全文获取类型
收费全文 | 591篇 |
免费 | 59篇 |
专业分类
林业 | 24篇 |
农学 | 5篇 |
67篇 | |
综合类 | 50篇 |
农作物 | 24篇 |
水产渔业 | 40篇 |
畜牧兽医 | 381篇 |
园艺 | 7篇 |
植物保护 | 52篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 15篇 |
2019年 | 15篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 23篇 |
2015年 | 15篇 |
2014年 | 11篇 |
2013年 | 43篇 |
2012年 | 27篇 |
2011年 | 22篇 |
2010年 | 25篇 |
2009年 | 20篇 |
2008年 | 26篇 |
2007年 | 25篇 |
2006年 | 20篇 |
2005年 | 20篇 |
2004年 | 30篇 |
2003年 | 22篇 |
2002年 | 15篇 |
2001年 | 6篇 |
2000年 | 14篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1996年 | 8篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 5篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1978年 | 3篇 |
1976年 | 11篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 9篇 |
1970年 | 3篇 |
1969年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有650条查询结果,搜索用时 640 毫秒
11.
New Forests - Direct seeding (sowing seeds directly into ground) is potentially a cost-effective method of forest restoration that could replace or complement conventional tree planting, under... 相似文献
12.
Soil Protozoa (primarily small naked amoebae and flagellates) were counted under control conditions and with stresses of nitrogen, water, or nitrogen and water under field conditions (Ecosystem Stress Area, Pawnee Site, northeastern Colorado, USA) in the summer of 1974. Protozoan populations were also measured in soil cores removed from the field and incubated under a wet-dry cycle. Protozoan numbers were higher in the top 1 cm of soil and overlying litter than at a depth of 5–6 cm in all treatments. After rainfall totaling 35 mm, the control and fertilized only treatments showed population increases with the fertilized only treatment showing the greater change. Protozoa showed marked responses to the addition of water to soil cores, with the largest numbers appearing after peak CO2 evolution. Numbers of active (trophic) forms ranged from about 20.000. g?1 dry soil in the control treatment under dry conditions to over 100,000. g?1 dry soil in the irrigated plus fertilized plot. There were few (<5%) cystic (dormant) forms in all treatments contrary to earlier studies in mesic climates. A rough estimate of protozoan production is presented. 相似文献
13.
Phytotoxicity was demonstrated in the aqueous extract of wheat (Triticum aestivum, L.) straw suspensions. When extracts were incubated under anaerobic conditions, the development of phytotoxicity was greater at 20°C than at 10°C. The toxic products formed during incubation depended upon the incubation medium. Acetic and butyric acids were the major toxins produced in liquid straw fermentations during the first 2 weeks. However, after that time the acids did not account for the total toxicity, suggesting formation of unidentified phytotoxins. Acetic, propionic and butyric acids were the toxins formed in sand culture. The development and accumulation of phytotoxins were favored where the sand-straw mixtures were water-saturated. The implications of these findings to wheat cultural practice is discussed. 相似文献
14.
15.
Ahmet E. Baydar Michael Elliott Andrew W. Farnham Norman F. Janes Bhupinder P. S. Khambay 《Pest management science》1988,23(3):247-257
Optimisation of activity within the structural constraints defined by the preceding work, by varying the substituents on phenyl in the acid fragment (10 variations), the nature of the group fulfilling the dimethyl function (three variations), the central linking group (four variations) and the presence or absence of a 4-fluoro substituent in the alcohol fragment, has led to achiral compounds as active as bioresmethrin against houseflies and mustard beetles. Statistical analysis of the effects has shown that particular combinations, for instance the cyclopropyl form of dimethyl with a central E-alkene group (but not a central ether group), lead to higher activity than expected. 4-Fluoro substitution enhances activity more strongly against mustard beetles. Difluorocyclopropyl compounds are on average slightly more active than cyclopropyl analogues. 相似文献
16.
