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   2104篇
  免费   97篇
  国内免费   7篇
耳鼻咽喉   22篇
儿科学   79篇
妇产科学   66篇
基础医学   183篇
口腔科学   36篇
临床医学   258篇
内科学   521篇
皮肤病学   79篇
神经病学   92篇
特种医学   41篇
外科学   373篇
综合类   102篇
预防医学   157篇
眼科学   31篇
药学   140篇
肿瘤学   28篇
  2016年   12篇
  2015年   18篇
  2014年   12篇
  2013年   32篇
  2011年   10篇
  2010年   26篇
  2009年   28篇
  2006年   13篇
  2001年   15篇
  2000年   10篇
  1999年   30篇
  1998年   48篇
  1997年   54篇
  1996年   45篇
  1995年   33篇
  1994年   46篇
  1993年   39篇
  1992年   34篇
  1991年   25篇
  1990年   21篇
  1989年   32篇
  1988年   28篇
  1987年   29篇
  1986年   23篇
  1985年   18篇
  1984年   22篇
  1983年   21篇
  1982年   28篇
  1981年   14篇
  1980年   22篇
  1979年   15篇
  1978年   17篇
  1977年   14篇
  1976年   11篇
  1973年   9篇
  1971年   16篇
  1970年   11篇
  1964年   8篇
  1963年   12篇
  1961年   10篇
  1960年   10篇
  1959年   90篇
  1958年   175篇
  1957年   174篇
  1956年   172篇
  1955年   171篇
  1954年   161篇
  1949年   87篇
  1948年   112篇
  1946年   14篇
排序方式: 共有2208条查询结果,搜索用时 343 毫秒
1.
Objective: To document the breastfeeding practices of Aboriginal mothers delivering in Perth. Design and methods: A cohort of mothers was followed from the time of delivery for six months to obtain details of infant feeding practices. Subjects: A total of 455 mothers delivered during the study period and were asked to participate. A total of 425 mothers completed the initial questionnaire. Setting: The study was undertaken in six public hospitals in Perth, Western Australia. Data analyses: The data were analysed using spss . Breastfeeding duration was calculated using Kaplan–Meier survival analysis. Main outcome measures: Breastfeeding initiation and duration. Results: The mean age of the Aboriginal mothers was 21.8 years (range 14–39 years, SD 5.32) and the average gestational age was 38.3 weeks. Almost 50% of the mothers in the study delivered by Caesarean section. At discharge from hospital 89.4% (CI 86.6–92.1) of mothers were breastfeeding, declining to 58.8% (CI 53.5–64.1) at six months. When compared with non‐Aboriginal mothers, the Aboriginal breastfeeding rates were higher than the non‐Aboriginal average breastfeeding rates, but lower than the highest socioeconomic group. Conclusions: The breastfeeding rates of Aboriginal mothers are higher than for other Australians. This is despite the low maternal age and level of education and the high rates of low‐birth‐weight infants and Caesarean section among this population. The World Health Organization recommendation for infant feeding is exclusive breastfeeding until six months, but less than one‐third of Aboriginal mothers achieved this recommendation.  相似文献   
2.
3.
4.
We used molecular modeling to examine the binding of 1, 2-dioctanoyl-sn-glycero-3-phosphocholine (a lecithin), 1-octanoyl-sn-glycero-3-phosphocholine (a lysolecithin) and their tetrahedral intermediates in the catalytic site of phospholipase A2 (PLA2). We performed energy minimization on each complex, computed the binding energy, determined the relative binding energy among the complexes and calculated the difference in inter- and intramolecular energies of the components in the complexes. We found that the calculated orientation of the sn-1 ester bond of lysolecithin in the active site is similar to that of the sn-2 ester bond in lecithin, thus permitting PLA2 to hydrolyze lysolecithin using the same mechanism as it uses to hydrolyze lecithin. On the other hand, the binding of lecithin is energetically more favorable by 4.5 kcal/mol than the binding of lysolecithin to the enzyme, and the binding of the lecithin tetrahedral intermediate is also energetically more favorable by 19.7 kcal/mol than the binding of the lysolecithin tetrahedral intermediate to the enzyme, which explains why lecithin is a better substrate than lysolecithin in the catalytic site. These results indicate that the activation energy for the hydrolysis of lysolecithin is higher than that for lecithin, consistent with the observed slower rate for the hydrolysis of lysolecithin.  相似文献   
5.
