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   105433篇
  免费   18098篇
  国内免费   10086篇
化学   71285篇
晶体学   1219篇
力学   6921篇
综合类   537篇
数学   11922篇
物理学   41733篇
  2024年   369篇
  2023年   2133篇
  2022年   3648篇
  2021年   3876篇
  2020年   4254篇
  2019年   4140篇
  2018年   3553篇
  2017年   3288篇
  2016年   5186篇
  2015年   4947篇
  2014年   6023篇
  2013年   7786篇
  2012年   9428篇
  2011年   9757篇
  2010年   6448篇
  2009年   6158篇
  2008年   6537篇
  2007年   6000篇
  2006年   5482篇
  2005年   4605篇
  2004年   3403篇
  2003年   2669篇
  2002年   2414篇
  2001年   1980篇
  2000年   1763篇
  1999年   2075篇
  1998年   1849篇
  1997年   1722篇
  1996年   1891篇
  1995年   1506篇
  1994年   1461篇
  1993年   1165篇
  1992年   1069篇
  1991年   984篇
  1990年   793篇
  1989年   564篇
  1988年   464篇
  1987年   382篇
  1986年   374篇
  1985年   318篇
  1984年   241篇
  1983年   154篇
  1982年   142篇
  1981年   106篇
  1980年   76篇
  1979年   44篇
  1978年   34篇
  1976年   36篇
  1975年   33篇
  1974年   45篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
对苯乙烯-丙烯腈-二乙烯基苯(S/AN/DVB)交联共聚机理研究曾发现,丙烯腈作为第三单体,可使DVB竞聚率比在S/DVB共聚体系中降低,相互分离显著,从而有利于合成性能较好的离子交换树脂;本文在此基础上,将S/AN/DVB共聚体中的氰基水解成羧基来合成含磺酸、羧酸双功能基树脂,解决了前人研究中仅有50%的氰基水解成羧基的问题,并首次将这种树脂应用于混合氨基酸的分离。  相似文献   
992.
不可逆电活性药物米托蒽醌与脱氧核糖核酸的相互作用   总被引:4,自引:0,他引:4  
时巧翠  彭图治  王素芬 《分析化学》2003,31(10):1212-1216
研究了抗癌新药米托蒽醌(MXT)的电化学行为及与脱氧核糖核酸(DNA)的相互作用,推导了适用于研究不可逆电活性分子与DNA相互作用的电化学公式,运用该公式可以简便、快速地测定靶向分子与DNA的结合常数和结合位点数。实验发现,MXT与小牛胸腺DNA的结合以蒽醌母核的嵌插作用为主,同时,烃氨基侧链与骨架磷酸基团之间的静电吸引对母核起稳定作用,使化合物易于嵌入DNA的平面结构。MXT与DNA相互作用引起的峰电流的变化可以用于分析测定DNA。  相似文献   
993.
用火焰原子吸收法测定了2000例甲亢病人的血清镁含量及1200例天津市正常人群血清镁含量,结果显示,甲亢病人血清镁含量显著低于正常人群,有显著统计意义(P〈0.01)。提示:甲亢病人血清镁含量对甲亢病诊断及治疗过程的镁的摄入补充有重要的意义。  相似文献   
994.
A modification of the procedure reported byJohnson andWalseth 1 for the preparation of (-32P)ATP:(-32P)GTP with a specific activity of more than 5000 Ci/mmol was made firstly, then it was used as the phosphate donor in the reaction catalyzed by the polynucleotide kinase, to transfer its radioactive phosphate to the 5-position of the 3-AMP, resulting (5-32P)3-ADP. After that, (5-32P)3-ADP was hydrolysed to (5-32P)AMP under the catalysis of Nuclease P1, the late was then phosphorylated to produce (-32P)ATP by the action of myokinase and pyruvate kinase. By this method, we firstly prepared (-32P)ATP with a specific activity of more than 4000 Ci/mmol which was measured by HPLC analysis.  相似文献   
995.
In this work, we used the hydrothermal method to synthesize Eu3+ ion-doped cubic BaF2 nanorods, which is a luminescent material. The clubbed structures were well crystallized and exhibited face-centred cubic structures, as indicated by powder X-ray diffraction, scanning electron microscopy, electron diffraction, and transmission electron microscopy. The luminescent properties were studied, and local symmetry surrounding Eu3+ ions and electronic transition processes included. The results indicated that Eu3+ occupied only one C4ν site in nanorods.  相似文献   
996.
A series of heat energy storage microcapsules was prepared using melamine-formaldehyde resin as the shell material and the mechanical properties of the shell were investigated. A phase change material whose melting point was 24 °C was used as core and the quantity of heat involved in phase transition was 225.5 J/g. Average diameter of the microcapsules varied from 5 to 10 μm, and the globular surface was smooth and compact. The mechanical properties of the shell were evaluated by observing the surface morphological structure change after application of pressure by means of scanning electron microscopy. When the mass ratio of the core and shell material is 3:1, a yield point of about 1.1×105 Pa was found and when the compression was increased beyond this point the microcapsules showed plastic behavior. This has been attributed to the cross-link density and to the high degree of reaction of the shell material. Different yield points subsequently reflected differences in the mechanical behavior. It was also found that the mechanical intensity of double-shell microcapsules was better than that of single shelled ones.  相似文献   
997.
Volumetric H2-uptake measurements on an Mo2N (79 m2g–1) sample reduced at 673 K have been carried out and the uptake isotherms in the temperature range of 308–623 K have been determined. Both the total and reversible hydrogen uptake increased with the uptake temperature. The irreversible hydrogen uptake increased abruptly when the uptake temperature was raised up to 423 K. The maximum of irreversible hydrogen uptake was measured at 473 K. The HIR/Mo ratio calculated from the uptakes obtained in the temperature range of 308–623 K varies in the range of 0.0010–0.0202. One possible mechanism for hydrogen adsorption is proposed to be heterolytic dissociation on Mo-N paris, in which the molybdenum atoms are in unsaturated coordination.  相似文献   
998.
本文报导的方法是在南京大学高鸿教授研究的K_3Fe(CN)_6示波极谱滴定法(在PH8的K_2HPO_4—KH_2PO_4—KBr底液中,用0.04660mol/LK_3Fe(CN)_6标准溶液对纯抗坏血酸测定)的基础上,考虑到L—抗坏血酸(以下简称V_e)在碱性、中性介质中稳定性差,如用于V_e含量很微的果蔬测定,对结果影响大。本文改为H_2C_2O_4—KBr的酸性介质作底液,用  相似文献   
999.
The photoelectron spectrum of the title compound is reported and assigned by correlation with the photoelectron spectra of related molecules.  相似文献   
1000.
The concerted mechanism of phosphate-catalyzed proton exchange in N,N'-dimethylurea has been studied. Kinetic data were measured using the technigue of NMR line-shape analysis. A significant kinetic isotope effect was observed for the concerted proton transfer in N,N'-dimethylurea and is attributed to the tunnelling effect.  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