全文获取类型
收费全文 | 1163篇 |
免费 | 87篇 |
专业分类
林业 | 23篇 |
农学 | 13篇 |
基础科学 | 4篇 |
56篇 | |
综合类 | 351篇 |
农作物 | 116篇 |
水产渔业 | 40篇 |
畜牧兽医 | 565篇 |
园艺 | 13篇 |
植物保护 | 69篇 |
出版年
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 11篇 |
2017年 | 19篇 |
2016年 | 20篇 |
2015年 | 15篇 |
2014年 | 22篇 |
2013年 | 18篇 |
2012年 | 35篇 |
2011年 | 36篇 |
2010年 | 18篇 |
2009年 | 32篇 |
2008年 | 53篇 |
2007年 | 27篇 |
2006年 | 33篇 |
2005年 | 37篇 |
2004年 | 44篇 |
2003年 | 33篇 |
2002年 | 41篇 |
2001年 | 33篇 |
2000年 | 33篇 |
1999年 | 17篇 |
1996年 | 10篇 |
1994年 | 11篇 |
1992年 | 11篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1973年 | 11篇 |
1947年 | 11篇 |
1946年 | 13篇 |
1943年 | 10篇 |
1936年 | 13篇 |
1935年 | 9篇 |
1907年 | 18篇 |
1906年 | 22篇 |
1905年 | 19篇 |
1904年 | 19篇 |
1903年 | 14篇 |
1902年 | 10篇 |
1901年 | 13篇 |
1900年 | 10篇 |
1899年 | 13篇 |
1898年 | 19篇 |
1897年 | 13篇 |
1896年 | 16篇 |
排序方式: 共有1250条查询结果,搜索用时 31 毫秒
41.
Ward MP 《Preventive veterinary medicine》2002,56(3):203-213
A retrospective study was undertaken to describe seasonal patterns of leptospirosis diagnosed at veterinary teaching hospitals in the United States and Canada, and to determine if occurrence of cases (diagnoses) was associated with rainfall. The veterinary medicine database (VMDB) was searched for records of dogs in which a diagnosis of leptospirosis was made, and average monthly rainfall recorded at the city where each hospital is located was calculated from historical data. Time-series analysis was used to identify the variables that best described occurrence of cases of leptospirosis. Three-hundred and forty dogs were diagnosed with leptospirosis at 22 veterinary teaching hospitals between 1983 and 1998. Most cases (n = 184) were diagnosed between August and November during each year of the study. A significant correlation (r = 0.41) was detected between the number of cases of leptospirosis diagnosed and average rainfall recorded 3-months prior to diagnosis. The best-fitting (Akaike's corrected information criterion = 2.01) regression on the leptospirosis case series included cases diagnosed in the previous month and 12-months previously, and rainfall recorded 3 months previously. Leptospirosis has a seasonal distribution (late summer to fall), and rainfall can be used to predict the occurrence of leptospirosis. Leptospirosis can affect the health of dogs seriously and its prevalence is increasing, but the disease is preventable by vaccination. 相似文献
42.
Simulation model of within-herd transmission of bovine tuberculosis in Argentine dairy herds 总被引:7,自引:0,他引:7
Transmission of bovine tuberculosis was quantified in three dairy herds located in south Santa Fe Province, Argentina. Using estimates of Mycobacterium bovis transmission (β) and a Reed–Frost simulation model, the prevalence of tuberculosis infection in the study herds over time was investigated. The Reed–Frost model was modified by incorporating randomness in both β and the incubation period () of M. bovis. The mean estimated herd β was 2.2 infective contacts per year and did not differ significantly between the study herds. Modeling as Poisson distributed (mean 24 months) best fit the observed prevalences. Infection was predicted by the model either to spread quickly (<10 years) within a herd and reach a high prevalence (>50%), or to persist at a low prevalence (<5–10%). The model was robust, predictions were realistic and the mean β estimated was consistent with previous studies of bovine tuberculosis. 相似文献
43.
OBJECTIVE: To determine whether expression of G proteins (G(i) and G(s)) is altered in thyroid gland adenomas obtained from hyperthyroid cats. SAMPLE POPULATION: Adenomatous thyroid glands obtained from 8 hyperthyroid cats and thyroid glands obtained from 4 age-matched euthyroid cats. PROCEDURE: Expression of G(i) and G(s) was quantified in enriched membrane preparations of thyroid gland tissue, using immunoblotting with G(i) and G(s) antibodies and toxin-catalyzed ADP-ribosylation. RESULTS: Expression of G(i) was significantly reduced in thyroid gland adenomas from hyperthyroid cats, compared with normal thyroid gland tissue from euthyroid cats. Expression of G(s) was similar between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE: A decrease in expression of G in adenomatous thyroid glands of cats may reduce the negative inhibition of the cAMP cascade in thyroid cells, leading to autonomous growth and hypersecretion of thyroxine. Understanding the molecular mechanisms for hyperthyroidism in cats may lead to better treatment or, ultimately, prevention of the disease. 相似文献
44.
