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   2871篇
  免费   152篇
  国内免费   18篇
耳鼻咽喉   17篇
儿科学   90篇
妇产科学   68篇
基础医学   262篇
口腔科学   91篇
临床医学   480篇
内科学   807篇
皮肤病学   105篇
神经病学   89篇
特种医学   54篇
外科学   358篇
综合类   100篇
一般理论   17篇
预防医学   137篇
眼科学   46篇
药学   255篇
中国医学   3篇
肿瘤学   62篇
  2017年   16篇
  2016年   22篇
  2015年   51篇
  2014年   51篇
  2013年   67篇
  2012年   26篇
  2011年   21篇
  2010年   104篇
  2009年   111篇
  2008年   19篇
  2007年   39篇
  2006年   32篇
  2004年   23篇
  2003年   26篇
  2001年   36篇
  2000年   20篇
  1999年   47篇
  1998年   105篇
  1997年   116篇
  1996年   132篇
  1995年   106篇
  1994年   83篇
  1993年   72篇
  1992年   65篇
  1991年   64篇
  1990年   47篇
  1989年   50篇
  1988年   73篇
  1987年   65篇
  1986年   75篇
  1985年   47篇
  1984年   55篇
  1983年   42篇
  1982年   47篇
  1981年   31篇
  1980年   35篇
  1979年   32篇
  1978年   33篇
  1977年   22篇
  1976年   24篇
  1975年   25篇
  1974年   18篇
  1959年   72篇
  1958年   101篇
  1957年   120篇
  1956年   105篇
  1955年   88篇
  1954年   77篇
  1949年   28篇
  1948年   49篇
排序方式: 共有3041条查询结果,搜索用时 15 毫秒
41.
42.
PROBLEM : To determine whether seminal fluid influences the expression of MHC class I antigens on the surface of basal trophoblast cells in the placenta of the rat. METHODS : Transfer of DA × DA embryos into a WF (allogeneic) or DA (syngeneic) recipient made pseudopregnant by hormonal treatment followed by mating with a vasectomized male (seminal fluid) or by mechanical stimulation (no seminal fluid). Antigen expression was determined by electron microscopic immunocytochemistry using the appropriate gold-labeled monoclonal antibodies. RESULTS : Seminal fluid did not affect the expression of MHC class I antigens on the surface of the basal trophoblast in either allogeneic or syngeneic matings. CONCLUSIONS : The suppression of the expression of paternal class I antigens on the surface of the basal trophoblast cells in allogeneic pregnancies most likely occurs at the genome level shortly after fertilization.  相似文献   
43.
Historically, the healing of tracheal or bronchial anastomoses has been the Achilles heel in pulmonary transplantation. In the past, steps taken to enhance healing of these structures and have allowed single-lung, double-lung, and heart-lung transplantation to be accomplished safely. This report presents a simplified technique for protection of the tracheal anastomosis in heart-lung and double-lung transplantation. This technique, wherein the pericardial fat pad from the right side is utilized to wrap the tracheal anastomosis, not only allows for excellent healing of the anastomosis but separates the aorta from the trachea. In 19 patients having heart-lung (N = 13) or double-lung (N = 6) transplantation there were no tracheal healing problems, dehiscence or stenosis found.  相似文献   
44.
This report presents results of a field trial of Substance Use Disorders as defined by DSM-III-R, DSM-IV (proposed) and ICD-10. Diagnoses based on the three systems were derived from interviews using the Composite International Diagnostic Interview (CIDI) in a heterogeneous sample of 521 adults drawn from clinical and community settings. Two issues are addressed: (1) cross system agreement; and (2) syndrome coherence of proposed criterion sets for Substance Dependence in each of the three systems. Findings were as follows: (1) Cross system agreement for Dependence was generally high, especially between DSM-III-R and DSM-IV. (2) Cross system agreement was lower for DSM-III-R and DSM-IV Abuse and very low for DSM-IV Abuse and ICD-10 Harmful Use. (3) Agreement varied across drug categories with lowest DSM-III-R/DSM-IV agreement for alcohol abuse and DSM-IV/ICD-10 agreement for marijuana use disorders. (4) Overall prevalence differed for the three systems with DSM-IV yielding highest rates followed by DSM-III-R and ICD-10 in that order. (5) Factor analysis of Dependence criteria showed high loadings of all items on a single factor across the three diagnostic systems and for all categories of drugs. Implications for validity of the dependence syndrome construct and for revisions in DSM-IV are discussed.  相似文献   
45.
Non-thoracotomy implantation of implantable cardioverter defibrillators (ICDs) has simplified the process of device inserfion, promising to decrease associated procedural coniplications while providing sudden death protection at least equal to epicardial systems. This study presents the acute and chronic results of 110 patients who underwent attempted non-thoracotomy ICD impiuntation wiih the Medtronic Transvene lead system and PCD model 7217 or 7219. Of the 110 patients attempted, 100 (91%) had the system successfully implanted without the need for an epicar-dial patch. One patient died 1 week postoperatively of septic shock related to the implantation (0.9% perioperative mortality). During folloiv-up of 16 ± 11 months, 45% of the patients had an event detected as ventricular tachycardia; 26% of these detections were felt clinically to be due to supraventricular rhythms. Of the remainder, 87% were successfully treated with the first VT therapy, and 98% were terminated by the final therapy; 66% of the patients had at least one episode of ventricular fibrillation, of which 5% were felt to be inappropriate detections; 65% of the appropriate episodes were successfully treated with the first VF therapy, and all were converted by the final therapy. Total mortality at 6, 12, and 24 months was 3%, 11%, and 19% respectively. Only one patient had sudden cardiac death, occurring at 13 months postimplant. Overall, the non-thoracotomy lead system for this ICD displayed infrequent implant complications and proved to be reliable ai terminating arrhythmias and maintaining a low rate of sudden cardiac death in this high risk popuiation.  相似文献   
46.
