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   281篇
  免费   43篇
  324篇
  2023年   2篇
  2021年   2篇
  2020年   3篇
  2018年   4篇
  2017年   8篇
  2016年   9篇
  2015年   5篇
  2014年   13篇
  2013年   16篇
  2012年   17篇
  2011年   10篇
  2010年   9篇
  2009年   10篇
  2008年   11篇
  2007年   17篇
  2006年   8篇
  2005年   13篇
  2004年   13篇
  2003年   8篇
  2002年   21篇
  2001年   6篇
  2000年   9篇
  1999年   5篇
  1998年   8篇
  1997年   11篇
  1996年   5篇
  1995年   3篇
  1994年   3篇
  1993年   5篇
  1992年   2篇
  1991年   4篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   6篇
  1986年   6篇
  1985年   7篇
  1984年   3篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1977年   3篇
  1976年   3篇
  1948年   1篇
  1943年   2篇
  1942年   1篇
  1912年   1篇
  1908年   3篇
  1903年   1篇
  1892年   1篇
排序方式: 共有324条查询结果,搜索用时 15 毫秒
1.
The biochemical state and treatment of 73 children and 44 adults up to the age of 40 with proved congenital hypothyroidism were assessed in a regional study in the north of England. The findings showed that a substantial proportion of the patients were having inappropriate treatment or were not taking their treatment regularly and that in some of these there were clinical effects.  相似文献   
2.
3.
BothPseudomonas putida F1 and a mixed culture were used to study TCE degradation in continuous culture under aerobic, non-methanotrophic conditions. TCE mass balance studies were performed with continuous culture reactors to determine the total percent removed in the reactors, and to quantify the percent removed by air stripping and biodegradation. Adsorption of TCE to biomass was assumed to be negligible. This research demonstrated the feasibility of treating TCE-contaminated water under aerobic, non-methanotrophic conditions with a mixed-culture, continuous-flow system.Initially glucose and acetate were fed as primary substrates. Pnenol, which has been shown to induce TCE-degrading enzymes, was fed at a much lower concentration (20mg/L). Little degradation of TCE was observed when acetate and glucose were the primary substrates. After omitting glucose and acetate from the feed and increasing the phenol concentration to 50mg/L, TCE biotransformation was observed at a significant level (46%). When the phenol concentration in the feed was increased to 420mg/L, 85% of the incoming TCE was estimated to have been biodegraded. Under the same conditions, phenol utilization by the mixed culture was greater than that ofP. putida F1, and TCE degradation by the mixed culture (85%) exceeded that ofP. putida F1 (55%). The estimated percent-of-TCE biodegraded by the mixed culture was consistently greater than 80% when phenol was fed at 420mg/L. Biodegradation of TCE was also observed in mixed-culture, batch experiments.  相似文献   
4.
OBJECTIVE: To compare in psychiatric and psychosocial terms the outcome of hysterectomy and endometrial ablation for the treatment of dysfunctional uterine bleeding. DESIGN: Prospective randomised controlled trial. SETTING--Obstetrics and gynaecology department of a large teaching hospital. SUBJECTS: 204 women with dysfunctional bleeding for whom hysterectomy would have been the preferred treatment were recruited over 24 months and randomly allocated to hysterectomy (99 women) or to hysteroscopic surgery (transcervical resection (52 women) or laser ablation (53 women). MAIN OUTCOME MEASURES: Mental state, martial relationship, psychosocial and sexual adjustment in assessments conducted before the operation and one month, six months, and 12 months later. RESULTS: Both treatments significantly reduced the anxiety and depression present before the operation, and there were no differences in mental health between the groups at 12 months. Hysterectomy did not lead to postoperative psychiatric illness. Sexual interest after the operation did not vary with treatment. Overall, 46 out of 185 (25%) women reported a loss sexual interest and 50 out of 185 (27%) reported increased sexual interest. Marital relationships were unaffected by surgery. Personality and duration of dysfunctional uterine bleeding played no significant part in determining outcome. CONCLUSIONS: Hysteroscopic surgery and hysterectomy have a similar effect on psychiatric and psychosocial outcomes. There is no evidence that hysterectomy leads to postoperative psychiatric illness.  相似文献   
5.
