全文获取类型
收费全文 | 1784篇 |
免费 | 104篇 |
国内免费 | 1篇 |
专业分类
林业 | 101篇 |
农学 | 45篇 |
基础科学 | 15篇 |
219篇 | |
综合类 | 281篇 |
农作物 | 141篇 |
水产渔业 | 83篇 |
畜牧兽医 | 832篇 |
园艺 | 26篇 |
植物保护 | 146篇 |
出版年
2022年 | 14篇 |
2021年 | 24篇 |
2020年 | 28篇 |
2019年 | 30篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 22篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 73篇 |
2012年 | 69篇 |
2011年 | 77篇 |
2010年 | 67篇 |
2009年 | 29篇 |
2008年 | 75篇 |
2007年 | 66篇 |
2006年 | 66篇 |
2005年 | 79篇 |
2004年 | 71篇 |
2003年 | 67篇 |
2002年 | 54篇 |
2001年 | 40篇 |
2000年 | 42篇 |
1999年 | 32篇 |
1998年 | 13篇 |
1996年 | 16篇 |
1995年 | 22篇 |
1994年 | 14篇 |
1992年 | 28篇 |
1991年 | 29篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 20篇 |
1986年 | 24篇 |
1985年 | 29篇 |
1984年 | 20篇 |
1983年 | 18篇 |
1982年 | 22篇 |
1979年 | 17篇 |
1978年 | 12篇 |
1977年 | 16篇 |
1976年 | 18篇 |
1975年 | 16篇 |
1974年 | 14篇 |
1973年 | 23篇 |
1972年 | 21篇 |
1971年 | 16篇 |
1948年 | 13篇 |
1947年 | 13篇 |
排序方式: 共有1889条查询结果,搜索用时 15 毫秒
1.
Lampreys have a complex life cycle which includes a multi‐year infaunal larval stage (ammocoete). Gut content analysis has generally identified detritus (i.e., unidentifiable organic matter) as the major dietary component to ammocoetes, though algae can also be important. However, gut content preserves only a snapshot of the animal's diet and does not reflect assimilated material. In order to better characterise the nutritional sources supporting ammocoete growth, we analysed ammocoete body tissue and potential dietary sources at two streams using natural Δ14C and δ15N to estimate time‐integrated nutritional support. Bayesian isotope mixing models revealed differences in the importance of sources supporting ammocoetes between sites. Ammocoetes from a stream in a mixed land usage area (~50% agriculture, ~40% forest and ~10% developed) were primarily supported (mean: ~50%) by fresh terrestrial organic matter but were also supported by substantial contributions (mean: ~30%) by aged organic matter (AOM) and autochthonous material (algae; mean ~20%). In a predominantly forested (~90%) headwater stream, different modelling scenarios (uninformed or informed priors) suggested that algal support of ammocoete nutrition ranged from 7% to 45%. However, the model relying on informed priors developed from gut content analysis produced the low estimates, suggesting these were more reliable. When algae were a minor component of the nutrition at the forested site, ammocoetes were highly dependent on AOM (83 ± 26%; mean ± SD). Based on these findings, ammocoete growth and development are predicted to be strongly influenced by both land use and the availability of allochthonous and autochthonous materials of varying ages within streams. 相似文献
2.
1. The effect of supplementing grower diets with bicarbonate or chloride on haematological variables, pulmonary hypertension syndrome and ascites in broilers exposed to cold temperature was investigated. 2. High concentrations of dietary chloride had no effect on the pH of the venous blood but a low chloride/high bicarbonate diet significantly increased blood pH. There was no consistent effect of dietary chloride or bicarbonate concentrations on growth performance, although in 1 experiment birds given a low chloride/high bicarbonate diet consumed less food and gained less weight than controls. 3. Birds fed on high-chloride diets tended to have a higher incidence of ascites and pulmonary hypertension than controls. Birds fed on low-chloride and high-bicarbonate diets had significantly lower pulmonary hypertension and lower heart weights, which may have indicated a decrease in pulmonary and systemic blood pressure. 4. We conclude that increasing dietary bicarbonate and reducing dietary chloride has potential as a low cost and effective method to reduce the pulmonary hypertension which leads to ascites in broiler chickens. 相似文献
3.
