全文获取类型
收费全文 | 220篇 |
免费 | 1篇 |
专业分类
林业 | 10篇 |
农学 | 8篇 |
13篇 | |
综合类 | 33篇 |
农作物 | 2篇 |
水产渔业 | 35篇 |
畜牧兽医 | 89篇 |
植物保护 | 31篇 |
出版年
2023年 | 2篇 |
2013年 | 2篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 4篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1966年 | 1篇 |
1963年 | 3篇 |
1962年 | 1篇 |
1961年 | 2篇 |
1959年 | 6篇 |
1958年 | 5篇 |
1957年 | 6篇 |
1956年 | 7篇 |
1955年 | 1篇 |
1954年 | 4篇 |
1953年 | 8篇 |
1952年 | 1篇 |
1948年 | 2篇 |
1946年 | 3篇 |
1945年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
It is generally thought that fusion of intermittent photic stimuli occurs when the duration between successive pulses of light is reduced to a certain value, this value being a function of the illumination and viewing conditions. The findings described in this report show that fusion is determined not only by the duration between successive stimuli but also by the temporal pattern of successive stimuli. 相似文献
75.
76.
This analysis provides the first precise molecular parameters for sucrose. All hydrogen atoms are included. Carbon-carbon distances are 1.51 1.53 A; carbon-oxygen 1.40 to 1.44 A; carbon-hydrogen 1.08 to 1.11 A; oxygen-hydrogen 0.94 to 0.99 A. The furanose ring conformation differs from that in sucrose sodium bromide dihydrate. Hydrogen bonds (two of them intramolecular) utilize every hydroxyl group except one. 相似文献
77.
ABSTRACT The transmission of knowledge diminishes with physical distance, one factor explaining the geographic clustering of scientific and industrial activity. The authors investigate how those distances have stretched over time—between collaborating inventors, and between inventors and the technology that inspires them. While physical distance is still a factor, it is clear that its constraining effects have weakened, especially for particular types of innovators, technologies, and regions of the United States. 相似文献
78.
Potato progenies in a line x tester mating design and the clonal parents were screened for field resistance to potato leafroll virus (PLRV) to determine the heritability of this trait. Twelve advanced potato clones or varieties were crossed as pistillate parents to two pollen testers. The seedling progenies and clonal parents were exposed to aphid-transmitted potato leafroll virus for two growing seasons. Cumulative infection by potato leafroll virus was determined by post-season sero-logical indexing of foliage grown from sprouted tubers after 2 years of exposure. Narrow-sense heritability was estimated from regression of mid-parent on progeny as h = 0.72. This estimate indicates a high level of useabie genetic variance for PLRV resistance in advanced breeding materials. Although variation in resistance to PLRV appears to be a quantitative trait in susceptible and moderately resistant clones, per-formance of the most resistant parents suggests that genes with major effects may be present. These results are similar to the conclusions of other researchers who found one or two genes controlling the pheno-types of extreme resistance, resistance to infection, or suppression of virus titre. 相似文献
79.
Continuity and Change in an Old Industrial Region 总被引:1,自引:0,他引:1
Analysts have debated the extent to which recent economic changes represent a continuation of earlier patterns or a fundamental shift to a new industrial order. We trace and extend the spatial implications of this debate for a mature industrial region, the Ohio River Valley, part of the American Manufacturing Belt, for the 1980-90 period. The paper builds on recent research arguing that such regions had a diverse, rather than homogeneous, space-economy. Empirical findings clearly demonstrate diversity of economic structures, sectorally and spatially, emphasizing both continuity and change in an old industrial region, and the totality of economic activity rather than specific sectors identified with the rise or transformation of industrial capitalism. In terms of change, aggregate trends follow national ones, but do not wash evenly over the Ohio River Valley. Nor do they mirror, when considered at a sub-regional scale, patterns indicated by de-industrialization and post-Fordist transition frameworks. Findings provide implications for elaborating or augmenting these perspectives, and types of research needed to accomplish the task. 相似文献
80.
Design of a database for Scottish soils 总被引:1,自引:0,他引:1