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   19349篇
  免费   1265篇
  国内免费   67篇
耳鼻咽喉   171篇
儿科学   419篇
妇产科学   478篇
基础医学   2891篇
口腔科学   710篇
临床医学   2202篇
内科学   4050篇
皮肤病学   352篇
神经病学   1834篇
特种医学   510篇
外科学   2034篇
综合类   115篇
一般理论   9篇
预防医学   1845篇
眼科学   285篇
药学   1511篇
  1篇
中国医学   104篇
肿瘤学   1160篇
  2024年   21篇
  2023年   189篇
  2022年   254篇
  2021年   511篇
  2020年   312篇
  2019年   537篇
  2018年   705篇
  2017年   508篇
  2016年   549篇
  2015年   708篇
  2014年   794篇
  2013年   1105篇
  2012年   1653篇
  2011年   1673篇
  2010年   807篇
  2009年   672篇
  2008年   1232篇
  2007年   1246篇
  2006年   1174篇
  2005年   1117篇
  2004年   1083篇
  2003年   978篇
  2002年   885篇
  2001年   188篇
  2000年   158篇
  1999年   136篇
  1998年   103篇
  1997年   92篇
  1996年   108篇
  1995年   77篇
  1994年   52篇
  1993年   51篇
  1992年   75篇
  1991年   70篇
  1990年   66篇
  1989年   56篇
  1988年   47篇
  1987年   51篇
  1986年   57篇
  1985年   56篇
  1984年   65篇
  1983年   44篇
  1982年   43篇
  1981年   52篇
  1980年   37篇
  1979年   26篇
  1978年   23篇
  1977年   19篇
  1975年   19篇
  1972年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Several genes with an essential role in the regulation of eating behavior and body weight are considered candidates involved in the etiology of eating disorders (ED), but no relevant susceptibility genes with a major effect on anorexia nervosa (AN) or bulimia nervosa (BN) have been identified. Brain-derived neurotrophic factor (BDNF) has been implicated in the regulation of food intake and body weight in rodents. We previously reported a strong association of the Met66 allele of the Val66Met BDNF variant with restricting AN (ANR) and low minimum body mass index in Spanish patients. Another single nucleotide polymorphism located in the promoter region of the BDNF gene (-270C>T) showed lack of association with any ED phenotype. In order to replicate these findings in a larger sample, we performed a case-control study in 1142 Caucasian patients with ED consecutively recruited in six different centers from five European countries (France, Germany, Italy, Spain and UK) participating in the 'Factors in Healthy Eating' project. We have found that the Met66 variant is strongly associated to all ED subtypes (AN, ANR, binge-eating/purging AN and BN), and that the -270C BDNF variant has an effect on BN and late age at onset of weight loss. These are the first two variants associated with the pathophysiology of ED in different populations and support a role for BDNF in the susceptibility to aberrant eating behaviors.  相似文献   
102.
Vascular dementia appears rarer than previously thought, but the contribution of vascular lesions to cognitive impairment in Alzheimer's disease (AD) affected patients (mixed dementias) is now recognized as frequent. The role of strategic areas of the brain involved in the cognitive decline induced by vascular lesions and their relative contributions to the severity of the dementing process remain poorly understood. We determined the relationship between the severity of clinical dementia and the volume of different brain areas affected by infarcts in a prospective clinicopathological study in elderly patients. A volumetric study of the functional zones of Mesulam's human brain map affected by vascular lesions was made and correlations between quantified neuropathological data and the severity of dementia were performed in cases with large vascular lesions only, pure AD, and both lesions. The severity of cognitive impairment was significantly correlated with the total volume of infarcts but in a multi-variate model the volume destroyed in the limbic and heteromodal association areas, including the frontal cortex and in the white matter explained 50% of the variability in MMSE and GDS. The total volume of ischemic lesions explained only 0.1-5% of the variability in MMSE and GDS. Age only explained an extra of 0.1-1.6%. This study confirms that infarcts located in strategic areas have a role in the mechanism of cognitive impairment and brings a key for their quantification. It may be useful for developing neuropathological criteria in multi-infarct and mixed dementias.  相似文献   
103.
