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   18610篇
  免费   1394篇
  国内免费   46篇
耳鼻咽喉   170篇
儿科学   486篇
妇产科学   330篇
基础医学   2464篇
口腔科学   662篇
临床医学   1845篇
内科学   4312篇
皮肤病学   190篇
神经病学   1748篇
特种医学   720篇
外国民族医学   1篇
外科学   2274篇
综合类   391篇
一般理论   16篇
预防医学   1553篇
眼科学   517篇
药学   1313篇
中国医学   10篇
肿瘤学   1048篇
  2023年   70篇
  2022年   98篇
  2021年   251篇
  2020年   145篇
  2019年   252篇
  2018年   287篇
  2017年   232篇
  2016年   257篇
  2015年   308篇
  2014年   439篇
  2013年   779篇
  2012年   1035篇
  2011年   1108篇
  2010年   585篇
  2009年   603篇
  2008年   1105篇
  2007年   1210篇
  2006年   1232篇
  2005年   1226篇
  2004年   1140篇
  2003年   1103篇
  2002年   1108篇
  2001年   272篇
  2000年   256篇
  1999年   260篇
  1998年   279篇
  1997年   248篇
  1996年   218篇
  1995年   227篇
  1994年   185篇
  1993年   172篇
  1992年   196篇
  1991年   171篇
  1990年   195篇
  1989年   152篇
  1988年   189篇
  1987年   182篇
  1986年   161篇
  1985年   171篇
  1984年   163篇
  1983年   146篇
  1982年   196篇
  1981年   197篇
  1980年   152篇
  1979年   129篇
  1978年   99篇
  1977年   81篇
  1976年   72篇
  1975年   69篇
  1974年   86篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Little systematic information is available on mental health issues related to bioterrorism. Five focus groups were conducted with Capitol Hill office staff (n = 28 total participants) to learn about their experience of the anthrax incident on October 15, 2001. More than 2,000 verbal passages were coded into categories and themes by using qualitative analysis software. Issues emerging from the discussions included difficulties utilizing customary social supports, concerns over potential long-term dangers created by efforts to eradicate the anthrax, and nonadherence to antianthrax medication regimens. Nonadherence to antibiotic prophylaxis is of immediate concern for response to future bioterrorist events as well as infectious disease epidemics. Other topics that warrant attention are social support and mental health interventions.  相似文献   
992.
BACKGROUND: Earlier studies have reported that endovascular abdominal aortic aneurysm (EAAA) repair yields lower total profit margins than open AAA (OAAA) repair. This study compared EAAA versus OAAA based on contribution margin per day, which may better measure profitability of new clinical technologies. Contribution margin equals revenue less variable direct costs (VDCs). VDCs capture incremental resources tied directly to individual patients' activity (eg, invoice price of endograft device, nursing labor). Overhead costs factor into total margin, but not contribution margin. METHODS: The University of Michigan Health System's cost accounting system was used to extract fiscal year 2002-2003 information on revenue, total margin, contribution margin, and duration of stay for Medicare patients with principal diagnosis of AAA (ICD-9 code 441.4). RESULTS: OAAA had revenues of $37,137 per case versus $28,960 for EAAA, similar VDCs per case, and thus higher contribution margin per case ($24,404 for OAAA vs $13,911 for EAAA, P < .001). However, OAAA had significantly longer mean duration of stay per case (10.2 days vs 2.2 days, P < .001). Therefore, mean contribution margin per day was $2948 for OAAA, but $8569 for EAAA ( P < .001). CONCLUSIONS: On the basis of contribution margin per day, EAAA repair dominates OAAA repair. The shorter duration of stay with EAAA allows higher throughput, fuller overhead amortization, better use of scarce inpatient beds, and higher health system profits. Surgeons must understand overhead allocation to devices, especially when new technologies cut duration of stay markedly.  相似文献   
993.
994.
