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   31981篇
  免费   2183篇
  国内免费   1925篇
林业   3735篇
农学   2249篇
基础科学   1564篇
  2751篇
综合类   14041篇
农作物   2576篇
水产渔业   1909篇
畜牧兽医   4172篇
园艺   1777篇
植物保护   1315篇
  2024年   112篇
  2023年   551篇
  2022年   914篇
  2021年   1103篇
  2020年   1104篇
  2019年   1254篇
  2018年   868篇
  2017年   1023篇
  2016年   1343篇
  2015年   1640篇
  2014年   2100篇
  2013年   2107篇
  2012年   2776篇
  2011年   2406篇
  2010年   1892篇
  2009年   1969篇
  2008年   1695篇
  2007年   1952篇
  2006年   1728篇
  2005年   1451篇
  2004年   962篇
  2003年   843篇
  2002年   679篇
  2001年   643篇
  2000年   601篇
  1999年   415篇
  1998年   343篇
  1997年   272篇
  1996年   203篇
  1995年   181篇
  1994年   183篇
  1993年   123篇
  1992年   130篇
  1991年   94篇
  1990年   88篇
  1989年   73篇
  1988年   65篇
  1987年   44篇
  1986年   23篇
  1985年   34篇
  1984年   27篇
  1983年   12篇
  1982年   6篇
  1981年   19篇
  1980年   12篇
  1979年   5篇
  1978年   4篇
  1977年   4篇
  1975年   3篇
  1956年   5篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
国有林场在内蒙古林业生态建设中具有骨架作用,是祖国生态安全屏障的重要组成部分与支撑点,也是贯彻落实生态文明建设,践行“绿水青山就是金山银山”理念不可或缺的重要实施主体。在深入了解与掌握内蒙古自治区西部地区6个市国有林场经营现状的基础上,总结归纳了内蒙古西部地区国有林场经营的特点,深入分析了内蒙古西部地区国有林场面临的问题与困境,并探讨解决这些问题的途径,为国有林场今后的发展提出了合理化建议。  相似文献   
12.
马铃薯产业是宁夏“1+4”特色优势产业,是西吉县所有农作物中种植面积最大、涉及农户最多、比较效益最高的农民脱贫致富的主导产业。近年来西吉县马铃薯产业由商品薯种植大县向种薯繁育大县的转变,推动了农业增效,农民增收的快速发展。但各类土传性病害的发生影响了马铃薯产业的发展,同时磋商了农民种植的积极性。为了测定筛选出对马铃薯枯萎病和干腐病防治效果好、成本较低药剂,为大田防治提供科学依据。  相似文献   
13.
Aux/IAA 基因家族在植物茎尖发育过程发挥重要作用。为了探究大豆Aux/IAA 基因家族在大豆茎尖发育过程的调控作用,本文以拟南芥Aux/IAA 基因家族蛋白序列为参照鉴定了大豆全基因组Aux/IAA 家族基因,包括63个成员;然后以拟南芥、鹰嘴豆和大豆的Aux/IAA 家族为研究对象,比对这些基因全长氨基酸序列并构建进化树,结果表明三种作物的Aux/IAA 家族成员间亲缘关系差异明显,进化过程中同源重组频率不同;进而利用RNA-seq技术分析东农594(DN)、Charleston(CH)及二者杂交后代的RIL群体的高矮秆池(WH、WS)和F2群体的高矮秆池(JH、JS)的差异表达基因及其功能,共有17个Aux/IAA 基因在3组材料中差异表达。CHvsDN组有15个差异表达基因,JHvsJS组有2个,WHvsWS组只有1个;其中,Glyma.10G180100 在JHvsJS组和WHvsWS组均差异表达,这些结果为进一步研究大豆Aux/IAA 基因家族的功能及调控茎尖发育提供理论依据。  相似文献   
14.
