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   1026819篇
  免费   82350篇
  国内免费   2774篇
耳鼻咽喉   13246篇
儿科学   35199篇
妇产科学   29045篇
基础医学   150410篇
口腔科学   28722篇
临床医学   94398篇
内科学   200307篇
皮肤病学   23479篇
神经病学   81534篇
特种医学   40320篇
外国民族医学   305篇
外科学   155648篇
综合类   24032篇
一般理论   401篇
预防医学   80772篇
眼科学   23092篇
药学   73464篇
  4篇
中国医学   2076篇
肿瘤学   55489篇
  2018年   11041篇
  2017年   8705篇
  2016年   9984篇
  2015年   11522篇
  2014年   15970篇
  2013年   24157篇
  2012年   30062篇
  2011年   31847篇
  2010年   19794篇
  2009年   18806篇
  2008年   29729篇
  2007年   31229篇
  2006年   31857篇
  2005年   30472篇
  2004年   29742篇
  2003年   28496篇
  2002年   27498篇
  2001年   47355篇
  2000年   48413篇
  1999年   40817篇
  1998年   11952篇
  1997年   10807篇
  1996年   10900篇
  1995年   10485篇
  1994年   9687篇
  1993年   9032篇
  1992年   32789篇
  1991年   31956篇
  1990年   31459篇
  1989年   30409篇
  1988年   27726篇
  1987年   27864篇
  1986年   25928篇
  1985年   25147篇
  1984年   18895篇
  1983年   16019篇
  1982年   9841篇
  1981年   8878篇
  1979年   17305篇
  1978年   12673篇
  1977年   10781篇
  1976年   10141篇
  1975年   10521篇
  1974年   12624篇
  1973年   12151篇
  1972年   11183篇
  1971年   10378篇
  1970年   9585篇
  1969年   8923篇
  1968年   8286篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
The dietary history method was used to determine the total energy and macronutrient intake, the distribution of daily energy from the different meals and the energy contribution of various food groups, in a population of 299 boys, aged between 10 and 15 years. The effects of age, the social status of the father (SPS), the ponderal index, the importance of breakfast or lunch, and the level of energy intake on dietary indicators, were studied. In our population, energy intake increased with increasing age but the energy contribution of macronutrients did not vary. The diet of boys whose fathers were in the upper SPS classes differed from the diet of those boys whose fathers were manual workers: for example they consumed less energy and pastries, but more animal protein (in percentage of energy intake), more dairy products, and more fruit. The ponderal index was negatively related to energy intake but positively related to protein intake, especially from meat and meat products. The energy intake from protein, animal protein and the energy contribution of dairy products, meat and meat products, fish and vegetables was lower among large eaters than among small eaters. The energy contribution of pastries, sugar and sweets was higher among large eaters.
Similarily, the energy intake from morning and evening snacks was also higher among large eaters. It should be noted that boys who had a substantial breakfast took in less energy from all other meals (including snacks and main meals). Such informaton is necessary in order to develop an effective health programme.  相似文献   
983.
For certain genetic conditions DNA testing identifies carriers and determines the risk status of foetuses, thus helping parents to make more informed prenatal decisions. Data, collected from three genetic centres in England and Wales from August 1986 to July 1990, are used to describe trends in demand for DNA testing, the impact of DNA tests on carrier risk assessment, and the use of DNA tests in relation to pregnancy outcome. Altogether the data include 23,388 subjects and 681 pregnancies in 8738 families divided into five cohorts by year of entry and referral. The most frequent gene disorders referred to the genetic centres are currently being tested or will soon be tested. For these disorders the initial high level of activity has declined and may have reached steady state. Demand for DNA services is high for cystic fibrosis and Duchenne muscular dystrophy, intermediate for Huntington's disease, and low for adult polycystic kidney disease, phenylketonuria and tuberous sclerosis. Based on these findings we suggest that demand for DNA tests will be high in serious, untreatable and slow progressing conditions with early onset; intermediate for conditions affecting intellect and neurological integrity with later onset; and low for treatable, late-onset conditions, or those for which there is evidence of heterogeneity, and variable penetrance. It would be helpful to assess the extent to which this view of demand is confirmed when the new disorders being DNA tested are considered and for the pattern of activity of DNA testing for some types of cancer. Since no DNA centre could offer a fully comprehensive testing service, it is recommended that a structure is created to audit overall activity, assist in policy formulation, and influence supraregional service organisation, in order that the spread of DNA services be planned as effectively as possible. This structure would facilitate monitoring of the evolution of contract specifications agreed by commissioners and providers on a regional basis.  相似文献   
984.
