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   1277323篇
  免费   95730篇
  国内免费   1627篇
耳鼻咽喉   16499篇
儿科学   41328篇
妇产科学   35328篇
基础医学   191468篇
口腔科学   35101篇
临床医学   119175篇
内科学   250339篇
皮肤病学   27551篇
神经病学   103006篇
特种医学   47303篇
外国民族医学   266篇
外科学   180412篇
综合类   25916篇
现状与发展   3篇
一般理论   590篇
预防医学   105781篇
眼科学   28419篇
药学   93479篇
  7篇
中国医学   2035篇
肿瘤学   70674篇
  2018年   13782篇
  2017年   10586篇
  2016年   11544篇
  2015年   13330篇
  2014年   18310篇
  2013年   28088篇
  2012年   38276篇
  2011年   40828篇
  2010年   23537篇
  2009年   22663篇
  2008年   38471篇
  2007年   41166篇
  2006年   40677篇
  2005年   39815篇
  2004年   38319篇
  2003年   36652篇
  2002年   35598篇
  2001年   56163篇
  2000年   57139篇
  1999年   48232篇
  1998年   13576篇
  1997年   12384篇
  1996年   12791篇
  1995年   12047篇
  1994年   11232篇
  1993年   10513篇
  1992年   38271篇
  1991年   37747篇
  1990年   36516篇
  1989年   35335篇
  1988年   32761篇
  1987年   32107篇
  1986年   30589篇
  1985年   28866篇
  1984年   22038篇
  1983年   19263篇
  1982年   11494篇
  1981年   10417篇
  1979年   21008篇
  1978年   15468篇
  1977年   12854篇
  1976年   11903篇
  1975年   12849篇
  1974年   15649篇
  1973年   15412篇
  1972年   14554篇
  1971年   13586篇
  1970年   12810篇
  1969年   12092篇
  1968年   11249篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
As part of a larger investigation to determine the effect of animal vs. plant proteins on the vitamin B-6 requirement of young women, clinical changes during vitamin B-6 depletion were documented. Eight healthy young women were confined to a metabolic unit and fed a defined formula diet nearly devoid of vitamin B-6 (less than 0.05 mg/d). Serial electroencephalographic (EEG) tracings, peripheral nervous system tests, periodontal evaluations, and biochemical measures of vitamin B-6 status were conducted. Within 12 d on the depletion diet, two of the eight women exhibited abnormal EEG tracings. These changes were readily reversed by repletion of vitamin B-6 at the 0.5-mg/d level. Biochemical measures reflected lowered vitamin B-6 status but were not predictive of the onset of EEG changes. No detectable alterations in oral or periodontal status were found, nor did plaque flora change markedly. This study is the first report of EEG changes occurring in women undergoing vitamin B-6 depletion and the first report to document EEG changes in adults within 12 d on a vitamin B-6-depletion regimen.  相似文献   
992.
993.
We conducted a retrospective study of 411 women to determine whether a significant relationship existed between method of infant feeding (breast vs bottle) and postpartum weight loss at 6 weeks and 12 months. In addition to method of infant feeding, the variables parity, gravidity, mode of delivery, maternal age, maternal prepregnancy weight, infant sex, and payment status (whether receiving assistance from the Aid to Dependent Children [ADC] program) were studied in terms of their association with weight loss. In general, no consistent relationship was found between method of infant feeding and postpartum weight loss. However, in the ADC group at 6 weeks and in the non-ADC group at 12 months, nonlactating women had lost more weight than had their lactating counterparts, in spite of the theoretical energy deficiency of breast-feeding women. Women who gained more weight during pregnancy consistently lost more weight following delivery, regardless of their prepregnancy weight. These results indicate that infant feeding method was not related to differences in postpartum weight loss between lactating and nonlactating counterparts.  相似文献   
994.
We evaluated the consistency of three questionnaire methods of assessing work and leisure activity in the rural biethnic population of the San Luis Valley Diabetes Study. A 7-d physical activity recall (PAR), a ranking of usual activity, and a history of usual participation in vigorous activity were used. Energy expenditure (kJ.kg-1.wk-1) (EE) was estimated from PAR. Subjects were 503 adults [49% non-Hispanic white (NHW), 51% Hispanic]. Physical activity at work rather than leisure-time activity largely determined total energy expenditure. Average EE at work increased with work rank for all subjects combined [mean EE (SEE) for rank 1 (low) = 324.2 (24.4), rank 4 (high) = 874.0 (102.1)] and within sex, ethnic, and occupational subgroups. Leisure EE increased with leisure rank only for NHW men and employed women. Similar patterns were observed in comparisons of PAR data with history of vigorous activity. Further development and validation of instruments appropriate for use across population subgroups are needed.  相似文献   
995.
996.
