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   2121篇
  免费   125篇
  国内免费   11篇
耳鼻咽喉   11篇
儿科学   109篇
妇产科学   36篇
基础医学   398篇
口腔科学   29篇
临床医学   244篇
内科学   397篇
皮肤病学   60篇
神经病学   163篇
特种医学   108篇
外科学   244篇
综合类   22篇
一般理论   3篇
预防医学   174篇
眼科学   21篇
药学   137篇
中国医学   4篇
肿瘤学   97篇
  2022年   11篇
  2021年   15篇
  2020年   22篇
  2019年   26篇
  2018年   36篇
  2017年   21篇
  2016年   44篇
  2015年   35篇
  2014年   40篇
  2013年   63篇
  2012年   93篇
  2011年   130篇
  2010年   69篇
  2009年   65篇
  2008年   106篇
  2007年   110篇
  2006年   100篇
  2005年   103篇
  2004年   90篇
  2003年   78篇
  2002年   109篇
  2001年   69篇
  2000年   91篇
  1999年   63篇
  1998年   29篇
  1997年   30篇
  1996年   19篇
  1995年   23篇
  1994年   23篇
  1993年   22篇
  1992年   46篇
  1991年   39篇
  1990年   36篇
  1989年   24篇
  1988年   24篇
  1987年   17篇
  1986年   20篇
  1985年   25篇
  1984年   14篇
  1983年   21篇
  1982年   9篇
  1980年   9篇
  1979年   23篇
  1978年   14篇
  1977年   11篇
  1976年   9篇
  1971年   8篇
  1969年   10篇
  1968年   8篇
  1942年   10篇
排序方式: 共有2257条查询结果,搜索用时 31 毫秒
51.
OBJECTIVE: Continuous positive airway pressure (CPAP) by face mask is an effective method of treating severe cardiogenic pulmonary edema (CPE). However, to our knowledge, no study has provided a precise evaluation of the effects of CPAP on cardiac function in patients presenting with CPE and preserved left ventricular (LV) function. DESIGN: Prospective observational clinical study. SETTING: A 14-bed, medical ICU at a university hospital. PATIENTS: Nine consecutive patients presenting with hypoxemic acute CPE. INTERVENTIONS: All patients were selected for 30 min of CPAP with 10 cm H(2)O by mask with fraction of inspired oxygen adjusted for a cutaneous saturation > 90%. Doppler echocardiography was performed before CPAP application and during the last 10 min of breathing with CPAP. Two-tailed, paired t-tests were used to compare data recorded at baseline (oxygen alone) and after CPAP. MEASUREMENTS AND RESULTS: Four patients presented CPE with preserved left ventricular (LV) function (a preserved LV ejection fraction [LVEF] > 45%, and/or aortic velocity time integral > 17 cm in the absence of aortic stenosis or hypertrophic cardiomyopathy). Oxygenation and ventilatory parameters were improved by CPAP in all patients. Hemodynamic monitoring and Doppler echocardiographic analysis demonstrated that in patients with preserved LV systolic function, mean arterial pressure and LV end-diastolic volume were decreased significantly by CPAP (p < 0.04). In patients with LV systolic dysfunction, CPAP improved LVEF (p < 0.05) and decreased LV end-diastolic volume (p = 0.001) significantly. CONCLUSION: CPAP improves oxygenation and ventilatory parameters in all kinds of CPE. In patients with preserved LV contractility, the hemodynamic benefit of CPAP results from a decrease in LV end-diastolic volume (preload).  相似文献   
52.
In a community-based, time-location sampling survey in San Francisco, Internet-met partners were not more likely to be HIV seroconcordant among HIV-negative and HIV-positive men who have sex with men (MSM) compared with partners met at bars and dance clubs. In addition, HIV-negative MSM were more likely to have unprotected anal intercourse with potentially serodiscordant partners met on the Internet compared with those met at bars and dance clubs (adjusted OR 1.5, 95% CI 1.1-2.0, P = 0.01).  相似文献   
53.
The molluscicidal activity of crushed seed pods of Swartzia madagascariensis was assessed by laboratory and field trials. Mature dry seed pods were ground and extracted in tap water for 24 h. Water extracts exerted a significant molluscicidal activity against Bulinus globosus up to dilutions of 100 mg of ground pods per litre. The chromatographically isolated saponin (1) responsible for the molluscicidal activity showed a toxicity of LC 100 at 3 mg/l after exposure of B. globosus and Biomphalaria glabrata for 24 h. Saponin (1) could be identified by FAB-MS and 13C-NMR-spectroscopy as oleanolic acid-3-O-beta-D-glucuronopyranosyl (1----3)-alpha-L-rhamnopyranoside. Two field trials with S. madagascariensis pod extracts in ponds (60 and 160 m3) harbouring dense populations of B. globosus compared well with the laboratory findings and showed the efficiency of the molluscicide in a natural habitat. A single application of the plant molluscicide significantly reduced the populations of B. globusus. The toxicity of S. madagascariensis pod extracts to non-target organisms remains an obstacle for its use in certain situations where schistosomiasis control is envisaged and where S. madagascariensis is found. However, S. madagascariensis is a valid candidate molluscicide which may be applied in selected epidemiological settings as part of integrated schistosomiasis control measures.  相似文献   
54.

