首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   730篇
  免费   28篇
  国内免费   47篇
林业   180篇
农学   28篇
基础科学   135篇
  98篇
综合类   272篇
农作物   4篇
水产渔业   14篇
畜牧兽医   57篇
园艺   4篇
植物保护   13篇
  2023年   3篇
  2022年   4篇
  2021年   7篇
  2020年   8篇
  2019年   18篇
  2018年   11篇
  2017年   15篇
  2016年   20篇
  2015年   17篇
  2014年   22篇
  2013年   22篇
  2012年   34篇
  2011年   55篇
  2010年   62篇
  2009年   79篇
  2008年   65篇
  2007年   53篇
  2006年   94篇
  2005年   57篇
  2004年   34篇
  2003年   32篇
  2002年   29篇
  2001年   9篇
  2000年   20篇
  1999年   14篇
  1998年   9篇
  1997年   1篇
  1996年   2篇
  1995年   2篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1990年   1篇
  1987年   1篇
  1982年   1篇
排序方式: 共有805条查询结果,搜索用时 15 毫秒
91.
设计一套集疲劳驾驶计时功能、疲劳驾驶检测功能、疲劳驾驶警示灯显示功能、GPS疲劳语音提示功能及GPS定位功能于一体的防疲劳驾驶系统,绘制工作流程图.通过模拟驾驶器模拟实际驾驶,对比分析头部位置检测系统、车道偏离报警系统、转向盘监测系统、驾驶员警示系统及PERCLOS系统检测疲劳驾驶的优缺点,得出了PERCLOS系统为最优疲劳驾驶检测方法.依据人因工程理论,给出了车体外部警示灯的位置和颜色的设计方案.  相似文献   
92.
RTK测量技术是GPS测量技术与数据传输技术的结合,可实时获得高精度三维定位信息,是测量领域又一次技术革命。本文以四方井水库古树名木保护定位测量为例,阐述RTK的含义、系统组成,分析RTK测量系统的优点以及在测量过程中应注意的问题,为提高林业勘测效率和结果准确性提供参考。  相似文献   
93.
随着科学技术的不断创新,信息手段已经渗透到各个领域,GPS技术和ArcGIS地理信息系统软件也应用于林业工作中,使得林业工作效率得到了极大的提高,林业工作者可以获取精确性更高的数据。文章主要介绍了GPS技术和ArcGIS地理信息系统软件在林地勘验工作中的应用及其优缺点,为以后的林地勘验工作所参考。  相似文献   
94.
Airag, (Fermented horse milk) is a traditional milk product in Mongolia. Herders separate foals from their dams and tie them at a milking site during the daytime to produce airag. To evaluate the effects of horse management on the movement of dams, we tracked three dams in a herd in camp 1 during summer and camp 2 during autumn of 2013 and analyzed their movements during the milking (daytime) and non‐milking (nighttime) periods in an area famous for its high‐quality airag. Dams were gathered every 1.7 ± 0.0 h between 07.46 and 15.47 hours at the milking sites and milked 4.6 ± 0.2 times/day during the study period (86 days). Daily cumulative and maximum linear distances from the milking sites were longer (< 0.01) during the non‐milking period than during the milking period. Daily home ranges were 91 and 26 times greater during the non‐milking period (< 0.001) in camps 1 and 2, respectively. The greater range during the non‐milking period would reflect the spatial distributions of water, salt and forage. The dams initially used similar areas and gradually shifted their daily home ranges after several days. This shift suggests that the dams grazed farther afield as forage availability declined around the milking site. For better airag production and sustainable pasture use, our results provide insights useful for evaluating the effects of milking management on vegetation and soil in those pastures, for selecting the appropriate milking times and frequency, and for choosing the right timing to shift milking sites.  相似文献   
95.
The improvement of Data Communication has made the design of line driver,line receiver and other interface circuits complicated.In accordance with some communication protocols,this paper recommends several IC interface chips and their application in overcoming the influence of noise.  相似文献   
96.
