全文获取类型
收费全文 | 808篇 |
免费 | 75篇 |
国内免费 | 2篇 |
专业分类
林业 | 46篇 |
农学 | 18篇 |
基础科学 | 3篇 |
139篇 | |
综合类 | 84篇 |
农作物 | 28篇 |
水产渔业 | 60篇 |
畜牧兽医 | 434篇 |
园艺 | 21篇 |
植物保护 | 52篇 |
出版年
2024年 | 3篇 |
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 21篇 |
2019年 | 21篇 |
2018年 | 20篇 |
2017年 | 31篇 |
2016年 | 26篇 |
2015年 | 33篇 |
2014年 | 35篇 |
2013年 | 33篇 |
2012年 | 52篇 |
2011年 | 63篇 |
2010年 | 47篇 |
2009年 | 46篇 |
2008年 | 64篇 |
2007年 | 62篇 |
2006年 | 53篇 |
2005年 | 35篇 |
2004年 | 50篇 |
2003年 | 42篇 |
2002年 | 37篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有885条查询结果,搜索用时 15 毫秒
11.
Marine fisheries target and catch fish both for direct human consumption (DHC) as well as for fishmeal and fish oil, and other products. We derived the fractions used for each for 1950–2010 by fishing country, and thus provide a factual foundation for discussions of the optimal use of fisheries resources. From 1950 to 2010, 27% (~20 million tonnes annually) of globally reconstructed marine fisheries landings were destined for uses other than DHC. Importantly, 90% of fish destined for uses other than DHC are food‐grade or prime food‐grade fish, while fish without a ready market for DHC make up a much smaller proportion. These findings have implications for how we are using fish to feed ourselves or, more appropriately, how we are not using fish to feed ourselves. 相似文献
12.
Energy and resource consumption of land-based Atlantic salmon smolt hatcheries in the Pacific Northwest (USA) 总被引:1,自引:0,他引:1
John Colt Steve Summerfelt Tim Pfeiffer Sveinung Fivelstad Michael Rust 《Aquaculture (Amsterdam, Netherlands)》2008,280(1-4):94-108
This paper evaluates the resource and energy requirements of six different types of land-based, hatchery production systems located in the U.S. Pacific Northwest: flow-through with a gravity water supply, flow-through with a pumped water supply, flow-through with pure oxygen, partial reuse system, partial reuse with heating, and a reuse system for the production of Atlantic salmon (Salmo salar) smolts. Key parameters used in the evaluation include direct energy, indirect energy, transportation energy, greenhouse gas emissions, and pollutant discharges.Power (electricity and natural gas) and feed energy accounted for the majority of the required energy for all the rearing option evaluated. The sum of the fixed capital and chemicals components accounted for less than 2–12% of the total energy budget for any rearing option. The energy efficiency (energy output/energy input) of the six options ranges from 0.97% for flow-through with pumped supply to 3.49% for the flow-through with gravity supply. The rearing options with the three highest energy efficiencies were flow-through with gravity supply (3.49%), partial reuse (2.75%), and reuse (2.64%).On a kg of smolt produced basis, the six rearing options showed a wide range in performance. The reuse system had the lowest water (2 m3 kg− 1) and land (0.13 m2 kg− 1) requirements and the third lowest total energy requirement (288 MJ kg− 1). The partial reuse system had the second lowest total power requirement (276 MJ kg− 1), a low land requirement (0.21 m2 kg− 1), and moderate water requirements (33 m3 kg− 1). The partial reuse with temperature control had the second highest total power requirement (657 MJ kg− 1) and land and water requirements similar to the partial reuse system without temperature control. The flow-through system with pumped water supply had the highest water (289 m3 kg− 1), land (2.19 m2 kg− 1), and energy requirements (786 MJ kg− 1) of any of the rearing options. By comparison, the flow-through system with gravity water supply had the lowest energy requirement (218 MJ kg− 1), a moderate land requirement (0.78 m2 kg− 1), and a high water requirement (214 m3 kg− 1). The ranking of the six rearing options based capital and operating costs are likely to be quite different from those based on energy, water, and greenhouse gas emissions. 相似文献
13.
Landscape Ecology - Animals must move to find food, shelter and mates, and escape predation and competition. Changes in landscape configuration and resource availability can disrupt natural... 相似文献
14.
