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   116篇
  免费   14篇
  国内免费   19篇
  149篇
  2024年   1篇
  2023年   3篇
  2022年   1篇
  2021年   4篇
  2020年   7篇
  2019年   14篇
  2018年   5篇
  2017年   8篇
  2016年   4篇
  2015年   5篇
  2014年   3篇
  2013年   8篇
  2012年   10篇
  2011年   7篇
  2010年   7篇
  2009年   6篇
  2008年   4篇
  2007年   7篇
  2006年   5篇
  2005年   5篇
  2004年   3篇
  2003年   2篇
  2002年   4篇
  2001年   7篇
  2000年   2篇
  1999年   4篇
  1998年   2篇
  1997年   2篇
  1993年   2篇
  1991年   2篇
  1989年   1篇
  1986年   1篇
  1985年   2篇
  1983年   1篇
排序方式: 共有149条查询结果,搜索用时 0 毫秒
71.
Abstract. Population size, reproductive timing and habitats, seasonal behaviors, and juvenile activity were assessed in a British Columbia population of the endangered Oregon forestsnail, Allogona townsendiana , over a period of 4 years. Adult snail population size ranged from seven to 47 snails in four × 24-m2 sampling sites. The mating period peaked in March and April; adults aggregated in clusters of eight to 14 snails before mating. Pairs of snails were observed to mate for 225 min or more in close proximity to coarse woody debris and stinging nettle, Urtica dioica. Nesting peaked in April–May and resulted in a mean clutch size of 34 eggs (SD=9). Hatching for two nests occurred at 63 and 64 d after oviposition. Within hours of hatching, juveniles began dispersing from the nest site; by 1 month most had disappeared. Snails tracked with harmonic radar became less active or aestivated from late July to early September and hibernated from early November to mid-March within leaf litter and soil. Preliminary measurements of growth rate indicate this species takes a minimum of 2 years to reach adulthood and has a typical life span of at least 5 years.  相似文献   
72.

1. 1. Experiments were carried out concerning the characteristics of wettedness revealed under constant average skin temperature using sitting-resting nude subjects. From the basic measurements of both environmental parameters and human physiological responses, the conclusions detailed below were proposed regarding the changes of wettedness under constant average skin temperature.

2. 2. There is positive correlation between the wettedness and environmental humidity, and negative correlation between the wettedness and air temperature.

3. 3. There is positive correlation between the evaporative heat loss from the skin surface and air temperature, and negative correlation between the evaporative heat loss and environmental humidity.

4. 4. There is negative correlation between the wettedness and evaporative heat loss.

5. 5. Wettedness is not constant but takes varying values, that is, corresponding to each average skin temperature both the maximum and the minimum wettedness values occur.

6. 6. Deriving from the items mentioned above, the theoretical locus of equal average skin temperature is not a straight line, but is a curved line plotted on the psychrometric chart.

Author Keywords: Wettedness; sweat rate; evaporative heat loss; equal average skin temperature line; psychrometric chart; ET*; thermal comfort  相似文献   

