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   1617篇
  免费   94篇
  国内免费   42篇
耳鼻咽喉   5篇
儿科学   66篇
妇产科学   18篇
基础医学   179篇
口腔科学   165篇
临床医学   144篇
内科学   401篇
皮肤病学   22篇
神经病学   83篇
特种医学   295篇
外科学   151篇
综合类   29篇
预防医学   76篇
眼科学   6篇
药学   45篇
中国医学   3篇
肿瘤学   65篇
  2019年   10篇
  2018年   15篇
  2017年   12篇
  2016年   13篇
  2015年   29篇
  2014年   30篇
  2013年   30篇
  2012年   30篇
  2011年   47篇
  2010年   24篇
  2009年   28篇
  2008年   46篇
  2007年   80篇
  2006年   44篇
  2005年   49篇
  2004年   34篇
  2003年   37篇
  2002年   35篇
  2001年   37篇
  2000年   36篇
  1999年   37篇
  1998年   48篇
  1997年   49篇
  1996年   51篇
  1995年   42篇
  1994年   59篇
  1993年   39篇
  1992年   41篇
  1991年   43篇
  1990年   33篇
  1989年   65篇
  1988年   64篇
  1987年   71篇
  1986年   58篇
  1985年   64篇
  1984年   32篇
  1983年   27篇
  1982年   26篇
  1981年   21篇
  1980年   23篇
  1979年   26篇
  1978年   16篇
  1977年   15篇
  1976年   12篇
  1974年   18篇
  1973年   9篇
  1972年   11篇
  1970年   15篇
  1968年   8篇
  1967年   9篇
排序方式: 共有1753条查询结果,搜索用时 21 毫秒
991.
INTRODUCTION: Previous trials of surfactant therapy in premature infants have demonstrated a survival advantage associated with prophylactic therapy as an immediate bolus, compared with the rescue treatment of established respiratory distress syndrome. The optimal strategy for prophylactic therapy, however, remains controversial. When administered as an endotracheal bolus immediately after delivery, surfactant mixes with the absorbing fetal lung fluid and may reach the alveoli before the onset of lung injury. This approach, however, causes a brief delay in the initiation of standard neonatal resuscitation, including positive pressure ventilation, and is associated with a risk for surfactant delivery into the right main stem bronchus or esophagus. As an alternative approach, surfactant prophylaxis may be administered in small aliquots soon after resuscitation and confirmation of endotracheal tube position. Although this strategy has substantial logistical advantages in clinical practice, its efficacy has not been established. OBJECTIVE: The purpose of this study was to determine whether the established benefits of the immediate bolus strategy for surfactant prophylaxis could still be achieved using a postventilatory aliquot strategy after initial standard resuscitation and stabilization. DESIGN: Multicenter randomized clinical trial with patients randomized before delivery to immediate bolus or postventilatory aliquot therapy. PARTICIPANTS: Inborn premature infants delivered to mothers at an estimated gestational age of 24[0/7] to 28[6/7] weeks. INTERVENTIONS: Those infants who were randomized to the immediate bolus strategy were intubated as rapidly as possible after birth, and a 3-mL intratracheal bolus of calf lung surfactant extract (Infasurf) was administered before the initiation of positive pressure ventilation. Those infants who were randomized to the postventilatory aliquot strategy received standard resuscitation measures with intubation by 5 minutes of age, if not required earlier. At 10 minutes after birth, 3 mL of surfactant was administered in 4 divided aliquots of 0.75 mL each. Patients in both groups were eligible to receive up to three additional doses of surfactant as rescue therapy in the neonatal intensive care unit, if needed. OUTCOME MEASURES: The primary outcome variable was survival to discharge to home. Secondary variables included neonatal complications and requirement for oxygen therapy at 36 weeks' postmenstrual age. RESULTS: Among three centers, 651 infants were enrolled and randomized before delivery. Survival to discharge to home was similar for the two strategies for surfactant therapy as prophylaxis: 76% for the immediate bolus group and 80% for the postventilatory aliquot group. In a secondary analysis, the rate of supplemental oxygen administration at 36 weeks' postmenstrual age was 18% for the immediate bolus group and 13% for the postventilatory aliquot group. CONCLUSIONS: Survival to discharge to home was similar with immediate bolus and postventilatory aliquot strategies for surfactant prophylaxis. Because of its logistical advantages in the delivery room and its beneficial effects on prolonged oxygen requirements, we recommend the postventilatory aliquot strategy for surfactant prophylaxis of premature infants delivered before 29 weeks' gestation.  相似文献   
992.
