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   4370篇
  免费   626篇
  国内免费   946篇
化学   5132篇
晶体学   48篇
力学   62篇
综合类   21篇
数学   14篇
物理学   665篇
  2024年   10篇
  2023年   62篇
  2022年   134篇
  2021年   187篇
  2020年   188篇
  2019年   188篇
  2018年   169篇
  2017年   194篇
  2016年   297篇
  2015年   259篇
  2014年   298篇
  2013年   565篇
  2012年   359篇
  2011年   358篇
  2010年   307篇
  2009年   339篇
  2008年   306篇
  2007年   292篇
  2006年   246篇
  2005年   183篇
  2004年   168篇
  2003年   147篇
  2002年   95篇
  2001年   58篇
  2000年   48篇
  1999年   31篇
  1998年   43篇
  1997年   35篇
  1996年   29篇
  1995年   39篇
  1994年   41篇
  1993年   29篇
  1992年   28篇
  1991年   15篇
  1990年   19篇
  1989年   19篇
  1988年   17篇
  1987年   12篇
  1986年   10篇
  1985年   10篇
  1984年   6篇
  1983年   4篇
  1982年   11篇
  1981年   8篇
  1980年   13篇
  1979年   21篇
  1978年   13篇
  1977年   10篇
  1976年   11篇
  1973年   6篇
排序方式: 共有5942条查询结果,搜索用时 546 毫秒
31.
The limiting molar conductances ° of deuterium chloride DCl in D2O were determined as a function of pressure and temperature in order to examine the proton-jump mechanism in detail. The excess deuteron conductances °E(D +), as estimated by the equation [°E(D +) = °(DCl/D 2 O) – °(KCl/D 2 O)], increases with an increase in the pressure and temperature as well as the excess proton conductance [°E(H +) = °(HCl/H 2 O) – °(KCl/H 2 O)]. The isotope effect on the excess conductances, however, depends on the pressure and temperature contrary to the model proposed by Conway et al.: °E(H +)/°E(D +) decreases with increasing pressure and temperature. The magnitude of the decrease with pressure becomes more prominent at lower temperature. These results are discussed in terms of the pre-rotation of adjacent water molecules, the bending of hydrogen bonds with pressure, and the difference in strength of hydrogen bonds between D2O and H2O.  相似文献   
32.
Ionic liquids are a new kind of room-temperature molten organic salts. It can be used as solvents in the organic/polymeric syntheses, and some of them are called "green" solvents because of its recyclability1. Ionic liquids possess the superior properties, such as thermal stability up to 200(C, involatility and re-designability(for both cation and anion). The ionic liquid employed in this work is [bmim] [PF6]- ( butylmethylimidazolium hexafluorophosphate ) which is immiscible with water and h…  相似文献   
33.
Enthalpies of solution have been measured from 5 to 85°C for aqueous tetraethyl- and tetrapropylammonium bromides, and the integral heat method is employed to evaluate for these electrolytes over a wide temperature range. Data taken from the literature have been used to evaluate for aqueous Bu4NBr over a similar temperature range. These data, along with similar data for Me4NBr, previously reported, have been used to evaluate absolute ionic heat capacities. While the absolute values agree only qualitatively with two other methods of division, the temperature dependences of the three methods essentially agree up to 65°C. Heat capacities due to structural effects on the solvent, obtained by subtracting the inherent heat capacities of the ions, are extraordinarily positive for all four tetraalkylammonium ions and have negative temperature coefficients, indicating that all four ions, including the tetramethylammonium ion, are structure-making ions.  相似文献   
34.
35.
null   总被引:28,自引:0,他引:28  
本文对近10年来出现的新型离子液体进行了分类综述,并对其发展前景提出了一些见解.  相似文献   
36.
采用水热晶化反应,制备出传统需要高温固相反应合成的掺杂NASICON化合物Na(1-x)Zr(2-x)NbxP3O12(0<x<1),并应用XRD、IR方法对产物的晶体结构进行了研究,表明水热晶化产物是纯的物相并具有与NaZr2P3O12相同的结构.固体31PNMR研究证实Nb(5+)部分取代了Zr(4+)所在位置,参与骨架的组成,并统计分布于结构中.水热晶化产物与固相反应产物具有相同的离子电导性能.  相似文献   
37.
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   
38.
Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex.  相似文献   
39.
本文用DSC方法研究了羟酸型含氟离聚体中不同金属离子种类、可离子化基团含量、配位结构单元构型及离子微区大小对离聚体中离子微区稳定性的影响。实验表明:离聚体中金属离子配位能力愈强,羟酸含量愈高,离子微区尺寸愈大,则相应离聚体中离子微区稳定性愈大。铅高聚体>锌离聚体>钙离聚体>钠离聚体。  相似文献   
40.
Poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide (PEMEImI) as a single-ion conductor was designed and synthesized. When appropriate amount of suitable plasticizers, I2 and polyacrylonitrile (PAN) were incorporated into it, the complex formed gel polymer electrolyte. Chemical structure, thermal behavior and ionic conductive properties of the gel polymer electrolyte were investigated by Raman spectra, UV-Vis spectra, differential scanning calorimetry (DSC), and complex impedance analysis, respectively. For the new gel polymer electrolyte, the ionic conductivity of about 1 × 10−3 S cm−1 at room temperature was achieved.  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