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   160篇
  免费   10篇
  170篇
  2024年   1篇
  2023年   1篇
  2022年   1篇
  2021年   2篇
  2020年   1篇
  2019年   1篇
  2017年   4篇
  2016年   4篇
  2015年   7篇
  2014年   9篇
  2013年   4篇
  2012年   15篇
  2011年   12篇
  2010年   12篇
  2009年   8篇
  2008年   11篇
  2007年   10篇
  2006年   14篇
  2005年   2篇
  2004年   10篇
  2003年   8篇
  2002年   5篇
  2001年   1篇
  2000年   5篇
  1999年   2篇
  1998年   4篇
  1997年   2篇
  1995年   1篇
  1994年   1篇
  1991年   1篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1978年   1篇
  1977年   2篇
  1976年   1篇
  1973年   2篇
  1924年   1篇
排序方式: 共有170条查询结果,搜索用时 15 毫秒
71.
72.

Background  

A minority of stroke patients is eligible for thrombolytic therapy. Small pilot case series have hinted that elevation of incident arterial blood pressure might be associated with a favorable prognosis either in acute or subacute stroke. However, these patients were not considered for thrombolytic therapy and were not followed – up systematically. We used pharmacologically induced hypertension in a stroke patient with middle cerebral artery (MCA) occlusion ineligible for thrombolysis that was followed-up by radiological, clinical and functional outcome assessment.  相似文献   
73.
74.
The costs and benefits of different social options are best understood when individuals can be followed as they make different choices, something that can be difficult in social insects. In this detailed study, we follow overwintered females of the social wasp Polistes carolina through different nesting strategies in a stratified habitat where nest site quality varies with proximity to a foraging area, and genetic relatedness among females is known. Females may initiate nests, join nests temporarily or permanently, or abandon nests. Females can become helpers or egglayers, effectively workers or queens. What they actually do can be predicted by a combination of ecological and relatedness factors. Advantages through increased lifetime success of individuals and nests drives foundresses of the social wasp Polistes from solitary to social nest founding. We studied reproductive options of spring foundresses of P. carolina by monitoring individually-marked wasps and assessing reproductive success of each foundress by using DNA microsatellites. We examined what behavioral decisions foundresses make after relaxing a strong ecological constraint, shortage of nesting sites. We also look at the reproductive consequences of different behaviors. As in other Polistes, the most successful strategy for a foundress was to initiate a nest as early as possible and then accept others as subordinates. A common feature for many P. carolina foundresses was, however, that they reassessed their reproductive options by actively monitoring other nests at the field site and sometimes moving permanently to new nests should that offer better (inclusive) fitness prospects compared to their original nests. A clear motivation for moving to new nests was high genetic relatedness; by the end of the foundress period all females were on nests with full sisters.  相似文献   
75.
76.
Urinary tract infection (UTI) is a common disease with significant morbidity and economic burden, accounting for a significant part of the workload in clinical microbiology laboratories. Current clinical chemisty point-of-care diagnostics rely on imperfect dipstick analysis which only provides indirect and insensitive evidence of urinary bacterial pathogens. An electronic nose (eNose) is a handheld device mimicking mammalian olfaction that potentially offers affordable and rapid analysis of samples without preparation at athmospheric pressure. In this study we demonstrate the applicability of ion mobility spectrometry (IMS) –based eNose to discriminate the most common UTI pathogens from gaseous headspace of culture plates rapidly and without sample preparation. We gathered a total of 101 culture samples containing four most common UTI bacteries: E. coli, S. saprophyticus, E. faecalis, Klebsiella spp and sterile culture plates. The samples were analyzed using ChemPro 100i device, consisting of IMS cell and six semiconductor sensors. Data analysis was conducted by linear discriminant analysis (LDA) and logistic regression (LR). The results were validated by leave-one-out and 5-fold cross validation analysis. In discrimination of sterile and bacterial samples sensitivity of 95% and specificity of 97% were achieved. The bacterial species were identified with sensitivity of 95% and specificity of 96% using eNose as compared to urine bacterial cultures. In conclusion: These findings strongly demonstrate the ability of our eNose to discriminate bacterial cultures and provides a proof of principle to use this method in urinanalysis of UTI.  相似文献   
77.

