全文获取类型
收费全文 | 3208篇 |
免费 | 176篇 |
国内免费 | 1256篇 |
专业分类
林业 | 109篇 |
农学 | 88篇 |
基础科学 | 59篇 |
3053篇 | |
综合类 | 630篇 |
农作物 | 134篇 |
水产渔业 | 9篇 |
畜牧兽医 | 456篇 |
园艺 | 22篇 |
植物保护 | 80篇 |
出版年
2024年 | 25篇 |
2023年 | 95篇 |
2022年 | 93篇 |
2021年 | 115篇 |
2020年 | 124篇 |
2019年 | 165篇 |
2018年 | 173篇 |
2017年 | 189篇 |
2016年 | 225篇 |
2015年 | 206篇 |
2014年 | 177篇 |
2013年 | 347篇 |
2012年 | 440篇 |
2011年 | 202篇 |
2010年 | 195篇 |
2009年 | 183篇 |
2008年 | 149篇 |
2007年 | 157篇 |
2006年 | 182篇 |
2005年 | 134篇 |
2004年 | 122篇 |
2003年 | 120篇 |
2002年 | 81篇 |
2001年 | 89篇 |
2000年 | 95篇 |
1999年 | 75篇 |
1998年 | 76篇 |
1997年 | 68篇 |
1996年 | 61篇 |
1995年 | 60篇 |
1994年 | 49篇 |
1993年 | 42篇 |
1992年 | 32篇 |
1991年 | 16篇 |
1990年 | 21篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1981年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有4640条查询结果,搜索用时 15 毫秒
1.
Abstract. Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plant-available phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (≶9mgPL−1 ) some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses. 相似文献
2.
A. Bhogal A. Bhogal M.A. Shepherd D.J. Hatch L. Brown S.C. Jarvis 《Soil Use and Management》2001,17(3):163-172
Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization. 相似文献
3.
Abstract. A two year field experiment was carried out in a semiarid Mediterranean area in order to evaluate, the effect on soil erosion of adding different urban organic wastes: a stabilized municipal waste (compost), an unstabilized municipal waste, and an aerobic sewage sludge. All the treatments significantly reduced soil erosion, compared to the control soil. The soil amended with compost was the most effective treatment, reducing soil loss by 94% and runoff by 54%. 相似文献
4.
Abstract. In field and laboratory experiments the conditioner‘Agri-SC’has shown improvements in the structure of loamy sand soils in east Shropshire, UK. It resulted in statistically significant decreases in soil bulk density values and increases in soil porosity and aggregate stability. Further experiments are in progress on both loamy sand and silt loam soils. 相似文献
5.
6.
上虞市海涂实验农场中心试验区的排水系统,能满足十年一遇的年最大24h降雨,两天内排出的要求。滨海盐土的地下水位高,农田基本建设除用浅、密的排水沟布置外,还应结合平整土地、发展灌溉以及适用的农、林技术等综合措施,才能达到治盐改土的效果。 相似文献
7.
8.
草地是发展畜牧业的重要基础,退牧还草工程是恢复、更新天然草地和保护生态环境的重要手段。本文就新疆实施退牧还草工程中所出现的一些问题进行了探讨。 相似文献
9.
草原区沙地放牧草地合理利用途径 总被引:9,自引:0,他引:9
本文通过对草原区沙地放牧草地在畜牧业生产实践中出现大面积退化和沙化现象的分析 ,探讨了沙地放牧草地合理利用的途径 ,认为对于沙地放牧草地的保护 ,重点应放在草地的合理利用方面。通过以草定畜 ,合理调整载畜量 ;建立合理的利用制度 ;发展季节畜牧业 ;调整畜群结构 ,增加良种畜比例 ;以及改良天然草地 ,建立人工、半人工草地等措施 ,达到草原区沙地草地的可持续利用。 相似文献
10.
亚热带牧用草地中威提特东非狼尾草的种子繁殖研究 总被引:4,自引:0,他引:4
在3月和4月对全日制放牧的东非狼尾草草地上的风干牛粪取样,进行发芽试验,分别测定其中的东非狼尾草发芽种子数量。结果,3月取样平均432.5 g的牛粪中东非狼尾草平均发芽种子数量为118.25粒,4月取样平均437.8 g的牛粪中东非狼尾草平均发芽种子数量为52.8粒,二者平均牛粪重为435.15 g,平均发芽种子为85.5粒,说明牛粪中东非狼尾草种子数量较多,是其繁殖扩展较快的主要原因;3月取样的种子数量为4月取样数量的1.38倍,说明人工利用牛粪进行东非狼尾草繁殖时,需在有降雨来临前准备,即1~3月进行牛粪的准备工作。 相似文献