全文获取类型
收费全文 | 685篇 |
免费 | 39篇 |
国内免费 | 1篇 |
专业分类
林业 | 72篇 |
农学 | 22篇 |
基础科学 | 6篇 |
135篇 | |
综合类 | 89篇 |
农作物 | 20篇 |
水产渔业 | 45篇 |
畜牧兽医 | 267篇 |
园艺 | 15篇 |
植物保护 | 54篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 20篇 |
2019年 | 21篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 25篇 |
2012年 | 35篇 |
2011年 | 55篇 |
2010年 | 26篇 |
2009年 | 30篇 |
2008年 | 50篇 |
2007年 | 41篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 29篇 |
2003年 | 37篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 3篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1974年 | 4篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1958年 | 1篇 |
1945年 | 1篇 |
1941年 | 1篇 |
1926年 | 2篇 |
排序方式: 共有725条查询结果,搜索用时 15 毫秒
31.
Agent-based land-use models: a review of applications 总被引:9,自引:0,他引:9
Robin B. Matthews Nigel G. Gilbert Alan Roach J. Gary Polhill Nick M. Gotts 《Landscape Ecology》2007,22(10):1447-1459
Agent-based modelling is an approach that has been receiving attention by the land use modelling community in recent years,
mainly because it offers a way of incorporating the influence of human decision-making on land use in a mechanistic, formal,
and spatially explicit way, taking into account social interaction, adaptation, and decision-making at different levels. Specific
advantages of agent-based models include their ability to model individual decision-making entities and their interactions,
to incorporate social processes and non-monetary influences on decision-making, and to dynamically link social and environmental
processes. A number of such models are now beginning to appear—it is timely, therefore, to review the uses to which agent-based
land use models have been put so far, and to discuss some of the relevant lessons learnt, also drawing on those from other
areas of simulation modelling, in relation to future applications. In this paper, we review applications of agent-based land
use models under the headings of (a) policy analysis and planning, (b) participatory modelling, (c) explaining spatial patterns
of land use or settlement, (d) testing social science concepts and (e) explaining land use functions. The greatest use of
such models so far has been by the research community as tools for organising knowledge from empirical studies, and for exploring
theoretical aspects of particular systems. However, there is a need to demonstrate that such models are able to solve problems
in the real world better than traditional modelling approaches. It is concluded that in terms of decision support, agent-based
land-use models are probably more useful as research tools to develop an underlying knowledge base which can then be developed
together with end-users into simple rules-of-thumb, rather than as operational decision support tools.
This paper arises from research conducted as part of the UK Research Councils’ RELU Programme (award number RES-224-25-0102).
RELU is funded jointly by the Economic and Social Research Council, the Biotechnology and Biological Sciences Research Council
and the Natural Environment Research Council, with additional funding from the Department for Environment, Food and Rural
Affairs and the Scottish Executive Environment and Rural Affairs Department. 相似文献
32.
Crop wild relatives are invaluable sources of novel genes for crop improvement and adaptation to changing environments. We
assessed phylogenetic relationships among 29 Linum accessions representing 16 species, including cultivated flax and its progenitor pale flax, based on four non-coding regions
of chloroplast DNA sequences. We obtained a cpDNA network showing that these 16 Linum species are appropriately connected based on previously defined taxonomic sections; these connections reflect the same evolutionary
pathways as determined from earlier morphological and cytological data. These relationships also support an earlier hypothesis
that cultivated flax is probably descended from a single domestication of pale flax plants, apparently for oil usage. The
detailed species network not only is significant for understanding evolutionary relationships of Linum species, but also useful for classifying exotic gene pools of cultivated flax as a part of the ongoing exploration of new
genetic diversity for flax improvement. 相似文献
33.
ABSTRACT In France, chestnut blight, caused by Cryphonectria parasitica, has been controlled since 1974 in orchards, but never in coppice forests, by releasing hypovirulent strains infected with CHV1 hypovirus. We tested the hypothesis that this biological control (BC) has lead to a decrease in blight severity, spread of hypovirulence, and change in C. parasitica populations. The low severity of chestnut blight was confirmed in the six regions studied (subdivided into zones). The remission of cankers was associated with the presence of white isolates presumed to be hypovirulent. These two parameters were also correlated, at the zonal level, to the frequency of sites where BC was used. However, the estimates of the natural background level of hypovirulence, independent of BC, ranged from 4% in forests in Dordogne to 60% in orchards in Lozère. Differences in the rate of hypovirulent isolates among regions were consistent with the diversity of vegetative compatibility (VC) types in populations of C. parasitica. The highest VC-type diversity and mean allelic diversity for known vegetative incompatibility (vic) genes were observed in Dordogne. We showed that the current diversity of VC types in populations of C. parasitica was lower than in 1981. We found 30 VC types among 1,113 isolates of C. parasitica. Ten VC types were incompatible with known EU testers, suggesting that one additional vic gene or allele at one of the six vic loci known should be present in Europe. 相似文献
34.
