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   6481篇
  免费   528篇
  国内免费   12篇
耳鼻咽喉   57篇
儿科学   152篇
妇产科学   112篇
基础医学   783篇
口腔科学   100篇
临床医学   849篇
内科学   1335篇
皮肤病学   102篇
神经病学   510篇
特种医学   195篇
外科学   1089篇
综合类   60篇
一般理论   3篇
预防医学   612篇
眼科学   93篇
药学   465篇
中国医学   7篇
肿瘤学   497篇
  2023年   60篇
  2022年   102篇
  2021年   324篇
  2020年   185篇
  2019年   246篇
  2018年   280篇
  2017年   201篇
  2016年   176篇
  2015年   269篇
  2014年   272篇
  2013年   377篇
  2012年   494篇
  2011年   520篇
  2010年   259篇
  2009年   185篇
  2008年   328篇
  2007年   308篇
  2006年   325篇
  2005年   246篇
  2004年   237篇
  2003年   218篇
  2002年   198篇
  2001年   111篇
  2000年   91篇
  1999年   99篇
  1998年   49篇
  1997年   39篇
  1996年   36篇
  1995年   39篇
  1994年   17篇
  1993年   26篇
  1992年   62篇
  1991年   53篇
  1990年   55篇
  1989年   53篇
  1988年   54篇
  1987年   48篇
  1986年   39篇
  1985年   40篇
  1984年   40篇
  1983年   25篇
  1980年   12篇
  1979年   18篇
  1978年   12篇
  1974年   15篇
  1973年   16篇
  1971年   16篇
  1970年   15篇
  1968年   15篇
  1966年   15篇
排序方式: 共有7021条查询结果,搜索用时 15 毫秒
991.
In this cross‐sectional study, we aimed to predict age‐related changes in bone microarchitecture and strength at the distal radius (DR) and distal tibia (DT) in 644 Canadian adults (n = 442 women and 202 men) aged 20 to 99 years. We performed a standard morphologic analysis of the DR and DT with high‐resolution peripheral quantitative computed tomography (pQCT) and used finite‐element analysis (FEA) to estimate bone strength (failure load) and the load distribution. We also calculated a DR load‐to‐strength ratio as an estimate of forearm fracture risk. Total bone area, which was 33% larger in young men at both sites, changed similarly with age in women and men at the DT but increased 17% more in men than in women at the DR (p < .001). Trabecular number and thickness (Tb.Th) were 7% to 20% higher in young men than in young women at both sites, and with the exception of Tb.Th at the DR, which declined more with age in men (?16%) than in women (?2%, p < .01), the age‐related decline in these outcomes was similar in women and in men. In the cortex, porosity (Ct.Po) was 31% to 44% lower in young women than in young men but increased 92% to 176% more with age in women than in men (p < .001). The DR cortex carried 14% more load in young women than in young men, and the percentage of load carried by the DR cortex did not change with age in women but declined by 17% in men (p < .01). FEA‐estimated bone strength was 34% to 47% greater in young men, but the predicted change with age was similar in both sexes. In contrast, the load‐to‐strength ratio increased 27% more in women than in men with age (p < .01). These results highlight important site‐ and sex‐specific differences in patterns of age‐related bone loss. In particular, the trends for less periosteal expansion, more porous cortices, and a greater percentage of load carried by the DR cortex in women may underpin sex differences in forearm fracture risk. © 2011 American Society for Bone and Mineral Research.  相似文献   
992.
993.
Study Type – Prognosis (inception cohort) Level of Evidence 1b What’s known on the subject? and What does the study add? Large population screening trials like the ERSPC, PCPT and PLCO have noted that men with seemingly low PSA (even as low as 0.5 ng/dL) still can have prostate cancer. Despite these findings, PSA is still predominantly used as a current indicator for possible presence of prostate cancer rather than also serving as a prognostic marker. This study examines a larger number of men in a diverse US population to determine the prognostic value of a man’s baseline or first PSA.

OBJECTIVES

? To assess the value of a PSA threshold of 1.5 ng/mL as a predictor of increased prostate cancer risk over a four‐year period based on a man’s first PSA test, including racial differences. ? To review the risk of progression of benign prostatic hyperplasia (BPH) based on a similar PSA threshold.

PATIENTS AND METHODS

? A retrospective review involving 21 502 men from a large Midwestern health system was performed. ? Men at least 40 years old with baseline PSA values between 0 and 4.0 ng/mL and at least four years of follow‐up after initial PSA test were included. ? Optimal PSA threshold and predictive value of PSA for development of prostate cancer were calculated.

RESULTS

? Prostate cancer rates were 15‐fold higher in patients with PSA ≥1.5 ng/mL vs patients with PSA <1.5 ng/mL (7.85% vs 0.51%). ? African American patients with baseline PSA <1.5 ng/mL faced prostate cancer rates similar to the whole study population (0.54% vs 0.51%, respectively), while African American patients with PSA 1.5–4.0 ng/mL faced a 19‐fold increase in prostate cancer.

