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   98499篇
  免费   18704篇
  国内免费   7495篇
化学   84027篇
晶体学   1046篇
力学   4062篇
综合类   373篇
数学   10233篇
物理学   24957篇
  2024年   128篇
  2023年   1249篇
  2022年   2009篇
  2021年   2511篇
  2020年   3734篇
  2019年   4746篇
  2018年   2960篇
  2017年   2642篇
  2016年   6167篇
  2015年   6233篇
  2014年   6679篇
  2013年   8457篇
  2012年   8481篇
  2011年   7856篇
  2010年   6683篇
  2009年   6377篇
  2008年   6389篇
  2007年   5432篇
  2006年   4711篇
  2005年   4455篇
  2004年   3629篇
  2003年   3026篇
  2002年   3594篇
  2001年   2521篇
  2000年   2334篇
  1999年   1588篇
  1998年   1103篇
  1997年   1073篇
  1996年   1030篇
  1995年   930篇
  1994年   795篇
  1993年   714篇
  1992年   575篇
  1991年   527篇
  1990年   456篇
  1989年   336篇
  1988年   260篇
  1987年   248篇
  1986年   237篇
  1985年   266篇
  1984年   198篇
  1983年   178篇
  1982年   128篇
  1981年   117篇
  1980年   97篇
  1979年   83篇
  1978年   76篇
  1976年   60篇
  1975年   71篇
  1974年   62篇
排序方式: 共有10000条查询结果,搜索用时 968 毫秒
901.
A new interfacial polymerization (IP) procedure is developed in order to synthesize polypiperazine-amide thin-film membrane on the inner surface of poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber ultrafiltration (UF) membrane.A hollow fiber composite membrane with good performance was prepared and studied by FT-IR and scanning electron microscopy.  相似文献   
902.
Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O(2). The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (approximately 700 degrees C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (approximately 800 degrees C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.  相似文献   
903.
Starting from the hydroxylamine (dimethyl amino ethanol, triethanolamine) and 1,3-propane sultone, a series of hydroxyl and sulfonyl dual-functionalized zwitterionic salts and corresponding acidic room temperature ionic liquids have been synthesized. The hydroxyl groups of the synthesized substances were confirmed by the 1H NMR measurement. These zwitterionic salts and ionic liquids may be used for synthesizing other functionalized ionic liquids or ionic liquid-polymer (polyelectrolyte).  相似文献   
904.
In order to achieve "postponement of school without suspension of learning" during the prevention and control of new coronavirus pneumonia, the online teaching strategy was constructed based on Enterprise WeChat and Integrated Online Education Platform for the online teaching of Separation Science and Technology. The student-centered teaching methods were applied in online teaching process.  相似文献   
905.
A new fluorescent compound based on calix[4] arene skeleton was synthesized.Its complexation ability with transition metal ions,such as Fe^3 ,Co^2 ,Ni^2 ,Cu^2 ,Zn^2 and Ag^ ,Was investigated by UV-vis and fluorescent spectra.  相似文献   
906.
A fluorimetric determination method for N-arachidonoylethanolamine (anandamide) was developed using a precolumn fluorescence derivatization followed by coupled-column high-performance liquid chromatography (HPLC). Anandamide extracted from the rat brain tissue was derivatized with 4-N-chloroformylmethyl-N-methylamino-7-N, N-dimethylaminosulfonyl-2,1,3-benzoxadiazole (DBD-COCl), purified by a solid-phase extraction (Emporetrade mark), and assayed by the coupled-column HPLC. The HPLC consisted of phenyl (100 x 4.6 mm i.d. ) and octadecylsilica columns (250 x 4.6 mm i.d.), both connected by a six-port valve. The concentration of anandamide in rat brain was 3. 37 +/- 0.73 pmol/g with 6.47 and 3.57% of intra- and inter-day precisions, respectively. Using this method, we investigated the alteration of anandamide concentration in rat brain 30 min after administration of anandamide (2 mg/kg, i.p.) to rats pretreated with or without phenylmethylsulfonyl fluoride (PMSF; 30 mg/kg, i.p.), an inhibitor of amidohydrolase. In rats pretreated with PMSF, the brain concentration of anandamide was approx. 16-fold higher than that of rats without PMSF (p < 0.01).  相似文献   
907.
Aminylferrocene is successfully immobilized on nanosized gold colloid particles associated with a 1,4-benzenedimethanethiol monolayer on a gold electrode surface and characterized by cyclic voltammograms and electrochemical impedance spectroscopy. In a pH 7.0 phosphate buffer solution, the formal potential (E 0’) of Fc is 0.432 V (SCE), and the apparent surface electron-transfer rate constant is 0.89 s. The immobilized Fc gives an excellent electrocatalytic response to the terbutaline oxidation. The catalytic-current response of differential pulse voltammograms increases linearly with the terbutaline concentration from 1.75 × 10−7 to 5.62 × 10−4 mol/l. The detection limit is 2.30 × 10−8 mol/l. The determination of terbutaline in a tablet dosage is satisfactory. The method is simple, quick, and sensitive. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 8, pp. 969–974. The text was submitted by the authors in English.  相似文献   
908.
李华  杨翌秋 《分析化学》1995,23(1):25-28
本文讨论了29个不对称色酸双偶氮膦酸型显色剂的分子联接性指数,并将其与结构选择性因子相结合,用于偶氮类剂结构与铈显色反应灵敏度的相关性研究,讨论了显色剂结构对显色反应灵敏度的影响。  相似文献   
909.
杨勇  李骏 《电化学》1996,2(4):363-371
贮氢合金材料电化学与表面性能的研究进展①杨勇李骏林祖赓(厦门大学化学系,固体表面物理化学国家重点实验室,厦门361005)八十年代后期以来,人们对地球的环境保护提出了更高的要求,而便携式电器(如移动电话,摄像机与笔记本电脑等)对电池的需求也大量增加...  相似文献   
910.
电泳中介微分析法测定超氧化物歧化酶   总被引:1,自引:0,他引:1  
傅崇岗  杨冬芝 《分析化学》2006,34(4):517-520
基于超氧化物歧化酶(SOD)对邻苯三酚自氧化的抑制作用和电泳中介微分析(EMMA)技术建立了一种测定SOD的新方法。采用“三明治”式不同pH缓冲液部分填充法,有利于邻苯三酚的自氧化反应,便于观察SOD的抑制作用,有利于反应产物与反应物的分离。对溶液填充模式、反应条件等实验参数进行了优化。在最优条件下,邻苯三酚自氧化反应的抑制率I与SOD浓度C在1.00×102~6.00×102μg/L范围内呈良好的线性关系,回归方程为:I(%)=0.0895C(μg/L) 17.633(r=0.9973)。  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