全文获取类型
收费全文 | 410篇 |
免费 | 44篇 |
出版年
2021年 | 2篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 11篇 |
2014年 | 11篇 |
2013年 | 47篇 |
2012年 | 25篇 |
2011年 | 16篇 |
2010年 | 10篇 |
2009年 | 12篇 |
2008年 | 17篇 |
2007年 | 29篇 |
2006年 | 17篇 |
2005年 | 23篇 |
2004年 | 18篇 |
2003年 | 19篇 |
2002年 | 15篇 |
2001年 | 19篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 4篇 |
1996年 | 8篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1981年 | 9篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有454条查询结果,搜索用时 46 毫秒
71.
Gustavo A Fontecha Ana L Sanchez Meisy Mendoza Engels Banegas Rosa E Mejía-Torres 《Memórias do Instituto Oswaldo Cruz》2014,109(4):492-493
Countries could use the monitoring of drug resistance in malaria parasites as an
effective early warning system to develop the timely response mechanisms that are
required to avert the further spread of malaria. Drug resistance surveillance is
essential in areas where no drug resistance has been reported, especially if
neighbouring countries have previously reported resistance. Here, we present the
results of a four-year surveillance program based on the sequencing of the
pfcrt gene of Plasmodium falciparum populations
from endemic areas of Honduras. All isolates were susceptible to chloroquine, as
revealed by the pfcrt “CVMNK” genotype in codons 72-76. 相似文献
72.
Changes in fossil chironomid remains along a depth gradient: evidence for common faunal thresholds within lakes 总被引:1,自引:0,他引:1
Many environmental variables that are important for the development of chironomid larvae (such as water temperature, oxygen
availability, and food quantity) are related to water depth, and a statistically strong relationship between chironomid distribution
and water depth is therefore expected. This study focuses on the distribution of fossil chironomids in seven shallow lakes
and one deep lake from the Plymouth Aquifer (Massachusetts, USA) and aims to assess the influence of water depth on chironomid
assemblages within a lake. Multiple samples were taken per lake in order to study the distribution of fossil chironomid head
capsules within a lake. Within each lake, the chironomid assemblages are diverse and the changes that are seen in the assemblages
are strongly related to changes in water depth. Several thresholds (i.e., where species turnover abruptly changes) are identified
in the assemblages, and most lakes show abrupt changes at about 1–2 and 5–7 m water depth. In the deep lake, changes also
occur at 9.6 and 15 m depth. The distribution of many individual taxa is significantly correlated to water depth, and we show
that the identification of different taxa within the genus Tanytarsus is important because different morphotypes show different responses to water depth. We conclude that the chironomid fauna
is sensitive to changes in lake level, indicating that fossil chironomid assemblages can be used as a tool for quantitative
reconstruction of lake level changes. 相似文献
73.
Valerie van den Bos Otto Brinkkemper Ian D. Bull Stefan Engels Tom Hakbijl Mans Schepers Marieke van Dinter Guido van Reenen Bas van Geel 《Vegetation History and Archaeobotany》2014,23(3):277-298
Castellum Fectio was one of the largest fortifications along the Limes, the northern border of the Roman Empire. The castellum, situated 5 km southeast of Utrecht, the Netherlands, was occupied from around the start of our Era to ca. a.d. 260. It was situated along a river bend of the Rhine that was cut off from the main stream during the occupation of the Roman fort. A 6 m long sediment sequence was recovered from the infill of the residual channel and pieces of Roman wall plaster, glume bases of Triticum spelta and radiocarbon dates indicate that the sediments were deposited during the period of Roman occupation. The combined palaeoecological analyses—palynological, macrobotanical, entomological and geochemical—allow a detailed reconstruction of changing environmental conditions as a consequence of the Roman occupation. The pollen record reveals a dramatic decrease in arboreal pollen, suggesting that the Romans were involved in large-scale deforestation, transforming semi-open parkland to a landscape of meadows and agricultural fields. Non-pollen palynomorphs, botanical macrofossils and insect remains support this conclusion. The recorded mycoflora shows a shift from assemblages characterised by the tree pathogen Kretzschmaria deusta to assemblages dominated by spores of fungi associated with herbaceous plants, concurrent with the decrease in arboreal pollen. The presence of masticated bran fragments of cereals, clover remains, eggs of intestinal parasites and entomological and geochemical data in the upper part of the sequence indicates that these sediments largely consist of faeces that were dumped into the former channel. Surprisingly, seeds of salt tolerant species are encountered in the sediments of this inland site, which was situated outside the influence of the sea. Horses may have brought these seeds to Fectio in their intestinal tracts after grazing in coastal meadows. 相似文献
74.
