全文获取类型
收费全文 | 3784篇 |
免费 | 225篇 |
国内免费 | 419篇 |
专业分类
林业 | 215篇 |
农学 | 292篇 |
基础科学 | 336篇 |
1333篇 | |
综合类 | 1169篇 |
农作物 | 275篇 |
水产渔业 | 115篇 |
畜牧兽医 | 489篇 |
园艺 | 85篇 |
植物保护 | 119篇 |
出版年
2024年 | 13篇 |
2023年 | 65篇 |
2022年 | 88篇 |
2021年 | 106篇 |
2020年 | 114篇 |
2019年 | 141篇 |
2018年 | 88篇 |
2017年 | 149篇 |
2016年 | 167篇 |
2015年 | 138篇 |
2014年 | 171篇 |
2013年 | 250篇 |
2012年 | 302篇 |
2011年 | 265篇 |
2010年 | 242篇 |
2009年 | 279篇 |
2008年 | 248篇 |
2007年 | 292篇 |
2006年 | 210篇 |
2005年 | 208篇 |
2004年 | 113篇 |
2003年 | 117篇 |
2002年 | 81篇 |
2001年 | 61篇 |
2000年 | 79篇 |
1999年 | 52篇 |
1998年 | 56篇 |
1997年 | 46篇 |
1996年 | 53篇 |
1995年 | 48篇 |
1994年 | 28篇 |
1993年 | 34篇 |
1992年 | 18篇 |
1991年 | 25篇 |
1990年 | 22篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 14篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有4428条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
Sap flow meters based on the stem heat balance method were used to measure the mass flow rates or water use in young potted tea (Camellia sinensis L.) plants of clones AHP S15/10 and BBK35. The meters were constructed on site and installed onto the stem or branch sections of field growing plants in an experiment originally designed to study the effects of plant population density and drought on the productivity and water use of young tea clones. The objective of the study was to use the SHB method as a first attempt to use sap flow meters for determining the water use of young tea growing in the field under well watered conditions in Tanzania. The results are reported and recommendation made for further work on using the technique. 相似文献
85.
86.
The consumption of water by irrigation in agriculture is very large and thus the effects of the management of irrigation systems on aquifers are very important. The basis of this preliminary study into the reduction of this consumption is to improve our understanding of the losses resulting from water transport and deep seepage inside the irrigated areas of cultivation (parcels) at the regional level (100 km) by studying water-table variations with reference to anthropogenic contributions. The use of a hydrodynamic model that incorporates adjustment of the quantity of irrigation water by a reduction coefficient enables actual water-table behaviour to be simulated. Losses can thus be deduced from the quantity of irrigation water flowing into the irrigation system and from hydrometeorological parameters.
Application of the technique in the Lower Durance (France) indicates that, in this region, 53% of the water remains in the irrigation network and 19% is lost by deep seepage, leaving only 28% of the water supplied for use by plants. 相似文献
87.
This work describes the analysis of the uncertainty linked to the annual direct and indirect losses of different nitrogenous compounds at the scale of a group of farms. The nitrogen (N) forms taken into account are: ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), dinitrogen (N2) and nitrate (NO3). The gaseous N emissions for the different components of the farms are estimated with a selection of adapted emission factors. The NO3 losses at the farm scale are calculated as the difference between the surplus of the farm-gate N balance and the gaseous N emissions. 相似文献
88.
Water and nutrient use efficiency of a low-cost hydroponic greenhouse for a cucumber crop: An Australian case study 总被引:3,自引:0,他引:3
Harsharn S. GrewalBasant Maheshwari Sophie E. Parks 《Agricultural Water Management》2011,98(5):841-846
The Australian greenhouse industry is primarily dominated by low-cost hydroponic greenhouses for delivery of water and nutrients to plants to grow a variety of vegetable crops including cucumber and tomato. The nutrient rich drainage water from these greenhouses is generally released into the local environment causing pollution concerns. This study was initiated to investigate the opportunities in recycling drainage water to increase water and nutrient-use efficiency of hydroponic greenhouses and reduce the environmental impact of the drainage water discharge. Results indicated that a total of 4.15 ML/ha of irrigation water was applied during the 13 weeks crop growing period of which 2.56 ML/ha was drained off and 1.59 ML/ha was used to meet the crop evapotranspiration demand. The study showed that the recycling of the drainage water resulted in a 33% reduction in potable water used for irrigation in cucumber production. The drainage water contained 59% applied N, 25% applied P and 55% applied K and illustrated the potential for nutrient recovery and production cost savings through the reuse of drainage water. This case study demonstrates that some relatively simple changes in irrigation practices within greenhouse systems to recycle drainage water can considerably improve sustainability of low-cost hydroponic greenhouses and help minimise the environmental footprint of the greenhouse industry. 相似文献
89.
Landscape irrigation scheduling efficiency and adequacy by various control technologies 总被引:1,自引:0,他引:1
M.S. McCreadyM.D. Dukes 《Agricultural Water Management》2011,98(4):697-704
Automated residential irrigation systems tend to result in higher water use than non-automated systems. Increasing the scheduling efficiency of an automated irrigation system provides the opportunity to conserve water resources while maintaining good landscape quality. Control technologies available for reducing over-irrigation include evapotranspiration (ET) based controllers, soil moisture sensor (SMS) controllers, and rain sensors (RS). The purpose of this research was to evaluate the capability of these control technologies to schedule irrigation compared to a soil water balance model based on the Irrigation Association (IA) Smart Water Application Technologies (SWAT) testing protocol. Irrigation adequacy and scheduling efficiency were calculated in 30-day running totals to determine the amount of over- or under-irrigation for each control technology based on the IA SWAT testing protocol. A time-based treatment with irrigation 2 days/week and no rain sensor (NRS) was established as a comparison. In general, the irrigation adequacy ratings (measure of under-irrigation) for the treatments were higher during the fall months of testing than the spring months due to lower ET resulting in lower irrigation demand. Scheduling efficiency values (measure of over-irrigation) decreased for all treatments when rainfall increased. During the rainy period of this testing, total rainfall was almost double reference evapotranspiration (ETo) while in the remaining three testing periods the opposite was true. The 30-day irrigation adequacy values, considering all treatments, varied during the testing periods by 0-68 percentile points. Looking at only one 30-day testing period, as is done in the IA SWAT testing protocol, will not fully capture the performance of an irrigation controller. Scheduling efficiency alone was not a good indicator of controller performance. The amount of water applied and the timing of application were both important to maintaining acceptable turfgrass quality and receiving good irrigation adequacy and scheduling efficiency scores. 相似文献
90.