Six horses with chronic obstructive pulmonary disease (COPD) and 8 horses with recurrent urticaria were skin tested with 67 extracts from 58 allergens, including pollens, epidermals, cultivated farm plants, dusts, molds, and insects. Reactions were evaluated 3 times over a 24-hour period immediately after the injections. Results were compared with those obtained from 11 clinically normal horses. All horses had positive skin test reactions. Significant differences was evident between horses with COPD and clinically normal horses for only 3.0% of the possible extract reactions, and between horses with urticaria and clinically normal horses for only 4.5% of the possible extract reactions. Horses with COPD or urticaria had greater total percentage of allergen extract reactions than did clinically normal horses. Positive reactions were observed at all 3 evaluation periods, and late-onset reactions were not always preceded by positive reaction at earlier periods. All horses with COPD or urticaria had at least 1 skin test reaction that exceeded the mean +/- 2 SD, as calculated for each of the 67 extracts for the group of clinically normal horses. 相似文献
4.
5.
Tim J Evans 《Veterinary Clinics of North America: Equine Practice》2002,18(2):371-8, viii
Ergopeptine alkaloid exposure is common in pregnant mares. Many mares live in geographic areas where Neotyphodium coenophialum-infected tall fescue is the dominant grass in pastures and hay. A variety of grasses and cereal grains can be infected by Claviceps purpurea, and fungal sclerotia can contaminate forage and especially ground and pelleted feed. An understanding of the endocrine alterations associated with ergopeptine alkaloid exposure during pregnancy is necessary for the diagnosis of potential exposure to these compounds and for eective prophylaxis and therapy. 相似文献
6.
U Giger S M Evans M J Hendrick S M Dudek 《Journal of the American Veterinary Medical Association》1989,195(5):627-630
A 1 1/2-year-old castrated Boxer with a progressive left forelimb lameness of 1 month's duration had a solitary immunoblastic B-cell lymphoma of the proximal portion of the ulna. This primary lymphoma of bone was successively treated with orthovoltage radiation (45 Gy divided into 10 fractions over 22 days). The dog gradually regained normal gait function and did not develop any local recurrence over 34 months. In dogs, primary lymphoma of bone is a rare primary bone tumor, and the ulna is an unusual location for extranodal lymphoma. Local administration of radiation appears to be an effective treatment, allowing retention of normal function. 相似文献
7.
8.
9.
Shapiro JL Julian RJ Hampson RJ Trenton RG Yo IH 《The Canadian veterinary journal. La revue veterinaire canadienne》1988,29(8):636-639
A diagnosis of toxic necrotizing cholangiohepatitis was made in approximately 35% of a flock of 23,000 commercial broiler chickens. Affected chickens were small, and had discrete green foci throughout the liver. Seven to twelve days prior to shipping the flock to slaughter, premixes containing oxytetracycline, monensin, and 3-nitro-4-hydroxyphenylarsonic acid had been added to the ration because the birds had wet droppings and were growing slowly. The 3-nitro-4-hydroxyphenylarsonic acid had been inadvertently incorporated at ten times the recommended level. Liver and kidney of affected birds had elevated levels of total arsenic, and special strains demonstrated arsenic in necrotic foci in liver. Histologically there was marked dilation of intrahepatic bile ducts, and patchy necrosis and hyperplasia of the bile duct epithelium. Damage to bile ducts may have been a toxic manifestation of altered metabolism and excretion of the three drugs being fed to birds suffering from intercurrent diarrhea and/or undefined interactions among the drugs. 相似文献
10.