全文获取类型
收费全文 | 14073篇 |
免费 | 563篇 |
国内免费 | 1420篇 |
专业分类
林业 | 1229篇 |
农学 | 1546篇 |
基础科学 | 774篇 |
2384篇 | |
综合类 | 6403篇 |
农作物 | 1317篇 |
水产渔业 | 366篇 |
畜牧兽医 | 999篇 |
园艺 | 455篇 |
植物保护 | 583篇 |
出版年
2024年 | 76篇 |
2023年 | 198篇 |
2022年 | 334篇 |
2021年 | 405篇 |
2020年 | 404篇 |
2019年 | 486篇 |
2018年 | 333篇 |
2017年 | 591篇 |
2016年 | 728篇 |
2015年 | 533篇 |
2014年 | 770篇 |
2013年 | 837篇 |
2012年 | 1134篇 |
2011年 | 1155篇 |
2010年 | 907篇 |
2009年 | 935篇 |
2008年 | 891篇 |
2007年 | 970篇 |
2006年 | 795篇 |
2005年 | 640篇 |
2004年 | 444篇 |
2003年 | 324篇 |
2002年 | 253篇 |
2001年 | 225篇 |
2000年 | 192篇 |
1999年 | 197篇 |
1998年 | 177篇 |
1997年 | 146篇 |
1996年 | 134篇 |
1995年 | 144篇 |
1994年 | 108篇 |
1993年 | 102篇 |
1992年 | 91篇 |
1991年 | 75篇 |
1990年 | 74篇 |
1989年 | 67篇 |
1988年 | 49篇 |
1987年 | 35篇 |
1986年 | 25篇 |
1985年 | 13篇 |
1984年 | 9篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1962年 | 3篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
深化馆系资料室共建-扬馆系所长 总被引:2,自引:0,他引:2
本文分析了系部资料室在服务教学科研工作中的特殊地位与优势,同时分析了系部资料室建设存在的一些问题,提出系部资料室信息深化服务的建议。 相似文献
13.
This paper depicted the physiographic landscape features and natural vegetation situation of study area (the eastern Jilin
Province), and expatiates the definition, basic characters and its development of Ecological Land Classification (ELC). Based
on the combination of relief map, satellite photography for study area and vegetation inventory data of 480 sample sites,
a 5-class and a 15-class ecological land type map was concluded according to 4 important factors including slope, aspect,
vegetation and elevation. Ecological Classification System (ECS) is a method to identify, characterize, and map ecosystems.
The Ecological Land Type (ELT) was examined and applied initially in eastern Jilin Province.
Foundation item: This paper was supported by Chinese Academy of Sciences “100 people” project and the Open Research Station of Changbai Mountain
Forest Ecosystem.
Biography: XIAO Bao-ying (1974-), female, postgraduate in Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016,
P. R. China
Responsible editor: Zhu Hong 相似文献
14.
施肥对红三叶群落营养元素含量和积累量的影响 总被引:1,自引:0,他引:1
本文研究了施肥对红三叶群落地上部和地下部 1 0种营养元素的影响 ,结果如下 :( 1 )从含量看 ,施氮肥后 ,地上部B明显降低 ,地下部B明显升高 ;施磷肥后 ,地上部N、B显著下降 ,地下部K、P、N上升幅度较大。 ( 2 )就积累量而言 ,施氮肥后 ,地上部大多数元素增高 ,地下部多数元素降低或无变化 ;施磷肥后 ,无论地上部还是地下部 ,大多数元素均有所增高 相似文献
15.
依据干旱胁迫下数种植物幼苗体内游离脯氨酸、叶气孔、叶水量的变化,剖析了植物与环境因子、气孔因子、氧气因子、酶因子及能量因子之间的相互依存关系,提出了PRO积累系统(PAS)。认为水分胁迫下植物体内PRO的大量积累是氧化受抑和合成受激共同调控的结果。氧气最有可能为直接触发因子。 相似文献
16.
