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   7533篇
  免费   209篇
  国内免费   104篇
林业   3567篇
农学   142篇
基础科学   57篇
  640篇
综合类   2795篇
农作物   76篇
水产渔业   45篇
畜牧兽医   81篇
园艺   185篇
植物保护   258篇
  2024年   20篇
  2023年   68篇
  2022年   88篇
  2021年   99篇
  2020年   148篇
  2019年   183篇
  2018年   47篇
  2017年   138篇
  2016年   219篇
  2015年   229篇
  2014年   376篇
  2013年   330篇
  2012年   569篇
  2011年   751篇
  2010年   569篇
  2009年   660篇
  2008年   599篇
  2007年   513篇
  2006年   343篇
  2005年   314篇
  2004年   257篇
  2003年   238篇
  2002年   188篇
  2001年   135篇
  2000年   133篇
  1999年   124篇
  1998年   65篇
  1997年   59篇
  1996年   64篇
  1995年   63篇
  1994年   66篇
  1993年   45篇
  1992年   46篇
  1991年   26篇
  1990年   32篇
  1989年   18篇
  1988年   17篇
  1987年   7篇
排序方式: 共有7846条查询结果,搜索用时 15 毫秒
951.
森林火灾可燃物蓄积量的提取为森林火灾蔓延模型提供了定量的森林火灾可燃物信息。利用遥感影像对森林火灾可燃物的分类结果,采用多元回归法、参数优化的神经网络法和支持向量机法建立森林火灾可燃物蓄积量模型。研究了遥感影像的数据处理、建模方法对森林火灾可燃物蓄积量模型精度的影响。利用最优的森林火灾可燃物蓄积量模型,进行整个研究区域的森林火灾可燃物蓄积量反演。结果表明,数据处理后的遥感影像,采用支持向量机法建立的模型精度较高。  相似文献   
952.
Cultural identity of rural areas is discussed with some basic concepts such as culture, territory, contemporary globalization, and individuation processes. This case study of cultural identity in the Slovenian countryside focuses on its spiritual culture, of which several components are presented in detail: the language of rural areas, (handy)crafts, nutrition and food culture, co-operation and mutual help among rural residents at work and in leisure, and the art products of Slovenian farmers. In discussing the present status and the future of rural cultural identity, the danger of idolizing (romanticizing) traditions for the sake of selling them to tourists is pointed out and the necessity of traditions being part of everyday life of rural residents stressed. As a part of work and leisure life of rural residents, traditions are constantly changing due to local as well as to international socio-economic processes, to inner and outer stimuli to keep existing traditions and to create new ones.  相似文献   
953.
高职旅游与酒店管理专业实践教学模式初探   总被引:6,自引:0,他引:6  
实践教学在现代高职教学实施中,具有与理论教学同等重要且不可替代的地位和作用。作为高职院校的旅游与酒店管理教育,更应考虑旅游行业对管理层面人才的特殊性需求。强调厚基础、强能力、广适应的素质教育是旅游与酒店管理专业的大方向,因此必须加强专业教学的实践环节。实践环节的设计不仅是为了服务技能和业务操作能力的培养,更是为了毕业生能真正胜任旅游与酒店行业的管理工作,同时也是对理论知识的巩固与加强。  相似文献   
954.
从政策、区位、交通条件,市场,基础、服务设施建设等方面,分析天津市北辰区前堡村乡村旅游开发的可行性,并提出开发策略。  相似文献   
955.
[目的]为桂西北石漠化地区退耕还林生态建设提供一定的理论依据。[方法]对桂西北5种退耕林分枯落物蓄积量与持水特性进行研究。[结果]5种林分林下枯落物总蓄积量大小依次为尾叶桉(11.59 t/hm~2)、任豆(7.99 t/hm~2)、核桃(7.71 t/hm~2)、板栗(7.14 t/hm~2)、香椿(3.70 t/hm~2);5种不同林分各分解层枯落物持水能力表现基本一致,从大到小均为香椿、板栗、任豆、尾叶桉、核桃,半分解层枯落物持水量大于未分解层;不同林分林下枯落物持水量随着时间增加而增加,半分解层在浸泡2 h有较快上升,未分解层在浸泡4 h明显上升,之后进入平稳阶段;不同林分枯落物吸水速率随着时间增加而减小,枯落物半分解层与未分解层吸水速率在浸泡2 h内最快,2~8 h逐渐变小,8 h之后明显减缓;不同林分林下枯落物的有效拦蓄量大小为尾叶桉(36.89 t/hm~2)、板栗(26.65 t/hm~2)、任豆(23.19 t/hm~2)、香椿(16.64 t/hm~2)、核桃(15.36 t/hm~2)。[结论]尾叶桉具有较大蓄积量和有效拦蓄量,今后在以涵养水源与水土保持为目标的森林经营中,可适当增加该树种的种植。  相似文献   
956.
分析了我国历次节假日调整引起居民闲暇时间结构变化,由些对我国旅游发展的影响及其特征,阐述了新假日制度对均衡我国旅游市场、丰富旅游产品文化内涵、促进我国旅游业转型的重要意义。  相似文献   
957.
德国林业体系及森林经营技术与管理   总被引:9,自引:0,他引:9  
通过德国的培训考察,对其林业管理体系与政策、森林经营与理念、生物圈保护、森林公共教育等方面归纳叙述。  相似文献   
958.
Small‐scale fisheries provide food and livelihoods for thousands of people along the Brazilian coastline. However, considerable uncertainties still surround the extent to which artisanal and subsistence fisheries contribute to the total of national landings and their historical ecological significance. Fisheries monitoring is deficient in Brazil, and historical records are limited to irregular accounts spanning the last few decades, while this coastline has supported human populations for at least 6,000 years. Here, we estimate pre‐Columbian subsistence catches for a large subtropical estuary in southern Brazil. Our results suggest that prehistoric populations may have extracted volumes of fish biomass higher than or comparable with historical subsistence fisheries in the region, and that the latter is likely underestimated. If a long‐term perspective is required to evaluate the current economic value and status of fisheries in subtropical and tropical South America, this should go beyond the historical time interval and integrate the contribution of pre‐Columbian archaeology.  相似文献   
959.
Forest integrity has been proposed as one conservation endpoint that integrates desirable characteristics such as natural biodiversity, stand structure and continuity. Although its defining criteria are still under discussion, any surrogates must effectively represent or predict their status, and be easier to measure than the criteria themselves. Bryophytes have been proposed as such surrogates, because they are important components of forest integrity, and considerable research indicates that some groups are sensitive to the changes associated with specific forest management regimes. The objectives of this paper are (1) to review the issues in determining indicators of forest integrity, including desirable qualities in such indicators, (2) to review the state of knowledge concerning bryophytes as components of forest integrity (i.e. their responses to forest management practices), and (3) to assess bryophytes as potential indicators of forest integrity, in terms of both qualities desirable in indicators and our understanding of bryophyte response patterns. Although bryophytes possess some characteristics that suggest potential indicator value, many challenges prevent their reliable application. I highlight key areas in which research is required to identify operational bryophyte indicators of forest integrity. Along with a standardized protocol to select and calibrate such indicators, we urgently require strategic research to compile data on undisturbed reference forests on which to base selection of endpoints; species-specific ecological tolerances, with consideration of complex interactions; mechanisms of response to disturbance, with consideration of temporal aspects; population viability thresholds; and recruitment effects on community assembly. Whether we succeed in finding bryophyte indicators of forest integrity, this research would also provide the data to monitor and interpret the integrity of the bryophyte community.  相似文献   
960.
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