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   123291篇
  免费   8054篇
  国内免费   535篇
耳鼻咽喉   1313篇
儿科学   3632篇
妇产科学   2062篇
基础医学   16385篇
口腔科学   2207篇
临床医学   12186篇
内科学   26093篇
皮肤病学   1479篇
神经病学   11959篇
特种医学   3814篇
外国民族医学   1篇
外科学   17699篇
综合类   1658篇
现状与发展   1篇
一般理论   156篇
预防医学   10748篇
眼科学   3319篇
药学   8722篇
  1篇
中国医学   278篇
肿瘤学   8167篇
  2023年   609篇
  2022年   1066篇
  2021年   2368篇
  2020年   1410篇
  2019年   2402篇
  2018年   2803篇
  2017年   2039篇
  2016年   2379篇
  2015年   2743篇
  2014年   3958篇
  2013年   5557篇
  2012年   8473篇
  2011年   9096篇
  2010年   4966篇
  2009年   4631篇
  2008年   8025篇
  2007年   8514篇
  2006年   8070篇
  2005年   8122篇
  2004年   7667篇
  2003年   7067篇
  2002年   6816篇
  2001年   1192篇
  2000年   890篇
  1999年   1228篇
  1998年   1452篇
  1997年   1224篇
  1996年   949篇
  1995年   945篇
  1994年   799篇
  1993年   786篇
  1992年   664篇
  1991年   607篇
  1990年   540篇
  1989年   501篇
  1988年   502篇
  1987年   484篇
  1986年   419篇
  1985年   497篇
  1984年   562篇
  1983年   522篇
  1982年   697篇
  1981年   610篇
  1980年   534篇
  1979年   368篇
  1978年   347篇
  1977年   348篇
  1976年   291篇
  1975年   272篇
  1974年   279篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
PURPOSE: To evaluate the feasibility of dose escalation in non-small cell lung cancer (NSCLC) using three-dimensional conformal radiation therapy. PATIENTS AND METHODS: The main eligibility criteria of the trial were: pathologically proven inoperable NSCLC, ECOG performance status or=grade 3 (SWOG), grade 3 early and grade 2 late esophageal toxicity or any other (RTOG) grade 3 or 4 complications). RESULTS: Fifty-five patients were included. Tumor stage was I/II in 47%, IIIA in 33% and IIIB in 20%. The majority of the patients received a dose of 74.3 Gy (n=17) or 81.0 Gy (n=23). Radiation pneumonitis occurred in seven patients: four patients developed a grade 2, two patients grade 3 and one patient a grade 4. Esophageal toxicity was mild. In 50 patients tumor response at 3 months follow-up was evaluable. In six patients a complete response was recorded, in 38 a partial response, five patients had stable disease and one patient experienced progressive disease. Only one patient developed an isolated failure in an uninvolved nodal area. So far the radiation dose was safely escalated to 87.8 Gy in group 1 (lowest rMLD), 81.0 Gy in groups 2 and 3 and 74.3 Gy in group 4. CONCLUSION: Three-dimensional conformal radiotherapy enables significant dose escalation in NSCLC. The maximum tolerable dose has not yet been reached in any risk group.  相似文献   
992.
Background. Abnormalities of the pulmonary arteries following palliative or corrective surgery for tetralogy of Fallot (TOF) are common. Our purpose was to compare the usefulness of magnetic resonance imaging (MRI) and echocardiography in the post- operative evaluation of the pulmonary arteries in children with TOF. Objective. Our hypothesis was that MRI is more sensitive than echocardiography in the detection of branch pulmonary artery abnormalities in children with TOF. Materials and methods. Pulmonary artery MRI and echocardiography were performed in 20 children following palliative and/or corrective surgery for TOF. MRI and echocardiography were compared in their ability to detect abnormalities of the pulmonary arteries. Angiographic or surgical correlation was available in 15 children. A perfusion scan for confirmation of pulmonary artery patency was available in one additional child. Results. Abnormalities of the branch pulmonary arteries identified by MRI included: absence or occlusion (2), focal stenosis (15), hypoplasia (2), aneurysm (1), and non-confluence (1). Echocardiography could not adequately visualize the right and left branch pulmonary arteries in eight and ten children, respectively. Echocardiography missed stenosis in 13 branch pulmonary arteries, patency of hypoplastic pulmonary arteries in two children, non-confluence of the pulmonary arteries in one child, and a left pulmonary artery aneurysm in one child. Abnormalities identified by MRI were confirmed in 16 children by angiography, surgery or perfusion scan. Conclusion. MRI is more sensitive than echocardiography for the evaluation of branch pulmonary artery abnormalities in children following surgery for TOF. Received: 13 January 1997 Accepted: 31 July 1997  相似文献   
993.
