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   3224篇
  免费   2篇
  国内免费   1篇
化学工业   42篇
金属工艺   5篇
机械仪表   3篇
建筑科学   21篇
轻工业   9篇
水利工程   2篇
石油天然气   1篇
无线电   9篇
一般工业技术   19篇
冶金工业   3108篇
原子能技术   4篇
自动化技术   4篇
  2023年   1篇
  2022年   1篇
  2021年   1篇
  2020年   2篇
  2019年   2篇
  2018年   3篇
  2017年   1篇
  2016年   2篇
  2015年   5篇
  2013年   2篇
  2012年   8篇
  2011年   5篇
  2010年   4篇
  2009年   1篇
  2008年   2篇
  2007年   5篇
  2006年   2篇
  2005年   7篇
  2004年   5篇
  2003年   9篇
  2002年   4篇
  2001年   1篇
  2000年   3篇
  1999年   115篇
  1998年   1006篇
  1997年   593篇
  1996年   374篇
  1995年   181篇
  1994年   188篇
  1993年   185篇
  1992年   24篇
  1991年   17篇
  1990年   21篇
  1989年   24篇
  1988年   28篇
  1987年   30篇
  1986年   17篇
  1985年   17篇
  1984年   1篇
  1983年   7篇
  1982年   22篇
  1981年   17篇
  1980年   22篇
  1979年   2篇
  1978年   7篇
  1977年   87篇
  1976年   160篇
  1975年   3篇
  1973年   1篇
  1965年   2篇
排序方式: 共有3227条查询结果,搜索用时 15 毫秒
121.
Since blood is a biologic product, it is unlikely that the risk for transfusion-transmitted infection will ever be reduced to zero. The approach to emerging infections associated with transfusion of blood and blood products includes assessing the transmissibility of the agent by this route; developing effective prevention strategies, including screening tests and donor deferral policies; improving viral and bacterial inactivation procedures; and surveillance for known, as well as emerging and poorly characterized, transfusion-transmitted agents. Vigilance is needed to help ensure proper balance between safety and the availability of blood. Finally, vigilance needs to extend to the developing world, where the basic elements to reduce transfusion-transmitted infections and systems of disease surveillance are often not available.  相似文献   
122.
123.
Three hundred and forty-five Touch football players were retrospectively surveyed to determine the nature and incidence of injuries sustained over a one year period. The definition of injury was that it prevented playing or training for at least one week. A total of 177 injuries were sustained by 117 players who participated in a total of 1043 hours of playing and training each week. The injury rate was 4.85/1000 hours of playing or training which was less than in other football codes. This rate was significantly more (p < 0.05) among males and no relationship was evident based on representative or training status. 71% of injuries were to the lower limb. 23% of all injuries involved the ankle. Less than 3% of injuries affected the head or neck. 54% of injuries were considered mild in that they only prevented playing or training for less than two weeks. Only 17% of injuries were stated to have been caused by contact with another player. This study found that the injury rate in Touch was much less than in other football codes.  相似文献   
124.
125.
126.
127.
We tested the hypothesis that the effect of systemic injections of diazepam (DZ, 125 mg/kg) to reduce the quality of the reproductive behavior, lordosis, and to reduce the EMG of lumbar back muscles involved in lordosis (Schwartz-Giblin et al., 1984) is exerted through a reticulospinal pathway with cells of origin in the nucleus gigantocellularis that excites lumbar motoneurons indirectly (Robbins et al., 1990, Robbins et al., 1992). In contrast, DZ facilitates lordosis behavior when infused into the midbrain central gray (McCarthy et al., 1995). Direct deposits of crystalline mixtures of DZ (20-80 ng) in dextrose were delivered to the medullary reticular formation (MRF) by diffusion from a cannula inserted through a guide to which a bipolar stimulating electrode was attached. The multiunit EMG response evoked by 20 (300 ms long) stimulus trains was recorded in back and neck muscles, lateral longissimus and splenius before and 5, 15, 30 and 60 min after local DZ deposits. There was a significant reduction in EMG response over this time period when stimulus intensities were within the range of 1.2-1.5 times threshold (Friedman two-way non-parametric test, P < 0.002). Large amplitude motor units that provide large tensions were the most sensitive to DZ-induced inhibition. Control deposits of dextrose had no significant effect. Systemic injections of progesterone (1 mg, i.p.) 60 min after DZ deposits, but not after dextrose deposits, further reduced the MRF-evoked EMG responses over the course of 1 h. As predicted, DZ infusions into the midbrain central gray did not reduce the reticulospinal-evoked axial muscle response, consistent with the facilitatory effect of midbrain central gray infusions of DZ on the lordosis quotient. The results suggest that benzodiazepine agonists (if endogenous) acting at sites in the MRF would be effective muscle relaxants during pregnancy, prior to the fall in progesterone that precedes labor.  相似文献   
128.
A universal suture device (USD) able to make simultaneous two-line and cross-shaped circular clips stitches on various tube-shaped organs (vessels, intestines, esophagus, stomach, ets), creating end-to-end and end-to-side anastomosis with the external cuff is proposed. The results of experimental trials of USD and its clinical use in anastomosing main vessels were published before (8, 9, 11, 12). In this article the results of experiments with the use of USD in intestinal and esophageal sutures in 35 dogs are analysed. There were 4 series of experiments with 45 anastomoses (31 intestinal and 14 esophageal anastomoses). The anastomosed segments of the intestines and esophagus healed at the level of the lower side of the cuff. The cuff completely resumes its shape in 2.5-5 months, and the clips come off by month 7-8 after the surgery. The mucous layer of the esophagus straightened by the 2-3d month, while adventitial-muscular layer does not straigheten at all, and the clips from it could be found till the 10th month after the surgery. There were no cases of anastomotic incompetence.  相似文献   
129.
Using a highly sensitive allele-specific PCR amplification method, we have previously shown that maternal cells could be detected in all 10 cord bloods tested. This raised the question of whether maternal cells are released into cord blood during the process of delivery or whether they are already present during pregnancy. We have now used the same PCR method to detect the presence of maternal cells in nine fetal blood samples collected at different gestational ages. Maternal cells were detected in eight samples obtained between 24 and 35 weeks of gestation. They were estimated to amount between 10(-4) and 10(-5) of nucleated fetal blood cells. In two cases mononuclear and polymorphonuclear cell fractions were separated by Ficoll gradient centrifugation and maternal cells were detected as comparable levels in both fractions. Maternal cells could not be detected in the one fetal blood sample obtained at 20 weeks of gestation, suggesting that maternal cells could appear at detectable levels in fetal blood during the third trimester of pregnancy. These results are discussed in terms of materno-fetal immune tolerance and of transmission of viruses (and more specifically of the human immunodeficiency virus) from mother to child.  相似文献   
130.
Distinct lipid compositions of intracellular organelles could provide a physical basis for targeting of membrane proteins, particularly where transmembrane domains have been shown to play a role. We tested the possibility that cholesterol is required for targeting of membrane proteins to the Golgi complex. We used insect cells for our studies because they are cholesterol auxotrophs and can be depleted of cholesterol by growth in delipidated serum. We found that two well-characterized mammalian Golgi proteins were targeted to the Golgi region of Aedes albopictus cells, both in the presence and absence of cellular cholesterol. Our results imply that a cholesterol gradient through the secretory pathway is not required for membrane protein targeting to the Golgi complex, at least in insect cells.  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