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   1907397篇
  免费   138892篇
  国内免费   4074篇
耳鼻咽喉   25137篇
儿科学   63426篇
妇产科学   53057篇
基础医学   273261篇
口腔科学   54577篇
临床医学   169092篇
内科学   373062篇
皮肤病学   43569篇
神经病学   146596篇
特种医学   72327篇
外国民族医学   281篇
外科学   290771篇
综合类   44833篇
现状与发展   5篇
一般理论   666篇
预防医学   139446篇
眼科学   45620篇
药学   138854篇
  7篇
中国医学   4993篇
肿瘤学   110783篇
  2021年   14337篇
  2019年   15043篇
  2018年   22365篇
  2017年   16988篇
  2016年   18705篇
  2015年   21344篇
  2014年   29413篇
  2013年   43126篇
  2012年   59010篇
  2011年   62072篇
  2010年   37227篇
  2009年   34686篇
  2008年   57655篇
  2007年   61568篇
  2006年   61945篇
  2005年   58948篇
  2004年   56978篇
  2003年   54124篇
  2002年   51970篇
  2001年   100332篇
  2000年   102492篇
  1999年   84530篇
  1998年   21933篇
  1997年   19303篇
  1996年   19243篇
  1995年   18533篇
  1994年   16975篇
  1993年   15658篇
  1992年   63220篇
  1991年   61222篇
  1990年   58874篇
  1989年   56565篇
  1988年   51392篇
  1987年   50043篇
  1986年   47239篇
  1985年   44809篇
  1984年   32908篇
  1983年   28002篇
  1982年   15787篇
  1979年   29007篇
  1978年   20090篇
  1977年   17115篇
  1976年   15857篇
  1975年   16894篇
  1974年   20341篇
  1973年   19687篇
  1972年   18256篇
  1971年   16868篇
  1970年   15779篇
  1969年   14636篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The in vitro ability of bacterial purified antigenic fractions to interfere with the immune system has been investigated on human mononuclear cells from peripheral blood. Exposure of purified monocytes to the drug at concentrations from 1 to 1000 micrograms/ml, for different periods from 0 to 18 h, significantly increased cell-mediated cytotoxicity against TU5 target cells. Moreover, monocytes exposed for 1 to 18 h to drug concentrations from 0.1 to 1000 micrograms/ml released significant amounts of tumor necrosis factor alpha in a dose-dependent manner in the culture supernatants. The drug was also tested on natural killer (NK) cell activity; mononuclear cells exposed to antigenic fractions for different periods showed a significant increase of NK cytotoxic activity against K562 target cells after 3 and 6, but not 0 and 18 h. Active concentrations were from 1 to 100 micrograms/ml, higher and lower doses being ineffective. Bacterial purified antigenic fractions thus have some ability to interfere in vitro with mechanisms of cytolysis mediated by cells and soluble factors.  相似文献   
992.
Summary Split or full thickness eyelid defects resulting from tumor destruction or surgical excision present a dilemma for plastic and reconstructive surgeons. Full thickness eyelid replacement requires composite grafting of the skin, together with tarsal support of its substitute and mucosa. The flap described by Fricke in 1829 was used for reconstruction of anterior lamella in six lower eyelid defects. In three of our cases chondromucosal grafts taken from nasal septum were utilized for posterior lamella repair. The results have been satisfactory from a functional and cosmetic standpoint.  相似文献   
993.