15.
Tim R. McVicar Tom G. Van Niel LingTao Li ZhongMing Wen QinKe Yang Rui Li Feng Jiao 《Forest Ecology and Management》2010,259(7):1277-1290
The Chinese Central government's policy to re-vegetate large areas of the Loess Plateau is currently being rapidly implemented at the provincial, prefecture, county, township, and village levels of government. Managers at these five levels of government need access to information to assist them to plan the land use change prior to performing on-ground activities. To this end, the suitability of 38 predominately native species in the 113,000 km2 Coarse Sandy Hilly Catchments (CSHC) has been mapped at a 100 m resolution. In this data-sparse region, this was achieved by using a five-variable spatial overlay approach as we were able to readily access the required environmental variables and rule-set defining the species’ requirements (or tolerances). As the rules did not consider optimal growth they were possibly ‘too inclusive’, so the spatial extent of areas suggested for re-planting was refined by defining ‘target areas’ for trees, shrubs and grasses based on precipitation, aspect, landform, and slope. In the land-use planning criteria developed here we suggest that hill-slopes and gullies with slopes greater than or equal to 15° (defined from a 100 m resolution DEM) be left for natural succession. Due to lateral flow of water, sediment and nutrients from these steep slope and gullies, further prioritising re-vegetation target areas to the zone adjacent to and down slope from these steep portions of the landscape reduces sediment entering the river network with a minimal decrease of regional stream flow. These two functions (mapping species suitability and locating where priority and target re-vegetation activities should be undertaken) are available at a 100 m resolution for the entire CSHC by accessing a bilingual decision support tool called ReVegIH (Re-Vegetation Impacts on Hydrology). Finally, an ecohydrological model was used to simulate changes in average annual stream flow originating from the CSHC based on implementing the ‘target’ and ‘priority’ area re-vegetation activities within the constraints of two land limits. 相似文献
16.
Jan C Ramer Roberto Maria Tim Reichard Peter J Tolson Tai C Chen Michael F Holick 《Journal of zoo and wildlife medicine》2005,36(2):188-191
Calcidiol (25-hydroxyvitamin D) values are reported for 22 wild Ricord's iguanas (Cyclura ricordii) and seven wild rhinoceros iguanas (Cyclura cornuta cornuta). Calcitriol (1,25-hydroxyvitamin D) values are reported for 12 wild Ricord's iguanas and seven wild rhinoceros iguanas. These animals were captured as part of a larger health assessment study being conducted on Ricord's iguanas in Isla Cabritos National Park, Dominican Republic. A total of 13 captive rhinoceros iguanas held outdoors at Parque Zoológico Nacional were also sampled for comparison. Mean concentrations of 25-hydroxyvitamin D were 554 nmol/L (222 ng/ml) with a range of 250-1,118 nmol/L (100-448 ng/ml) for wild Ricord's iguanas, 332 nmol/L (133 ng/ml) with a range of 260-369 nmol/L (104-148 ng/ml) for wild rhinoceros iguanas, and 317 nmol/L (127 ng/ml) with a range of 220-519 nmol/L (88-208 ng/ml) for captive rhinoceros iguanas. On the basis of these results, serum concentrations of at least 325 nmol/L (130 ng/ml) for 25-hydroxyvitamin D should be considered normal for healthy Ricord's and rhinoceros iguanas. 相似文献
17.
18.
Cloning,expression, purification,and biological activity of five feline type I interferons 总被引:1,自引:0,他引:1
Wonderling R Powell T Baldwin S Morales T Snyder S Keiser K Hunter S Best E McDermott MJ Milhausen M 《Veterinary immunology and immunopathology》2002,89(1-2):13-27
Type I interferons (IFN) are important mediators of the host defense against viral infections in mammals. In humans multiple subtypes of IFN-alpha exist, most of which possess antiviral activity. Little is known about the type I IFN genes in cats and the role they may play in feline immunological responses to viruses. We have isolated cDNAs encoding five feline IFN-alpha (feIFN) subtypes that share from 95 to 99% amino acid sequence identity. FeIFN-alpha5 has five additional amino acids inserted at position 139, which are not present in the other four subtypes. Sequence identity of the feIFN proteins encoded by the five clones compared to human IFN-alpha2 is approximately 60%. Unlike most of the human subtypes, each of the five feline IFN sequences has an N-glycosylation recognition site. Expression of all five feIFN-alpha subtypes in Chinese hamster ovary (CHO) cells was confirmed by Western blot analysis, and all resulting proteins were glycosylated. The antiviral activity of each feIFN-alpha subtype produced in transiently transfected CHO cell cultures was tested in vitro. In addition, subtype feIFN-alpha6 was expressed in the yeast, Pichia pastoris. The resulting secreted mature recombinant protein was purified and demonstrated significant antiviral activity and induction of 2',5'-oligoadenylate synthetase activity in vitro. 相似文献
19.
