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   39747篇
  免费   2690篇
  国内免费   112篇
耳鼻咽喉   418篇
儿科学   1325篇
妇产科学   1072篇
基础医学   5471篇
口腔科学   655篇
临床医学   6230篇
内科学   7293篇
皮肤病学   659篇
神经病学   3647篇
特种医学   738篇
外科学   3944篇
综合类   482篇
一般理论   60篇
预防医学   4921篇
眼科学   479篇
药学   2332篇
中国医学   69篇
肿瘤学   2754篇
  2023年   196篇
  2022年   386篇
  2021年   822篇
  2020年   505篇
  2019年   828篇
  2018年   950篇
  2017年   669篇
  2016年   704篇
  2015年   901篇
  2014年   1258篇
  2013年   1890篇
  2012年   2806篇
  2011年   2980篇
  2010年   1619篇
  2009年   1352篇
  2008年   2681篇
  2007年   2693篇
  2006年   2717篇
  2005年   2564篇
  2004年   2431篇
  2003年   2317篇
  2002年   2165篇
  2001年   364篇
  2000年   292篇
  1999年   408篇
  1998年   449篇
  1997年   404篇
  1996年   371篇
  1995年   325篇
  1994年   308篇
  1993年   277篇
  1992年   238篇
  1991年   201篇
  1990年   223篇
  1989年   207篇
  1988年   161篇
  1987年   184篇
  1986年   153篇
  1985年   189篇
  1984年   222篇
  1983年   215篇
  1982年   225篇
  1981年   183篇
  1980年   179篇
  1979年   143篇
  1978年   115篇
  1977年   122篇
  1976年   110篇
  1975年   103篇
  1974年   106篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
As part of a detailed study of limb defects and associated patterns of congenital malformations, cases with lower limb deficiencies were analysed separately. We identified a total of 130 cases with deficiencies of the lower limbs without defects of the upper limbs. This gives an incidence of 1.07/10,000 livebirths, or 1/9,337 for this group of limb defects. Most common were femur deficiencies and deficiencies of the foot. A preponderance of males was found in the group of transverse defects of the leg (fibula/tibia deficiencies) and central axis deficiencies, while females had significantly more often longitudinal tibia defects and preaxial ray defects. © 1993 Wiley-Liss, Inc.  相似文献   
82.
Objectives. To evaluate the process of soft-tissue electrovaporization and to study variables that affect tissue clearance rates in a laboratory setting, in order to identify parameters that can optimize transurethral electrovaporization of the prostate.Methods. Fresh bovine skeletal muscle, equivalent in impedance and surface properties to the human prostate, was submerged in 3.3% sorbitol solution and electrovaporized with a grooved monopolar electrode attached to the weighted arm of a linear actuator. The effects of excursion rate, applied mechanical load, power setting, electrode configuration, and generator performance on the volume of tissue removed, were assessed.Results. Tissue removal increased significantly when electrode excursion rate was slowed from 25 to 15 mm/s (P <0.05) and then to 10 mm/s (P <0.05); when the load was increased from 20 to 50 g (P <0.005); and when dial power was increased from 120 to 150 W (P <0.01). Tissue removal was generator dependent. There was no significant difference between the Force 40 and the Force 2 (P > 0.4), but a new computer-controlled constant power output generator (Force FX) did significantly improve tissue vaporization at an equivalent power setting (P <0.005 and P <0.01, respectively). Tissue removal was also dependent upon electrode configuration, with the VaporTrode-Grooved Bar removing significantly more tissue than either an ungrooved roller bar of equivalent size or 2-mm smooth roller ball, respectively, both after a single pass (P <0.001 and P <0.05) and after five repeated passes (P <0.05 and P <0.005). The histologic depth of tissue thermal effect was less than 1 mm, but it was 38% greater for the VaporTrode-Grooved Bar (0.68 mm) than for the standard cutting loop (0.5 mm, P <0.01).Conclusions. Using a novel method to quantify tissue removal, we have demonstrated that electrode configuration, excursion rate, applied load, power setting, and generator performance are interdependent factors that influence the efficacy of the electrovaporization process in a fluid environment.  相似文献   
83.
A strong correlation exists between the presence of specifictypes of human papillomavirus (HPV) and the development of anogenitalcancer, as well as significant epidemiologic evidence suggestingsmokers are at increased risk of developing cervical, vulvarand/or anal carcinomas. Primary and human papillomavirus type18 (HPV-8)-immortalized human keratinocytes were used to addressthe co-carcinogenic potential of HPV and nitrosomethylurea (NMU)in tumorigenesis. Only cells containing HPV-18 and treated withNMU and the tumor-promoting phorbol ester, TPA, were transformedto a malignant phenotype. An in vitro system is described whichinitiates studies involving the mechanisms of HPV and chemicalcarcinogen co-operation in the etiology of squamous cell carcinomas.  相似文献   
84.
