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   66622篇
  免费   5665篇
  国内免费   169篇
耳鼻咽喉   748篇
儿科学   1850篇
妇产科学   1365篇
基础医学   8625篇
口腔科学   1022篇
临床医学   7272篇
内科学   13830篇
皮肤病学   782篇
神经病学   6117篇
特种医学   2520篇
外科学   11241篇
综合类   790篇
现状与发展   1篇
一般理论   90篇
预防医学   6014篇
眼科学   1139篇
药学   4775篇
中国医学   45篇
肿瘤学   4230篇
  2023年   559篇
  2022年   966篇
  2021年   2324篇
  2020年   1240篇
  2019年   2014篇
  2018年   2407篇
  2017年   1721篇
  2016年   1744篇
  2015年   1925篇
  2014年   2775篇
  2013年   3354篇
  2012年   5266篇
  2011年   5188篇
  2010年   2721篇
  2009年   2339篇
  2008年   3793篇
  2007年   4039篇
  2006年   3473篇
  2005年   3181篇
  2004年   2892篇
  2003年   2503篇
  2002年   2266篇
  2001年   900篇
  2000年   936篇
  1999年   838篇
  1998年   511篇
  1997年   415篇
  1996年   361篇
  1995年   359篇
  1994年   309篇
  1993年   275篇
  1992年   582篇
  1991年   586篇
  1990年   559篇
  1989年   555篇
  1988年   512篇
  1987年   531篇
  1986年   473篇
  1985年   446篇
  1984年   395篇
  1983年   324篇
  1982年   265篇
  1981年   213篇
  1979年   300篇
  1978年   293篇
  1977年   208篇
  1976年   213篇
  1975年   206篇
  1974年   228篇
  1972年   215篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Cardiovascular disease (CVD), which includes myocardial infarction(MI), stroke, and peripheral vascular disease, remains the leading cause of death in the United States and in most developed countries. In the United States today, 25% of patients have metabolic syndrome-including those who have had a prior occlusive vascular disease event, those who are having an acute MI or ischemic stroke, and finally, the largest segment of the population,namely those who have not yet experienced a clinical CVD, but whose risks are substantial (10-year risk 10%). This article reviews the totality of evidence for aspirin in the treatment and prevention of CVD and emphasizes its importance as adjunctive therapy for patients with metabolic syndrome.  相似文献   
83.
Recently, a family tree with a predisposition for the gene of multiple endocrine neoplasia Type 1 has been identified in Tasmania. As the surgical identification and localisation of parathyroid adenomas is facilitated by the administration of methylene blue, an opportunity has presented to measure the plasma concentration of methylene blue and methaemoglobin production. The study was undertaken to establish whether significant methaemoglobin concentrations were generated during the infusion and whether these concentrations could be related to the corresponding methylene blue concentrations. Mean peak methylene blue concentrations of 3.72 micrograms l-1, mean percentage methaemoglobin of 10.0 and a PaO2 within acceptable clinical ranges were found. No apparent relationship between methylene blue concentration and methaemoglobin production was found.  相似文献   
84.
Although it has been demonstrated that many of the behavioral responses to psychomotor stimulants are gender dependent and hormonally sensitive, few studies have examined the possibility that the estrous cycle interacts with drug reinforcement in laboratory animals. The present experiment assessed the effect of the estrous cycle on two aspects of cocaine self-administration behavior: the breaking point on a progressive ratio (PR) schedule and the rate of cocaine intake on a fixed ratio one (FR1) schedule. On the PR schedule, the first lever response produced a drug infusion. Subsequent response requirements escalated with each injection until the behavior extinguished. Breaking points were defined as the final ratio completed. On a FR1 schedule, the estrous cycle had no effect on the rate of drug intake. On a PR schedule, female rats reached higher breaking points during estrus than during other stages of the estrous cycle. Furthermore, female rats displayed higher breaking points than male rats. It appears that the estrous cycle influences an animal's motivation to self-administer cocaine.  相似文献   
85.
86.
In situ cDNA:mRNA hybridization is a technique that has been developed for the visualization of cDNA:mRNA hybrids in individual cells. To use this technique to answer questions of regulation in heterogeneous populations of cells in the brain, it must be combined with other procedures allowing for the identification of functional subgroups of neurons. We report here a procedure by which in situ cDNA:mRNA hybridization may be combined with retrograde axonal tracing using the fluorescent tracer fast blue. Using this technique, it now becomes possible to measure mRNA regulation in functional subsets of cells defined by their axonal projections.  相似文献   
87.
88.
