全文获取类型
收费全文 | 947篇 |
免费 | 38篇 |
专业分类
林业 | 40篇 |
农学 | 5篇 |
基础科学 | 1篇 |
151篇 | |
综合类 | 119篇 |
农作物 | 40篇 |
水产渔业 | 41篇 |
畜牧兽医 | 475篇 |
园艺 | 12篇 |
植物保护 | 101篇 |
出版年
2022年 | 8篇 |
2021年 | 10篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 53篇 |
2012年 | 30篇 |
2011年 | 31篇 |
2010年 | 28篇 |
2009年 | 14篇 |
2008年 | 42篇 |
2007年 | 35篇 |
2006年 | 35篇 |
2005年 | 42篇 |
2004年 | 34篇 |
2003年 | 40篇 |
2002年 | 33篇 |
2001年 | 21篇 |
2000年 | 33篇 |
1999年 | 25篇 |
1998年 | 22篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 22篇 |
1991年 | 16篇 |
1990年 | 18篇 |
1989年 | 12篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1972年 | 6篇 |
1971年 | 13篇 |
1970年 | 8篇 |
1967年 | 5篇 |
排序方式: 共有985条查询结果,搜索用时 15 毫秒
41.
Edwards JF 《Veterinary pathology》2002,39(6):744-746
Three cases of bovine, ovarian epidermoid cysts were diagnosed as unilateral benign lesions in three out of 1,971 cows at slaughter. A stratified, cornifying, and squamous epithelium without associated skin adnexal structures or tissues from other embryonic tissue layers lined the cysts. The cysts were small, usually multiple, and contained keratin debris. Macroscopically, they resembled abscesses. These are benign, congenital lesions that are a separate entity from dermoids and teratomas, and they appear to have a higher incidence in cattle with Bos indicus breeding. 相似文献
42.
43.
44.
45.
Survival and inactivation of classical swine fever virus 总被引:2,自引:0,他引:2
Edwards S 《Veterinary microbiology》2000,73(2-3):175-181
Classical swine fever virus, like many enveloped viruses, may be regarded as moderately fragile. It shows a short but variable survival time in the environment, depending on physical conditions, but may remain viable for prolonged periods in favourable circumstances as found, for example, in stored meat. Published information is reviewed on the survival time of the virus under a variety of physical and chemical conditions, including the variable influence of environmental factors. The principles of virus inactivation by heat, pH or chemicals are discussed, with a consideration of the principles of containment for laboratories working with the virus. 相似文献
46.
The western corn rootworm, Diabrotica virgifera virgifera LeConte, is the most important pest of maize in the Midwestern USA, and since its detection in 1992 in Europe, also in several countries of Central and Eastern Europe. Methods for managing this pest vary from region to region, depending upon: the different cultural practices in maize production, climatic conditions, soil types, pest behaviour, infestation level and socio-economic conditions. Factors including date of planting, amount of rotated or continuous maize, irrigation, date of rootworm hatching and differences in behaviour of the pest, necessitate developing different management strategies in different areas of the infested countries. Pest monitoring, damage evaluation, threshold development, use of insecticides, risk estimation and crop rotation are some of the starting points in the development of management strategies. Approaches and experiences in D. v. virgifera control and management in Italy, Hungary and the USA, based on the understanding of local agro-ecosystems and socio-economic conditions, are reported. 相似文献
47.
48.
Abstract. The mean extractable sulphur (S) concentration in 315 upland topsoil samples collected in 1988/89 from beneath pasture in NE Scotland was 13 μg S g−1 (range 2–77 μg S g−1 ). More than two thirds of the samples had S concentrations less than that acceptable for productive soils. Continued decreases in atmospheric S inputs may have increased this proportion subsequently. The analysis of herbage S also indicated that two-thirds of the samples were below 0.2% S. A 'respirometric index', namely CO2 produced during cellulose decomposition without added S as a percentage of that produced with added S, was significantly less than 100% in a quarter of the soils. Results of three different extraction procedures suggested that sulphate in the soils was present mainly as free plus adsorbed rather than precipitated forms. Soil extraction identified a significant non-sulphate S fraction, presumably organic S. The variability in extractable S stemmed from a combination of geographical, depositional and local site and soil factors. Extractable S was significantly correlated with soil organic matter content and inversely with soil pH and together these factors explained 37% of the variability. While significant differences in mean concentrations between geographical area, soil association and drainage status were evident, no trends could be observed between the major soil subgroups or with altitude. 相似文献
49.
We examined the extent of osmotic adjustment and the changes in relative water content (RWC) and transpiration rate (i.e., relative stomatal function) that occur in water-deficit-conditioned 6-year-old Thuja occidentalis L. (eastern white cedar) trees in response to a severe drought. Trees conditioned by successive cycles of mild or moderate nonlethal water stress (conditioning) and nonconditioned trees were exposed to drought (i.e., -2.0 MPa predawn water potential) to determine if water deficit conditioning enhanced tolerance to further drought stress. Following drought, all trees were well watered for 11 days to evaluate how quickly osmotic potential, RWC and transpiration rate returned to preconditioning values. Both nonconditioned trees and mildly conditioned trees exhibited similar responses to drought, whereas moderately conditioned trees maintained higher water potentials and transpiration rates were 38% lower. Both conditioned and nonconditioned trees exhibited a similar degree of osmotic adjustment (-0.39 MPa) in response to drought relative to the well-watered control trees. The well-watered control trees, nonconditioned trees and mildly conditioned trees had similar leaf RWCs that were about 3% lower than those of the moderately conditioned trees. Following the 11-day stress relief, there were no significant differences in osmotic potential between the well-watered control trees and any of the drought-treated trees. Daily transpiration rates and water potential integrals (WPI) of all drought-treated trees approached those of the well-watered control trees during the stress relief period. However, the relationship between cumulative transpiration and WPI showed that previous exposure to drought stress reduced transpiration rates. Leaf RWC of the moderately conditioned trees remained slightly higher than that of the nonconditioned and mildly conditioned trees. 相似文献
50.
Hanson PJ Samuelson LJ Wullschleger SD Tabberer TA Edwards GS 《Tree physiology》1994,14(12):1351-1366
Extrapolation of the effects of ozone on seedlings to large trees and forest stands is a common objective of current assessment activities, but few studies have examined whether seedlings are useful surrogates for understanding how mature trees respond to ozone. This two-year study utilized a replicated open-top chamber facility to test the effects of subambient, ambient and twice ambient ozone concentrations on light-saturated net photosynthesis (P(max)) and leaf conductance (g(l)) of leaves from mature trees and genetically related seedlings of northern red oak (Quercus rubra L.). Gas exchange measurements were collected four times during the 1992 and 1993 growing seasons. Both P(max) and g(l) of all foliage followed normal seasonal patterns of ontogeny, but mature tree foliage had greater P(max) and g(l) than seedling foliage at physiological maturity. At the end of the growing season, P(max) and g(l) of the mature tree foliage exposed to ambient ( approximately 80-100 ppm-h) and twice ambient ( approximately 150-190 ppm-h) exposures of ozone were reduced 25 and 50%, respectively, compared with the values for foliage in the subambient ozone treatment ( approximately 35 ppm-h). In seedling leaves, P(max) and g(l) were less affected by ozone exposure than in mature leaves. Extrapolations of the results of seedling exposure studies to foliar responses of mature forests without considering differences in foliar anatomy and stomatal response between juvenile and mature foliage may introduce large errors into projections of the response of mature trees to ozone. 相似文献