全文获取类型
收费全文 | 480篇 |
免费 | 46篇 |
专业分类
林业 | 11篇 |
农学 | 7篇 |
基础科学 | 3篇 |
56篇 | |
综合类 | 30篇 |
农作物 | 11篇 |
水产渔业 | 37篇 |
畜牧兽医 | 348篇 |
园艺 | 8篇 |
植物保护 | 15篇 |
出版年
2024年 | 3篇 |
2023年 | 18篇 |
2022年 | 12篇 |
2021年 | 22篇 |
2020年 | 14篇 |
2019年 | 23篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 27篇 |
2013年 | 13篇 |
2012年 | 32篇 |
2011年 | 34篇 |
2010年 | 18篇 |
2009年 | 13篇 |
2008年 | 24篇 |
2007年 | 20篇 |
2006年 | 20篇 |
2005年 | 37篇 |
2004年 | 33篇 |
2003年 | 35篇 |
2002年 | 39篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1983年 | 1篇 |
1888年 | 1篇 |
排序方式: 共有526条查询结果,搜索用时 15 毫秒
41.
Two complementary studies were performed to examine (1) the effect of 18 years of nitrogen (N) fertilization, and (2) the effects of N fertilization during one growing season on soil microbial community composition and soil resource availability in a grassland ecosystem. N was added at three different rates: 0, 5.44, and 27.2 g N m−2 y−1. In both studies, Schizachyrium scoparium was the dominant plant species before N treatments were applied. Soil microbial communities from each experiment were characterized using fatty acid methyl ester (FAME) analysis. Discriminant analysis of the FAMEs separated the three N fertilizer treatments in both experiments, indicating shifts in the composition of the microbial communities. In general, plots that received N fertilizer at low or high application rates for 18 years showed increased proportions of bacterial FAMEs and decreased fungal FAMEs. In particular, control plots contained a significantly higher proportion of fungal FAMEs C18:1(cis9) and C18:2(cis9,12) and of the arbuscular mycorrhizal fungal (AMF) FAME, C16:1(cis11), than both of the N addition treatment plots. A significant negative effect of N fertilization on the AMF FAME, C16:1(cis11), was measured in the short-term experiment. Our results indicate that high rates of anthropogenic N deposition can lead to significant changes in the composition of soil microbial communities over short periods and can even disrupt the relationship between AMF and plants. 相似文献
42.
Microbial activity is known to continue during the winter months in cold alpine and Arctic soils often resulting in high microbial biomass. Complex soil nutrient dynamics characterize the transition when soil temperatures approach and exceed 0 °C in spring. At the time of this transition in alphine soils microbial biomass declines dramatically together with soil pools of available nutrients. This pattern of change characterizes alpine soils at the winter-spring transition but whether a similar pattern occurs in Arctic soils, which are colder, is unclear. In this study amounts of microbial biomass and the availability of carbon (C), nitrogen (N) and phosphorus (P) for microbial and plant growth in wet peaty soils of an Arctic sedge meadow have been determined across the winter-spring boundary. The objective was to determine the likely causes of the decline in microbial biomass in relation to temperature change and nutrient availability. The pattern of soil temperature at depths of 5-15 cm can be divided into three phases: below −10 °C in late winter, from −7 to 0 °C for 7 weeks during a period of freeze-thaw cycles and above 0 °C in early spring. Peak microbial biomass and nutrient availability occurred early in the freeze-thaw phase. Subsequently, a steady decrease in inorganic N occurred, so that when soil temperatures rose above 0 °C, pools of inorganic nutrients in soils were very low. In contrast, amounts of microbial C and soluble organic C and N remained high until the end of the period of freeze-thaw cycles, when a sudden collapse occurred in soluble organic C and N and in phosphatase activity, followed by a crash in microbial biomass just prior to soil temperatures rising consistently above 0 °C. Following this, there was no large pulse of available nutrients, implying that competition for nutrients from roots results in the collapse of the microbial pool. 相似文献
43.
Fernando Machado-Stredel Benedictus Freeman Daniel Jiménez-Garcia Marlon E.Cobos Claudia Nu?ez-Penichet Laura Jiménez Ed Komp Utku Perktas Ali Khalighifar Kate Ingenloff Walter Tapondjou Thilina de Silva Sumudu Fernando Luis Osorio-Olvera A.Townsend Peterson 《中国鸟类》2022,(1):1-10
Studies of biodiversity dynamics have been cast on either long(systematics)or short(ecology)time scales,leaving a gap in coverage for moderate time scales of de... 相似文献
44.
Debra C. Sellon Jay Levine Everett Millikin Kate Palmer Carol Grindem Patrice Covington 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1996,10(3):127-132
The records of 3,952 equine patients presenting to the Veterinary Teaching Hospital at North Carolina State University College of Veterinary Medicine were evaluated to determine risk factors associated with thrombocytopenia. Of 2,346 horses from which a CBC was obtained, 35 (1.49%) were thrombocytopenic (platelet count < 75,000/μL). A reference population of 189 horses with normal platelet counts (75,000 to 300,000/μL) was also studied. Standardbred horses were at increased risk for thrombocytopenia. but age and gender were not identified as significant risk factors. Horses with infectious or inflammatory diseases were at increased risk for thrombocytopenia. The potential association of clinical and clinicopathologic factors with thrombocytopenia were assessed by reviewing a series of multiple logistic regression models. Clinical and clinicopathologic variables significantly associated with thrombocytopenia in the final model included increased PCV, increased band neutrophil count, increased total WBC, and decreased plasma protein concentration. Increased mature neutrophil count was associated with normal platelet counts. Thrombocytopenic horses were significantly more likely to die or be euthanized than were horses with normal platelet counts. J Vet Intern Med 1996;10:127–132. Copyright © 1996 by the American College of Veterinary Internal Medicine . 相似文献
45.
46.
47.
Holmstrom SE Bellows J Colmery B Conway ML Knutson K Vitoux J;AAHA 《Journal of the American Animal Hospital Association》2005,41(5):277-283
The purpose of this document is to provide guidelines for the practice of companion animal dentistry for the veterinary profession. Dental care is necessary to provide optimum health and quality of life. Diseases of the oral cavity, if left untreated, are often painful and can contribute to other local or systemic diseases. This paper includes guidelines for materials and equipment, dental cleaning and evaluation, client communication, and pet home care. 相似文献
48.
49.
50.
Use of a jugular vein autograft for reconstruction of the cranial vena cava in a dog with invasive thymoma and cranial vena cava syndrome 总被引:1,自引:0,他引:1
Holsworth IG Kyles AE Bailiff NL Hopper K Long C Ilkiw JE 《Journal of the American Veterinary Medical Association》2004,225(8):1205-10, 1196
A spayed female dog was evaluated because of edema of the ventral cervical region, lethargy, cough, and reduced exercise tolerance. Invasive thymoma and cranial vena cava syndrome were diagnosed by use of ultrasound-guided fine-needle biopsy and contrast-enhanced helical computed tomography. Resection of the cranial vena cava and an autogenous jugular vein graft were used for restoration of normal venous return to the right atrium and alleviation of the cranial vena cava syndrome. 相似文献