OBJECTIVES: To correlate the effect of bilateral in-vivo bladder ischaemia/reperfusion on superoxide dismutase activity (SOD) and then to correlate this with contractile responses to various forms of stimulation. MATERIALS AND METHODS: Twenty mature male New Zealand White rabbits were divided into five equal groups: group 1 (controls); group 2, 2 h of in-vivo bilateral bladder ischaemia; and groups 3-5, 2 h of in-vivo ischaemia followed by 1, 7 or 14 days of reperfusion (recovery). At the end of the treatment period, bladder strips were incubated and placed in isolated baths for contractile studies. The contractile responses to field stimulation, carbachol (10 micromol/L), ATP and KCl were determined. The balance of the bladder body was separated into muscle and mucosa sections and analysed for SOD activity. RESULTS: There were few effects on contraction either directly after ischaemia or after 1 day of reperfusion. However, all contractile responses were significantly reduced at 7 and 14 days after ischaemia. SOD activity of the detrusor muscle was reduced significantly immediately after ischaemia and at 7 and 14 days of reperfusion. SOD activity of the mucosa was significantly greater than that of the muscle, and was significantly reduced by both ischaemia and all times of reperfusion. CONCLUSIONS: These studies show clearly that both ischaemia and reperfusion result in significantly lower activity of SOD, and in contractile dysfunctions, and that reperfusion results in greater decreases in both SOD activity and contractile responses than ischaemia alone.  相似文献   
995.
Apoptosis and proliferation in human undescended testes   总被引:2,自引:0,他引:2  
OBJECTIVE: To study apoptosis and proliferation in the testes of children with undescended testes; the degree to which undescended testes contributes to a patient's ultimate fertility is debatable, but undescended testes have fewer germ cells, and some have proposed that apoptosis is an important cause. PATIENTS AND METHODS: Testis biopsies were taken at the time of orchidopexy in a consecutive series of children undergoing surgical repair for undescended testes. Immunohistological techniques were used to detect apoptosis and proliferation, and the numbers of cells undergoing apoptosis or proliferation per 50 seminiferous tubules were recorded. RESULTS: Inguinal testes had less apoptosis than abdominal testes, with a mean (sd) of 0.71 (1.31) vs 1.63 (1.95) apoptotic cells per 50 seminiferous tubules (P < 0.02). Similarly, there was less apoptosis in children aged > 1 years than in children aged < 1 years (0.68 (1.40) vs 1.35 (1.56); P < 0.03). Proliferation was very limited in all cryptorchid testes. In contrast to cryptorchid testes, five autopsy controls had many more apoptotic cells, (10.60 (1.34) per 50 seminiferous tubules), and many more proliferating cells, (8.40 (6.43) per 50 seminiferous tubules). CONCLUSION: In contrast to animal studies, neither apoptosis nor proliferation was common in undescended testes from 6 months of age onward. However, apoptosis was more common in abdominal testes and in children aged < 1 year. It is likely that, if substantial apoptosis occurs in human undescended testes, it occurs before 6 months of age.  相似文献   
996.
All Australian States and Territories have low rates (< or = 0.32 cases per 100,000 population) of notification for Shiga toxin-producing Escherichia coli (STEC), except for South Australia where the rates are ten-fold higher at 2.58 cases per 100,000 population. To explore possible reasons for the variation in rates we surveyed public health reference laboratories to determine the methods used and number of specimens tested for these organisms. Only five of eight jurisdictions routinely conducted testing for STEC, and polymerase chain based tests were most common. Culture was also common and in one jurisdiction that tests specimens with culture, approximately 1.2 per cent of specimens were positive. The notification rates for different jurisdictions reflected the number of specimens tested, with jurisdiction testing < or = 500 specimens having rates < or = 0.32 cases per 100,000 population. The use of culture as a test method may also influence notification rates. Public health agencies must consider the number of specimens tested in interpreting surveillance data.  相似文献   
997.
PURPOSE: Participants in epidemiology studies are often asked to complete an interview and to provide biospecimens. In a population-based case-control study of kidney cancer involving an interview and optional biospecimens, we examined whether mentioning the biospecimens in the initial contact letter adversely affects willingness to be interviewed. METHODS: Eligible cases (n = 434) and controls (n = 775) in Detroit were alternately assigned to receive one of two versions of the contact letter. Both explained that the study involves an interview with 100 dollars compensation plus an optional component with additional compensation; only one disclosed that the optional component involved biospecimens. RESULTS: There were no meaningful differences between the groups in willingness to be interviewed. However, among 303 cases and 351 controls already interviewed, the proportion providing biospecimens was higher in the fully informed group: for blood, the differences were 10.8 (95% CI, 2.0, 19.5) for cases and 6.7% (95% CI, -1.7, 15.1) for controls. Findings were similar for saliva. CONCLUSIONS: In a study involving an interview and optional biospecimens, informing people about the samples in the contact letter seems preferable to a non-specific reference to a second study component. Both approaches yielded similar interview participation rates, but biospecimen participation rates were higher among those informed about the samples in the contact letter.  相似文献   
998.
