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   1365篇
  免费   58篇
  国内免费   33篇
耳鼻咽喉   26篇
儿科学   65篇
妇产科学   24篇
基础医学   115篇
口腔科学   27篇
临床医学   125篇
内科学   387篇
皮肤病学   109篇
神经病学   38篇
特种医学   211篇
外科学   119篇
综合类   29篇
预防医学   77篇
眼科学   6篇
药学   37篇
中国医学   3篇
肿瘤学   58篇
  2019年   10篇
  2018年   8篇
  2017年   13篇
  2016年   16篇
  2015年   22篇
  2014年   25篇
  2013年   69篇
  2012年   16篇
  2011年   18篇
  2010年   52篇
  2009年   57篇
  2008年   23篇
  2007年   33篇
  2006年   27篇
  2005年   31篇
  2004年   16篇
  2003年   13篇
  2002年   21篇
  2001年   20篇
  2000年   15篇
  1999年   20篇
  1998年   83篇
  1997年   72篇
  1996年   77篇
  1995年   49篇
  1994年   62篇
  1993年   51篇
  1992年   14篇
  1991年   17篇
  1990年   25篇
  1989年   43篇
  1988年   43篇
  1987年   32篇
  1986年   27篇
  1985年   26篇
  1984年   25篇
  1983年   13篇
  1982年   23篇
  1981年   19篇
  1980年   15篇
  1979年   17篇
  1978年   16篇
  1977年   17篇
  1976年   19篇
  1975年   12篇
  1973年   15篇
  1972年   12篇
  1969年   7篇
  1965年   7篇
  1957年   7篇
排序方式: 共有1456条查询结果,搜索用时 15 毫秒
991.
Doppler characteristics of normally functioning tilting disk prostheses in aortic position were studied in 55 patients (30 Medtronic-Hall and 25 Sorin) whose valvular function was considered normal using clinical and echocardiographic evaluation. Peak gradients, mean gradients and effective orifice area were estimated for different sizes of prostheses. The peak gradient calculated from maximal aortic velocity was 27.3 +/- 11.1 mmHg in Sorin and 21.1 +/- 9.7 mmHg in Medtronic-Hall valves; the mean gradients were 12.9 +/- 6.2 mmHg and 10.8 +/- 5.7 mmHg in Sorin and Medtronic-Hall valves respectively. The effective orifice area calculated by the continuity equation was 1.4 +/- 0.5 cm2 in Sorin and 1.5 +/- 0.57 cm2 in Medtronic-Hall prostheses; the performance index calculated as the ratio between functional area and manufactured area was 0.4-0.6 for Medtronic-Hall and 0.45-0.52 for Sorin prostheses. Prosthetic regurgitation was found in 64% of Sorin valves and 80% of Medtronic-Hall valves; prosthetic regurgitation was mild in 81% and moderate in 19% of cases. Doppler echocardiography is a reliable method for the characterization of the normal function of prosthetic aortic valves and provides information similar to cardiac catheterization.  相似文献   
992.
The pathogenesis of anaphylactic shock is not completely understood. Mast cell degranulation products may stimulate endothelial cells, leading to activation of fibrinolytic and coagulation systems. We investigated the activation of these systems in insect-sting anaphylaxis. Fifty-five patients with a previous insect-sting anaphylactic reaction and 8 volunteers were challenged with an in- hospital sting. Plasma levels of von Willebrand factor (vWF), coagulation, and fibrinolytic parameters were assessed. After the sting challenge, 20 patients developed anaphylactic symptoms, 7 of whom developed hypotension. In only these 7 patients, but not in the volunteers or in the other patients with no or mild anaphylactic symptoms, vWF levels increased from 107% +/- 33% (mean +/- SD) before, to 235% +/- 134% 60 minutes after the onset of clinical symptoms. This increase of vWF was accompanied by an increase of circulating tissue- type plasminogen-activator (tPA) levels from 5 +/- 3 micrograms/L to 50 +/- 59 micrograms/L and of plasminogen-alpha 2-antiplasmin complex (PAP- c) levels from 6 +/- 3 nmol/L to 297 +/- 225 nmol/L. Both tPA and PAP-c levels peaked 5 minutes after the onset of clinical symptoms. Such increases of tPA and PAP-c were not observed in the volunteers or in the patients who did not develop shock. The increase of tPA and PAP-c levels in the hypotensive patients correlated positively with the degree of mast cell degranulation and inversely with the mean arterial pressure. We conclude that activation of plasminogen may be involved in the pathogenesis of anaphylactic shock induced by insect venom.  相似文献   
993.
Chromium labelling characteristics of both ACD-stored and previously frozen red cells were evaluated. The chromium uptake of previously frozen red cells processed by agglomeration was inversely related to the hemoglobin level of the suspending fluid. Ascorbic acid was not needed for the labelling of previously frozen, agglomerated red cells.
Cellular injury, as measured by increase in supernatant hemoglobin during post-thaw storage at 4 C, occurred with the agglomerated, previously frozen red cells when: (1) Na2 EDTA was present in the glycerolizing solution; (2) the disaggregation of the agglomerated red cell mass was carried out with 75 rather than 250 ml of isotonic saline; and (3) the storage temperature of the glycerolized red cells was interrupted for one week with a storage interim at either 4 C or −20 C.
By use of a phthalate ester technic, red cells were separated into three fractions on the basis of cellular density. Preferential chromium labelling of red cells was noted: the lightest fraction contained significantly more radioactivity than the heaviest fraction.  相似文献   
994.
Background and purpose Rapid recovery protocols after total hip arthroplasty (THA) have been introduced worldwide in the last few years and they have reduced the length of hospital stay. We show the results of the introduction of a rapid recovery protocol for primary THA for unselected patients in our large teaching hospital.