OBJECTIVE: To evaluate a case management/home visitation intervention to improve access to and utilization of well-child care (WCC) visits. STUDY DESIGN: Randomized, controlled trial with baseline and follow-up interview surveys. Mothers and infants in the intervention group were assigned to a case manager who made at least four home visits during the infant's first year of life. In addition, the case managers contacted clients by telephone and mail to see if they had kept their WCC appointments and to follow up on other issues. SAMPLE AND DATA COLLECTION: A population-based random sample of African-American mothers of newborns from South Central Los Angeles: 185 mothers in the intervention group and 180 in the control group completed both interview surveys. The principal outcome variable was number of WCC visits. Additional outcome variables included the child's type of insurance, the number of months with insurance coverage during the first year of life, age when first enrolled in Medi-Cal, age at the first WCC visit, usual source of WCC, travel time to the usual source of care, whether the child had a regular provider, and whether the child ever needed care but did not get it. RESULTS: There was little change in the overall distribution of number of WCC visits during the first year of life. Comparisons of the cumulative numbers of visits for each possible cutoff showed that children in the intervention group were more likely than children in the control group to have at least four visits (81% vs 70%). Because this split was identified empirically rather than through an antecedent hypothesis, we conducted a Smirnov test to account for multiple comparisons. This test showed a reduced level of significance. Other outcome variables did not show significant differences for the control and intervention groups. CONCLUSIONS: In light of the high expense of this intervention, our evaluation shows that our moderate-intensity case management and home visitation program is not an effective way to increase the number of WCC visits.  相似文献   
993.
In 1981 the American Association of Gynecologic Laparoscopists and the Division of Reproductive Health, Centers for Disease Control, jointly conducted a study of vasectomies performed in outpatient facilities in 1980 in the United States. One hundred twenty-nine facilities that responded to either a mailed questionnaire or a telephone interview stated that vasectomies were performed there in 1980. The average cost was $273, with a range of $50-1,000. Facilities differed markedly in the use of anesthesia. Freestanding surgical centers reported the use of general anesthesia for 29% of the vasectomies. Other types of facilities were more likely to use local or regional anesthesia. Our data suggest areas for further research to improve the availability and safety of vasectomy.  相似文献   
994.
ABSTRACT. We investigated peripheral blood lymphocyte phenotypes of 74 patients at weekly intervals during the course of acute hepatitis A. In the second week after onset of jaundice, a significant elevation of total lymphocytes was observed (4096 × 106± 1003 × 106/l vs. controls 3038 × 106± 1208 × 106/l, p < 0.005). However, no change in the relative percentages of B-cells (CD20+), T-cells (CD3+ or CD2+), or T-cell subpopulations (CD4+ helper cells and CD8+ suppressor cells) could be demonstrated during the course of the disease. Activated T-cells (CD3+DR+) were elevated during the first week (204 × 106± 134 × 106/l vs. normal 91 × 106± 54 × 106/l, p <0.005) and during the second week (202 × 106± 82 × 106/l, p < 0.0005) after onset of disease and returned to normal values until the third week. Cells expressing phenotypes of lymphocytes capable of exerting non-MHC-restricted cellular cytotoxicity, i.e. Natural Killer cell activity (CD57+, CD16+, and CD56+) were significantly elevated in percentage in the first week of disease, as compared to controls (CD57: 14.5 ± 7.0% vs. 9.3 ± 5.8%, p <0.05; CD16: 13.4 ± 7.3 vs. 9.5 ± 5.1%, p < 0.05; CD56: 10.5 ± 3.5% vs. 8.0 ± 1.5%, p < 0.005). Also the absolute numbers of these lymphocyte subpopulations were found to be elevated during the first and second week. The increase in NK cells in the initial phase of acute hepatitis A suggests an important role of these cells in the first line of defence in this disease.  相似文献   
995.
In 1981 the American Association of Gynecologic Laparoscopists and the Division of Reproductive Health, Centers for Disease Control, jointly conducted a study of tubal sterilizations performed in 141 freestanding, ambulatory-care surgical facilities in 1980 in the United States. Information was collected through mailed questionnaires and telephone interviews. Of 330 potential responding facilities, 141 we identified as freestanding, ambulatory-care surgical facilities. About 16,500 tubal sterilizations were performed in these facilities in 1980. The mean number of tubal sterilizations per freestanding, ambulatory-care surgical facility was 212. Sixty-seven percent of tubal sterilizations were performed in the south and west. General anesthesia was the anesthetic method used in 97% of the procedures. Nearly 91% of tubal sterilizations were done via laparoscopy, with bipolar electrocoagulation the tubal-occlusion method used most frequently. After tubal sterilization the patients were observed for an average of 2.4 hours before discharge. The average cost of laparoscopic tubal sterilization was $801; for nonlaparoscopic tubal sterilization it was $850.  相似文献   
996.
We investigated the value of image analysis in discriminating among oral white lesions with hyperplasia without dysplasia and oral white or white-and-red lesions with moderate or severe dysplasia. Normal oral epithelial tissue was used as a control. Image analysis was applied to 5-μm formalin-fixed sections stained with the azure A-Feulgen reaction for nuclear DNA. For 150–200 cells from each section, 5 nuclear variables were assessed: area, form factor, total stain, average stain and ellipticity. For each variable, 2 measurements were obtained, the mean and the interquartile range, and were used for stepwise discriminant analysis. Using this test, a model of 3 measurements with the most discriminating power was developed. When the jackknife classification test was applied to this model, we could discriminate with 81% accuracy between the 4 groups of tissue studied.  相似文献   
997.
998.
999.
1000.
Scintigraphic appearances of osteoid osteoma   总被引:3,自引:0,他引:3  
Smith  FW; Gilday  DL 《Radiology》1980,137(1):191
  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