Glucose, and certain sugars that can readily be converted to glucose 6-phosphate, bring about an activation of adipose-tissue lipoprotein lipase when epididymal fat-bodies from starved rats are incubated in the presence of cycloheximide. Other substrates do not support the activation. If the tissue is preincubated in the presence of cycloheximide for longer than 2h, the ability of added glucose to activate the enzyme is lost. On the other hand, the addition of glucose still brings about an increase in lipoprotein lipase activity after preincubation in the absence of cycloheximide for as long as 4h. The magnitude of the increase in enzyme activity brought about by the addition of glucose is increased when protein synthesis is stimulated during the preincubation period by insulin. The results are interpreted in terms of the existence in adipose tissue of a proenzyme pool of lipoprotein lipase that is normally maintained by protein synthesis and that is converted to complete enzyme of higher specific activity by a process that specifically requires glucose.  相似文献   
6.
7.
The effects of light quality (color) on the 14CO2 fixation rates of natural population of photosynthetic sulfur bacteria were tested. The phototrophic bacteria were collected from the sulfide containing waters of 3 stratified lakes. The populations sampled survive in environments where light intensities are very low. Not only are the light intensities low but, due to the light filtering characteristics of the lake water, the light is of specific color. It was determined that the spectral properties of the three lakes differed, hence the quality of light reaching the phototrophic bacteria in each lake differed. It was also observed that only green sulfur bacteria were present in the study lake which transmits mainly red light and both purple and green sulfur bacteria were present in the two study lakes which transmit predominantly green light. Enrichment cultures were set up with phototrophic bacteria from two of the lakes serving as the inocula. Enrichment culture studies and photosynthetic responses of the natural populations indicate that light quality is a major factor in determining the composition of phototrophic bacterial population in some lakes.Non-Common Abbreviations Bchl Bacteriochlorophyll - DPM Disintegrations per minute  相似文献   
8.
Members of the Deinococcaceae (e.g., Thermus, Meiothermus, Deinococcus) contain A/V-ATPases typically found in Archaea or Eukaryotes which were probably acquired by horizontal gene transfer. Two methods were used to quantify the extent to which archaeal or eukaryotic genes have been acquired by this lineage. Screening of a Meiothermus ruber library with probes made against Thermoplasma acidophilum DNA yielded a number of clones which hybridized more strongly than background. One of these contained the prolyl tRNA synthetase (RS) gene. Phylogenetic analysis shows the M. ruber and D. radiodurans prolyl RS to be more closely related to archaeal and eukaryal forms of this gene than to the typical bacterial type. Using a bioinformatics approach, putative open reading frames (ORFs) from the prerelease version of the D. radiodurans genome were screened for genes more closely related to archaeal or eukaryotic genes. Putative ORFs were searched against representative genomes from each of the three domains using automated BLAST. ORFs showing the highest matches against archaeal and eukaryotic genes were collected and ranked. Among the top-ranked hits were the A/V-ATPase catalytic and noncatalytic subunits and the prolyl RS genes. Using phylogenetic methods, ORFs were analyzed and trees assessed for evidence of horizontal gene transfer. Of the 45 genes examined, 20 showed topologies in which D. radiodurans homologues clearly group with eukaryotic or archaeal homologues, and 17 additional trees were found to show probable evidence of horizontal gene transfer. Compared to the total number of ORFs in the genome, those that can be identified as having been acquired from Archaea or Eukaryotes are relatively few (approximately 1%), suggesting that interdomain transfer is rare.  相似文献   
9.
The bacterial [NiFe]-hydrogenases have been classified as either 'standard' or 'O2-tolerant' based on their ability to function in the presence of O2. Typically, these enzymes contain four redox-active metal centers: a Ni-Fe-CO-2CN- active site and three electron-transferring Fe-S clusters. Recent research suggests that, rather than differences at the catalytic active site, it is a novel Fe-S cluster electron transfer (ET) relay that controls how [NiFe]-hydrogenases recover from O2 attack. In light of recent structural data and mutagenic studies this article reviews the molecular mechanism of O2-tolerance in [NiFe]-hydrogenases and discusses the biosynthesis of the unique Fe-S relay.  相似文献   
10.
Affecting Performance: Meaning, Movement and Experience in Okiek Women's Initiation. Corinne A. Kratz. Washington, DC: Smithsonian Institution Press, 1994. 470 pp.  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