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排序方式: 共有136条查询结果,搜索用时 31 毫秒
71.
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Suzuki Y St Onge RP Mani R King OD Heilbut A Labunskyy VM Chen W Pham L Zhang LV Tong AH Nislow C Giaever G Gladyshev VN Vidal M Schow P Lehár J Roth FP 《Nature methods》2011,8(2):159-164
Phenotypes that might otherwise reveal a gene's function can be obscured by genes with overlapping function. This phenomenon is best known within gene families, in which an important shared function may only be revealed by mutating all family members. Here we describe the 'green monster' technology that enables precise deletion of many genes. In this method, a population of deletion strains with each deletion marked by an inducible green fluorescent protein reporter gene, is subjected to repeated rounds of mating, meiosis and flow-cytometric enrichment. This results in the aggregation of multiple deletion loci in single cells. The green monster strategy is potentially applicable to assembling other engineered alterations in any species with sex or alternative means of allelic assortment. To test the technology, we generated a single broadly drug-sensitive strain of Saccharomyces cerevisiae bearing precise deletions of all 16 ATP-binding cassette transporters within clades associated with multidrug resistance. 相似文献
73.
Sigurd Einum Anders G. Finstad Grethe Robertsen Keith H. Nislow Simon McKelvey John D. Armstrong 《Population Ecology》2012,54(2):285-294
If competitive ability depends on body size, then the optimal natal movement from areas of high local population density can
also be predicted to be size-dependent. Specifically, small, competitively-inferior individuals would be expected to benefit
most from moving to areas of lower local density. Here we evaluate whether individual variation in natal movement following
emergence from nests is consistent with such a size-dependent strategy in Atlantic salmon, and whether such a strategy is
evident across a range of environmental conditions (principally predator presence and conspecific density). In stream channel
experiments, those juveniles that stayed close to nests were larger than those that emigrated. This result was not sensitive
to predator presence or conspecific density. These observations were mirrored in natural streams in which salmon eggs were
planted in nests and the resulting offspring were sampled at high spatial resolution. A negative relationship was found between
juvenile body size and distance from nests early in development whereas in those streams sampled later in ontogeny, individuals
that had moved furthest were largest. Thus, movement away from nests appeared to result in a reduced competitive intensity
and increased growth rate. The fact that there is ultimately a growth advantage associated with moving suggests that there
is also a cost that selects against movement by the larger individuals. Thus, natal movement in juvenile Atlantic salmon appears
to represent a body size-dependent strategy. 相似文献
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Shah A S Rahim KH Bhatti A Khan N Din M Imran M Mohsin M Ishtiaq A Nabila A Ansari S Hussain M Zafar M Mushtaq E Mumtaz J Iqbal 《Phyton》2015,84(1):34-44
Sargodha district is one of the least studied regions of Pakistan regarding its ethnobotanical values. This paper is the first report related to the documentation and conservation status of the tree species in the Sargodha district, and their folk ethnobotanical uses. An interview base survey was conducted in the study area in 2010-2013. The ethnobotanical data revealed the use of 100 tree species (6 gymnosperms, 94 angiosperms) belonging to 77 genera (6 gymnosperms, 71 angiosperms) and 39 families (4 gymnosperms, 35 angiosperms), with the Fabaceae ranking first with 19 tree species, followed by the Moraceae (12 species). Tree species like Aegle marmelos, Butea monosperma, Diospyrus malabarica, Gmelina arborea, Kigelia africana, Manilkara hexandra, Manilkara zapota, Mimusops elengi, Nyctanthes arbor-tristis, Putranjiva roxburghii, Terminalia arjuna and Terminalia bellerica are not only unique in their medicinal value but also interesting because of their unusual occurrence here. Thevetia peruviana, Cassia fistula, Celtis australis, Delonix regia, Diospyrus malabarica, Grevillea robusta, Haplophragma adenophylum, Jacaranda mimosifolia, Lagerstroemia speciosa, Plumeria rubra, Pterospermum acerifolium, Roystonea regia, Taxodium distichum and Tectona grandis are included among the worth looking ornamental tree species. Capparis decidua, Dalbergia sissoo, Tamarix aphylla, Tamarix dioica, Prosopis cineraria and Ziziphus mauritiana are the most commonly used timber species. Other common ethnobotanical utilization of these trees includes either sheltering or fuel or agricultural uses. Lack of awareness about the potential uses of these species, and particularly ignorance of the concerned authorities, have led to a decline in the population of this precious tree flora. Documentation of this tree flora, and as-sociated indigenous knowledge, can be used as a basis for developing management plans for conservation and sustainable use of this flora in the study area. A well-organized management is critical to restore and conserve this endangered natural resource in the District Sargodha, Pakistan. The immense medicinal and timber value of these tree species make it necessary to promote their conservation to simultaneously alleviate the poverty and improve the socio-economic status of the study area. 相似文献
76.
