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   1268篇
  免费   67篇
  国内免费   15篇
耳鼻咽喉   7篇
儿科学   101篇
妇产科学   38篇
基础医学   198篇
口腔科学   9篇
临床医学   88篇
内科学   200篇
皮肤病学   32篇
神经病学   112篇
特种医学   112篇
外科学   233篇
综合类   38篇
预防医学   37篇
眼科学   5篇
药学   56篇
肿瘤学   84篇
  2023年   7篇
  2022年   8篇
  2021年   10篇
  2019年   12篇
  2018年   16篇
  2017年   14篇
  2016年   21篇
  2015年   25篇
  2014年   26篇
  2013年   40篇
  2012年   46篇
  2011年   42篇
  2010年   41篇
  2009年   42篇
  2008年   42篇
  2007年   49篇
  2006年   51篇
  2005年   56篇
  2004年   39篇
  2003年   46篇
  2002年   40篇
  2001年   47篇
  2000年   45篇
  1999年   47篇
  1998年   43篇
  1997年   43篇
  1996年   24篇
  1995年   18篇
  1994年   24篇
  1993年   21篇
  1992年   26篇
  1991年   24篇
  1990年   27篇
  1989年   18篇
  1988年   18篇
  1987年   23篇
  1986年   17篇
  1985年   20篇
  1983年   13篇
  1982年   7篇
  1981年   12篇
  1980年   10篇
  1979年   10篇
  1978年   8篇
  1976年   8篇
  1974年   7篇
  1973年   7篇
  1933年   16篇
  1932年   30篇
  1931年   18篇
排序方式: 共有1350条查询结果,搜索用时 31 毫秒
991.
An increased cortisol response to challenge is associated with a variety of age-related disorders such as Alzheimer's disease, depression, diabetes, metabolic syndrome, and hypertension. Among the healthy elderly, an increased cortisol response to challenge may be a risk factor for developing these age-related disorders. We searched Pubmed, Embase, PsychInfo, Biosis, and Digital Dissertations (January 1966-June 2003) and included 45 parallel-group (young vs. old subjects) studies that used either a pharmacological or psychological challenge in healthy volunteers and measured cortisol response to challenge. We calculated effect sizes (Cohen's d) for the standardized mean differences between groups. Compared to younger controls (n=670, mean age 28 years +/-5), older subjects (n=625, 69+/-6) showed a larger cortisol response to challenge defined as stronger response to stimulation or less inhibition after a suppression test (d=0.42, 95% confidence interval (CI), 0.26-0.57). The effect of age on cortisol release was significantly stronger in women (d=0.65, 95% CI 0.34-0.97) than men (d=0.24, 95% CI 0.02-0.47). Our results demonstrate that aging increases the cortisol response to challenge. This effect of age on cortisol response is almost three-fold stronger in women than men. Prospective studies should explore whether the higher cortisol response in the elderly is a risk factor for developing neuropsychiatric and medical disorders.  相似文献   
992.
Clinical trials evaluating the potential benefit of anticoagulant treatment in pregnant women with inherited thrombophilia are based on the observation that a genetic predisposition to thrombosis is associated with frequent abortions and preterm birth. It was the aim of our study to delineate the impact of genetic polymorphisms with prothrombotic and antithrombotic effects on the occurrence of preterm birth in a large cohort of very-low-birth-weight (VLBW)-infants and their mothers. We examined the factor V Leiden and the prothrombin G20210A mutation, the factor VII 121del/ins and the factor XIII Val34Leu polymorphism in preterm very-low-birth-weight (VLBW, n=593) and term-born-infants (n=278) and their mothers (n=785). The primary outcome was preterm vs.term birth. From all polymorphisms tested, the maternal factor VII-121del/ins polymorphism (26.2 vs. 17.6 %; p=0.009) and the infant's factor VII-121del/ins polymorphism (29.0 vs. 20.0 %; p=0.009) were more frequent in singleton VLBW and their mothers compared to term infants and their mothers. Furthermore, the frequency of the factor XIII-Val34Leu polymorphism was significantly lower in singleton VLBW than in term infant controls (5.1 vs. 9.6%, p=0.025). In a multivariate regression analysis, previous preterm delivery (OR=3.8, 95% CI: 1.7-8.4), the maternal carrier status of the factor-VII-121del/ins polymorphism (OR=1.7, 95% CI: 1.12-2.5, p=0.007) and the lower frequency of infant's factor-XIII-Val34Leu polymorphism (OR=0.53; 95% CI: 0.29-0.96; p=0.038) were found to be independently associated with preterm delivery. InVLBW mothers with pathological CTG as cause of preterm delivery, the frequency of factor V Leiden mutation was significantly increased compared to VLBW mothers without pathological CTG (14.1 vs. 6.1%, p=0.01). The investigated haemostasis gene polymorphisms have a much lower impact on subsequent preterm delivery than known risk factors such as previous preterm birth. The reported association of the factor-VII-121del/ins polymorphism on preterm delivery and its clinical relevance needs to be further elucidated.  相似文献   
993.
