全文获取类型
收费全文 | 1596篇 |
免费 | 89篇 |
专业分类
林业 | 36篇 |
农学 | 35篇 |
基础科学 | 16篇 |
157篇 | |
综合类 | 292篇 |
农作物 | 76篇 |
水产渔业 | 102篇 |
畜牧兽医 | 876篇 |
园艺 | 36篇 |
植物保护 | 59篇 |
出版年
2021年 | 15篇 |
2019年 | 27篇 |
2018年 | 15篇 |
2017年 | 26篇 |
2016年 | 27篇 |
2015年 | 25篇 |
2014年 | 19篇 |
2013年 | 118篇 |
2012年 | 48篇 |
2011年 | 78篇 |
2010年 | 40篇 |
2009年 | 32篇 |
2008年 | 64篇 |
2007年 | 49篇 |
2006年 | 55篇 |
2005年 | 46篇 |
2004年 | 58篇 |
2003年 | 48篇 |
2002年 | 53篇 |
2001年 | 51篇 |
2000年 | 45篇 |
1999年 | 23篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 21篇 |
1994年 | 14篇 |
1992年 | 34篇 |
1991年 | 27篇 |
1990年 | 22篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 25篇 |
1986年 | 30篇 |
1985年 | 22篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 21篇 |
1978年 | 23篇 |
1976年 | 16篇 |
1974年 | 20篇 |
1973年 | 20篇 |
1972年 | 16篇 |
1971年 | 16篇 |
1970年 | 15篇 |
1969年 | 20篇 |
1967年 | 11篇 |
1966年 | 11篇 |
排序方式: 共有1685条查询结果,搜索用时 15 毫秒
41.
Barling KS McNeill JW Paschal JC McCollum FT Craig TM Adams LG Thompson JA 《Preventive veterinary medicine》2001,52(1):53-61
A study was conducted with a 1998 retained-ownership population of Texas (USA) beef calves to determine the ranch-management practices associated with calf seroprevalence to Neospora caninum. Management practices of 76 Texas ranches that consigned 760 calves to a retained-ownership feedlot program were reviewed from a mailed questionnaire. Ninety-nine of 760 (13%; 95% CI, 9.4%, 17.7%) calves were positive to N. caninum and 59% of the ranches consigned at least one positive calf. In the logistic multiple-regression model which controlled for overdispersion, increased odds of calf-level seropositivity was associated with seasonal calving patterns, with stocking>1cow/calfunit/2.2ha, using a round-bale feeder, allowing wildlife access to the weaning supplement, and self-reared replacement heifers. However, decreased odds of seropositivity was associated with using a cattle-working dog and with using a self-contained cattle feeder. There was substantial overdispersion due to ranch. 相似文献
42.
Aerial spray applications of the herbicide glyphosate were made over a forest canopy under various meteorological conditions. A ‘Thru Valve Boom’ dispersal system carried by a Cessna 188 fixed-wing aircraft flying at 49 m s?1 was used to generate an aqueous spray cloud with a volume median diameter of 150 μm. Glyphosate deposits from multiple overlaid crosswind line sources released at 10 m above ground level were measured on ground sheets and artificial foliage at downwind distances between 50 and 400 m. Trials were conducted in stable, neutral and unstable atmospheric boundary layers with average wind speeds between 2·2 and 5·7 m s?1 and vertical intensities of turbulence between 0·07 and 0·16. Linear regression lines fitted to logarithmically transformed measurements and downwind distances (x) gave statistically significant correlation coefficients (P = 0·01), and were compared by ANOVA. Glyphosate deposits on ground sheets and artificial foliage were attenuated at rates inversely proportional to x to the power 1·7-4·3. Regression line comparison showed that, in general, deposits on ground sheets decreased with increasing wind speed and intensity of turbulence, and some statistically significant differences were found in slopes and elevations of regression lines from different trials. However, deposits at the 50-m station increased with wind speed due to the large-drop cloud component. Regression line comparison for deposits on artificial foliage showed that, in general, they were highest in the intermediate wind speed-neutral stability case and similar in the high wind speed-unstable and low wind speed-stable boundary layers, although deposits at the 50-m station also increased with wind speed. 相似文献
43.
