全文获取类型
收费全文 | 370篇 |
免费 | 34篇 |
专业分类
林业 | 36篇 |
农学 | 11篇 |
基础科学 | 2篇 |
87篇 | |
综合类 | 19篇 |
农作物 | 19篇 |
水产渔业 | 63篇 |
畜牧兽医 | 130篇 |
园艺 | 13篇 |
植物保护 | 24篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 27篇 |
2019年 | 12篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 15篇 |
2015年 | 17篇 |
2014年 | 15篇 |
2013年 | 30篇 |
2012年 | 22篇 |
2011年 | 39篇 |
2010年 | 27篇 |
2009年 | 15篇 |
2008年 | 23篇 |
2007年 | 14篇 |
2006年 | 21篇 |
2005年 | 10篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1981年 | 1篇 |
1968年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 31 毫秒
401.
The technique of diffusive gradients in thin films or diffusive gradient in thin films (DGT) has been used in this work for the in situ measurement of labile Cr(III) and Cr(VI) species. Direct measurement of Cr(VI) was also carried out in parallel with a field-based colourimetric technique based on the EPA 7196 diphenyl-carbohydrazide (DPC) method. The efficiency of the DGT and DPC methods were tested (a) in the laboratory, using synthetic solutions in the presence of realistic concentrations of Cr, humic substances (HS), and ethylenediaminetetraacetic acid (EDTA), and (b) in the field, in river water affected by effluents discharged by the tannery industry. The main advantage of the DGT method is that it allows the in situ separation of labile species of Cr(III) and Cr(VI), though there are still uncertainties about its performance in field conditions. The DPC method proved to be a fast, accurate, and relatively economical option for the field-based determination of Cr(VI). Sample acidification and ageing of unacidified samples from contaminated aquatic environments, produced significant errors in the determination of ‘dissolved’ Cr. The concentration of Cr(VI) determined by either the DGT or the DPC method exceeds recommended international guidelines. 相似文献
402.
Sergio Tonolli Michele Dalponte Loris Vescovo Mirco Rodeghiero Lorenzo Bruzzone Damiano Gianelle 《European Journal of Forest Research》2011,130(4):569-577
In this paper, we present a study on the efficiency of multi-return LIDAR (Light Detection Ranging) data in the estimation
of forest stem volume over a multi-layered forest area in the Italian Alps. The goals of this paper are (1) to verify the
usefulness of multi-return LIDAR data compared to single-return data in forest volume estimation and (2) to define the optimal
resolution of a stem volume distribution raster map over the investigated area. To achieve these goals, raw data were segmented
into a net, and different cell dimensions were investigated to maximize the relationship between the LIDAR data and the ground-truth
information. Twenty predicting variables (e.g., mean height, coefficient of variation) have been extracted from multi-return
LIDAR data, and a multiple linear regression analysis has been used for predicting tree stem volume. Experimental results
found that the optimal resolutions of the net square cells were 40 m. The analysis indicated that in a mixed multi-layered
forest, characterized by a complex vertical structure, the correct selection of the map spatial resolution and the inclusion
of the secondary-return data were important factors for improving the effectiveness of the laser scanning approach in forest
inventories. The experimental tests showed that the chosen model is effective for the estimation of stem volume over the analyzed
area, providing good results on all the three considered validation methods. 相似文献
403.
Toncian T Borghesi M Fuchs J d'Humières E Antici P Audebert P Brambrink E Cecchetti CA Pipahl A Romagnani L Willi O 《Science (New York, N.Y.)》2006,312(5772):410-413
We present a technique for simultaneous focusing and energy selection of high-current, mega-electron volt proton beams with the use of radial, transient electric fields (10(7) to 10(10) volts per meter) triggered on the inner walls of a hollow microcylinder by an intense subpicosecond laser pulse. Because of the transient nature of the focusing fields, the proposed method allows selection of a desired range out of the spectrum of the polyenergetic proton beam. This technique addresses current drawbacks of laser-accelerated proton beams, such as their broad spectrum and divergence at the source. 相似文献
404.
Borruso Luigimaria Esposito Alfonso Bani Alessia Ciccazzo Sonia Papa Marianna Zerbe Stefan Brusetti Lorenzo 《Journal of Soils and Sediments》2017,17(1):253-265
Journal of Soils and Sediments - Spatial distribution on a regional scale of the rhizobacterial communities of Phragmites australis stands was investigated along the Yellow River watershed, China.... 相似文献