Background

Techniques enabling targeted re-sequencing of the protein coding sequences of the human genome on next generation sequencing instruments are of great interest. We conducted a systematic comparison of the solution-based exome capture kits provided by Agilent and Roche NimbleGen. A control DNA sample was captured with all four capture methods and prepared for Illumina GAII sequencing. Sequence data from additional samples prepared with the same protocols were also used in the comparison.

Results

We developed a bioinformatics pipeline for quality control, short read alignment, variant identification and annotation of the sequence data. In our analysis, a larger percentage of the high quality reads from the NimbleGen captures than from the Agilent captures aligned to the capture target regions. High GC content of the target sequence was associated with poor capture success in all exome enrichment methods. Comparison of mean allele balances for heterozygous variants indicated a tendency to have more reference bases than variant bases in the heterozygous variant positions within the target regions in all methods. There was virtually no difference in the genotype concordance compared to genotypes derived from SNP arrays. A minimum of 11× coverage was required to make a heterozygote genotype call with 99% accuracy when compared to common SNPs on genome-wide association arrays.

Conclusions

Libraries captured with NimbleGen kits aligned more accurately to the target regions. The updated NimbleGen kit most efficiently covered the exome with a minimum coverage of 20×, yet none of the kits captured all the Consensus Coding Sequence annotated exons.  相似文献   
78.
An improved pulse sequence, intraresidual i(HCA)CO(CA)NH, is described for establishing solely 13C′(i), 15N(i), 1HN(i) connectivities in uniformly 15N/13C-labeled proteins. In comparison to the “out-and-back” style intra-HN(CA)CO experiment, the new pulse sequence offers at least two-fold higher experimental resolution in the 13C′ dimension and on average 1.6 times higher sensitivity especially for residues in α-helices. Performance of the new experiment was tested on a small globular protein ubiquitin and an intrinsically unfolded 110-residue cancer/testis antigen CT16/PAGE5. Use of intraresidual i(HCA)CO(CA)NH experiment in combination with the established HNCO experiment was crucial for the assignment of highly disordered CT16.  相似文献   
79.
Crucian carp (Carassius carassius) is an excellent vertebrate model for studies on temperature adaptation in biological excitable membranes, since the species can tolerate temperatures from 0 to +36 degrees C. To determine how temperature affects the lipid composition of brain, the fish were acclimated for 4 wk at +30, +16, or +4 degrees C in the laboratory, or seasonally acclimatized individuals were captured from the wild throughout the year (temperature = +1 to +23 degrees C), and the brain glycerophospholipid and sphingolipid compositions were analyzed in detail by electrospray-ionization mass spectrometry. Numerous significant temperature-related changes were found in the molecular species composition of the membrane lipids. The most notable and novel finding was a large (approximately 3-fold) increase of the di-22:6n-3 phosphatidylserine and phosphatidylethanolamine species in the cold. Since the increase of 22:6n-3 in the total fatty acyl pool of the brain was small, the formation of di-22:6n-3 aminophospholipid species appears to be a specific adaptation to low temperature. Such highly unsaturated species could be needed to maintain adequate membrane fluidity in the vicinity of transporters and other integral membrane proteins. Plasmalogens increased somewhat at higher temperatures, possibly to protect membranes against oxidation. The modifications of brain lipidome during the 4-wk laboratory acclimation were, in many respects, similar to those found in the wild, which indicates that the seasonal changes observed in the wild are temperature dependent rather than induced by other environmental factors.  相似文献   
80.
Temperature restraints on energy forestry in Sweden   总被引:2,自引:0,他引:2  
Temperature sums (TSUM) and growth units (GU) were used as driving variables in the modelling of energy forest production in Sweden. To construct regional maps of forest production for years with good, average and poor weather conditions, it was necessary to deduce formulae of TSUM and GU on a regional basis for a growing season, defined by daily mean temperatures exceeding 5 ÐC. Temperatures north of the 900 day-degrees line are too low for intensive growing of energy forests of willow clones studied so far. With an average production of 10 tonnes dry matter per hectare per year on one million hectares, available for energy farming in the remaining part of Sweden, energy forests could replace about 20% of the Swedish oil import.  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