CONCLUSION

? Both Caucasian and African American men with baseline PSA values between 1.5 and 4.0 ng/mL are at increased risk for future prostate cancer compared with those who have an initial PSA value below the 1.5 ng/mL threshold. ? Based on a growing body of literature and this analysis, it is recommended that a first PSA test threshold of 1.5 ng/mL and above, or somewhere between 1.5 and 4.0 ng/mL, represent the Early‐Warning PSA Zone (EWP Zone). ? This should serve to inform patients and clinicians alike to future clinical activities with respect to prostate cancer and BPH.  相似文献   
994.
995.
Throughout the current conflicts in Afghanistan and Iraq, there have been more than 1100 combat-related major limb amputations, with approximately 80% involving the lower extremity. There is, however, a paucity of data regarding the number of amputations below the level of the ankle. Although not as common, partial foot amputations, in the appropriate setting, offer a way to improve function and decrease energy consumption when compared to proximal amputations. Sound surgical tenets are prerequisite for successful outcomes when performing a distal amputation. Maintaining a robust soft tissue envelope allowing for tension-free wound closure is paramount in determining the feasibility of a partial foot amputation. Careful consideration of tendon balancing is also of utmost importance in avoiding common complications of contracture and deformity. Partial foot amputations present a viable surgical option for successful outcomes and maximization of patient function in the combat injured when certain criteria are met.  相似文献   
996.
997.
OBJECTIVES: We used McCubbin's Resiliency Model of Family Stress, Adjustment and Adaptation ( McCubbin, Thompson, & McCubbin, 2001) to examine how demographic factors, family stress, grandmother resourcefulness, support, and role reward affect perceptions of family functioning for grandmothers raising grandchildren, grandmothers living in multigenerational households, and grandmothers not caregiving for grandchildren. METHODS: A sample of 486 grandmothers completed a mailed questionnaire. We used structural equation modeling to (a) test the effects of demographic factors (i.e., grandmother's age, race, marital status, and employment), family stressful life events and strain, grandmother's resourcefulness, subjective and instrumental support, and role reward on perceptions of family functioning for each grandmother group; (b) evaluate differences in the measurement and structural models between the grandmother groups using multisample analysis; and (c) test the model on the full sample, coding for caregiver status. RESULTS: The models did not differ significantly by grandmother group; therefore we assessed the composite model using a multisample analysis. We found general support for the resiliency model and equivalence of the models across grandmother groups. Less support, resourcefulness, and reward, and more intrafamily strain and stressful family life events contributed to perceptions of worse family functioning. DISCUSSION: Findings demonstrate the importance of the quality of family functioning for grandmothers in all types of families.  相似文献   
998.
999.
Lau AH, Soltys K, Sindhi RK, Bond G, Mazariegos GV, Green M. Chronic high Epstein–Barr viral load carriage in pediatric small bowel transplant recipients.
Pediatr Transplantation 2010: 14:549–553. © 2010 John Wiley & Sons A/S. Abstract: The development of EBV infection and PTLD is normally associated with a high EBV load in peripheral blood. Often, children undergoing primary or reactivation of EBV infection subsequent to ITx will have chronically elevated EBV loads. To better understand this phenomenon and its consequences, we retrospectively reviewed the records of children who underwent ITx (either isolated or part of multivisceral transplantation) at our center from 1992 to 2007, to identify chronic high EBV load carriers in this population. CHL state was defined as the presence of high load for >50% of samples for greater than or equal to six months following either asymptomatic infection or complete clinical resolution of EBV disease/PTLD. Thirty‐five CHL carriers were identified from our patient population. Pretransplant serologies were available on 34 of these patients: 17 were EBV negative and 17 seropositive; one had unknown EBV serostatus prior to transplant. Seven of the 17 seronegative patients developed their CHL carrier state at the time of their primary EBV infection. Thirteen of the 35 (37%) HLC patients developed EBV disease after meeting the definition of high‐load carrier states. EBV‐related diseases developing in CHL carriers included EBV adenitis (n = 1), EBV enteritis (n = 7), PTLD (n = 4), and EBV+ spindle cell tumor (n = 1). Disease was seen in 7/17 of the seronegative (one PTLD) and 6/17 of the seropositive patients (three PTLD). Thirteen of 35 patients (37%) resolved their CHL state without apparent sequelae while nine remain asymptomatic CHL carriers. Three children have had more than one episode of CHL. These data provide important information about the outcome of chronic EBV high‐load carriage in pediatric intestinal transplant recipients.  相似文献   
1000.
BACKGROUND AND PURPOSE: Most patients have minimal pain after percutaneous radiofrequency ablation (RFA) of a renal tumor. However, anecdotally, there is some variation in the amount of patient discomfort. Our goal was to identify relevant patient factors and characteristics of their renal tumors that may influence pain after percutaneous RF ablation. PATIENTS AND METHODS: We performed a retrospective chart review of 59 sequential patients who received percutaneous RFA between 2001 and 2005 at a single institution. Data on patient age, sex, body mass index (BMI), and narcotic administration in the periprocedural period were available for 46 patients. Preoperative imaging (CT or MRI) was reviewed to determine tumor size and location, as well as the shortest distance of the mass to the body-wall musculature. RESULTS: The distance from the renal mass to the body-wall musculature was significantly correlated with the total narcotics received in the periprocedural period. This measured distance did not correlate with the patient's BMI. No other relations between patient factors or tumor characteristics and peri-procedural narcotic usage were identified. CONCLUSION: Patients whose tumors lie close to their body-wall musculature have greater narcotic requirements in the periprocedural period. Knowledge of this correlation should result in better patient counseling and help anticipate periprocedural analgesia requirements.  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