A study was conducted to determine the prevalence and possible significance of campylobacteria in pig abortions in Denmark. Surface-cauterised liver and kidney samples from 55 aborted pig fetuses submitted to the Danish Veterinary Laboratory were taken and a sensitive isolation procedure used to examine pooled tissue samples for Campylobacter, Arcobacter and Helicobacter spp. Routine microbiological, immunological, and histopathological examinations were also performed to identify concurrent infections or histopathological changes. The abortions tested negative for established abortifacient pathogens (Brucella, Leptospira, PPV, PRRSV), but Arcobacter spp. were recovered from 23/55 abortions. Co-infections with Streptococcus suis, Escherichia coli, and haemolytic streptococci were observed in 7/23 Arcobacter-positive fetuses, and in 4/32 Arcobacter-negative fetuses. Histopathological analyses identified placentitis, pneumonia, hepatitis and encephalitis among the study group. However, no obvious pathologic features were solely associated with Arcobacter-positive cases, nor were Arcobacter-like bacteria observed in tissue samples. Protein profile analyses of the 27 Arcobacter isolates identified 11 as A. cryaerophilus and 10 as A. skirrowii. Six strains could not be classified into any existing species and were phenotypically distinct, thus, potentially representing at least one new species. The identification results showed that multiple taxa could be found in a single fetus, and in distinct aborted fetuses from a single sow. The high prevalence of arcobacters in Danish pig abortions may account for at least some of the >90% of cases in which no established abortifacient agent is detected, but further studies are needed to define the role of each species, especially where co-infections with other bacteria are present. 相似文献
20.
ABSTRACT Five areas in urban Miami were identified to study the spread of Xanthomonas axonopodis pv. citri to determine if the practice of removing exposed citrus trees within 38.1 m of trees affected by citrus canker was adequate to curtail further bacterial spread. To accomplish this, 18,769 trees in dooryards were surveyed, geo-referenced by differential global positioning systems (GPS), and assayed for disease severity, age of infection, citrus cultivar, location of infection in tree, and canopy size. For each tree, the date the tree became infected was estimated and used to separate trees into contiguous 30-day categories. For each area studied, distance measurements between focal trees and newly infected trees were calculated for various temporal periods of 30, 60, 90, and 120 days in duration, corresponding to intervals of inspection survey. A visual basic application was used to calculate the distances between each newly diseased tree and all prior focal trees. The nearest distance was used because it was considered the most conservative estimate possible. It is therefore likely to be an underestimate of spread but is a good estimate of the minimum possible distances of spread. For the first four 30-day periods among the five study areas, calculated maximum distances of spread ranged from 12 to 3,474 m, indicating a broad continuum of distance for bacterial spread was possible. Disease increased during the first two-thirds of the time studied and reached an asymptote due to dry conditions in the final one-third of the duration of the study. Cross correlation analysis indicated that disease was best visualized 107 days following rainstorms with wind. Analysis of regional spatial point patterns was performed temporally for each 30-day period via a modified Ripley's K-function. Spatiotemporal analyses between periods over areas larger than previously examined were accomplished via spatiotemporal semivariogram analysis. These methods in combination demonstrated rapid increases in range of spatial dependency and range of spatiotemporal dependency for all study sites. This corresponded to rapid spread of disease across the regions studied in response to rainstorms with wind followed by a "filling in" of disease on remaining noninfected susceptible trees through time by less intense rain events. A stochastic quadratization technique demonstrated that disease incidence and disease severity were not greatly affected by urban host density but were positively correlated to host susceptibility within local 0.25-km(2) quadrats. 相似文献