Patients and methods In a retrospective cohort study, we included all 1,180 patients who underwent a primary THA between July 1, 2008 and June 30, 2012. These patients were divided into 3 groups: patients operated before, during, and after the introduction of the rapid recovery protocol. There were no exclusion criteria. All complications, re-admissions, and reoperations were registered and analyzed.

Results The mean length of hospital stay decreased from 4.6 to 2.9 nights after the introduction of the rapid recovery protocol. There were no statistically significant differences in the rate of complications, re-admissions, or reoperations between the 3 groups.

Interpretation In a large teaching hospital, the length of hospital stay decreased after introduction of our protocol for rapid recovery after THA in unselected patients, without any increase in complications, re-admissions, or reoperation rate.  相似文献   
995.
The SINERGIE (South Italian Network for Rational Guidelines and International Epidemiology) project is intended to set up a collaborative network comprising virologists, clinicians and public health officials dealing with patients affected by HCV disease in the Calabria Region. A prospective observational data-base of HCV infection will be developed and used for studies on HCV natural history, response to treatment, pharmaco-economics, disease complications, and HCV epidemiology (including phylogenetic analysis). With this approach, we aim at improving the identification and care of patients, focusing on upcoming research questions. The final objective is to assist in improving care delivery and inform Public Health Authorities on how to optimize resource allocation in this area.  相似文献   
996.
Understanding the skeletal effects of resistance exercise involves delineating the spatially heterogeneous response of bone to load distributions from different muscle contractions. Bone mineral density (BMD) analyses may obscure these patterns by averaging data from tissues with variable mechanoresponse. To assess the proximal femoral response to resistance exercise, we acquired pretraining and posttraining quantitative computed tomography (QCT) images in 22 subjects (25–55 years, 9 males, 13 females) performing two resistance exercises for 16 weeks. One group (SQDL, n = 7) performed 4 sets each of squats and deadlifts, a second group (ABADD, n = 8) performed 4 sets each of standing hip abductions and adductions, and a third group (COMBO, n = 7) performed two sets each of squat/deadlift and abduction/adduction exercise. Subjects exercised three times weekly, and the load was adjusted each session to maximum effort. We used voxel‐based morphometry (VBM) to visualize BMD distributions. Hip strength computations used finite element modeling (FEM) with stance and fall loading conditions. We used QCT analysis for cortical and trabecular BMD, and cortical tissue volume. For muscle size and density, we analyzed the cross‐sectional area (CSA) and mean Hounsfield unit (HU) in the hip extensor, flexor, abductor, and adductor muscle groups. Whereas SQDL increased vertebral BMD, femoral neck cortical BMD and volume, and stance hip strength, ABADD increased trochanteric cortical volume. The COMBO group showed no changes in any parameter. VBM showed different effects of ABADD and SQDL exercise, with the former causing focal changes of trochanteric cortical bone, and the latter showing diffuse changes in the femoral neck and head. ABADD exercise increased adductor CSA and HU, whereas SQDL exercise increased the hip extensor CSA and HU. In conclusion, we observed different proximal femoral bone and muscle tissue responses to SQDL and ABADD exercise. This study supports VBM and volumetric QCT (vQCT) to quantify the spatially heterogeneous effects of types of muscle contractions on bone. © 2014 American Society for Bone and Mineral Research.  相似文献   
997.

