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   21081篇
  免费   5878篇
  国内免费   103篇
林业   3366篇
农学   1249篇
基础科学   1228篇
  6868篇
综合类   10559篇
农作物   458篇
水产渔业   454篇
畜牧兽医   992篇
园艺   444篇
植物保护   1444篇
  2025年   234篇
  2024年   695篇
  2023年   668篇
  2022年   745篇
  2021年   682篇
  2020年   782篇
  2019年   888篇
  2018年   583篇
  2017年   968篇
  2016年   1112篇
  2015年   934篇
  2014年   1271篇
  2013年   1311篇
  2012年   1939篇
  2011年   1875篇
  2010年   1435篇
  2009年   1455篇
  2008年   1348篇
  2007年   1441篇
  2006年   1274篇
  2005年   1006篇
  2004年   805篇
  2003年   645篇
  2002年   450篇
  2001年   441篇
  2000年   336篇
  1999年   299篇
  1998年   263篇
  1997年   200篇
  1996年   190篇
  1995年   144篇
  1994年   149篇
  1993年   114篇
  1992年   98篇
  1991年   90篇
  1990年   75篇
  1989年   46篇
  1988年   31篇
  1987年   16篇
  1986年   3篇
  1985年   7篇
  1984年   2篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
  1977年   2篇
  1962年   5篇
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
1.
利用1981—2010年宣城地区逐日气象资料,对宣城地区各县市的气温、光照、降水等主要气象因子的时空变化特征进行分析,再结合温湿指数和风效指数,确定各个测站各月份的气候舒适度等级。结果表明,宣城地区全年气温适宜,光照丰富,降水充足,气候宜人。宣城各县市最佳旅游季节为秋季和春季,最佳旅游的月份为5、6和9月。  相似文献   
2.
完善的利益机制是台湾农村社区土地重划成功的重要保证。该文采用文献资料法和案例分析法,运用公共选择理论、外部性理论等理论全面解析台湾农村社区土地重划的利益机制。以过沟农村社区土地重划为例,深入剖析其改善农业生产条件、农民生活水平、农村生态环境所依赖的利益机制,认为大陆地区土地整治应借鉴其经验,完善土地整治利益的形成机制、改善土地整治利益的分配机制、构建土地整治利益的变动机制、落实土地整治利益的保障机制。  相似文献   
3.
农用地分等与定级估价研究--以呼和浩特市清水河县为例   总被引:2,自引:2,他引:2  
在认识清水河县自然、社会经济条件的基础上,对清水河县农用地质量特别是耕地质量进行评定,探讨农用地分等与定级估价计算模型及方法,为加强农用土地资源管理与土地资产管理打下良好基础。  相似文献   
4.
农用地估价的常用方法有:收益还原法、收益倍数法、成本法、假设开发法、市场比较法、影子价格法、享乐定价法、土壤潜力估价法、标准田法等。这些估价方法对我国农用地的可操作性、适用范围.学术界有不同的看法,文章对这些观点进行了综述与分析。  相似文献   
5.
The dusuns of Central Maluku which improve fallows by planting spice trees such as clove (Syzygium aromaticum syn. Eugenia aromatica), nutmeg (Myristica fragrans), or coconut (Cocos nucifera) and tending spontaneous regeneration, are an example of a species-rich forest garden system in the eastern hemisphere of the Indonesian archipelago. In this paper we report the influence of site conditions, as slope inclination, soil type, and soil depth, on species composition, tree species diversity, and stand structure in old dusuns in four villages on Saparua, a small island south of Seram. In addition, we compared the floristic composition and stand structure of old dusuns with those of primary forest and advanced fallow vegetation (∼15-yr old). Soil conditions, particularly the depth of the mineral soil layer, and the relief have a major influence on species selection in dusuns. The most common species in old dusuns were absent both in primary forest and forest fallow. Floristic similarity between old dusuns and the unmanaged stands was low. However, in two study villages species richness of old dusuns was similar to that of the primary forest. Old dusuns showed an open structure with an average reduction of basal area by about half compared to the primary forest. Less than half of all individuals found above 10 cm DBH in old dusuns were planted. Only very few species were exclusively planted. Most species were both planted and emerged from spontaneous regeneration. The results indicate the important role of spontaneous regeneration in this forest garden system. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
6.
