全文获取类型
收费全文 | 54215篇 |
免费 | 2855篇 |
国内免费 | 6016篇 |
专业分类
林业 | 5644篇 |
农学 | 7109篇 |
基础科学 | 4707篇 |
8453篇 | |
综合类 | 18741篇 |
农作物 | 3125篇 |
水产渔业 | 2113篇 |
畜牧兽医 | 7563篇 |
园艺 | 2306篇 |
植物保护 | 3325篇 |
出版年
2024年 | 289篇 |
2023年 | 844篇 |
2022年 | 2174篇 |
2021年 | 2620篇 |
2020年 | 2493篇 |
2019年 | 2331篇 |
2018年 | 1702篇 |
2017年 | 2349篇 |
2016年 | 2075篇 |
2015年 | 2740篇 |
2014年 | 2699篇 |
2013年 | 3174篇 |
2012年 | 3986篇 |
2011年 | 4162篇 |
2010年 | 3832篇 |
2009年 | 3486篇 |
2008年 | 3147篇 |
2007年 | 2955篇 |
2006年 | 2603篇 |
2005年 | 2285篇 |
2004年 | 1102篇 |
2003年 | 859篇 |
2002年 | 739篇 |
2001年 | 748篇 |
2000年 | 805篇 |
1999年 | 946篇 |
1998年 | 829篇 |
1997年 | 720篇 |
1996年 | 675篇 |
1995年 | 684篇 |
1994年 | 539篇 |
1993年 | 473篇 |
1992年 | 494篇 |
1991年 | 370篇 |
1990年 | 323篇 |
1989年 | 228篇 |
1988年 | 189篇 |
1987年 | 140篇 |
1986年 | 64篇 |
1985年 | 36篇 |
1984年 | 35篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1964年 | 5篇 |
1963年 | 5篇 |
1956年 | 10篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
52.
为探究云南植烟区域对烤后硃砂烟叶质量的影响,运用统计性描述、主成分分析和聚类分析探讨了不同植烟区域硃砂烟叶外观质量和理化特性差异。结果表明,硃砂烟中部烟叶颜色和色度、上部烟叶外观质量指标受植烟区域的影响较大;中上部烟叶平衡含水率相对稳定,但叶面密度波动较大,其变异系数CV值分别为17.05%和20.52%;植烟区域对中上部烟叶化学成分也有较大影响,尤其是烟碱、新烟碱、假木贼碱和氯含量差异较大,其CV值高达32.89%~97.29%;主成分和聚类分析发现,滇中植烟区中上部外观质量、中部理化特性与其它烟区存在明显差异,表明滇中植烟区的中部硃砂烟叶具有明显区域特色。 相似文献
53.
54.
The method "Material Flow Analysis (MFA)" is one of the effective tools to study law and quantification of material flow between economic system and ecological system. On the national level, economy-wide material flow analysis has been published for a number of countries. However, published studies on the regional or local level are still very limited and a standardized method does not exist yet. On the basis of framework of Material Flow Analysis proposed by Eurostat, the paper collected related data and analyzed material input and output for the Chengyang district in Qingdao. The results showed that DMI (Direct Material Input) and TMR (Total Material Requirement) in absolute number increased about 3.6 and 3.9 times, respectively from 1995 to 2004. Fossil fuel and mineral contributed to about 50.3%-76.3% of DMI. Imports of material increased about 5.0 times and became the most important Contributor to DMI, which showed that local economic growth was highly dependent on resources from other regions and countries. DPO (Domestic Processed Output) and TDO (Total Domestic Output) represent slow increasing trend, and DPO contributed to 22.2%-58.1% of TDO, suggesting local hidden flows were of obvious effect on TDO. The biggest component of DPO is CO2, approximately accounting for 90% of DPO. The material productivity increased 57.7% in last decade, reflecting improvement of efficiency of resources utilization in some extent. However, compared to developed countries and regions, material productivity of Chengyang district was relatively low. Therefore, in order to promote the sustainability, it is essential to develop circular economy and enhance materials productivity. 相似文献
55.
厚层客土喷播基质中不同有机质添加物对护坡植物早期生长的影响 总被引:2,自引:1,他引:1
针对目前大量开挖草炭土用于厚层客土喷播绿化工程,导致严重破坏草炭富集区的植被,造成大量新裸露地的现状.本研究将3种不同的农业废弃物组合:Ⅱ、生玉米秸秆+生活垃圾堆肥,Ⅲ、生玉米秸秆+尿素堆肥,Ⅳ、生玉米秸秆来替代草炭土应用于厚层客土喷播绿化工程中,与草炭土(I)的绿化防护进行对比试验,对其理化性质及植物初期生长状况进行对比分析.结果表明,对照样方混合基质各项指标均满足植物正常生长所需的条件,植物早期生长状况良好,能达到有效代替草炭土的效果,具有较高的可行性. 相似文献
56.
57.
58.
Lingyu Xu Chenfu Cao Zhiyi Yang Weixin Jia 《Journal of veterinary science (Suw?n-si, Korea)》2022,23(4)
BackgroundASF was first reported in Kenya in 1910 in 1921. In China, ASF spread to 31 provinces including Henan and Jiangsu within six months after it was first reported on August 3, 2018. The epidemic almost affected the whole China, causing direct economic losses of tens of billions of yuan. Cause great loss to our pig industry. As ELISA is cheap and easy to operate, OIE regards it as the preferred serological method for ASF detection. P54 protein has good antigenicity and is an ideal antigen for detection.ObjectiveTo identify a conservative site in the African swine fever virus (ASFV) p54 protein and perform a Cloth-enzyme-linked immunosorbent assay (ELISA) for detecting the ASFV antibody in order to reduce risks posed by using the live virus in diagnostic assays.MethodWe used bioinformatics methods to predict the antigen epitope of the ASFV p54 protein in combination with the antigenic index and artificially synthesized the predicted antigen epitope peptides. Using ASFV-positive serum and specific monoclonal antibodies (mAbs), we performed indirect ELISA and blocking ELISA to verify the immunological properties of the predicted epitope polypeptide.ResultsThe results of our prediction revealed that the possible antigen epitope regions were A23–29, A36–45, A72–94, A114–120, A124–130, and A137–150. The indirect ELISA showed that the peptides A23–29, A36–45, A72–94, A114–120, and A137–150 have good antigenicity. Moreover, the A36–45 polypeptide can react specifically with the mAb secreted by hybridoma cells, and its binding site contains a minimum number of essential amino acids in the sequence 37DIQFINPY44.ConclusionsOur study confirmed a conservative antigenic site in the ASFV p54 protein and its amino acid sequence. A competitive ELISA method for detecting ASFV antibodies was established based on recombinant p54 and matching mAb. Moreover, testing the protein sequence alignment verified that the method can theoretically detect antibodies produced by pigs affected by nearly all ASFVs worldwide. 相似文献
59.
60.