Reductions in serum levels of Gc globulin, a hepatically synthesized component of the extracellular actin scavenger system responsible for complexing circulating actin and attenuating intravascular microthrombus formation, are associated with poor outcome in acute liver failure. Clinically applicable assays of the important actin-free fraction (Af-Gc) have not been available until now. We measured actin-free Gc globulin levels with a novel, rapid assay in 61 cases of acute liver failure (ALF) and in 91 patients with cirrhosis (40 of whom were clinically unstable with extrahepatic organ dysfunction), and studied associations with liver dysfunction, extrahepatic organ dysfunction, indices of disseminated coagulation, and outcome. Reductions in Af-Gc levels mirrored hepatic dysfunction and organ dysfunction in both groups, and discriminated patients with poor prognosis from those with good prognosis in the ALF cohort. Levels were lowest in patients with ALF (10% of control values), but levels were also markedly reduced in both unstable (28%) and stable (44%) patients with cirrhosis. Associations with markers of disseminated intravascular coagulation were seen in both groups, most notably in the cirrhosis cohort, supporting a pathophysiological role for reduced Af-Gc in the evolution of organ dysfunction. In acetaminophen-induced ALF, Af-Gc identified patients with poor prognosis as well as did the Acute Physiology and Chronic Health Evaluation (APACHE II) score (area under the receiver operating characteristic curve, 0.7), and in cirrhosis, Af-Gc was an independent predictor of mortality by multifactorial analysis. In conclusion, the importance of Af-Gc reductions in the development of multiple organ dysfunction in ALF and cirrhosis is highlighted, probably resulting from reduced hepatic production and peripheral exhaustion of this arm of the extracellular actin scavenger system.  相似文献   
89.
The sentence production capabilities of young children undergo major changes during the same period in which grammar develops. This article reports data from a cross-sectional sample of 52 children between the ages of 1;10 (years; months) and 4;0, and looks specifically at the dichotomy between stalls, sentence disruptions that are the result of glitches in sentence production, and revisions, sentence disruptions that involve self-monitoring and the rapid replacement of words or morphosyntactic alternatives. It was found that revision rate increased with level of grammatical development, but that stall rate was not related to grammatical development. These results indicate that children's capacities for self-monitoring and maintenance of multiple linguistic alternatives increase during the period of grammatical development.  相似文献   
90.
Three years of daily alendronate treatment increases microdamage in vertebral bone but does not significantly increase it beyond levels of microdamage found after 1 yr of treatment. This suggests microdamage accumulation peaks during the early period of bisphosphonate treatment and does not continue to accumulate with longer periods of treatment. INTRODUCTION: Clinically relevant doses of alendronate increase vertebral microdamage by 4- to 5-fold in skeletally mature beagles after 1 yr of treatment. The goal of this study was to determine whether microdamage would continue to accumulate with 3 yr of alendronate treatment in an intact beagle dog model. MATERIALS AND METHODS: One-year-old female beagles were treated with daily oral doses of vehicle (VEH, 1 ml/kg/d) or alendronate (ALN, 0.2 or 1.0 mg/kg/d) for 3 yr. These ALN doses were chosen to approximate, on a milligram per kilogram basis, those used to treat osteoporosis (ALN0.2) and Paget's disease (ALN1.0). Microdamage accumulation, static and dynamic histomorphometry, densitometry, and mechanical properties of lumbar vertebrae were assessed. Comparisons were made among the three groups treated for 3 yr and also within each treatment group to animals treated under the same conditions for 1 yr. RESULTS: Overall microdamage accumulation (crack surface density) was not significantly higher in animals treated for 3 yr with either dose of ALN, whereas crack density increased significantly (100%; p < 0.05) with the higher dose of ALN compared with VEH. Both ALN doses significantly suppressed the rate of bone turnover (-60% versus VEH). There was no difference among groups for any of the structural biomechanical properties-ultimate load, stiffness, or energy absorption. However, when adjusted for areal BMD, ALN-treated animals had significantly lower energy absorption (-20%) compared with VEH. Toughness, the energy absorption capacity of the bone tissue, was significantly lower than VEH for both ALN0.2 (-27%) and ALN1.0 (-33%). Compared with animals treated for 1 yr, there was no significant difference in microdamage accumulation for either ALN dose. VEH-treated animals had significantly lower bone turnover (-58%) and significantly higher levels of microdamage (+300%) compared with values in 1-yr animals. Toughness was significantly lower in animals treated for 3 yr with ALN1.0 (-18%) compared with animals treated for 1 yr, whereas there was no difference in toughness between the two treatment durations for either VEH or ALN0.2. CONCLUSIONS: Although 3 yr of ALN treatment resulted in higher microcrack density in vertebral trabecular bone compared with control dogs, the amount of microdamage was not significantly higher than animals treated for 1 yr with similar doses. This suggests that bisphosphonate-associated increases in microdamage occur early in treatment. Because toughness continued to decline significantly over 3 yr of treatment at the higher ALN dose, decreases in toughness are probably not dependent on damage accumulation.  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