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   1639881篇
  免费   124644篇
  国内免费   3886篇
耳鼻咽喉   23613篇
儿科学   50175篇
妇产科学   47889篇
基础医学   233854篇
口腔科学   47297篇
临床医学   140126篇
内科学   322508篇
皮肤病学   34060篇
神经病学   131972篇
特种医学   66381篇
外国民族医学   490篇
外科学   257815篇
综合类   40368篇
现状与发展   2篇
一般理论   494篇
预防医学   123440篇
眼科学   38240篇
药学   119977篇
中国医学   3174篇
肿瘤学   86536篇
  2018年   15332篇
  2015年   15369篇
  2014年   22029篇
  2013年   33923篇
  2012年   45293篇
  2011年   47993篇
  2010年   28642篇
  2009年   27142篇
  2008年   45752篇
  2007年   49260篇
  2006年   49174篇
  2005年   48466篇
  2004年   46914篇
  2003年   45419篇
  2002年   44113篇
  2001年   71048篇
  2000年   72821篇
  1999年   61956篇
  1998年   17989篇
  1997年   16488篇
  1996年   16239篇
  1995年   15297篇
  1994年   14626篇
  1993年   13735篇
  1992年   50561篇
  1991年   48957篇
  1990年   47986篇
  1989年   46252篇
  1988年   43197篇
  1987年   42539篇
  1986年   40671篇
  1985年   39034篇
  1984年   29764篇
  1983年   25411篇
  1982年   15763篇
  1981年   14194篇
  1980年   13422篇
  1979年   29035篇
  1978年   20715篇
  1977年   17464篇
  1976年   16304篇
  1975年   17768篇
  1974年   21717篇
  1973年   20775篇
  1972年   19754篇
  1971年   18269篇
  1970年   17515篇
  1969年   16688篇
  1968年   15496篇
  1967年   14263篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
991.
Puncture wound osteochondritis of the foot caused by CDC group Vd.   总被引:4,自引:4,他引:0       下载免费PDF全文
A case of puncture wound osteochondritis of the foot caused by CDC group Vd is presented because of the unusual nature of the infecting organism. This organism may be confused with Pseudomonas aeruginosa, the usual pathogen responsible for this type of infection, but does not have a similar antimicrobial susceptibility profile. For this reason, it is important to obtain appropriate culture specimens and to identify and test the susceptibility of bacterial isolates from cases of puncture wound-associated osteochondritis so that optimal therapeutic regimens can be determined.  相似文献   
992.
J D Carroll  W H Gaasch 《Herz》1981,6(3):131-137
Following surgical correction of chronic aortic regurgitation, left ventricular (LV) volume falls to normal or near normal in most patients; this change generally occurs within the first week after surgery. During the ensuing six months, a significant regression of LV hypertrophy occurs, but most patients do not achieve a normal LV mass. The systolic ejection fraction may increase while the LV end-diastolic pressure almost uniformly falls to normal. Postoperative studies of LV volume mass and function should be aimed at identifying those patients which do not undergo these favorable changes so that medical therapy can be directed at this high risk group.  相似文献   
993.
994.
Symptoms of tobacco withdrawal. A replication and extension   总被引:19,自引:0,他引:19  
Smokers (n = 315) who wished to quit were randomly assigned in a double-blind manner to groups using either nicotine or placebo gum. Self-reported and observed symptoms of tobacco withdrawal were collected before cessation and at follow-ups of 1 to 2 weeks, 1 month, and 6 months. Self-reported and/or observed anger, anxiety, craving, difficulty concentrating, hunger, impatience, and restlessness were the most prominent symptoms of tobacco withdrawal. These symptoms had returned to precessation levels by 1 month except increased weight, hunger, and craving continued for 6 months in many smokers. Nicotine gum decreased most symptoms, including craving and hunger but not weight. Abstinent smokers with more intense withdrawal were not more likely to relapse. Abstinent smokers who gained more weight were less likely to relapse.  相似文献   
995.
