全文获取类型
收费全文 | 1502篇 |
免费 | 166篇 |
出版年
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 22篇 |
2017年 | 25篇 |
2016年 | 17篇 |
2015年 | 51篇 |
2014年 | 54篇 |
2013年 | 68篇 |
2012年 | 66篇 |
2011年 | 70篇 |
2010年 | 54篇 |
2009年 | 56篇 |
2008年 | 67篇 |
2007年 | 69篇 |
2006年 | 59篇 |
2005年 | 61篇 |
2004年 | 64篇 |
2003年 | 63篇 |
2002年 | 44篇 |
2001年 | 51篇 |
2000年 | 47篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 21篇 |
1996年 | 14篇 |
1995年 | 10篇 |
1994年 | 19篇 |
1993年 | 18篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1990年 | 26篇 |
1989年 | 24篇 |
1988年 | 29篇 |
1987年 | 29篇 |
1986年 | 26篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 19篇 |
1976年 | 11篇 |
1974年 | 17篇 |
1973年 | 19篇 |
1972年 | 12篇 |
1971年 | 9篇 |
排序方式: 共有1668条查询结果,搜索用时 15 毫秒
141.
Verhagen AM Kratina TK Hawkins CJ Silke J Ekert PG Vaux DL 《Cell death and differentiation》2007,14(2):348-357
Direct IAP binding protein with low pI/second mitochondrial activator of caspases, HtrA2/Omi and GstPT/eRF3 are mammalian proteins that bind via N-terminal inhibitor of apoptosis protein (IAP) binding motifs (IBMs) to the baculoviral IAP repeat (BIR) domains of IAPs. These interactions can prevent IAPs from inhibiting caspases, or displace active caspases, thereby promoting cell death. We have identified several additional potential IAP antagonists, including glutamate dehydrogenase (GdH), Nipsnap 3 and 4, CLPX, leucine-rich pentatricopeptide repeat motif-containing protein and 3-hydroxyisobutyrate dehydrogenase. All are mitochondrial proteins from which N-terminal import sequences are removed generating N-terminal IBMs. Whereas most of these proteins have alanine at the N-terminal position, as observed for previously described antagonists, GdH has an N-terminal serine residue that is essential for X-linked IAP (XIAP) interaction. These newly described IAP binding proteins interact with XIAP mainly via BIR2, with binding eliminated or significantly reduced by a single point mutation (D214S) within this domain. Through this interaction, many are able to antagonise XIAP inhibition of caspase 3 in vitro. 相似文献
142.
Macrofouling of aquatic man-made structures by zebra mussels (Dreissena polymorpha) poses significant economic burdens on commercial freshwater shipping and facilities utilising raw water. The negative environmental impact of some current antifouling technologies has limited their use and prompted investigation of non-organometallic and non-oxidising antifoulants as possible environment-friendly alternatives. The plant-derived natural product capsaicin and 18 other compounds with one or more capsaicin-like structural features were tested for their potential to inhibit zebra mussel byssal attachment at a single high concentration of 30 microM. Of these, three compounds displaying the highest levels of attachment inhibition where selected for further concentration-response testing. This testing revealed that capsaicin (8-methyl-N-vanillyl-trans-6-nonenamide), N-vanillylnonanamide, and N-benzoylmonoethanolamine benzoate all inhibited byssal attachment with potency values (EC(50)) in the micromolar range. None of these compounds were lethal to adult specimens of the water flea, Daphnia magna, at concentrations that inhibited mussel byssal attachment. 相似文献
143.
Range maps and species richness patterns: errors of commission and estimates of uncertainty 总被引:1,自引:0,他引:1
Range maps are often combined into “range overlap maps” to estimate spatial variation in species richness. Range maps are, in most cases, designed to represent a species’ maximum geographical extent and not patterns of occupancy within the range. As a consequence, range maps overestimate occupancy by presenting false occupancy (errors of commission) within the interior of the range. To assess the implications of errors of commission when developing and applying range overlap maps, we used neutral landscapes to simulate range maps and patterns of occupancy within ranges. We explored several scenarios based on combinations of six parameters defining biogeographical and cartographic factors typically encountered by investigators. Our results suggest that, in general, uncertainty is lowest when map resolutions are moderately fine, the majority of species have geographically restricted ranges, species occur throughout their range, patterns of occupancy within the range are not correlated among species, and geographically local and widespread species tend to occupy different regions. Several of these outcomes are associated with broad geographical extents, the scale at which range overlap maps are typically applied. Thus, under most circumstances, reasonably accurate and precise representation of species richness patterns can be achieved. However, these representations can be improved by enhancing occupancy data for widespread species – a primary source of uncertainty – and selecting a map resolution that captures relevant biological and environmental heterogeneity. Hence, by determining where a study is situated within the scenarios examined in our simulations, uncertainty and its sources and implications can be ascertained. With this knowledge, research goals, methods, and data sources can be reassessed and refined and, in the end, conclusions and recommendations can be qualified. Alternatively, unique regional, taxonomic, or cartographic factors could be included in future simulations to provide direct assessments of uncertainty. 相似文献
144.
