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   2093篇
  免费   203篇
  国内免费   14篇
耳鼻咽喉   20篇
儿科学   47篇
妇产科学   25篇
基础医学   359篇
口腔科学   35篇
临床医学   283篇
内科学   471篇
皮肤病学   39篇
神经病学   241篇
特种医学   43篇
外科学   251篇
综合类   40篇
一般理论   1篇
预防医学   182篇
眼科学   34篇
药学   156篇
中国医学   3篇
肿瘤学   80篇
  2022年   18篇
  2021年   47篇
  2020年   11篇
  2019年   33篇
  2018年   30篇
  2017年   36篇
  2016年   30篇
  2015年   37篇
  2014年   46篇
  2013年   74篇
  2012年   119篇
  2011年   130篇
  2010年   77篇
  2009年   82篇
  2008年   109篇
  2007年   121篇
  2006年   105篇
  2005年   125篇
  2004年   108篇
  2003年   89篇
  2002年   102篇
  2001年   38篇
  2000年   50篇
  1999年   47篇
  1998年   29篇
  1997年   24篇
  1996年   18篇
  1995年   12篇
  1994年   18篇
  1993年   17篇
  1992年   40篇
  1991年   40篇
  1990年   28篇
  1989年   25篇
  1988年   23篇
  1987年   34篇
  1986年   41篇
  1985年   35篇
  1984年   27篇
  1983年   30篇
  1980年   13篇
  1979年   13篇
  1978年   14篇
  1977年   13篇
  1976年   10篇
  1975年   10篇
  1972年   10篇
  1971年   11篇
  1969年   13篇
  1968年   10篇
排序方式: 共有2310条查询结果,搜索用时 15 毫秒
21.
An 18- to 20-nm virus particle was isolated from the Olson strain of quail bronchitis, an avian adenovirus. On density gradient separation the small virions were primarily found at densities of 1.39 and 1.42 g/cm(3). The majority of the infectious particles were at the heavier density. The virus had a hexagonal outline and contained single-stranded deoxyribonucleic acid. It was resistant to heating at 56 C for more than an hour and was not inactivated by treatment with chloroform or low pH. Purified virus did not agglutinate erythrocytes of various avian and mammalian species. Replication of the small particles occurred either in chicken embryos or in cultures of embryo kidney cells coinfected with an adenovirus helper. Antigenically the virus was distinct from the adeno-associated viruses types 1, 2, 3, and 4. The virus is the avian equivalent of the adeno-associated viruses of primates and lower animals.  相似文献   
22.
Alcohol and physical inactivity are risk factors for a variety of cancer types. However, alcohol use often co-occurs with physical activity (PA), which could mitigate the cancer-prevention benefits of PA. Alcohol is integrated into the culture of one of the most popular physical activities for adults in the United States (U.S.), golf. This study examined how alcohol use was associated with total PA, golf-specific PA, and motives for golfing in a national sample of golfers in the U.S. Adult golfers (n = 338; 51% male, 81% White, 46 ± 14.4 years) self-reported alcohol use, golfing behavior and motives, and PA. Most (84%) golfers consumed alcohol, averaging 7.91 servings/week. Golf participation, including days/week, holes/week, and practice hours/week, was not associated with alcohol use. Golfers with stronger social motives were 60% more likely to consume alcohol. Weekly walking (incident risk ratio (IRR) = 7.30), moderate-to-vigorous PA (MVPA; IRR = 5.04), and total PA (IRR = 4.14) were associated with more alcohol servings/week. Golfers’ alcohol use may be higher than the general adult population in the U.S. and contributes 775 extra kilocalories/week, a surplus that may offset PA-related energy expenditure and cancer-protective effects. Alcohol use interventions targeting golfers may facilitate weight loss and reduce cancer risk, especially for golfers motivated by social status.  相似文献   
23.
