全文获取类型
收费全文 | 2096篇 |
免费 | 124篇 |
国内免费 | 10篇 |
专业分类
林业 | 195篇 |
农学 | 150篇 |
基础科学 | 39篇 |
635篇 | |
综合类 | 174篇 |
农作物 | 192篇 |
水产渔业 | 150篇 |
畜牧兽医 | 445篇 |
园艺 | 44篇 |
植物保护 | 206篇 |
出版年
2023年 | 22篇 |
2022年 | 59篇 |
2021年 | 94篇 |
2020年 | 99篇 |
2019年 | 118篇 |
2018年 | 149篇 |
2017年 | 148篇 |
2016年 | 107篇 |
2015年 | 60篇 |
2014年 | 80篇 |
2013年 | 215篇 |
2012年 | 109篇 |
2011年 | 127篇 |
2010年 | 95篇 |
2009年 | 77篇 |
2008年 | 91篇 |
2007年 | 47篇 |
2006年 | 62篇 |
2005年 | 34篇 |
2004年 | 30篇 |
2003年 | 40篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 27篇 |
1999年 | 22篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 18篇 |
1993年 | 6篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1973年 | 9篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 7篇 |
1968年 | 7篇 |
排序方式: 共有2230条查询结果,搜索用时 312 毫秒
31.
Muhammad Nawaz Bhutta Muhammad Latif Jacob W. Kijne 《Irrigation and Drainage Systems》1991,5(3):229-247
This study was conducted on Gugera Branch of Lower Chenab Canal, Punjab, Pakistan. Sample distributaries off taking from Gugera Branch were selected for the study. The existing conditions of water distribution among the distributaries were studied. Field data were collected during the whole of 1988. Field observations suggested that the variability at the head of distributaries is much greater than the variability in the Gugera Branch under existing operational practices. The distribution of water among the distributaries is rarely in accordance with design criteria. Some channels get priority over other channels. The annual closure period varied from 17 to 41 days for different channels. The discharge at the head of distributaries remained lower than the standard operational range for 69 to 183 days in a year. The data suggested that a regulating gate at the head of the distributary can reduce discharge variation up to 2.4 times compared with a Karrees System (wooden stop logs used for water regulation). The data indicated that the adjustments in the head gate of a distributary on daily basis can substantially improve discharge conditions at the head of distributary. Rotational schedules are not being followed as per design and need to be improved. Most of the existing head discharge relationships of discharge measuring structures are not reliable. A frequent calibration of these structures is recommended. 相似文献
32.
T. Aftab M. M. A. Khan M. Idrees M. Naeem M. Ram 《Journal of Agronomy and Crop Science》2010,196(6):423-430
Boron is an essential plant micronutrient and the range between deficient and toxic levels of boron is narrow for most of the plants. Like other elements, boron becomes toxic to growth at high concentrations. High boron concentrations in soil reduce crop productivity in many areas of the world. The effect of increasing levels of boron (0, 0.50, 1.00, 1.50, 2.00 mm ) on oxidative stress, antioxidant defence response and changes in artemisinin content in Artemisia annua were investigated in the present study. Boron toxicity reduced the growth parameters viz. stem height, fresh weight and dry weight. Treatments induced oxidative stress resulting in lower net photosynthetic rate, stomatal conductance, internal CO2 and total chlorophyll content. The increased activities of antioxidant enzymes like CAT, POX and SOD were also noted in response to increasing levels of boron stress. However, H2O2 and artemisinin content were found to be high up to 1.00 mm concentration of boron compared to control, and on applying higher doses, further reduced contents were obtained. Thus, the results suggest that a mild stress of boron can be utilized for enhanced artemisinin production. 相似文献
33.
34.
35.
36.
Five potato cultivars of autumn crop, dipped in corn oil, were observed for 90 days at room temperature under natural light. Chlorophyll formation took place in minute quantities in treated tubers of ‘Désirée’ and ‘Prima’, and a little more in ‘Primura’, ‘Montana’ and ‘Multa’, whereas all control tubers became completely green after 90 days. Sugars were significantly lower and starch higher in treated tubers than in controls. No sprout-development was observed in treated tubers of all cultivars, but 50–70% control tubers had sprouted during this period. Peeling-losses were minimum in treated tubers and were 67.5–85.4% in controls. The oil-dipped potato tubers of all cultivars could safely be stored for 60 days without quality deterioration under ordinary conditions of temperature and light. 相似文献
37.
38.
39.
40.
A Q Khan 《The British veterinary journal》1968,124(4):171-173