Development of a RIVPACS-type predictive model for bioassessment of wadeable streams in Wyoming 总被引:3,自引:0,他引:3
Eric G. Hargett Jeremy R. ZumBerge Charles P. Hawkins John R. Olson 《Ecological Indicators》2007,7(4):807-826
RIVPACS models produce a community-level measure of biological condition known as O/E, which is derived from a comparison of the observed (O) biota with those expected (E) to occur in the absence of anthropogenic stress. We used benthic macroinvertebrate and environmental data collected at 925 stream monitoring stations, from 1993 to 2001, to develop, validate, and apply a RIVPACS model to assess the biological condition of wadeable streams in Wyoming. From this dataset, 296 samples were identified as reference, 157 of which were used to calibrate the model, 46 to validate it, and 93 to examine temporal variability in reference site O/E-values. We used cluster analyses to group the model development reference sites into biologically similar classes of streams and multiple discriminant function analysis to determine which environmental variables best discriminated among reference groups. A suite of 14 categorical and continuous environmental variables best discriminated among 15 reference groups and explained a large proportion of the natural variability in biota within the reference dataset. Eleven of the predictor variables were derived from GIS. As expected, mean O/E-values for reference sites used in model development and validation were near unity and statistically similar. Temporal variability in O/E-values for reference sites was low. Test site values ranged from 0 to 1.45 (mean = 0.73). The model was accurate in both space and time and precise enough (S.D. of O/E-values for calibration data = 0.17) to detect modest alteration in biota associated with anthropogenic stressors. Our model was comparable in performance to other RIVPACS models developed in the United States and can produce effective assessments of biological condition over a broad, ecologically diverse region. We also provide convincing evidence that RIVPACS models can be developed primarily with GIS-based predictor variables. This framework not only simplifies the extraction of predictor variable information while potentially reducing expenditures of time and money in the collection of predictor variable information, but opens the door for development and/or application of RIVPACS models in regions where there is a paucity of local-scale, abiotic information. 相似文献
145.
Bioprocessing analysis of Pyrococcus furiosus strains engineered for CO2‐based 3‐hydroxypropionate production 下载免费PDF全文
146.
Background
Although simulation studies show that combining multiple breeds in one reference population increases accuracy of genomic prediction, this is not always confirmed in empirical studies. This discrepancy might be due to the assumptions on quantitative trait loci (QTL) properties applied in simulation studies, including number of QTL, spectrum of QTL allele frequencies across breeds, and distribution of allele substitution effects. We investigated the effects of QTL properties and of including a random across- and within-breed animal effect in a genomic best linear unbiased prediction (GBLUP) model on accuracy of multi-breed genomic prediction using genotypes of Holstein-Friesian and Jersey cows.Methods
Genotypes of three classes of variants obtained from whole-genome sequence data, with moderately low, very low or extremely low average minor allele frequencies (MAF), were imputed in 3000 Holstein-Friesian and 3000 Jersey cows that had real high-density genotypes. Phenotypes of traits controlled by QTL with different properties were simulated by sampling 100 or 1000 QTL from one class of variants and their allele substitution effects either randomly from a gamma distribution, or computed such that each QTL explained the same variance, i.e. rare alleles had a large effect. Genomic breeding values for 1000 selection candidates per breed were estimated using GBLUP modelsincluding a random across- and a within-breed animal effect.Results
For all three classes of QTL allele frequency spectra, accuracies of genomic prediction were not affected by the addition of 2000 individuals of the other breed to a reference population of the same breed as the selection candidates. Accuracies of both single- and multi-breed genomic prediction decreased as MAF of QTL decreased, especially when rare alleles had a large effect. Accuracies of genomic prediction were similar for the models with and without a random within-breed animal effect, probably because of insufficient power to separate across- and within-breed animal effects.Conclusions
Accuracy of both single- and multi-breed genomic prediction depends on the properties of the QTL that underlie the trait. As QTL MAF decreased, accuracy decreased, especially when rare alleles had a large effect. This demonstrates that QTL properties are key parameters that determine the accuracy of genomic prediction.Electronic supplementary material
The online version of this article (doi:10.1186/s12711-015-0124-6) contains supplementary material, which is available to authorized users. 相似文献147.
148.
149.
Sally A. Keith Roger J.H. Herbert Paul A. Norton Stephen J. Hawkins Adrian C. Newton 《Diversity & distributions》2011,17(2):275-286
Aim Evidence indicates that species are responding to climate change through distributional range shifts that track suitable climatic conditions. We aim to elucidate the role of meso‐scale dispersal barriers in climate‐tracking responses. Location South coast of England (the English Channel). Methods Historical distributional data of four intertidal invertebrate species were logistically regressed against sea surface temperature (SST) to determine a climate envelope. This envelope was used to estimate the expected climate‐tracking response since 1990 along the coast, which was compared with observed range expansions. A hydrodynamic modelling approach was used to identify dispersal barriers and explore disparities between expected and observed climate tracking. Results Range shifts detected by field survey over the past 20 years were less than those predicted by the changes that have occurred in SST. Hydrodynamic model simulations indicated that physical barriers produced by complex tidal currents have variably restricted dispersal of pelagic larvae amongst the four species. Main conclusions We provide the first evidence that meso‐scale hydrodynamic barriers have limited climate‐induced range shifts and demonstrate that life history traits affect the ability of species to overcome such barriers. This suggests that current forecasts may be flawed, both by overestimating range shifts and by underestimating climatic tolerances of species. This has implications for our understanding of climate change impacts on global biodiversity. 相似文献
150.
Saslis-Lagoudakis CH Klitgaard BB Forest F Francis L Savolainen V Williamson EM Hawkins JA 《PloS one》2011,6(7):e22275