全文获取类型
收费全文 | 2071篇 |
免费 | 113篇 |
国内免费 | 348篇 |
专业分类
林业 | 238篇 |
农学 | 109篇 |
基础科学 | 186篇 |
946篇 | |
综合类 | 752篇 |
农作物 | 39篇 |
水产渔业 | 16篇 |
畜牧兽医 | 171篇 |
园艺 | 16篇 |
植物保护 | 59篇 |
出版年
2024年 | 25篇 |
2023年 | 77篇 |
2022年 | 89篇 |
2021年 | 92篇 |
2020年 | 95篇 |
2019年 | 96篇 |
2018年 | 89篇 |
2017年 | 114篇 |
2016年 | 158篇 |
2015年 | 117篇 |
2014年 | 129篇 |
2013年 | 168篇 |
2012年 | 181篇 |
2011年 | 158篇 |
2010年 | 110篇 |
2009年 | 125篇 |
2008年 | 85篇 |
2007年 | 95篇 |
2006年 | 101篇 |
2005年 | 68篇 |
2004年 | 75篇 |
2003年 | 56篇 |
2002年 | 27篇 |
2001年 | 31篇 |
2000年 | 34篇 |
1999年 | 30篇 |
1998年 | 24篇 |
1997年 | 32篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 12篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1956年 | 1篇 |
排序方式: 共有2532条查询结果,搜索用时 0 毫秒
41.
ELIZABETH A. BALLEGEER LISA J. FORREST ROBERT JERAJ T. ROCKWELL MACKIE R. JEROME NICKLES 《Veterinary radiology & ultrasound》2006,47(2):228-233
A primary lung tumor in a dog treated with intensity-modulated radiation therapy was imaged approximately 6 weeks and 1-year posttreatment with combined positron emission tomography (PET) and computed tomography, utilizing the radiotracers 18F-fluorodeoxyglucose and 18F-fluorothymidine. These two tracers allowed discrimination of tumor from inflammation, and demonstrated spread of tumor along airways over time after treatment. Fusion of functional imaging with anatomic imaging is a useful tool, particularly in the field of oncology, with the potential for PET markers that delineate tumor from normal or reactive tissue, and potential or actual response to therapy. 相似文献
42.
43.
44.
研究水稻对稻田甲烷排放的影响对有效控制或减少大气甲烷含量、保护大气环境等具有非常重要的意义.笔者从水稻根系对稻田甲烷产生的影响、水稻对稻田甲烷的传输影响和水稻根系的氧化能力对稻田甲烷排放的影响三个方面,对国内外水稻植株影响稻田甲烷排放的研究做一综述,并且分析了未来需要加强的研究内容. 相似文献
45.
以湖南省1990-1999年的SO2监测和统计数据为基础,对湖南省排放SO2的现状进行了分析,计算了湖南省各地区SO2排放强度,并对湖南省今后SO2排放趋势进行了预测.结果表明,湖南省SO2污染最为严重的地带是处于沅江和澧水流域的吉首和洪江南北走廊带,其次是以长沙为中心的湘江谷地;排放强度最大的区域位于湖南省中部的娄底、湘潭和株洲等地,排放强度大于10.0
t/km2·a,其次是岳阳,排放强度在7.50~10.0 t/km2·a之间.预测结果显示,湖南省SO2排放量在2005年将达到77.15×104
t,到2010年将达到92.41×104 t. 相似文献
46.
运用文献计量学方法考察1989~2010年公开发表在CNKI、维普和万方三大数据库的我国碳排放研究文献,较为系统地分析我国碳排放研究发文年度分布、期刊分布、高产作者及引文分布等问题,同时通过关键词统计分析,初步揭示出碳排放研究的新方向。 相似文献
47.
《植物养料与土壤学杂志》2017,180(2):252-266
Due to their high emission potential, the reporting of CO2 emissions from peatlands requires exact emission factors for different land use categories. Recently used emission factors are mainly based on CO2 flux measurements by chamber techniques or the micrometeorological eddy covariance (EC) method. However, evidence about the reliability and comparability of annual CO2 balances based on these methods is scarce. Therefore, manual chamber measurements of ecosystem respiration (RECO) and net ecosystem exchange (NEE) were conducted for two years (March 2012–April 2014) to model annual balances of two sites on fen soils with different land use intensity in northern Germany: an unutilized and rewetted grassland (UG) and an intensively utilized wet grassland (GW). Simultaneously, EC measurements of NEE were conducted on the sites. Two reasons for occasionally great deviations in NEE between the methods could be observed: (1) the accordance of both methods was most hampered during transition periods such as the beginning of the growing season and the onset of regrowth after a grassland defoliation due to different spatial scales of EC and chamber measurements and (2) RECO and gross primary production (GPP) partitioned from EC NEE measurements were systematically lower than those from the chamber‐based model, which could be a result of the EC energy balance gap. Differences were more pronounced for the managed site GW as a result of more frequent regrowth periods. It is concluded that the EC and chamber method can show comparable results for the CO2 exchange of grasslands on fen soils when the limitations of both methods are known and considered for the reporting of emission factors. These limitations are due to energy balance closure and potentially biased footprints for EC and a restricted representativeness especially during early stages of plant development for the chamber method. 相似文献
48.
大米称誉为"五谷之首",是我国的主要粮食作物。大米产地鉴别方法的研究对于保护广大消费者和生产厂家的利益、推动我国大米出口业的发展等都具有重要意义。为此,选取了19个响水大米样品和10个非响水大米样品,使用等离子体原子发射光谱的方法测定了样品中P,B,Zn,Fe,Cu,Mn,Na,K,Mg和Ca等10种微量元素的含量,并利用样品中的微量元素含量数据,使用K-Means聚类法和Hierarchical聚类法对大米样品进行了聚类分析。结果表明,K-Means和Hierarchical聚类法对于样品有聚类趋势。研究结果能够为大米生产厂商与质检部门鉴别大米产地提供参考和借鉴。 相似文献
49.
50.