全文获取类型
收费全文 | 27401篇 |
免费 | 1725篇 |
国内免费 | 2260篇 |
专业分类
林业 | 1627篇 |
农学 | 1966篇 |
基础科学 | 824篇 |
7950篇 | |
综合类 | 11659篇 |
农作物 | 1754篇 |
水产渔业 | 560篇 |
畜牧兽医 | 1823篇 |
园艺 | 858篇 |
植物保护 | 2365篇 |
出版年
2024年 | 210篇 |
2023年 | 730篇 |
2022年 | 1090篇 |
2021年 | 1165篇 |
2020年 | 1141篇 |
2019年 | 1256篇 |
2018年 | 930篇 |
2017年 | 1415篇 |
2016年 | 1611篇 |
2015年 | 1283篇 |
2014年 | 1538篇 |
2013年 | 1803篇 |
2012年 | 2301篇 |
2011年 | 1925篇 |
2010年 | 1489篇 |
2009年 | 1485篇 |
2008年 | 1291篇 |
2007年 | 1499篇 |
2006年 | 1344篇 |
2005年 | 1061篇 |
2004年 | 796篇 |
2003年 | 630篇 |
2002年 | 508篇 |
2001年 | 430篇 |
2000年 | 405篇 |
1999年 | 273篇 |
1998年 | 255篇 |
1997年 | 238篇 |
1996年 | 227篇 |
1995年 | 199篇 |
1994年 | 126篇 |
1993年 | 138篇 |
1992年 | 136篇 |
1991年 | 123篇 |
1990年 | 88篇 |
1989年 | 79篇 |
1988年 | 62篇 |
1987年 | 50篇 |
1986年 | 24篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1973年 | 1篇 |
1963年 | 1篇 |
1962年 | 4篇 |
1956年 | 1篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 953 毫秒
81.
以干旱、半干旱地区荒漠草地不同沙漠化阶段土壤为研究对象,研究不同沙漠化阶段土壤易氧化有机碳与溶解性有机碳含量和分配比例变异规律,分析不同沙漠化阶段土壤碳库指数变化,探讨荒漠草地沙漠化过程中土壤易氧化有机碳与溶解性有机碳对土壤碳库的表征作用。结果表明,随着荒漠草地沙漠化程度的加剧,易氧化有机碳含量表现出一定的波动性,但整体呈下降趋势,溶解性有机碳含量呈线性下降。易氧化有机碳和溶解性有机碳分配比例均在荒漠草地达到最大值,在半固定沙地达到最小值。利用易氧化有机碳含量计算的土壤碳库管理指数随荒漠草地沙漠化程度增加表现出先下降后上升趋势,利用溶解性有机碳含量计算的土壤碳库管理指数呈线性下降趋势。易氧化有机碳、溶解性有机碳含量与土壤有机碳均显著正相关,但溶解性有机碳的相关系数略高于易氧化有机碳。通过比较活度敏感指数和碳库管理指数敏感指数发现,荒漠草地逆向演替至固定沙地过程中,易氧化有机碳的各项敏感指数均高于溶解性有机碳。固定沙地演替至流动沙地过程中,溶解性有机碳的各项敏感指数均高于易氧化有机碳,表明易氧化有机碳能够较好地表征荒漠草地沙漠化前期土壤碳库变化,而荒漠草地沙漠化中期和后期利用溶解性有机碳表征效果更好。 相似文献
82.
Response of labile organic C and N pools to plastic film removal from semiarid farmland soil
下载免费PDF全文
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
S. S. Luo L. Zhu J. L. Liu L. D. Bu S. C. Yue Y. F. Shen S. Q. Li 《Soil Use and Management》2016,32(4):535-542
To examine the effects of plastic film removal on grain yield and soil organic matter (SOM), a spring maize (Zea may L.) field experiment was conducted for 5 yr at Changwu Agricultural and Ecological Experimental Station of Northwest China. Compared with traditional plastic film mulching during entire growing stages (FM), plastic film removal at the silking stage (RM) resulted in a 6.3% higher average maize yield. Under the RM treatment, soil organic carbon and total nitrogen significantly increased after the 5‐yr cultivation in the 0‐ to 20‐cm layer. Significant increases in extractable organic C (EOC), KMnO4‐oxidizable C (KMnO4‐C) and C management index (CMI) in the 0‐ to 20‐cm layer, and light fraction organic C and EOC in the 20‐ to 40‐cm layer were observed in response to plastic film removal after the 1‐yr treatment; the responses were more significant after 5 yr. Under the RM treatment, significant increases in microbial biomass C, light fraction organic N, extractable organic N, KMnO4‐C and CMI were also observed after five years in the 20‐ to 40‐cm layer. Moreover, KMnO4‐C and EOC were much more sensitive than other labile SOM fractions to the application of RM, even after only 1 yr of cultivation. Therefore, compared with mulching for the whole growing season, plastic film removal at the maize silking stage is an effective option for increasing yields and enhancing SOM concentration and soil sustainability in the regions with semiarid monsoon climates that have sufficient rainfall during maize reproductive stages. 相似文献
83.
HUANG Ping ZHANG Jia-bao XIN Xiu-li ZHU An-ning ZHANG Cong-zhi MA Dong-hao ZHU Qiang-gen YANG Shan WU Sheng-jun 《中国农业科学(英文版)》2015,(1)
Cropland productivity has been signiifcantly impacted by soil acidiifcation resulted from nitrogen (N) fertilization, especialy as a result of excess ammoniacal N input. With decades’ intensive agricul... 相似文献
84.
