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   21606篇
  免费   4201篇
  国内免费   3230篇
化学   15803篇
晶体学   299篇
力学   1336篇
综合类   302篇
数学   2592篇
物理学   8705篇
  2024年   55篇
  2023年   387篇
  2022年   750篇
  2021年   762篇
  2020年   911篇
  2019年   895篇
  2018年   769篇
  2017年   732篇
  2016年   1016篇
  2015年   1094篇
  2014年   1332篇
  2013年   1642篇
  2012年   1977篇
  2011年   2069篇
  2010年   1490篇
  2009年   1499篇
  2008年   1615篇
  2007年   1412篇
  2006年   1322篇
  2005年   1097篇
  2004年   919篇
  2003年   700篇
  2002年   708篇
  2001年   604篇
  2000年   473篇
  1999年   420篇
  1998年   328篇
  1997年   332篇
  1996年   287篇
  1995年   241篇
  1994年   224篇
  1993年   161篇
  1992年   115篇
  1991年   131篇
  1990年   111篇
  1989年   76篇
  1988年   78篇
  1987年   64篇
  1986年   46篇
  1985年   33篇
  1984年   29篇
  1983年   28篇
  1982年   27篇
  1981年   18篇
  1980年   16篇
  1979年   6篇
  1976年   6篇
  1975年   8篇
  1959年   5篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
161.
镧系离子与L-羟脯氨酸、DL-瓜氨酸配位作用研究   总被引:2,自引:0,他引:2  
稀土与体内广泛存在的生物配体氨基酸的配位作用,尤其是三元体系的研究对于阐明稀土元素在体内的存在形态及探索稀土生物效应具有重要意义.羟脯氨酸和瓜氨酸均是人体中存在的重要氨基酸,它们在人体血浆中的浓度与必需的氨基酸相近[‘j.稀土与氨基酸配位作用的研究已有较多报道「’‘,但模拟生理条件下稀土离子与羟脯氨酸、瓜氨酸的二元、三元配合物的PH电位法研究尚未见报道.本文报道在模拟生理条件下(37C,0·15mol/LNaCI)湖系离子(Pm和Lu除外)与上述2种氨基酸的二元及三元配合物PH电位法研究结果.1实验部分1.1试剂和仪…  相似文献   
162.
差热分析(DTA)法研究五水硫酸铜的失水过程   总被引:2,自引:0,他引:2  
关于五水硫酸铜的失水过程有不同的说法。归纳起来,主要有以下几种:1.五水硫酸铜的失水过程分三步进行,即  相似文献   
163.
大肠杆菌有限生长的微量热及非线性动力学研究   总被引:2,自引:0,他引:2  
The finite growth of Escherichia coli was studied by using a LKB 2277 BioActivity Mollitor. We found that the finite growth is a nonliear dynamic process. The nonlinear dynamic behaviour in the finite growth process and the nonlinear dynamic models describing the process were discovered and established. The curve of logistic map corresponding to the finite growth thermogram of Escherichia coli was obtained and the nonlinear dynamic parameters were calculated by means of a computer. Moreover, we also discussed the nonlinear dynamic characters of Escherichia colt in its finite growth process.  相似文献   
164.
High-resolution two-dimensional gel electrophoresis (2-DE), followed by computer-assisted image analysis was used to screen protein patterns of normal and infarcted myocardial tissues for quantitative and qualitative differences in protein expression. In the gels of pH 5–8 immobilized pH gradient (IPG) strips, 851 protein spots were detected in normal myocardial tissue and 1 032 protein spots were resolved in infarcted myocardial tissue. Thirteen protein spots only expressed in normal myocardial tissue, and 14 protein spots only expressed in infarcted myocardial tissue. Results also showed that 49 protein spots displayed quantitative changes in expression between normal and infarcted myocardial tissue. Eleven protein spots were subjected to mass spectrometry (MS) analysis and seven proteins were identified by peptide mass fingerprinting (PMF). These proteins may be involved in cardiovascular injury, and could play an important role in the treatment of coronary heart disease. __________ Translated from Chemical Journal of Chinese Universities, 2006, 8(27): 1467–1471 [译自: 高等学校化学学报]  相似文献   
165.
