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   1085篇
  免费   35篇
  国内免费   1篇
化学   708篇
晶体学   20篇
力学   80篇
数学   114篇
物理学   199篇
  2022年   12篇
  2021年   16篇
  2020年   19篇
  2019年   17篇
  2018年   11篇
  2017年   20篇
  2016年   27篇
  2015年   15篇
  2014年   39篇
  2013年   87篇
  2012年   72篇
  2011年   68篇
  2010年   41篇
  2009年   26篇
  2008年   42篇
  2007年   44篇
  2006年   39篇
  2005年   37篇
  2004年   23篇
  2003年   35篇
  2002年   31篇
  2001年   9篇
  2000年   10篇
  1999年   14篇
  1998年   10篇
  1997年   17篇
  1996年   12篇
  1995年   15篇
  1994年   12篇
  1993年   8篇
  1991年   10篇
  1990年   9篇
  1989年   13篇
  1988年   7篇
  1986年   10篇
  1985年   14篇
  1984年   8篇
  1983年   12篇
  1982年   14篇
  1981年   11篇
  1980年   12篇
  1979年   14篇
  1978年   13篇
  1977年   13篇
  1976年   11篇
  1974年   8篇
  1973年   13篇
  1945年   6篇
  1941年   11篇
  1936年   9篇
排序方式: 共有1121条查询结果,搜索用时 15 毫秒
1.
2.
3.
Studies conducted by Atomic Minerals Directorate of Exploration and Research (AMD) of Hyderabad, India had established the presence of higher concentrations of uranium in Lambapur and Peddagattu areas of Nalgonda district, AP, India and it was estimated that it could be a viable source for commercial extraction. The envisaged extraction process involves dispersion of radioactive particulate matter into atmosphere. Environmental radioactive studies in and around proposed mining areas at this point of time will be extremely useful for establishing base line data before a large scale uranium extraction process comes into existence. To this end, Solid State Nuclear Track Detectors were installed to evaluate indoor radon and thoron concentration levels in the dwellings of the area. The geometric means of radon and thoron concentration levels were found to be (7.1±0.2)×101 and (6.7±0.3)×101 Bq/m3, respectively. Simultaneously, natural background radiation measurements were also made and these levels are found to vary from 770 to 3995 μGy/y in the spatial distribution.  相似文献   
4.
5.
A mild and efficient oxidation of alcohols with o-iodoxybenzoic acid (IBX) catalyzed by beta-cyclodextrin in a water/acetone mixture (86:14) has been developed. A series of alcohols were oxidized at room temperature in excellent yields.  相似文献   
6.
Fragmentation patterns resulting from electron impact ionization of 3-(2′-hydroxyethyl)quinolin-2(1H)-one, three of its monosubstituted derivatives and four of its disubstituted derivatives were studied. The molecular ion of quinolinone-2-etbanol undergoes initial fragmentation with the loss of OH·, H2O, CO, ·CHO, CH2O, CH2OH·, CH2?CHOH and HCNO species. The [M – CHO]+ ion is tentatively suggested to have been formed by the expulsion of H· from the [M – CO] ion and the [M - CHO]+ peak may be considered as diagnostic of a 2-quinolone-3-ethanol.  相似文献   
7.
2‐Acetyl thiophenethiocynate (ATT) was synthesized and its characterization study was carried out using elemental analysis, IR and NMR techniques. The new reagent was proposed as an extractant for the development of the extractive spectrophotometric method for determination of Pt(IV) metal. The reagent complexes with the metal to produce a yellow colored complex which was then extracted into ethyl acetate at pH 11.2–11.6 having an absorption maxima at 400 nm. The thermal study showed that the extraction reactions are exothermic in nature with the reagent, and the stoichiometric ratio of Pt(IV) to 2‐acetyl thiophenethiocynate in the organic phase was 1:2. The method permits separation and determination of platinum from real and binary mixtures. The separation of Pt(IV) from bivalent metal ions has been also studied.  相似文献   
8.
The maximum number of non-vanishing and independent second order photoelastic coefficients required by the seven pentagonal and the two icosahedral point groups 5(C5), (S10), (C5h ), m2(D5h ), 52(D5), 5m(C5v ), 2m(D5d ); 235(I), 2/m (I h )—that describe the quasicrystals symmetry groups in two and three dimensions—is obtained. The schemes of non-vanishing and independent coefficients have been calculated and listed. Finally the results of this group-theoretical study are briefly discussed.  相似文献   
9.
The transport coefficients for the nine point groups —which represent the symmetry groups of the quasicrystals in two and three dimensions—have been evaluated and tabulated in this work, employing group-theoretical methods.  相似文献   
10.
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