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   250篇
  免费   24篇
  2021年   3篇
  2020年   3篇
  2019年   6篇
  2018年   5篇
  2017年   2篇
  2016年   7篇
  2015年   8篇
  2014年   13篇
  2013年   14篇
  2012年   21篇
  2011年   14篇
  2010年   17篇
  2009年   7篇
  2008年   11篇
  2007年   9篇
  2006年   12篇
  2005年   14篇
  2004年   7篇
  2003年   4篇
  2002年   6篇
  2001年   7篇
  2000年   3篇
  1999年   2篇
  1998年   7篇
  1997年   4篇
  1996年   3篇
  1994年   3篇
  1993年   5篇
  1992年   2篇
  1991年   6篇
  1990年   3篇
  1989年   4篇
  1987年   6篇
  1986年   5篇
  1984年   1篇
  1983年   4篇
  1982年   3篇
  1981年   5篇
  1978年   2篇
  1977年   3篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1972年   1篇
  1969年   2篇
  1967年   1篇
  1964年   1篇
  1960年   1篇
  1959年   1篇
  1916年   1篇
排序方式: 共有274条查询结果,搜索用时 31 毫秒
1.
1) All existing records of Monhysteridae sensu stricto from the marine sublitoral cannot be regarded als reliable because essential family characters have not been described (gonadal characters) or if so, are doubtful (cuticular structure).

2) Four marine monhysterid species are described: Monhystera cuspidospiculum Allgen 1932 and Monhystrella inaequispiculum sp. n. from the southern Chilean coast, and Monhystera pusilla Boucher and Helléouet 1977 and M. venusta sp. n. from the offshore benthos of the North Sea. The two latter species represent the first definite record of monhysterid species from the marine sublitoral. Monhystrella inaequispiculum stands out from all other Monhysteridae by having an asymmetrical spicular apparatus.  相似文献   
2.

Background

The Centers for Disease Control and Prevention recommends nontargeted opt-out HIV screening in healthcare settings. Cost effectiveness is critical when considering potential screening methods. Our goal was to compare programmatic costs of nontargeted opt-out rapid HIV screening with physician-directed diagnostic rapid HIV testing in an urban emergency department (ED) as part of the Denver ED HIV Opt-Out Trial.

Methods

This was a prospective cohort study nested in a larger quasi-experiment. Over 16 months, nontargeted rapid HIV screening (intervention) and diagnostic rapid HIV testing (control) were alternated in 4-month time blocks. During the intervention phase, patients were offered HIV testing using an opt-out approach during registration; during the control phase, physicians used a diagnostic approach to offer HIV testing to patients. Each method was fully integrated into ED operations. Direct program costs were determined using the perspective of the ED. Time-motion methodology was used to estimate personnel activity costs. Costs per patient newly-diagnosed with HIV infection by intervention phase, and incremental cost effectiveness ratios were calculated.

Results

During the intervention phase, 28,043 eligible patients were included, 6,933 (25%) completed testing, and 15 (0.2%, 95% CI: 0.1%–0.4%) were newly-diagnosed with HIV infection. During the control phase, 29,925 eligible patients were included, 243 (0.8%) completed testing, and 4 (1.7%, 95% CI: 0.4%–4.2%) were newly-diagnosed with HIV infection. Total annualized costs for nontargeted screening were $148,997, whereas total annualized costs for diagnostic HIV testing were $31,355. The average costs per HIV diagnosis were $9,932 and $7,839, respectively. Nontargeted HIV screening identified 11 more HIV infections at an incremental cost of $10,693 per additional infection.