OBJECTIVE: The purpose of this study was to investigate the heritability of body composition measured by DXA in the Diabetes Heart Study (DHS). RESEARCH METHODS AND PROCEDURES: Participants were 292 women and 262 men (age, 38 to 86 years; BMI, 17 to 57 kg/m(2)) from 244 families. There were 492 white and 49 African-American sibling pairs. DXA measurements of percentage fat mass (FM), whole body FM, and lean mass (LM), as well as regional measurements of trunk fat mass (TFM) and appendicular lean mass (ALM), were obtained. Heritability of FM, LM, and BMI were estimated using Sequential Oligogenic Linkage Analysis Routines. RESULTS: After adjusting for age, gender, ethnicity, and height, the heritability estimates of various compositional attributes were %FM = 0.64, whole body FM = 0.71, TFM = 0.63, whole body LM = 0.60, ALM = 0.66, and BMI = 0.64 (all p < 0.0001). Additional adjustment for diabetes status, smoking, dietary intake, and physical activity resulted in only minor changes in the heritability estimates (h(2) = 0.63 to 0.72, all p < 0.0001). Furthermore, heritability of TFM after additional adjustment for whole body FM was significant (h(2) = 0.55, p < 0.0001), and heritability of ALM after additional adjustment for whole body LM was also significant (h(2) = 0.51, p < 0.0001). DISCUSSION: These data suggest that FM and LM measured by DXA are highly heritable and can be effectively used in designing linkage studies to locate genes governing body composition. In addition, regional distribution of FM and LM may be genetically determined.  相似文献   
999.
Monda KL  Popkin BM 《Obesity research》2005,13(6):1042-1051
OBJECTIVE: To use cluster analysis to create patterns of overall activity and inactivity in a diverse sample of Chinese youth and to evaluate their use in predicting overweight status. RESEARCH METHODS AND PROCEDURES: The study populations were drawn from the 1997 and 2000 years of the longitudinal China Health and Nutrition Survey, comprised of 2702 and 2641 schoolchildren in the 1997 and 2000 cross-sectional samples, respectively, and 1175 children in the longitudinal cohort. Cluster analysis was used to group children into nonoverlapping activity/inactivity "clusters" that were subsequently used in models of prevalent and incident overweight. Results were compared with traditional models, with activity and inactivity coded separately, to assess whether further insight was gained with the cluster analysis methodology. RESULTS: Moderately and highly active youth were shown to have significantly decreased odds of overweight in both cross-sectional and longitudinal analyses using cluster analysis. In incident longitudinal models, youth in the high activity/high inactivity cluster had the lowest odds of overweight [odds ratio=0.12 (0.03, 0.44)]; in contrast, results from traditional models failed to show any significant relationship between overweight and activity or inactivity. DISCUSSION: Cluster analysis methods allow researchers to simultaneously capture activity and inactivity in new ways. In this comparative study, only with the clustering methodology did we find a significant effect of activity on incident overweight, furthering our ability to examine this complex relationship. Interestingly, no effect of increasing levels of inactivity was observed using either method, indicating that activity seems to be the more important determinant of overweight in this population.  相似文献   
1000.
Given the absence of empirical measures that assess acculturation patterns among male Arab immigrants, a new acculturation instrument was developed and evaluated. One hundred and fifteen adult male Arab immigrants were administered the Male Arab Acculturation Scale (MAAS), and psychometrically established measures of ethnic identity and self-esteem. Satisfactory reliability is reported for the two acculturation scales, separation/assimilation and integration/marginalization. Ethnic identity, self-construal, personal self-esteem, and collective self-esteem appear to be differentially associated with acculturation patterns among male Arab immigrants.  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