全文获取类型
收费全文 | 4222篇 |
免费 | 267篇 |
国内免费 | 360篇 |
专业分类
林业 | 313篇 |
农学 | 446篇 |
基础科学 | 141篇 |
438篇 | |
综合类 | 1911篇 |
农作物 | 340篇 |
水产渔业 | 106篇 |
畜牧兽医 | 674篇 |
园艺 | 169篇 |
植物保护 | 311篇 |
出版年
2024年 | 14篇 |
2023年 | 93篇 |
2022年 | 140篇 |
2021年 | 179篇 |
2020年 | 149篇 |
2019年 | 190篇 |
2018年 | 132篇 |
2017年 | 180篇 |
2016年 | 206篇 |
2015年 | 190篇 |
2014年 | 263篇 |
2013年 | 257篇 |
2012年 | 341篇 |
2011年 | 299篇 |
2010年 | 253篇 |
2009年 | 249篇 |
2008年 | 186篇 |
2007年 | 242篇 |
2006年 | 163篇 |
2005年 | 144篇 |
2004年 | 113篇 |
2003年 | 113篇 |
2002年 | 64篇 |
2001年 | 81篇 |
2000年 | 76篇 |
1999年 | 57篇 |
1998年 | 60篇 |
1997年 | 62篇 |
1996年 | 53篇 |
1995年 | 57篇 |
1994年 | 36篇 |
1993年 | 37篇 |
1992年 | 19篇 |
1991年 | 32篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 5篇 |
1956年 | 1篇 |
排序方式: 共有4849条查询结果,搜索用时 15 毫秒
91.
92.
本研究设置干燥、布袋与保鲜袋包装以及系列温度处理,开展了3a西南桦种子贮藏试验。结果表明:布袋与保鲜袋处理对西南桦种子贮藏影响极不影响;在常温常规条件下,西南桦种子贮藏3个月即失去生活力,而在常温干燥条件下,西南桦种子贮藏10个月种子发芽率尚未显著下降;在15℃条件下贮藏10个月几乎丧失发芽能力,非常有趣的,西南桦种子在10、5、0℃和-5℃各温度条件下贮藏3a,效果十分理想,10℃似乎是西南桦种子低温贮藏的临界温度。本研究促进了西南桦的扩大栽培和基因资源的保存。 相似文献
93.
介绍由可编程控制器PLC控制的跳汰机风阀控制系统,详细叙述了风阀自动控制的思想,以及各种跳汰参数的调整方法。 相似文献
94.
Satoshi Saito 《Journal of Forest Research》2002,7(3):137-143
The effects of a typhoon on forest dynamics and the response of major tree species were studied in a warm-temperate evergreen
broad-leaved forest in southwestern Japan. The strongest typhoon on record (T9313) passed through this region in 1993. Return
periods of typhoons over 30 ms−1 in instantaneous wind velocity and T9313 were estimated to be 2.2 and 104.5 years, respectively. Approximately 10% of all
stems suffered some damage from T9313 and annual stem mortality rose from 1.3 to 2.7%. The estimated period that the number
of stems would fall below 10% of the initial was four years shorter with T9313-class typhoons than without them. Thus, the
disturbance by T9313 was not catastrophic at the site although T9313 was an episodic typhoon. The short-term responses of
major tree species to T9313 were classified into four types: 1) blunt-response type with little decrease and recruitment of
stems in the DBH ≥ 5 cm class (Distylium racemosum), 2) retreat type with larger decrease than recruitment (e.g. Quercus acuta), 3) sharp-response type with a large decrease and much recruitment (e.g. Cinnamomum japonicum), and 4) advance type with less decrease than recruitment (Eurya japonica). Among the four regeneration types classified by previous studies (climax, light-demanding, subcanopy, and few-sapling),
the climax and few-sapling types each showed a specific short-term response, the blunt-response and retreat types, respectively,
that explains one aspect of the regeneration strategies of each type. On the other hand, the light-demanding or sub-canopy
type showed multiple short-term responses, indicating that each regeneration type contains species with various regeneration
strategies.
In this paper, I analyzed data from the database that was compiled by the Aya Research Team. 相似文献
95.
四季竹发笋及幼竹高生长规律研究 总被引:2,自引:0,他引:2
研究表明:四季竹发笋期在4月下旬至10月下旬,6月发笋数最多,9月次之。6月出笋占总出笋棵数的35.56%,笋重量占总重的39.14%;9月出笋占总出笋棵数的20.78%,笋重量占总重的17.83%。四季竹幼竹高生长表现为生长初期和后期相对缓慢,整个生长期平均日生长量12.7 cm。生长高峰在笋出土后第15~35 d,平均日生长量19.2 cm,最大日生长量25.4 cm。四季竹日高生长量方程式为y=-3.785 5 1.791 8 t-0.018 t2-0.000 5 t3。 相似文献
96.
97.
98.
毛竹笋用林合理竹龄结构及其笋期生长规律 总被引:4,自引:0,他引:4
通过多年不同毛竹林分观测分析,提出2度竹的比例在一定范围内影响着笋用林的产量。分析丽水市郊山地笋用林盛期出现的时间及其发生规律,认为笋用林笋期生长规律和气象因子关系密切,丽水市郊的山地笋用林通常是在3月下旬至4月上旬为出笋盛期。对刚露箨叶至出土后10天的笋个体分析表明,对单支笋重的影响长度比笋径大,留笋时间的长短对产量有决定性影响,但从营养成分、加工适性等方面考虑,以笋刚出土时挖掘为最适时期,此时,笋长与笋径相关极显著。 相似文献
99.
100.
M. van Noordwijk 《Agroforestry Systems》1999,47(1-3):223-237
Management of crop—fallow rotations should strike a balance between exploitation, during cropping, and restoration of soil fertility during the fallow period. The Trenbath model describes build-up of soil fertility during a fallow period by two parameters (a maximum level and a half-recovery time) and decline during cropping as a simple proportion. The model can be used to predict potential crop production for a large number of management options consisting of length of cropping period and duration of fallow. In solving the equations, the model can be restricted to sustainable systems, where fallow length is sufficient to restore soil fertility to its value at the start of the previous cropping period. The model outcome suggests that the highest yields per unit of land can be obtained by starting a new cropping period after soil fertility has recovered to 50–60% of its maximum value. This prediction is virtually independent of the growth rate of the fallow vegetation. The nature of the fallow vegetation (natural regrowth, planted trees, or cover crops) mainly influences the crop yield by modifying the required duration of fallow periods. Intensification of land use by shortening fallow periods will initially increase returns per unit land at the likely costs of returns per unit labor. When fallows no longer restore soil fertility to 50% of the maximum, overall productivity will decline both per unit land and per unit labor, unless external inputs replace the soil fertility restoring functions of a fallow.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献