全文获取类型
收费全文 | 481篇 |
免费 | 30篇 |
专业分类
林业 | 60篇 |
农学 | 14篇 |
基础科学 | 4篇 |
71篇 | |
综合类 | 55篇 |
农作物 | 30篇 |
水产渔业 | 62篇 |
畜牧兽医 | 147篇 |
园艺 | 32篇 |
植物保护 | 36篇 |
出版年
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 8篇 |
2019年 | 20篇 |
2018年 | 12篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 16篇 |
2014年 | 14篇 |
2013年 | 24篇 |
2012年 | 24篇 |
2011年 | 26篇 |
2010年 | 18篇 |
2009年 | 18篇 |
2008年 | 28篇 |
2007年 | 27篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 26篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2000年 | 9篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 10篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 5篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1969年 | 2篇 |
1962年 | 2篇 |
1960年 | 3篇 |
1959年 | 2篇 |
1958年 | 2篇 |
排序方式: 共有511条查询结果,搜索用时 15 毫秒
81.
82.
Kouassi N’Guessan Louis Berenger Yao Koffi Marcellin Sangare Naminata Trokourey Albert Metongo Bernard Soro 《Journal of Soils and Sediments》2019,19(2):929-944
Journal of Soils and Sediments - Trace metals accumulate in the food web and can pose high risks to human health and aquatic biota. We investigated seasonal and spatial variations of Cu, Zn, Pb,... 相似文献
83.
Contribution of technic materials to the mobile fraction of metals in urban soils in Marrakech (Morocco) 总被引:5,自引:2,他引:3
Hicham El Khalil Christophe Schwartz Ouafae Elhamiani Jochen Kubiniok Jean Louis Morel Ali Boularbah 《Journal of Soils and Sediments》2008,8(1):17-22
Background, Aim and Scope In urban areas, soils are often dramatically altered by anthropogenic activity and these modifications distinguish these soils
(Anthrosols, Technosols) from those in natural systems. In urban environments, they receive considerable pollution from industry,
traffic and refuse. Since contaminated soil particles can be easily inhaled or ingested, there is a potential transfer of
toxic pollutants to humans. Risk assessment is essentially based on the determination of the total or mobile contents of pollutants
in soils using chemical extractions. This approach could be improved by taking into consideration the bioavailable fractions
of these toxic elements as measured by biotests. The coarse soil fraction usually neglected in analyses can nevertheless have
an effect on the concentration of metals in the soil solution. This coarse fraction is made up of the natural materials and
of technic materials constituting anthropogenic soils (plastic, paper, fabric, wood, bones, metallic elements and building
materials). These materials have variable capacities to release or adsorb trace elements. Samples representative of different
technic fraction components of Marrakech urban soils permit one to quantify their contribution to the enrichment of the soluble
metal concentrations. Works are carried out to achieve partial extractions of metals from the three fractions (less than 2
mm, coarse natural and coarse technic) of selected urban soils in order to determine their contribution to the metal contamination
of soils.
Materials and Methods Selected soils were collected from 9 sites according to a gradient of increasing anthropogenic influence from suburban to
urban zones. Soils were air-dried, homogenized, and sieved (2 mm). The coarse fraction was sorted to separate the different
technic materials and natural materials. Water extractions were run, on the natural, coarse fraction, on the complete technic
fraction of the 9 soils and on average samples made of technic materials sorted out of 58 topsoils sampled from different
sites in the city of Marrakech.
Results Results show that the percentage of the technic fraction increases while approaching the historic city center. It represented
about 14% in the most anthropogenically disturbed soils. Along this gradient, soils changed progressively from Anthrosols
to Technosols according to the WRB classification of urban and industrial soils. Analyses of metal contents showed that the
fine fraction (<2 mm) mainly contributed to the metallic contamination of the water soluble fraction. The natural coarse fraction
had the highest contribution to the copper release and was responsible for the release of all water-extractable copper in
some soils. Concerning the technic fraction, it has a significant contribution essentially in the most anthropogenically disturbed
soils as characterized by an elevated percentage of anthropogenic elements. The water extractable metal contents of average
samples of these anthropogenic elements shows that elevated metal concentrations were released by bones, wood, plastic and
fabric/paper.
Discussion This study concerns soils in urban areas, which are strongly impacted by human activities. Part of the soils can be classified
as Anthrosols, profoundly impacted through the addition of organic materials from household wastes, irrigation, or cultivation.