994.

Background  

The percentage of women giving birth after the age of 35 increased in many western countries. The number of women remaining childless also increased, mostly due to aging oocytes. The method of oocyte donation offers the possibility for infertile older women to become pregnant. Gestation after oocyte-donation-IVF, however, is not without risks for the mother, especially at advanced age.  相似文献   
995.
In the past few years, knowledge acquired in reproductive medicine has led to the development of a wide range of methods of assisted reproduction (ART). Ovarian hyperstimulation using gonadotrophins is a standardized and highly efficient treatment option for inducing polyfollicular development to obtain a large number of oocytes and guarantee acceptable pregnancy rates. However, this technique has various disadvantages, and alternative new methods of assisted reproduction are thus being sought. In vitro maturation (IVM) is designed to aspirate immature cumulus-enclosed oocytes from small antral follicles in order to support their maturation from the germinal vesicle stage to the fertilizable metaphase 2 stage in vitro. IVM is now a simple and cost-saving technique. The technical framework has also been considerably improved. The data obtained to date suggest that IVM is safe. Due to the relatively short time in which IVM has been developed, this technique cannot yet approach the IVF/ICSI method, and it produces fewer pregnancies. However, IVM has great potential for development.  相似文献   
996.
OBJECTIVES: To analyze the mechanism of injury for foot and ankle fractures resulting from automobile accidents to create a basis for developing an improved design for protection. DESIGN: Retrospective. SETTING: Level I trauma center with accident research unit. PATIENTS: Automobile accident reports and medical records of individuals injured in the accidents. MAIN OUTCOME MEASUREMENTS: Technical indicators (collision type, impulse angle, deltav, and extent of vehicle deformation) and clinical data (injury location and severity [abbreviated injury scale and injury severity score] and long-term outcome). RESULTS: From 1973 to 1996, 15,559 car accidents were analyzed. Two hundred sixty-one front seat occupants sustained fractures of the foot and ankle (ankle, 41 percent; forefoot, 29 percent; midfoot, 20 percent; and hindfoot, 10 percent). Seventy-five percent of the fractures were classified abbreviated injury scale(foot) 2. The incidence, location, and abbreviated injury scale(foot) category of fractures were similar between driver (n = 210) and front seat passenger (n = 51). Fifty percent of the fractures occurred in head-on collisions and 34 percent occurred in accidents with multiple collisions. The deltav ranged in 82 percent of car crashes between fifteen and sixty kilometers per hour. The deltav and extent of foot compartment deformation correlated with the abbreviated injury scale. During our investigation, deltav increased; the injury severity score decreased; and the extent of deformation did not differ significantly. CONCLUSIONS: Although overall car passenger safety has improved, the relative incidence of foot and ankle fractures has increased. Comparing drivers and front seat passengers, the foot pedals, steering wheel, or the asymmetric design of the dashboard did not influence injury incidence, mechanism, or severity. Foot fractures are mainly caused by the foot compartment deformation in head-on collisions, and therefore improvements in foot compartments are essential for fracture prevention.  相似文献   
997.
The plasticity of the brain   总被引:3,自引:0,他引:3  
  相似文献   
998.
