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   353篇
  免费   37篇
  国内免费   37篇
化学   251篇
晶体学   8篇
力学   12篇
综合类   12篇
数学   26篇
物理学   118篇
  2024年   2篇
  2023年   2篇
  2022年   9篇
  2021年   7篇
  2020年   10篇
  2019年   10篇
  2018年   10篇
  2017年   19篇
  2016年   13篇
  2015年   11篇
  2014年   20篇
  2013年   33篇
  2012年   11篇
  2011年   22篇
  2010年   19篇
  2009年   12篇
  2008年   19篇
  2007年   13篇
  2006年   10篇
  2005年   17篇
  2004年   11篇
  2003年   8篇
  2002年   3篇
  2001年   9篇
  2000年   19篇
  1999年   5篇
  1996年   4篇
  1995年   4篇
  1994年   5篇
  1993年   9篇
  1992年   10篇
  1991年   7篇
  1990年   5篇
  1988年   2篇
  1987年   4篇
  1985年   7篇
  1984年   8篇
  1982年   3篇
  1980年   6篇
  1977年   3篇
  1976年   2篇
  1974年   5篇
  1973年   4篇
  1972年   2篇
  1968年   1篇
  1967年   1篇
  1966年   1篇
  1965年   3篇
  1961年   1篇
  1959年   1篇
排序方式: 共有427条查询结果,搜索用时 343 毫秒
1.
基于MATLAB的异步电动机线性化控制系统的仿真   总被引:1,自引:0,他引:1  
从异步电动机在同步旋转坐标系下的状态方程出发,在一定的条件下,对其系数矩阵简化.推出异步电动机的线性化控制模型.并基于该模型得出异步电动机的线性化控制系统.以给定电机为例,对该模型的有效性、响应用MATLAB进行仿真分析.验证的结果说明上述模型具有实用价值.  相似文献   
2.
Introduction Migrationandrecruitmentofleukocytesfromblood toinflammatorylesionsitesaresequentiallyregulated byadhesionmoleculesandtheirreceptors[1].These lectinfamilyplaysamajorroleininitiatingattachement ofneutrophilstotheactivatedendothelium.P selectin,…  相似文献   
3.
This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.  相似文献   
4.
The results of the electronic structures and conduction properties of four novel donor-acceptor polymers based on polysilole, obtained on the basis of ab initio Hartree-Fock crystal orbital method using their optimized geometries, are reported. The repeat unit of these polymers consists of bicyclopentadisilole unit bridged by an electron-accepting group Y(Y=CCH2 in PSICH, CO in PSICF, CCF2 and CC(CN)2 in PSICN). All the polymers on the basis of their geometries and π-bond order values are found to have benzenoid-type electronic structures. Comparison of the important electronic properties such as ionization potential, electron affinity and band-gap of these polymers indicates PSICN to be the best candidate for intrinsic conductivity and reductive (n-) doping while PSICH is predicted to be the best candidate for oxidative (p-) doping. All these polymers are estimated to have band-gap values ranging between 1 and 2 eV. The low band-gap values of these polymers are rationalised on the basis of the patterns of their frontier orbitals.  相似文献   
5.
Insertion of CS(2) into the Ru-H bond of cis-[(dppe)(2)Ru(H)(2)] takes place to afford the hydride dithioformate complex trans-[(dppe)(2)Ru(H)(SC(S)H)]. The hydride dithioformate complex reacts under very mild conditions with MeX (X = OTf, I) to give the hydride methyldithioformate derivative trans-[(dppe)(2)Ru(H)(SC(SMe)H)][X]. Three different pathways have been found to cleave off the ester moiety from the metal complex. A method to recover the ruthenium starting material upon elimination of the methyldithioformate is presented. This is a novel case of C(1) chemistry using carbon disulfide.  相似文献   
6.
在无定型硅胶上化学键合十八烷基三氯硅烷,键合率17%-20%,粒度5μm-10μm,以此键合的吸附剂可有效地吸附香烟烟气中的焦油、亚硝胺,吸附率分别为15%-18%和37%-43%,研究了化学键合吸附剂的粒度和加入量对吸附性能的影响。  相似文献   
7.
Addition of excess carbon disulfide to cis/trans-[(dppm)(2)Ru(H)(2)] results in the methanedithiolate complex [(dppm)(2)Ru(eta(2)-S(2)CH(2))] 4 via the intermediacy of cis-[(dppm)(2)Ru(H)(SC(S)H)] 2. The X-ray crystal structure of this species has been determined.  相似文献   
8.
The relative importance of individual microbial pathways in nitrous oxide (N(2)O) production is not well known. The intramolecular distribution of (15)N in N(2)O provides a basis for distinguishing biological pathways. Concentrated cell suspensions of Methylococcus capsulatus Bath and Nitrosomonas europaea were used to investigate the site preference of N(2)O by microbial processes during nitrification. The average site preference of N(2)O formed during hydroxylamine oxidation by M. capsulatus Bath (5.5 +/- 3.5 per thousand) and N. europaea (-2.3 +/- 1.9 per thousand) and nitrite reduction by N. europaea (-8.3 +/- 3.6 per thousand) differed significantly (ANOVA, f((2,35)) = 247.9, p = 0). These results demonstrate that the mechanisms for hydroxylamine oxidation are distinct in M. capsulatus Bath and N. europaea. The average delta(18)O-N(2)O values of N(2)O formed during hydroxylamine oxidation for M. capsulatus Bath (53.1 +/- 2.9 per thousand) and N. europaea (-23.4 +/- 7.2 per thousand) and nitrite reduction by N. europaea (4.6 +/- 1.4 per thousand) were significantly different (ANOVA, f((2,35)) = 279.98, p = 0). Although the nitrogen isotope value of the substrate, hydroxylamine, was similar in both cultures, the observed fractionation (delta(15)N) associated with N(2)O production via hydroxylamine oxidation by M. capsulatus Bath and N. europaea (-2.3 and 26.0 per thousand, respectively) provided evidence that differences in isotopic fractionation were associated with these two organisms. The site preferences in this study are the first measured values for isolated microbial processes. The differences in site preference are significant and indicate that isotopomers provide a basis for apportioning biological processes producing N(2)O.  相似文献   
9.
10.
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