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   15537篇
  免费   1156篇
  国内免费   70篇
耳鼻咽喉   265篇
儿科学   602篇
妇产科学   450篇
基础医学   1899篇
口腔科学   242篇
临床医学   1599篇
内科学   3496篇
皮肤病学   483篇
神经病学   1280篇
特种医学   513篇
外科学   2526篇
综合类   184篇
一般理论   20篇
预防医学   984篇
眼科学   338篇
药学   955篇
中国医学   32篇
肿瘤学   895篇
  2023年   113篇
  2022年   171篇
  2021年   587篇
  2020年   343篇
  2019年   456篇
  2018年   522篇
  2017年   379篇
  2016年   425篇
  2015年   416篇
  2014年   553篇
  2013年   740篇
  2012年   1061篇
  2011年   1084篇
  2010年   586篇
  2009年   550篇
  2008年   837篇
  2007年   924篇
  2006年   836篇
  2005年   788篇
  2004年   737篇
  2003年   627篇
  2002年   548篇
  2001年   224篇
  2000年   203篇
  1999年   208篇
  1998年   136篇
  1997年   88篇
  1996年   78篇
  1995年   67篇
  1994年   71篇
  1993年   75篇
  1992年   121篇
  1991年   130篇
  1990年   111篇
  1989年   120篇
  1988年   106篇
  1987年   106篇
  1986年   116篇
  1985年   113篇
  1984年   102篇
  1983年   84篇
  1982年   83篇
  1981年   102篇
  1980年   70篇
  1979年   85篇
  1978年   74篇
  1977年   65篇
  1975年   45篇
  1974年   51篇
  1972年   45篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
In order to evaluate the incidence and risk factors of infection by hepatitis C virus (HCV) among injecting drug users (IDUs), we conducted a prospective cohort study of HCV- and human immunodeficiency virus (HIV)-negative IDUs in the North and East of France. A total of 231 HCV and HIV IDUs who had injected drugs at least once in their lifetime were followed up every 3 months over a 12-month period. Serum anti-HCV and anti-HIV were tested at inclusion in the study and at the end of the follow-up. Data on injecting practices were collected at inclusion and at each visit. Of the 231 participants included, 165 (71.4%) underwent a final HCV and HIV serum test. The incidence was nil for HIV infection and 9/100 person-years (95% CI 4.6-13.4) for HCV infection. In a multivariable analysis, we found that syringe and cotton sharing were the only independent predictive factors of HCV seroconversion.  相似文献   
992.
993.
994.
Clusters are recognized when meningococcal cases of the same phenotypic strain (markers: serogroup, serotype, and subtype) occur in spatial and temporal proximity. The incidence of such clusters was compared to the incidence that would be expected by chance by using space-time nearest-neighbor analysis of 4,887 confirmed invasive meningococcal cases identified in the 9-year surveillance period 1993-2001 in the Netherlands. Clustering beyond chance only occurred among the closest neighboring cases (comparable to secondary cases) and was small (3.1%, 95% confidence interval 2.1%-4.1%).  相似文献   
995.
996.
INTRODUCTION: We report two cases of morbidly obese patients with huge infected abdominal aprons who underwent apronectomies at Alice Springs Hospital, Northern Territory, Australia. We describe a novel technique which to date has not been described in the available literature. Patients afflicted by morbid obesity with large aprons can be incapacitated by immobility as well as suffer from recurrent infections. Apronectomy in this situation can be difficult because of the heavy weight of the apron. METHOD: This technique involves the use of a small crane and large orthopaedic K-nails. Two K-nails were inserted into the apron and attached to a small crane. This facilitated the elevation and manipulation of the apron during surgical dissection. The abdominal tissue removed from the female and male weighed 30 kg and 64 kg, respectively. The wounds were closed primarily and drained by three large bore suction drains. RESULTS: The female patient had a largely uneventful postoperative course with a minor wound infection that resolved with conservative treatment. The other patient required a more protracted course of antibiotics for his more severe infection. Mobility was markedly improved in both individuals. CONCLUSION: This novel technique can be used successfully for severely morbidly obese individuals and can significantly reduce the surgeon's and assistants' difficulty in manipulating and handling a heavy apron during dissection.  相似文献   
997.