Stuart M. Taylor Christopher T. Elliott William J. Blanchflower 《Pest management science》1987,21(1):39-43
Ten dairy cows were separated into two groups of five. One group was ear tagged with a PVC ear tag containing 8-5 g kg?1 cypermethrin in each ear. A PVC strip impregnated with the same quantity of cypermethrin was attached to the tail of each cow in the other group. The concentration of cypermethrin in hair samples from the neck, flanks and the anterior, sides and the posterior of the udder was measured for a period of 10 weeks after application. Concentrations were found to be high in those body areas nearest to the points of application, moderate on the flanks but low on the front and sides of the udder. 相似文献
17.
Michael Elliott Richard L. Elliott Norman F. Janes Bhupinder P. S. Khambay David A. Pulman 《Pest management science》1986,17(6):691-700
Over 100 benzyl esters of pyrethroidal acids were synthesised and tested for insecticidal activity to establish detailed structure–activity relationships in compounds with side-chains similar to those in the natural pyrethrins. Alkenyl, and corresponding alkynyl, side-chains were effective, both at the 3- and 4-positions, as were side-chains with extended substitution in either E or Z forms. A cyano group at the α-position increases activity if the side-chain is at C-3, but lowers it drastically if the substituent is at C-4. Similarly, methyl groups at C-2 and/or C-6 may increase activity whether the unsaturated side-chain is at C-3 or C-4, but only in the absence of an α-cyano group. 相似文献
18.
19.
In a previous cross-sectional study of feline chronic renal failure (CRF), metabolic acidosis was identified in 52.6 per cent of animals with severe renal failure (plasma creatinine concentration >400 micromol/litre). The aim of this longitudinal study was to determine whether metabolic acidosis preceded or accompanied a deterioration in renal function in cats with CRF. Data were analysed from 55 cats with CRF that had been followed longitudinally for at least four months. Twenty-one cases showed deterioration in renal function over the period of the study, as evidenced by significant rises in their plasma creatinine concentrations and decreases in bodyweight. In five of the 21 cases, acidaemia accompanied the deterioration in renal function. Only one of these cats had evidence of metabolic acidosis before renal function deterioration. One other case developed metabolic acidosis without a rise in plasma creatinine concentration. These data suggest that biochemical evidence of metabolic acidosis does not generally occur until late in the course of feline CRF. 相似文献
20.
OBJECTIVE: To determine in vitro vasoactive potency of monoamines formed in the cecum and found in the systemic circulation of horses. SAMPLE POPULATION: Segments of digital blood vessels obtained from 6 healthy mixed-breed horses and ponies euthanatized at an abattoir and platelets isolated from 4 healthy ponies. PROCEDURE: Paired rings of digital artery and vein from the same horse were examined, and isometric tension was recorded. Concentration-response curves for tryptamine (TRP), tyramine (TYR), phenylethylamine (PEA), isoamylamine (IAA), and isobutylamine (IBA) were obtained. Vasoconstrictor mechanisms were investigated for TRP and TYR by the use of antagonists. Washed platelets loaded with [3H]-5-hydroxytryptamine (5-HT) were incubated with monoamines; the amount of radioactivity displaced after 30 minutes was estimated. RESULTS: TRP, TYR, and PEA were potent constrictors of arteries and veins, with TRP and TYR being more potent in veins than arteries. Constrictions induced by TYR were inhibited by benextramine (alpha-antagonist) and nisoxetine (neuronal-uptake blocker), whereas TRP responses were inhibited by ketanserin (5-HT receptor antagonist). All 5 amines displaced 5-HT from platelets with the order of potency being TYR > TRP > PEA > IAA > IBA. CONCLUSIONS AND CLINICAL RELEVANCE: Amines from the equine cecum cause digital vasoconstriction. The most potent (TRP and TYR) cause selective venoconstriction. Tyrosine activates predominantly alpha-adrenoceptors through the release of neuronal norepinephrine, whereas TRP activates 5-HT receptors. All amines tested released 5-HT from platelets. Amines formed in the cecum and released into the systemic circulation warrant additional investigation as trigger factors for digital ischemia and subsequent laminitis. 相似文献