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   10383篇
  免费   2287篇
  国内免费   1483篇
化学   7885篇
晶体学   182篇
力学   629篇
综合类   134篇
数学   1065篇
物理学   4258篇
  2024年   62篇
  2023年   331篇
  2022年   536篇
  2021年   587篇
  2020年   621篇
  2019年   605篇
  2018年   498篇
  2017年   433篇
  2016年   577篇
  2015年   706篇
  2014年   765篇
  2013年   872篇
  2012年   1043篇
  2011年   989篇
  2010年   677篇
  2009年   716篇
  2008年   747篇
  2007年   618篇
  2006年   555篇
  2005年   432篇
  2004年   321篇
  2003年   227篇
  2002年   222篇
  2001年   157篇
  2000年   152篇
  1999年   116篇
  1998年   103篇
  1997年   73篇
  1996年   67篇
  1995年   48篇
  1994年   41篇
  1993年   49篇
  1992年   37篇
  1991年   18篇
  1990年   24篇
  1989年   20篇
  1988年   14篇
  1987年   16篇
  1986年   22篇
  1985年   15篇
  1984年   10篇
  1983年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1976年   2篇
  1971年   4篇
  1966年   2篇
  1959年   5篇
  1957年   2篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A novel tripodand having 3-hydroxy-2-naphthoeic amide groups was prepared by the reaction of 1,3,5-tris(aminomethyl)-2,4,6-trimethylbenzene with 3-allyloxy-2-naphthoeic acid chloride followed by thermal Claisen rearrangement. This tripodand can exhibit the anion binding ability in chloroform solution. In particular, it can bind with acetate, dihydrogen phosphate, and fluoride ions to form 1:1 complexes.  相似文献   
992.
993.
本文针对过冷沸腾中汽泡顶部射流现象进行分析与模拟。建立汽泡界面模型,考虑蒸发凝结以及Marangoni效应。利用CFD软件Fluent6.0对模型进行计算分析,成功模拟得到泡顶射流流场。模拟结果无论是流场结构,还是流场强度,都与实验一致吻合,充分证明泡顶射流由Marangoni效应引起。  相似文献   
994.
All-optical microwave filters are important parts of fiber-optic microwave/millimeter wave processing systems. In this paper, two novel passive tunable all-optical microwave filters based on fiber loop and chirped fiber Bragg gratings (CFBGs) are demonstrated, where the frequency response of the both filters can be continuously tuned by adjusting the wavelength of the input light. The required free spectral range (FSR) of the filters can be obtained by carefully controlling the length of fiber loop and the positions of the CFBGs in the fiber loop. Experimental results prove the feasibility of the proposed filtering structures.  相似文献   
995.
Hu  Xiaoling  Sun  Jianguo  Wang  Guangji  Zhu  Xiaoyan  Hao  Gang  Gu  Yongchuan  Pruijn  Frederik B. 《Chromatographia》2008,67(11):883-892

SHR110008 is a representative 9-β-dihydro-9,10-O-acetal taxane with greater anticancer activity and less toxicity than docetaxel. To support a preclinical study of its pharmacokinetics and to predict the effect of 9-β-dihydro-9,10-O-acetal modification on its pharmacokinetic properties, we have developed a sensitive and rapid liquid chromatographic–tandem mass spectrometric method for quantitative analysis of SHR110008 in rat and dog plasma. Plasma was extracted with ethyl acetate. The analytes were separated on a 150 × 4.6 mm i.d., 5 μm particle, reversed-phase C18 column with 90:10 (v/v) methanol–0.1% formic acid as mobile phase at a flow rate of 0.3 mL min−1. Detection was performed by triple-quadrupole tandem mass spectrometry in selected reaction monitoring (SRM) mode with an electrospray ionization source. The precursor-to-product ion transition m/z 933 → 142 was used. The method was validated for accuracy and precision, and linearity in the two matrices was good. Lower limits of quantification (LLOQ) in rat and dog plasma were 5 and 2 ng mL−1, respectively. There were no stability-related problems in the procedure for analysis of SHR110008. The method was successfully used in a preclinical study of the pharmacokinetics of SHR110008 in rats and beagle dogs. The pharmacokinetics of SHR110008 were non-linear in rats and dogs. The elimination half-life ranged from 5.18 to 7.32 h for the rats and from 6.42 to 8.42 h for the dogs.

  相似文献   
996.
城市交通管理中的出租车规划模型   总被引:1,自引:0,他引:1  
最佳数量的确定和价格的制定是城市出租车规划中的两个核心问题.对影响出行强度的市区人口和建成区面积分析建立了出行总量预测模型,再通过分析出租车最佳数量与出租车运营里程的关系,得出出租车最佳数量的预测模型.在出租车最佳数量模型的基础上,分析出租车数量的差异和差异产生的原因,给出了出租车定价判断模型,为出租车定价机制的调整指明了方向.最后以长沙市为例进行了实证分析.  相似文献   
997.
998.
A series of 2‐aminopyridine Ni(II) complexes bearing different substituent groups {(2‐PyCH2NAr)NiBr, Ar = 2,4,6‐trimethylphenyl ( 3a) , 2,6‐dichlorophenyl ( 3b ), 2,6‐dimethylphenyl ( 3c) , 2,6‐diisopropylphenyl ( 3d ), 2,6‐difluorophenyl ( 3e ); (2‐PyCH2NHAr)2NiBr2, Ar = 2,6‐diisopropylphenyl ( 4a )} have been synthesized and investigated as precatalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). High molecular weight branched polymers as well as short‐chain oligomers were simultaneously produced with these complexes. Enhancing the steric bulk of the ortho‐aryl‐substituents of the catalyst resulted in higher ratio of solid polymer to oligomer and higher molecular weight of the polymer. With ortho‐haloid‐substitution, the catalysts afforded a product with low polymer/oligomer ratio ( 3b ) and even only oligomers ( 3e ) in which C14H28 had the maximum content. Compared with complex 3d containing ionic ligand, complex 4a containing neutral ligand exhibited obviously low catalytic activity for ethylene polymerization. The molecular weight, molecular weight distribution, and microstructure of the resulted polymer were characterized by gel permeation chromatography and 13C NMR spectrogram. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1618–1628, 2008  相似文献   
999.
合成并表征了3个Schiff碱配体及由其桥联的3个双核钌配合物,并通过核磁共振谱、红外光谱、质谱及元素分析等测试手段对配体及化合物进行了表征.电化学测试结果表明,在3个双核配合物中存在着分子内的金属-金属间相互作用,且连接两个金属的桥配体是影响金属间相互作用强弱的关键因素.  相似文献   
1000.
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