全文获取类型
收费全文 | 82篇 |
免费 | 0篇 |
专业分类
林业 | 23篇 |
6篇 | |
综合类 | 4篇 |
农作物 | 3篇 |
水产渔业 | 5篇 |
畜牧兽医 | 36篇 |
园艺 | 2篇 |
植物保护 | 3篇 |
出版年
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 3篇 |
2011年 | 2篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 4篇 |
2007年 | 10篇 |
2006年 | 4篇 |
2005年 | 7篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有82条查询结果,搜索用时 15 毫秒
41.
42.
Joshua H. Goldstein Wayne E. Thogmartin Kenneth J. Bagstad James A. Dubovsky Brady J. Mattsson Darius J. Semmens 《Human Dimensions of Wildlife》2014,19(4):347-354
Migratory species provide economically beneficial ecosystem services to people throughout their range, yet often, information is lacking about the magnitude and spatial distribution of these benefits at regional scales. We conducted a case study for Northern Pintails (hereafter pintail) in which we quantified regional and sub-regional economic values of subsistence harvest to indigenous communities in Arctic and sub-Arctic North America. As a first step, we used the replacement cost method to quantify the cost of replacing pintail subsistence harvest with the most similar commercially available protein (chicken). For an estimated annual subsistence harvest of ?15,000 pintail, our mean estimate of the total replacement cost was ?$63,000 yr?1 ($2010 USD), with sub-regional values ranging from $263 yr?1 to $21,930 yr?1. Our results provide an order-of-magnitude, conservative estimate of one component of the regional ecosystem-service values of pintails, providing perspective on how spatially explicit values can inform migratory species conservation. 相似文献
43.
Amandine Caillaud Pablo de la Iglesia H. Taiana Darius Serge Pauillac Katerina Aligizaki Santiago Fraga Mireille Chinain Jorge Diogène 《Marine drugs》2010,8(6):1838-1907
Ciguatera fish poisoning (CFP) occurs mainly when humans ingest finfish contaminated with ciguatoxins (CTXs). The complexity and variability of such toxins have made it difficult to develop reliable methods to routinely monitor CFP with specificity and sensitivity. This review aims to describe the methodologies available for CTX detection, including those based on the toxicological, biochemical, chemical, and pharmaceutical properties of CTXs. Selecting any of these methodological approaches for routine monitoring of ciguatera may be dependent upon the applicability of the method. However, identifying a reference validation method for CTXs is a critical and urgent issue, and is dependent upon the availability of certified CTX standards and the coordinated action of laboratories. Reports of CFP cases in European hospitals have been described in several countries, and are mostly due to travel to CFP endemic areas. Additionally, the recent detection of the CTX-producing tropical genus Gambierdiscus in the eastern Atlantic Ocean of the northern hemisphere and in the Mediterranean Sea, as well as the confirmation of CFP in the Canary Islands and possibly in Madeira, constitute other reasons to study the onset of CFP in Europe [1]. The question of the possible contribution of climate change to the distribution of toxin-producing microalgae and ciguateric fish is raised. The impact of ciguatera onset on European Union (EU) policies will be discussed with respect to EU regulations on marine toxins in seafood. Critical analysis and availability of methodologies for CTX determination is required for a rapid response to suspected CFP cases and to conduct sound CFP risk analysis. 相似文献
44.
45.
Phiri BJ Benschop J Stevenson M Swai ES Karimuribo ED French NP 《Tropical animal health and production》2012,44(4):827-834
A combination of survival and spatial analyses was applied to a dataset containing cattle mortalities on smallholder dairy
farms in two separate regions (Tanga and Iringa) of Tanzania. Cattle mortality data for the year 1998 were collected retrospectively
during the period January to April 1999. The objectives of the current study were, firstly, to quantify the hazard of mortality
and, secondly, to investigate whether there was a spatial pattern in the variation that was unaccounted for in the hazard
of mortality. A Cox regression model with farm as a frailty term was used to quantify the hazard of mortality. Geostatistical
techniques were used to explore the first- and second-order spatial distribution of the farm frailty term. A total of 1,790
cattle from 400 randomly sampled smallholder dairy farms were included in the study. The overall mortality incidence rate
for the study was 11.8 per 100 animal years (95% CI 10.0–13.8). The hazard of mortality for male cattle was 2.4 (95% CI 1.7–3.4)
times higher than that of female cattle. There was evidence of a first-order spatial pattern, i.e., a tendency for farms with
higher frailty to aggregate. 相似文献
46.
