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   8632篇
  免费   745篇
  国内免费   32篇
耳鼻咽喉   96篇
儿科学   296篇
妇产科学   347篇
基础医学   1232篇
口腔科学   164篇
临床医学   745篇
内科学   1870篇
皮肤病学   265篇
神经病学   881篇
特种医学   182篇
外国民族医学   1篇
外科学   1381篇
综合类   63篇
一般理论   5篇
预防医学   707篇
眼科学   175篇
药学   458篇
中国医学   33篇
肿瘤学   508篇
  2023年   56篇
  2022年   110篇
  2021年   215篇
  2020年   124篇
  2019年   224篇
  2018年   284篇
  2017年   185篇
  2016年   206篇
  2015年   257篇
  2014年   310篇
  2013年   356篇
  2012年   519篇
  2011年   564篇
  2010年   351篇
  2009年   312篇
  2008年   461篇
  2007年   513篇
  2006年   431篇
  2005年   397篇
  2004年   385篇
  2003年   337篇
  2002年   306篇
  2001年   227篇
  2000年   241篇
  1999年   218篇
  1998年   82篇
  1997年   80篇
  1996年   68篇
  1995年   65篇
  1994年   51篇
  1993年   37篇
  1992年   125篇
  1991年   123篇
  1990年   109篇
  1989年   106篇
  1988年   125篇
  1987年   91篇
  1986年   101篇
  1985年   69篇
  1984年   61篇
  1983年   45篇
  1982年   33篇
  1981年   34篇
  1980年   28篇
  1979年   44篇
  1978年   31篇
  1977年   34篇
  1976年   36篇
  1974年   44篇
  1973年   27篇
排序方式: 共有9409条查询结果,搜索用时 0 毫秒
41.
OBJECTIVES: To assess laparoscopic training curriculums in US Obstetrics and Gynecology residency programs. METHODS: A list of E-mail addresses was obtained for the accredited Obstetrics and Gynecology residency programs in the US from the CREOG Directory of Obstetric-Gynecologic Residency Programs and Directors. An E-mail survey containing 8 questions regarding laparoscopy training was sent to all residency directors with current E-mail addresses. RESULTS: Seventy-four residency directors responded to the survey for a response rate of 41%. Residency programs from all sections of the US were included in the study. Results of the survey indicate that 69% of residency programs had implemented a formal laparoscopy training program. At least half of the program directors surveyed stated that lack of faculty time and funds were the main barriers to laparoscopic surgery training. Seventy-two percent of those surveyed thought that in the future the health-care industry would demand proof of competency in laparoscopy as standard of care. CONCLUSIONS: Most US Obstetrics and Gynecology residency programs have implemented a formal laparoscopy training curriculum, use more than one method to train their residents, and involve almost half of their faculty on average in training residents to perform laparoscopic surgery.  相似文献   
42.
Malignant rhabdoid tumors are highly aggressive childhood tumors. Recently, all of the malignant rhabdoid tumors, whatever their location, have been related to the inactivation of the hSNF5/INI1 gene. A subset of cerebral tumors, associated with malignant rhabdoid tumors or isolated ones arising in siblings, showed similar molecular alterations. We report for the first time in monozygotic twins a congenital disseminated malignant rhabdoid tumor in one twin and a cerebellar tumor mimicking a medulloblastoma in the other. Molecular analysis revealed similar alterations for both tumors: a deletion of exon 7 of the hSNF5/INI1 gene in one allele, and a point mutation in the same exon in the other, suggesting a common genetic pathway. Analysis of constitutional DNA revealed a germline mutation. These findings are in favor of a common etiology for rhabdoid tumor and a subset of brain tumors developing in infancy.  相似文献   
43.
44.
45.
Subjective symptoms and experiences were explored within a group of 146 severe, chronic bronchitis and emphysema patients. Eighty-nine symptoms and experiences, derived from initial interviews with 29 patients, were rated according to the frequency of occurrence during breathing difficulties. Key cluster analyses were used to derive a Bronchitis-Emphysema Symptom Checklist (BESC) measuring 11 symptom categories: Helplessness-Hopelessness, Decathexis, Fatigue, Poor Memory, Peripheral-Sensory Complaints, Dyspnea, Congestion, Sleep Difficulties, Irritability, Anxiety, and Alienation. The BESC symptom categories are highly reliable and the relationships among categories are stable across two subgroups of patients. The BESC provides one way to describe how patients cope with and experience chronic bronchitis and emphysema.  相似文献   
46.
The density dependence of the maximum expiratory flow-volume curve, functional residual capacity (FRC), and specific airway conductance (SGaw) were determined before and during bronchial provocation with ragweed extract in 27 subjects with ragweed hypersensitivity and a history of either bronchial asthma (16 subjects) or allergic rhinitis (11 subjects). Mean baseline SGaw was significantly lower while mean volume of isoflow (Visov) and FrC were significantly higher in subjects with bronchial asthma. During antigen challenge, 10 of 16 subjects with bronchial asthma (63%) and five of 11 subjects with allergic rhinitis (45%) showed a greater than 35% decrease in SGaw ("reactors"): mean relative decreases in SGaw from baseline were 46% and 53%, respectively. The remaining subjects showed a less than 35% decrease in SGaw ("nonreactors") with mean relative decreases of 9% (allergic asthma) and 6% (allergic rhinitis). Mean Visov increased in all subjects with bronchial asthma and in eight of 11 subjects with allergic rhinitis. A significant increase in FRC (6%) was seen only in the "reactors" with bronchial asthma. Following antigen challenge, the beta adrenergic agonist, isoetharine, increased SGaw and decreased Visov. We conclude that in asymptomatic subjects with ragweed hypersensitivity, (1) central and peripheral airway function is more abnormal in subjects with bronchial asthma than in subjects with allergic rhinitis, (2) subjects of both groups show quantitatively and qualitatively comparable airway responses during antigen challenge with a decrease in SGaw or an increase in Visov, possibly representing increase in central and/or peripheral airflow resistance, respectively, (3) Visov may be a more sensitive indicator of airway response to antigen challenge than SGaw, and (4) the bronchodilator effects of a beta adrenergic agonist on antigen-induced bronchospasm are similar in both groups.  相似文献   
47.