The epidemiology of injury incidence in inner-city children has not previously been described. This study presents the methods used and the incidence rates found for severe injury (causing hospitalisation or death) in a population of 89,000 children under age 17 years in northern Manhattan, a largely poor area of New York City. The average annual incidence rate (measured from 1983 to 1987) for severe injuries to children under 17 was 846/100,000 a year. The vast majority (79%) were classified as unintentional. Nine per cent were due to assault, 3% were self-inflicted and in an additional 9% the intention was unclear. Classified by cause, the highest incidence (per 100,000/year) was found for falls (218), vehicle-related (141, primarily pedestrian), ingestion (119) and burns (110). Guns caused 3% of the injuries (27). The death rate from injury was 18.7/100,000, 36% of which was due to homicide. In an additional 28%, intentional injury was suspected. The suicide rate was 0.4/100,000. The leading causes of injury death included guns and burns (both 2.7/100,000). Compared with childhood injury rates in predominantly rural and suburban populations, the rates reported here for northern Manhattan are higher for overall injury incidence (fatal and non-fatal) and for homicide, but lower for injury mortality not due to homicide.  相似文献   
85.
86.
Background: Morbid obesity is a serious disease that afflicts over five million Americans, threatening their health with such co-morbidities as diabetes, arthritis, pulmonary failure and stroke. Surgery is the only effective therapy, providing long-term control of weight, diabetes, pulmonary failure, and hypertension for as long as 14 years. Because the operation presents a major expense, this study examined whether X-ray examination of the gut could be omitted safely as a cost-saving measure. Methods: The records of 814 consecutive morbidly obese patients who underwent gastric bypass were reviewed to determine: (1) whether these individuals had undergone an upper gastro-intestinal (GI) series, and (2) if these studies influenced therapy or caused cancellation or postponement of surgery. Results: Of the 814 patients, 657 (80.7%) underwent a preoperative GI radiography. Of these examinations, 393 (59.8%) were normal, with the following abnormalities in the remaining 264: hiatal hernia, 164; esophageal reflux, 39; Schatzki's ring, 18; small bowel diverticula, four; renal stones, four; malrotation, three; gall stones, two; pyloric ulcer, one; possible pelvic mass, one; calcified leiomyoma, one; and dysphagial lusoria, one. None of these findings resulted in cancellation or a delay in surgery. Conclusions: The upper GI series can be safely omitted from the routine preoperative evaluation of patients undergoing gastric bypass. At a cost of $741.00 per examination, this change represents significant potential savings. Similar evaluations of other routine preoperative tests may well provide a better basis for the evaluation of these complex patients.  相似文献   
87.
Abstract: Most individuals concerned about hereditary breast cancer risk will neither order nor benefit from genetic testing at the present time. Many will, however, seek information about their risk and testing. Risk assessment services, in addition to providing information about hereditary risk and genetic testing, need also to include assessment of non-hereditary risks, information about how to evaluate risks, early detection modalities, the etiology of cancer, and assistance in devising follow-up health care plans. Psychosocial factors, particularly those pertaining to the individual's past history with illness and beliefs about causes and prognosis, must be taken into account to provide relevant information that is understood. A case history with examples of some of the types of information that lead to informed consent in a cancer risk assessment setting is provided.  相似文献   
88.
89.
Excessive alcohol consumption causes damages to the stomach or duodenum by impairing the integrity of the mucosal barrier. The aim of this study was to estimate the association between alcohol consumption and peptic ulcer, utilizing a large representative sample of the U.S. population, while controlling for cigarette smoking and major sociodemographic variables. Results indicated that alcohol consumption only minimally increased the odds of peptic ulcer. Thus, this study offers little support for the association between ethanol intake and peptic ulcer.  相似文献   
90.
Prior studies of distraction osteogenesis in dog and rabbit models have shown predominantly intramembranous bone formation. Other models of fracture healing normally display mixtures of both endochondral and intramembranous bone formation. We have established a rat model of tibial lengthening that reliably reproduces the pattern of zonal osteogenesis previously observed in dog and rabbit models. A distraction rate of 0.25 mm twice a day with a 0-day latency period produced intramembranous bone with zones of progressive mineralization from collagen. With this protocol, rats bridged the distraction gap with a 25% increase in the tibial bone length. After 20 days of distraction and 50 days of consolidation, the three-point bending stiffness, as a percentage of the contralateral control, reached a level equivalent to that measured in the canine model for a 15% lengthening (28-day distraction and 84-day consolidation). Radiodensitometric analysis of the regenerate bones measured 97% of the unaffected contralateral tibial densities, and mineral analyses demonstrated that calcium and phosphorus levels in the regenerate bone reached 78% of contralateral tibial levels by day 70. We concluded that a rat model of distraction ostegenesis will be useful for a wide range of studies involving rapid intramembranous bone formation.  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