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   2412篇
  免费   600篇
  国内免费   251篇
化学   993篇
晶体学   38篇
力学   199篇
综合类   36篇
数学   94篇
物理学   1903篇
  2024年   7篇
  2023年   19篇
  2022年   78篇
  2021年   65篇
  2020年   83篇
  2019年   56篇
  2018年   78篇
  2017年   95篇
  2016年   106篇
  2015年   113篇
  2014年   152篇
  2013年   203篇
  2012年   174篇
  2011年   154篇
  2010年   139篇
  2009年   134篇
  2008年   143篇
  2007年   184篇
  2006年   148篇
  2005年   145篇
  2004年   125篇
  2003年   119篇
  2002年   136篇
  2001年   93篇
  2000年   91篇
  1999年   71篇
  1998年   60篇
  1997年   50篇
  1996年   30篇
  1995年   29篇
  1994年   41篇
  1993年   24篇
  1992年   21篇
  1991年   15篇
  1990年   12篇
  1989年   10篇
  1988年   12篇
  1987年   4篇
  1986年   5篇
  1985年   11篇
  1984年   7篇
  1983年   3篇
  1982年   3篇
  1981年   3篇
  1979年   2篇
  1978年   2篇
  1977年   2篇
  1976年   2篇
  1973年   2篇
  1957年   1篇
排序方式: 共有3263条查询结果,搜索用时 15 毫秒
21.
The parallel between orbital first and second electric moments and statistical first and second central moments is noted. Three measures of orbital spatial distribution in terms of their moments are proposed, and applied to the LMO's in a series of ten-electron hydrides. Consistent differences between bond and lone pair distributions are found. Using the statistical interpretation, for each LMO an effective solid angle around the central atom is postulated.  相似文献   
22.
Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.  相似文献   
23.
The structure of the double electric layer (DEL) on a liquid dropping Sn-Ga electrode containing 8 at. % of Sn is studied in acetonitrile (AN) solutions of electrolytes. It is shown that the transition from aqueous to AN solutions of electrolytes makes it possible to expand the region of investigation of parameters of DEL on an Sn-Ga electrode from negative charges to a zero charge and to small positive charges. As follows from the obtained data, throughout the entire interval of charges studied, an excess, as compared with an Hg electrode, chemisorption interaction (Sn-Ga)-AN is absent. It is established that the distance of the closest approach of AN dipoles to an ionic core increases upon going from Hg to Sn-Ga to Ga. The Ga, Bi-Ga, and Sn-Ga electrodes, which possess close values of the “electrochemical work function,” are used as an example to show that the metal-solvent chemisorption interaction increases with decreasing distance of the closest approach of its dipoles to the ionic core of the metal. The effect of this factor becomes stronger as the donor number of the solvent increases.  相似文献   
24.
We have measured heat capacity and thermal expansion of rare earth dodecaborides REB12 (RE=Y, Tb-Tm, Lu). YB12 and LuB12 are diamagnetics whereas the other dodecaborides are ordered antiferromagnetically. The amplitude of the heat capacity discontinuity at the Néel temperature and the shape of the heat capacity variation in the critical region for all these antiferromagnetics are characteristics for amplitude-modulated magnetic structures. In the ordered state TbB12 reveals two first-order phase transitions, most likely due to magnetic structure changes. The heat capacity of ErB12 just below the Néel point shows an anomaly of unclear origin. From the Schottky contribution to the heat capacity we have determined crystal field parameters. They are completely different than that is estimated from Point Charge Model.  相似文献   
25.
微量元素锌在治疗Bell麻痹中的作用   总被引:1,自引:0,他引:1  
为探讨急性早期应用补锌和综合疗法治疗Bell麻痹 ,将 1 5 8例Bell麻痹患者 ,随机分成两组 :(1 )补锌组 (补锌 +综合疗法 ) ;(2 )对照组 (单纯综合疗法 )。对其进行了观察对比治疗 ,同时检测了所有患者治疗前后自身对照发锌值 ,还对所有患者进行了定位诊断、面神经电反应测试、并对面肌功能进行评分。结果表明 ,对定位诊断其病变在D段、面肌功能评分在 1 1分以下、面神经无电反应患者 ,即使给予早期综合治疗 ,效果仍较差 ,而早期给予补锌加综合治疗效果优于对照组 ,其它段内患者治疗次数和治愈天数也均优于对照组。可见微量元素锌在发挥免疫应答、免疫调控中的重要作用  相似文献   
26.
本文论证了“QE-2”型静电场描迹中模拟聚焦电场的电极在设计上有误的观点。  相似文献   
27.
Numerical simulations are done of Langevin dynamics for a uniform-orderparameter, field-swept Landau model,= –|a/2|m 2+|b/4|m 4mh(t) , to study hysteresis effects. The field is swept at a constant rateh(t)=h(0)+ht. The stochastic jump values of the field {hJ from an initially prepared metastable minimumm(0) are recorded, on passage to a global minimum m(). The results are: (a) The mean jump¯h J(h) increases (hysteresis loop widens) with h, confirming a previous theoretical criterion based on rate competition between field-sweep and inverse mean first-passage time (FPT); (b) The broad jump distribution(h J,h) is related to intrinsically large FPT fluctuations ( 22)/ 2 O(1), and can be quantitatively understood. Possible experimental tests of the ideas are indicated.  相似文献   
28.
本文利用等温电导法考察了醋酸锰和草酸的室温固相配位化学反应的制样方法对实验结果的影响,并获得了该反应的动力学参量。  相似文献   
29.
Attempts to miniaturize electrophoresis (EP) to save time or enhance productivity and efficiency remains a challenge for science and industry. Other advantages of miniaturization include: increased sensitivity, saving of reagents, greater yield of data, and enabling studies where only small samples are available. Since electrophoresis that takes hours may be reduced to a matter of minutes, the limitations of miniaturization in clinical, industrial, and research applications are evaluated. Clinical electrophoresis (EP) on cellulose acetate media can be performed in 3.5 min instead of 20–45 min and on SDS polyacrylamide gels in 15–30 min compared with conventional 3–8 h.  相似文献   
30.
应用液/液界面微电极对二苯并18-冠-6(DB18-C-6)辅助推动Ba~(2+)在1,2-二氯乙烷/水(DCE/W)界面转移的电化学过程进行了详细探讨,证明该过程遵循TIC机理,是受扩散控制的可逆过程。通过转移电流和反应物浓度之间的线性关系,测定了Ba~(2+)以及用其它方法难以测定的DB18-C-6。  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