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   15000篇
  免费   740篇
  国内免费   153篇
耳鼻咽喉   190篇
儿科学   307篇
妇产科学   188篇
基础医学   2263篇
口腔科学   359篇
临床医学   1359篇
内科学   2823篇
皮肤病学   537篇
神经病学   1154篇
特种医学   802篇
外科学   2098篇
综合类   74篇
一般理论   2篇
预防医学   676篇
眼科学   387篇
药学   1345篇
中国医学   188篇
肿瘤学   1141篇
  2023年   101篇
  2022年   320篇
  2021年   512篇
  2020年   280篇
  2019年   361篇
  2018年   406篇
  2017年   344篇
  2016年   491篇
  2015年   657篇
  2014年   762篇
  2013年   831篇
  2012年   1314篇
  2011年   1195篇
  2010年   747篇
  2009年   667篇
  2008年   857篇
  2007年   890篇
  2006年   767篇
  2005年   697篇
  2004年   566篇
  2003年   455篇
  2002年   430篇
  2001年   325篇
  2000年   297篇
  1999年   235篇
  1998年   98篇
  1997年   94篇
  1996年   59篇
  1995年   66篇
  1994年   36篇
  1993年   33篇
  1992年   89篇
  1991年   70篇
  1990年   89篇
  1989年   82篇
  1988年   82篇
  1987年   55篇
  1986年   58篇
  1985年   49篇
  1984年   31篇
  1983年   35篇
  1981年   29篇
  1980年   19篇
  1979年   39篇
  1978年   45篇
  1977年   28篇
  1976年   21篇
  1975年   33篇
  1974年   27篇
  1973年   20篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
81.
Bilateral congenital eventration of the diaphragm almost uniformly presents in infancy with respiratory compromise and is associated with a high mortality rate. Delayed presentation of diaphragmatic eventration in older children and adults may be associated with acute gastric volvulus. Thus, any patient with abdominal pain, vomiting, or nonspecific gastrointestinal symptoms in association with abnormal diaphragmatic findings on chest x-ray should undergo further diagnostic workup with upper gastrointestinal series or computed tomography (CT) scan. Treatment of gastric volvulus requires immediate surgical repair to prevent subsequent necrosis and perforation. The authors describe a case report of bilateral congenital diaphragmatic eventration complicated by a perforated gastric volvulus in a 13-year-old boy. Emergent reduction of the volvulus, closure of the perforated stomach, plication of the diaphragm, and placement of gastrostomy was performed successfully.  相似文献   
82.
Tailgut cyst in a neonate   总被引:1,自引:0,他引:1  
Tailgut cyst is a rare lesion of developmental origin located in the retrorectal space, which usually presents as a multilocular cystic mass. It is usually found in adults, and neonatal cases are extremely rare. The authors report a tailgut cyst in a neonate that was found by prenatal ultrasonogram, which was like a teratoma in gross appearance.  相似文献   
83.
OBJECTIVE: To compare the perioperative outcomes of two cesarean section methods, the finger-assisted stretching technique (FAST), based on a modified Joel-Cohen method, with the traditional technique. METHODS: A retrospective review of the records of 416 women who underwent cesarean sections at Guro Hospital, Seoul, Korea, between May 1993 and December 2001 was performed. Of the 416 women, 283 underwent cesarean sections with FAST and 133 with the traditional technique. RESULTS: Operative time was significantly shorter with FAST (15.3 vs. 42.6 min, P<.05), and FAST was associated with lower blood loss (601 vs. 928 mL, P<.05) and shorter hospital stay (3.7 vs. 6.5 days, P<.05). There were no significant differences in wound infection, voiding difficulty, and postoperative adhesions between the two methods. CONCLUSION: These results suggest that FAST may be the better technique.  相似文献   
84.
85.