Other soils strongly impacted by human activities are Technosols dominated or strongly influenced by man-made materials. Technosols
appear mostly in urban and industrial areas and are more likely to be contaminated than Anthrosols. The composition and heterogeneity
of urban soils lead to modifications of the mobility and availability of pollutants depending on successive land-uses and
on the composition of technic materials. The fine fraction offers a high transferring surface capacity, leading to a high
mobilization of metals. The technic fraction contributes significantly to the metal release in the Technosols. This property
can be explained by a reversible adsorption of metals on the organic matter.
Conclusions Results confirm that anthropogenic activity causes a wide spatial diversity of soil quality in the urban and suburban area.
It introduces large amounts of technic materials in soils that could have an impact on the metal availability. It therefore
acts on the metal bioavailability in the urban Technosols.
Recommendations and Perspectives These results show that it is necessary, in addition to the characterization of the fine particles, to take into account the
contribution of the coarse fraction of the Technosols in the evaluation of risks of transfer of metals to the food chain. 相似文献
84.
Isabelle Le Viol Romain Julliard Louis de Redon Nathalie Machon 《Biological conservation》2008,141(6):1581-1590
Road verges should play a crucial role as a refuge for native flora and fauna in human dominated landscapes. However, the influence of construction choices, such as plantation of woody species, on the biodiversity supported by roadsides has received little attention, although the presence of hedgerows in roadsides is likely to enhance their role as a refuge, notably for woodland species. Using standardised methods, we assessed the impact of planted hedgerows on two taxonomic groups (plants and spiders) inhabiting highway verges within an intensive agricultural landscape. We examined community richness, taxonomic and functional composition in sites with and without planted hedgerows. At the site level, the response of plant and spider communities to the presence of planted hedgerows differed markedly: hedgerows were associated with significantly higher plant richness (higher α-diversity), but similar spider richness. Plant communities in sites without hedgerows appeared as a subset of communities in sites with hedgerows, whereas spider communities in non-planted sites were complementary to that of planted sites (increased β-diversity). The presence of planted hedgerows was also associated with increased taxonomic and functional trait diversity at the landscape level (γ-diversity), through an increased β-diversity in both plants and spiders. Our results thus suggest that a mosaic of planted hedgerows and grassland habitats is crucial for the maintenance of biodiversity at a landscape scale. By providing information for road practitioners and policy makers regarding their potential impact on biodiversity, these results have important direct implications for the management of road networks. 相似文献
85.
86.
Herdt TH Neuder LM Green CD Fordyce MG Dill KJ Mahoney JH 《Journal of veterinary medical education》2008,35(1):48-50
Cooperative programs with agribusiness offer opportunities for colleges of veterinary medicine to expand their instructional programs in agricultural practice. Agribusinesses associated with livestock agriculture recognize the importance of veterinary medicine in maintaining a vibrant and successful industry. Stewardship of corporate support involves close communication with advocates within the companies, providing them with documentation of the potential effects of corporate investments. This article describes the creation of the Michigan State University (MSU) Training Center for Dairy Professionals, a key aspect of which was the identification of innovative and productive areas of mutual interest and benefit. In addition to supporting the dairy industry by training veterinary students, the program offers specific benefits to investors, including the use of MSU facilities and direct participation in veterinary instruction. 相似文献
87.
88.
Arends B Spee B Hoffmann G Jansen GE Slump E Auriemma E Ijzer J Hemrika W Romijn RA van der Heijden-Liefkens KH Sondermeijer PJ van den Ingh TS Penning LC Rothuizen J 《Veterinary journal (London, England : 1997)》2008,178(1):70-77
Hepatocyte growth factor (HGF) is crucial for the development and regeneration of the liver and offers a possible new therapeutic strategy for the treatment of canine liver disease. In this study, the in vitro and in vivo bioactivity of recombinant canine HGF (rcHGF) produced with a baculoviral expression system in insect cells was measured. In vitro rcHGF induced mitogenesis, motogenesis, and phosphorylated the HGF receptor c-MET and its downstream mediators PKB and ERK1/2 in two canine epithelial cell lines. After a partial hepatectomy (phx) in dogs, rcHGF increased phosphorylation of c-MET, PKB and ERK1/2. A moderate increase was seen with the cell cycle protein PCNA in rcHGF treated livers, but no HGF-induced increase in liver weight was seen 7 days after phx. Furthermore, rcHGF treated livers showed lower levels of the key mediator of apoptosis, caspase-3, at 7days after phx. It is concluded that rcHGF is a biologically active protein in vitro and in vivo and the baculoviral expression system supplies sufficient amounts of rcHGF for future clinical studies in dogs. 相似文献
89.