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   12125篇
  免费   1706篇
  国内免费   1442篇
化学   8250篇
晶体学   147篇
力学   876篇
综合类   95篇
数学   1519篇
物理学   4386篇
  2024年   21篇
  2023年   169篇
  2022年   256篇
  2021年   301篇
  2020年   396篇
  2019年   347篇
  2018年   308篇
  2017年   299篇
  2016年   453篇
  2015年   430篇
  2014年   564篇
  2013年   815篇
  2012年   892篇
  2011年   983篇
  2010年   670篇
  2009年   737篇
  2008年   773篇
  2007年   732篇
  2006年   692篇
  2005年   631篇
  2004年   497篇
  2003年   393篇
  2002年   353篇
  2001年   334篇
  2000年   296篇
  1999年   322篇
  1998年   329篇
  1997年   272篇
  1996年   269篇
  1995年   230篇
  1994年   247篇
  1993年   164篇
  1992年   159篇
  1991年   136篇
  1990年   139篇
  1989年   84篇
  1988年   80篇
  1987年   87篇
  1986年   89篇
  1985年   71篇
  1984年   48篇
  1983年   33篇
  1982年   35篇
  1981年   27篇
  1980年   20篇
  1979年   15篇
  1978年   14篇
  1977年   8篇
  1976年   8篇
  1973年   10篇
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
231.
基于壳聚糖膜固定双酶的胆碱传感器的研究   总被引:3,自引:0,他引:3  
提出了一种基于壳聚糖膜固定辣根过氧化物酶 胆碱氧化酶的胆碱传感器的制备方法。该传感器以电聚合于玻碳电极的硫堇作为电子传递介体,在pH6. 8,外加电压-0. 2V(vs.SCE)条件下,其峰电流与浓度范围 5. 0×10-5 ~3. 0×10-3 mol/L的胆碱呈良好的线性响应;检出限为 1. 0×10-5 mol/L。传感器有良好的选择性和稳定性,使用一月后,仍能保持其初始活性的 80%。  相似文献   
232.
密封罐微波消化法序列ICP-AES测定环境试样中多元素   总被引:7,自引:0,他引:7  
本文采用密闭罐微波消化方法快速分解生物、土壤、沉积物等环境样品。按样品性质,分别采用HNO3/H_2O_2或HNO_3/H_2O_2/HF在聚四氟乙稀密闭罐中于500W微波功率分解0.1~0.2g样品2~3min,溶液(或在其中加入10ml硼酸饱和溶液)稀释至2.5~5.0ml后,直接用序列ICP-AES法测定。方法准确度经分析6个生物、土壤、沉积物标准参考物质验证,10个元素的均值均与定值吻合。  相似文献   
233.
234.
核-壳型聚丙烯酸酯复合乳液   总被引:9,自引:0,他引:9  
简述了核-壳型聚丙烯酸酯复合乳液的合成方法、形态及其影响因素与判断方法、结构与性能等方面的研究进展;认为核-壳型复合乳液膜机械性能优良的原因是:核、壳两相间存在的过渡区适当地抑制了二者的相分离。  相似文献   
235.
An approach using the finite difference solution of the Poisson-Boltzmann equation to estimate binding free energy changes for two receptor–ligand systems, arabinose binding protein and sulfate binding protein, is presented. The eight calculated binding free energy changes agree with experiment, showing a correlation coefficient of 0.92 and energy deviations of 1 kcal/mol or less. More importantly, the decomposition of solvation and assembly energies in this approach provides an understanding of binding mechanisms and therefore could suggest directions to alter binding affinities. The method is demonstrated to be useful in analyzing experimental binding structures and predicting binding effects of mutants or modified ligands for macromolecular systems, in which the electrostatic forces dominate the overall interaction and the structural perturbations upon modifications are small. © 1995 by John Wiley & Sons, Inc.  相似文献   
236.
A dyad-anthraquinone-methyl ester of fluorescein-and its model compound-butyl ester-were synthesized. The effects of photo-induced electron transfer from fluorescein to an organic anthraquinone acceptor and injection into inorganic colloidal TiO(2) were studied respectively. It is found that the photo-induced electron transferring to an organic acceptor is much faster than injecting into inorganic colloidal particles when fluorescein was excited by visible light. While inorganic colloidal TiO(2) was excited by UV, the electron of fluorescein will inject into TiO(2).  相似文献   
237.
A highly selective ligand exchange reaction is realized in the self-assembled monolayer (SAM) of a triruthenium cluster on a gold electrode surface under precise electrochemical potential control. CO as well as NO molecules, which are known to play key roles in many chemical, biological, and environmental systems, can be efficiently introduced into the SAM by electrochemically tuning the electronic state of the Ru site. These unique surface reactions are more convenient and efficient than conventional ligand exchange reactions in solution and could be used for the elucidation of the electron-transfer mechanism in a biological system as well as in the development of molecular sensors and devices.  相似文献   
238.
茂基稀土胺化物(MeCp)2YbNPh2(THF)与异氰酸正己酯(n-HexylNCO)按11摩尔比反应, 分离出产物{(MeC5H4)2Yb[OC(NPh2)N(n-hexyl)]}2. 产物经元素分析和核磁共振表征, 并测定了其晶体结构. 配合物属三斜晶系, R-3空间群, 晶胞参数为a=2.9533(11) nm, b=2.9533(11) nm, c=1.5873(6) nm, V=11.9896(80) nm3, Z=9, Dc=1.562 mg·m-3, μ=3.536 mm-1 (Mo Kα), F(000)=5670, R=0.034, Rw=0.064. 该化合物具有二个对称氧桥的双分子结构, 并存在着由氮原子向中心金属镱分子内配位而形成的三环骨架, 中心金属镱的配位数是九, 整个分子呈中心对称.  相似文献   
239.
"Energy chemistry" was approved as one of the chemistry majors for undergraduate by the Ministry of Education in 2015. Based on the ideas and ways of emerging engineering education, this paper hereby proposed some of constructive suggestions on the training objectives, graduation requirements, curriculum system, teaching contents, teaching staff and conditions for development of "energy chemistry" major.  相似文献   
240.
Magnetic NiFe particles were synthesized through hydrothermal method using hydrazine as reductant. Composite particles with core-shell structure were further achieved by depositing silicon dioxide generated via carbonation decomposition of sodium silicate solution on the surface of magnetic cores. Characterized by XRD, the Ni9Fe particles are of fcc-type structure, and the structure of magnetic cores in composite particles was maintained despite being covered by SiO2 shell. The existence of SiO2 shells in the composite particles were demonstrated by SEM, EDS and IR. The results from TG and VSM indicated that the shell structure affected the physiochemical properties. The composite particles exhibited remarkable resistance to oxidation in comparison with Ni9Fe particles due to being protected by SiO2 shell. Meanwhile, both of them are soft magnetic materials, but Ms, Mr and Hc in Ni9[email protected]2 particle decreased compared with magnetic NiFe particles. The formation mechanisms of Ni9Fe micro-particles and composite Ni9Fe particles were discussed.  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