全文获取类型
收费全文 | 530篇 |
免费 | 54篇 |
国内免费 | 2篇 |
专业分类
林业 | 43篇 |
农学 | 25篇 |
基础科学 | 2篇 |
87篇 | |
综合类 | 56篇 |
农作物 | 35篇 |
水产渔业 | 36篇 |
畜牧兽医 | 221篇 |
园艺 | 19篇 |
植物保护 | 62篇 |
出版年
2022年 | 4篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 16篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 42篇 |
2012年 | 24篇 |
2011年 | 29篇 |
2010年 | 19篇 |
2009年 | 19篇 |
2008年 | 24篇 |
2007年 | 27篇 |
2006年 | 30篇 |
2005年 | 29篇 |
2004年 | 24篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 4篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1977年 | 3篇 |
1974年 | 3篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 4篇 |
1967年 | 3篇 |
1964年 | 4篇 |
1963年 | 4篇 |
1962年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有586条查询结果,搜索用时 15 毫秒
51.
52.
Benjamin M. Rau Dale W. Johnson Robert R. Blank Annmarrie. Lucchesi Todd G. Caldwell Eugene W. Schupp 《Strength and Conditioning Journal》2011,64(2):139-147
Vegetation changes associated with climate shifts and anthropogenic disturbance have major impacts on biogeochemical cycling. Much of the interior western United States currently is dominated by sagebrush (Artemisia tridentata Nutt.) ecosystems. At low to intermediate elevations, sagebrush ecosystems increasingly are influenced by cheatgrass (Bromus tectorum L.) invasion. Little currently is known about the distribution of belowground organic carbon (OC) on these changing landscapes, how annual grass invasion affects OC pools, or the role that nitrogen (N) plays in carbon (C) retention. As part of a Joint Fire Sciences-funded project called the Sagebrush Treatment Evaluation Project (SageSTEP), we quantified the depth distribution of soil OC and N at seven sites experiencing cheatgrass invasion. We sampled plots that retained sagebrush, but represented a continuum of cheatgrass invasion into the understory. Eighty-four soil cores were taken using a mechanically driven diamond-tipped core drill to a depth of 90 cm, or until bedrock or a restrictive layer was encountered. Samples were taken in 15-cm increments, and soil, rocks, and roots were analyzed for OC and total N. We determined that cheatgrass influences the vertical distribution of OC and N within the soil profile and might result in decreased soil OC content below 60 cm. We also found that OC and total N associated with coarse fragments accounted for at least 10% of belowground pools. This emphasizes the need for researchers to quantify nutrients in deep soil horizons and coarse fragments. 相似文献
53.
Jennifer M. Kiernan James W. Hendrix Dale M. Maronek 《Soil biology & biochemistry》1983,15(3):257-262
One isolate of Glomus clarus, two of G. etunicatus, and one of G. claroideum, obtained from plants growing on abandoned stripmine sites in Kentucky, and an isolate of G. fascicutatus known to stimulate growth of various woody plants, were evaluated for their influence on growth of sweetgum seedlings in a mixture of sand and stripmine soil. Soils were supplemented with various rates of a complete slow-release fertilizer. Throughout the growth period, G. fasciculatus, and most of the stripmine isolates, stimulated growth at low fertilizer rates. At higher fertilizer rates, including the level optimum for non-mycorrhizal plants, the stripmine isolates inhibited plant growth. After 14 weeks, plants inoculated with one of the four stripmine isolates overcame the early growth depression, and those inoculated with a second isolate appeared to be overcoming the growth depression. G. fasciculatus was not inhibitory at any fertilizer rate. Root colonization by all three isolates evaluated was inhibited by the highest fertilizer rate, but this effect was not related to growth inhibition of plants. The other two isolates colonized roots at an extremely low rate (< 1%). Sporulation of all the stripmine isolates, but not G. fasciculatus, was also inhibited by the highest fertilizer rate. The G. fasciculalus isolate used in this study may be atypical of mycorrhizal fungi occurring randomly in nature in its mutualistic or neutral effect on plants under a wide range of growth conditions. 相似文献
54.