Conclusions

Compared to diagnostic testing, nontargeted HIV screening was more costly but identified more HIV infections. More effective and less costly testing strategies may be required to improve the identification of patients with undiagnosed HIV infection in the ED.  相似文献   
3.
Human activities are decreasing biodiversity and changing the climate worldwide. Both global change drivers have been shown to affect ecosystem functioning, but they may also act in concert in a non‐additive way. We studied early‐stage litter mass loss rates and soil microbial properties (basal respiration and microbial biomass) during the summer season in response to plant species richness and summer drought in a large grassland biodiversity experiment, the Jena Experiment, Germany. In line with our expectations, decreasing plant diversity and summer drought decreased litter mass loss rates and soil microbial properties. In contrast to our hypotheses, however, this was only true for mass loss of standard litter (wheat straw) used in all plots, and not for plant community‐specific litter mass loss. We found no interactive effects between global change drivers, that is, drought reduced litter mass loss rates and soil microbial properties irrespective of plant diversity. High mass loss rates of plant community‐specific litter and low responsiveness to drought relative to the standard litter indicate that soil microbial communities were adapted to decomposing community‐specific plant litter material including lower susceptibility to dry conditions during summer months. Moreover, higher microbial enzymatic diversity at high plant diversity may have caused elevated mass loss of standard litter. Our results indicate that plant diversity loss and summer drought independently impede soil processes. However, soil decomposer communities may be highly adapted to decomposing plant community‐specific litter material, even in situations of environmental stress. Results of standard litter mass loss moreover suggest that decomposer communities under diverse plant communities are able to cope with a greater variety of plant inputs possibly making them less responsive to biotic changes.  相似文献   
4.
5.
Ixodes ricinus is the main vector for important infectious diseases in both humans and in animals. Microsatellite loci were isolated from a dinucleotide‐enriched library made from I. ricinus sampled in Norway. Seventeen polymorphic microsatellites were further characterized among 24 individuals sampled from an island in the Oslofjord region. The number of observed alleles ranged from two to 17 and the observed heterozygosities between 0.10 and 0.83. Analysis of family materials gives evidence of non‐Mendelian inheritance of several of the characterized loci, among which most could be explained by presence of null alleles.  相似文献   
6.
7.
Abstract: Morphological and reproductive features and cell wall ultrastructure and biochemistry of Proterozoic acritarchs are used to determine their affinity to modern algae. The first appearance datum of these microbiota is traced to infer a minimum age of the divergence of the algal classes to which they may belong. The chronological appearance of microfossils that represent phycoma‐like and zygotic cysts and vegetative cells and/or aplanospores, respectively, interpreted as prasinophyceaen and chlorophyceaen microalgae is related to the Viridiplantae phylogeny. An inferred minimum age of the Chlorophyte origin is before c. 1800 Ma, the Prasinophyceae at c. 1650 Ma and the Chlorophyceae at c. 1450 Ma. These divergence times differ from molecular clock estimates, and the palaeontological evidence suggests that they are older.  相似文献   
8.
This paper discusses issues of agrarian change in south-central Bali. The proximity to urban areas, especially the tourist centers along the southern coast, provides many off-farm employment opportunities for small-scale farming households. Although rice farming continues, for many households it has become a side business. The flexible nature of rice farming in terms of labor input and available casual off-farm work allows farming households to allocate their available labor to a variety of on-farm and off-farm income generating activities. The subak which unites farmers in the irrigation and cultivation of the rice crop plays an important role in supporting this flexibility. Still, the future of rice farming and the organization behind it looks rather dim with a younger generation unwilling to work in the “mud” and little appreciation of the many benefits the subak provides not only to the farming but to the wider community.  相似文献   
9.
10.

Microalgae are capable of producing up to 70% w/w triglycerides with respect to their dry cell weight. Since microalgae utilize the greenhouse gas CO2, they can be cultivated on marginal lands and grow up to ten times faster than terrestrial plants, the generation of algae oils is a promising option for the development of sustainable bioprocesses, that are of interest for the chemical lubricant, cosmetic and food industry. For the first time we have carried out the optimization of supercritical carbon dioxide (SCCO2) mediated lipid extraction from biomass of the microalgae Scenedesmus obliquus and Scenedesmus obtusiusculus under industrrially relevant conditions. All experiments were carried out in an industrial pilot plant setting, according to current ATEX directives, with batch sizes up to 1.3 kg. Different combinations of pressure (7–80 MPa), temperature (20–200 °C) and CO2 to biomass ratio (20–200) have been tested on the dried biomass. The most efficient conditions were found to be 12 MPa pressure, a temperature of 20 °C and a CO2 to biomass ratio of 100, resulting in a high extraction efficiency of up to 92%. Since the optimized CO2 extraction still yields a crude triglyceride product that contains various algae derived contaminants, such as chlorophyll and carotenoids, a very effective and scalable purification procedure, based on cost efficient bentonite based adsorbers, was devised. In addition to the sequential extraction and purification procedure, we present a consolidated online-bleaching procedure for algae derived oils that is realized within the supercritical CO2 extraction plant.

  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