Noel E.A. Murphy Robert Loughman Robin Wilson Evans S. Lagudah Rudi Appels Michael G.K. Jones 《Euphytica》2000,113(3):227-231
Septoria nodorum blotch is the most important leaf disease of wheat in Western Australia. A potentially useful source of resistance
has been identified in an accession of Aegilops tauschii. To study the genetics of resistance of this source a cross was made between the resistant Ae. tauschii accession, RL5271, and a susceptible accession, CPI110889. The resistant parent took significantly longer to develop symptoms,
developed significantly fewer lesions and expressed significantly lower levels of disease than the susceptible parent. The
F1 mean response for disease severity indicated there was no complete dominance. The F3 families were classified using three
approaches. In the first approach the individual F3 plant response was used to classify the F3 families. In the second approach
the F3 family means and standard errors were used to classify the F3 families. In the final approach Best Linear Unbiased
Predictors of disease score and standard error for each F3 family derived from a REML analysis were used to classify the F3
families. The genotypic ratios generated by each of the approaches suggested that resistance is controlled by a single gene.
The effectiveness of the resistance and its simple genetic control in the Ae. tauschii, accession RL5271 may be a useful resistance source for use in a bread wheat breeding program.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
35.
36.
Seed mass and relative growth rate (RGR) are important determinants of early seedling growth, and hence seedling establishment. Although a positive interspecific relationship between seed mass and seedling dry mass is well established, much less is known about the relationships among seed mass, seedling mass and RGR within species. We examined relationships among seed mass, seedling mass and RGR within and among maternal plant lines of Scots pine (Pinus sylvestris L.). To assess the effects of seed mass and maternal origin on RGR, individual seeds from two seed crops (years 2004 and 2005) of ten maternal plants growing under nursery conditions were weighed and then germinated. Seed mass was strongly determined by maternal plant, and seedling mass was largely determined by seed mass, with a positive correlation between these variables both across and within maternal plants. In contrast, RGR was weakly related to seed mass, with no consistent pattern in the sign of the relationship. It is well known that species differ in RGR and that RGR is related to seed mass across species. Lack of consistent evidence for this relationship within maternal lines, and for Scots pine overall, suggests that the relationship is not directly causal, but reflects consistent evolutionary covariation in these two physiologically independent traits. 相似文献
37.
Johannes Breidenbach Sonia M. Ortiz Manfred Reich 《European Journal of Forest Research》2010,129(5):813-823
Several TerraSAR-X satellite images acquired in high resolution spotlight mode with different polarisations for two study
sites in southern Germany were used to distinguish forest from other land cover classes (agriculture, built-up, water bodies)
using logistic regression models. In general, we observed that the mean and particularly the standard deviation of the backscatter
were viable measures to discriminate land cover classes. Both measures were lowest for water bodies and highest for built-up
areas, with agricultural areas and forest in intermediate positions. Trees outside forest were not differentiable from forest
with the applied method. The HH-polarised image was better suited for a classification of built-up areas, whereas the VV-polarised
image was more appropriate when classifying agricultural areas. Consequently, the combination of the two differently polarised
images leads to a significantly better model. Since forests in one study area were generally found on steeper slopes in comparison
to other land cover classes, the inclusion of terrain slope further improved the classification, which resulted in an overall
accuracy of 92–95%. Systematic differences in the parameter values of the explanatory variables for one class between the
study areas may be caused by differing class probabilities. Thus, transferring the model of one study area to the image of
another resulted in a 7–9% loss of accuracy. 相似文献
38.
