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   37956篇
  免费   3576篇
  国内免费   19篇
  41551篇
  2022年   247篇
  2021年   556篇
  2020年   318篇
  2019年   432篇
  2018年   507篇
  2017年   462篇
  2016年   771篇
  2015年   1209篇
  2014年   1412篇
  2013年   1858篇
  2012年   2205篇
  2011年   2313篇
  2010年   1453篇
  2009年   1387篇
  2008年   2046篇
  2007年   2096篇
  2006年   1989篇
  2005年   2050篇
  2004年   1959篇
  2003年   1932篇
  2002年   1856篇
  2001年   461篇
  2000年   266篇
  1999年   417篇
  1998年   521篇
  1997年   373篇
  1996年   372篇
  1995年   308篇
  1994年   340篇
  1993年   321篇
  1992年   296篇
  1991年   273篇
  1990年   270篇
  1989年   239篇
  1988年   263篇
  1987年   244篇
  1986年   226篇
  1985年   310篇
  1984年   394篇
  1983年   324篇
  1982年   384篇
  1981年   443篇
  1980年   417篇
  1979年   255篇
  1978年   263篇
  1977年   279篇
  1976年   266篇
  1975年   181篇
  1974年   235篇
  1973年   194篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
RHINOVIRUSES AND RESPIRATORY DISEASE   总被引:2,自引:1,他引:1       下载免费PDF全文
  相似文献   
122.
William Addleman 《CMAJ》1964,91(18):946-951
There is a proper time to advise removal of the colon and creation of a permanent ileostomy in the course of progressive toxic ulcerative colitis. When a thorough trial of medical therapy, including corticosteroids, has failed to halt progression of the disease, a properly timed colectomy may give the patient a new lease on life and enable him to maintain himself socially and economically.The development of ileostomy (Q-T) clubs has been an important factor in preparing them for and sustaining these young patients through the psychological trauma of an ileostomy. Two patients are described who illustrate the value of properly timed surgery and the contribution that ileostomy clubs can make.  相似文献   
123.
124.
125.
Atrial or ventricular myocardium from patients with surgically corrected rheumatic valvular disease was studied for rheumatic lesions in 86 cases. Histologically active Aschoff bodies were found in 20 per cent of the cases. A slight, but statistically not significant relationship was demonstrated in comparison of elevated serologic tests for rheumatic activity with the presence of Aschoff bodies.  相似文献   
126.
Anhidrotic ectodermal dysplasia in an inbred kindred was observed in three sisters and three first cousins. This was interpreted as presumptive evidence for autosomal recessive inheritance and it is suggested that in addition to its known genes, anhidrotic ectodermal dysplasia occasionally may be caused by an autosomal recessive gene.This investigation was supported by Public Health Service Research Grant No. FR 00123, from GCRC-DRFR and by a Fellowship in Pediatric Teratology of the Children's Hospital Research Foundation, Cincinnati.  相似文献   
127.
A study of 10 infants in severe metabolic acidemia (pH below 7) led to the conclusion that the clinical signs—hyperventilation, coma or lethargy, peripheral vascular collapse, a significantly palpable liver, and abdominal distension—may all be directly related to the metabolic acidemia. In five of 10 infants, an initial erroneous diagnosis of congestive heart failure or pneumonia was made. Dramatic clinical improvement followed correction of the acidemia with rapid intravenous administration of sodium bicarbonate. This rapid administration of sodium bicarbonate was safe, provided hypocalcemia was recognized and treated in its early stages. In severe metabolic acidemia the measurement of blood bicarbonate alone does not reflect adequately the magnitude of the acid-base derangement and repeated measurements of hydrogen ion concentration, Pco2 and bicarbonates are needed to evaluate and treat such infants correctly.  相似文献   
128.
Critchfield , William B. (Pacific SW Forest & Range Expt. Sta., Berkeley, Calif.) Leaf dimorphism in Populus trichocarpa. Amer. Jour. Bot. 47 (8) : 699–711. Illus. 1960.—In Populus trichocarpa and other species of Populus, each tree bears 2 kinds of leaves, referred to here as “early” and “late” leaves. Both leaf types are present on all long shoots. They differ in many features of external morphology, including petiole length, size and occurrence of marginal glands, venation, and stomatal distribution. This type of foliar dimorphism has its origins in a pronounced difference in leaf ontogeny. The early leaves originate in the developing bud and overwinter as embryonic leaves. The first late leaves are also present in the winter bud, but as arrested primordia, and succeeding late leaves are initiated at the tip of the growing shoot and develop uninterruptedly to maturity during the growing season. A similar correlation between leaf form and the circumstances of leaf ontogeny appears to be a common feature of many other instances of heterophylly. The expansion of the pre-formed early leaves is almost completed by late spring, when the first late leaves begin to grow rapidly. The formation of late leaves may then continue until late in the season. The rapid elongation of the stem does not begin until the first late leaves expand. Elongation is restricted to shoots producing late leaves. Consequently, the early leaves are confined to short shoots and the base of long shoots; adventitious shoots and the upper part of long shoots bear only late leaves. Certain other woody plants with long and short shoots also exhibit a restriction of elongation to those shoots on which a second set of leaves is produced.  相似文献   
129.
130.
N.A.T.O. Babies     
William W. Coppinger 《CMAJ》1960,82(4):202-212
  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