全文获取类型
收费全文 | 475篇 |
免费 | 35篇 |
国内免费 | 3篇 |
专业分类
林业 | 42篇 |
农学 | 10篇 |
基础科学 | 1篇 |
67篇 | |
综合类 | 103篇 |
农作物 | 12篇 |
水产渔业 | 41篇 |
畜牧兽医 | 201篇 |
园艺 | 19篇 |
植物保护 | 17篇 |
出版年
2023年 | 10篇 |
2022年 | 9篇 |
2021年 | 18篇 |
2020年 | 18篇 |
2019年 | 21篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 8篇 |
2015年 | 21篇 |
2014年 | 15篇 |
2013年 | 31篇 |
2012年 | 43篇 |
2011年 | 54篇 |
2010年 | 24篇 |
2009年 | 18篇 |
2008年 | 28篇 |
2007年 | 26篇 |
2006年 | 25篇 |
2005年 | 25篇 |
2004年 | 13篇 |
2003年 | 21篇 |
2002年 | 11篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1997年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1967年 | 1篇 |
1964年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有513条查询结果,搜索用时 15 毫秒
11.
R A Joshua 《Veterinary parasitology》1990,36(3-4):303-309
Quantitative methods were adopted to study the course of Trypanosoma congolense infection in mice and goats. The ease of initiating infection with a single organism (clone) was found to show a smooth correlation with the virulence of 24 isolates. Virulence of T. congolense was found to be directly related to the degree of viability of the parasite but inversely proportional to the capacity of the host to limit parasitaemia. Isolates obtained from the goat in the early stage of the infection were found to be highly infective but moderately virulent; subsequent isolates were of low infectivity and low virulence. Organisms obtained at the terminal stage of the infection were highly virulent. Generally, the highly virulent clones produced rapidly high parasitaemia and mortality in the host. The low virulence clones were characterised by low parasitaemia but very pronounced remission of trypanosomaemia. 相似文献
12.
13.
14.
15.
Bose M Hao X Ju J Husain A Park S Lambert JD Yang CS 《Journal of agricultural and food chemistry》2007,55(19):7695-7700
The effect of a combination of (-)-epigallocatechin-3-gallate (EGCG) with fish oil on intestinal tumorigenesis in Apc (Min/+) mice fed a high-fat diet was investigated in the present study. The combined treatment of EGCG and fish oil for 9 weeks reduced the tumor number by 53% as compared to controls while neither agent alone had a significant effect. Apoptosis was significantly increased in all treatment groups. beta-Catenin nuclear positivity in adenomas from the combination group was lower than control mice, implicating the modulation of Wnt signaling by the combination. Fish oil and the combination significantly reduced prostaglandin E 2 (PGE 2) levels in small intestinal tumors as compared to controls, suggesting modulation of aberrant arachidonic acid metabolism by fish oil. Akt phosphorylation in adenomas was significantly reduced in all treatment groups, which may have contributed to the observed increase in apoptosis. The results indicate that a combination of low doses of EGCG and fish oil can inhibit tumor multiplicity in Apc (Min/+) mice. 相似文献
16.
17.
Tim E. Carpenter Victor L. Coggins Clinton McCarthy Chans S. O’Brien Joshua M. O’Brien Timothy J. Schommer 《Preventive veterinary medicine》2014
Bighorn sheep currently occupy just 30% of their historic distribution, and persist in populations less than 5% as abundant overall as their early 19th century counterparts. Present-day recovery of bighorn sheep populations is in large part limited by periodic outbreaks of respiratory disease, which can be transmitted to bighorn sheep via contact with domestic sheep grazing in their vicinity. In order to assess the viability of bighorn sheep populations on the Payette National Forest (PNF) under several alternative proposals for domestic sheep grazing, we developed a series of interlinked models. Using telemetry and habitat data, we characterized herd home ranges and foray movements of bighorn sheep from their home ranges. Combining foray model movement estimates with known domestic sheep grazing areas (allotments), a Risk of Contact Model estimated bighorn sheep contact rates with domestic sheep allotments. Finally, we used demographic and epidemiologic data to construct population and disease transmission models (Disease Model), which we used to estimate bighorn sheep persistence under each alternative grazing scenario. Depending on the probability of disease transmission following interspecies contact, extirpation probabilities for the seven bighorn sheep herds examined here ranged from 20% to 100%. The Disease Model allowed us to assess the probabilities that varied domestic sheep management scenarios would support persistent populations of free-ranging bighorn sheep. 相似文献
18.