OBJECTIVE--To describe the human immunodeficiency virus (HIV) epidemic among socially and educationally disadvantaged young persons in the United States. DESIGN.-We analyzed demographic and geographic findings from the screening of Job Corps students for antibody to HIV. SETTING--The Job Corps is a federal training program for disadvantaged, out-of-school youth. POPULATION SCREENED--Residential students aged 16 to 21 years who entered the Job Corps from October 1987 through February 1990. MAIN OUTCOME MEASURE--Rates of observed HIV infection in entering students, stratified by demographic and geographic features. RESULTS--Of 137,209 Job Corps students screened, 488 were HIV seropositive (3.6 per 1000), a seroprevalence rate higher than that among military applicants of the same age. Overall seroprevalence was slightly higher in male (3.7 per 1000) than in female (3.2 per 1000) Job Corps students, but among those students aged 16 and 17 years, seroprevalence was higher among females (2.3 per 1000) than among males (1.5 per 1000) (P less than .05). For students aged 16 to 21 years, seroprevalence increased with year of age: 1.8 per 1000 per year for males and 0.7 per 1000 per year for females. Among those aged 21 years, HIV prevalence was 8.9 per 1000. For black and Hispanic students from large Northeastern cities, seroprevalence increased by 4.3 per 1000 per year of age and reached 24.8 per 1000 (one of 40) in students aged 21 years. However, among students from rural areas and small towns, HIV seroprevalence was disproportionately high in the Southeast. Compared with recently described US patients with the acquired immunodeficiency syndrome, HIV-infected students who entered the Job Corps were much more likely to be female. CONCLUSIONS--These findings show that disadvantaged, out-of-school adolescents are at high risk for HIV infection. The screening results identified surprisingly high seroprevalence in the southeastern United States and demonstrated a marked shift in the HIV epidemic to young women. Controlling the HIV epidemic among teenagers must include interventions that will reach adolescents early and outside of the formal educational system.  相似文献   
997.
OBJECTIVE.--To review our experience with lung transplantation, emphasizing recipient selection, choice of procedure, functional results, and outcome. DESIGN.--Retrospective review of patients who received lung transplants at Barnes Hospital, St Louis, Mo, between July 1, 1988, and January 31, 1991. SETTING.--Washington University School of Medicine, St Louis, Mo, and Barnes Hospital, a medical school and its affiliated referral hospital, respectively. PATIENTS.--Sixty-nine lung transplant procedures were performed in 66 recipients. Patients with clinically and physiologically severe lung disease were selected according to predetermined guidelines. Underlying diseases in the recipients included chronic obstructive pulmonary disease, alpha 1-antitrypsin deficiency emphysema, cystic fibrosis, pulmonary fibrosis, primary pulmonary hypertension, Eisenmenger's syndrome associated with an atrial septal defect, bronchiectasis, eosinophilic granuloma, and lymphangiomyomatosis. INTERVENTION.--Double-lung, bilateral sequential, and single-lung transplantations were performed. Eight patients underwent en bloc double-lung transplantations or a modification of this procedure with separate bronchial anastomoses. Thereafter, the bilateral sequential approach to replacement of both lungs was performed in 26 patients. Thirty-two patients underwent single-lung transplantations. MAIN OUTCOME MEASURES.--Pulmonary function tests, arterial blood gas levels, pulmonary artery pressure, pulmonary vascular resistance, and actuarial survival. RESULTS.--Actuarial survival at 1 year for the 66 lung transplant recipients was 79%. Actuarial survival at 1 year was 82% for the bilateral lung transplant recipients and was 90% for the single-lung transplant recipients. In patients with either restrictive or obstructive lung disease, pulmonary function tests and arterial blood gas levels improved markedly after lung transplantation. In patients with primary pulmonary hypertension or Eisenmenger's syndrome, the pulmonary artery pressure decreased and the cardiac index increased into the normal range after single-lung transplantation. CONCLUSIONS.--In carefully selected patients with end-stage lung disease, single-lung and bilateral lung transplantations can significantly improve functional capacity, with promising early actuarial survival statistics after 1 year.  相似文献   
998.
E B Larson 《JAMA》1991,265(23):3125-3126
  相似文献   
999.
To test the value of intensive management of diabetes before and during early pregnancy, 84 women recruited prior to conception were compared with 110 women who were already pregnant referred at 6 to 30 weeks' gestation. All underwent daily measurement of fasting and postprandial capillary blood glucose levels. Mean blood glucose levels during embryogenesis and organogenesis were within 3.3 to 7.8 mmol/L in 50% of preconception subjects and exceeded 10 mmol/L in 6.5%. One major congenital anomaly occurred in 84 infants (1.2%) of women treated before conception compared with 12 anomalies in 110 infants (10.9%) of mothers in the postconception group. Transient symptomatic hypoglycemia occurred during embryogenesis in 60% of women in the preconception group, with a median frequency of 2.7 episodes per week, but was not associated with excess malformations. We conclude that education and intensive management for glycemic control of diabetic women before and during early pregnancy will prevent excess rates of congenital anomalies in their infants.  相似文献   
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