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81.
C. Grenier P. J. Bramel-Cox M. Noirot K. E. Prasada Rao P. Hamon 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2000,101(1-2):190-196
A large collection, such as the sorghum [Sorghum bicolor (L.) Moench] landrace collection held at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT),
represents a challenge for the maintenance of both the accessions of and the information documented for the germplasm collection.
The accessibility and knowledge of the landrace collection are the essential factors for an efficient utilization of the genetic
resources by both breeders and farmers. Different sampling strategies, either random or non-random, were proposed to obtain
subsets of reduced size (core collection). Three subsets were established; a random sampling within a stratified collection
(logarithmic strategy: L); a sample based upon morpho-agronomic diversity (principal component score strategy: PCS); and a
sample based upon an empirical knowledge of sorghum (taxonomic strategy: T). Comparisons of these three samples for morpho-agronomic
characterization and passport information were assessed to determine their impact on phenotypic diversity. For their overall
diversity, the three subsets did not differ, as shown with the two-dimensional representation of the morpho-agronomic diversity
and the Shannon-Weaver diversity indices. When comparisons for morpho-agronomic and passport data were considered, the PCS
subset looked similar to the entire landrace collection. The L subset showed differences for characters associated with the
photoperiod reaction that was considered in the stratification of the collection. The T subset was the most distinct from
the entire landrace collection as it over-represented the landraces selected by farmers for specific uses and covered the
widest range of geographical adaptation and morpho-agronomic characteristics.
Received: 5 October 1999 / Accepted: 3 November 1999 相似文献
82.
A molecular simulation scheme, called Leap-dynamics, that provides efficient sampling of protein conformational space in solution is presented. The scheme is a combined approach using a fast sampling method, imposing conformational 'leaps' to force the system over energy barriers, and molecular dynamics (MD) for refinement. The presence of solvent is approximated by a potential of mean force depending on the solvent accessible surface area. The method has been successfully applied to N-acetyl-L-alanine-N-methylamide (alanine dipeptide), sampling experimentally observed conformations inaccessible to MD alone under the chosen conditions. The method predicts correctly the increased partial flexibility of the mutant Y35G compared to native bovine pancreatic trypsin inhibitor. In particular, the improvement over MD consists of the detection of conformational flexibility that corresponds closely to slow motions identified by nuclear magnetic resonance techniques. 相似文献
83.
84.
The species–area relationship (SAR) is one of the few generalizations in ecology. However, many different relationships are denoted as SARs. Here, we empirically evaluated the differences between SARs derived from nested-contiguous and non-contiguous sampling designs, using plants, birds and butterflies datasets from Great Britain, Greece, Massachusetts, New York and San Diego. The shape of SAR depends on the sampling scheme, but there is little empirical documentation on the magnitude of the deviation between different types of SARs and the factors affecting it. We implemented a strictly nested sampling design to construct nested-contiguous SAR (SACR), and systematic nested but non-contiguous, and random designs to construct non-contiguous species richness curves (SASRs for systematic and SACs for random designs) per dataset. The SACR lay below any SASR and most of the SACs. The deviation between them was related to the exponent f of the power law relationship between sampled area and extent. The lower the exponent f, the higher was the deviation between the curves. We linked SACR to SASR and SAC through the concept of “effective” area (Ae), i.e. the nested-contiguous area containing equal number of species with the accumulated sampled area (AS) of a non-contiguous sampling. The relationship between effective and sampled area was modeled as log(Ae) = klog(AS). A Generalized Linear Model was used to estimate the values of k from sampling design and dataset properties. The parameter k increased with the average distance between samples and with beta diversity, while k decreased with f. For both systematic and random sampling, the model performed well in predicting effective area in both the training set and in the test set which was totally independent from the training one. Through effective area, we can link different types of species richness curves based on sampling design properties, sampling effort, spatial scale and beta diversity patterns. 相似文献
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86.
