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   2646篇
  免费   251篇
  国内免费   22篇
耳鼻咽喉   6篇
儿科学   167篇
妇产科学   21篇
基础医学   309篇
口腔科学   78篇
临床医学   319篇
内科学   625篇
皮肤病学   33篇
神经病学   108篇
特种医学   492篇
外科学   182篇
综合类   38篇
预防医学   148篇
眼科学   21篇
药学   158篇
中国医学   3篇
肿瘤学   211篇
  2021年   22篇
  2020年   17篇
  2019年   24篇
  2018年   31篇
  2017年   23篇
  2016年   42篇
  2015年   45篇
  2014年   48篇
  2013年   107篇
  2012年   78篇
  2011年   74篇
  2010年   105篇
  2009年   86篇
  2008年   60篇
  2007年   72篇
  2006年   68篇
  2005年   64篇
  2004年   54篇
  2003年   52篇
  2002年   68篇
  2001年   50篇
  2000年   64篇
  1999年   58篇
  1998年   139篇
  1997年   130篇
  1996年   132篇
  1995年   109篇
  1994年   79篇
  1993年   90篇
  1992年   47篇
  1991年   45篇
  1990年   39篇
  1989年   84篇
  1988年   67篇
  1987年   65篇
  1986年   66篇
  1985年   63篇
  1984年   36篇
  1983年   47篇
  1982年   47篇
  1981年   25篇
  1980年   44篇
  1979年   23篇
  1978年   29篇
  1977年   22篇
  1976年   30篇
  1975年   37篇
  1974年   11篇
  1973年   10篇
  1971年   10篇
排序方式: 共有2919条查询结果,搜索用时 15 毫秒
991.
992.
BACKGROUND: Posttransfusion complications can be prevented by pretransfusion removal of donor white cells from platelet concentrate. The filtration used for this removal seems to have little effect on platelet function and activation, but more information is needed on its effect on function during subsequent long-term storage of concentrate. STUDY DESIGN AND METHODS: The effect of prestorage filtration of buffy coat-prepared platelet concentrates (PCs) on platelet function, metabolism, and activation was investigated. A pool of three PCs, each made of four buffy coats, was split into three equal volumes; two were filtered over two different filters and the third served as a control. Variables monitored immediately after filtration and during the subsequent 8-day storage period at 22 degrees C included aggregation upon stimulation with collagen and/or ADP, platelet adhesion capacity to collagen and fibrinogen in flowing blood, nucleotide content of and nucleobase release by the platelets, expression of activation-dependent antigens, and beta-thromboglobulin release by the platelets. RESULTS: No differences were observed between the PCs filtered over two different filters and the nonfiltered control PCs immediately after filtration and during storage, except for a selective removal (20%) of beta-thromboglobulin by one filter. CONCLUSION: PCs prepared from a pool of four buffy coats can be filtered and subsequently stored for 8 days (starting +/− 24 hours after whole blood collection) without detriment to platelet function, metabolism, or activation.  相似文献   
993.
BACKGROUND: Platelet concentrates (PCs) for premature infants may be subjected to filtration, centrifugation, and various storage conditions before transfusion. STUDY DESIGN AND METHODS: As there are few data on the cumulative effect of these procedures on PCs, platelet properties (including biochemical and functional in vitro assays) were evaluated after the processing of single units of PCs through a 1-unit-capacity high-efficiency white cell (WBC)-reduction filter followed by syringe storage at either 22 or 37 degrees C for 6 hours. Two- and 5-day-old PCs, volume-reduced PCs, and prestorage WBC-reduced PCs were evaluated. RESULTS: WBC filtration consistently resulted in a 3 to 4 log10 reduction in WBCs, with less than 15-percent platelet loss. No adverse effects of platelet function or evidence of increased platelet activation as determined by the percentage of P-selectin positivity were noted. A decrease in pH associated with increased lactate production and consumption of glucose was observed following syringe storage under all conditions tested. Such changes were most pronounced, however, with volume-reduced PCs stored at 37 degrees C (pH 6.31 +/− 0.15, lactate 23.0 +/− 3.06 mmol/L). All pH levels at the end of storage were above the minimum Food and Drug Administration requirement (pH 6.0). CONCLUSION: The in vitro data suggest that single units of PCs can undergo WBC filtration followed by syringe storage for up to 6 hours and still maintain acceptable storage characteristics. The practice of maintaining volume-reduced PCs in syringes for 6 hours at 37 degrees C in isolettes during transfusion should, however, be avoided.  相似文献   
994.