Seedlings of five boreal tree species differ in acclimation of net photosynthesis to elevated CO(2) and temperature 总被引:1,自引:0,他引:1
Biochemical models of photosynthesis suggest that rising temperatures will increase rates of net carbon dioxide assimilation and enhance plant responses to increasing atmospheric concentrations of CO(2). We tested this hypothesis by evaluating acclimation and ontogenetic drift in net photosynthesis in seedlings of five boreal tree species grown at 370 and 580 &mgr;mol mol(-1) CO(2) in combination with day/night temperatures of 18/12, 21/15, 24/18, 27/21, and 30/24 degrees C. Leaf-area-based rates of net photosynthesis increased between 13 and 36% among species in plants grown and measured in elevated CO(2) compared to ambient CO(2). These CO(2)-induced increases in net photosynthesis were greater for slower-growing Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., and Larix laricina (Du Roi) K. Koch than for faster-growing Populus tremuloides Michx. and Betula papyrifera Marsh., paralleling longer-term growth differences between CO(2) treatments. Measures at common CO(2) concentrations revealed that net photosynthesis was down-regulated in plants grown at elevated CO(2). In situ leaf gas exchange rates varied minimally across temperature treatments and, contrary to predictions, increasing growth temperatures did not enhance the response of net photosynthesis to elevated CO(2) in four of the five species. Overall, the species exhibited declines in specific leaf area and leaf nitrogen concentration, and increases in total nonstructural carbohydrates in response to CO(2) enrichment. Consequently, the elevated CO(2) treatment enhanced rates of net photosynthesis much more when expressed on a leaf area basis (25%) than when expressed on a leaf mass basis (10%). In all species, rates of leaf net CO(2) exchange exhibited modest declines with increasing plant size through ontogeny. Among the conifers, enhancements of photosynthetic rates in elevated CO(2) were sustained through time across a wide range of plant sizes. In contrast, for Populus tremuloides and B. papyrifera, mass-based photosynthetic rates did not differ between CO(2) treatments. Overall, net photosynthetic rates were highly correlated with relative growth rate as it varied among species and treatment combinations through time. We conclude that interspecific variation may be a more important determinant of photosynthetic response to CO(2) than temperature. 相似文献
39.
Annet Namayanja Robin Buruchara George Mahuku Patrick Rubaihayo Paul Kimani Stephen Mayanja Hellen Eyedu 《Euphytica》2006,151(3):361-369
Inheritance of resistance to angular leaf spot (ALS) disease caused by Phaeoisariopsis griseola (Sacc.) Ferr was investigated in two common bean cultivars, Mexico 54 and BAT 332. Both Andean and Mesoamerican backgrounds were used to determine the stability of the resistance gene in each of the two cultivars. Resistance to P. griseola was phenotypically evaluated by artificial inoculation with one of the most widely distributed pathotypes, 63–39. Evaluation of the parental genotypes, F1, F2 and backcross populations revealed that the resistance to angular leaf spot in the cultivars Mexico 54 and BAT 332 to pathotype 63–39 is controlled by a single dominant gene, when both the Andean and Mesoamerican backgrounds were used. Allelism test showed that ALS resistance in Mexico 54 and BAT 332 to pathotype 63–39 was conditioned by the same resistance locus. Resistant and susceptible segregating populations generated using Mexico 54 resistant parent were selected for DNA extraction and amplification to check for the presence /absence of the SCAR OPN02 and RAPD OPE04 markers linked to the Phg-2 resistance gene. The results indicated that the SCAR OPN02 was not polymorphic in the study populations and therefore of limited application in selecting resistant genotypes in such populations. On the other hand, the RAPD OPE04 marker was observed in all resistant individuals and was absent in those scored susceptible based on virulence data. Use of the RAPD OPE04 marker in marker-assisted selection is underway. 相似文献
40.
Quantitative trait loci for phytate in rice grain and their relationship with grain micronutrient content 总被引:6,自引:0,他引:6
James C. R. Stangoulis Bao-Lam Huynh Ross M. Welch Eun-Young Choi Robin D. Graham 《Euphytica》2007,154(3):289-294
Phytate (inositol-hexa-phosphate) has an important role in plants but it also may have anti-nutritional properties in animals
and humans. While there is debate within the plant breeding and nutrition communities regarding an optimum level in grain,
there appears to be little information at the molecular level for the genetics of this trait, and its association with important
trace elements, in particular, Fe and Zn. In this preliminary study, quantitative trait loci (QTL) for grain phytates, Zn
and Fe in glasshouse-grown rice lines from an IR64 × Azucena doubled haploid population were identified. Correlations between
phytate and essential nutrients were also studied. Transgressive segregation was found for most traits. Phytate and total
P concentrations had one QTL in common located on chromosome five with the (high concentration) allele contributed from Azucena.
There were significant positive correlations between phytate and inorganic phosphorus (P), total P, Fe, Zn, Cu and Mn concentrations
for both grain concentration and content. However, the QTLs of phytate were not located on the same chromosomal regions as
those found for Fe, Zn and Mn, suggesting that they were genetically different and thus using molecular markers in breeding
and selection would modify the phytate level without affecting grain micronutrient density. 相似文献