Evelien Kostermans Mike Stoolmiller Rebecca N. H. de Leeuw Rutger C. M. E. Engels James D. Sargent 《PloS one》2014,9(12)
Objective
We examine the association between exposure to depictions of reckless driving in movies and unsafe driving, modeling inattentive and reckless driving as separate outcomes.Methods
Data were obtained by telephone from 1,630 US adolescents aged 10 to 14 years at baseline who were drivers at a survey 6 years later. Exposure to movie reckless driving was measured based on movies seen from a randomly selected list of 50 movie titles that had been content coded for reckless driving among characters. Associations were tested with inattentive and reckless driving behaviors in the subsequent survey–controlling for baseline age, sex, socioeconomic status, parental education, school performance, extracurricular activities, daily television and video/computer game exposure, number of movies watched per week, self-regulation and sensation seeking.Results
Exposure to movie reckless driving was common, with approximately 10% of movie characters having driven recklessly. Confirmatory factor analysis revealed a significant distinction between items tapping reckless and inattentive driving at the 6th wave. Age and exposure to movie reckless driving at baseline were directly associated with wave-6 reckless (but not inattentive) driving. Additionally, growth in sensation seeking mediated a prospective relation between the total number of movies watched per week at baseline and reckless driving, independent of exposure to movie reckless driving. Males and high sensation seekers reported lower seatbelt usage and more reckless driving, whereas lower self-regulation predicted inattentive driving.Discussion
In this study, exposure to movie reckless driving during early adolescence predicted adolescents’ reckless driving, suggesting a direct modeling effect. Other aspects of movies were also associated with reckless driving, with that association mediated through growth in sensation seeking. Predictors of reckless driving were different from predictors of inattentive driving, with lower self-regulation associated with the latter outcome. Making a clear distinction between interventions for reckless or inattentive driving seems crucial for accident prevention. 相似文献75.
76.
Jannett Nguyen Tiffany Alexander Hong Jiang Natasha Hill Zied Abdullaev Svetlana D. Pack Amy P. Hsu Steven M. Holland Dennis D. Hickstein Eric A. Engels Isaac Brownell 《Pigment cell & melanoma research》2018,31(2):337-340
GATA2 deficiency is a recently described genetic disorder affecting hematopoietic stem cells and is associated with immunodeficiency, hematologic malignancy, and various cutaneous pathologies including cutaneous tumors. To explore the incidence and clinical course of melanoma in patients with germline GATA2 deficiencies, we conducted a retrospective chart review of 71 such patients and identified two with invasive melanoma. One melanoma was diagnosed early because it was associated with pruritus due to a graft‐versus‐tumor effect following bone marrow transplantation. The other one, a lentigo maligna melanoma, was locally excised but progressed to widespread metastasis and death several years later. Our observations and published studies of melanoma biology suggest an association between decreased GATA2 expression and melanoma progression. These findings suggest that GATA2 deficient patients may have an increased risk of melanoma and should be observed closely for new or changing skin lesions. 相似文献
77.
The effects of suboptimal root zone temperatures (RZTs) on net translocation rates from the roots to the shoots and the concentrations
of Fe, Mn, Zn, and Cu were examined in maize grown in nutrient solution or soil. Plants were grown at 12 °C, 18 °C and 24
°C RZT. At each RZT, the growth-related shoot demand for nutrients was varied by independently modifying the temperature of
the shoot base (SBT) including the apical shoot meristem.