The effects of hemorrhagic shock (HE) on duodenal pH, acid-neutralizing capacity and mucosal tolerance to acid were investigated in anesthetized rats, and they were compared with those of indomethacin. HE was performed by bleeding from the carotid artery to reduce arterial blood pressure to about 55 mmHg (3 ml of bleeding per 200 g of body weight), and indomethacin was given s.c. in a dose of 5 mg/kg. Duodenal pH was determined in the outflow from the proximal duodenum (1.7 cm) which was perfused with 10(-4) M HCl, and acid-neutralizing capacity was measured by back-titration of the perfusate to pH 4.0 with 10 mM HCl. Under these conditions, duodenal pH was kept at around 6.0 as the result of neutralization in the loop (approximately 8 microEq/hr). Both HE and indomethacin significantly decreased the pH and acid-neutralizing capacity. Administration of 16,16-dimethyl prostaglandin E2 (16-dmPGE2: 30 micrograms/kg, s.c.) significantly increased both pH and acid-neutralizing capacity in normal and indomethacin-treated rats, but failed to affect these parameters in rats under HE conditions. When the duodenal loop was perfused with 50 mM HCl for 1.5 hr, both HE and indomethacin induced extensive damage in the mucosa. Pretreatment with 16-dmPGE2 significantly reduced the formation of duodenal lesions induced by indomethacin but not by HE. These results suggest that HE as well as indomethacin impaired duodenal acid-neutralizing capacity to reduce the tolerance to acid of the mucosa. The deleterious effects of HE on the mucosa may be mainly due to a decreased mucosal blood flow, but not due to a deficiency of endogenous prostaglandins.  相似文献   
994.
Summary The effects of sodium salts of various bile acids on the contractile force and the electrophysiological properties of rat ventricular muscle were studied in vitro. Primary, conjugated, and secondary bile acids were studied in a concentration range of 10–9–10–6 mol/l, which corresponds to concentrations found in the plasm of patients with cholestatic jaundice. In general, the bile acid induced a negative inotropic effect which was manifested as a reduction in active tension, maximum rate of tension activation, and maximum rate of tension relaxation. Twitch duration and time to peak tension were unaffected by the bile acids. The negative inotropism was associated with a reduction in ventricular action potential duration. Resting potential, action potential amplitude, and maximum upstroke velocity of phase 0 depolarization were unaffected. Voltage clamp experiments in rat ventricular myocytes demonstrated that sodium taurocholate decreased the slow inward current and slightly increased the outward potassium current. Hence, these effects on the membrane currents are probably responsible for the negative inotropic effect. Send offprint requests to O. Binah at the above address  相似文献   
995.
996.
Neuroblastoma: the role of MR imaging   总被引:1,自引:0,他引:1  
Thirty-five MR examinations were performed in 17 children with neuroblastoma during the course of their diagnostic evaluation and treatment. Findings were confirmed by correlation with the results of other imaging techniques, biopsies, and surgical and autopsy findings. MR accurately detected the lesions and their extent in all patients. It correctly evaluated the possibility of resectability and showed metastases, response to treatment and development of complications. MR appears to be a reliable technique for the diagnosis, staging, and follow-up of children with neuroblastoma.  相似文献   
997.
A new classification of forms of progressive systemic scleroderma (PSS) is presented. Compared with previous classifications, it includes not only frequent, typical forms of PSS, but also rarer manifestations. For the first time, it considers pathogenetic factors, such as the phenomena which have become known concerning the immunological system, and distinguishes between noninflammatory and inflammatory subtypes. Etiological (in this case, immunogenetic) criteria are also considered. This classification is open to further differentiation and development.  相似文献   
998.
999.
Abstract A high frequency of serum complement component C4A deficiency may explain the higher prevalence and greater severity of systemic lupus erythematosus reported in Australian Aborigines. Inherited deficiencies of serum complement components C4A, C4B, and C2 were examined in two Australian Aboriginal populations from Darwin and Alice Springs and compared with the prevalence of complement deficiencies in white Australian blood donors. The frequency of C4A deficiency alleles was 29% in Darwin Aborigines compared with 12% in Alice Springs and 17% in Canberra blood donors. Partial C4B deficiency was also higher in Darwin Aborigines than in the other populations. Inherited deficiency of serum complement component C2 was not observed.  相似文献   
1000.
Ten knees with early tissue breakdown after knee arthroplasty resulting in exposed prostheses were treated with different plastic surgical techniques. Six knees were successfully covered: four using a gastrocnemius musculocutaneous flap, one using a fasciocutaneous flap, and one using split-skin grafts. Four knees failed: two using local skin flaps and two using split-skin grafts. A gastrocnemius musculocutaneous flap seems to provide a reliable coverage of the exposed knee joint.  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