In this paper, data are presented on the in situ demineralization of human enamel as a function of the demineralization period. To quantify the mineral loss parameters versus time, it is important to obtain information on the kinetics, and thus on the mechanism of dental caries. The results show that for in situ enamel demineralization, the lesion depth as well as the mineral loss parameter both vary linearly with the demineralization time. This is in contrast to in vitro lesion formation where the third power, or the square power of the lesion depth is linearly related to the demineralization time. In in situ demineralization, the rate-determining step of the demineralization process is the inhibitor-controlled dissolution process at the enamel crystallite surfaces, while the inhibitor content (F-, proteins etc.) in the lesion originating from the plaque, saliva and enamel is high. Furthermore, the study indicates that in in situ demineralization, interprismatic mineral loss is very important.  相似文献   
985.
986.
The pulmonary intravascular macrophages (PIMs) have been described in several species of animals. This study demonstrates for the first time that the equine lung has PIMs as resident phagocytes in its microvasculature. Their salient features such as globular surface coat, structures of the endocytic pathway, and related cell organelles closely resemble those of the calf, goat, and sheep. The exquisite organization of the coat globules in the form of a linear chain was structurally similar to the lipolytic lipase and the heparin-sensitive globular coat from PIMs of calf, goat, and sheep. Monastral blue (MB) when employed as a tracer to assess the phagocytic properties of equine PIMs induced similar modification of the globules of the coat into lipid droplets, reminiscent of neutral lipids. Lipids droplets (modified coat globules) were delivered into acid phosphatase-positive endosomes and lysosomes. Concurrently, the unaltered globules of the coat, probably internalized via fluid-phase constitutive pinocytoses, followed a different endocytic pathway. Large-scale platelet uptake by the PIMs was observed with thrombocytopenia in MB-treated ponies. The possible significance of hypothetical LDL-coat and the endocytic organelles as equivalents of synthetic apparatus of vasoactive lipids in the PIMs of horse needs to be assessed in future studies.  相似文献   
987.
988.
After treatment with two lateral percutaneous pins, 80 children with grade II-III supracondylar elbow fractures were reviewed. The result was good in 55 patients (68%) and was the same for extension- and flexion-type injuries. These patients had less than 10 degrees change in carrying angle and less than 20 degrees total change in range of motion. This method eliminates risk of iatrogenic injury to the ulnar nerve but is technically very demanding. Redisplacement, joint penetration, and damage to the capitellar side of growth plate can be avoided only by positioning the pins divergently.  相似文献   
989.
990.
The short section of the urethra that passes through the urogenital diaphragm is termed the membranous urethra. It is accompanied by several vessels and nerve fibers. In surgery on the membranous urethra the perineal body is of crucial importance, and precise knowledge of the course of the urethra through the pelvic floor is essential. Furthermore, the relationship between the membranous urethra and its accompanying structures is of great importance. These include the branches of the internal pudendal artery, the prostatic venous plexus and the cavernous nerves coursing ventrally from the pelvic plexus. The nerves supplying the membranous urethra were studied in fetuses with the help of a magnifying lens. The results of the dissections are documented by histological sections, photographs and paintings.  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