全文获取类型
收费全文 | 1710篇 |
免费 | 123篇 |
专业分类
林业 | 79篇 |
农学 | 31篇 |
基础科学 | 4篇 |
352篇 | |
综合类 | 166篇 |
农作物 | 87篇 |
水产渔业 | 136篇 |
畜牧兽医 | 804篇 |
园艺 | 60篇 |
植物保护 | 114篇 |
出版年
2024年 | 11篇 |
2023年 | 36篇 |
2022年 | 30篇 |
2021年 | 73篇 |
2020年 | 86篇 |
2019年 | 81篇 |
2018年 | 56篇 |
2017年 | 56篇 |
2016年 | 68篇 |
2015年 | 62篇 |
2014年 | 67篇 |
2013年 | 68篇 |
2012年 | 142篇 |
2011年 | 151篇 |
2010年 | 77篇 |
2009年 | 69篇 |
2008年 | 125篇 |
2007年 | 110篇 |
2006年 | 91篇 |
2005年 | 72篇 |
2004年 | 68篇 |
2003年 | 71篇 |
2002年 | 67篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有1833条查询结果,搜索用时 15 毫秒
131.
132.
Laura Volterra Lucia Bonadonna Francesca Anna Aulicino 《Water, air, and soil pollution》1986,29(4):403-413
The usual media and procedures were followed to measure the concentration of fecal streptococci (MPN on Azide Dextrose and Ethyl Violet Azide broths, membrane filtration on m-Enterococcus, KF and Pfizer Selective Enterococcus agars and according to the mE procedure) in samples collected along two different marine areas. The results were evaluated on the basis of three parameters: total concentrations, number of enterococci-like colonies (namely colonies gram positive, catalase negative, coccus shaped) and rate of strictly named fecal streptococci. From the results it appears that the various media and procedures employed gave different yields and their capacity to measure fecal streptococci varies according to the origin of samples. The accompanying bacterial flora may play an important role on the selectivity of each technique to measure the fecal streptococci. 相似文献
133.
Erin Nelson Laura Gómez Tovar Rita Schwentesius Rindermann Manuel Ángel Gómez Cruz 《Agriculture and Human Values》2010,27(2):227-237
Over the past two decades the growth of the organic sector has been accompanied by a shift away from first party, or peer
review, systems of certification and towards third party certification, in which a disinterested party is responsible for
the development of organic standards and the verification of producer compliance. This paper explores some of the limitations
of the third party certification model and presents the case of Mexico as an example of how an alternative form of participatory
certification has emerged. The paper suggests that participatory guarantee systems (PGS) are reflective of the growing “beyond
organic” movement, which focuses on reconstructing the local and re-embedding food systems into their socio-ecological contexts.
It argues that PGS offers a number of benefits for producers and consumers, particularly in the South, but that it faces a
number of challenges as well, such as a lack of formal recognition, social conflicts and dependence on donated resources. 相似文献
134.
FDI in Space Revisited: The Role of Spillovers on Foreign Direct Investment within the European Union 下载免费PDF全文
Luisa Alamá‐Sabater Benedikt Heid Eduardo Jiménez‐Fernández Laura Márquez‐Ramos 《Growth and change》2017,48(3):390-408
We estimate a spatial econometric interaction model for bilateral aggregate FDI stock data between 25 European Union member countries in 2010. We find evidence for spatial spillovers of foreign direct investment for three different types of spatial dependence. Our results document FDI spillovers between neighboring countries of FDI origin countries, neighboring countries of FDI destination countries as well as between neighboring countries of both FDI origin and destination countries. Relying on recently developed methods, we provide the first model‐consistent interpretation of marginal effects of market size (measured by GDP) as well as GDP per capita on bilateral FDI activity. Our research highlights the importance of taking into account spatial lags when estimating bilateral FDI gravity models. 相似文献
135.
Lindroos Antti-Jussi Derome John Paavolainen Laura Helmisaari Heljä-Sisko 《Water, air, and soil pollution》2001,131(1-4):153-167
In this article, the effects of the artificialrecharging of groundwater by infiltrating surface water throughforest soil, i.e. sprinkling infiltration, on the acidity andbase cation status of the soil are described. The study wascarried out in the Ahvenisto esker area, Hämeenlinna,southern Finland, during 1996–1998. The sample plots werelocated in a 110- to 160-yr-old Scots pine (Pinussylvestris L.) stand. The site was classified as the Oxalis-Maianthemum type. The soil consisted of a mixture oftill and glaciofluvial sediments. The pH of the organic layerincreased from 4.7 to >6.5 soon after the start of irrigationon the infiltration plot. The pH of the 0–10 cm mineral soillayer also increased from 4.9 to 6.4 as a result ofinfiltration. Sprinkling infiltration increased theexchangeable Ca and Mg concentrations in the organic anduppermost mineral soil layers. The output of Ca and Mg inpercolation water from the 0–100 cm thick layer was lower thanthe input to the soil surface via irrigation in 1996. Theretention of Ca and Mg on cation exchange sites took placewithin a relatively short period of time, since retention wasobserved only in 1996 but no longer in 1997 or 1998 indicatingsaturation of the cation exchange sites by base cations. Lakewater infiltration leads to the neutralisation of forest soilacidity, and increases the capacity of the soil to withstandacidic inputs by increasing the concentrations of exchangeablebase cations on cation exchange sites in the soil. 相似文献
136.
