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   289777篇
  免费   35777篇
  国内免费   198篇
  325752篇
  2016年   2798篇
  2015年   4156篇
  2014年   4852篇
  2013年   6892篇
  2012年   7761篇
  2011年   7698篇
  2010年   5291篇
  2009年   4993篇
  2008年   7012篇
  2007年   7215篇
  2006年   6844篇
  2005年   6795篇
  2004年   6618篇
  2003年   6728篇
  2002年   6407篇
  2001年   11046篇
  2000年   11162篇
  1999年   9186篇
  1998年   3562篇
  1997年   3732篇
  1996年   3716篇
  1995年   3460篇
  1994年   3458篇
  1993年   3426篇
  1992年   8171篇
  1991年   7958篇
  1990年   7755篇
  1989年   7680篇
  1988年   7249篇
  1987年   7197篇
  1986年   6663篇
  1985年   6813篇
  1984年   5710篇
  1983年   5126篇
  1982年   4094篇
  1981年   3938篇
  1980年   3574篇
  1979年   5924篇
  1978年   4635篇
  1977年   4438篇
  1976年   4236篇
  1975年   4580篇
  1974年   5039篇
  1973年   4928篇
  1972年   4585篇
  1971年   4135篇
  1970年   3645篇
  1969年   3668篇
  1968年   3271篇
  1967年   2823篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Blood smears of both male and female chicken Gallus domesticus were analysed by using the following topochemical methods: a) Periodic acid-Schiff (PAS) for glycogen. b) Mercury-bromophenol blue for protein. c) O-Toluidine for myeloperoxidase. d) Sudan black B for lipid. The PAS reaction revealed glycogen in the cytoplasm of all thrombocytes and in a few heterophils. The presence of proteins was evidenced in all types of cells. However variation in the intensity of staining of protein granules was observed in the fusiform structures of the heterophils. A negative reaction for myeloperoxidase was found in all cells. Although some evidence of myeloperoxidase activity was show in the polymorphonuclears it was not enough to ascertain a positive reaction. Lipids were detected in the cytoplasm of few heterophils, eosinophils and monocytes.  相似文献   
102.
Peak area matching and linear regression were used to quantify eight chlorinated pesticides and polychlorinated biphenyls (as Aroclor 1260) in human serum. There are no statistically significant differences in data obtained by these two quantifying techniques which were indicated by the paired t-test. For chlorinated pesticides, p = 0.053-0.62, and for polychlorinated biphenyls (as Aroclor 1260), p = 0.64. Analyte residues for the chlorinated pesticides ranged from 0.5 ppb for hexachlorobenzene (HCB) to 186 ppb for dichlorodiphenyldichloroethylene (DDE). Analyte residues for the polychlorinated biphenyls (as Aroclor 1260) ranged from 5-114 ppb. The absolute mean percent difference between the two quantifying techniques ranged from 0.06% for DDE to 8.06% for dieldrin (HEOD) among the chlorinated pesticides. The absolute mean percent difference between the two quantifying techniques for the polychlorinated biphenyls (as Aroclor 1260) was 3.4%. Peak area matching and linear regression were found to be comparable for quantifying these environmental residues in serum when the following conditions apply: 1) the concentration of the chlorinated pesticides is greater than or equal to 0.5 ppb (e.g., HCB, hexachlorocyclohexane (HCCH), oxychlordane (OC), heptachlor epoxide (HE), transnonachlor (TN), HEOD, and dichlorodiphenyltrichloroethane (DDT); 2) the concentration of the chlorinated pesticide is greater than or equal to 3 ppb (e.g., DDE); and 3) the total concentration of polychlorinated biphenyls (e.g., as Aroclor 1260) is greater than or equal to 5 ppb.  相似文献   
103.
104.
105.
106.
107.
W.-E. Kalisch 《Genetica》1982,60(1):21-24
Electron micrographs as well as light micrographs of individual surface-spread polytene (SSP) chromosomes indicate more detailed banding patterns than standard squash preparations do. For EM preparations of SSP chromosomes a simple technique is described, avoiding thin-sectioning of chromosomes.  相似文献   
108.
109.
Ten healthy middle-aged women volunteered for a study to test the effect of lactulose--a synthetic, non-absorbable disaccharide--on the colonic metabolism of bile acids and on bile lipid composition. Lactulose (60 g daily in eight cases, 39 g daily in two) was taken as a proprietary syrup for six weeks, and bile was collected by duodenal intubation before and immediately after six weeks. All subjects showed a fall in the percentage of the 7-alpha-dehydroxylated bile acid deoxycholic acid (mean 28.4 +/- SEM 3.7 to 15.6 +/- 2.4; p less than 0.002) and a rise in the percentage of the primary bile acid chenodeoxycholic acid (mean 33.2 +/- 42.9 +/- 2.9; p less than 0.001). The percentage of cholic acid rose in eight subjects but mean values did not differ significantly. Bile was initially super-saturated with cholesterol in most subjects and became less saturated with cholesterol in all but one (mean saturation index 1.40 +/- 0.11 to 1.19 +/- 0.07; p less these 0.005). These data support the theory colonic bacteria contribute to cholesterol gall-stone formation.  相似文献   
110.
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