Effects of genotype,environment, and postharvest storage on the total ascorbate content of potato (Solanum tuberosum) tubers 总被引:1,自引:0,他引:1
The total ascorbate content of potato tubers from 33 Solanum tuberosum genotypes grown at three geographically diverse sites in Europe in each of two years was determined immediately postharvest and after approximately 4 months of storage at 4 degrees C. Statistically significant differences in total ascorbate concentration were observed between genotypes both at harvest and after storage. In all genotypes, the levels of ascorbate decreased during storage. These results are discussed in terms of their implications for diet and health as well as in terms of breeding for improved vitamin C content in potatoes. 相似文献
55.
Garrossian M Gardner DR Panter KE James LF 《Journal of agricultural and food chemistry》2002,50(8):2235-2240
Isocupressic acid (1) was used to synthetically prepare a mixture of (8S,13R,S)-labda-15,19-dioic acid (tetrahydroagathic acid) (5) via a two-step oxidation procedure followed by hydrogenation of the double bonds at C13 and C8. Reduction of the C8,17 double bond was stereospecific producing only the 8S isomer and confirmed by the nOe interaction between the resulting C17 and C20 methyl groups. The 13R and 13S isomers of 5 were separated and analyzed by HPLC/MS, and (13S)-tetrahydroagathic acid was isolated and identified by comparison to a standard prepared by hydrogenation of naturally occurring (13S)-dihydroagathic acid (4). (13R,S)-dihydroagathic acid was prepared by selective sodium metal-catalyzed hydrogenation of the C13,14 allylic double bond of agathic acid (3). The prepared compounds were then used as standards to confirm the presence of 4 and 5 and their respective 13R and 13S isomers in bovine serum samples. Tetrahydroagathic acid was shown to be the only metabolite detected in serum samples taken from a suspected cattle abortion case submitted for diagnosis; and, thus, 5 could be a valuable diagnostic marker for pine needle-induced abortions. 相似文献
56.
Gaietta G Deerinck TJ Adams SR Bouwer J Tour O Laird DW Sosinsky GE Tsien RY Ellisman MH 《Science (New York, N.Y.)》2002,296(5567):503-507
Recombinant proteins containing tetracysteine tags can be successively labeled in living cells with different colors of biarsenical fluorophores so that older and younger protein molecules can be sharply distinguished by both fluorescence and electron microscopy. Here we used this approach to show that newly synthesized connexin43 was transported predominantly in 100- to 150-nanometer vesicles to the plasma membrane and incorporated at the periphery of existing gap junctions, whereas older connexins were removed from the center of the plaques into pleiomorphic vesicles of widely varying sizes. Selective imaging by correlated optical and electron microscopy of protein molecules of known ages will clarify fundamental processes of protein trafficking in situ. 相似文献
57.
58.
59.
60.
Dehydrins are proteins associated with conditions affecting the water status of plant cells, such as drought, salinity, freezing and seed maturation. Although the function of dehydrins remains unknown, it is hypothesized that they stabilize membranes and macromolecules during cellular dehydration. Red-osier dogwood (Cornus sericea L.), an extremely freeze-tolerant woody plant, accumulates dehydrin-like proteins during cold acclimation and the presence of these proteins is correlated with increased freeze tolerance (Karlson 2001, Sarnighausen et al. 2002, Karlson et al. 2003). Our objective was to determine the location of dehydrins in cold-acclimated C. sericea stems in an effort to provide insight into their potential role in the freeze tolerance of this extremely cold hardy species. Abundant labeling was observed in the nucleus and cytoplasm of cold-acclimated C. sericea stem cells. In addition, labeling was observed in association with plasmodesmata of cold-acclimated vascular cambium cells. The unique association of dehydrin-like proteins with plasmodesmata has not been reported previously. 相似文献