全文获取类型
收费全文 | 10722篇 |
免费 | 248篇 |
国内免费 | 332篇 |
专业分类
林业 | 962篇 |
农学 | 377篇 |
基础科学 | 237篇 |
1179篇 | |
综合类 | 1913篇 |
农作物 | 725篇 |
水产渔业 | 551篇 |
畜牧兽医 | 4138篇 |
园艺 | 530篇 |
植物保护 | 690篇 |
出版年
2023年 | 83篇 |
2022年 | 178篇 |
2021年 | 162篇 |
2020年 | 168篇 |
2019年 | 158篇 |
2018年 | 229篇 |
2017年 | 340篇 |
2016年 | 255篇 |
2015年 | 377篇 |
2014年 | 361篇 |
2013年 | 332篇 |
2012年 | 717篇 |
2011年 | 602篇 |
2010年 | 373篇 |
2009年 | 312篇 |
2008年 | 295篇 |
2007年 | 232篇 |
2006年 | 243篇 |
2005年 | 943篇 |
2004年 | 738篇 |
2003年 | 508篇 |
2002年 | 159篇 |
2001年 | 180篇 |
2000年 | 100篇 |
1999年 | 161篇 |
1992年 | 117篇 |
1991年 | 145篇 |
1990年 | 170篇 |
1989年 | 147篇 |
1988年 | 171篇 |
1987年 | 113篇 |
1986年 | 143篇 |
1985年 | 117篇 |
1984年 | 91篇 |
1983年 | 81篇 |
1979年 | 133篇 |
1978年 | 96篇 |
1977年 | 91篇 |
1976年 | 77篇 |
1975年 | 137篇 |
1974年 | 129篇 |
1973年 | 116篇 |
1972年 | 138篇 |
1971年 | 118篇 |
1970年 | 88篇 |
1969年 | 102篇 |
1968年 | 113篇 |
1967年 | 125篇 |
1966年 | 102篇 |
1965年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Comparison of water status indicators for young peach trees 总被引:12,自引:1,他引:12
We measured a series of physiological and physical indicators and compared them to xylem sap flow, to identify the most sensitive and reliable plant water status indicator. In the growing season of 1998, 4-year-old peach trees (Prunus persica Batsch cv. 'Suncrest', grafted on 'GF 677' rootstock) were studied under two irrigation treatments, 25 l dayу and no irrigation, and during recovery. Trials were conducted near Pisa (Italy) in a peach orchard situated on a medium clay loam soil and equipped with a drip-irrigation system (four 4 l hу drippers per tree). Measurements of leaf water potential (W), stem water potential (S), and leaf temperature (Tl) were taken over 5 days (from dawn to sunset) and analyzed in conjunction with climatic data, sap flow (SF), trunk diameter fluctuation (TDF) and soil water content (SWC). Physiological indicators showed substantial differences in sensitivity. The first indication of changes in water status was the decrease of stem radial growth. TDF and SF revealed significant differences between the two irrigation treatments even in the absence of differences in pre-dawn leaf water potential (pdW), up until now widely accepted as the benchmark of water status indicators. Irrigated trees showed a typical trend in SF rate during the day, while in non-irrigated plants the maximum peak of transpiration was anticipated. Measurements of water potential showed S to be a better indicator of tree water status than W. Tl was found to have poor sensitivity. In conclusion, we found the sensitivity of the indicators from the most to the least was: TDF >SF rate >SF cumulated = pdW=S>mdW>Tl. 相似文献
102.
103.
John?W.?HornbuckleEmail author Evan?W.?Christen James?E.?Ayars Richard?D.?Faulkner 《Irrigation and Drainage Systems》2005,19(2):145-159
Recent community based actions to ensure the sustainability of irrigation and protection of associated ecosystems in the Murrumbidgee Irrigation Area (MIA) of Australia has seen the implementation of a regional Land and Water Management Plan. This aims to improve land and water management within the irrigation area and minimise downstream impacts associated with irrigation. One of the plan objectives is to decrease current salt loads generated from subsurface drainage in perennial horticulture within the area from 20 000 tonnes/year to 17 000 tonnes/year. In order to meet such objectives Controlled Water table Management (CWM) is being investigated as a possible ‘Best Management Practice’, to reduce drainage volumes and salt loads.During 2000–2002 a trial was conducted on a 15 ha subsurface drained vineyard. This compared a traditional unmanaged subsurface drainage system with a controlled drainage system utilizing weirs to maintain water tables and changes in irrigation scheduling to maximize the potential crop use of a shallow water table. Drainage volumes, salt loads and water table elevations throughout the field were monitored to investigate the effects of controlled drainage on drain flows and salt loads.Results from the experiment showed that controlled drainage significantly reduced drainage volumes and salt loads compared to unmanaged systems. However, there were marked increases in soil salinity which will need to be carefully monitored and managed. 相似文献
104.
Yaohu?KangEmail author Feng-Xin?Wang Hai-Jun?Liu Bao-Zhong?Yuan 《Irrigation Science》2004,23(3):133-143
A field experiment comparing different irrigation frequencies and soil matric potential thresholds on potato evapotranspiration (ET), yield (Y) and water-use efficiency (WUE) was carried out in a loam soil. The experiment included five treatments for soil matric potential: F1 (-15 kPa), F2 (-25 kPa), F3 (-35 kPa), F4 (-45 kPa) and F5 (-55 kPa) and six treatments for irrigation frequency: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days). Results indicate that both soil matric potential and drip irrigation frequency influenced potato ET, Y and WUE. Potato ET increased as irrigation frequency and soil matric potential increased. Comparing soil water potential, the highest ET was 63.4 mm (32.1%) more than the lowest value. Based on irrigation frequency treatments, the highest ET was 36.7 mm (19.2%) more than the lowest value. Potato Y and WUE were also found to increase as irrigation frequency increased. Potato Y increased with an increase in soil water potential then started to decrease. The highest Y and WUE values were achieved with a soil matric potential threshold of -25 kPa and an irrigation frequency of once a day.Communicated by J. Ayars 相似文献
105.
106.
以中国中医科学院2007-2009年的164篇中医药博士学位论文的外文引文作为研究对象,采用文献计量学方法对其外文引文的类型、数量、期刊被引年代分布、学科专业分布、语种分布、外文期刊被引频次等指标进行了统计与分析,以此了解中医药科研人员对外文文献需求的特点和规律,为图书馆资源建设和用户服务提供指南和参考。 相似文献
107.
108.
109.
110.