GPS与船用计程仪及陀螺罗经的关系   总被引:1,自引:0,他引:1  
GPS的使用极大地方便了船舶驾驶,推动了航海仪器的发展。但它提供的某些信息是有局限性的,作者从GPS、船用计程仪和船用陀螺罗经的原理,实验观测及航海驾驶的习惯来分析它们在航海中的使用,并讨论GPS与船用计程仪及陀螺罗经之间的相互关系。  相似文献   
97.
“精细农业”发展与工程技术创新   总被引:174,自引:31,他引:143  
综述了目前国外“精细农业”实践的主要目标及其技术思想的内涵。着重围绕其主要支持技术发展,讨论了有关工程技术创新及推动我国开展试验研究的问题。针对目前国外对这一技术体系的研究与实践,主要集中在基于GPS和GIS技术应用的作物生产系统精细管理方面,提出用“精细农作”的译名来表达。进入21世纪,基于知识和信息的“精细农作”技术思想,必将扩展到大农业经营的各个领域,推动农业生产的信息化与知识化,逐步形成一个基于农业生物科学、电子信息技术及工程装备为主导的“精细农业”技术体系,为建立优质、高效和可持续发展的农业系统服务。  相似文献   
98.
A new methodology based in the use of fishers’ knowledge and cost‐effective tools to obtain information about marine recreational fisheries (MRF) is presented. The squid and cuttlefish fishery of the Ría of Vigo (NW Spain) was selected because it is managed in a data‐poor environment. In‐depth interviews (57) were conducted with fishers, collecting ecological and socio‐economic information. A cartography of fishing grounds based on their knowledge was obtained, while the intensity of effort and catches was mapped by the monitoring of two vessels with low‐cost GPS data loggers. The 102 shore anglers and 248 recreational boats catch 8 t/year of European squid Loligo vulgaris and 11 t/year of common cuttlefish Sepia officinalis (11% of total catches on these species in the area). Shore anglers fish from 11 ports, while boat fishers use 14 fishing grounds (covering 30 km2). Most of the catches (86%) are landed by boats, and their CPUE is higher in the outer part of the Ría of Vigo. The use of fishers’ knowledge and cost‐effective monitoring is encouraged to obtain information for the management of MRF. Given the economic contribution of MRF (260,000 €/year in direct expenses), this activity should be considered in the regulations.  相似文献   
99.
3S技术在中国湿地研究、调查与管理中的应用   总被引:10,自引:0,他引:10  
This paper introduces the state of waterlands in China and discribes the applications of Remote Sensing (RS), Geographical Information System (G1S) and Global Positioning System (GPS) in wetland research, including land-coverclassification and change detection, wetland evolutionary processes, landscape-change analyses, channel migration, flood and wetlands resource monitoring and spatial quantitative analyses/modeling, ecosystem service evaluation, ecological processes and risk assessments, disease control, water quality monitoring/modeling, pollution monitoring/modeling, wetlands hydrology, wetland information systems and WebGIS. The limitations and needs for optimal use of these technologies are discussed, such as the limited advanced technical knowledge and skills, low awareness and capacity, unclear link between GIS output and policy making, lack of supporting policies and standards, lack of a wetlands geo-information networklimite, and the use of these techniques in wetland research. It is suggested that for realising true applications of RS, GIS and GPS technologies, the availability, accessibility, reliability, homogeneity, and continuity of wetlands-related geo-information enabling environment, policies and standards, and funding are needed.  相似文献   
100.
农业机械导航中的GPS定位误差分析与建模   总被引:2,自引:0,他引:2  
为实现高精度的农业机械导航,分析了GPS定位误差及其相关性,运用时间序列分析方法建立GPS静态和动态定位误差的AR模型,给出了导航过程中的定位误差处理方法,并在自制的农田智能移动平台上进行了实验.结果表明,处理后的GPS定位误差信号的相关性明显下降,接近于白噪声,定位误差均值从0.1951m下降为-0.0022m.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号