73.
国外松衰退病与环境和林分因素关系的研究   总被引:1,自引:0,他引:1  
对安徽国外要公衰退病与其环境和林分因素关系的调查研究和数量化分析表明,在气候、土壤、林分、其它病虫害等4类因素18个变量因子中,有10个因子对病情有较大的贡献,成为该病发生的主要致病因素,它们是树龄、林分密度、割脂、降雨量、温度、粘性土、石砾土、土层瘠薄、积水、病虫危害,其中病情与土层浓度、降雨量呈负相关;与其它因素均呈正相关,以此建立病情线形回归预测模型,根据这一模型,可以预测任一给定条件下的林分国外松衰退病可能发生的水平,此外,依据各致病因素在病害发生发展过程中的作用大小和时间顺序,出国外松衰退病的螺旋图,为该类病原复杂的病害形象描述和定量分析作出了探讨。  相似文献   
74.
75.
76.
目的 应用统计过程控制理论分析指导医院服务质量持续改进。方法 联合使用多个控制图方法对医院服务质量评价指标的变化趋势进行监控,及时发现过程中的异常波动,制定针对性措施实施过程改进。结果 找出了影响医院服务质量数据波动的主要原因,制定改进措施,取得了良好的管理效果。结论 控制图可以准确全面反映医院服务质量的总体情况和过程控制情况,根据数据异常分布状态找到潜在的影响服务质量的原因并进行持续改进,是有效的过程管理工具。  相似文献   
77.
78.
Geographic information system-based analysis was used to derive comprehensive, consistent estimates of the potential area of broadly defined, shallow-water, tropical and subtropical coral ecosystems within the territorial sea and exclusive economic zone of the United States. A coral ecosystem is composed of habitats including unconsolidated sediment, mangrove, hermatypic coral, colonized hardbottom, and submerged vegetation, and major structural zones like reef crest, lagoon, and fore reef. This broad definition reflects the importance of both reef and non-reef habitats and structural zones in the function of these ecosystems. Nautical charts, published by the National Oceanic and Atmospheric Administration’s Office of the Coast Survey, provide a consistent source of 10-fathom (∼18 m) and 100-fathom (∼183 m) depth curve information. The 10-fathom or 100-fathom depth curves are used as surrogates for the potential distribution and extent of shallow-water coral ecosystems in tropical and subtropical U.S. waters. An estimated 36,813 sq·km area has been identified where coral ecosystems can potentially be found in waters less than 10 fathoms (18 m) deep. In addition, an estimated 143,059 sq·km area has been identified where coral ecosystems potentially can be found in U.S. waters at depths down to 100 fathoms (183 m). Results also indicate that previous studies underestimated the extent of potential coral ecosystems for some locations in U.S. tropical and subtropical waters by as much as 100% and that the regional distribution of coral ecosystems has been incorrectly reported.  相似文献   
79.
农作物虫害的机器检测与监测技术研究进展   总被引:8,自引:0,他引:8  
在早期发现并准确定位害虫, 对其未来的发展趋势作出评价, 可提高施药处方决策和综合防治的针对性和准确性。在作物虫害信息的获取中, 传统的检测和监测方法不但耗时、费力, 而且导致的预报滞后会进一步增加损失程度, 很难较好地满足现代农业的精准生产要求。本文介绍了国内外学者在田间作物上开展害虫及其危害状况的机器检测和监测技术研究取得的进展, 包括声特征检测法、雷达观测法、图像识别法以及光谱监测法等, 讨论了现有技术的局限性, 指出了未来作物虫害机器检测和监测技术的可能发展方向是采用多种技术相结合的组合式检测和监测方法, 从多个角度获取特定虫害的相关信息, 相互进行实证检验, 以提高作物虫害机器检测和监测的精度及效率。  相似文献   
80.
垂直监测昆虫雷达研究进展   总被引:2,自引:0,他引:2  
昆虫雷达可以远距离、 大范围、 快速地探测迁飞昆虫, 这极大促进了人类对昆虫迁飞行为的认识。垂直监测昆虫雷达技术是从20世纪70年代发展起来的一种监测高空迁飞昆虫种群的新工具。与传统的扫描雷达相比, 垂直监测昆虫雷达可以获得目标的位移速度、 位移方向、 定向、 体型大小和形状等参数, 因此, 对目标的识别能力更为精确。此外, 垂直监测昆虫雷达实现了在微机控制下的自动运行, 这使得应用昆虫雷达开展迁飞昆虫的日常监测成为可能。本文综述了垂直监测昆虫雷达的发展和应用, 介绍了设计原理和回波参数的解算方法, 讨论了其存在的不足及改进方案, 最后并对其在未来昆虫雷达网络建设中的应用进行了展望。  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