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   13766篇
  免费   961篇
  国内免费   1193篇
林业   1739篇
农学   1173篇
基础科学   911篇
  1967篇
综合类   6530篇
农作物   654篇
水产渔业   558篇
畜牧兽医   1012篇
园艺   308篇
植物保护   1068篇
  2024年   124篇
  2023年   302篇
  2022年   546篇
  2021年   571篇
  2020年   508篇
  2019年   651篇
  2018年   372篇
  2017年   630篇
  2016年   735篇
  2015年   655篇
  2014年   835篇
  2013年   907篇
  2012年   1194篇
  2011年   1129篇
  2010年   906篇
  2009年   850篇
  2008年   700篇
  2007年   848篇
  2006年   622篇
  2005年   497篇
  2004年   368篇
  2003年   316篇
  2002年   245篇
  2001年   230篇
  2000年   155篇
  1999年   165篇
  1998年   136篇
  1997年   121篇
  1996年   105篇
  1995年   97篇
  1994年   75篇
  1993年   70篇
  1992年   60篇
  1991年   58篇
  1990年   55篇
  1989年   28篇
  1988年   26篇
  1987年   6篇
  1986年   5篇
  1985年   3篇
  1984年   2篇
  1981年   3篇
  1980年   3篇
  1978年   2篇
  1977年   2篇
  1962年   1篇
  1956年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
传统的教育评价体系一定程度上阻碍了创造教育的实施,因此探索与创造教育相适应的评价体系将成为时代之必须。本文基于部队院校评价现状,在学习借鉴当今世界最新的评价理念和总结已有研究成果的基础上,从评价机构和评价指标和评价法方面,提出与部队院校相适应的创造教育评价体系。  相似文献   
92.
吉林省长白森林经营局发展的几点经验   总被引:1,自引:0,他引:1  
张光浩  张成波 《森林工程》2011,27(3):83-84,88
实施天然林保护工程后,木材产量的大幅度调减给企业带来了巨大的生存压力。在此压力下,吉林省长白森林经营局立足本地实际,充分发挥自然资源优势,选择优势项目进行综合开发,大力发展非林经济。通过关停和出售亏损企业等措施,减轻企业负担,积累企业资金。经过十年的努力,使企业逐步发展成为一个拥有林业、水利电力业和医药业的综合性地方森工企业。  相似文献   
93.
山东农业科技期刊学术影响力分析与动态评估   总被引:1,自引:0,他引:1  
利用动态评估模型对2008~2012年山东13种农业科技期刊的学术影响力进行分析。结果显示,2008~2012年中,13种农业类科技期刊的总被引频次和影响因子总体呈上升趋势,5年间,平均总被引频次增加了84.85%,平均影响因子增加了47.35%;平均学术影响力呈快速增长趋势,5年间增长了268%。各期刊发展不均衡,其中,《山东农业科学》和《中国烟草科学》学术影响力分别位居第一和第二,且发展态势良好。  相似文献   
94.
房威  朱安  李杨  张志转  朱永和 《安徽农业科学》2011,39(2):F0002-F0002,F0003
对学科影响指标反映期刊学术影响力的情况、与其他评价指标之间的联系、在期刊学科分类工作中的作用及其存在的局限性进行了初步分析和探讨。  相似文献   
95.
对保健食品中原花青素的测定进行不确定度的评定,建立不确定度评定程序和方法。依据《保健食品检验与评价技术规范》建立数学模型,进行不确定度的计算并合成不确定度。找出了影响保健食品中原花青素测定的主要因素,分析归纳了不确定度分量的主要来源。评定程序和方法符合规范要求,适用于同类型试验不确定度评定。  相似文献   
96.
充分发挥好烤烟合作社的桥梁纽带作用,稳定好烟农队伍和烤烟面积已迫在眉睫。本文通过以徽县金叶烤烟农民专业合作社为例,从合作社融合发展的现状、优缺点、今后发展的方向3方面详细介绍了烤烟专业合作社融合发展新模式,以期为其他烤烟专业合作社融合发展提供借鉴和思路。  相似文献   
97.