Interleukin-8 (IL-8), a potent neutrophilic chemoattractant and inflammatory cytokine, is present in middle ear effusions (MEEs) of children with otitis media and is thought to be responsible for the accumulation of neutrophils in MEEs. We hypothesized that IL-8 concentration predicts the total number and proportion of neutrophils in MEEs. IL-8 concentration and total and differential cell counts were measured in MEEs of children undergoing tympanostomy tube placement for otitis media. IL-8 was present in 80 (98%) of 82 effusions. The mean ± SEM value for IL-8 was 7342 ± 847 pg/mL. The mean ± SEM count and percentage of neutrophils were 1.34 × 106 ± 3.44 × 105 and 70.6 ± 3.1%, respectively. IL-8 concentrations correlated positively with the total number(r = +0.30; P = 0.02) and percentage of neutrophils(r= +0.32; P = 0.01) in the effusion. Additionally, purulent effusions had greater IL-8 concentrations (P = 0.003) and greater neutrophil count (P = 0.03) than mucoid or serous effusions. We conclude that IL-8 is consistently present in MEEs of children and IL-8 concentration predicts the total number and proportion of neutrophils. Furthermore, IL-8 concentration and the total number of neutrophils correlate positively with the type of effusion. These results support the hypothesis that IL-8 recruits neutrophils to the middle ear in MEEs.  相似文献   
994.
Fifty-three patients with T1 squamous cell cancer of the floor of mouth and ventral surface of the tongue with a known clinical outcome were retrospectively analyzed and arbitrarily divided into “aggressive” and “nonaggressive” groups based on their clinical behavior. Various host and tumor factors were then evaluated in an attempt to determine whether the tumor behavior could have been predicted. The paraffin-embedded tumor specimens were evaluated for tumor differentiation, tumor thickness and tumor invasion, microvessel density, and p53 expression. In addition, a composite morphologic grading score was obtained by combining cell differentiation, nuclear polymorphism, mitosis activity, depth of infiltration, type of infiltration, and lymphatic infiltration. No single technique appeared capable of identifying “aggressive” behavior, although possibly an evaluation of composite factors might show promise in the future.  相似文献   
995.
Brachytherapy can be employed in the primary or salvage treatment of head and neck cancer. The advantage of brachytherapy is the stereotactic limitation of radiation exposure to noninvolved tissues. Wound complications associated with brachytherapy have been discussed only sporadically in the literature. This retrospective study examines 28 patients, 20 for initial treatment and eight for salvage, with varying site and stage head and neck cancer treated with brachytherapy in addition to external beam radiation therapy and/or surgery. The overall complication rate was 50% (14/28), with infection and minor flap breakdown being the most common problems. Tumor site in the primary treatment group was the only significant factor in wound complications. In the salvage group complications were minor and primarily related to flap coverage of brachytherapy catheters.  相似文献   
996.
Objective To assess the effects of medroxyprogesterone acetate on bone density in women who have had a hysterectomy
Design Randomised, double-blind, placebo-controlled trial of medroxyprogesterone acetate 10 mg, 20 mg or placebo as an adjunct to oestrogen therapy.
Participants One hundred and twenty-three women, aged 18 to 45 years and currently receiving daily oestrogen, who presented at a university-based rheumatology practice.
Interventions The women were randomly assigned to receive either medroxyprogesterone acetate 10 mg, 20 mg or placebo daily beginning on day 15 of each month for one year. Forty-one women were randomised into each group.
Main outcome measure The primary outcome measurement was the percentage of change from baseline in bone mineral density of the lumbar spine (L2–L4). Secondary outcome measures included differences in femoral neck bone density, cholesterol and triglyceride levels between groups.
Results At one year, change in bone mineral density did not differ between either the treatment or placebo groups. Medroxyprogesterone acetate 20 mg and 10 mg led to statistically significant reductions in very low density lipoprotein cholesterol, total triglycerides, and very low density lipoprotein triglycerides when compared with placebo. Medroxyprogesterone acetate 20 mg also led to a statistically significant reduction in high density lipoprotein cholesterol, high density lipo-protein-2 cholesterol, and high density lipoprotein-2 triglycerides.
Conclusions Medroxyprogesterone acetate at either dose as an adjunct to oestrogen did not improve bone mineral density at one year when compared with placebo. Medroxyprogesterone acetate 10 mg may not adversely affect lipids. Medroxyprogesterone acetate 20 mg, however, did reduce high density lipoprotein cholestrol and therefore may increase cardiovascular risk.  相似文献   
997.