Background

Permanent low-dose-rate brachytherapy (BT) with iodine 125 is an established curative treatment for localized prostate cancer. After treatment, prostate-specific antigen (PSA) kinetics may show a transient rise (PSA bounce). Our aim was to investigate the association of PSA bounce with biochemical control.

Patients and methods

Patients treated with BT in Switzerland were registered in a prospective database. Only patients with a follow-up of at least 2 years were included in our analysis. Clinical follow-up and PSA measurements were assessed after 1.5, 3, 6, and 12 months, and annually thereafter. If PSA increased, additional follow-up visits were scheduled. Cases of PSA bounce were defined as a rise of at least 0.2 ng/ml above the initial PSA nadir with a subsequent decline to or below the initial nadir without treatment. Biochemical failure was defined as a rise to nadir +?2 ng/ml.

Results

Between March 2001 and November 2010, 713 patients with prostate cancer undergoing BT with at least 2 years of follow-up were registered. Median follow-up time was 41 months. Biochemical failure occurred in 28 patients (3.9?%). PSA bounce occurred in 173 (24.3?%) patients; only three (1.7?%) patients with PSA bounce developed biochemical failure, in contrast to 25 (4.6?%) patients without previous bounce (p?<?0.05). The median time to bounce was 12 months, the median time to biochemical failure was 30 months. The median bounce increase was 0.78 ng/ml. Twenty-eight patients with bounce (16.5?%) had a transient PSA rise of +?2 ng/ml above the nadir.

Conclusion

In most cases, an early increase in PSA after BT indicates PSA bounce and is associated with a lower risk of biochemical failure.
  相似文献   
55.
56.
The intestinal microbiota influences not only metabolic processes, but also the mucosal and systemic immune systems. Here, we compare innate and adaptive immune responses against the intracellular pathogen Listeria monocytogenes in germfree (GF) and conventional mice. We show that animals without endogenous microbiota are highly susceptible to primary infection with impaired activation and accumulation of phagocytes to the site of infection. Unexpectedly, secondary infection with otherwise lethal dose resulted in survival of all GF animals which cleared bacteria more rapidly and developed a stronger antilisterial CD8+ memory T‐cell response compared to conventional mice. In summary, lack of the intestinal microbiota impairs early innate immunity, but enhances activation and expansion of memory T cells.  相似文献   
57.
Thermoresponsive polymer gels exhibit pronounced swelling and deswelling upon changes in temperature, making them attractive for applications in sensing and actuation. This volume phase transition can be discussed in terms of mean‐field theoretical pictures to assess at which conditions it occurs continuously or discontinuously. However, this treatment disregards static nano‐ and micrometer‐scale inhomogeneities in gel polymer networks, which are a common feature of these materials. To check for the impact of such structural complexity, droplet‐based microfluidics are used to fabricate sub‐millimeter‐sized gel particles that exhibit critical compositions at the border between continuous to discontinuous volume phase transitions, along with determined static spatial polymer‐network heterogeneity on the nano­meter and micrometer length scales, which is characterized by low‐field NMR. These different microgels are then used to study their swelling and deswelling volume phase transitions from a sub‐millimeter perspective. In this investigation, microgel particles with similar content of crosslinker exhibit similar swelling and deswelling, independent of their extent of static polymer‐network inhomogeneity, in agreement with mean‐field theoretical predictions.

  相似文献   

58.

Background

The characteristics of patients with infective endocarditis (IE) vary significantly by region of the world. The aim of this study was to evaluate the contemporary epidemiology, characteristics, and outcome of IE in a large, nationwide cohort of Italian patients.

Methods

We conducted a prospective, observational study at 24 medical centers in Italy, including all the consecutive patients with a definite or possible diagnosis of IE (modified Duke criteria) admitted from January 2004 through December 2009. A number of clinical variables were collected through an electronic case report form and analyzed to comprehensively delineate the features of IE. We report the data on patients with definite IE.

Results

A total of 1,082 patients with definite IE were included. Of these, 753 (69.6?%) patients had infection on a native valve, 277 (25.6?%) on a prosthetic valve, and 52 (4.8?%) on an implantable electronic device. Overall, community-acquired (69.2?%) was more common than nosocomial (6.2?%) or non-nosocomial (24.6?%) health care-associated IE. Staphylococcus aureus was the most common pathogen (22.0?%). In-hospital mortality was 15.1?%. From the multivariate analysis, congestive heart failure (CHF), stroke, prosthetic valve infection, S. aureus, and health care-associated acquisition were independently associated with increased in-hospital mortality, while surgery was associated with decreased mortality.

Conclusions

The current mortality of IE remains high, and is mainly due to its complications, such as CHF and stroke.  相似文献   
59.
60.
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