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   876篇
  免费   0篇
化学工业   3篇
建筑科学   1篇
轻工业   4篇
一般工业技术   10篇
冶金工业   852篇
自动化技术   6篇
  2019年   1篇
  2015年   1篇
  2013年   1篇
  2012年   1篇
  2011年   4篇
  2010年   1篇
  2006年   1篇
  2005年   1篇
  2003年   1篇
  1999年   14篇
  1998年   263篇
  1997年   144篇
  1996年   85篇
  1995年   61篇
  1994年   37篇
  1993年   54篇
  1992年   9篇
  1991年   7篇
  1990年   18篇
  1989年   8篇
  1988年   15篇
  1987年   3篇
  1986年   6篇
  1985年   7篇
  1984年   1篇
  1983年   2篇
  1982年   2篇
  1981年   10篇
  1980年   6篇
  1979年   1篇
  1978年   1篇
  1977年   30篇
  1976年   76篇
  1961年   1篇
  1960年   1篇
  1955年   2篇
排序方式: 共有876条查询结果,搜索用时 15 毫秒
61.
This article presents data regarding the backgrounds and attitudes of 396 dependent children in Israel who had been living in boarding institutions for almost three years, and were at least 10 years old at the time of the research interview. Parents of the children were also interviewed, and background [corrected] information regarding the family and its experience with placement was abstracted from welfare department records. This detailed information, collected nearly a decade ago, was then compared with several very recent Israeli studies of institutionalized dependent children and it was found that many problematic features of placement still persist. Among these are lack of long or short-term planning by welfare agencies, poor agency follow-up after placement, and little personal contact with either the child or his family. More older children were accepting placement than were younger children, and the majority of the parents did not contemplate the child's return home, being quite satisfied with placement in the institution. The findings from this study should have direct implications for child welfare policy and practices.  相似文献   
62.
63.
64.
A theoretical model is developed to predict pressure changes and velocity profiles within the foetal lung during its sporadic bursts of activity. Because of the small volume flow rates and relatively high frequencies, the linearised, unidirectional Navier-Stokes equations are used to calculate these values. About 70% of the pressure drop occurs in the first four generations and is an order of magnitude higher than the equivalent Poiseuille pressure drop. Velocity profiles, pressure falls within each generation together with the total pressure drop at different times during the cycle are illustrated.  相似文献   
65.
66.
67.
BACKGROUND AND PURPOSE: Clinical and experimental data indicate that hyperglycemia can aggravate the consequences of stroke and cerebral ischemia. The purpose of this study was to examine the effects of moderate hyperglycemia on the response of the blood-brain barrier to normothermic (37 degrees C) and hypothermic (30 degrees C) global forebrain ischemia. METHODS: Sixteen rats underwent 20 minutes of four-vessel occlusion followed by 30 minutes of postischemic recirculation. We used the protein tracer horseradish peroxidase as an indicator of increased vascular permeability, and rats were perfusion-fixed for microscopic analysis. To produce moderate hyperglycemia, we gave an intraperitoneal injection of 50% dextrose 15 minutes before the ischemic insult. RESULTS: After normothermic brain ischemia, normoglycemic rats (plasma glucose level, 115 +/- 3 mg/dl) demonstrated extravasated horseradish peroxidase mainly restricted to the cerebral cortex. In contrast, more severe and widespread protein extravasation was documented throughout the neuraxis of hyperglycemic (plasma glucose level, 342 +/- 27) rats. Sites of protein leakage included the cerebral cortex, striatum, hippocampus, thalamus, and cerebellum. Foci of protein extravasation were associated with pial and large penetrating vessels. Intraischemic hypothermia significantly attenuated the blood-brain barrier consequences of hyperglycemic brain ischemia. CONCLUSIONS: Under normothermic ischemic conditions, hyperglycemia significantly worsens the degree of acute blood-brain barrier breakdown compared with normoglycemia. Postischemic blood-brain barrier disruption may play an important role in the pathogenesis of increased brain damage associated with systemic hyperglycemia.  相似文献   
68.
Unequal metabolic responses to trauma by women and men have been suggested, but an explicit investigation demonstrating this conjecture has not been made. The responses of resting energy expenditure (REE) and nitrogen balance for 3 days before and 7 days after skeletal trauma were determined for female and male rats. Food intake and body weight were recorded daily, and 24-h urine samples were collected. Baseline REE and nitrogen balance were obtained for 3 consecutive days before induction of trauma. Then rats were divided into female trauma (n = 8), male trauma (n = 7), female control (n = 8), and male control (n = 7) groups. Trauma was produced by bilateral femoral fracture to anesthetized rats. Control rats were anesthetized without skeletal trauma. Traumatized rats were fed ad libitum for 7 days, and control rats were pair fed with the traumatized rats. The results showed that REE increased and nitrogen balance decreased in traumatized male rats relative to their controls. Traumatized female rats had increased REE and unchanged nitrogen balance compared with their controls. Traumatized female rats had a larger percentage increase in REE on days 5 through 7 than did traumatized male rats. These findings demonstrate a difference between female and male rats in response to trauma. Female rats use more energy and lose less nitrogen after trauma than do male rats. The results suggest that recommendations for increased energy and protein needs after trauma should consider the sex of the subject intended to be fed.  相似文献   
69.
Sixty-five patients initially seropositive for IgM anti-phenolic glycolipid-I (PGL-I) antibodies were tested for antibody levels to PGL-I, lipoarabinomannan (LAM), and the 35-kDa protein of Mycobacterium leprae at regular intervals for up to 30 months following the commencement of multidrug therapy (MDT). There was a steady decline in IgM anti-PGL-I and anti-35-kDa antibody levels to a mean of 17% and 14%, respectively, of the starting level at 24 months. The development of type 1 and type 2 reactions or the presence of drug-resistant organisms in a small number of patients had no significant influence on the changes in antibody level. The rate of decline was similar in different disease categories, but a higher proportion of lepromatous patients remained seropositive at the end of 2 years of treatment than borderline tuberculoid patients. By contrast, the mean IgG anti-LAM antibody levels remained stable or increased. Again the occurrence of type 1 or type 2 reactions had no significant effect on antibody level over 2 years. Falls in the IgM anti-PGL-I antibody levels mirrored the falls in the bacterial index in individual patients and provide an additional parameter for monitoring the response to chemotherapy.  相似文献   
70.
We describe a novel technique for isolation of sequences that are present in one genome (tracer), but absent in another (driver). Tracer DNA, cleaved with Sau 3A and capped with a single stranded PCR adapter, is allowed to hybridize with an excess of sheared biotinylated driver; biotinylated DNA and its hybrids with the tracer are removed by phenol/chloroform extraction after incubation with streptavidin. After several rounds of subtraction the ends of self-annealed tracer molecules from the nonextractable fraction are filled-in with Tag polymerase and amplified, using the single stranded PCR adapter as a primer. The method has been applied to purification of fragments from a 2.9 kb plasmid added to E. coli DNA at equimolar quantity. Plasmid derived fragments (250-1000 bp), initially comprising 1/1400th part of tracer DNA, were purified to homogeneity after two rounds of subtraction followed by PCR.  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