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   4508篇
  免费   827篇
  国内免费   511篇
化学   3376篇
晶体学   40篇
力学   223篇
综合类   44篇
数学   486篇
物理学   1677篇
  2024年   13篇
  2023年   75篇
  2022年   163篇
  2021年   136篇
  2020年   179篇
  2019年   196篇
  2018年   156篇
  2017年   132篇
  2016年   247篇
  2015年   208篇
  2014年   272篇
  2013年   306篇
  2012年   377篇
  2011年   369篇
  2010年   273篇
  2009年   295篇
  2008年   310篇
  2007年   272篇
  2006年   255篇
  2005年   225篇
  2004年   163篇
  2003年   145篇
  2002年   183篇
  2001年   156篇
  2000年   94篇
  1999年   105篇
  1998年   64篇
  1997年   64篇
  1996年   70篇
  1995年   44篇
  1994年   56篇
  1993年   33篇
  1992年   20篇
  1991年   42篇
  1990年   38篇
  1989年   29篇
  1988年   12篇
  1987年   12篇
  1986年   11篇
  1985年   19篇
  1984年   6篇
  1983年   7篇
  1982年   3篇
  1981年   5篇
  1970年   1篇
  1966年   1篇
  1964年   1篇
  1962年   1篇
  1959年   1篇
  1936年   1篇
排序方式: 共有5846条查询结果,搜索用时 15 毫秒
11.
巯基乙酸锑配合物的合成与X射线粉末衍射数据指标化   总被引:2,自引:0,他引:2  
一些锑和铋的配合物可以应用于医药研究[1,2 ] ,已合成了许多锑的有机配体配合物[3~ 7] ,但其中大多数没有生物活性。因此 ,研究锑或铋离子的配合物不仅对主族元素化学、生物无机化学而且对医药都有着非常重要的意义。我们用三氯化锑与巯基乙酸液相反应法合成的二巯基乙酸锑 (Ⅲ)配合物 ,其组成为HSb(SCH2 COO) 2 ,用X射线粉末多晶衍射数据指标化来研究配合物晶体结构[8] 。1 实验部分1 1 仪器与试剂EA - 1 1 0 6型元素分析仪 (意大利卡拉欧巴公司制造 ) ,D Max -YB型多晶X射线粉末衍射仪(日本理学 ,CuKα射线 ,…  相似文献   
12.
The use of Cu-doped (K0.5Na0.5)0.2(Sr0.61Ba0.39)0.9Nb2O6 as self-pumped phase conjugators using internal reflection is reported. Reflectivities as high as 63% at 5145.5 nm and 60% at 632.8 nm were realized. It was found that the photorefractive response changes significantly at different doping concentration. The responses of the crystals to the laser wavelength, incident angle and dopant concentration are studied.  相似文献   
13.
IntroductionInmaterialscience,differentmicrostructuresofthesamematerialsmayinducediversebehaviorsanddifferentcharacteristics.Westwood(1988)showed,asanexample,thatthetreatmentofaluminumsurfacewithcommercialphosphoricacidproducedmechanicallyinterlockedoxide搘hiskers?approximately10nmindiameterand400nminlength,whichmechanicallyinterlocked.Thismicro-structurecankeepsuchaconglomeratebondedoverconsiderablerangesofstressandtemperature.Inahumidatmosphere,especiallythatcontainingchlorine,however,suchox…  相似文献   
14.
Al-Cu-Fe thin films were prepared by laser induced arc (laser-arc) method from a single source—Al63Cu25Fe12 alloy, which was proved to consist of quasicrystalline phase together with approximant phase. The composition of the deposited films meets the requirement for formation of icosahedral symmetry phase. Quasicrystalline phase was obtained after annealing the amorphous as-deposit film samples. The optical properties of the samples were investigated. Thin film samples of Al, Cu and Fe deposited under the same condition were employed for comparison. The results showed specific reflective properties of Al-Cu-Fe quasicrystal thin film in some wavelength range. The optical conductivity of the films exhibited a negative peak, centered about 440 nm in range of 190 to 800 nm. The Al-Cu-Fe quasicrystal thin films could absorb almost all the ray in the wavelength range from 420nm to 450 nm. The ratio of absorption was greater than 99%.  相似文献   
15.
A novel epoxy system was developed through the in situ curing of bisphenol A type epoxy and 4,4′‐diaminodiphenylmethane with the sol–gel reaction of a phosphorus‐containing trimethoxysilane (DOPO–GPTMS), which was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with 3‐glycidoxypropyltrimethoxysilane (GPTMS). The preparation of DOPO–GPTMS was confirmed with Fourier transform infrared, 1H and 31P NMR, and elemental analysis. The resulting organic–inorganic hybrid epoxy resins exhibited a high glass‐transition temperature (167 °C), good thermal stability over 320 °C, and a high limited oxygen index of 28.5. The synergism of phosphorus and silicon on flame retardance was observed. Moreover, the kinetics of the thermal oxidative degradation of the hybrid epoxy resins were studied. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2354–2367, 2003  相似文献   
16.
基于Schr¨odinger方程 ,利用耦合常数解析延拓方法研究了球对称的方势阱、Woods Saxon势和谐振子势中的单粒子共振态的能量与宽度 .分析了耦合常数的取值区间和Pad啨多项式阶数对计算结果的影响 .结果发现 ,在适当的耦合常数取值范围内 ,随着Pad啨多项式阶数的增加可以得到稳定和收敛的单粒子共振态能量与宽度 .  相似文献   
17.
Tumor cells transduced with herpes simplex virus thymidine kinase gene have been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facile preparation of 5‐[125I] iodoarabinosyl uridine starting from commercially available uridine is reported herein.  相似文献   
18.
Hydroxyapatite Ca10(PO4)6(OH)2 (HAP) is known as a bioactive and biocompatible material, HAP coatings were used to improve the biocompatible of substrate by many researcher, In this work, HAP thin films on porous silicon (PS) substrates have been prepared by aqueous precipitation method with rapid thermal annealing (RTA) processes. The HAP films had been prepared under the annealing temperature ranging from 300 to 1000 °C. By the measurement of X-ray diffraction (XRD), it was found that for the crystallinity optimization, the heat-treatment at 850–950 °C for 1 h would be favorable. Atomic force microscopy (AFM) and scanning electron microscope (SEM) measurements reveal a dense and smooth surface of the HAP film, and tightly adherence of the coating on porous silicon substrate after sintered. Thus, by this method, porous silicon could be increased its bioactivity and so that could be used in the biomedical area.  相似文献   
19.
In this paper we prove that (1<p<+∞), give the characteristics of xo and the optimal subspace for n-width dn in space X=l n N . Where dn in the n-width, in the sense of Kolmogorov, ofD in X, dn is the n-width ofD with respect to X, in the sense of Gel'fand, δ is the linear n-width ofD with respect to X.  相似文献   
20.
膦配位的过渡金属氢化物被看作是烯烃及其他一些不饱含有机化合物催化加氢反应及氢甲酰化反应的催化活性物种,关于它们的结构与催化活性关系的研究,有着重要的理论意义和实际意义,通常单齿膦配位表现出较高的催化活性,而不同的金属中心在催化活性和选择性上也表现出明显的差别,反映了催化功能与催化活性物种的电子结构和空间结构之间存在着依存关系.膦配体过渡金属氢化物,通常是以它们的相应卤化物经氢化锂铝或硼氢化钠或肼还原得  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