Complete genomic screen in Parkinson disease: evidence for multiple genes.   总被引:28,自引:1,他引:27  
CONTEXT: The relative contribution of genes vs environment in idiopathic Parkinson disease (PD) is controversial. Although genetic studies have identified 2 genes in which mutations cause rare single-gene variants of PD and observational studies have suggested a genetic component, twin studies have suggested that little genetic contribution exists in the common forms of PD. OBJECTIVE: To identify genetic risk factors for idiopathic PD. DESIGN, SETTING, AND PARTICIPANTS: Genetic linkage study conducted 1995-2000 in which a complete genomic screen (n = 344 markers) was performed in 174 families with multiple individuals diagnosed as having idiopathic PD, identified through probands in 13 clinic populations in the continental United States and Australia. A total of 870 family members were studied: 378 diagnosed as having PD, 379 unaffected by PD, and 113 with unclear status. MAIN OUTCOME MEASURES: Logarithm of odds (lod) scores generated from parametric and nonparametric genetic linkage analysis. RESULTS: Two-point parametric maximum parametric lod score (MLOD) and multipoint nonparametric lod score (LOD) linkage analysis detected significant evidence for linkage to 5 distinct chromosomal regions: chromosome 6 in the parkin gene (MLOD = 5.07; LOD = 5.47) in families with at least 1 individual with PD onset at younger than 40 years, chromosomes 17q (MLOD = 2.28; LOD = 2.62), 8p (MLOD = 2.01; LOD = 2.22), and 5q (MLOD = 2.39; LOD = 1.50) overall and in families with late-onset PD, and chromosome 9q (MLOD = 1.52; LOD = 2.59) in families with both levodopa-responsive and levodopa-nonresponsive patients. CONCLUSIONS: Our data suggest that the parkin gene is important in early-onset PD and that multiple genetic factors may be important in the development of idiopathic late-onset PD.  相似文献   
24.
CONTEXT: The human tau gene, which promotes assembly of neuronal microtubules, has been associated with several rare neurologic diseases that clinically include parkinsonian features. We recently observed linkage in idiopathic Parkinson disease (PD) to a region on chromosome 17q21 that contains the tau gene. These factors make tau a good candidate for investigation as a susceptibility gene for idiopathic PD, the most common form of the disease. OBJECTIVE: To investigate whether the tau gene is involved in idiopathic PD. DESIGN, SETTING, AND PARTICIPANTS: Among a sample of 1056 individuals from 235 families selected from 13 clinical centers in the United States and Australia and from a family ascertainment core center, we tested 5 single-nucleotide polymorphisms (SNPs) within the tau gene for association with PD, using family-based tests of association. Both affected (n = 426) and unaffected (n = 579) family members were included; 51 individuals had unclear PD status. Analyses were conducted to test individual SNPs and SNP haplotypes within the tau gene. MAIN OUTCOME MEASURE: Family-based tests of association, calculated using asymptotic distributions. RESULTS: Analysis of association between the SNPs and PD yielded significant evidence of association for 3 of the 5 SNPs tested: SNP 3, P =.03; SNP 9i, P =.04; and SNP 11, P =.04. The 2 other SNPs did not show evidence of significant association (SNP 9ii, P =.11, and SNP 9iii, P =.87). Strong evidence of association was found with haplotype analysis, with a positive association with one haplotype (P =.009) and a negative association with another haplotype (P =.007). Substantial linkage disequilibrium (P<.001) was detected between 4 of the 5 SNPs (SNPs 3, 9i, 9ii, and 11). CONCLUSIONS: This integrated approach of genetic linkage and positional association analyses implicates tau as a susceptibility gene for idiopathic PD.  相似文献   
25.
Notfall + Rettungsmedizin - Der Europäische Rat für Wiederbelebung hat diese Leitlinie –&nbsp;Basismaßnahmen zur Wiederbelebung&nbsp;– auf Grundlage des...  相似文献   
26.
Archives of Sexual Behavior - Gender variance is a broad term used to describe gender non-conforming behaviors. Past studies have used the parental response to Child Behavior Checklist (CBCL) Item...  相似文献   
27.
Serum and/or plasma samples from 360 Whites and 126 Blacks were assayed for activity of the lysosomal hydrolase α-N-acetyl-D-glucosaminidase (NAG). The samples from the Blacks had an increased mean (0.50 nm/ml/min) and standard deviation (0.30 nm/ml/min) compared to those from the Whites (0.29 nm/ml/min and 0.10 nm/ml/min, respectively). After loge transformation and admixture analysis, it was possible to demonstrate the presence of 3 distributions of NAG activity in Blacks and at least 2 in Whites. Segregation analysis of the NAG activity of 29 White half-sib twin families indicated that a genetic model for the inheritance of NAG activity provided a better fit (P < 0.01) with the data than the “environmental” model. Thus, the study suggests the presence of a genetic polymorphism for NAG activity in Black and White populations. The presence of alleles for high and low NAG activity in the normal population could lead to incorrect interpretation of serum carrier tests for Sanfilippo syndrome, type B.  相似文献   
28.