The pathophysiology of anaphylaxis is very complex, and the sequelae of events are not fully explained in terms of the effects of histamine and peptide leukotrienes alone. Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine, PAF-acether) has been detected in animals undergoing anaphylaxis. Injection of synthetic PAF-acether induces similar effects, including bronchoconstriction, respiratory arrest, systemic hypotension, neutropenia, and thrombocytopenia. The results reported here demonstrate that the histamine- and leukotriene-independent component of guinea pig anaphylaxis in vivo and in isolated lung parenchymal strips in vitro is mediated by PAF-acether. However, PAF-acether is not responsible for the anaphylaxis-induced thrombocytopenia. 相似文献
47.
The physiological status of forest canopy foliage is influenced by a range of factors that affect leaf pigment content and function. Recently, several indices have been developed from remotely sensed data that attempt to provide robust estimates of leaf chlorophyll content. These indices have been developed from either hand-held spectroradiometer spectra or high spectral resolution (or hyperspectral) imagery. We determined if two previously published indices (Datt 1999), which were specifically developed to predict chlorophyll content in eucalypt vegetation by remote sensing at the leaf scale, can be extrapolated accurately to the canopy. We derived the two indices from hand-held spectroradiometer data of eucalypt leaves exhibiting a range of insect damage symptoms. We also derived the indices from spectra obtained from high spectral and spatial resolution Compact Airborne Spectrographic Imager 2 (CASI-2) imagery to determine if reasonable estimates at a scale of < 1 m can be achieved. One of the indices (R 850/R 710 index, where R is reflectance) derived from hand-held spectroradiometer data showed a moderate correlation with relative leaf chlorophyll content (r = 0.59, P < 0.05) for all dominant eucalypt species in the study area. The R (850)/R (710) index derived from CASI-2 imagery yielded slightly lower correlations over the entire data set (r = 0.42, P < 0.05), but correlations for individual species were high (r = 0.77, P < 0.05). A scaling analysis indicated that the R (850)/R (710) index was strongly affected by soil and water cover types when pixels were mixed, but appeared to be invariant to changes in proportions of understory, which may limit its application. 相似文献
48.
D. M. Phiri B. Coulman H. A. Steppler C. S. Kamara F. Kwesiga 《Agroforestry Systems》1993,23(1):79-84
The effect of feeding maize husk and leucaena as a mixture on voluntary intake of maize husk was studied over a 40-day period. Ten male goats with an average weight of 15 kg were used. The treatments were: (a) maize husk fed in a mixture with leucaena and (b) maize husk plus leucaena offered in separate troughs but at the same time. The maize husk intake and total dry matter intake for the two feeding methods were about the same. Thus total dry matter intake was not affected (P<0.05) by the method of feeding. There was also no significant difference (P<0.05) between the two methods of feeding in the digestibility values. The data were considered to indicate that there were no significant differences in the intake of maize husk when fed in a mixture withLeucaena leucocephala or when offered separately but at the same time. 相似文献
49.
D. M. Phiri B. Coulman H. A. Steppler C. S. Kamara F. Kwesiga 《Agroforestry Systems》1992,17(2):153-158
The effect of browse supplementation on maize husk (Zea mays) utilization by goats was studied in a 12 week feeding and 2 week digestibility trial. Twenty-four goats were stratified
according to their weight, and then randomly allocated to four treatments. Browse supplementation significantly increased
(P < 0.05) the total dry matter intake, diet dry matter digestibility and diet organic matter digestibility (P < 0.05) but
did not have any significant effect on acid detergent fibre digestibility (P > 0.05). The browse supplemented goats gained
more weight than the non browse supplemented goats. 相似文献
50.
This study considers a carbon tax system as a policy tool for encouraging carbon sequestration through modification of management in existing forests and examines its welfare impacts and costs of the carbon sequestered. The simulated carbon tax leads to reduced harvest and increased carbon stock in the standing trees and understory biomass. Changes in the level of silvicultural investments vary by owner, depending on the nature of their initial inventory. In general investment under the tax is concentrated in regimes that establish faster growing plantations. Average rotation age increases, varying in extent across ownerships and site qualities. The carbon tax reduces both consumer and producer surpluses in regional timber markets. Producers are compensated by the carbon subsidies, except at low carbon tax levels. Not all rates of carbon tax will attract interest from private owners if participation is voluntary. Estimates of the marginal cost of sequestering carbon in western Oregon private forests are shown to be within the range of costs for projects considering afforestation alone in some eastern regions of the United States. 相似文献