Twenty-six infants due to undergo major abdominal or thoracic surgery under general anaesthesia were randomized to receive additional analgesia with group A) spinal/epidural analgesia; B) epidural analgesia or C) opioid analgesia with fentanyl. We wished to determine if spinal analgesia followed by epidural analgesia might result in more complete control of cardiovascular or stress responses than the other two treatment groups. Heart rate and blood pressure were recorded at five min intervals throughout surgery. Blood samples were taken for measurement of catecholamines and whole blood sugar on induction, 45 min after skin incision and at the end of surgery. Heart rate rose significantly at the start of surgery in groups B and C but not group A. Systolic blood pressures were higher in group C compared to A and B. The rise in plasma glucose concentrations was significantly different between the groups in the order C>B>A (P<0·05). A similar trend was seen in the plasma adrenaline and noradrenaline concentrations but this failed to achieve significance due to the limited sample size.  相似文献   
47.
Age-related changes in cortical porosity of the midshaft of the human femur   总被引:1,自引:1,他引:0  
Complete cross-sections from the femoral midshaft of 180 individuals of known height and weight, aged 21–97 y, from a modern Australian population were examined using automatic video image analysis to quantify total subperiosteal porosity (TSPP). More specifically, the aim was to investigate whether age changes were similar in both sexes in (1) total subperiosteal area (TSPA), cortical area (CA) and medullary area (MA), (2) intracortical porosity (ICP), and (3) the respective contributions to TSPP made by MA and intracortical void area (ICVA). Our findings indicated that both sexes showed a significantly greater height normalised TSPA in the 70s as compared with the 20s. Males had consistently larger bones with a greater height normalised CA. In both sexes CA showed a tendency to increase till the 7th decade and then to decline, more so in females. MA approximately trebled in females and doubled in males over the age range studied. Although ICP also increased, from 4–6% in young adults to over 9% in the elderly, it showed a significant difference between the sexes only in the 3rd decade, being greater in males at this stage. By contrast, TSPP became significantly greater in females (from that recorded in the 3rd decade) by the time they reached the 50s, while in males this did not occur till the 80s. It increased from ∼25% in young adults of both sexes to ∼50% in females and ∼37% in males in their 80s. However, in the elderly there was great variability in both sexes in the appearance of bones from individuals of similar chronological age. Some bones differed little from those in younger subjects, others showed greatly increased ICP, still others displayed reduced cortical widths with low ICP. The femoral midshaft resembles other skeletal sites in that age changes in TSPP are more marked in females than males.  相似文献   
48.
The indication for treatment of paroxysmal supraventricular tachycardia depends on the frequency and severity of the tachycardia attacks. If the tachycardia attacks are mildly symptomatic and occur only once or twice a year, there is no indication for either continuous drug therapy or radiofrequency oblation. The only therapeutic measure required is termination of each acute event. If symptoms occur frequently, long-term antiarrhythmic drug therapy is then indicated and will be effective for chronic prophylaxis in most individuals with a low risk of proarrhythmic events. Only in patients with severe or life-threatening symptoms or cases refractory to drug therapy would radiofrequency ablation possibly be justified.  相似文献   
49.
Naloxone administration to fasting normal male volunteers reversesthe acute ethanol-induced increase in the blood [lactate]/[pyruvate]ratio, but fails to lower blood-ethanol concentration. The resultsare discussed in relation to factors affecting ethanol eliminationand the mechanism of antagonism of acute alcohol intoxicationby naloxone.  相似文献   
50.
Oral bropirimine (an immunomodulator shown to induce interferon)was administered to timed-pregnant Sprague-Dawley rats in fiveexperiments utilizing several different dosing schedules. Concentrationsof 100, 200, and 400 mg/kg of bropirimine were used. Interferonlevels were determined in maternal serum, spleen, and wholeembryo extracts and uterine contents were evaluated for survivalof the embryos. Maternal toxicity occurred in all experimentsas evidenced by dose-related decreases in body weight duringthe first 24 hr postdosing. Hematoxicology analyses of maternalserum revealed significant decreases in urea nitrogen, potassium,and albumin, along with increases in aspartate transaminase,alanine transaminase, and total bilirubin, in bropirimine-treateddams as compared to the vehicle controls. In addition, the meansfor maternal thymus weight decreased while the means for spleenweight increased with increasing concentration of bropirimine.As compared to the vehicle controls, interferon titers werehigh in maternal serum, maternal spleen, and, to a lesser extent,whole embryos, 2 hr postdosing, but had decreased or were belowdetectable levels 24 hr postdosing. Embryolethality was pronounced(increases in pre- and postimplantational loss) after a singledose (Gestation Day 3, 4, 5, 8, 9, or 10) of bropirimine, aswell as after 7 or 8 consecutive days (Gestation Days 6–12or 6–13) of treatment. Although embryotoxicity never occurredin these experiments in the absence of pronounced maternal toxicity,the pregnant dams never died as the result of bropirimine treatment,whereas the embryos frequently failed to survive.  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