Saltman  DL; Ross  JA; Banks  RE; Ross  FM; Ford  AM; Mackie  MJ 《Blood》1989,74(6):2062-2065
To establish the clonal origin of a case of concomitant B-cell chronic lymphocytic leukemia (IgM kappa) and multiple myeloma (IGA lambda), we analyzed the immunoglobulin (Ig) gene rearrangements in the patient's blood and bone marrow. Despite the different isotypes, pretreatment investigation of the heavy chain gene (JH) revealed a germline fragment and two identical rearrangements in the blood and marrow. Both kappa and lambda light-chain genes were rearranged in the blood, suggesting peripheral blood lymphocyte involvement in the myeloma. Analysis of the Ig genes after chemotherapy demonstrated no change in the JH or CK rearrangements; however, the lambda genes were now in a germline configuration. Our results suggest that in this patient both chronic lymphocytic leukemia and myeloma originated from the same B-cell progenitor.  相似文献   
995.
A substantial proportion of hospitalizations of nursing home (NH) residents may be avoidable. Medicare payment reforms, such as bundled payments for episodes of care and value-based purchasing, will change incentives that favor hospitalization but could result in care quality problems if NHs lack the resources and training to identify and manage acute conditions proactively. Interventions to Reduce Acute Care Transfers (INTERACT) II is a quality improvement intervention that includes a set of tools and strategies designed to assist NH staff in early identification, assessment, communication, and documentation about changes in resident status. INTERACT II was evaluated in 25 NHs in three states in a 6-month quality improvement initiative that provided tools, on-site education, and teleconferences every 2 weeks facilitated by an experienced nurse practitioner. There was a 17% reduction in self-reported hospital admissions in these 25 NHs from the same 6-month period in the previous year. The group of 17 NHs rated as engaged in the initiative had a 24% reduction, compared with 6% in the group of eight NHs rated as not engaged and 3% in a comparison group of 11 NHs. The average cost of the 6-month implementation was $7,700 per NH. The projected savings to Medicare in a 100-bed NH were approximately $125,000 per year. Despite challenges in implementation and caveats about the accuracy of self-reported hospitalization rates and the characteristics of the participating NHs, the trends in these results suggest that INTERACT II should be further evaluated in randomized controlled trials to determine its effect on avoidable hospitalizations and their related morbidity and cost.  相似文献   
996.
The purpose of this paper is to present the outcomes of a nationwide nursing research project in Australia. Utilising the Delphi technique, ninety‐four clinically based nephrology nurses reviewed a series of competency based standards documents. The purpose of this research was to reveal the ways in which nephrology nurses practice at an advanced level. The results will facilitate the way in which advanced practice nephrology nursing is understood and inform nursing curricula development.  相似文献   
997.
