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   5386篇
  免费   520篇
  国内免费   13篇
耳鼻咽喉   94篇
儿科学   269篇
妇产科学   177篇
基础医学   868篇
口腔科学   70篇
临床医学   791篇
内科学   1106篇
皮肤病学   74篇
神经病学   333篇
特种医学   211篇
外国民族医学   2篇
外科学   547篇
综合类   83篇
一般理论   12篇
预防医学   583篇
眼科学   47篇
药学   346篇
中国医学   3篇
肿瘤学   303篇
  2022年   41篇
  2021年   83篇
  2020年   45篇
  2019年   76篇
  2018年   95篇
  2017年   62篇
  2016年   84篇
  2015年   90篇
  2014年   95篇
  2013年   136篇
  2012年   212篇
  2011年   226篇
  2010年   124篇
  2009年   120篇
  2008年   255篇
  2007年   236篇
  2006年   213篇
  2005年   200篇
  2004年   224篇
  2003年   201篇
  2002年   191篇
  2001年   183篇
  2000年   213篇
  1999年   149篇
  1998年   91篇
  1997年   65篇
  1996年   56篇
  1995年   68篇
  1994年   60篇
  1993年   58篇
  1992年   144篇
  1991年   132篇
  1990年   128篇
  1989年   136篇
  1988年   121篇
  1987年   110篇
  1986年   105篇
  1985年   117篇
  1984年   71篇
  1983年   67篇
  1982年   47篇
  1981年   49篇
  1979年   67篇
  1978年   58篇
  1977年   57篇
  1976年   44篇
  1975年   40篇
  1974年   66篇
  1973年   44篇
  1970年   41篇
排序方式: 共有5919条查询结果,搜索用时 15 毫秒
101.
OBJECTIVE: To examine incidence and progression of retinopathy using retinal photographs in Pima Indians and to compare the results with those obtained when retinopathy is assessed by direct ophthalmoscopy. RESEARCH DESIGN AND METHODS: We undertook an analysis of examinations conducted between 1 April 1982 and 31 December 1990 in residents of the Gila River Community in central Arizona. Data were taken from 411 people with diabetes who had at least two examinations during this period. Incidence and progression of retinopathy were evaluated by retinal photography and fundoscopy, and hazard rate ratios were calculated for various potential risk factors measured at baseline. RESULTS: Previously diagnosed retinopathy tended to progress, except in individuals with minimal nonproliferative retinopathy, among whom follow-up examinations were more likely to show no retinopathy. Diabetes duration (hazard rate ratio [HRR], 1.06 per year difference [P = 0.007]), hyperglycemia (HbA(1) HRR, 1.27 per 1% difference [P < 0.0001]), the type of treatment for diabetes (insulin use HRR, 3.06 [P = 0.0007], and oral hypoglycemic use HRR, 2.40 [P = 0.0034], compared with individuals on no pharmacotherapy), and macroalbuminuria (HRR, 2.86, compared with individuals without macroalbuminuria [P = 0.0486]) were associated with the development of retinopathy. Although fundoscopy detected fewer cases of retinopathy, HRRs for most risk factors were similar when retinopathy was assessed by fundoscopy rather than retinal photography. CONCLUSIONS: Although retinopathy tends to worsen over time, some eyes show improvement, especially in patients with minimal nonproliferative retinopathy. As in other populations, glycemic control is the major modifiable risk factor for the development and progression of retinopathy.  相似文献   
102.
103.
We tested 190 Klebsiella pneumoniae bloodstream isolates recovered from 189 patients in 30 U.S. hospitals in 23 states to determine the occurrence of extended-spectrum beta-lactamase (ESBL) and AmpC beta-lactamase producers. Based on growth inhibition by clavulanic acid by disk and MIC test methods, 18 (9.5%) of the isolates produced ESBLs. Although the disk diffusion method with standard breakpoints identified 28 cefoxitin-nonsusceptible isolates, only 5 (18%) of these were confirmed as AmpC producers. Of two AmpC confirmatory tests, the three-dimensional extract test was easier to perform than was the double-disk approximation test using a novel inhibitor, Syn2190. Three of the five AmpC producers carried the bla(FOX-5) gene, while the other two isolates harbored the bla(ACT-1) gene. All AmpC genes were transferable. In vitro susceptibility testing with standard inocula showed that all five AmpC-producing strains were susceptible to cefepime, imipenem, and ertapenem but that with a high inoculum, more of these strains were susceptible to the carbapenems than to cefepime. All but 1 of 14 screen-positive AmpC nonproducers (and ESBL nonproducers) were susceptible to ceftriaxone and cefepime at the standard inoculum as were 6 of 6 isolates that were randomly selected and tested with a high inoculum. These results indicate that (i). a significant number of K. pneumoniae bloodstream isolates harbor ESBL or AmpC beta-lactamases, (ii). confirmatory tests are necessary to identify true AmpC producers, and (iii). in vitro, carbapenems are active against AmpC-producing strains of K. pneumoniae.  相似文献   
104.
