全文获取类型
收费全文 | 89775篇 |
免费 | 5535篇 |
国内免费 | 46篇 |
专业分类
林业 | 3735篇 |
农学 | 3466篇 |
基础科学 | 632篇 |
11271篇 | |
综合类 | 13526篇 |
农作物 | 3361篇 |
水产渔业 | 4943篇 |
畜牧兽医 | 47637篇 |
园艺 | 1165篇 |
植物保护 | 5620篇 |
出版年
2020年 | 732篇 |
2019年 | 955篇 |
2018年 | 1584篇 |
2017年 | 1850篇 |
2016年 | 1661篇 |
2015年 | 1407篇 |
2014年 | 1721篇 |
2013年 | 3719篇 |
2012年 | 2932篇 |
2011年 | 3588篇 |
2010年 | 2341篇 |
2009年 | 2330篇 |
2008年 | 3470篇 |
2007年 | 3214篇 |
2006年 | 3136篇 |
2005年 | 2671篇 |
2004年 | 2578篇 |
2003年 | 2592篇 |
2002年 | 2374篇 |
2001年 | 3389篇 |
2000年 | 3304篇 |
1999年 | 2553篇 |
1998年 | 983篇 |
1997年 | 1051篇 |
1996年 | 883篇 |
1995年 | 1022篇 |
1994年 | 895篇 |
1993年 | 896篇 |
1992年 | 1845篇 |
1991年 | 1919篇 |
1990年 | 1856篇 |
1989年 | 1859篇 |
1988年 | 1607篇 |
1987年 | 1595篇 |
1986年 | 1627篇 |
1985年 | 1526篇 |
1984年 | 1225篇 |
1983年 | 1032篇 |
1982年 | 713篇 |
1979年 | 1060篇 |
1978年 | 816篇 |
1975年 | 815篇 |
1974年 | 897篇 |
1973年 | 864篇 |
1972年 | 805篇 |
1971年 | 795篇 |
1970年 | 800篇 |
1969年 | 780篇 |
1968年 | 708篇 |
1967年 | 734篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Jennifer E Stokes S Dru Forrester 《Veterinary Clinics of North America: Small Animal Practice》2004,34(4):909-22, vi
This article provides a source for easy reference, summarizing in one location newly recognized and unusual causes of acute renal failure (ARF) in dogs and cats. Several of the causes discussed in this article have been described previously. New or unusual causes of ARF in dogs and cats include infectious diseases (leptospirosis,borreliosis, and babesiosis), nephrotoxicants (aminoglycosides,vitamin D, and nonsteroidal anti-inflammatory drugs), and plant material (lilies and raisins/grapes). 相似文献
993.
994.
S. Kennou Sebei R. Bergaoui M. Ben Hamouda R. G. Cooper 《Tropical animal health and production》2009,41(7):1427-1438
The aim of the current investigation was to determine wild ostrich reproductive behaviour in Orbata Nature Reserve by observing
16 hens and 28 cocks over a seven-year period. Intense laying commenced in January, one month after the cessation of the rainy
season, and 92% of the eggs were produced during the dry season (January to May, peaking in March). Over the seven years,
1,322 eggs were laid in 69 nests, which corresponded to an annual average production of 19.2 ± 9.1 eggs/nest and 11.8 eggs/hen.
24 nests (34.78%) were non-brooded, 17 nests (24.64%) were deserted in the course of incubation, and 28 nests (40.58%) possessed
hatched eggs. All the non-incubated nests had egg losses equivalent to 46.6 ± 12.6%. Hatchability success of incubated eggs
was 41.9 ± 12.0%. Ostriches tended to dig their nests adjacent to the reserve enclosure which had direct access by road and
track, the latter subjecting them to human disturbance and predation. The systematic obstruction of these nests stimulated
ostriches to build additional nests within the reserve perimeter. The authors discussed the results recorded in an ostrich
flock in relation to the environmental factors (climatic factors, food disponibility and predation) and suggested possibilities
for improved wildlife management. 相似文献
995.
Waldron DF Taylor CA Walker JW Campbell ES Lupton CJ Willingham TD Landau SY 《Journal of animal science》2009,87(2):491-495
Data from goats (n = 505), collected over a 4-yr period, were used to estimate the heritability of juniper consumption. Juniper consumption was determined by near-infrared spectroscopy on fecal samples (n = 1,080) collected from female Boer-cross goats grazing pastures with a variety of plants, including juniper. The animals with records were progeny of 72 sires. Individual goats had from 1 to 4 observations over a 4-yr period. Predicted juniper consumption for individual observations ranged from -5 to +62% of the diet. Data were analyzed with a mixed model that included management group as a fixed effect, BW as a covariate, and permanent environment, animal, and residual as random effects. Management group was a significant source of variation. Least squares means of juniper consumption, as a percentage of the total intake, for management groups varied from 19 to 47%. Heritability of juniper consumption was 13%. Repeatability of juniper consumption was 31%. These results suggest that progress to selection for goats that will consume greater amounts of juniper is obtainable, but is expected to be slow. 相似文献
996.
997.
998.
Christopher A. Ellison Quentin D. Skinner Larry S. Hicks 《Strength and Conditioning Journal》2009,62(4):371-386
Quantifying the effects of watershed improvement efforts is critical to agencies responsible for protecting water resources of the semiarid western United States. A complex water quality data set collected from 1994 to 2004 of upper Muddy Creek Basin was subjected to cluster analysis, discriminant analysis, and canonical correlation analysis to improve understanding of basin fluvial processes and to investigate whether livestock grazing best-management practices (BMPs) improved the water quality of the watershed. Hierarchical agglomerative cluster analysis grouped nine sampling sites into two clusters based on similarity of biological indices, separating the clusters into aquatic communities more and less tolerant of degraded stream conditions. Discriminant analysis yielded strong spatial and temporal distinctions, providing important data reduction by rendering seven key parameters (total dissolved solids [TDS], temperature, elevation, slope, 10-dominant taxa, percent collector-gatherers, and percent Plecoptera) for the spatial variation and four parameters (TDS, dissolved oxygen, total taxa, and community tolerance quotient) for the temporal variation. Canonical correlation analysis identified strong negative relationships among Plecoptera taxa and total taxa with TDS and turbidity in addition to strong positive associations with elevation, slope, and channel substrate weighted embeddedness value. Despite the onset of severe drought midway through the study period, overall reductions of 13% for TDS and a 30% increase in macroinvertebrate total taxa occurred across years, strongly suggesting that improvements in water quality were correlated to BMPs that stabilized stream channels and improved the condition of riparian areas. 相似文献
999.
1000.
A mail survey of factors associated with morbidity and mortality in feedlot calves in southwestern Ontario. 下载免费PDF全文
The design and results of a mail survey of a simple random sample of southwestern Ontario feedlot owners are presented. The survey provided general data about management of feedlot calves and the association between a number of factors and disease and/or death rates. The number of calves purchased was related positively, in a linear manner, to mortality and morbidity rates. Increased levels of morbidity and mortality were noted when the ration was changed to corn silage from dry-hay within the first month after arrival. However, it was not clear whether the ration changes preceded or followed increased rates of morbidity and mortality. Prophylactic levels of antimicrobials in the water supply were associated with increased death losses. Shipping cattle by truck, rather than train, was associated with decreased rates of disease. Processing factors, including using vaccines against respiratory disease, were not associated significantly with mortality or morbidity. It was concluded that reducing the number of calves, to approximately 100 per group, not changing the ration to silage within the first month and not using antibiotics in the water supply on arrival could significantly reduce disease and death losses. 相似文献