Valve-related morbidity and mortality after heart valve replacement with the Hancock I porcine bioprosthesis has been retrospectively analyzed. From June 1974 through December 1976, 253 Hancock I bioprostheses (150 mitral and 103 aortic) were inserted in 220 selected patients who survived the operation and had follow-up until June 1989 (mean follow-up 13.5 years, with an accumulative follow-up of 2956.4 patient-years). One hundred seventeen patients had mitral valve replacement, 70 had aortic valve replacement, and 33 had combined mitral and aortic valve replacement. There were 27 thromboembolic events. The probability of being free from thromboembolism at 14 years was 81.0% +/- 7.4% for the mitral valve replacement group, 85.4% +/- 6.7% for the aortic group, and 67.1% +/- 18.4% for the mitral-aortic group. Fifteen episodes of prosthetic valve endocarditis occurred. There were 10 instances of nonstructural dysfunction (paravalvular leaks) in seven mitral valves (4.6%) and in three aortic valves (2.9%). One hundred twenty-two bioprostheses in 106 patients resulted in structural deterioration. The probability of freedom from structural deterioration at 14 years was 37.2% +/- 3.9% for the mitral group, 43.9% +/- 7.1% for the aortic group, and 30.1% +/- 8.9% for the mitral-aortic group. The logistic regression analysis between age at the time of operation and bioprosthetic life (structural deterioration-free period) demonstrates a linear regression curve (r = 0.53). There were 56 late deaths (27 patients died at reoperation). The actuarial survival rate (including hospital mortality) at 14 years was 57.2% +/- 5.4% for the entire series, with no statistically significant difference between groups. The probability of remaining free from valve-related morbidity and mortality at 14 years was 16.7% +/- 4.8% for the mitral group, 20.8% +/- 6.2% for the aortic group, and 14.0% +/- 7.0% for the mitral-aortic group. The long-term results of this series show that the clinical performance of the Hancock I porcine valve appears satisfactory during the first 6 years. The behavior of this bioprosthesis at 14 years' follow-up changes drastically, because only a minor group of patients is free from valve-related complications, justifying the restriction of its use for selected patients.  相似文献   
996.
997.
Brain, livers, and subcutaneous fat of 50 Cormorants (Phalacrocorax carbo sinensis, Blumenbach 1798) were analyzed for 6 PCB congeners. The birds had been shot in autumn 1985 and 1986 in Schleswig-Holstein, FRG. Subcutaneous fat was the highest contaminated tissue, while brain had accumulated the lowest concentrations. An accumulation by age was statistically significant between the groups of 1st year/2nd year birds and after 2nd year birds. There were no differences evident between sex and between weight groups. Pooled samples were analyzed by GC-MS; 61 congeners could be identified in adipose tissue, 54 in liver, and 49 in brain. 18 congeners were quantified in spotchecks, and some samples were analyzed by multidimensional gaschromatography. In comparison to fish they consume, the fat of cormorants was concentrated with PCBs 10–100 times more than marine fish, and 100–1,000 times more than freshwater fish. This species is a suitable bioindicator for PCBs.  相似文献   
998.
alpha 2-Adrenergic receptors (ARs) are involved in central nervous system (CNS) control of blood pressure. It is now known that there are three human genes that encode subtypes of alpha 2-ARs, but little is known regarding the distribution of these subtypes throughout the CNS. The availability of receptor clones allows the mapping of mRNAs encoding the individual alpha 2-AR subtypes in the CNS. In this communication, we report that there are three, closely related rat alpha 2-AR genes. We have developed subtype-specific hybridization probes from each of these genes and have used these reagents to measure alpha 2-AR subtype mRNA accumulation in extracts of discrete regions of the rat CNS. We found that mRNAs encoding the alpha 2A-AR and alpha 2C-AR subtypes are distributed widely, but unevenly, throughout the rat CNS. The A subtype is prominent in the midbrain, brainstem, spinal cord, pituitary and diencephalon while the C subtype predominates in basal ganglia and cerebellum. The cortex, olfactory bulb and hippocampus contain roughly equal amounts of the alpha 2A- and alpha 2C-AR mRNAs. A third subtype's (alpha 2B-AR) mRNA is far less abundant in brain tissues, and is only found in the diencephalon.  相似文献   
999.
1000.
We isolated cDNA clones from an Aplysia sensory-cell library encoding two isoforms of protein kinase C (PKC). Several isozyme-specific regions are conserved in the Aplysia kinases, notably the variable regions V5 in the Ca(2+)-dependent PKC (Apl I) and V1 in the Ca(2+)-independent PKC (Apl II). Neuronal proteins with the properties expected of these two isoforms can be identified with antibodies raised against peptides synthesized from the amino acid sequences deduced from the clones. Sacktor and Schwartz (1990) measured the proportion of kinase activity that can be translocated to membrane in Aplysia sensory neurons and ganglia by stimuli that produce the presynaptic facilitation underlying behavioral sensitization. Much less Apl I and Apl II are translocated, suggesting that still other isoforms of PKC exist in these cells.  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