全文获取类型
收费全文 | 884篇 |
免费 | 63篇 |
国内免费 | 70篇 |
专业分类
林业 | 61篇 |
农学 | 117篇 |
基础科学 | 32篇 |
128篇 | |
综合类 | 350篇 |
农作物 | 70篇 |
水产渔业 | 78篇 |
畜牧兽医 | 89篇 |
园艺 | 43篇 |
植物保护 | 49篇 |
出版年
2024年 | 5篇 |
2023年 | 20篇 |
2022年 | 17篇 |
2021年 | 28篇 |
2020年 | 29篇 |
2019年 | 33篇 |
2018年 | 36篇 |
2017年 | 33篇 |
2016年 | 41篇 |
2015年 | 45篇 |
2014年 | 44篇 |
2013年 | 62篇 |
2012年 | 54篇 |
2011年 | 87篇 |
2010年 | 70篇 |
2009年 | 63篇 |
2008年 | 56篇 |
2007年 | 45篇 |
2006年 | 46篇 |
2005年 | 26篇 |
2004年 | 11篇 |
2003年 | 23篇 |
2002年 | 20篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1993年 | 14篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 7篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1017条查询结果,搜索用时 15 毫秒
81.
This study was carried out to determine the effect of water stress on five different generative stages of soybeans and to evaluate the CROPGRO-soybean model under semi-arid climatic conditions. The study was conducted at the Faculty of Agricultural Engineering, Harran University research field in 2003 and 2004 growing seasons. Plants received full irrigation during vegetative stages, after which it was cut off at different reproductive stages (treatments): R1-2, beginning of flowering and full bloom; R3, beginning of pod; R4, full pod; R5, beginning of seed; and R6, full seed. The control treatment was full irrigation throughout. Observed yields ranged from 1955 (R6) to 3684 kg ha−1 (control) in 2003, and from 1867 (R6) to 3952 kg ha−1 (control) in 2004, respectively. Generally, in both of the years any water stress imposed on soybeans in three different generative stages (R3, R5, and R6) resulted in substantial yield reduction compared with full irrigation; yield reduction was greatest at the R6 stage. Biomass and 1000 seed weight also showed significant difference. Overall, CROPGRO-soybean simulated parameters from all treatments were higher compared with observed ones. Although simulated yield results were close to measured ones, they could not track observed yield patterns. Generally, the CROPGRO-soybean simulation model failed to satisfactorily mimic observed soybean yield, biomass, and 1000 seed weight and therefore it is suggested not to be used for similar scenarios and climatic conditions. 相似文献
82.
Genetic yield improvements in oat (Avena sativa L.) cultivars grown at high latitudes have resulted from marked changes in harvest index and yield components. This study was designed to investigate whether such changes have entailed alterations in duration of different developmental phases: vegetative, generative and grain filling phases and pre-anthesis generative sub-phases such as pre-fertile, pre-abortion, fertile pre-abortion, fertile and abortion sub-phases. We tested 14 oat cultivars released between 1921 and 1988 and 6 breeding lines. Ten randomly sampled plants of each oat entry were collected every 3–4 d (18 times) from seedling emergence until pollination, and apical developmental stages were determined on the most advanced spikelet. Cumulated degree-days (Cdd) for each critical developmental stage and component phases were determined (5 °C as a base temperature). At each measurement the number of leaves, green leaves and tillers on main shoot, apex length (mm) and height to the uppermost node, and stipule (cm) were recorded. Phyllochron (°C d leaf−1) and relative elongation rates (RER) for height characterising traits were calculated. Grain filling was the only period altered by breeding, while no consistent effects on duration of vegetative and generative pre-anthesis phases and sub-phases were detected. Different developmental phases were interrelated: in some cases cultivars with similar duration of pre-anthesis phase, however, differed in duration of some pre-anthesis sub-phases. Their duration was not, however, consistently associated with measured growth and yield parameters. Likely long days that make the northern growing conditions exceptional and unique, substantially narrowed the differences among oat entries in duration of different developmental phases, thereby making their role also less critical in yield determination contrary to the situation in the main global temperate cereal production regions. 相似文献
83.
84.
赵京音 《上海交通大学学报(农业科学版)》1988,(3)
研究了6个种皮单宁含量不同的蚕豆品种,发现高、低单宁品种间,在籽粒发育过程中种皮干物质和单宁含量的变化有明显的差异。这个发育过程可分为合成期和分解期。依据品种在单宁合成期和分解期变化的差异,可将蚕豆品种分为四种类型,其中种皮单宁缓慢合成快速分解型是低单宁品种。发育过程中,种皮单宁含量与种皮干物质量呈显著正相关。 相似文献
85.
运用系统科学和协调发展观建立REES指标体系和综合评价模型,计算获得1990,1995 ̄2004年内江市生态可持续发展综合评价值,对内江市生态可持续发展水平进行了评价。得出结论:①内江市近15a来可持续发展总体水平处于弱可持续发展阶段;在生态和发展之间的关系上,总体是发展不足;2000—2004年社会经济系统进入快速发展阶段,表现出对西部大开发的响应。②采用综合模糊评价法进行区域生态可持续发展水平评价,具有层次分明、形象直观、符合实际的特点;评价中选用标准参考系,与区域时间序列数据相对照,具有时空有机结合的优点。 相似文献
86.
“六位一体”高效生态农业产业发展模式与实施途径研究 总被引:7,自引:0,他引:7
"六位一体"生态农业产业发展模式是在生态农业产业发展模式基础上,针对我国生态农业产业中存在的问题,把"龙头企业-基地-加工-沼气发酵-物流-销售市场"六者紧密、有机结合而构建而成,形成典型高效生态良性循环的农业生态经济系统。该模式指出必须把实现高效生态农业产业化,恰当地采取最有效的生态农业产业模式作为我国农业发展的研究方向。本研究构建了该模式的基本框架,并根据该模式的特征,同时结合典型案例,提出了该模式的适宜范围、实施方案和有效实施途径。 相似文献
87.
88.
党的十六届三中全会明确提出的科学发展观使人成为社会发展的目标主体,反映了人类在发展理论上的不断深化.科学发展观的提出内含着深刻的人学思考.马克思主义人学理论为科学发展观的提出提供了理论根据.正因为科学发展观以马克思主义人学理论为指导,注重以人为本,才彰显了其科学性.也正是得益于坚实的马克思主义人学基础,科学发展观达到了对经济社会发展问题的新的更高的认识境界. 相似文献
89.
90.
Summary This second paper of the review describes the development of the potato tuber and whole plant based on research data and literature.
The development and growth, daily changes of fresh and dry matter, and of the contents of organic and inorganic components
(dry matter, starch, sugars, organic acids, ascorbic acid, nitrogenous compounds, nitrate, crude lipid, glycoalkaloids, P,
K, Ca, Mg, Mn, Na), discolouration indices, and physiological parameters (rate of assimilation and respiration, activity of
enzymes) are reviewed. 相似文献