Effects of β-adrenoceptor agonists and antagonists have been examined on open/total arm entry ratio (OTR) over a wide range of doses in the rat elevated X-maze 'anxiety' model. For clenbuterol, terbutaline and adrenaline, OTR was reduced only at doses at or above those reducing total entries; dobutamine was inactive. Neither the β(1)-adrenoceptor antagonist metoprolol nor the β( 2)-adrenoceptor antagonist ICI 118,551 affected OTR or total entries. The peripherally acting β(1)-antagonist practolol was also inactive. The elevated X-maze therefore does not appear to detect β-adrenoceptor-mediated changes in 'anxiety'. Among the β-adrenoceptor antagonists which also bind to 5-HT(1) receptors, sotalol and timolol were inactive but restricted doses of alprenolol (0.1 mg/kg) and pindolol (0.1-0.25 mg/kg) caused an anxiolytic-like increase in OTR while propranolol (5-10 mg/kg) and pindolol (1.0 mg/kg) reduced OTR without affecting total entries. These effects may be attributable to the activity of these agents at 5-HT( 1) receptors. Since metoprolol (3.0 mg/kg) and ICI 118,551 (1.0 mg/kg) did not alter the fall in OTR caused by the selective 5-HT(1A) agonist 8-OH-DPAT, the antagonism of this fall by alprenolol (0.5 mg/kg), pindolol (0.5 mg/kg), propranolol (3.0 mg/kg) and timolol (3.0 mg/kg) is most likely to represent a 5-HT(1) receptor antagonist effect of these agents.  相似文献   
29.
RX336-M (7,8-dihydro-5',6'-dimethylcyclohex-5'-eno-1',2',8',14 codeinone) induced a complex of simultaneous rapid movements of body parts accompanied by a single squeak-vocalization, which occurred at irregular intervals, when injected i.p. in mice. The complex included whole body jerks and head-shakes and its frequency was dose dependent between 0.1 and 20 mg/kg. Frequency after a 5 mg/kg dose was reduced by haloperidol (0.5-10 mg/kg, i.p.), ritanserin (0.1-10 mg/kg, i.p.) and ICI 169,369 (2.0 mg/kg, i.p.), suggesting the possible involvement of 5-HT(2A) and/or dopamine receptors. The possible relevance of the behavioural effects of RX336-M to the tics and vocalization of Tourette's syndrome is discussed.  相似文献   
30.
Effects of water deprivation and restraint were compared in the rat elevated X-maze. Water deprivation for 12–48 h increased corticosterone and had a duration-dependent anxiolytic effect in the elevated X-maze, increasing the ratio of open/total arm entries (OTR) and the proportion of time spent on the open arms (% time) without affecting total entries. Brain 5HIAA/5HT was increased only after 24 or 48 h deprivation. Restraint for 15 min also increased plasma corticosterone and brain 5HIAA/5HT but had no effect on behaviour in the elevated X-maze when rats were tested immediately afterwards. However, 1 h restraint was anxiogenic in the elevated X-maze immediately after release, reducing OTR and % time, but with a less consistent reduction in total entries; reductions in OTR and % time were still present 24 h later. The 5HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (0.1–0.2 mg/kg), administered 10 min before testing in the elevated X-maze, had anxiogenic actions in non-stressed rats. The effect of 0.1 mg/kg 8-OH-DPAT was not significantly altered by 24 or 48 h water deprivation but was abolished by restraint for 1 h immediately beforehand, despite the anxiogenic effect of restraint alone. Similar mutual antagonism of 8-OH-DPAT and restraint occurred when the dose of 8-OH-DPAT was increased to 0.2 mg/kg. Twenty-four hours after restraint, restrained rats which had received 8-OH-DPAT (0.1–0.2 mg/kg) still did not show any significant anxiogenic effect compared with non-restrained vehicle treated controls. Restraint-induced deficits in elevated X-maze exploration may prove a useful model with which to study the pharmacology of depression-related anxiety. However, the effects of the stressors examined, and their interaction with 8-OH-DPAT in the elevated X-maze, appear to depend on the nature of the stressor.  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