PURPOSE: To assess the educational impact of Accreditation Council for Graduate Medical Education resident work-hour limits implemented in July 2003. METHOD: All trainees in all 76 accredited programs at two large teaching hospitals were surveyed between May and June 2003 (before work-hour reductions) and then between May and June 2004 (after work-hour reductions) about hours, education, and fatigue. Based on changes in weekly duty hours, 13 programs experiencing substantial reduction in hours were classified into a reduced-hours group. Differences in assessments of educational endpoints before and after policy implementation by trainees in the reduced-hours group were compared with those in other programs to control for potential temporal trends, using two-way ANOVA with interaction. RESULTS: The number of respondents was 1,770 (60% response rate). The reduced-hours group reported a significant decrease in time spent directly caring for patients (from 48.5 to 42.3 mean h/wk, P = 0.03), but the volume of important clinical experiences, including procedures, was preserved, as was the sense of clinical preparedness. On 22 questions related to educational quality and adequacy, only three differences in differences were significant, with the reduced-hours group reporting a relative increase in opportunities for research, decrease in quality of faculty teaching, and decrease in educational satisfaction. The percentage of trainees reporting frequent negative effects of fatigue dropped more in the reduced-hours programs than in the other programs (P < 0.05). CONCLUSION: This study shows that it may be possible to reduce residents' hours--and the perceived adverse impact of fatigue--while generally preserving the self-assessed quality, quantity, and outcomes of graduate medical education.  相似文献   
104.
Malaria, a major endemic tropical disease, is caused by the infection of blood cells by Plasmodium protozoa. Most patients control their parasitemia by a not fully understood spleen-dependent mechanism. SDF-1alpha is a chemokine produced by stromal cells such as reticular spleen cells. Nitric oxide (NO) has several immune functions, including killing of intracellular pathogens and its function in malaria is debated. We have previously shown that SDF-1alpha production peaks during the ascending parasitemia in Plasmodium chabaudi infection and its supplementation in lethal models could reduce the parasitemia. In the present study, we analyzed SDF-1 production by spleen cells as related to NO metabolism in the P. chabaudi rodent malaria model using IFN-gamma; TNFR and iNOS-knockout mice or iNOS-blocked, L-NAME- or aminoguanidine-treated mice. Parasitemia and production of SDF-1alpha and SDF-1beta were determined by RT-PCR. In vitro NO production by spleen adherent cells was also tested. The data showed that parasitemia was less intense in both iNOS(-/-) or NO-inhibited mice than in controls, with increased and long-lasting production of SDF-1alpha mRNA. In the absence of cytokines involved in the final regulation of NO production by effector cells, as is the case for TNFR(-/-) and GKO mice, the infection progressed in an uncontrolled manner regardless of SDF-1alpha production, suggesting that these cytokines must be involved in the control of parasitemia after the SDF-1alpha dependent process. The SDF-1beta isoform was constitutive in all experiments, with elevated levels only clearly seen in TNFR(-/-) mice. We conclude that SDF-1 is involved in the promotion of parasitemia control in malaria, and excessive NO could affect its production.  相似文献   
105.
X-linked severe combined immunodeficiency (X-SCID) is a rare, life-threatening immune disorder, caused by mutations in the gamma c chain gene, which encodes an essential component of the cytokine receptors for interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21. A 13-month-old boy with recurrent infections who had reduced serum immunoglobulin levels and decreased numbers of CD3, CD16/56 cells was evaluated for gamma c chain gene mutation and protein expression. The patient had a C-to-T point mutation at nucleotide position 690, one of the hot spots, resulting in a single amino acid substitution of cysteine for arginine (R226C), as determined by direct sequencing and PCR-RFLP. The patient's mother was a heterozygous carrier. Percutaneous umbilical cord blood sampling was performed at the 6-month of gestation in a subsequent pregnancy. As the immunophenotype of the fetus showed an identical pattern, the pregnancy was terminated and genetic analysis of the abortus confirmed recurrence. This is the first report of the molecular diagnosis of X-SCID in Korea. Genetic analysis of the gamma c chain gene is useful for definite diagnosis and genetic counseling for X-SCID.  相似文献   
106.
