全文获取类型
收费全文 | 2989篇 |
免费 | 158篇 |
国内免费 | 418篇 |
专业分类
林业 | 183篇 |
农学 | 346篇 |
基础科学 | 321篇 |
601篇 | |
综合类 | 1289篇 |
农作物 | 97篇 |
水产渔业 | 78篇 |
畜牧兽医 | 544篇 |
园艺 | 23篇 |
植物保护 | 83篇 |
出版年
2024年 | 30篇 |
2023年 | 71篇 |
2022年 | 99篇 |
2021年 | 95篇 |
2020年 | 118篇 |
2019年 | 117篇 |
2018年 | 75篇 |
2017年 | 117篇 |
2016年 | 146篇 |
2015年 | 121篇 |
2014年 | 165篇 |
2013年 | 176篇 |
2012年 | 201篇 |
2011年 | 221篇 |
2010年 | 174篇 |
2009年 | 157篇 |
2008年 | 157篇 |
2007年 | 194篇 |
2006年 | 188篇 |
2005年 | 132篇 |
2004年 | 115篇 |
2003年 | 95篇 |
2002年 | 70篇 |
2001年 | 62篇 |
2000年 | 50篇 |
1999年 | 70篇 |
1998年 | 42篇 |
1997年 | 34篇 |
1996年 | 37篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 46篇 |
1992年 | 35篇 |
1991年 | 22篇 |
1990年 | 10篇 |
1989年 | 20篇 |
1988年 | 11篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1962年 | 1篇 |
1955年 | 8篇 |
排序方式: 共有3565条查询结果,搜索用时 125 毫秒
41.
42.
43.
44.
基于GIS的黄河下游分布式水资源模拟 总被引:1,自引:1,他引:1
分布式水文模型是水文界研究的焦点问题之一。该研究选用黄河下游流域作为典型研究流域,应用ARC/INFO技术和遥感信息、国内最新水资源调查资料和我国自行开发的LL-Ⅱ分布式水文模型对流域的水资源量进行模拟计算。黄河下游流域内主河道由于泥沙的不断淤积属于典型的地上悬河,而且该地区随着经济的不断发展,人类活动对水资源的影响日益显著,尤其是跨流域调水的影响。本研究充分考虑各种人类活动对水资源的影响,对径流过程进行连续模拟,并取得了较好的模拟结果。 相似文献
45.
介绍了用Visual Basic提供的串行通讯控件,通过编程实现了PC机与应用单片机触发电路的直流传动系统的通信。 相似文献
46.
The sustainability of self-governingirrigation schemes is currently underpressure in many countries as publicfinancial support is decreasing.Furthermore, growing global concernregarding water scarcity means thatefficient water use is essential.Theoretically the choice and implementationof a water-pricing system should play acentral role in achieving this objective,both by recovering water costs and byencouraging farmers to adopt more efficientbehaviour. In the Senegal River Delta newlyestablished water users associations (WUAs)have chosen low water charges, which areaffordable for the majority of farmers butwhich underestimate long-term maintenancecosts. Combined with the difficulty ofcollecting and managing farmers' fees, thischoice has drawn them into a vicious circleleading to scheme deterioration and poorwater service. New alternatives have beendiscussed with them using a simulation toolthat takes into account both the watercosts and the farmers' incomes. Comparedwith the present fixed water charge basedonly on cultivated land, a two-part optionbased both on equipped and irrigated areasensures the recovery of fixed expenses suchas maintenance, while encouraging farmersto intensify their farming systems byadopting double cropping. Neverthelesschoosing a relevant water charge does notensure by itself the sustainability of anirrigation scheme. Combined supportproviding WUAS and farmers with efficientadvice regarding management andorganisational skills should alsocontribute significantly to achieve thisprime objective. 相似文献
47.
During the past two decades with farmer participation in irrigation management moving to center stage, the traditional view of having a centralized control over the water resources for better management has changed. Nevertheless, success of irrigation management transfer depend on a whole set of institutional arrangements or the rules-in-use and the willingness of the users to comply and enforce and/or change the rules in the light of changing circumstances. There are many institutional analyses of water sector, much of them touch on law, policy and administration, and characteristics of the users. The present paper is based on the study carried out to examine the institutional arrangements in one of the water users association that was first in the Maharashtra state. It focuses on the institutional arrangements governing water use and distribution and attempts to elicit the perceptions of the members regarding the rules-in-use. The findings reveal that the WUA has been successful in devising and enforcing the rules for water distribution, fee collection and conflict resolution for over a decade. However, current socio-economic developments such as political heterogeneity have required explicit conflict resolution mechanisms. These issues have now become issues demanding immediate attention and may be use of existing courts or legal institutions to help the WUA sustain in future. 相似文献
48.
应用准稳态传热传质理论,在考虑水蒸气扩散对传热作用情况下,分别建立了奶牛初乳在真空冷冻干燥中多孔干燥层有效导热系数,冻结层导热系数和水蒸气扩散系数的测试模型,利用在冻干机上测取的试验数据,回归得到初乳的传热系数与水蒸气扩散系数,分析了压力与系数间的关系,结果表明,在10Pa~120Pa范围内,干燥层有效导热系数随压力增大而增加,尤其在10Pa~60Pa范围内更为明显,而水蒸气扩散系数随压力的改变变 相似文献
49.
依据传热的基本原理,提出了分析干燥系统室体结构传热特性的特征参数新概念,实现了干燥室隔热体传热系数的非稳态测量,并可同时确定蓄热当量系数。在建立室体传热非稳态分析理论的基础上,提出了相应的试验分析方法,并进行了理论分析及试验验证。 相似文献
50.
The Turkish program of irrigationmanagement transfer has gained worldwidecelebrity for its speed and effectiveness. This paper describes the program brieflyand assesses its effectiveness from anational perspective. The assessmentincludes changes in staffing levels,operational costs, service fee levels, andcost recovery from farmers. A companionpaper examines impacts at the local leveland looks specifically at changes in systemperformance. 相似文献