BACKGROUND: Elevated right ventricle pressure resulting from pulmonary artery stenoses may affect outcome and survival after liver transplantation in patients with Alagille syndrome. METHODS AND RESULTS: Between 1984 and 1997, among 444 pediatric liver transplant recipients, 17 had liver transplantation for Alagille syndrome (mean age 3.5 years, range 1.2-13 years), mainly because of poor quality of life with intractable pruritus, and failure to thrive. All patients had pulmonary artery stenosis. In 10 patients considered to have elevated RV pressure on ECG and/or Doppler-echocardiography, a cardiac catheterization was performed before liver transplantation. Mean RV systolic pressure was 55 mmHg (median 49.5 mmHg, range 35-98 mm Hg), mean RV to left ventricular systolic pressure ratio 0.53 (median 0.53, range 0.29-0.78) with a ratio above 0.5 in 6 patients (median 0.66, range 0.5-0.8). All patients underwent successful liver transplantation. Five patients died 1 to 9 months after transplantation from noncardiac causes. In two of them, cardiac catheterization before transplantation showed a RV to left ventricular pressure ratio of 0.51 in one and 0.37 in the second. In the three others, echocardiography before transplantation estimated RV pressures below 0.5 systemic pressures. At follow-up (median 6 years, range 1.5-15 years), liver tests were normal in all, none complained of pruritus and body weight was normalized in 70%. None of the patients presented cardiac symptoms, arrhythmias, or worsening of their cardiac status. CONCLUSIONS: Liver transplantation can be performed safely in children with Alagille syndrome, even in the presence of elevated right ventricular pressure.  相似文献   
999.
Alterations of the hypothalamic-pituitary-adrenal (HPA) axis and sleep disturbances have been described separately in post-traumatic stress disorder (PTSD). It is not known if HPA alterations and sleep disturbances are associated in PTSD. This study examined sleep and HPA activity in 20 male medication-free subjects with PTSD and 16 matched healthy controls. Two nights of polysomnography were obtained and 24-h urinary cortisol was collected during day 2. Subjects self-administered a low-dose (0.5 mg) salivary dexamethasone test at home. Compared with controls, PTSD subjects had higher 24-h urinary microg cortisol/g creatinine (mean+/-SD 40+/-17 vs 28+/-12, p=0.03) but not significantly higher 24-h urinary cortisol (mean+/-SD 52+/-15 microg/day vs 43+/-23, p=0.19). PTSD subjects showed a trend towards less cortisol suppression after dexamethasone (73%+/-18 vs 83%+/-10, p=0.06). In the combined sample, delta sleep was significantly and negatively correlated with 24-h urinary cortisol (r=-0.36, p=0.04), and with 24-h urinary cortisol/g creatinine on a trend level (r=-0.34, p=0.06). Our results suggest that increased cortisol is negatively associated with delta sleep. This may contribute to sleep abnormalities in conditions associated with elevated cortisol, possibly including PTSD. Future studies should explore the temporal relationship between HPA activity, sleep disturbances, and psychopathology after a traumatic event.  相似文献   
1000.
PURPOSE: To evaluate known and suggested prognostic markers, especially insulin-like growth factor type 1 receptor (IGF-1R), in highly malignant soft tissue sarcomas (STS). EXPERIMENTAL DESIGN: A cohort of 101 patients with primary STS of high malignancy grade was studied with respect to development of metastasis, local recurrence, and survival during a minimum of 5 years follow-up. All tumors were analyzed by immunohistochemistry for expression of Ki-67, p53, p27, Bcl-2, IGF-1R, and microvessel density. The traditional clinical variables size, malignancy grade (3 or 4), necrosis, mitotic frequency, infiltrative tumor growth, vascular invasion, depth, and surgical margins were also evaluated. RESULTS: A significant association was shown between high expression of IGF-1R and favorable outcome. Among STS with positive IGF-1R immunoreactivity, cases with high expression (76-100% positive cells) had the best outcome, whereas cases with the lowest expression (1-25% positive cells) had the worst. As expected, large tumor size (>11 cm), presence of necrosis, high mitotic count, intralesional surgery, and deep location were all significantly associated with poor outcome, both in univariate and multivariate analyses. No difference in outcome was observed between cases of malignancy grade 3 versus 4, whereas the included and more objective variables necrosis and mitotic count were found to be reliable prognostic markers. CONCLUSION: IGF-1R expression is a common feature of highly malignant STS. Further elucidation of the role of IGF-1R and the IGF system in STS may both provide a basis for development of new prognostic tools in STS, as well as shed light on the basic mechanisms of the STS development.  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