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   514297篇
  免费   33288篇
  国内免费   615篇
耳鼻咽喉   6898篇
儿科学   16841篇
妇产科学   13524篇
基础医学   85064篇
口腔科学   14475篇
临床医学   44362篇
内科学   93661篇
皮肤病学   12204篇
神经病学   36197篇
特种医学   18454篇
外国民族医学   63篇
外科学   77051篇
综合类   8472篇
一般理论   118篇
预防医学   38978篇
眼科学   12134篇
药学   40554篇
中国医学   1007篇
肿瘤学   28143篇
  2018年   4930篇
  2015年   4516篇
  2014年   6065篇
  2013年   9549篇
  2012年   12884篇
  2011年   14281篇
  2010年   8311篇
  2009年   7776篇
  2008年   13705篇
  2007年   14703篇
  2006年   14947篇
  2005年   14364篇
  2004年   14054篇
  2003年   13400篇
  2002年   13279篇
  2001年   24075篇
  2000年   25089篇
  1999年   20561篇
  1998年   5431篇
  1997年   4706篇
  1996年   5042篇
  1995年   4626篇
  1994年   4319篇
  1993年   4136篇
  1992年   15728篇
  1991年   16311篇
  1990年   16425篇
  1989年   15803篇
  1988年   14583篇
  1987年   14429篇
  1986年   13603篇
  1985年   12985篇
  1984年   9631篇
  1983年   8251篇
  1982年   4560篇
  1981年   4230篇
  1979年   9424篇
  1978年   6857篇
  1977年   5773篇
  1976年   5602篇
  1975年   6402篇
  1974年   7636篇
  1973年   7131篇
  1972年   6964篇
  1971年   6687篇
  1970年   6173篇
  1969年   5888篇
  1968年   5559篇
  1967年   5012篇
  1966年   4451篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Pneumonia: a deadly disease despite intensive care treatment   总被引:3,自引:0,他引:3  
In a retrospective study of 30 patients with pneumonia treated in the intensive care unit, it was found that cultures from sputum and bronchial secretions did poorly correspond with blood cultures or serological tests. In only 15 of the patients a reliable etiological diagnosis was ever established. Mechanical ventilation was used in 22 patients, usually with a high oxygen need. At the start of this ventilation a significant blood pressure fall and a further pulmonary deterioration was observed. In fatal cases this pulmonary dysfunction was progressive. The overall mortality was 47%. When an FI02 above 0.6 was needed in the ventilator the mortality was 13/14 (93%).  相似文献   
993.
1. A significant linear increase in egg-shell defects from 60-week-old laying hens, and corresponding significant linear decreases in various egg-shell-quality measurements, were observed in response to increasing concentrations of sodium chloride in the drinking water, to the maximum concentration of 600 mg/l used in the present study. 2. The incidence of damaged egg shells was increased 3-fold by including NaCl in the drinking water at a concentration of 600 mg/l. 3. Shell defects declined when birds were placed on normal water for 5 weeks but were still 1.4- to 2.1-fold greater than control values. 4. After an induced rest from lay on normal water, shell defects were still 1.3- to 3.2-fold greater in birds which had previously received the NaCl in the drinking water. 5. The increased incidence of shell damage was not related to decreased food intake or increased egg weight or production.  相似文献   
994.
M J Belman  S G Thomas  M I Lewis 《Chest》1986,90(5):662-669
In order to investigate the effect of resistive breathing training on ventilatory muscular endurance, we examined the maximal sustained ventilatory capacity in ten patients with chronic obstructive pulmonary disease (COPD) before and after a six-week program of resistive breathing training. In addition, we investigated the effect of altered breathing strategy on resistive breathing performance. The patients performed two 15-minute sessions of resistive breathing daily for six weeks using an inspiratory resistive device (Pflex). Before and after the training, we found no significant change in spirometric data, pulmonary volumes, maximal inspiratory pressure, and maximal expiratory pressure. Of the ten patients, seven failed to show an improvement in their performance of resistive breathing. Furthermore, the maximal sustained ventilatory capacity was unchanged after the resistive breathing training. After the completion of the training program, seven of the patients participated in an additional experiment in which they were instructed to take long slow inspirations while breathing through the resistive device. With this change in breathing pattern, five of the seven were able to improve their performance of resistive breathing. Analysis of the breathing strategy showed that a reduction in the peak mouth pressure, breathing frequency, and external resistive work with a longer inspiratory time was beneficial. We conclude that neither resistive breathing performance nor ventilatory muscular endurance, as measured by sustained hyperpnea, is improved by resistive breathing training performed according to the current instructions with the resistive device, and alterations in breathing strategy have a profound effect on the performance of resistive breathing. The lack of details of breathing strategy in previous studies of resistive breathing makes it difficult to determine if previously demonstrated improvements were due to a real enhancement of ventilatory muscular performance or merely secondary to a different strategy.  相似文献   
995.
996.
997.
Multidrug resistance in human renal cell carcinoma is mainly caused by expression of the MDR1 gene and is characterized by a broad spectrum cross resistance to many natural product chemotherapeutic agents. This resistance can be overcome by applying chemosensitizers which inhibit the function of the MDR1 gene product P-glycoprotein. The development of new reversing agents with fewer side effects and a higher potency in modifying resistance is a high priority of research on drug resistance. We have evaluated four new verapamil derivatives on 21 primary human renal cell carcinomas in vitro, and also tested them in an MDR-transgenic mice model. These mice express the human MDR1 gene in their bone marrow cells and measurement of their white blood counts provides a simple, rapid and reliable system to screen for the potency of MDR-reversing agents in vivo. We demonstrate here that all four drugs are effective in reversing multidrug resistance in primary cultures of human renal cell carcinomas when used in combination with vinblastine chemotherapy, and to a lesser extent with doxorubicin or daunomycin chemotherapy. Our in vivo data indicate that two of these reversing agents display low toxicity at high concentrations and are more effective at low, clinically achievable concentrations, than the other two drugs and R-verapamil. These results make the two new drugs attractive candidates to be taken into clinical trials.  相似文献   
998.
999.
1000.
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