The preparation of clovanes 4, 5, 6, 8, and 9, which bear different levels of oxidation on ring C, is described for the first time. The biotransformation of compounds 5, 6, and 9 by the fungus Botrytis cinerea is investigated, yielding compounds 10, 11, and 12, which are described for the first time, together with compounds 4-6, 8, and 9. The evaluation of the fungistatic activity against B. cinerea of compounds 6, 9, 12, 18, 19, 20, and 21 is reported. Comparison of these results with previously published data shows first that the inclusion of hydroxyl groups on ring C leads to a decrease in the biological activity and, second, that the presence of a 9alpha-hydroxyl group and an alkyl chain at C-2 plays an important role in the fungistatic activity against B. cinerea of compounds with a clovane skeleton.  相似文献   
105.
Less than 20 years elapsed between the 1982 report of the identification and isolation of Borrelia burgdorferi and the licensure and marketing in the USA of a prophylactic vaccine against this pathogen. However, the manufacturer removed the vaccine from the market under 4 years after its release. The low demand undoubtedly was the result of limited efficacy, need for frequent boosters, the high price of the vaccine, exclusion of children, fear of vaccine-induced musculoskeletal symptoms and litigation surrounding the vaccine. Second-generation polyvalent outer surface protein (Osp)C vaccines may overcome some of these concerns but the precise antigenic components required for efficacy are uncertain. The development of the next generation of Lyme disease vaccines is in its infancy.  相似文献   
106.
While the concept of advanced practice nursing (APN) is still relatively new, distinct patterns of evolution from specialty practice to advanced practice nursing are evident over the last 100 years. The purpose of this article is to describe 3 stages in this evolutionary process, as well as discuss several internal and external issues that represent challenges facing APN educators and clinicians who seek to strengthen advanced practice in the current healthcare system. We clarify our definition of advanced practice nursing, and note the critical need for cohesion within the profession regarding the definition and core competencies of advanced practice. Our aim is to suggest a preferred vision for advanced credentialing. We encourage dialogue among our nursing colleagues to move this agenda forward.  相似文献   
107.
This study examines how key demographic variables and specific child sexual assault (CSA) incident characteristics were related to whether adolescents reported that they had told anyone about an alleged sexual assault. The study also investigates whether there were differences in the correlates of CSA disclosure as a function of gender and race/ethnicity. A national household probability sample of 4,023 adolescents was interviewed by telephone about childhood experiences, including CSA history. Significant gender and racial/ethnic differences were obtained in rates of CSA disclosure: Sexually abused boys and African American youth were less likely to report telling anyone they had been sexually abused. Separate regression models examining correlates of CSA disclosure yielded differences as a function of gender and race/ethnicity.  相似文献   
108.
109.
Polymicrogyria and absence of pineal gland due to PAX6 mutation   总被引:4,自引:0,他引:4  
Identification of genes involved in human cerebral development is important for our understanding of disorders with potential neurodevelopmental causes such as epilepsy and learning disability. Murine models suggest that PAX6 plays a key role in human brain development. With magnetic resonance imaging in 24 humans heterozygous for defined PAX6 mutations, we demonstrated widespread structural abnormalities including absence of the pineal gland and unilateral polymicrogyria.  相似文献   
110.
BACKGROUND: Annual foot examinations (FE) constitute a critical component of care for diabetes. Documented evidence of FE is central to quality-of-care reporting; however, manual abstraction of electronic medical records (EMR) is slow, expensive, and subject to error. The objective of this study was to test the hypothesis that text mining of the EMR results in ascertaining FE evidence with accuracy comparable to manual abstraction. METHODS: The text of inpatient and outpatient clinical reports was searched with natural-language (NL) queries for evidence of neurological, vascular, and structural components of FE. A manual medical records audit was used for validation. The reference standard consisted of 3 independent sets used for development (n=200 ), validation (n=118), and reliability (n=80). RESULTS: The reliability of manual auditing was 91% (95% confidence interval [CI]= 85-97) and was determined by comparing the results of an additional audit to the original audit using the records in the reliability set. The accuracy of the NL query requiring 1 of 3 FE components was 89% (95% CI=83-95). The accuracy of the query requiring any 2 of 3 components was 88% (95% CI=82-94). The accuracy of the query requiring all 3 components was 75% (95% CI= 68- 83). CONCLUSIONS: The free text of the EMR is a viable source of information necessary for quality of health care reporting on the evidence of FE for patients with diabetes. The low-cost methodology is scalable to monitoring large numbers of patients and can be used to streamline quality-of-care reporting.  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