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   16507篇
  免费   1375篇
  国内免费   510篇
耳鼻咽喉   173篇
儿科学   284篇
妇产科学   385篇
基础医学   2126篇
口腔科学   326篇
临床医学   1927篇
内科学   2947篇
皮肤病学   314篇
神经病学   1126篇
特种医学   662篇
外国民族医学   3篇
外科学   1994篇
综合类   1293篇
一般理论   2篇
预防医学   1089篇
眼科学   445篇
药学   1472篇
  5篇
中国医学   387篇
肿瘤学   1432篇
  2024年   40篇
  2023年   180篇
  2022年   445篇
  2021年   635篇
  2020年   348篇
  2019年   445篇
  2018年   444篇
  2017年   396篇
  2016年   401篇
  2015年   574篇
  2014年   668篇
  2013年   717篇
  2012年   1170篇
  2011年   1228篇
  2010年   730篇
  2009年   622篇
  2008年   906篇
  2007年   874篇
  2006年   837篇
  2005年   790篇
  2004年   714篇
  2003年   607篇
  2002年   546篇
  2001年   489篇
  2000年   413篇
  1999年   422篇
  1998年   163篇
  1997年   164篇
  1996年   189篇
  1995年   159篇
  1994年   114篇
  1993年   91篇
  1992年   201篇
  1991年   190篇
  1990年   162篇
  1989年   139篇
  1988年   132篇
  1987年   111篇
  1986年   106篇
  1985年   104篇
  1984年   77篇
  1983年   70篇
  1982年   57篇
  1981年   55篇
  1980年   47篇
  1979年   60篇
  1978年   50篇
  1977年   33篇
  1975年   27篇
  1974年   43篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The 16-year old girl studied here had ambiguous external genitalia, ie, enlarged clitoris, pseudo vagina, and rudiments of Wolffian tubes. Her karyotype was 46,XY and she was H-Y antigen-positive. In spite of absence of gonadal tissue, genital virilization suggests presence of testes during embryogenesis. This patient is compared to 20 others with testicular regression from the literature. Autosomal-recessive inheritance of this condition is proposed.  相似文献   
42.
We report a case of papillary carcinoma arising in a thyroglossal duct cyst, presenting with an anterior neck mass of a 31-year-old woman. The tumor was judged to be a primary lesion on the basis of intraoperative examination of the thyroid and pathologic findings of the mass. One year later, a small nodular mass in the left thyroid gland and lymph node enlargement of the right cervical lymph node were noted by follow-up imaging studies. Total thyroidectomy, right modified radical neck dissection and central neck dissection were performed. The thyroid gland revealed nodular hyperplasia without evidence of malignancy. On the other hand, the dissected neck lymph nodes revealed metastatic papillary carcinoma. Taken together, these findings suggested the tumor was a primary papillary carcinoma arising in the thyroglossal duct cyst.  相似文献   
43.
BACKGROUND: Matrix metalloproteinase-9 (MMP-9) is capable of degrading elastin, whereas tissue inhibitor of metalloproteinase-1 (TIMP-1) can inhibit MMP-9 activity. We observed reduced airway tissue elastin volume density in six subjects with nocturnal asthma (NA) as compared with seven subjects with nonnocturnal asthma (NNA) and seven normal controls (NL) when endobronchial biopsies were evaluated morphometrically at 4:00 PM and 4:00 AM. OBJECTIVE: We hypothesized that increased metalloproteinases and decreased tissue inhibitors of metalloproteinases in the airways of subjects with NA may be responsible for reduced elastin volume density. METHODS: Ten additional subjects with NA, 10 subjects with NNA, and 7 normal control subjects underwent bronchoscopy with bronchoalveolar lavage at 4:00 PM and 4:00 AM. Levels of MMP-2, MMP-9, TIMP-1, and TIMP-2 were determined in bronchoalveolar lavage by enzyme-linked immunosorbent assay. RESULTS: There was a fourfold circadian increase in bronchoalveolar lavage levels of MMP-9, and there was a twofold increase in MMP-9:TIMP-1 ratio in NA subjects from 4:00 PM to 4:00 AM. There were no circadian changes in the NNA and NL subjects. At 4:00 AM, MMP-9 levels and the MMP-9:TIMP-1 ratio were highest in NA subjects. At 4:00 PM, no significant group differences were observed. The MMP-9 levels positively correlated with the overnight fall in forced expiratory volume in 1 second and the MMP-9/TIMP-1 ratio negatively correlated with the 4:00 AM % predicted forced expiratory volume in 1 second. CONCLUSIONS: Our results from these two pilot studies suggest that increased MMP-9 and decreased TIMP-1 at night in NA may lead to reduced elastin density.  相似文献   
44.
The effect of selected UV stabilizers on the stability of mechanical properties of a polyurethane material, Calthane ND2300, was evaluated. The addition of UV stabilizers prolonged the service life of the systems studied but did not achieve completely satisfactory results. The tensile strength and modulus of elasticity decreased after extended exposure to UV. The rate of decrease, however, was much less for the specimens with UV stabilizers. The polyurethane system that contains a mixture of a UV stabilizer and an antioxidant is considered to be the best of the groups tested, in terms of the percentage of retention of tensile strength and modulus of elasticity. It was also found that elongation at break was increased when the duration of UV aging was increased. This phenomenon occurred in all the systems, with or without UV stabilizers, and can be understood in terms of the concepts of the fragmentation of macromolecules that resulted from UV aging. The physical appearance in conjunction with mechanical property tests are needed to ensure the successful performance of any UV stabilizer.  相似文献   
45.