The insulin-deficient state induces profound changes in bile formation. The present work was to test the effect of acute insulin administration on lipid secretion into bile in diabetic rats. Diabetes was induced by streptozotocin injection (6 mg/100 g body-weight, i.p., 6 days before the experiments). Bile formation was stimulated by taurocholate infusion (0.5 mumol/min/100 g body-weight). Intravenous administration of insulin (bolus: 100 mU/100 g body-weight, plus infusion: 5 mU/min/100 g body-weight) induced choleresis accompanied by a slight and transient enhancement in bile acid output which was similar to that found in lecithin and cholesterol output in the control group. However, insulin induced a rapid and significant (P less than 0.05) reduction in biliary lipid output in the diabetic rats. These results suggest that insulin may play an important role in mechanisms other than synthesis involved in the supply of biliary lipids towards the canaliculi.  相似文献   
48.
This study first investigates the effects of mash diet, or mash supplemented with either 2.5% mannose-oligosaccharide (MOS) or palm kernel meal (PKM), on the microflora of the hen caecal contents. Second, it investigates the effect of caecal contents of hens (HCC) fed mash or mash supplemented with MOS or PKM on the major microflora groups of chicks, and their inhibitory effect on Salmonella enterica serovar Enteritidis (PT4) colonization. Finally, this study investigates the effect over time of diets supplemented with MOS or PKM on S. Enteritidis colonization and the microflora of chicks. In hens, supplemented diets increased Bifidobacterium spp., while decreasing members of Enterobacteriaceae and Enterococcus spp., compared with the mash diet. Chicks dosed with the HCC showed, on average, increased numbers of anaerobes, while the numbers of aerobes decreased including coliforms and S. Enteritidis compared with controls without HCC. In chicks fed the MOS-supplemented or PKM-supplemented diets, S. Enteritidis colonization decreased over time, compared with mash alone. Four-week-old PKM birds showed an increase in Bifidobacterium spp. and Lactobacillus spp., with a decrease in S. Enteritidis compared with week 2. Generally, the HCC and diets supplemented with MOS or PKM affected the birds intestinal microflora by increasing the Bifidobacterium spp. and Lactobacillus spp., while decreasing the Enterobacteriaceae groups. They also reduced susceptibility in young chickens to colonization by S. Enteritidis.  相似文献   
49.
Summary. We have previously reported on the use of a tobacco mosaic virus (TMV) vector TMV-30B to express foreign viral antigens for use as experimental immunogens. Here we describe the development of an improved TMV-30B vector that adds a sequence of 7 histidine residues to the C-terminus of recombinant proteins expressed in the vector. We used this TMV-30B-HISc vector to express the VP8* fragment of the VP4 protein from bovine rotavirus (BRV) strain C-486 in plants. Recombinant VP8* protein was purified from N. benthamiana leaves at 7 days post-inoculation by immobilized metal affinity chromatography. The plant-produced VP8* was initially detected using anti-His tag mAb and its antigenic nature was confirmed using both monoclonal and polyclonal specific antisera directed against BRV. Adult female mice, inoculated by the intraperinoteal route with an immunogen containing 4µg of recombinant VP8*, developed a specific and sustained response to the native VP8* from the homologous BRV. Eighty five percent of suckling mice from immunized dams that were challenged with the homologous virus at the fifth day of age were protected from virus as compared to 35% of the pups from mothers immunized with a control protein. These results demonstrate that the plant-produced VP8* was able to induce passive protection in the new born through the immunization of dams. This suggests that the technology presented here provides a simple method for using plants as an inexpensive alternative source for production of recombinant anti-rotavirus antigens.Authors contributed equally to the results presented in this report.  相似文献   
50.
Loss of cell polarity causes severe brain dysplasia in Lgl1 knockout mice   总被引:13,自引:0,他引:13  
Disruption of cell polarity is seen in many cancers; however, it is generally considered a late event in tumor progression. Lethal giant larvae (Lgl) has been implicated in maintenance of cell polarity in Drosophila and cultured mammalian cells. We now show that loss of Lgl1 in mice results in formation of neuroepithelial rosette-like structures, similar to the neuroblastic rosettes in human primitive neuroectodermal tumors. The newborn Lgl1(-/-) pups develop severe hydrocephalus and die neonatally. A large proportion of Lgl1(-/-) neural progenitor cells fail to exit the cell cycle and differentiate, and, instead, continue to proliferate and die by apoptosis. Dividing Lgl1(-/-) cells are unable to asymmetrically localize the Notch inhibitor Numb, and the resulting failure of asymmetric cell divisions may be responsible for the hyperproliferation and the lack of differentiation. These results reveal a critical role for mammalian Lgl1 in regulating of proliferation, differentiation, and tissue organization and demonstrate a potential causative role of disruption of cell polarity in neoplastic transformation of neuroepithelial 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