全文获取类型
收费全文 | 280147篇 |
免费 | 16431篇 |
国内免费 | 4404篇 |
专业分类
林业 | 26385篇 |
农学 | 17776篇 |
基础科学 | 5757篇 |
46172篇 | |
综合类 | 39674篇 |
农作物 | 19398篇 |
水产渔业 | 17867篇 |
畜牧兽医 | 94455篇 |
园艺 | 8128篇 |
植物保护 | 25370篇 |
出版年
2022年 | 2717篇 |
2021年 | 4059篇 |
2020年 | 4358篇 |
2019年 | 5152篇 |
2018年 | 4775篇 |
2017年 | 5866篇 |
2016年 | 5965篇 |
2015年 | 6180篇 |
2014年 | 7549篇 |
2013年 | 18383篇 |
2012年 | 8590篇 |
2011年 | 10575篇 |
2010年 | 10008篇 |
2009年 | 10233篇 |
2008年 | 9234篇 |
2007年 | 7977篇 |
2006年 | 8361篇 |
2005年 | 7200篇 |
2004年 | 6462篇 |
2003年 | 6091篇 |
2002年 | 5549篇 |
2001年 | 5750篇 |
2000年 | 5397篇 |
1999年 | 5117篇 |
1998年 | 4373篇 |
1997年 | 4355篇 |
1996年 | 4066篇 |
1995年 | 4589篇 |
1994年 | 3993篇 |
1993年 | 3695篇 |
1992年 | 4140篇 |
1991年 | 4280篇 |
1990年 | 4048篇 |
1989年 | 4055篇 |
1988年 | 3573篇 |
1987年 | 3569篇 |
1986年 | 3440篇 |
1985年 | 3816篇 |
1984年 | 3566篇 |
1983年 | 3384篇 |
1982年 | 2851篇 |
1981年 | 2796篇 |
1980年 | 2740篇 |
1979年 | 3141篇 |
1978年 | 2829篇 |
1977年 | 2641篇 |
1976年 | 2494篇 |
1974年 | 2599篇 |
1973年 | 2495篇 |
1972年 | 2365篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Soil protection for a sustainable future: options for a soil monitoring network for Ireland 下载免费PDF全文
The increased recognition of the importance of soil is reflected in the UN Post‐2015 Development Agenda with sustainable development goals that directly and indirectly relate to soil quality and protection. Despite a lack of legally binding legislation for soil protection, the European Commission remains committed to the objective of soil protection. However, the achievement of a legally binding framework for soil protection relies on the implementation of a soil monitoring network (SMN) that can detect changes to soil quality over time. As beneficiaries do not pay for the provision of soil information, the options for soil monitoring are limited. The use of existing data sets should be considered first. Using Ireland as an example, this research explored the opportunities for a SMN for Ireland considering three existing national data sets. The options for a SMN are considered in terms of their spatial and stratified distribution, the parameters to be measured and an economic analysis of the options proposed. This research finds that for Ireland, either a 10 or a 16 km2 grid interval stratified by land use and drainage class offers the best potential in relation to the spatial distribution of existing data sets to reflect local data at a national level. With existing data, the stratified SIS data using the 16 km2 grid offers the best value for money, with baseline costs for analysis, excluding field costs, of between €706 481 and €2.8 million. Acknowledging the impossibility of measuring all parameters with ideal frequency, this study proposes a two‐tier system for optimized monitoring frequency. Parameters must anticipate future policy requirements. Finally, the implementation of a SMN must be accompanied by standardized methods, defined thresholds and action mandates to maintain soil quality within allowable limits. 相似文献
22.
23.
In a feeding trial lasting for months Halothane-positive fattening pigs were put on a diet containing different concentrations of vitamin E and selenium. After a Myostress application vitamin E and selenium were additionally injected in order to examine stress resistance (CK-test) and regenerative capacity (histological examination of Musculus longissimus dorsi) of skeletal muscle. The study revealed that neither high dietary levels of vitamin E/selenium nor a vitamin E/selenium treatment applied after stress are capable of preventing stress related myopathy nor can they influence its healing up favourably. 相似文献
24.
25.
R W Blowey 《The Veterinary record》1992,131(14):312-315
Thirteen chronically lame female breeding pigs were examined clinically and post mortem. Of the eight sows with hindleg lameness, one showed detachment of the ischial tuberosity and a second showed detachment of the ischial tuberosity on the left and a mid-shaft femoral fracture on the right. Two showed no lesions apart from a change in the positional relationship between the femoral head and the greater trochanter, resulting in a lowering of the femoral head. In the remaining four sows an apparently unreported condition was seen, which produced a proliferative osteitis of the greater trochanter. All five animals lame in the forelimb showed varying degrees of proliferative osteitis of the medial epicondyle of the humerus. Advanced cases could be palpated in the live animal. It is proposed that proliferative osteitis may be a response, at the point of attachment of the muscle masses of the major limbs, to the trauma of over exertion. 相似文献
26.
M C Vickers W J Hartley R W Mason J P Dubey L Schollam 《Journal of the American Veterinary Medical Association》1992,200(11):1723-1725
Seven of 30 canaries in an aviary in New Zealand developed ophthalmic problems. Clinically, 5 birds had unilateral and 2 birds had bilateral lesions characterized by conjunctivitis, crusty exudates on eyelids, and collapse of the eyeball. Microscopic lesions in 12 of 14 eyes examined included inflammation of the choroid and retina, with osseous replacement of the globe in some. Numerous Toxoplasma gondii tachyzoites were seen in the detached retina and vitreous humor of acutely affected birds. The diagnosis of toxoplasmosis was confirmed by immunohistochemical staining with T gondii antiserum. Affected birds had encephalitis, and T gondii was localized in the brains of these by immunohistochemical examination and by use of bioassays in mice. Toxoplasmosis should be considered in differential diagnosis of ophthalmitis in canaries. 相似文献
27.
Differences in gas exchange parameters i.e. carbon exchange rate (CER), transpiration (Tr), water vapor conductance (g) were investigated, under a controlled environment, in a semi-dwarf (SD) Triticum aestivum line, its tall (TL) near isoline and the Payne (PA) variety characterized by small leaves. The plants were maintained in: (a) optimal substrate moisture condition (CTR); (b) salinized by watering with a 0.12 m NaCl solution (SLT); (c) water stressed by withholding waterings during a period of six days (STR); (d) stressed and salinized during the same period and with the same saline solution (S + S). CER and Tr were negatively affected by the stresses; SLT and S + S treatments had a higher WUE compared to their respective controls CTR and STR.
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO2 concentration curves contributed to explaining the SD performance. 相似文献
SD line had a better performance in terms of CER and WUE, particularly when water and salt stresses interacted. Leaf anatomy and assimilation/internal CO
28.
29.
Abstract. A humoral antibody response was demonstrated by ELISA in rainbow trout immunized intraperitoneally with extracts from the branchiuran ectoparasite Argulus foliaceus. A similar immunization protocol produced a higher titre response in a rabbit. Both trout and rabbit identified several antigenic components on immunoblots. ELISA and immunoblotting indicated that rainbow trout and rabbit anti-A. foliaceus sera identified components from the parasitic copepods Lepeophtheirus salmonis and Caligus elongatus. 相似文献
30.