血糖感应型胰岛素给药智能载体的研究进展   总被引:1,自引:0,他引:1  
胰岛素控制释放高分子载体系统一直是国内外科技工作者的研究热点 ,迄今已经研究报道了多种具有不同工作原理的血糖感应型胰岛素给药智能载体。本文基于国内外大量研究文献 ,综述了血糖感应型胰岛素控制释放智能化高分子载体的研究进展。  相似文献   
46.
The emergence of ciprofloxacin-resistant Salmonella enterica serovar Choleraesuis in recent years has become an important public health issue in Taiwan. The resistant strains that cause human infections are considered to be from pigs. In this study, we characterized 157 swine and 42 human Salmonella serovar Choleraesuis isolates by pulsed-field gel electrophoresis (PFGE) and drug susceptibility testing to investigate the epidemiologic relationship among the isolates. By PFGE analyses, two major clusters (clusters GA and GB) were identified. Isolates in cluster GA were of both human and swine origins, while those in cluster GB were from pigs only. Among the various genotypes identified, genotype gt-1a was the most prevalent, which was found in 71% (30 of 42) and 48% (76 of 157) of human and swine isolates, respectively. The susceptibility tests for the 106 gt-1a isolates identified 44 susceptibility profiles and showed that 73% of human isolates and 34% of swine isolates were resistant to three fluoroquinolones (ciprofloxacin, enrofloxacin, and norfloxacin). Our findings indicate that a clonal group of Salmonella serovar Choleraesuis may have been circulating in human and swine populations in Taiwan for years and that the fluoroquinolone-resistant Salmonella serovar Choleraesuis strains most likely evolved from a gt-1a clone that emerged in 2000 and that then caused widespread infections in humans and pigs. Nevertheless, it is still debatable whether those Salmonella infections in humans are caused by isolates derived from pigs, on the basis of the higher fluoroquinolone and other antimicrobial resistance percentages in human isolates than in pig isolates.  相似文献   
47.
During Drosophila neural development, neuroblasts delaminate from the neuroectoderm of each hemisegment in a stereotypic orthogonal array of five rows and three columns (ventral, intermediate, and dorsal). Prevailing evidence indicates that the individual neuroblast fate is determined by the domain-specific expression of genes along the dorsoventral and anteroposterior axis. Here, we analyze the role of Vnd, a NK-2 homeodomain protein, expressed initially in the ventral neuroectoderm adjacent to the ventral midline, in the dorsoventral patterning of the neuroectoderm and the neuroblasts. We show that in vnd null mutants most ventral neuroblasts do not form and the few that form do not develop ventral fates, but instead develop intermediate-like fates. Furthermore, we demonstrate that Vnd influences the gene expression patterns in the ventral proneural clusters and neuroectoderm, and that its action in neuroblast formation includes, but is not exclusive to the activation of proneural AS-C genes. Through the use of GAL4/UAS gene-expression system we show that ectopic Vnd expression can promote ventral-like fates in intermediate and dorsal neuroblasts and can suppress certain normal characteristics of the intermediate and dorsal neuroectoderm. Our results are discussed in the context of the current evidence in dorsoventral patterning in the Drosophila neuroectoderm.  相似文献   
48.
胡萝卜籽挥发油的抗生育作用   总被引:3,自引:0,他引:3  
胡萝卜籽挥发油对小鼠有抗着床,抗早、中和晚期妊娠作用。对大鼠也有抗着床作用。挥发油中的萜类碳氢化合物部位,对小鼠皮下注射抗早期妊娠的ED_(50)为2.9ml/kg,甲地孕酮和hCG能明显逆转其作用;对假孕小鼠蜕膜瘤有抑制作用,此作用不能被甲地孕酮拮抗,皮下注射于早孕大鼠24、48小时后血浆孕酮浓度明显下降。以上提示其抗早孕作用机制可能与抑制孕酮合成和蜕膜反应有关。此外,挥发油碳氢部分无雌激素和抗雌激素活性,低浓度时对早孕大鼠离体子宫的收缩活动没有影响,高浓度则表现抑制作用。  相似文献   
49.
A Y Chu  W Lopatin 《Clinical chemistry》1986,32(9):1666-1671
Pattern recognition techniques--discriminant analysis and principal component analysis--are utilized in selecting the wavelengths for monitoring, by reflectance spectroscopy, color-generating reactions involving uric acid and cholesterol in serum. The data base we used was accumulated by a rapid-scanning reflectance spectrophotometer that measured reflectance at 16 wavelengths every 5 s after the reaction was initiated. The data were then analyzed in multidimensional space mainframe computer with commercial statistical software packages. The most appropriate wavelengths were those that yielded the largest generalized distance between analyte concentration by discriminant analysis and the largest weighting coefficient by principal component analysis. For uric acid, taking the ratio of reflectance measured at two wavelengths instead of at a single wavelength much better separates the clinically significant concentrations. For cholesterol, the initiated. The data were then analyzed in multidimensional space hemoglobin, can be clearly demonstrated y the "pattern" generated with principal component analysis. generalized distance between analyte generalized distance between analyte concentration by discriminant  相似文献   
50.
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