Haplotypes constructed from Y-chromosome markers were used to trace the paternal origins of the Jewish Diaspora. A set of 18 biallelic polymorphisms was genotyped in 1,371 males from 29 populations, including 7 Jewish (Ashkenazi, Roman, North African, Kurdish, Near Eastern, Yemenite, and Ethiopian) and 16 non-Jewish groups from similar geographic locations. The Jewish populations were characterized by a diverse set of 13 haplotypes that were also present in non-Jewish populations from Africa, Asia, and Europe. A series of analyses was performed to address whether modern Jewish Y-chromosome diversity derives mainly from a common Middle Eastern source population or from admixture with neighboring non-Jewish populations during and after the Diaspora. Despite their long-term residence in different countries and isolation from one another, most Jewish populations were not significantly different from one another at the genetic level. Admixture estimates suggested low levels of European Y-chromosome gene flow into Ashkenazi and Roman Jewish communities. A multidimensional scaling plot placed six of the seven Jewish populations in a relatively tight cluster that was interspersed with Middle Eastern non-Jewish populations, including Palestinians and Syrians. Pairwise differentiation tests further indicated that these Jewish and Middle Eastern non-Jewish populations were not statistically different. The results support the hypothesis that the paternal gene pools of Jewish communities from Europe, North Africa, and the Middle East descended from a common Middle Eastern ancestral population, and suggest that most Jewish communities have remained relatively isolated from neighboring non-Jewish communities during and after the Diaspora.  相似文献   
998.
Collagenous colitis and lymphocytic colitis cause chronic watery diarrhea. Multiple therapies have been found to improve symptoms but there have been few long-term follow-up studies. Our goal was to obtain long-term clinical follow-up on a cohort of patients with independently confirmed typical histopathologic changes. Pathology slides from 32 cases of collagenous or lymphocytic colitis patients from 1988-1992 were independently reviewed. Twenty-five cases were confirmed by both groups of pathologist as collagenous or lymphocytic colitis. For these 25 patients, charts were reviewed and telephone follow-up interviews were performed in 1992 and 1995. Seven of 32 (22%) of the original cases were not confirmed on independent pathologic interpretation. A 15.8% discordance rate was found between the different groups of pathologists. Patient demographics were similar to previously published reports except one-half of our patients had diarrhea of only 6 months or less. Eighty-one percent of patients receiving 5-ASA agents reported improvement as well as 100% of those receiving prednisone. At 23 month follow-up 86% of patients reported improvement in diarrhea and only 32% required routine medications. At 47 month follow-up all patients reported improved diarrhea and only 29% required routine medications. Collagenous and lymphocytic colitis can sometimes be identified in patients with relatively brief duration diarrhea. Clinical parameters and response to therapy are similar for collagenous or lymphocytic colitis. Most patients with lymphocytic and collagenous colitis improve with therapy such as 5-ASA preparations or steroids. Over a follow-up period of several years, most patients have improvement in diarrhea and generally do not require maintenance medications. Independent pathologic confirmation of the diagnosis should be obtained in patients not responding to therapy.  相似文献   
999.

Background  

The objective of this study was to establish 1) the performance of chest X-ray (CXR) in all suspects of tuberculosis (TB), as well as smear-negative TB suspects and 2) to compare the cost-effectiveness of the routine diagnostic pathway using Ziehl-Neelsen (ZN) sputum microscopy followed by CXR if case of negative sputum result (ZN followed by CXR) with an alternative pathway using CXR as a screening tool (CXR followed by ZN).  相似文献   
1000.
OBJECTIVE: We sought to examine whether use of nonsteroidal antiinflammatory drugs (NSAIDs) in an outpatient inflammatory bowel disease (IBD) population is associated with an increased likelihood of active disease. METHODS: We reviewed records of initial outpatient visits of IBD patients to the principal author from June 1995 to December 1997, with regard to use of aspirin and other NSAIDs and disease activity. RESULTS: Of 40 Crohn's patients seen with active disease, three (7.5%) were using NSAIDs; 14 of 72 (19.4%) Crohn's patients seen with inactive disease were using NSAIDs. Fifty-eight ulcerative colitis patients were seen with active disease, with eight (13.7%) using NSAIDs. Among 21 UC patients initially seen while in remission, five (23.8%) were using NSAIDs. CONCLUSIONS: Among this group of outpatients, NSAID use was not associated with a higher likelihood of active IBD. NSAID use in IBD deserves further study before recommending that patients refrain from their use under all circumstances.  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