A national sample of 1500 mothers of 1-year-old children received a postal questionnaire concerned with the sleeping patterns of their children. The response rate was 69%. Seventeen per cent of mothers reported that their 1-year-old presented a moderate or severe sleep problem and 26% said their child woke at night on at least five nights a week. While these two measures correlated, 10% of those who reported their infant woke on at least five nights a week did not consider this to be a problem. Neither sex of infant, social class, method of infant feeding or numbers of house moves were associated with sleep problems. The pattern of results strongly suggest an association between night waking and other sleeping difficulties and stress for mothers. This was indicated by the association we found with complaints about housing, overcrowding, more negative attitudes toward motherhood, lower assessments of maternal well-being, lack of practical support from partners, the use of more negative adjectives to describe their baby and more frequent feelings of being dominated by their baby. While these associations may be explained by the stresses of living with a night-waking baby, it is also likely that a mother who is feeling somewhat depressed and negative toward her baby is more likely to see night waking as significant and as a problem. There were class differences in how parents coped with a shortage of space. Middle-class parents were more likely to put a baby in with a sibling while working class parents more often had the baby in their own room. Middle-class parents were more likely to leave a night-waking baby to cry.  相似文献   
6.
Platelet aggregation and thrombosis play an important role in the onset of acute coronary events. Regardless of the stimulus for activation, platelet thrombus formation is ultimately regulated through the IIb/IIIa receptor complex. The effects of oral administration of xemilofiban, a non-peptide mimetic of the RGDF sequence of the IIb/IIIa receptor complex, on thrombus formation were evaluated in a canine model. Xemilofiban significantly reduced platelet deposition on severely damaged arterial wall. Platelet deposition was reduced at both low (13 ± 1 from 56 ± 18 × 106 platelets cm−2; P  < 0.05) and high (23 ± 2 from 111 ± 21 × 106 platelets cm−2; P  < 0.01) shear rates. Platelet deposition was reduced to a monolayer as seen by electron microscopy (platelet–vessel wall interaction). Therefore, the availability of an orally active IIb/IIIa antagonist for chronic use may have significant value in preventing thrombus formation in those clinical situations associated with severe arterial injury, such as atherosclerotic plaque disruption.  相似文献   
7.
The classic approach to anterior skull base lesions uses bifrontal craniotomies together with lateral rhinotomies. This approach requires frontal lobe retraction and is associated with postoperative anosmia and the development of frontal lobe encephalomalacia. The transglabellar/subcranial approach permits removal of anterior skull base lesions without frontal lobe retraction and avoids facial scars. No studies to date, however, have directly compared the two approaches in terms of patient morbidity. The present retrospective study compares the two approaches when used for the removal of anterior skull base lesions in terms of estimated blood loss, number of transfusions, number of days in the hospital and intensive care unit, and postoperative complications. Twenty patients with anterior skull base lesions were examined. The classic approach was used on 10, and the transglabellar/subcranial route was used on 10. When compared with the classic approach, the transglabellar/subcranial approach resulted in a lower estimated blood loss and subsequent transfusion rate, fewer days in the hospital and intensive care unit, and lower numbers and less severe types of complications. Furthermore, visualization of the tumors before resection with the transglabellar/subcranial approach allowed preservation of olfaction in virtually all of these patients. Although this study represents a small sample population, the results are sufficiently impressive to favor the transglabellar/subcranial approach for the removal of a variety of anterior skull base lesions. (Otolaryngol Head Neck Surg 1997;116:642-6.)  相似文献   
8.
9.
Abstract While the volume of a liquid meal has been identified as the principal accelerator of gastric emptying of liquids, the relationship between meal volume and gastric emptying of solids has been controversial. With solid foods, the need to reduce solid foods into small particles (trituration) before passage might obscure the effect of meal volume on solid propulsion. To distinguish trituration from driving force as the rate-limiting factor for emptying, 75 (1.6 mm) nylon spheres were fed along with different amounts of steak meals (150, 300 and 600 g), or alternatively, 50, 100 or 200 (1.6 mm) nylon spheres were fed to six dogs with 300 g steak meals. To examine the effect of meal volume on gastric emptying, we studied the effect of different meal volumes on the speed of gastric emptying of liquids (150, 300, 600 and 1200 ml of phosphate buffer) and solids (150, 300 and 600 g of cooked beef steak) in five dogs with duodenal fistulas. Intestinal inhibition was eliminated by diverting all chyme through the fistulas. In the absence of intestinal feedback, we found that gastric emptying of steak and spheres were different in that steak emptying was independent of meal volume (g min-1 was constant across 150–600 g) while sphere emptying was affected by the number of spheres in the stomach and that liquid emptying was dependent on the meal volume (ml min-1 increased across 150–1200 ml). Thus, meal volume accelerated gastric emptying provided the process is not rate-limited by trituration.  相似文献   
10.
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