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91.
92.
Rock barrens support rare plant species but may be threatened by forest expansion. We determined the extent of forest expansion
onto open coastal barrens and identified environmental correlates of dynamic versus persistent barrens in Nova Scotia, Canada.
We used aerial photos to quantify the amount of forest expansion over the last 70 years at five coastal barrens sites and
GIS to derive topographic and other environmental predictors to differentiate persistent coastal barrens compared with persistent
forests or barrens that succeed to forests. Linear discriminant and classification tree analyses identified the variables
associated with each class of habitat. Coastal barrens decreased by an average of 7.9% (from 4.2 to 24.6% depending on the
site) in the last 70 years due to forest expansion. The best predictors of persistent barrens were elevation and distance
to coast. Environmental factors such as topographical heterogeneity and evidence of fire varied among sites. Climatic and
edaphic conditions near the coast and in exposed inland areas may protect coastal barrens vegetation from forest expansion.
Evidence of fire was not found at all barrens sites, thus at least some of the persistent open barrens are likely maintained
by shallow soils, salt spray, and wind exposure. All three classes of habitat had distinct vegetation, and the only rare species
was found in a persistent barren. Management of human activities in such landscapes should take into account the dynamic nature
of barrens vegetation, while prioritizing conservation efforts in persistent barrens. 相似文献
93.
94.
The Columbian Exchange resulted in a widespread movement of humans, plants and animals between the Old and New Worlds. The late 15th to early 16th century transfer of cattle from the Iberian Peninsula and Canary Islands to the Caribbean laid the foundation for the development of American creole cattle (Bos taurus) breeds. Genetic analyses of modern cattle from the Americas reveal a mixed ancestry of European, African and Indian origins. Recent debate in the genetic literature centers on the ‘African’ haplogroup T1 and its subhaplogroups, alternatively tying their origins to the initial Spanish herds, and/or from subsequent movements of taurine cattle through the African slave trade. We examine this problem through ancient DNA analysis of early 16th century cattle bone from Sevilla la Nueva, the first Spanish colony in Jamaica. In spite of poor DNA preservation, both T3 and T1 haplogroups were identified in the cattle remains, confirming the presence of T1 in the earliest Spanish herds. The absence, however, of “African-derived American” haplotypes (AA/T1c1a1) in the Sevilla la Nueva sample, leaves open the origins of this sub-haplogroup in contemporary Caribbean cattle. 相似文献
95.
Four proteins from NCBI cog1816, previously annotated as adenosine deaminases, have been subjected to structural and functional characterization. Pa0148 (Pseudomonas aeruginosa PAO1), AAur1117 (Arthrobacter aurescens TC1), Sgx9403e, and Sgx9403g have been purified and their substrate profiles determined. Adenosine is not a substrate for any of these enzymes. All of these proteins will deaminate adenine to produce hypoxanthine with k(cat)/K(m) values that exceed 10(5) M(-1) s(-1). These enzymes will also accept 6-chloropurine, 6-methoxypurine, N-6-methyladenine, and 2,6-diaminopurine as alternate substrates. X-ray structures of Pa0148 and AAur1117 have been determined and reveal nearly identical distorted (β/α)(8) barrels with a single zinc ion that is characteristic of members of the amidohydrolase superfamily. Structures of Pa0148 with adenine, 6-chloropurine, and hypoxanthine were also determined, thereby permitting identification of the residues responsible for coordinating the substrate and product. 相似文献
96.
Kamat SS Bagaria A Kumaran D Holmes-Hampton GP Fan H Sali A Sauder JM Burley SK Lindahl PA Swaminathan S Raushel FM 《Biochemistry》2011,50(11):1917-1927
Adenine deaminase (ADE) catalyzes the conversion of adenine to hypoxanthine and ammonia. The enzyme isolated from Escherichia coli using standard expression conditions was low for the deamination of adenine (k(cat) = 2.0 s(-1); k(cat)/K(m) = 2.5 × 10(3) M(-1) s(-1)). However, when iron was sequestered with a metal chelator and the growth medium was supplemented with Mn(2+) prior to induction, the purified enzyme was substantially more active for the deamination of adenine with k(cat) and k(cat)/K(m) values of 200 s(-1) and 5 × 10(5) M(-1) s(-1), respectively. The apoenzyme was prepared and reconstituted with Fe(2+), Zn(2+), or Mn(2+). In each case, two enzyme equivalents of metal were necessary for reconstitution of the deaminase activity. This work provides the first example of any member of the deaminase subfamily of the amidohydrolase superfamily to utilize a binuclear metal center for the catalysis of a deamination reaction. [Fe(II)/Fe(II)]-ADE was oxidized to [Fe(III)/Fe(III)]-ADE with ferricyanide with inactivation of the deaminase activity. Reducing [Fe(III)/Fe(III)]-ADE with dithionite restored the deaminase activity, and thus, the diferrous form of the enzyme is essential for catalytic activity. No evidence of spin coupling between metal ions was evident by electron paramagnetic resonance or Mo?ssbauer spectroscopy. The three-dimensional structure of adenine deaminase from Agrobacterium tumefaciens (Atu4426) was determined by X-ray crystallography at 2.2 ? resolution, and adenine was modeled into the active site on the basis of homology to other members of the amidohydrolase superfamily. On the basis of the model of the adenine-ADE complex and subsequent mutagenesis experiments, the roles for each of the highly conserved residues were proposed. Solvent isotope effects, pH-rate profiles, and solvent viscosity were utilized to propose a chemical reaction mechanism and the identity of the rate-limiting steps. 相似文献
97.