To develop the new gel formulations that show sustained release for a period of time, the bioadhesive carbopol gels containing tretinoin were prepared. The release characteristics of drug from the carbopol gel were studied according to temperature, receptor medium and drug concentration. For the enhancement of its percutaneous absorption, some kinds of penetration enhancer were used. As the concentration of drug increased, the release of drug from the gel increased, showing concentration dependency. The increase of temperature showed the increased drug release, depending on the activation energy of permeation. Among the enhancers used such as the glycols and the non-ionic surfactants, polyoxyethylene 2-oleyl ether showed the best enhancing effect. The carbopol gels of tretinoin containing an enhancer could be developed for the enhanced transdermal delivery of drug.  相似文献   
86.
Epidemiologic studies of dietary marine n-3 fatty acids and risk of colorectal cancer have been inconsistent, and their relation to risk of colorectal adenoma has not been evaluated in detail. We examined dietary marine n-3 fatty acids and the ratio of marine n-3 to total n-6 fatty acids (n-3/n-6 ratio) in relation to risk of adenoma of the distal colon or rectum among 34,451 U.S. women who were initially free of colorectal cancer or polyps, who completed a semiquantitative food frequency questionnaire in 1980, and who underwent endoscopy from 1980 to 1998. We documented 1,719 distal colorectal adenoma cases (705 large adenomas, 897 small adenomas, 1,280 distal colon adenomas, and 505 rectal adenomas) during 18 years of follow-up. Neither dietary marine n-3 fatty acids nor n-3/n-6 ratio were associated with risk of total distal colorectal adenoma after adjustment for age and established risk factors [multivariable relative risk (RR) for extreme quintiles of dietary marine n-3 fatty acids = 1.04; 95% confidence interval (95% CI), 0.84-1.27, P(trend) = 0.66; RR for extreme quintiles of n-3/n-6 ratio = 1.02; 95% CI, 0.83-1.25; P(trend) = 0.86]. Similarly, no significant associations were observed separately for distal colon or rectal adenoma. However, higher intake of dietary marine n-3 fatty acids was nonsignificantly but suggestively inversely associated with large adenoma (RR, 0.74; 95% CI, 0.54-1.01; P(trend) = 0.16) but directly associated with small adenoma (RR, 1.36; 95% CI, 1.02-1.81; P(trend) = 0.09). Our findings do not support the hypothesis that a higher intake of marine n-3 fatty acids or a higher n-3/n-6 ratio reduces the risk of distal colorectal adenoma but are suggestive that higher intake may reduce the progression of small adenomas to large adenomas.  相似文献   
87.
The Comet assay has gained increasing popularity for use in human biomonitoring or epidemiologic studies; however, one of the shortcomings of the Comet assay is a lack of agreement on a single appropriate Comet parameter that is capable of adequately describing observed DNA damages. Among the tail parameters of Comet features, the most frequently used are the tail moments (both the Olive tail moment and the extent tail moment), the tail DNA, and the tail length. Some studies comparing Comet parameters have been found in cell toxicity research, but there are few comparative studies that use human biomonitoring or epidemiologic data. In this study, we evaluate those four tail parameters in both high and low DNA damaged cells with the use of epidemiologic data. To do this, a new graphical approach, the so-called quantile dispersion graphs (QDGs) are used. In a comparison of an exposed group and a control group, either the tail moment or tail DNA is preferable to the tail length. With respect to providing smaller variability in quantiles for the amount of DNA damage, however, the tail moment is the preferred parameter for both groups. Moreover, the tail moment provides the most stable estimates for DNA damage because it has a larger degree of uniformity in quantile dispersions. To study high degrees of damage from toxic exposure using B cells or G cells, however, the tail DNA showed more significant discrepancies than the other parameters, in terms of both the mean differences and the graphical differences between the two groups. In view of this result, it is suggested that both the tail moment and the tail DNA be presented as tail parameters in human biomonitoring studies.  相似文献   
88.