In this study we compared a "baseline" condition of uncontrolled diesel engine exhaust (DEE) emissions generated with current (circa 2003) certification fuel to an emissions-reduction (ER) case with low sulfur fuel and a catalyzed particle trap. Lung toxicity assessments (resistance to respiratory viral infection, lung inflammation, and oxidative stress) were performed on mice (C57Bl/6) exposed by inhalation (6 hr/day for 7 days). The engine was operated identically (same engine load) in both cases, and the inhalation exposures were conducted at the same exhaust dilution rate. For baseline DEE, this dilution resulted in a particle mass (PM) concentration of approximately 200 microg/m3 PM, whereas the ER reduced the PM and almost every other measured constituent [except nitrogen oxides (NOx)] to near background levels in the exposure atmospheres. These measurements included PM, PM size distribution, PM composition (carbon, ions, elements), NOx, carbon monoxide, speciated/total volatile hydrocarbons, and several classes of semivolatile organic compounds. After exposure concluded, one group of mice was immediately sacrificed and assessed for inflammation and oxidative stress in lung homogenate. Another group of mice were intratracheally instilled with respiratory syncytial virus (RSV), and RSV lung clearance and inflammation was assessed 4 days later. Baseline DEE produced statistically significant biological effects for all measured parameters. The use of low sulfur fuel and a catalyzed trap either completely or nearly eliminated the effects.  相似文献   
998.
The use of transgenic crops as feeds for ruminant animals has prompted study of the possible uptake of transgene fragments by ruminal micro-organisms and/or intestinal absorption of fragments surviving passage through the rumen. The persistence in buffered ruminal contents of seven different recombinant DNA fragments from GM rapeseed expressing the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) transgene was tracked using PCR. Parental and transgenic (i.e. glyphosphate-tolerant; Roundup Ready, Monsanto Company, St Louis, MO, USA) rapeseed were incubated for 0, 2, 4, 8, 12, 24 and 48 h as whole seeds, cracked seeds, rapeseed meal, and as pelleted, barley-based diets containing 65 g rapeseed meal/kg. The seven transgene fragments ranged from 179 to 527 bp and spanned the entire 1363 bp EPSPS transgene. A 180 bp ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit fragment and a 466 bp 16S rDNA fragment were used as controls for endogenous rapeseed DNA and bacterial DNA respectively. The limit of detection of the PCR assay, established using negative controls spiked with known quantities of DNA, was 12.5 pg. Production of gas and NH3 was monitored throughout the incubation and confirmed active in vitro fermentation. Bacterial DNA was detected in all sample types at all time points. Persistence patterns of endogenous (Rubisco) and recombinant (EPSPS) rapeseed DNA were inversely related to substrate digestibility (amplifiable for 48, 8 and 4 h in whole or cracked seeds, meal and diets respectively), but did not differ between parental and GM rapeseed, nor among fragments. Detection of fragments was representative of persistence of the whole transgene. No EPSPS fragments were amplifiable in microbial DNA, suggesting that transformation had not occurred during the 48 h incubation. Uptake of transgenic DNA fragments by ruminal bacteria is probably precluded or time-limited by rapid degradation of plant DNA upon plant cell lysis.  相似文献   
999.
In light of recent and increasing incidences of pathogenic E. coli outbreaks at public bathing facilities attributable to non-toilet-trained infants and toddlers, many such facilities are restricting water contact for this age group. A number of manufacturers are now offering disposable "swim diapers," which claim to effectively retain fecal material under typical pool play conditions. The study reported here examined the solids retention effectiveness of three major brands of swim diapers as well as of conventional disposable diapers, under simulated water play conditions. Swim diapers of all three brands exhibited an approximately equal fine-solids retention capability of about 98 to 99 percent over 30 minutes of water immersion activity. Conventional disposable diapers invariably fell down or came apart during the experiments, resulting in very limited solids retention. This study indicates that commercially available swim diapers represent a vast improvement in reducing the potential for fecal material release in public pool facilities, but that some release will still generally occur with these products.  相似文献   
1000.
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