文章简要探讨农业科研机构创新绩效评价的目的意义、内容方法、评价指标体系和结果运用等,为农业科研机构创新绩效评价体系建立提供参考。  相似文献   
98.
弹性模量是衡量人造板材料力学性能的重要指标,用标准差法对其进行综合评价尤为必要,对其实测及方差分析具有较好的应用价值。采用三点弯曲静力法和悬臂梁自由端振动法,测定各向同性HDF、三合板和OSB试材的静弹性模量和动弹性模量。在实测数据分析中,为反映总体弹性模量实测值数据集的离散程度及落在样本统计值某一区内的概率,还确定了其置信区间,评价了置信度。结果表明:各向同性人造板材料的静弹性模量和动弹性模量测试结果一致,其置信区间越大,置信水平越高。  相似文献   
99.
Summary

It is some years now since forest decline was a major public concern in Europe and was one of the principal environmental issues around which international research programs were focused. A number of internationally coordinated activities were initiated in the 1980s and 1990s and have continued until now; these contributed significantly to our current understanding of forestry and to the way in which forestry policies have developed. In short, the concept of sustainable development has had an increasing influence and is now of immeasurable value in forest policy, with sustainable forest management well established as its guiding principle. This sequence of events is examined here. The extent to which understanding has advanced is remarkable; much has changed. Arguably this period gave the first indication of the extent to which forests and ecosystems globally are threatened by environmental change. On the basis of the last 20 years, it is tempting to conclude that we now have an effective institutional framework and have made excellent progress. However, some of the recorded ecosystem responses seem anomalous; there are surprises in system responses, e.g., the linkage between sulphur and nitrogen depositions and forest growth. Even more importantly some specific pollutant problems remain and will intensify, and climate change has become an environmental issue of overwhelming importance.  相似文献   
100.
Genomic selection (GS) is now practiced successfully across many species. However, many questions remain, such as long-term effects, estimations of genomic parameters, robustness of genome-wide association study (GWAS) with small and large datasets, and stability of genomic predictions. This study summarizes presentations from the authors at the 2020 American Society of Animal Science (ASAS) symposium. The focus of many studies until now is on linkage disequilibrium between two loci. Ignoring higher-level equilibrium may lead to phantom dominance and epistasis. The Bulmer effect leads to a reduction of the additive variance; however, the selection for increased recombination rate can release anew genetic variance. With genomic information, estimates of genetic parameters may be biased by genomic preselection, but costs of estimation can increase drastically due to the dense form of the genomic information. To make the computation of estimates feasible, genotypes could be retained only for the most important animals, and methods of estimation should use algorithms that can recognize dense blocks in sparse matrices. GWASs using small genomic datasets frequently find many marker-trait associations, whereas studies using much bigger datasets find only a few. Most of the current tools use very simple models for GWAS, possibly causing artifacts. These models are adequate for large datasets where pseudo-phenotypes such as deregressed proofs indirectly account for important effects for traits of interest. Artifacts arising in GWAS with small datasets can be minimized by using data from all animals (whether genotyped or not), realistic models, and methods that account for population structure. Recent developments permit the computation of P-values from genomic best linear unbiased prediction (GBLUP), where models can be arbitrarily complex but restricted to genotyped animals only, and single-step GBLUP that also uses phenotypes from ungenotyped animals. Stability was an important part of nongenomic evaluations, where genetic predictions were stable in the absence of new data even with low prediction accuracies. Unfortunately, genomic evaluations for such animals change because all animals with genotypes are connected. A top-ranked animal can easily drop in the next evaluation, causing a crisis of confidence in genomic evaluations. While correlations between consecutive genomic evaluations are high, outliers can have differences as high as 1 SD. A solution to fluctuating genomic evaluations is to base selection decisions on groups of animals. Although many issues in GS have been solved, many new issues that require additional research continue to surface.  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