Background

A quality improvement collaborative is an intensive project involving a combination of implementation strategies applied in a limited “breakthrough” time window. After an implementation project, it is generally difficult to sustain its success. In the current study, sustainability was described as maintaining an implemented innovation and its benefits over a longer period of time after the implementation project has ended. The aim of the study was to explore potentially promising strategies for sustaining the Enhanced Recovery After Surgery (ERAS) programme in colonic surgery as perceived by professionals, three to six years after the hospital had successfully finished a quality improvement collaborative.

Methods

A qualitative case study was performed to identify promising strategies to sustain key outcome variables related to the ERAS programme in terms of adherence, time needed for functional recovery and hospital length of stay (LOS), as achieved immediately after implementation. Ten hospitals were selected which had successfully implemented the ERAS programme in colonic surgery (2006–2009), with success defined as a median LOS of 6 days or less and protocol adherence rates above 70%. Fourteen semi-structured interviews were held with eighteen key participants of the care process three to six years after implementation, starting with the project leader in every hospital. The interviews started by confronting them with the level of sustained implementation results. A direct content analysis with an inductive coding approach was used to identify promising strategies. The mean duration of the interviews was 37 minutes (min 26 minutes – max 51 minutes).

Results

The current study revealed strategies targeting professionals and the organisation. They comprised internal audit and feedback on outcomes, small-scale educational booster meetings, reminders, changing the physical structure of the organisation, changing the care process, making work agreements and delegating responsibility, and involving a coordinator. A multifaceted self-driven promising strategy was applied in most hospitals, and in most hospitals promising strategies were suggested to sustain the ERAS programme.

Conclusions

Joining a quality improvement collaborative may not be enough to achieve long-term normalisation of transformed care, and additional investments may be needed. The findings suggest that certain post-implementation strategies are valuable in sustaining implementation successes achieved after joining a quality improvement collaborative.
  相似文献   
998.
Depression leads to a poorer quality of life (QOL) which is a determinant of healthy ageing. Cost-effective solutions for enhancing QOL in the older population are much needed in China, with its rapidly ageing population. We conducted a randomized controlled trial involving 112 community-dwelling older participants with mild to moderate depression, to evaluate the effect of Tai Chi with music on QOL (57 in intervention group, 55 in control group). WHO Quality of Life-BREF was used to measure QOL at baseline and at every month for three months. Following the adjustments for sociodemographic data, the effect of intervention on QOL was assured (F = 25.145, P < 0.001, ηp2= 0.435, F = 18.696, P < 0.001, ηp2= 0.364, F = 17.473, P< 0.001, ηp2= 0.348, and F = 29.576, P < 0.001, ηp2= 0.475 for physical, psychological, social, and environment domains respectively). This intervention represents an economically viable solution to better QOL and healthy ageing in a highly populous developing nation.  相似文献   
999.
1000.
1,3,5-苯三甲酰氯和叠氮化钠在水和1,2.二氯乙烷中反应生成的苯三甲酰叠氮不予分离,一锅制备得到1,3,5.三异氰酸基苯,收率97%。操作安全。进而制备三氨基苯等衍生物。  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