全文获取类型
收费全文 | 222篇 |
免费 | 9篇 |
专业分类
林业 | 5篇 |
农学 | 18篇 |
5篇 | |
综合类 | 27篇 |
农作物 | 4篇 |
水产渔业 | 14篇 |
畜牧兽医 | 156篇 |
植物保护 | 2篇 |
出版年
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 5篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 5篇 |
2009年 | 9篇 |
2008年 | 11篇 |
2007年 | 1篇 |
2006年 | 5篇 |
2005年 | 5篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 12篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 10篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
1963年 | 1篇 |
1940年 | 2篇 |
1937年 | 1篇 |
1932年 | 1篇 |
1920年 | 1篇 |
排序方式: 共有231条查询结果,搜索用时 250 毫秒
81.
82.
83.
84.
85.
William A. Link Sarah J. Converse Amy A. Yackel Adams Nathan J. Hostetter 《Journal of Agricultural, Biological & Environmental Statistics》2018,23(4):463-477
In capture-mark-reencounter studies, Pollock’s robust design combines methods for open populations with methods for closed populations. Open population features of the robust design allow for estimation of rates of death or permanent emigration, and closed population features enhance estimation of population sizes. We describe a similar design, but for use with removal data. Data collection occurs on secondary sampling occasions clustered within primary sampling periods. Primary sampling periods are intervals of brief enough duration that it can be safely assumed that the population is unchanged by births, deaths, immigration or emigration during them; all population change and movement occurs between primary sampling periods. Our model provides a basis for inference about population size, changes in population size, and movement rates among sample locations between primary sampling periods. Movement rates are modeled as functions of distance and time. Capture probabilities are modeled as a function of effort. We apply the model to data obtained in attempting to eradicate an introduced population of veiled chameleons (Chamaeleo calyptratus) on the island of Maui in Hawaii.Supplementary materials accompanying this paper appear online. 相似文献
86.
Fish‐Net: Probabilistic models for fishway planning,design and monitoring to support environmentally sustainable hydropower 下载免费PDF全文
Martin Wilkes Lee Baumgartner Craig Boys Luiz G M Silva Justin O'Connor Matthew Jones Ivor Stuart Evelyn Habit Oscar Link J Angus Webb 《Fish and Fisheries》2018,19(4):677-697
The construction of fishways for upstream and downstream connectivity is the preferred mitigation measure for hydropower dams and other riverine barriers. Yet empirical evidence for effective design criteria for many species is missing. We therefore assembled a group of international fishway designers and combined their knowledge with available empirical data using a formal expert elicitation protocol and Bayesian networks. The expert elicitation method we use minimizes biases typically associated with such approaches. Demonstrating our application with a case‐study on the temperate Southern Hemisphere, we use the resulting probabilistic models to predict the following, given alternative design parameters: (i) the effectiveness of technical fishways for upstream movement of migratory fish; (ii) habitat quality in nature‐like bypasses for resident fish; and (iii) rates of mortality during downstream passage of all fish through turbines and spillways. The Fish Passage Network (Fish‐Net) predicts that fishways for native species could be near 0% or near 100% efficient depending on their design, suggesting great scope for adequate mitigation. Sensitivity analyses revealed the most important parameters as follows: (i) design of attraction and entrance features of technical fishways for upstream migration; (ii) habitat preferences of resident fish in nature‐like bypasses; and (iii) susceptibility of fish to barotrauma and blade strike during turbine passage. Numerical modelling predicted that mortality rates of small‐bodied fish (50–100 mm TL) due to blade strike may be higher for Kaplan than Francis turbines. Our findings can be used to support environmentally sustainable decisions in the planning, design and monitoring stages of hydropower development. 相似文献
87.
<正>用最具成本效益的方法配制猪饲料是提高养猪场经济利润的一种重要手段。但是,具有最低成本的饲料配制方法往往会就几种主要饲料原料的饲喂价值进行过于简单的假设,同时还假定各饲料原料的养分具有相加性。这种情况会因饲料添加剂的加入而进一步混乱,或受到潜在的损害,因为饲料添加剂旨在使饲料释放更多的能量和/或氨基酸。因此,饲料配方师不得不充分确保某种添加剂将持 相似文献
88.
The implementation of ecosystem management requires ecosystem modelling within the context of a natural resource management process. Ecopath with Ecosim (EwE) is the most widely used modelling platform for investigating the dynamics of marine ecosystems, but has played a limited role in fisheries management and in multi-sector resource decision-making. We review 10 case studies that demonstrate the use of EwE to support operational resource management. EwE models are being used to inform tactical decision-making in fisheries and other ocean use sectors, as well as to identify key trade-offs, develop appropriate policy objectives, and reconcile conflicting legislative mandates in a variety of ecosystems. We suggest the following criteria to enhance the use of EwE and other ecosystem models in operational resource management: (1) a clear management objective that can be addressed through modelling; (2) an important trade-off and a receptive policy context amenable to trade-off evaluation; (3) an accessible and well-documented model that follows best practices; (4) early and iterative engagement among scientists, stakeholders, and managers; (5) integration within a collaborative management process; (6) a multi-model approach; and (7) a rigorous review process. Our review suggests that existing management frameworks are as much or more of a limitation to the operational use of EwE than technical issues related to data availability and model uncertainty. Ecosystem models are increasingly needed to facilitate more effective and transparent decision-making. We assert that the requisite conditions currently exist for enhanced strategic and tactical use of EwE to support fisheries and natural resource management. 相似文献
89.
The atmospheric residence time for methyl bromide (CH3Br) has been estimated as 0.8 +/- 0.1 years from its empirical spatial variability relative to C2H6, C2Cl4, CHCl3, and CH3Cl. This evaluation of the atmospheric residence time, based on Junge's 1963 general proposal, provides an estimate for CH3Br that is independent of source and sink estimates. Methyl bromide from combined natural and anthropogenic sources furnishes about half of the bromine that enters the stratosphere, where it plays an important role in ozone destruction. This residence time is consistent with the 0.7-year value recently calculated for CH3Br from the combined strength estimates for its known significant sinks. 相似文献
90.
Three neonatal alpacas were treated for MCP flexural deformities. Two crias responded well to conservative therapy using splints made from fibreglass cast material. One cria with severe deformity failed to respond to conservative treatment but recovered satisfactorily after transection of the suspensory ligament in both legs. It seems that mild cases of flexural deformity of the MCP joint in alpaca crias respond well to conservative therapy but that surgical correction may be required in more severe cases. Sequential transection of the structures limiting extension of the MCP joint may result in fewer complications than previously reported techniques. 相似文献