耕地低碳利用对于减少农业温室气体排放,促进农业持续健康发展具有积极意义。建立资本禀赋、技术认知的理论分析模型和研究假说,利用湖北省347户农户的调研数据,在测度农户资本禀赋、耕地低碳利用技术认知的基础上,采用Logit模型、中介效应模型、调节效应检验方法,就资本禀赋、技术认知与农户耕地低碳利用意愿的关系进行实证研究。结果发现,资本禀赋不仅对农户耕地低碳利用意愿在1%水平上有显著的直接正向影响,还会通过技术认知这一中介变量在1%水平上产生显著的间接正向影响,环境素养在农户自我效能认知和耕地低碳利用意愿间发挥正向调节作用。据此,建议从经济资本、社会资本、文化资本3个角度提升农户的资本禀赋,通过多种渠道提升农户对耕地低碳利用的认知水平,提高农户环境素养。  相似文献   
15.
[Objective] The aim of this study is to understand the dynamics of cotton rhizosphere bacterial community structure in cotton continuous cropping field soil. [Method] 16S rDNA genes were sequenced by high-throughput sequencing technology to determine the community structure of cotton rhizosphere bacteria in different developmental stages using an upland cotton cultivar (Gossypium hirsutum cv. TM-1). [Result] Four dominant phyla were found in the cotton rhizosphere bacterial community including Proteobacteria, Acidobacteria, Planctomycetes, and Bacteroidetes. The four dominant phyla and Firmicutes were largely influenced by cotton root. The relative abundances of Acidobacteria, Planctomycetes, Bacteroidetes were promoted, and Proteobacteria and Firmicutes were inhibited, by cotton root. There were significant differences in community structure, but not species richness or α-diversity among different developmental stages of the cotton rhizosphere bacterial community; the differences between the flowering stage and the budding stage were greater than the differences between the budding stage and the seedling stage. The diversity of the rhizosphere bacterial community in cotton continuous cropping field soil was significantly higher than that of the bulk soil; the β-diversity values of both the rhizosphere and bulk soil bacterial communities were highest in the flowering stage. [Conclusion] The structure and dynamics of the cotton rhizosphere bacterial community in cotton continuous cropping field soil was defined by high-throughput sequencing. The effect of cotton on the rhizosphere bacterial community structure was most significant in the flowering stage.  相似文献   
16.
The double-rice cropping system is a very important intensive cropping system for food security in China. There have been few studies of the sustainability of yield and accumulation of soil organic carbon(SOC) in the double-rice cropping system following a partial substitution of chemical fertilizer by Chinese milk vetch(Mv). We conducted a 10-year(2008–2017) field experiment in Nan County, South-Central China, to examine the double-rice productivity and SOC accumulation in a paddy soil in response to different fertilization levels and Mv application(22.5 Mg ha~(–1)). Fertilizer and Mv were applied both individually and in combination(sole chemical fertilizers, Mv plus 100, 80, 60, 40, and 0% of the recommended dose of chemical fertilizers, labeled as F100, MF100, MF80, MF60, MF40, and MF0, respectively). It was found that the grain yields of double-rice crop in treatments receiving Mv were reduced when the dose of chemical fertilizer was reduced, while the change in SOC stock displayed a double peak curve. The MF100 produced the highest double-rice yield and SOC stock, with the value higher by 13.5 and 26.8% than that in the F100. However, the grain yields increased in the MF80(by 8.4% compared to the F100), while the SOC stock only increased by 8.4%. Analogous to the change of grain yield, the sustainable yield index(SYI) of double rice were improved significantly in the MF100 and MF80 compared to the F100, while there was a slight increase in the MF60 and MF40. After a certain amount of Mv input(22.5 Mg ha~(–1)), the carbon sequestration rate was affected by the nutrient input due to the stimulation of microbial biomass. Compared with the MF0, the MF100 and MF40 resulted in a dramatically higher carbon sequestration rate(with the value higher by 71.6 and 70.1%),whereas the MF80 induced a lower carbon sequestration rate with the value lower by 70.1% compared to the MF0. Based on the above results we suggested that Mv could partially replace chemical fertilizers(e.g., 40–60%) to improve or maintain the productivity and sustainability of the double-rice cropping system in South-Central China.  相似文献   
17.