Christina C. Dahm Ruth H. Keogh Marleen A.H. Lentjes Elizabeth A. Spencer Tim J. Key Darren C. Greenwood Janet E. Cade Victoria J. Burley Martin J. Shipley Eric J. Brunner Alison M. Stephen Gita Mishra Diana Kuh Ian S. Fentiman Ian R. White Robert Luben Kay Tee Khaw Sheila A. Rodwell 《Cancer epidemiology》2011,35(5):501
98.
Nucleotide polymorphism in the acidic chitinase locus (ChiA) region of the wild plant Arabidopsis thaliana 总被引:3,自引:0,他引:3
To investigate DNA variation in natural plant populations, a 1.8-kb region
of the acidic chitinase locus (ChiA)was analyzed for 17 ecotypes of
Arabidopsis thaliana sampled worldwide and 3 Arabis species in Japan. As in
the Adh region, dimorphism was detected throughout the investigated ChiA
region, suggesting the possibility that dimorphic DNA variation exists in
the entire nuclear genome of A. thaliana. The ChiA region was divided into
two blocks by an intragenic recombination between two parental sequence
types, which diverged 7.4 MYA under the assumption that nucleotide mutation
rate per site per year is mu = 10(- 9). Nucleotide diversity in the entire
ChiA region was 0.0104. Tajima's test was significantly negative for both
nucleotide and indel variations, which was manifested as an excess of
unique polymorphisms. However, the level and pattern of polymorphism in the
ChiA region were inconsistent with simple theoretical explanations. The HKA
test detected no difference in the levels of intra- and interspecific
variations between the ChiA and Adh regions. In the ChiA coding region, no
difference in the patterns of synonymous and replacement variation was
found in intra- and interspecific comparisons by the MK test. Although it
was difficult to determine the exact genetic mechanism acting on the ChA
locus, these results suggested that the ChA locus region was under the same
genetic mechanism before and after the establishment of A. thaliana as a
species.
相似文献
99.
Biochemical and biological functions of proteins are the product of both the overall fold of the polypeptide chain, and, typically, structural motifs made up of smaller numbers of amino acids constituting a catalytic center or a binding site that may be remote from one another in amino acid sequence. Detection of such structural motifs can provide valuable insights into the function(s) of previously uncharacterized proteins. Technically, this remains an extremely challenging problem because of the size of the Protein Data Bank (PDB) archive. Existing methods depend on a clustering by sequence similarity and can be computationally slow. We have developed a new approach that uses an inverted index strategy capable of analyzing >170,000 PDB structures with unmatched speed. The efficiency of the inverted index method depends critically on identifying the small number of structures containing the query motif and ignoring most of the structures that are irrelevant. Our approach (implemented at motif.rcsb.org) enables real-time retrieval and superposition of structural motifs, either extracted from a reference structure or uploaded by the user. Herein, we describe the method and present five case studies that exemplify its efficacy and speed for analyzing 3D structures of both proteins and nucleic acids. 相似文献
100.
Phosphorus release from sediments in hardwater eutrophic lakes: the effects of redox-sensitive and -insensitive chemical treatments 总被引:4,自引:0,他引:4
1. Phosphorus (P) release from bottom sediments is an important source of nutrient enrichment in many lakes in sedimentary basins, such as those in western Canada. On the Boreal Plain, sediment P release is particularly strong during periods of seasonal anoxia.
2. In this study, the effects of reduction–oxidation (redox)-sensitive and -insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.
3. Contrary to expectations, redox-sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox-insensitive treatments. Redox-sensitive treatments with FeCl3 and FeCl3 + O2 reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox-insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O2 treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively.
4. The fraction of P that adsorbed and co-precipitated with iron and aluminium in the sediment cores was low (non-apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism. 相似文献
2. In this study, the effects of reduction–oxidation (redox)-sensitive and -insensitive chemicals on P release were examined in sediment cores collected from three eutrophic lakes.
3. Contrary to expectations, redox-sensitive treatments were no more effective at lowering total phosphorus (TP) in sediment cores than some redox-insensitive treatments. Redox-sensitive treatments with FeCl
4. The fraction of P that adsorbed and co-precipitated with iron and aluminium in the sediment cores was low (non-apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacterial metabolism. 相似文献