of graft polymers in aqueous solution prove that the length and graft density had positive co‐relationship with the lower critical solution temperature value and mean diameter of micelles as well as the size distribution, while the effect of graft length of polymers is more significant than that of density. Transmission electron microscopy analysis shows that the conformations of PGMA45g‐PNIPAM20 and PGMA45g‐PNIPAM46 with longer length and bigger grafting density in aqueous solutions are spherical nanoparticles with the increasing trend of the diameters, while that of PGMA45g‐PNIPAM(73, 50%) shows a spherical‐like morphology, which indicates that the graft length and density have a significant effect on the mean diameter of micelle but not on the self‐assembly morphology. These results reveal that to obtain desired thermoresponsive behavior and self‐assembly morphology of functional polymers, it is essential to design and fabricate the structure of graft polymers with proper length and graft density. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2442–2453  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