J. Müller 《Journal of Agronomy and Crop Science》1993,171(4):217-235
Dry Matter Production, CO2 Exchange, Carbohydrate and Nitrogen Content of Winter Wheat at Elevated CO2 Concentration and Drought Stress
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO2 concentration and changing climatic conditions on agricultural ecosystems. In this context, detailed knowledge is required about the possible effects on crop growth and physiological processes. To this aim, the influence of an elevated CO2 concentration and of drought stress on dry matter production, CO2 exchange, and on carbohydrate and nitrogen content was studied in two winter wheat varieties from shooting to milk ripeness. Elevated CO2 concentration leads to a compensation of drought stress and at optimal water supply to an increase of vegetative dry matter and of yield to the fourfold value. This effects were caused by enhanced growth of secondary tillers which were reduced in plants cultivated at atmospheric CO2 concentration. Analogous effects in the development of ear organs were influenced additionally by competitive interactions between the developing organs. The content and the mass of ethanol soluble carbohydrates in leaves and stems were increased after the CO2 treatment and exhausted more completely during the grain filling period after drought stress. Plants cultivated from shooting to milk ripeness at elevated CO2 concentration showed a reduced response of net photosynthesis rate to increasing CO2 concentration by comparison with untreated plants. The rate of dark respiration was increased in this plants. 相似文献
Methods of mathematical modelling and simulation are being used to an increasing degree in estimating the effects of rising atmospheric CO
17.
目前农业信息化发展面临的问题与几点建议 总被引:3,自引:1,他引:2
本文探讨了农业信息服务特点及开展与推广所面临的主要问题,对完善农业信息服务、实现农业信息化提出相关建议。 相似文献
18.
改善E1级胶合板用UF胶粘剂预压性能的研究 总被引:1,自引:0,他引:1
利用氧化淀粉在树脂合成后期、API在调胶时加入分别对脲醛树脂进行改性,探讨改性UF对胶合板预压强度的影响。采用正交实验法对比改性后胶合板的预压性能和改性后胶合板的甲醛释放量的变化。结果表明:随着API量的加大,胶合板的预压性能得以提高;而氧化淀粉改性后则随着量的加大,一定范围内胶合板的预压性能得以提高,加入量继续加大后反而下降。 相似文献
19.
我国农村信息化建设存在的问题及对策研究 总被引:9,自引:1,他引:8
农村信息化建设是国家信息化战略的重要组成部分,是实现小康社会的重要途径。我国的农村信息化建设取得了初步的成绩,但还存在许多问题,针对这些问题本文提出了具体的应对策略。 相似文献
20.
A field experiment was conducted to find out the critical physiological stages of irrigation schedules inducing better growth, physiological efficiency and seed yield potential of berseem ( Trifolium alexandrinum L., Var. S-99-1). For this purpose eight irrigation treatments were made comprised of four treatments of three irrigation (W1 , W2 , W3 and W4 ), three treatments of four irrigation (W5 , W7 and W8 ) and one treatment of five irrigation (W6 ) at various physiological stages i. e. regeneration, flower initiation, full bloom, seed initiation and advance seed development stage.
Thus based on the experimental results the physiological role of watering in berseem seed production could be discussed as:
With-holding of irrigation either at regeneration or at full bloom stage developed potential water stress in plants as indicated by high proline content of irrigation treatments — W4 , W1 and W7 ; and further brought out disturbance on the formation of carotene, synthesis of water soluble sugar and translocation of sugar towards reproductive organs during grain development stage. These stresses adversely affected the plant growth and flowering behaviour. The irrigation at seed initiation stage increased the seed yield. Continuous irrigation did not appear to be useful. Thus it can be concluded that irrigation at three critical physiological stages i. e. regeneration, full bloom and seed initiation was found to be essential for obtaining potential seed yield of berseem. 相似文献
Thus based on the experimental results the physiological role of watering in berseem seed production could be discussed as:
With-holding of irrigation either at regeneration or at full bloom stage developed potential water stress in plants as indicated by high proline content of irrigation treatments — W