The effect of predators on prey populations depends on how predator-caused mortality changes with prey population density.
Predators can enforce density-dependent prey mortality and contribute to population stability, but only if they have a positive
numerical or behavioral response to increased prey density. Otherwise, predator saturation can result in inversely density-dependent
mortality, destabilizing prey populations and increasing extinction risk. Juvenile salmon and trout provide some of the clearest
empirical examples of density-dependent mortality in animal populations. However, although juvenile salmon are very vulnerable
to predators, the demographic effects of predators on juvenile salmon are unknown. We tested the interactive effects of predators
and population density on the mortality of juvenile Atlantic salmon (Salmo salar) using controlled releases of salmon in natural streams. We introduced newly hatched juvenile salmon at three population
density treatments in six study streams, half of which contained slimy sculpin (Cottus cognatus), a common generalist predator (18 release sites in total, repeated over two summers). Sculpin reversed the direction of
density dependence for juvenile salmon mortality. Salmon mortality was density dependent in streams with no sculpin, but inversely
density dependent in streams where sculpin were abundant. Such predator-mediated inverse density dependence is especially
problematic for prey populations suppressed by other factors, thereby presenting a fundamental challenge to persistence of
rare populations and restoration of extirpated populations. 相似文献
77.
Population response to habitat fragmentation in a stream-dwelling brook trout population 总被引:1,自引:0,他引:1
Fragmentation can strongly influence population persistence and expression of life-history strategies in spatially-structured populations. In this study, we directly estimated size-specific dispersal, growth, and survival of stream-dwelling brook trout in a stream network with connected and naturally-isolated tributaries. We used multiple-generation, individual-based data to develop and parameterize a size-class and location-based population projection model, allowing us to test effects of fragmentation on population dynamics at local (i.e., subpopulation) and system-wide (i.e., metapopulation) scales, and to identify demographic rates which influence the persistence of isolated and fragmented populations. In the naturally-isolated tributary, persistence was associated with higher early juvenile survival ( approximately 45% greater), shorter generation time (one-half) and strong selection against large body size compared to the open system, resulting in a stage-distribution skewed towards younger, smaller fish. Simulating barriers to upstream migration into two currently-connected tributary populations caused rapid (2-6 generations) local extinction. These local extinctions in turn increased the likelihood of system-wide extinction, as tributaries could no longer function as population sources. Extinction could be prevented in the open system if sufficient immigrants from downstream areas were available, but the influx of individuals necessary to counteract fragmentation effects was high (7-46% of the total population annually). In the absence of sufficient immigration, a demographic change (higher early survival characteristic of the isolated tributary) was also sufficient to rescue the population from fragmentation, suggesting that the observed differences in size distributions between the naturally-isolated and open system may reflect an evolutionary response to isolation. Combined with strong genetic divergence between the isolated tributary and open system, these results suggest that local adaptation can 'rescue' isolated populations, particularly in one-dimensional stream networks where both natural and anthropogenically-mediated isolation is common. However, whether rescue will occur before extinction depends critically on the race between adaptation and reduced survival in response to fragmentation. 相似文献
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pedagog is a Windows program that can be used to determine power for, and validate inferences drawn from, eco-evolutionary studies. It models dynamics of multiple populations and their interactions through individual-based simulations while simultaneously recording genotype, pedigree and trait information at the individual level. pedagog also allows for specification of heritable traits, natural and sexual selection acting upon those traits, population sampling schemes and incorporation of genetic and demographic errors into the output. Overall, parameters can be specified for genetic diversity, demographics, mating design, genetic and demographic errors, individual growth models, trait heritability and selection, and output formatting. Demographic parameters can be either age or function based, and all parameters can be drawn from 12 statistical distributions where appropriate. Simulation results can be automatically formatted for 57 existing software programs to facilitate postsimulation analyses. pedagog is freely available for download at https://bcrc.bio.umass.edu/pedigreesoftware/. 相似文献
80.