全文获取类型
收费全文 | 505篇 |
免费 | 27篇 |
专业分类
532篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 17篇 |
2015年 | 19篇 |
2014年 | 26篇 |
2013年 | 23篇 |
2012年 | 32篇 |
2011年 | 48篇 |
2010年 | 24篇 |
2009年 | 12篇 |
2008年 | 35篇 |
2007年 | 25篇 |
2006年 | 15篇 |
2005年 | 31篇 |
2004年 | 25篇 |
2003年 | 13篇 |
2002年 | 29篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 11篇 |
1993年 | 5篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有532条查询结果,搜索用时 20 毫秒
31.
Cees S. Roselaar Ronald Sluys Mansour Aliabadian Peter G. M. Mekenkamp 《Journal of Ornithology》2007,148(3):271-280
A database was created of digitized equal area distribution maps of 3,036 phylogenetic species of Palearctic songbirds. Biogeographic
patterns are reported for two data sets: (1) including all passeriform bird species reported as breeding within the boundaries
of our study map, (2) passeriform species restricted in their distribution to our study region, thus excluding the partly
extra-limital taxa. With respect to the data set excluding partly extra-limital taxa, the average range size is 238 grid cells
(grid cell area: 4,062 km2). Analysis of the geographic distribution of species richness for the full data set showed several hotspot regions, mostly
located in mountainous areas. The index of range-size rarity identified similar hotspot regions as that for species richness,
albeit that the range-size rarity de-emphasized the central Siberian hotspot. Range-size rarity hotspots that are not evident
on the measure of species richness concern a great number of islands. Much more prominent on the index of range-size rarity
are the Atlas Mountains of northern Africa, the Jabal al Akhdar region in NE Libya, and the eastern border of the Mediterranean.
Restricting the analysis of geographic variation to the 25% of the species with smallest ranges resulted in a greatly simplified
pattern of hotspots.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
32.
33.
Anke Stekelenburg Gustav J Strijkers Henry Parusel Dan L Bader Klaas Nicolay Cees W Oomens 《Journal of applied physiology》2007,102(5):2002-2011
A rat model was used to distinguish between the different factors that contribute to muscle tissue damage related to deep pressure ulcers that develop after compressive loading. The separate and combined effects of ischemia and deformation were studied. Loading was applied to the hindlimb of rats for 2 h. Muscle tissue was examined using MR imaging (MRI) and histology. An MR-compatible loading device allowed simultaneous loading and measurement of tissue status. Two separate loading protocols incorporated uniaxial loading, resulting in tissue compression and ischemic loading. Uniaxial loading was applied to the tibialis anterior by means of an indenter, and ischemic loading was accomplished with an inflatable tourniquet. Deformation of the muscle tissue during uniaxial loading was measured using MR tagging. Compression of the tissues for 2 h led to increased T2 values, which were correlated to necrotic regions in the tibialis anterior. Perfusion measurements, by means of contrast-enhanced MRI, indicated a large ischemic region during indentation. Pure ischemic loading for 2 h led to reversible tissue changes. From the MR-tagging experiments, local strain fields were calculated. A 4.5-mm deformation, corresponding to a surface pressure of 150 kPa, resulted in maximum shear strain up to 1.0. There was a good correlation between the location of damage and the location of high shear strain. It was concluded that the large deformations, in conjunction with ischemia, provided the main trigger for irreversible muscle damage. 相似文献
34.
Yvonne M. Mos Arnold C. Vermeulen Cees J. N. Buisman Jan Weijma 《Geomicrobiology journal》2018,35(6):511-517
In X-ray diffraction, a good combination of configuration and sample is essential. Copper radiation for iron containing materials leads to a high background. Although this has been recognized, many researchers still use this combination. To clearly show the unsuitability of copper radiation for iron oxides, magnetite, goethite, maghemite, and hematite were analysed in different configurations using copper or cobalt radiation. Results show effects of fluorescence repressing measures and different radiation sources. Copper radiation diffractograms make phase identification contestable. Studies using copper radiation for iron oxides must therefore be carefully evaluated. Cobalt radiation yielded high quality diffractograms, making phase identification unambiguous. 相似文献
35.
36.
Karel Wernars Theo Goosen Bert M. J. Wennekes Klaas Swart Cees A. M. J. J. van den Hondel Henk W. J. van den Broek 《Molecular & general genetics : MGG》1987,209(1):71-77
Summary When a non-selected DNA sequence was added during the transformation of amdS320 deletion strains of Aspergillus nidulans with a vector containing the wild-type amdS gene the AmdS+ transformants were cotransformed at a high frequency. Cotransformation of an amdS320, trpC801 double mutant strain showed that both the molar ratio of the two vectors and the concentration of the cotransforming vector affected the cotransformation frequency. The maximum frequency obtained was defined by the gene chosen as selection marker for transformation. Cotransformation was used to induce a gene replacement in A. nidulans. An amdS320 strain was transformed to AmdS+ and cotransformed with a DNA fragment containing a fusion between a non-functional A. nidulans trpC gene and the Escherichia coli lacZ gene. Ten AmdS+, LacZ+ transformants with a Trp– mutant phenotype were selected. All of these strains could be transformed with a functional copy of the A. nidulans trpC gene, but only two strains yielded TrpC+ transformants which, with a low frequency, had a LacZ– phenotype. These latter transformants had also lost the AmdS+ phenotype. Southern blotting analysis of DNA from these transformants confirmed the inactivation of the wild-type trpC gene, but revealed that amdS vector sequences were also involved in the gene replacement events. 相似文献
37.
Alexander NJ McCormick SP Waalwijk C van der Lee T Proctor RH 《Fungal genetics and biology : FG & B》2011,48(5):485-495
Certain Fusarium species cause head blight of wheat and other small grains worldwide and produce trichothecene mycotoxins. These mycotoxins can induce toxicoses in animals and humans and can contribute to the ability of some fusaria to cause plant disease. Production of the trichothecene 3-acetyldeoxynivalenol (3-ADON) versus 15-acetyldeoxynivalenol (15-ADON) is an important phenotypic difference within and among some Fusarium species. However, until now, the genetic basis for this difference in chemotype has not been identified. Here, we identified consistent DNA sequence differences in the coding region of the trichothecene biosynthetic gene TRI8 in 3-ADON and 15-ADON strains. Functional analyses of the TRI8 enzyme (Tri8) in F. graminearum, the predominant cause of wheat head blight in North America and Europe, revealed that Tri8 from 3-ADON strains catalyzes deacetylation of the trichothecene biosynthetic intermediate 3,15-diacetyldeoxynivalenol at carbon 15 to yield 3-ADON, whereas Tri8 from 15-ADON strains catalyzes deacetylation of 3,15-diacetyldeoxynivalenol at carbon 3 to yield 15-ADON. Fusarium strains that produce the trichothecene nivalenol have a Tri8 that functions like that in 15-ADON strains. TRI3, which encodes a trichothecene carbon 15 acetyltransferase, was found to be functional in all three chemotypes. Together, our data indicate that differential activity of Tri8 determines the 3-ADON and 15-ADON chemotypes in Fusarium. 相似文献
38.
39.
40.
Sebastian Dolff Daniel Quandt Benjamin Wilde Thorsten Feldkamp Fan Hua Xin Cai Christof Specker Andreas Kribben Cees GM Kallenberg Oliver Witzke 《Arthritis research & therapy》2010,12(4):R150