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   4022篇
  免费   301篇
  国内免费   80篇
耳鼻咽喉   58篇
儿科学   241篇
妇产科学   44篇
基础医学   520篇
口腔科学   257篇
临床医学   324篇
内科学   817篇
皮肤病学   159篇
神经病学   231篇
特种医学   194篇
外科学   636篇
综合类   51篇
现状与发展   1篇
预防医学   329篇
眼科学   79篇
药学   153篇
中国医学   2篇
肿瘤学   307篇
  2021年   39篇
  2020年   33篇
  2019年   40篇
  2018年   43篇
  2017年   45篇
  2016年   38篇
  2015年   41篇
  2014年   62篇
  2013年   91篇
  2012年   131篇
  2011年   165篇
  2010年   101篇
  2009年   101篇
  2008年   154篇
  2007年   209篇
  2006年   174篇
  2005年   171篇
  2004年   177篇
  2003年   164篇
  2002年   160篇
  2001年   185篇
  2000年   141篇
  1999年   131篇
  1998年   74篇
  1997年   84篇
  1996年   58篇
  1995年   54篇
  1994年   40篇
  1993年   33篇
  1992年   89篇
  1991年   97篇
  1990年   89篇
  1989年   96篇
  1988年   101篇
  1987年   78篇
  1986年   84篇
  1985年   95篇
  1984年   70篇
  1983年   72篇
  1982年   36篇
  1981年   33篇
  1980年   31篇
  1979年   46篇
  1978年   35篇
  1977年   35篇
  1976年   36篇
  1975年   39篇
  1974年   29篇
  1973年   40篇
  1970年   33篇
排序方式: 共有4403条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Background: Bupivacaine retards myocardial acidosis during ischemia. The authors measured function of rat isolated hearts after prolonged storage to determine whether bupivacaine improves cardiac protection compared with standard cardioplegia alone.

Methods: After measuring cardiac function on a Langendorff apparatus, hearts were perfused with cardioplegia alone (controls), cardioplegia containing 500 [mu]m bupivacaine, or cardioplegia containing 2 mm lidocaine; were stored at 4[degrees]C for 12 h; and were then reperfused. Heart rate and left ventricular developed pressures were measured for 60 min. Maximum positive rate of change in ventricular pressure, oxygen consumption, and lactate dehydrogenase release were also measured.

Results: All bupivacaine-treated, four of five lidocaine-treated, and no control hearts beat throughout the 60-min recovery period. Mean values of heart rate, left ventricular developed pressure, maximum positive rate of change in ventricular pressure, rate-pressure product, and efficiency in bupivacaine-treated hearts exceeded those of the control group (P < 0.001 at 60 min for all). Mean values of the lidocaine group were intermediate. Oxygen consumption of the control group exceeded the other groups early in recovery, but not at later times. Lactate dehydrogenase release from the bupivacaine group was less than that from the control group (P < 0.001) but did not differ from baseline.  相似文献   

5.
A juvenile animal model has been developed to study the growth potential of ileum in the urinary tract. Patch ileocystoplasties of known surface area were constructed in dogs of Group 1. Nonrefluxing ileal nipple valves of known length were created to replace one ureter in dogs of Group 2. After the juvenile animals grew and at minimum doubled their weight, they were reoperated and augmentation surface areas were remeasured at various physiologic intravesical pressures. Nipple valve lengths were remeasured after cystograms ruled out reflux. Results show that the bowel augmentation and an identical control segment increased in surface area proportionate to animal growth and that hydrostatic dilation caused further surface area increase. Nipple valves did not grow and in fact shortened, but remained nonrefluxing. The conclusion is that in the pediatric population, consideration should be given to downscaling the size of bladder augmentations or diversions in anticipation of future bowel growth, but that one should not shorten the ileal nipple valves.  相似文献   
6.
7.
Allogeneic hematopoietic stem cell transplantation (HSCT) is established therapy for selected patients with acute leukemia. After transplantation, antileukemic immune responses are believed to eliminate residual leukemia cells and decrease the likelihood of relapse. However, the clinical effect of successful antigen-specific immune reconstitution after HSCT on the likelihood of leukemic relapse and overall survival is not known. Pediatric recipients of unrelated cord blood transplants who underwent transplantation for acute leukemia were sequentially evaluated for their development of antigen-specific T-lymphocyte immunity to herpes viruses. The clinical effect of a positive antigen-specific response on relapse-free survival was determined. The presence of an antigen-specific response resulted in a relapse-free survival advantage (P = .0001), which was primarily due to a decrease in leukemic relapse (P = .003). Proportional hazards modeling for time to relapse and time to relapse or death defined 3 variables that were strongly associated with a poor outcome: female gender, poor remission status before transplantation, and negative antigen-specific T-lymphocyte proliferation. Notably neither acute nor chronic graft-versus-host disease had any effect on the incidence of leukemic relapse. Successful antigen-specific immune reconstitution after unrelated cord blood transplantation results in decreased leukemic relapse and improved overall survival.  相似文献   
8.
Spectral slope of vowels produced by tracheoesophageal speakers   总被引:1,自引:0,他引:1  
Spectra of vowels were analyzed to determine whether differences exist between the spectral slope of vowels produced by tracheoesophageal (TE) speakers and normal speakers and, if so, to quantify such differences. The linear predictive autocorrelation method was used to calculate smoothed spectra and the spectra were normalized with respect to a low frequency component. Comparisons between normalized spectral energy within a selected high frequency range revealed that energy within this frequency range for vowels produced by TE speakers was significantly higher than that produced by normal speakers. A least-square distance matching procedure was used to quantify speaker group differences in the spectral slope of vowels. Average spectra of vowels produced by the normal speakers could be matched to average spectra of vowels produced by the TE speakers by decreasing the spectral slope of their vowels by 2-3 dB/octave.  相似文献   
9.
This article describes how genetic components of disease susceptibility can be evaluated in case-control studies, where cases and controls are sampled independently from the population at large. Subjects are assumed unrelated, in contrast to studies of familial aggregation and linkage. The logistic model can be used to test collapsibility over phenotypes or genotypes, and to estimate interactions between environmental and genetic factors. Such interactions provide an example of a context where non-hierarchical models make sense biologically. Also, if the exposure and genetic categories occur independently and the disease is rare, then analyses based only on cases are valid, and offer better precision for estimating gene-environment interactions than those based on the full data.  相似文献   
10.
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