107.
Proliferation of ovarian stromal cells is a common phenomenon in peri- and post-menopausal ovaries. It is generally assumed to be secondary to the rise in circulating gonadotrophins at the menopause, though the process by which it occurs is poorly understood. This study aimed to examine the effect of menopausal levels of pituitary gonadotrophins on the growth of primary cultures of ovarian stroma. A culture system was developed using primary explants of ovarian stroma on a collagen substrate. The effect of follicle stimulating hormone (FSH; 10(-5) g/l) and luteinizing hormone (LH; 10(-5) g/l) on the proliferation of cultures derived from the cortices and medullae of ten ovaries was evaluated using a dual radiothymidine labelling technique. FSH was stimulatory to cortical cultures from 9/10 ovaries and medullary cultures from 7/10 ovaries, while LH was stimulatory to cortical cultures from 6/9 ovaries and medullary cultures from 5/10 ovaries. The responsiveness of the cultures did not correlate with the degree of hyperplasia in vivo. This study demonstrates that pituitary gonadotrophins may modulate the growth of stromal cells in culture, and thus may play a role in the process whereby stromal proliferation occurs in peri- and post-menopausal ovaries.  相似文献   
108.
PURPOSE: This study is part of an ongoing National Cancer Institute multidisciplinary, etiologically-focused, cross-sectional study of Familial Testicular Cancer (FTC). The current report targets interest in clinical genetic testing for susceptibility to FTC. METHODS: Demographics, knowledge, health beliefs, and psychological and social factors were evaluated as covariates related to interest in genetic testing. RESULTS: The majority (66%) of 229 participants (64 affected men, 66 unaffected men, and 99 women) from 47 multiple-case FTC families expressed interest in having a genetic test within 6 months, should such a test become available. Interest was similar among the three subgroups mentioned above. Worries about insurance discrimination based on genetic test results were associated with a significantly lower interest in testing. Alternatively, participants were more likely to be interested in genetic testing if they were younger and had higher levels of family support, a physician's recommendation supporting testing, cancer distress, and a need for information to inform the health care of their children. CONCLUSIONS: This study reveals social and relationship factors that FTC survivors and their relatives considered important when contemplating the use of new genetic technologies. This is the first study describing hypothetical interest in genetic testing for familial testicular cancer.  相似文献   
109.
Fresh and processed cashew (Anacardium occidentale) apple juice (CAJ) are among the most popular drinks in Brazil. Besides their nutritional benefits, these juices have antibacterial and antitumor potential. The chemical constituents of both the fresh juice and the processed juice (cajuina) were analyzed and characterized as complex mixtures containing high concentrations of vitamin C, various carotenoids, phenolic compounds, and metals. In the present study, these beverages exhibited direct and rat liver S9-mediated mutagenicity in the Salmonella/microsome assay with strains TA97a, TA98, and TA100, which detect frameshifts and base pair substitution. No mutagenicity was observed with strain TA102, which detects oxidative and alkylating mutagens and active forms of oxygen. Both CAJ and cajuina showed antioxidant activity as determined by a total radical-trapping potential assay. To test whether this antioxidant potential might result in antimutagenesis, we used a variation of the Salmonella/microsome assay that included pre-, co-, and posttreatment of hydrogen peroxide-exposed Salmonella typhimurium strain TA102 with the juices. CAJ and cajuina protected strain TA102 against mutation by oxidative damage in co- and posttreatments. The antimutagenic effects during cotreatment with hydrogen peroxide may be due to scavenging free radicals and complexing extracellular mutagenic compounds. The protective effects in posttreatment may be due to stimulation of repair and/or reversion of DNA damage. The results indicate that CAJ and cajuina have mutagenic, radical-trapping, antimutagenic, and comutagenic activity and that these properties can be related to the chemical constituents of the juices.  相似文献   
110.
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