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   335814篇
  免费   37542篇
  国内免费   189篇
  2018年   2910篇
  2017年   2754篇
  2016年   3952篇
  2015年   5473篇
  2014年   6389篇
  2013年   8924篇
  2012年   10219篇
  2011年   10181篇
  2010年   6921篇
  2009年   6236篇
  2008年   8987篇
  2007年   9445篇
  2006年   8736篇
  2005年   8417篇
  2004年   8125篇
  2003年   7869篇
  2002年   7859篇
  2001年   18177篇
  2000年   18405篇
  1999年   14147篇
  1998年   4259篇
  1997年   4516篇
  1996年   4344篇
  1995年   4028篇
  1994年   3959篇
  1993年   3806篇
  1992年   11511篇
  1991年   11146篇
  1990年   10717篇
  1989年   10284篇
  1988年   9510篇
  1987年   8861篇
  1986年   8098篇
  1985年   7983篇
  1984年   6413篇
  1983年   5581篇
  1982年   4111篇
  1981年   3609篇
  1980年   3365篇
  1979年   6136篇
  1978年   4587篇
  1977年   4137篇
  1976年   3769篇
  1975年   4345篇
  1974年   4514篇
  1973年   4407篇
  1972年   4108篇
  1971年   3511篇
  1970年   3188篇
  1969年   2987篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
The copper (II)-inosine system in water-DMSO solutions was investigated as a function of pH and the molar ratio between the ligand and copper(II) ion by the EPR, NMR, CD and visible absorption spectrometric methods. It was concluded that a simple M.[-N]L copper(II)-inosine 1:1 complex is formed over the pH range 1.4-5.0, while M.[-N]L2 complexes are present in the solutions of pH 5.0-6.2. From pH 6.2 to 7.8 a diamagnetic, hydroxybridged complex M2.(OH)2.[-N]L4 dominates. At pH values of 7.8-9.2 an insoluble, oxybridged species (M.O.[-N]L)n is formed in addition to the soluble paramagnetic M.[-N-1)L4 complex. Above pH 9.1 the nitrogenbridged polymeric complex (M.[-N-1].M[-N-7] )n is formed which is stable up to pH 12.5, and above pH 12.5 the only species found is the M.[-OH]L2 chelate complex in which inosine is coordinated to copper through the two ionized hydroxyl groups.  相似文献   
994.
In view of the importance of impedance plethysmography requirements are formulated for a modern impedance measuring device basing on a long experience with this method of measurement. The principle mode of action of the measuring equipment and the pneumatics with the timing element are described. A number of recordings is shown to illustrate the universality of the measuring equipment.  相似文献   
995.
996.
997.
998.
999.
Of the 1,972 deaths investigated by autopsy at the Los Angeles County Hospital in 1951, 64 were attributed to bronchogenic carcinoma. However, in some of these cases the protocols did not contain sufficient data to substantiate the diagnosis or the tissue specimens were not conclusive evidence. Although the survey left no doubt that the lung was the most common site of primary carcinoma in the series studied, a wider application of the findings is limited by the facts that patients with bronchogenic carcinoma are more likely than others to die in hospitals and that selection of cases for autopsy depends on the interest of the physician and the consent of the patient's survivors.  相似文献   
1000.
Free and derivatized aglycones and parent ascarosides of Ascaris lumbricoides and A. columnaris (Nematoda) were isolated by thin-layer and gas chromatography and analyzed by mass spectrometry and polarimetry. Results for monol aglycones confirmed previous chain-length assignments and the location of the l-hydroxyl group at C-2. The major monols of even carbon number possessed a methyl branch on the penultimate carbon (ω ? 1). Diol alycones were entirely unbranched homologues, mainly 31 and 33 carbons long, and had hydroxyl groups on C-2 and C-(ω ? 1). These aglycones were truly symmetrical, for they were optically inactive with the center bearing the glycone in diol ascaroside (C-2), being mostly or entirely the l configuration. Three major features of ascaroside structure—chain length composition of the aglycones, molecular weight of the unusual glycone (a dideoxyhexose), the kind and position of acyl groups—were clearly discernible in the spectra of intact ascarosides.  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