Purpose: The purpose of this study was to evaluate the clinical effectiveness of subcutaneous estradiol pellets in donor oocyte recipients with an inadequate endometrial response. Methods: The subjects were 13 women with ovarian failure and a maximal endometrial thickness <10 mm on standard estrogen regimens, as demonstrated during mock and/or prior oocyte donation cycles. They underwent pellet implantation (100–250 mg of estradiol) 6–13 weeks before oocyte donation. Results: Maximal (mean ± SD) endometrial thickness was 8.7±1.5 mm on standard regimens, in contrast to 11.7± 1.8 mm on pellets, while estradiol levels were 674±844 and 815±706 pg/ml, respectively. The estradiol:estrone ratio on pellets was >1. There was 1 pregnancy with early loss during 10 cycles on other estrogen regimens and 12 pregnancies during 19 cycles on pellets. The pregnancy and implantation rates were, respectively, 63 and 27% on pellets and 41 and 14% on standard regimens in historical controls. Conclusions: We conclude that estradiol pellets after a single administration provide constant estradiol levels extending into the first trimester of pregnancy, a physiologic estradiol:estrone ratio, and a better endometrial response than standard estrogen regimens. Implantation and pregnancy rates are higher. This approach may be especially suitable for recipients with a poor endometrial response. Presented at the IXth World Congress on In Vitro Fertilization and Assisted Reproduction, Vienna, Austria, April 3, 1995, and the 51st Annual Meeting of the American Society for Reproductive Medicine, Seattle, Washington, October 7–12, 1995.  相似文献   
998.
The field of molecular genetics continues to see an ever increasing number of applications to pediatric tumor analysis. Studies in pediatric tumors have identified novel genes and other genetic changes, a large number of which reflect one of the following mechanisms: (1) activation of proto-oncogenes; (2) loss of tumor suppressor genes; or (3) creation of novel fusion proteins. At least one of these mechanisms is operational in each of the following pediatric tumors: neuroblastoma, Ewing sarcoma and peripheral primitive neuroectodermal tumor (pPNET), intra-abdominal desmoplastic small-cell tumor, rhabdomyosarcoma, synovial sarcoma, and Wilms tumor. Out of this research has come not only an increased understanding of oncogenesis but also, for each of the tumors listed above, diagnostic and/or prognostic markers that can be used by the pathologist and oncologist to improve overall patient management. Received November 20, 1997; accepted April 20, 1998.  相似文献   
999.
In neonates with pulmonary atresia and intact ventricular septum the aims of therapy are maintenance of pulmonary blood flow and right ventricular decompression in order to achieve right ventricular support of the pulmonary circulation. Recent developments in interventional heart catheterization with pulmonary radiofrequency-assisted balloon valvuloplasty and ductal stent implantation offer an alternative to the classical surgical approach. We report on a neonate with membranous pulmonary atresia and intact ventricular septum, in whom a large interatrial right-to-left shunt via the foramen ovale persisted after radiofrequency-assisted pulmonary balloon valvuloplasty on the 2nd day of life. The interatrial shunt prevented adequate right ventricular filling and antegrade pulmonary perfusion leading to severe cyanosis (transcutaneous oxygen saturation 40%). In order to increase pulmonary blood flow and raise left atrial pressure, the arterial duct was stented. After ductal stenting, prostaglandin was discontinued and the transcutaneous oxygen saturation remained stable around 89%. At follow up after 7 weeks the foramen ovale had decreased in size and only a small left-to-right shunt was present, documenting the effectiveness of this approach. Conclusion Based on the present case we propose a stepwise interventional approach for the neonate with pulmonary atresia and intact ventricular septum. If cyanosis persists after isolated pulmonary valvuloplasty despite adequate right ventricular function, ductal stent implantation can reduce interatrial shunting and thus improve oxygen saturation. Received: 12 January 1998 / Accepted: 15 February 1998  相似文献   
1000.
Objective: Our purpose was to determine the incidence of gestational diabetes mellitus in an adolescent population and to determine the cost of screening. Study Design: A retrospective review of 509 adolescent pregnancies was performed. The incidence of gestational diabetes mellitus was determined and the cost of screening analyzed. Results: Five hundred nine adolescent pregnancies were screened for gestational diabetes mellitus with a 1-hour, 50 gm oral glucose challenge test. Twenty-three of the screens (4.5%) had positive results at a plasma glucose level of ≥140 mg/dl. Three-hour 100 gm oral glucose tolerance tests were performed on screen-positive women, six of whom were diagnosed with gestational diabetes mellitus, for an incidence of 1.18%. The cost per case diagnosed was $2733. Conclusions: The incidence of gestational diabetes mellitus in an adolescent population is low. The cost of universal screening may be prohibitive in this population. Large prospective studies are needed to better analyze outcome data and efficacy of screening in adolescent pregnancies. (Am J Obstet Gynecol 1998;178:1251-6.)  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