0 IntroductionMetallosupramolecular oligomers and polymerscan result from the interaction of metal ions with ap-propriate multidentate ligands designed for multinucle-ar binding[1,2], and there are considerable interests in thedesign of species containing known numbers of metalions in defined spatial arrangements. The electronic andphotophysical properties of oligopyridine complexes oftransition-metal ions make their incorporation particu-larlyattractive and the possibilityofinter-metallic ele…  相似文献   
166.
A New Asterosaponin from the Starfish Culcita novaeguineae   总被引:1,自引:0,他引:1  
A new asterosaponin named novaeguinoside A, along with a known saponin, asteronyl pentaglycoside sulfate, was isolated from the starfish Culcita novaeguineae. The new compound was identitied to be sodium 6α-O-{β-D-fucopyranosyl-(1→2)-β-D-fucopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-xylopyranosyl-(1→3)-[β-D-quinovopyranosyl}-5α-pregn-9(11)-en-20-one-3β-yl-sulfate by extensive spectral analysis and chemical evidence.  相似文献   
167.
朱红  赵丰  李津如  江龙 《广州化学》2002,27(2):35-37
用不同浓度的NaCl和表面活性剂直链的十二烷基苯磺酸钠(LAS)、稳定剂聚丙烯酰胺和水所组成的泡沫体系为研究对象,通过表面压松弛的方法,利用计算机数据拟合,得到了计算表面膨胀粘度的方法。  相似文献   
168.
本文合成了疏水性高氯酸二水(四胺)合钴(Ⅲ)配合物,研究了它与非离子表面活性剂Brij35形成的金属2胶束催化二(对硝基苯酚)磷酸二酯水解的动力学及其机理。结果表明此金属胶束对磷酸二酯水解的速率大约提高10^4倍,这主要是由于表面活性剂胶束的pH效应和浓聚效应所致,暗示着顺式二水类配合物形成的金属胶束是一个潜在的磷酸二酯水解剪切的催化剂。  相似文献   
169.
液芯光纤光度法在乙醇水溶液中测定铂(Ⅱ)、钛(Ⅳ)   总被引:4,自引:0,他引:4  
采用氟塑料长光纤管,以42%乙醇水溶液作液芯,组成液芯光纤,基于铂与氯化亚锡、钛与过氧化氢形成黄色络合物在乙醇水溶液中很稳定,拟定了测定铂、钛的液芯光纤光度法。该法灵敏度高,用 1m长光纤作吸收池,铂的灵敏度为 4. 845 A/mg· L-1,钛的灵敏度为1.41A/mg· L-1(A为吸光度),与常规法(1cm)比色皿相比灵敏度提高了 100倍。该法测定了催化剂中铂,煤灰粉中钛,结果与推荐值相符。  相似文献   
170.
There have been remarkable progresses in manipulating heterogeneous catalysts' nanostructures in the past decade. The concept of single atom alloy (SAA) was firstly proposed in 2012 when researchers successfully stabilized single Pd atoms on the Cu(111) surface. However, earlier work in 2009, which focused on replacing one Au atom with a Pd atom in thiolate protected Au25 nanoclusters, could also be considered as the pioneer work of single atom alloy. Both kinds of single atom alloys exhibited the potential of maximum utilization of scarce elements and attractive catalytic performances. The well‐defined structures of SAA catalysts make accurate modeling possible, which further realizes the rational design of single atom alloy catalysts. In this review, we summarize the research trajectory of single atom alloys as well as recent achievements in this field. We also introduce several commonly adopted characterization methods for SAA catalysts such as scanning tunneling microscopy (STM), temperature programmed reaction (TPR), extended X‐ray absorption fine structure (EXAFS) spectra, matrix assisted laser desorption/ionization mass spectrum (MALDI‐MS) and differential pulse voltammetry (DPV). Through discussing recent progresses in SAA catalysts, we propose that future researches in this filed should be focused on exploring new kinds of metal nanocrystals and controlling the nanostructure of SAA even more precisely.  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