Heidrun Feuchtmayr Dermot McKee Ian F. Harvey David Atkinson Brian Moss 《Hydrobiologia》2007,584(1):425-432
There is increasing concern about the effect of climate change on aquatic systems. We examined changes in macroinvertebrate
communities caused by increased temperature (3°C above ambient during summer only and continuous 3°C above ambient all year
round), influences of fish (Gasterosteus aculeatus L.) and addition of nutrients (nitrogen and phosphorus) in 48 large-scale (3000 l) tanks over a 2 year period. While numbers
of Isopoda, Chaoborus, Corixidae, Ephemeroptera, Notonectidae and Odonata were reduced by the presence of fish, nutrient addition caused isopods,
corixids, mayflies and odonates to increase in abundance. Impacts of temperature increase were surprisingly low, with only
gastropods increasing in heated tanks, suggesting that, overall abundances of most macroinvertebrate taxa will not be severely
affected by the predicted temperature rise. To determine if taxa were sampled representatively during the experiment, net
sweep samples taken towards the end of the experiment were compared with final macroinvertebrate abundances when the complete
contents of each tank were harvested. We found that net sweeping is an appropriate semi-quantitative method for most taxa
in mesocosm tanks. However, mites, coleopteran adults and larvae, dipterans and Chaoborus were not adequately sampled. This might explain why we could not detect any treatment effects of temperature, fish or nutrients
on mites, coleopterans and dipterans and calls for different sampling techniques for these taxa, especially in ponds with
vegetation stands. 相似文献
87.
G.-Y. Zhong C. O. Qualset 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(6-7):1064-1073
Dasypyrum villosum (L.) Candargy is a weedy annual diploid (2n = 14, VV genomes) allogamous grass species (Poaceae, Triticeae). Genetic variation for 12 traits was studied in 43 natural populations (31 from Italy and 12 from Croatia and Montenegro of former Yugoslavia) grown in a common field environment in California. Although 7 of 12 traits followed the theoretical prediction that a larger proportion of genetic variation was distributed within populations than among populations, exceptions were found for spike length, plant height, and days to flag-leaf emergence, heading, and anthesis. Covariate analysis showed that developmentally closely related characters were more likely correlated at both population and family within population levels. Geographically closer populations shared more genetic similarity than distant populations as indicated by mean coefficients of variation and cluster analysis of the Euclidean distances among populations. As few as five populations, each population with five or more half-sib seeds taken randomly from 5 plants, is expected to capture more than 95% of the total genetic variation of this species in the region sampled, but sampling a much larger number of seeds per population (> 1000) for long-term storage would supply research and plant breeding needs for several decades. If seed regeneration is required, populations can be sampled from clusters having similar genetic variation, and grown in reproductive isolation or bulked seed samples from all populations of each cluster group can be grown in isolation. The former is recommended if population integrity is desired while the latter is sufficient to provide genetic resources for plant-breeding purposes. 相似文献
88.
Michael A. Huffman Shunji Gotoh Linda A. Turner Miya Hamai Kozo Yoshida 《Primates; journal of primatology》1997,38(2):111-125
A longitudinal study of nematode infection in chimpanzees was conducted between 1989 and 1994 on the M group chimpanzees of
the Mahale Mountains National Park, Tanzania during two annual dry and rainy season periods and a third rainy season. Chemical
and physical antiparasite properties of medicinal plant use against the strongyle nematodeOesophagostomum stephanostomum have recently been reported at Mahale. Here, the incidence of nematode infections were analyzed for seasonal trends to elucidate
the possible influence of parasite infection on previously reported seasonality of medicinal plant use and to test the hypothesis
that the use of these plants is stimulated byO. stephanostomum. The number of chimpanzees infected byO. stephanostomum was significantly higher in the rainy season than in the dry season of both 1989–1990 and 1991–1992. However, the incidence
ofTrichuris trichura andStrongyloides fuelleborni showed no seasonality. Reinfection of individuals byO. stephanostomum occurred in synchrony with annual variation in rainfall: there was a sharp rise in the occurrence of new infections per individual
within one to two months after the beginning of the first heavy rains of the season. This pattern coincides with the reproductive
cycle of this nematode species.O. stephanostomum (95%) infections were associated significantly more frequently with medicinal plant use than eitherT. trichiura (50%) orS. fuelleborni (40%) infections. These observations are consistent with previous reports for the increased use of these plants during the
rainy season and are consistent the hypothesis that medicinal plant use is stimulated byO. stephanostomum infection. 相似文献
89.
90.