全文获取类型
收费全文 | 3668篇 |
免费 | 180篇 |
国内免费 | 124篇 |
专业分类
林业 | 596篇 |
农学 | 187篇 |
基础科学 | 99篇 |
199篇 | |
综合类 | 1828篇 |
农作物 | 548篇 |
水产渔业 | 68篇 |
畜牧兽医 | 192篇 |
园艺 | 180篇 |
植物保护 | 75篇 |
出版年
2024年 | 13篇 |
2023年 | 22篇 |
2022年 | 58篇 |
2021年 | 74篇 |
2020年 | 76篇 |
2019年 | 113篇 |
2018年 | 33篇 |
2017年 | 93篇 |
2016年 | 227篇 |
2015年 | 145篇 |
2014年 | 418篇 |
2013年 | 185篇 |
2012年 | 411篇 |
2011年 | 323篇 |
2010年 | 230篇 |
2009年 | 213篇 |
2008年 | 147篇 |
2007年 | 180篇 |
2006年 | 165篇 |
2005年 | 130篇 |
2004年 | 95篇 |
2003年 | 95篇 |
2002年 | 60篇 |
2001年 | 74篇 |
2000年 | 63篇 |
1999年 | 60篇 |
1998年 | 43篇 |
1997年 | 31篇 |
1996年 | 33篇 |
1995年 | 25篇 |
1994年 | 35篇 |
1993年 | 30篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有3972条查询结果,搜索用时 15 毫秒
71.
M. Hühn 《Journal of Agronomy and Crop Science》1998,181(4):249-255
A general approach to determine the effect of accuracy of sowing technique on yield per area
Caused by nonperfect seed placement accuracy of sowing machines as well as by many other abiotic and biotic factors the resulting plant stands exhibit nonregular plant distributions. Based on several simplifying assumptions a stochastic approach provides a quantitative determination of the effects of accuracy of sowing technique on yield per area. In this approach, two random variables are assigned to each individual plant: single plant yield E and single plant area A, which is calculated in this paper by the construction and quadrature of the so-called Thiessen-polygons. The yield per area F is calculated as the expectation of the ratio E/A. By assuming a deterministic mathematical relationship between E and A, the calculation of F reduces to the calculation of the expectation of a function of only one random variable A. A simple approximation with sufficient accuracy for many applications only depends on the mean and on the variance of the areas of the individual plants. For demonstration purposes, the theoretical approaches and results have been finally applied to three data sets for drilled seeds of winter oilseed rape (plant density: 60 plants/m2 and distance between rows: 10 cm). These data sets exhibit different accuracies of the longitudinal distributions within rows which have been quantitatively measured by the coefficient of variation for the distances between plants within rows: Yield depression increases with an increasing variability of plant distances within rows. 相似文献
Caused by nonperfect seed placement accuracy of sowing machines as well as by many other abiotic and biotic factors the resulting plant stands exhibit nonregular plant distributions. Based on several simplifying assumptions a stochastic approach provides a quantitative determination of the effects of accuracy of sowing technique on yield per area. In this approach, two random variables are assigned to each individual plant: single plant yield E and single plant area A, which is calculated in this paper by the construction and quadrature of the so-called Thiessen-polygons. The yield per area F is calculated as the expectation of the ratio E/A. By assuming a deterministic mathematical relationship between E and A, the calculation of F reduces to the calculation of the expectation of a function of only one random variable A. A simple approximation with sufficient accuracy for many applications only depends on the mean and on the variance of the areas of the individual plants. For demonstration purposes, the theoretical approaches and results have been finally applied to three data sets for drilled seeds of winter oilseed rape (plant density: 60 plants/m
72.
金光杏梅品种表现及优质高产栽培技术研究 总被引:1,自引:0,他引:1
金光杏梅是河南省新乡市农业局从杏与李的自然杂交后代中选出的优良变异类型,具有较高的栽培推广价值,1999年通过省级鉴定。介绍了金光杏梅的品种表现,从选择壮苗、高标准建园,分季、分批采用不同方法高接,加强土肥水管理,精细整形修剪,合理调整结果量,综合防治病虫害等方面提出了一套优质高产栽培技术规程。 相似文献
73.
详细阐述了听力训练在高职学生的英语学习中的重要作用以及高职学生在英语听力训练中存在的问题及采用的对策与方法。 相似文献
74.
多媒体数据库关键技术的探讨 总被引:1,自引:0,他引:1
随着多媒体技术和网络技术的飞速发展,以及多媒体信息的日益丰富,多媒体数据库技术已成为当前研究的热点.本文介绍了多媒体数据库的特点,探讨了多媒体数据库中的若干关键技术,并给出了一个多媒体数据库的简单实例. 相似文献
75.
76.
77.
78.
80.
树莓在贵阳地区引种栽培情况初报 总被引:1,自引:0,他引:1
2000年从中国林科院森林生态环境研究所引种树莓2个系列6个品种。经比较,有4个品种值得在贵州推广。其果实在6月上中旬成熟,单果平均重6.2g,可溶性固形物含量平均10.3%,味酸甜,风味独特,适应性广。 相似文献