The net translocation rates of Mn and Zn from the roots to the shoots were reduced at low RZTs, irrespective of the SBT and
of the substrate (soil or nutrient solution). Obviously, the net translocation rates of Mn and Zn at low RZT were mainly regulated
by temperature effects on the roots and not by the chemical nutrient availability in the rhizosphere or by shoot growth rate
as controlled by SBTs. When both RZT and SBT were reduced, the decrease in net translocation rates of Mn and Zn was similar
to the decline in the shoot growth rate and concentrations of Mn and Zn in the shoot fresh matter were not greatly affected
or were even increased by low RZT. However, at high SBT and low RZT in nutrient solution, the depressed net translocation
rates of Mn and Zn combined with the increased shoot growth resulted in significantly decreased concentrations of Mn and Zn
in the shoot, indicating that Mn and Zn may become deficient even at high chemical availability.
By contrast to Mn and Zn, the net translocation rates of Fe and Cu at all RZTs were markedly enhanced by increased SBTs. Accordingly,
the concentrations of Fe and Cu in the shoot fresh matter were not greatly affected by RZTs, irrespective of the SBTs. These
results indicate that the ability of roots to supply Fe and Cu to the shoot was internally regulated by the growth related
shoot demand per unit of roots.
Deceased 21 September 1996
Deceased 21 September 1996 相似文献
78.
Test plantings with varieties ofLolium multiflorum andL perenne were harvested 4 to 7 times a year in 1991 and 1992. Samples were checked for the presence ofFusaria, the mycotoxins zearalenone, T-2 toxin, and diacetoxyscirpenol (DAS). Spectrum of species and the incidence ofFusaria and fusariotoxins are discussed in relation to the influencing factors site, variety ofLolium, harvesting time and year. Depending on these factors, 41 % to 100 % of the samples wereFusarium positive. Differences in infestation with Fusarium among varieties ofLolium perenne were dependent on location and did not correlate with yield. The six species ofFusarium pathogenic toLolium spp. (F. graminearum, F. culmorum, F. avenaceum, F. oxysporum, F. solani, and F. acuminatum) totaled 35.7 % of all the isolated strains. 14 species could be isolated fromLolium samples (descending frequency):F. culmorum, F. sambucinum, F. equiseti, F. acuminatum, F. semitectum, F. oxysporum, F. subglutinans, F. avenaceum, F. sporotrichioides, F. proliferatum, F. tricinctum, F. anthophilum, F. dimerum and F. graminearum. For the detection ofFusaria a promising new immunological method is presented. It is based on the genus specific production of exopolysaccharides byFusarium species. Mycotoxin contents in grass ranged from 0.01 to 4.75 ppm for zearalenone with 67 % positive samples and 0.3 % samples above 1 ppm, 0.04 to 2.78 ppm for T-2 toxin with 25 % positive samples and 2.8 % samples above 1 ppm, and 0.003 to 0.06 for DAS with 21.6 % positive samples. In silages, no T-2 toxin was detectable. IsolatedFusarium strains were checked for the ability to produce the mycotoxins zearalenone, T-2 toxin and DAS in culture. Most of the strains were positive for at least one of the toxins. 相似文献
79.
Axel H. Meyer Karin Schmuck Corinne Morel William Wishart Hermann Lübbert Peter Engels 《Genomics》1996,38(3):435
Phospholipases A2 (PLA2) form an extended class of enzymes that play an important role in signal transduction. Phospholipase A2-like (PLA2L) belongs to the secreted forms of phospholipases A2, but constitutes a new subgroup. We have assigned the gene for this enzyme to human chromosome 8q24–qter using fluorescencein situhybridization and radiation hybrid mapping techniques. 相似文献
80.
Matthias Mag Jochen Muth Kerstin Jahn Anusch Peyman Gerhard Kretzschmar Joachim W. Engels Eugen Uhlmann 《Bioorganic & medicinal chemistry》1997,5(12):2213-2220
A method for the synthesis of chimeric oligodeoxynucleotides comprised of phosphodiester and phenylphosphonate [3′-O-P(=O)(C6H5)-O-5′] or phenylphosphono-thioate [3′-O-P(=S)(C6H5)-O-5′] linkages has been developed. Synthesis was performed using suitably protected nucleoside phenylphosphonamidites as building blocks following an adjusted solid-phase phosphoramidite synthesis protocol. The new oligodeoxy-nucleotide analogues were characterized by electrospray ionization- and matrix-assisted laser desorption mass spectrometry, as well as by 31P NMR spectroscopy. Additionally, their binding properties to complementary oligodeoxynucleotides has been studied. 相似文献