BACKGROUND: Venous thromboembolism (VT) after injury is a major health problem. Literature data on methods of VT prophylaxis are not consistent with regard to safety and efficacy, and a recent evidence-based report could not conclude that any method was superior to any other or to no prophylaxis. Because no study exists on the cost-effectiveness (C-E) of the different methods of prophylaxis, data from the evidence-based report were used to design a C-E analysis. This analysis will assist in the design of future randomized trials with adequate power to show significant outcome differences. METHODS: A decision-tree model was designed on the basis of outcomes from the evidence-based report or relevant literature. We then calculated the cost of prevention of VT by one of the most commonly used methods-low-dose heparin (LDH), low-molecular-weight heparin (LMWH), or sequential compression devices (SCDs)-using different probabilities of incidence of VT. Finally, we adjusted the cost for expected years of life after the episode of VT to calculate the cost per life-year saved by preventing VT. RESULTS: We produced two tables that can be used to calculate the cost per life-year saved for any patient according to his or her age and the method of prophylaxis used. VT prophylaxis becomes less cost-effective as age progresses, because of decreased life-expectancy. With a widely accepted cost limit of $50,000 per life-year saved to indicate cost-effective treatment, LDH is more cost-effective than LMWH or SCDs. CONCLUSION: Our C-E model can help future investigators plan VT-related research with appropriate sample sizes to evaluate cost-effective methods of prophylaxis. LMWH and SCDs must demonstrate substantial improvements in measured outcomes to be more cost-effective than LDH. C-E must be incorporated as a primary outcome in future studies comparing different methods of VT prophylaxis.  相似文献   
89.
Phloretin is one of the apple polyphenols with anticancer activities. Since tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) serves important roles in inducing apoptosis, the present study examined the effect of phloretin on TRAIL-induced apoptosis in colon cancer cells. Treatment with both phloretin and TRAIL markedly suppressed the survival of cancer cells from several colon cancer cell lines compared with that of cells treated with either TRAIL or phloretin. Additionally, decreased numbers of colonies were observed following addition of phloretin and TRAIL. Furthermore, TRAIL- and phloretin-treated HT-29-Luc cells exhibited decreased luciferase activity. Increased apoptosis was observed in phloretin- and TRAIL-treated HT-29-Luc colon cancer cells, accompanying elevated levels of cleaved poly(ADP-ribose) polymerase, and caspase-3, −8 and −9. The expression levels of MCL1 apoptosis regulator BCL2 family member (Mcl-1) were decreased following addition of phloretin in colon cancer cells. In addition, overexpression of Mcl-1 in phloretin- and TRAIL-treated HT-29-Luc cells resulted in increased cell survival. Treatment of HT-29-Luc cells with a combination of cycloheximide (CHX) and phloretin led to a more prominent decrease in Mcl-1 expression compared with that in cells treated with CHX alone, while Mcl-1 expression was recovered by treatment with MG132. Binding of ubiquitin with Mcl-1 was verified using immunoprecipitation. Intraperitoneal injection of both TRAIL and phloretin into tumor xenografts was associated with a decreased tumor volume compared with that following injection with either TRAIL or phloretin. Overall, the present results suggest a synergistic effect of phloretin on TRAIL-induced apoptosis in colon cancer cells.  相似文献   
90.
Two new polyketide glycosides jejuketomycins A (1) and B (2), were isolated from a culture of Streptomyces sp. KCB15JA151. Their chemical structures including the absolute configurations were determined by detailed analyses of the NMR and HRMS data and ECD calculations and spectral data. Compounds 1 and 2 possess an unusual 6/6/8 tricyclic ring system. Biological evaluation with the wound healing assay and time-lapse cell tracking analysis revealed that compounds 1 and 2 have significant inhibitory activities against cancer cell migration with low cytotoxicity.

Two new polyketide glycosides jejuketomycins A (1) and B (2), were isolated from a culture of Streptomyces sp. KCB15JA151.  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