土地闲置原因分析及对策研究   总被引:1,自引:0,他引:1  
刘志华  孙鹏举 《山西农业科学》2011,39(4):345-347,369
2010年3月8日《国土资源部关于加强房地产用地供应和监管有关问题的通知》中提出,2010年3—7月在全国范围内开展房地产用地专项整治工作,8月19日国土资源部通报了房地产用地专项整治情况,整治过程中,发现违法用地面积近1.26万hm2,其中,闲置土地占90%以上,已成当前最大问题。以城市建设用地为主要研究对象,分析了当前房地产用地中土地闲置产生的原因及其所带来的危害,并对如何预防土地闲置、盘活已闲置土地进行了探讨。  相似文献   
7.
    
The paper provides an overview of the—evolving methodology for the land degradation neutrality (LDN) assessment based on studies at national, regional, and local levels in Russia. A review of more than one hundred publications in Russian language over the past 6–7 years allowed for analysis of the following areas: LDN terminology, LDN assessment at different levels, adapting a transition matrix; using the LDN concept for economic valuation of land, estimating LDN baseline, and using LDN as an integral indicator for sustainable land management. With the LDN concept, a global approach to monitoring land degradation has become applicable beyond the limited geographic scope of the drylands. The paper observes how the LDN concept has been broadened with the introduction of the LDN Index proposed to evaluate the rate of LDN achievement; a proposal on reconstructing transition matrices and adding land cover sub-categories; approach of integrating traditional national sectoral systems for assessing land quality with an LDN add-on. The broader relevance of the paper includes the justification that it provides for using the LDN concept by policy-makers at national and subnational levels, in particular in Russian-speaking countries. It includes the application of additional indicators to capture soil erosion, salinity, soil depletion, aridity, etc., and using different site-specific LDN baselines, not only those time-based but also factoring natural background trends like climate change, natural succession cycles linked with geological and geomorphological processes. Approaches for LDN-based economic valuation of lands and typology of sustainable land management practices and models were also fruitful.  相似文献   
8.
The Aeta Magbukún of Mariveles are one of the least known and researched Indigenous peoples remaining on the fringe of the bay, and within the remaining forests in Bataan province on Luzon Island in the Philippines. This work describes the unique cultural systems and language of the Aeta Magbukún tribe in Biaan, Mariveles, and both the traditional forest resource use and the evolving new subsistence practices developed to adapt to the encroachment of non-Indigenous peoples onto ancestral lands. The Aeta's forest resource use practices are discussed from a sustainable Indigenous development context within unique socioeconomic, cultural, and environmental circumstances in Bataan.  相似文献   
9.
Dry forests represent the most endangered ecosystem in tropical regions and continue to be one of the most sought after environments for human colonization, development and production. In spite of this, dry forests are one of the least well studied tropical habitats. This special issue is dedicated to reviewing much of the information that exists about tropical dry forest in the Americas. The introduction summarizes the articles presented herein, highlighting management strategies that are suggested throughout the special issue that may be useful for conserving tropical dry forest environments.  相似文献   
10.
    
The paper describes the transformation of the coastal landscape near former Davislaguna Lake, SE Spitsbergen. It is a comparative study which outlines the changing state of the area based on old maps, other archival materials, remote sensing data from the years 1900 to 2021, and our own fieldwork performed since 2005. The indirect cause of this transformation is identified herein as climate warming which has produced a progressive degradation of the cryosphere and triggered three key forces behind the said transformation: glacial recession in the 20th century, shortening of the sea-ice season, permafrost thawing in the 21st century. From the year 1900 to the 1920s the coastal landscape of the study area consisted of a bay with beaches between a mountain range in the west and a tidewater glacier tongue protruding into the sea in the northeast. The tongue subsequently melted and the bay became transformed into a coastal plain, with the resulting lake becoming separated from the sea by a gravel-sand bar by 1936. Afterwards, both the plain and lake dwindled in size due to the decline of the bar found to the west. This process continued until the lake became divided into two parts in the 1980s; one of these then disappeared between 2006 and 2010, and the second one by 2021. Hence, the land in question, with the coastal plain partly glaciated and surrounding the bay, then unglaciated and surrounding the lake, became over time replaced by the sea. Today, the process of abrasion acting near the sea is destroying the remaining beaches and cutting down the steep slopes of area mountains and ice-cored moraines.  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