Redesigning IT systems for specific user groups encompasses a lot of effort with respect to analysing and understanding user behaviour. The goal of this paper is to provide insights into patterns of behaviour of agricultural users, during the usage of a decision support system called OPTIRas™. This system aids agricultural users in their cultivar selection activities. We analyse logs resulting from OPTIRas™, and we get insights into user’s navigational patterns. We claim that the results of our analysis can be used to support the redesign of decision support systems in order to address specific agricultural users’ characteristics. 相似文献
137.
Optimized denitrification bioreactor treatment through simulated drainage containment 总被引:1,自引:0,他引:1
In the design of wood-based, enhanced-denitrification bioreactors to treat nitrate in agricultural drainage, the consideration of the highly variable flow rates and nitrate concentrations inherent to many drainage systems is important. For optimized mitigation of these nitrate loads, it may be best to contain drainage water prior to treatment in order to facilitate longer, more constant retention times rather than to allow cycles of flushing and dry periods in the denitrification bioreactor. Simulated containment prior to bioreactor treatment compared to passing drainage directly through a bioreactor was investigated with the use of six pilot-scale denitrification bioreactors constructed with plywood and filled with Pinus radiata woodchips at Massey University No. 4 Dairy Farm (Palmerston North, New Zealand). Initial bromide tracer tests were followed with a series of five simulated drainage events each at successively declining inflow nitrate concentrations. During each drainage event, three pilot bioreactors received a simulated hydrograph lasting 1.5 days (Non-Containment treatment) and three pilot bioreactors received the same total drainage volume treated over 4 days at a constant flow rate (i.e. constant retention time; Containment treatment). Results showed significantly different total mass removal efficiencies of 14.0% vs. 36.9% and significantly different removal rates of 2.1 g N m−3 day−1 vs. 6.7 g N m−3 day−1 for the Non-Containment and Containment treatments, respectively, which indicated that treating drainage at constant retention times provided more optimized nitrate removal. While this work was done to evaluate treatment under New Zealand drainage conditions, it also provides valuable information for optimizing agricultural drainage denitrification bioreactor performance in general. 相似文献
138.
In this paper, we present highly disaggregated estimates of expenditure‐based poverty in Fiji using data from the 2007 national census and 2008–2009 Household Income and Expenditure Survey. Predicted poverty is estimated at provincial and tikina levels. Poverty in Fiji is marked by considerable spatial heterogeneity that cannot be gauged by the division level household survey estimates revealing pockets of poverty even within relatively well‐off regions. Predicted poverty is highest in Cakaudrove province in Northern Division. Most strikingly, we find that 50% of all the poor in Fiji are concentrated in just 6 out of 85 tikinas, namely Suva, Labasa, Ba, Naitasiri, Vuda and Nadi. This finding has important implications for efficiency of targeted poverty alleviation programmes. We also focus on squatter settlements for which poverty headcount estimates using the Household Income and Expenditure Survey are not feasible. We find these settlements have rates of poverty headcount ratio that range from 38–55% depending on the Division the squatter settlement is located in; this range is significantly higher compared with the average urban poverty estimated at 26% and raises important social policy issues for addressing urban poverty. 相似文献
139.
140.
Eckert RE Neuder LE Bell JL Trujillo JC Jones SL 《Veterinary immunology and immunopathology》2007,118(3-4):294-303
The goal of this study was to define the role for p38 mitogen-activated kinase (MAPK) in the signaling mechanism regulating pro-inflammatory cyclooxygenase (COX) gene expression in lipopolysaccharide (LPS)-activated equine leukocytes for the purposes of identifying novel targets for anti-inflammatory therapy in endotoxemic horses. The p38 MAPK has been shown to positively regulate inflammatory gene expression in human leukocytes and can be activated by a variety of stimuli including LPS, TNF-alpha, and IL-1. Activation-associated phosphorylated p38 MAPK has been implicated in the up-regulation of several inflammatory genes, including COX-2 which ultimately results in the production of prostanoids that are responsible for the pathophysiology associated with endotoxemia. Our hypothesis is that activation of p38 MAPK is essential for LPS-induced COX-2 expression in equine peripheral blood leukocytes. We tested our hypothesis by investigating the effects of the specific p38 MAPK inhibitors SB203580 and SB202190 on LPS-induced COX-2 protein expression and PGE(2) production in equine leukocytes. LPS stimulation activated p38 MAPK and increased COX-2 expression in a dose-dependent manner with maximal activation observed after 30min and 4h, respectively, at a concentration of 10 ng/ml LPS. In contrast, LPS stimulation did not affect COX-1 protein expression. Pretreatment with SB203580 or SB202190 significantly inhibited LPS-induced activation-associated p38 MAPK phosphorylation, COX-2 mRNA and protein levels, and PGE(2) production in equine leukocytes. Maximal inhibition of LPS-induced COX-2 protein expression was achieved at a concentration of 10 microM SB203580. We concluded that p38 MAPK is essential for LPS-induced COX-2 expression suggesting that p38 MAPK is a potential target for anti-inflammatory therapy during equine endotoxemia. 相似文献