采用大田裂区试验,研究了施用锌肥和不同遮阴程度互作对花生生长发育、抗病性及产量的影响。结果表明,与不施锌肥相比,施用锌肥能提高花生不同部位锌含量、增加叶片SPAD值,提高花生叶片中可溶性糖、蛋白质和生长素含量,减少花生病害的发生,平均降低7.1个百分点,花生产量平均增加19.4%。相同施锌水平下,随着遮阴程度的增加,花生不同部位锌的含量和不同生育期叶片SPAD值以及花生叶片中可溶性糖、蛋白质和生长素含量呈增加趋势,花生的发病率比不遮阴对照增加4.8、10.2个百分点,花生产量平均降低16.5%、10.0%。在30%、70%的遮阴条件下,施用锌肥的花生产量比不施锌的分别提高21.1%、25.0%。本试验条件下,施用七水硫酸锌30 kg/hm2,使花生具有较强的抗低温寡照能力及抗病性能,增产显著,可在花生产区推广应用。  相似文献   
18.
李天奇 《林业科技情报》2020,52(1):53-54,57
在黑龙江盘中自然保护区区位、用地和资源的现状分析基础上,对保护区进行类型划分,确定保护区主要保护对象和规划目标,划分出保护区的核心区、缓冲区、实验区三大功能区域的范围和面积,进而再对保护区的规划管理设施和规划管理措施进行总体探讨,从而保证黑龙江盘中自然保护区的可持续发展。  相似文献   
19.
A foliar nematode, Litylenchus crenatae ssp. mccannii, is associated with beech leaf disease (BLD) symptoms. Information about the types of tissues parasitized and how nematode populations fluctuate in these tissues over time is needed to improve surveys as well as understand the nematodes role in BLD. During this study, the nematode was detected throughout the known range of BLD by researchers at both Canadian and US institutions using a modified pan method to extract nematodes. Monthly collections of symptomatic and asymptomatic leaves during the growing season (May–October), and leaves and buds between growing seasons (November–March), revealed that nematodes were present in all tissue types. Progressively larger numbers of nematodes were detected in symptomatic leaves from Ohio and Ontario, with the greatest detections at the end of the growing season. Smaller numbers of nematodes were detected in asymptomatic leaves from BLD‐infected trees, typically at the end of the growing season. The nematode was detected overwintering in buds and detached leaves. The discovery of small numbers of nematodes in detached leaves at one location before BLD was detected indicates that nematodes may have been present before disease symptoms were expressed. Other nematodes, Plectus and Aphelenchoides spp., were infrequently detected in small numbers. Our findings support the involvement of the nematode in BLD and indicate that symptoms develop only when certain requirements, such as infection of buds, are met. We also found that the nematode can be reliably detected in buds and leaves using the modified pan extraction method.  相似文献   
20.
在研究博物馆旅游相关内涵的基础上,系统地阐述了博物馆和旅游的关系,认为博物馆旅游是未来的发展趋势。文中依托国家植物博物馆建设的基本情况,对国家植物博物馆发展旅游具备的政策机遇、游客基数、区位、行业地位、资源、特色等方面的优势及国内没有成熟的经验和成功的案例可借鉴、藏品艺术价值不高等劣势进行分析。提出建立合理的运维机制,处理好馆、库、园一体统筹的关系;按照国家5A级旅游景区标准,高起点、高规格建设;以人为本,强化深度体验;重视人才、科普和营销;与茨坝生物科技特色小镇融合发展,打造云南省“健康生活目的地”示范园区;整合资源,建立旅联体,打造科普文旅融合产业走廊等国家植物博物馆旅游发展的策略及建议。  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