全文获取类型
收费全文 | 250篇 |
免费 | 38篇 |
专业分类
林业 | 8篇 |
农学 | 2篇 |
17篇 | |
综合类 | 23篇 |
农作物 | 15篇 |
水产渔业 | 5篇 |
畜牧兽医 | 189篇 |
园艺 | 12篇 |
植物保护 | 17篇 |
出版年
2021年 | 2篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 10篇 |
2010年 | 9篇 |
2009年 | 13篇 |
2008年 | 6篇 |
2007年 | 13篇 |
2006年 | 11篇 |
2005年 | 6篇 |
2004年 | 10篇 |
2003年 | 11篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 3篇 |
1984年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1967年 | 3篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1964年 | 2篇 |
1963年 | 3篇 |
1960年 | 2篇 |
1941年 | 2篇 |
排序方式: 共有288条查询结果,搜索用时 15 毫秒
281.
P. Smith R. Milne D.S. Powlson J.U. Smith P. Falloon K. Coleman 《Soil Use and Management》2000,16(4):293-295
Abstract. The soil sequestration components of recent estimates of the carbon mitigation potential of UK agricultural land were calculated on the basis of a percentage change to the soil carbon stock present in the soil. Recent data suggest that the carbon stock of soil in UK arable land has been overestimated, meaning that potential soil carbon sequestration rates were also overestimated. Here, we present a new estimate of the carbon stock in UK arable land, and present revised estimates for the carbon mitigation potential of UK agricultural land. The stock of soil organic carbon in UK arable land (0–30 cm) is estimated to be 562 Tg, about half of the previous estimate. Consequently, the soil carbon sequestration component of each mitigation option is reduced by about half of previously published values. Since above-ground carbon accumulation and fossil fuel carbon savings remain unchanged by these new soil carbon data, options with a significant non-soil carbon mitigation component are reduced by less than those resulting from soil carbon sequestration alone. The best single mitigation option (bioenergy crop production on surplus arable land) accounts for 3.5 Tg C yr−1 , (2.2% of the UK's 1990 CO2 -carbon emissions), whilst an optimal combined land-use mitigation option accounts for 6.1 Tg C yr−1 (3.9% of the UK's 1990 CO2 -carbon emissions). These revised figures suggest that through manipulation of arable land, the UK could, at best, meet 49% of its contribution to the EU's overall Kyoto CO2 -carbon emission reduction target (8% of 1990 emissions), and 31% of the greater target accepted by the UK (12.5%). Even these reduced estimates show a significant carbon mitigation potential for UK arable land. 相似文献
282.
283.
A 5‐year‐old Arabian stallion was managed for breeding with fresh/extended semen during a period of 8 months with a resulting per cycle pregnancy rate of 26.3%. The stallion was in good health and no abnormalities of the reproductive tract were observed. Evaluation of several ejaculates revealed that sperm production and semen quality were mostly unchanged during the period of evaluation, that sperm production was normal and that semen quality was extremely poor. The most prevalent sperm defects were abnormal heads and mid‐pieces. Most abnormal heads were microcephalic and/or tapered and considerable variation in sperm head dimensions within and among ejaculates was observed. A unique defect characterized by swollen/roughened mid‐piece caused by accumulation of cytoplasmic‐like material and abnormal mitochondrial sheath was observed. Nuclear vacuoles, acrosome defects, and teratoids were also prevalent and most sperm presented multiple abnormalities. The absence of any clear cause or any signs of testicular degeneration, combined with normal sperm production, and constant abnormal sperm production suggest an inherent, congenital disturbance of spermatogenesis as the cause of teratospermia in this case. 相似文献
284.
The United Nations Framework Convention on Climate Change andits Kyoto Protocol (KP) have created a clear need for methodsthat enable accurate accounting of carbon (C) stocks and stockchanges in forest ecosystems. The rate of accumulation of Cin plantation forests in the Republic of Ireland was estimatedfor the period 19062002 using the record of afforestationand a dynamic C accounting model (C-flow). Projections for theperiod 20032012 were made using different afforestationrates. It was assumed that Sitka spruce planted in the period19061989 was Yield Class (YC) 16 m3 ha1 year1and that after 1990 this increased to 20 m3 ha1 year1.All other conifers were assumed to have the growth characteristicsof YC 8 m3 ha1 year1 lodgepole pine. Broadleaveswere assumed to have the growth characteristics of YC 6 m3 ha1year1 beech. In 2002, the total forest C stock was 37.7Mt C representing an increase of 14.8 Mt C since 1990. In 2002,the rate of increase in trees, products, litter and soil was0.7, 0.1, 0.1 and 0.5 Mt C, respectively. Under a business-as-usualscenario, afforestation since 1990 is estimated to create anannual average C sink of 0.9 Mt C year1 during the period20082012. This accounts for 22 per cent of Ireland'sreduction commitment under the KP. Afforestation on peat soilswas found to reduce the net C sink, although the extent to whichit does so is highly dependent on assumptions regarding therate of peat C loss. 相似文献
285.
Recent work in landscape ecology suggests that organisms use environmental cues at a variety of scales to select habitat. As a result, habitat studies that evaluate environmental conditions at multiple spatial scales have become increasingly common. We examined whether the way in which data are rescaled influences inferred relationships between organisms and habitat features. Using a habitat model developed at fine scales, we systematically rescaled habitat (canopy density, slope, and cover type) and distribution maps according to a variety of different rescaling rules, including spatial averaging, thresholding, presence/absence, and majority. We found that the spatial autocorrelation of habitat data interacts with rescaling rules to alter the correspondence between species presence and habitat across scale. Different rules lead to substantially divergent and sometimes opposite correlations among the species and habitat features on the landscape. Such differences in interpretation due to variation in methodology can lead to very different interpretations of a species habitat requirements and thus have important implications for both ecology and conservation. 相似文献
286.
287.
Clinical enzymology studies the enzyme activity in serum or other body fluids for the diagnosis, prognosis or monitoring of a variety of diseases. Clinical enzymology has greatly benefited from advances in technology and is now an integral part of laboratory analysis. However, to maximise the clinical benefits of serum enzyme measurement, clinicians and clinical pathologists must have a good understanding of the pathophysiology behind serum enzyme alterations. They must also be aware of the preanalytical and analytical factors that can affect the accuracy of serum enzyme activity measurement. This review article first covers the basic concepts of clinical enzymology and the general mechanisms related to serum enzyme alterations. Then, the review discusses the potential effects of various preanalytical and analytical factors on enzyme activity measurement. Lastly, it explores the pathophysiology and clinical use of various serum enzymes in canine and feline medicine. The present review article aims to be a comprehensive one-stop source for clinical pathologists and small animal practitioners. 相似文献
288.
This case report describes the successful management of a stingray laceration and suspected envenomation using a combination of opioid analgesia, heat compression, antimicrobial therapy, surgical debridement and closure. Stingray envenomation in the dog is a rare clinical presentation and is yet to be documented in the Australian veterinary literature. Envenomation can be markedly painful and may cause swelling and local tissue necrosis. No consensus on treatment guidelines has been published. Diagnostics and treatments performed are outlined with recommendations on a management plan for future cases. 相似文献