Scott J. Nissen Robert A. Masters W. Mack Thompson Robert N. Stougaard 《Pest management science》1995,45(4):325-329
Imazapyr absorption, translocation, root release and metabolism were examined in leafy spurge (Euphorbia esula L.). Leafy spurge plants were propagated from root cuttings and [14C]imazapyr was applied to growth-chambergrown plants in a water + 28% urea ammonium nitrate + nonionic surfactant solution (98.75 + 1 + 0.25 by volume). Plants were harvested two and eight days after herbicide treatment (DAT) and divided into: treated leaf, stem and leaves above treated leaf, stem and leaves below the treated leaf, crown, root, dormant and elongated adventitious shoot buds. Imazapyr absorption increased from 62.5% 2 DAT to 80.0% 8 DAT. Herbicide translocation out of the treated leaf and accumulation in roots and adventitious shoot buds was apparent 2 DAT. By the end of the eight-day translocation period only 14% of applied 14C remained in the treated leaf, while 17% had translocated into the root system. Elongated and dormant adventitious shoot buds accumulated 3.2- and 1.8-fold more 14C, respectively, 8 DAT than did root tissue based on Bq g?1 dry weight. Root release of 14C was evident 2 DAT, and by 8 DAT 19.4% of the 14C reaching the root system was released into the rooting medium. There was no metabolism of imazapyr in crown, root or adventitious shoot buds 2 DAT; however, imazapyr metabolism was evident in the treated leaf 2 and 8 DAT. Imazapyr phytotoxicity to leafy spurge appears to result from high imazapyr absorption, translocation to underground meristematic areas (roots and adventitious shoot buds), and a slow rate of metabolism. 相似文献
44.
OBJECTIVE: Genetic and biological characterisation of 12 isolates of Cryptosporidium from pigs and comparing them with Cryptosporidium isolates from humans and cattle. DESIGN: Cryptosporidium isolates from pigs were compared with those obtained from human and cattle using rDNA sequence analysis. The infectivity of two of the porcine isolates was determined in neonatal mice and the clinical history of the infected pigs recorded. RESULTS: Pig-derived isolates of Cryptosporidium exhibited two distinct genotypes; a porcine genotype and a bovine genotype, which is common to cattle and other livestock. The porcine genotype did not produce any infection in neonatal mice whereas the bovine genotype did. CONCLUSION: Two distinct genetically and biologically differing strains of Cryptosporidium appeared to be associated with acute diarrhoea in pigs. Whether Cryptosporidium was a primary or secondary pathogen is unclear but warrants further investigation. As the bovine genotype is known to infect humans, the results suggest that pigs can act as reservoirs of cryptosporidial infections for humans and other live-stock. The zoonotic potential of the pig-adapted genotype is uncertain and requires further study. 相似文献
45.
46.
47.
48.
49.
A glass-lined trough was divided into six compartments by vertical transverse partitions and filled with soil to a height of 5 cm above the top of each partition. The base of the box and the surface of the soil sloped forwards one end with a gradient of 1 in 3·7. Dieldrin was applied (22 kg active ingredient/ha) to the soil surface in the uppermost compartment and the movement of dieldrin into leachate and down the slope was followed for 17 weeks. During this time 19·5 cm of rain fell. Less than 0·02% of the dieldrin appeared in the leachate and 99% of this was collected during the first 9 weeks, mainly from the uppermost compartment. Very little dieldrin moved down the slope and it was not detected in the leachate from compartments other than the treated one during 9–17 weeks after treatment. In other experiments, 3 cylinders were filled respectively with sandy loam, heavy clay loam and peat which were transferred from the field as intact cores. Three other cylinders were filled with soils of the same types but broken up. Approximately 2% of the dieldrin leached through one column but usually it was much less than 0·1%. The largest amounts of dieldrin were leached down columns of heavy clay loam, intermediate amounts down columns of peat, and least through sandy loam. Ten times as much dieldrin leached down the columns of intact soil as through those with broken soil. The results indicate that the movement of dieldrin from treated soil into water systems by leaching is limited and is unlikely to be a major pathway for the contamination of water. 相似文献
50.
Results are presented for the determination of organochlorine insecticide residues in grain, pulses and nuts sampled on arrival in Britain during the 2½ years up to June 1969. BHC was detected in nearly every sample but the general level was low, most samples containing less than 0·1 ppm. DDT was found less frequently. Very few samples contained more than 1 ppm of either insecticide. DDE in trace amounts was found in about 10% of the samples of grain and nuts and TDE was found in one sample of grain. The only other organochlorine compounds detected were aldrin in one sample of pulses and hexachlorobenzene in 7 samples of wheat. 相似文献