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   50399篇
  免费   4594篇
  国内免费   32篇
  55025篇
  2022年   365篇
  2021年   763篇
  2020年   454篇
  2019年   572篇
  2018年   704篇
  2017年   654篇
  2016年   1047篇
  2015年   1764篇
  2014年   1950篇
  2013年   2560篇
  2012年   3243篇
  2011年   3292篇
  2010年   2134篇
  2009年   1913篇
  2008年   2719篇
  2007年   2833篇
  2006年   2757篇
  2005年   2639篇
  2004年   2547篇
  2003年   2414篇
  2002年   2320篇
  2001年   559篇
  2000年   475篇
  1999年   629篇
  1998年   738篇
  1997年   555篇
  1996年   476篇
  1995年   435篇
  1994年   414篇
  1993年   442篇
  1992年   487篇
  1991年   424篇
  1990年   411篇
  1989年   398篇
  1988年   371篇
  1987年   339篇
  1986年   357篇
  1985年   380篇
  1984年   470篇
  1983年   382篇
  1982年   488篇
  1981年   498篇
  1980年   392篇
  1979年   325篇
  1978年   339篇
  1977年   296篇
  1976年   331篇
  1975年   228篇
  1974年   281篇
  1973年   272篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A method for the selective degradation of polysaccharides containing uronic acid residues is described. It involves methylation of hydroxyl and carboxyl groups, base-catalysed elimination, and mild hydrolysis with acid. The degraded product is etherified with trideuteriomethyl or ethyl groups and hydrolysed, and the resulting mixture of etherified sugars is analysed, as the alditol acetates, by g.l.c.—m.s. Comparison of this analysis with the methylation analysis of the original polysaccharide gives information on the nature of the sugar residues on either side of the uronic acid residue.  相似文献   
142.
Studies on platelet proteins. IX. The identity of fibrinogen   总被引:1,自引:0,他引:1  
  相似文献   
143.
A simple and safe procedure has been described for the preparation of short-chain aliphatic hydroxamic acids in quantities as large as 1 mole and as small as 0.01 mole. The procedure is equally suitable for the preparation of isotopically labeled hydroxamates, as has been demonstrated in the case of 1-14C-acetohydroxamic acid and 3H-acetohydroxamic acid. Some physical and chemical characteristics, including infrared spectra of formo-, aceto-, propiono-, and isobutyro-hydroxamic acids prepared by this method have been described.  相似文献   
144.
145.
The histories of 117 patients with left axis deviation and complete right bundle branch block (rbbb) on the electrocardiogram were reviewed for evidence of clinical cardiac disease, hypertension or emphysema. One hundred fifty-four patients with complete right bundle branch block alone served as controls. The incidence of coronary artery disease (myocardial infarction or angina) was significantly greater in the group with pronounced left axis deviation; the other factors evaluated showed no significant difference between the two groups. Pronounced left axis deviation of the mean qrs axis is associated with a high prevalence of clinical coronary artery disease. The presence of complete right bundle branch block does not alter their relationship. Some patients with complete rbbb, or with rbbb and pronounced left axis deviation, have no clinical evidence of heart disease.  相似文献   
146.
Although Dupuytren''s contracture was first described more than 300 years ago, the cause is not yet certainly known. It is only agreed that the disease process affecting the palmar fascia is most commonly found in older-aged males of Caucasian descent.Conservative or non-surgical treatment is usually ineffective. Surgical treatment includes fasciotomy, partial fasciectomy and total fasciectomy. Fasciotomy is indicated for localized disease or for patients with medical conditions which preclude more extensive operation. Subtotal fasciectomy with or without skin graft is the most commonly employed procedure. Total palmar fasciectomy is seldom indicated. Improved function of the hand can be anticipated after adequate surgical intervention.  相似文献   
147.
148.
Relationship Between Amino Sugars and Meat Microbial Quality   总被引:5,自引:2,他引:3       下载免费PDF全文
The amino sugar content of spoiling beef increased with the microbial count and appeared to be responsible for the increased hydration capacity of spoiled meats.  相似文献   
149.
150.
An automated follow-up register for the detection of iatrogenic thyroid disease has been established as a joint venture between the general practitioners in the north-east of Scotland and the thyroid clinic of Aberdeen General Hospitals.The data-processing operations in the system are handled by an International Computers Limited 4/50 computer. Patients are followed up at predetermined intervals and the system has been designed to process, screen, and store clinical and biochemical follow-up data and report results to the patients, general practitioners, and the hospital records department.  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