Rosa C. Goodman Juan A. Oliet Joshua L. Sloan Douglass F. Jacobs 《European Journal of Forest Research》2014,133(1):153-164
Physiological mechanisms by which nitrogen (N) fertilization affects growth and development in temperate deciduous forest trees are not clearly understood, especially under intensive silvicultural systems. Grafted, Tippecanoe 1 cultivar black walnut (Juglans nigra L.) trees were grown in an intensively managed plantation in west-central Spain and subjected to six, fixed-nutrient-ratio complete fertilizer treatments (defined as 0, 25, 50, 75, 150, and 300 g N tree?1) delivered via daily fertigation. Leaf chemistry and morphology were evaluated from June to September, and gas exchange was measured in July. Specific leaf mass, leaflet nitrogen (N), and chlorophyll concentrations varied over the course of the growing season, yet consistently increased with increasing fertilization. Net photosynthesis at ambient (A net) and light-saturated (A max) conditions increased from the unfertilized control to lowest treatment (25 g N) but did not increase at higher fertilizer rates. Photosynthetic N and chlorophyll use efficiencies decreased with increasing fertilization, but photosynthetic phosphorus and water use efficiencies increased. Transpiration rates and dark respiration were not significantly affected by treatment. Overall, the lowest fertilizer treatment (25 g N) had the greatest photosynthetic efficiency. Interactions between N and other nutrients with increasing fertilizer application suggested potential for nutrient imbalances at high fertilization rates. Our results provide a physiological justification for the use of low-to-moderate fertilization as an efficient strategy to promote black walnut plantation establishment under intensive cultural systems. 相似文献
19.
Nathan H. Schumaker Allen Brookes Jeffrey R. Dunk Brian Woodbridge Julie A. Heinrichs Joshua J. Lawler Carlos Carroll David LaPlante 《Landscape Ecology》2014,29(4):579-592
Source-sink dynamics are an emergent property of complex species–landscape interactions. A better understanding of how human activities affect source-sink dynamics has the potential to inform and improve the management of species of conservation concern. Here we use a study of the northern spotted owl (Strix occidentalis caurina) to introduce new methods for quantifying source-sink dynamics that simultaneously describe the population-wide consequences of changes to landscape connectivity. Our spotted owl model is mechanistic, spatially-explicit, individual-based, and incorporates competition with barred owls (Strix varia). Our observations of spotted owl source-sink dynamics could not have been inferred solely from habitat quality, and were sensitive to landscape connectivity and the spatial sampling schemes employed by the model. We conclude that a clear understanding of source-sink dynamics can best be obtained from sampling simultaneously at multiple spatial scales. Our methodology is general, can be readily adapted to other systems, and will work with population models ranging from simple and low-parameter to complex and data-intensive. 相似文献
20.
Joshua D. Gamble Gregg Johnson Craig C. Sheaffer Dean A. Current Donald L. Wyse 《Agroforestry Systems》2014,88(1):75-85
In May 2010, alley cropping systems consisting of switchgrass (Panicum virgatum L.), prairie cordgrass (Spartina pectinata Bosc ex Link), an alfalfa (Medicago sativa L.) and intermediate wheatgrass (Thinopyrum intermedium [Host] Barkworth and Dewey) mixture, and a native tallgrass-forb-legume polyculture, planted between multi-row strips of poplar hybrid ‘NM6’ (Populus maximowiczii x P. nigra) and willow cultivar ‘Fish Creek’ (Salix purpurea) were established at Empire and Granada, Minnesota, USA. Crop establishment and productivity were characterized for each species over two growing seasons and at two distances from the tree-crop interface. Prairie cordgrass and the native polyculture were among the most productive herbaceous crops at both sites, averaging between 7.1 and 11.9 Mg DM ha?1, and have shown no evidence of competition for resources along the tree-crop interface thus far. Basal area (BA) was similar at Empire for NM6 (1,744 mm2 tree?1) and Fish Creek (1,609 mm2 tree?1), but was greater for NM6 (1,045 mm2 tree?1) than Fish Creek (770 mm2 tree?1) at Granada. Despite this, stand basal area (SBA) was greater for Fish Creek at both sites due to greater planting density. Across species, BA and SBA were greater for trees along the alley than those in center rows at Empire, whereas no difference was observed at Granada. Results suggest that alley cropping provides suitable conditions for establishment of short-rotation woody and certain herbaceous biomass crops, and that some of these crops may be well suited to the alley cropping environment. However, continued research is needed to evaluate crop persistence and productivity as crops and trees mature and the potential for interspecies competition increases. 相似文献