85.
多品种叶面肥水稻田间应用效果探析 总被引:1,自引:0,他引:1
[目的]为大面积推广应用多品种叶面肥提供科学依据。[方法]在水稻作物上施用不同品种的叶面肥产品,对比不同叶面肥产品在水稻上的应用效果和经济效益。[结果]在抽穗阶段喷施根外生长调节剂,取得较明显的效果。[结论]根外追肥取得良好的效果,可以继续推广。 相似文献
86.
S.‐E. Jacobsen 《Journal of Agronomy and Crop Science》2011,197(5):390-399
In Bolivia, one of the world’s most important centres of plant domestication, there is growing awareness of the value of native Andean crops, both for domestic consumption and for market sale – notably the virtually boom‐like consumer demand for quinoa around the world. The southern altiplano of Bolivia, south of Oruro, relies almost purely on the production of quinoa and breeding of llamas, which have also been selected as the two commodities of priority to the government to increase the income of the country. Presently, however, quinoa is facing increasing problems in production, owing to its increasing export market and price. The flat areas around the salt desert of the southern altiplano, previously characterized by natural vegetation fed by the llamas, are being increasingly sown with quinoa, hence transformed into deserts, because intensive cultivation methods make the soil loose its fertility. Possible solutions to these problems will require extensive efforts in the south, in addition to various strategies, which also include other parts of the Bolivian altiplano and a strengthened focus on other Andean crops. 相似文献
87.
Limited effects of land use on soil dissolved organic matter chemistry as assessed by excitation–emission fluorescence spectroscopy and molecular weight fractionation
下载免费PDF全文
![点击此处可从《Soil Use and Management》网站下载免费的PDF全文](/ch/ext_images/free.gif)
P. Roberts J. M. Gibbons P. W. Hill D. L. Jones M. Farrell 《Soil Use and Management》2016,32(4):662-665
Dissolved organic matter (DOM) in soil solution represents a complex mixture of organic molecules and plays a central role in carbon and nitrogen cycling in plant–microbial–soil systems. We tested whether excitation–emission matrix (EEM) fluorescence spectroscopy can be used to characterize DOM and support previous findings that the majority of DOM is of high molecular weight (MW). EEM fluorescence spectroscopy was used in conjunction with MW fractionation to characterize DOM in soil solution from a grassland soil land management gradient in North Wales, UK. Data analysis suggested that three distinct fluorescence components could be separated and identified from the EEM data. These components were identified as being of humic‐like or fulvic‐like origin. Contrary to expectations, the majority of the fluorescence signal occurred in the small MW (<1 kDa) fraction, although differences between soils from the differently managed grasslands were more apparent in larger MW fractions. We conclude that following further characterization of the chemical composition of the fluorophores, EEM has potential as a sensitive technique for characterizing the small MW phenolic fraction of DOM in soils. 相似文献
88.
本文旨在研究等磷、钾量条件下,化肥减氮及有机肥不同用量配施对水稻产量及土壤养分的影响,试验共设6个处理,分别为T1∶80%N+20%有机肥;T2∶80%N+40%有机肥;T3∶70%N+60%有机肥;T4∶70%N+80%有机肥;T5∶60%化肥+100%有机肥;CK:100%N+0,对水稻生育期株高、群体动态、产量、构产因子以及秋季土壤养分含量进行分析,结果表明:1化肥减氮20%时,不会对水稻造成明显减产,且当有机肥配施量为500kg·mu-2时,水稻籽粒产量最高,为775.19kg·mu-2,比CK增产17.20%;2有机肥的施用能提高水稻基本苗,对水稻穗长有显著提高效果,对空秕率影响较大,对枝梗数影响最小;3化肥减氮+有机肥配施可以提高土壤肥力,增加土壤有机质含量,提高土壤碱解氮、速效钾含量。 相似文献
89.
崔峻桥 《国际沙棘研究与开发》2011,9(4):33-35
围连环夜蛾在我国多有分布,但看见其幼虫的还是很少,因资料中寄主不祥,笔者经室内外观察。发现其危害多种植物的叶片,更喜欢危害沙棘树的叶片,笔者经2a的室内外观察得知。其生物学特性在辽宁西部每年1代,以蛹越夏及冬。对沙棘树危害较重,对栽植的大果沙棘危害尤为严重,在5a生的沙棘树上有100多头幼虫危害,成虫善飞翔。 相似文献
90.
In May 2018,a new shoot dieback disease was found in several walnut orchards in Rizhao,Shandong Province.The fungal pathogen was obtained on PDA plate from diseased walnut shoots using a tissue isolation method.The purified fungal isolates formed white to grey colonies on PDA plate and three single spore isolates SDWa1-SDWa3 were obtained.Based on morphological characteristics and analysis of rDNA internal transcribed spacer (ITS),calmodulin (CAL),translation elongation factor 1-α (TEF1) and β-tubulin (TUB) sequences,the fungal isolates were identified as Diaporthe nobilis,a new pathogen on walnut.The test of Koch's rule confirmed that D.nobilis was the pathogen of walnut shoot dieback.To determine optimal growing conditions for the pathogen,its biological characteristics test was conducted.The results showed that the optimal growth temperature and pH value were at 25℃ and pH 5-9,respectively.The optimum carbon source was glucose,and favourable nitrogen source was peptone. 相似文献