Todd SE Mellor DJ Stafford KJ Gregory NG Bruce RA Ward RN 《Research in veterinary science》2000,68(2):125-134
The effects of food withdrawal for 30 hours and transport for up to 12 hours on 5- to 10-day-old calves were determined by monitoring plasma concentrations of glucose, beta-hydroxybutyrate, urea, lactate and creatine phosphokinase. In addition gamma-glutamyl transferase activity, packed cell volume, total plasma protein concentration, bodyweight and rectal temperature were recorded. Food withdrawal for 30 hours caused hypoglycemia but calves maintained normothermia and although their beta-hydroxybutyrate level increased indicating lipid mobilisation, the changes in blood urea level were minimal indicating low amino acid catabolism. When calves were transported for 12 hours in addition to having food withdrawn for 30 hours, they remained normoglycemic for six hours longer than non-transported calves, probably due to an effect of muscular activity during bracing against truck movements. Stocking calves at a lower density during transport apparently had a beneficial effect, as calves were able to lie down throughout the journey and therefore produced a similar metabolic profile to resting, non-transported animals. Transport and food withdrawal had no obvious effects on calf hydration. The results of this study suggest that food withdrawal for up to 30 hours and transport for up to 12 hours had no detrimental effects on the metabolism of healthy and clinically normal calves. With correct feeding regimes and transport protocols, welfare compromise in young, healthy calves being transported for up to 12 hours can be minimised when they are slaughtered within 30 hours of the start of transport. 相似文献
45.
The reported occurrence of blowfly strike in 57 sheep flocks in Queensland, Australia, was investigated for time-space clustering in an exploratory study using Knox's method. Flystrike occurrence peaked in late spring and early summer, with an additional late-autumn peak in southern-Queensland flocks. A total of 1596 case-pairs was examined. Significant clustering (P = 0.07) was only detected for case-pairs occurring within 3 months and 150 km of each other; 164 case-pairs were declared close compared to an expectation of 151. We suggest that factors common to a district (such as rainfall and temperature) are responsible for clustering of flystrike in Queensland. 相似文献
46.
Sheafor SE Couto CG Ward H Essinger C Nicol SJ 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2000,14(1):86-89
We conducted a clinical evaluation of FCE 23762, a methoxymorpholino analog of doxorubicin, in 48 dogs with metastatic, nonresectable, or chemotherapy-resistant spontaneous malignancies at an initial dosage of 50-60 microg/kg IV every 3 weeks. Clinical evidence of toxicity was minimal; 6 dogs developed grades I, II, and III hematologic toxicities after the 1st treatment, and 1 dog developed grade II gastrointestinal toxicity. One dog became pancytopenic 4 months after discontinuation of FCE 23762. No other adverse effects were noted. Partial or complete remissions were observed in 32% of the dogs. Responses were observed both in previously untreated dogs and in those that had received prior chemotherapy, including doxorubicin. FCE 23762 is a promising new antineoplastic agent that can be used safely in dogs with cancer; doses higher than those used in this study may be used eventually in practice. 相似文献
47.
Retrobulbar abscessation is the most common orbital disease of rabbits, and the lesions are notoriously difficult to treat successfully. This article describes the diagnosis, surgical treatment, and long-term management of an extensive abscess located within the right maxilla and retrobulbar space of a domestic rabbit. Preoperative assessment and long-term monitoring were achieved with a combination of radiography, ophthalmic ultrasonography, and CT. Extraoral rigid endoscopy via a fenestration in the maxilla was used to facilitate surgical debridement of the lesion, and extraction of multiple cheek teeth has been fundamental to achieving control. The long-term use of topical and systemic antibiotic preparations and nonsteroidal anti-inflammatory medication is discussed. 相似文献
48.
Urban forests are unique and highly valued resources. However, trees in urban forests are often under greater stress than those in rural or undeveloped areas due to soil compaction, restricted growing spaces, high temperatures, and exposure to air and water pollution. In addition, conditions change more quickly in urban as opposed to rural and undeveloped settings. Subsequently, proactive management of urban forests can be challenging and requires the availability of current and comprehensive information. Geospatial tools, such as, geographic information systems (GIS), global positioning systems (GPS) and remote sensing, work extremely well together for gathering, analyzing, and reporting information. Many urban forest management questions could be quickly and effectively addressed using geospatial methods and tools. The geospatial tools can provide timely and extensive spatial data from which urban forest attributes can be derived, such as land cover, forest structure, species composition and condition, heat island effects, and carbon storage. Emerging geospatial tools that could be adapted for urban forest applications include data fusion, virtual reality, three-dimensional visualization, Internet delivery, modeling, and emergency response. 相似文献
49.
50.