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   238435篇
  免费   18139篇
  国内免费   58篇
  2021年   2104篇
  2018年   3715篇
  2017年   3397篇
  2016年   4262篇
  2015年   4788篇
  2014年   5669篇
  2013年   7765篇
  2012年   9056篇
  2011年   9125篇
  2010年   6210篇
  2009年   5384篇
  2008年   7820篇
  2007年   7958篇
  2006年   7643篇
  2005年   6971篇
  2004年   7091篇
  2003年   6752篇
  2002年   6582篇
  2001年   9656篇
  2000年   9744篇
  1999年   7300篇
  1998年   2494篇
  1997年   2397篇
  1996年   2193篇
  1995年   2041篇
  1993年   1938篇
  1992年   5765篇
  1991年   5891篇
  1990年   5602篇
  1989年   5582篇
  1988年   5145篇
  1987年   4878篇
  1986年   4441篇
  1985年   4596篇
  1984年   3688篇
  1983年   3142篇
  1982年   2126篇
  1981年   1911篇
  1979年   3493篇
  1978年   2752篇
  1977年   2459篇
  1976年   2250篇
  1975年   2724篇
  1974年   3091篇
  1973年   3004篇
  1972年   2830篇
  1971年   2596篇
  1970年   2296篇
  1969年   2186篇
  1968年   2050篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
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   
93.
Twenty four male Wistar rats weighing 250 +/- 10 g, in three groups of 8 rats each, were used. Group A was used as control and the content of its drinking water was 6.5 mg/l Ca; 2.4 mg/l Mg. The drinking water of groups B and C was supplemented with 20 mM (SrCl2) and 20 mM (MgCl2), respectively. Once the 20 days of mineral supplementation had passed, arterial blood was extracted by puncture in the abdominal aorta. In the serum obtained after centrifugation, Ca, Mg, Sr and the total proteins (TP) were determined. Afterwards the serum was subjected to ultrafiltration. Concentrations of Ca, Mg and TP were measured in the obtained ultrafiltrates (u), with the above described techniques. The pH was measured before and after the ultrafiltration. The TP decreased significantly both in group B (supplemented with Sr), and in group C (supplement with Mg). Increases in Ca were found in group B and in Mg in group C. The Mg/Ca ratio increased 10% after the supplementation with Mg. At the ultrafiltrate a significant increase in Cau after supplementation with Sr and with Mg was observed. The Mgu/Cau ratio decreased 14% in the group supplemented with Sr and 38% after the supplementation with Mg. In conclusion, the supplementation with Sr (20 mM) in rats increases the Cau and could have the effect of reducing protein synthesis. These facts should be borne in mind when Sr is used for therapeutical purposes.  相似文献   
94.
The existence of duodeno-gastric reflux was evaluated in a group of 15 healthy subjects, in fasting and for 24 hours. The assessment of duodeno-gastric reflux was made by quantitation of the bile acids (BA) present in the gastric juice. The individual free and conjugated BA were separated and quantified by means of thin-layer chromatography and in situ spectrofluorometry. In 7 of the subjects studied no BA were detected, and in the other 8 subjects the BA levels were below 6 mumol reflux/hour. There were no free BA detected in any of the subjects. The levels of BA in gastric juice increased progressively with age, but there were no differences between sex. The chromatographic technique used is highly sensitive for the analysis of BA in biological samples. The study of BA in the gastric juice provides a quantitative and reliable assessment of the degree of duodeno-gastric reflux.  相似文献   
95.
96.
The potent rat-liver mitogen 4-acetylaminofluorene (4AAF) is shown here to provide an effective replacement for the surgical procedure of 2/3 partial hepatectomy (2/3PH) in the in vivo rat-liver micronucleus assay described by Tates and his colleagues. This protocol modification enables the assay to be conducted on a routine basis. Control observations for both 2/3PH and 4AAF-treated rats are presented, together with evidence indicating 4AAF itself to be without activity in the assay, irrespective of the mitogenic stimulus. The activities of the rat carcinogens DMN, 2AAF, DMH and 6BT, and of the non-carcinogens 4AAF and 4N are demonstrated. Recommendations for the conduct of the modified assay are made.  相似文献   
97.
98.
99.
100.
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