全文获取类型
收费全文 | 3252篇 |
免费 | 173篇 |
国内免费 | 461篇 |
专业分类
林业 | 296篇 |
农学 | 431篇 |
基础科学 | 388篇 |
633篇 | |
综合类 | 1015篇 |
农作物 | 171篇 |
水产渔业 | 119篇 |
畜牧兽医 | 496篇 |
园艺 | 153篇 |
植物保护 | 184篇 |
出版年
2024年 | 12篇 |
2023年 | 34篇 |
2022年 | 93篇 |
2021年 | 163篇 |
2020年 | 126篇 |
2019年 | 108篇 |
2018年 | 74篇 |
2017年 | 140篇 |
2016年 | 138篇 |
2015年 | 140篇 |
2014年 | 131篇 |
2013年 | 174篇 |
2012年 | 208篇 |
2011年 | 209篇 |
2010年 | 209篇 |
2009年 | 179篇 |
2008年 | 154篇 |
2007年 | 179篇 |
2006年 | 178篇 |
2005年 | 169篇 |
2004年 | 85篇 |
2003年 | 100篇 |
2002年 | 79篇 |
2001年 | 83篇 |
2000年 | 93篇 |
1999年 | 127篇 |
1998年 | 65篇 |
1997年 | 85篇 |
1996年 | 57篇 |
1995年 | 62篇 |
1994年 | 43篇 |
1993年 | 23篇 |
1992年 | 30篇 |
1991年 | 27篇 |
1990年 | 43篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1982年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有3886条查询结果,搜索用时 15 毫秒
91.
92.
为解决农用运输车前悬架存在振动过大等问题,基于ADAMS软件对农用汽车前悬架进行模拟仿真试验,以指导农用运输车前悬架的优化设计,使其具备更好的动力学性能。优化结果:上横臂长度、上横臂在汽车横向平面的倾角为332.6mm、12.5°,下横臂长度、下横臂在汽车横向平面的倾角为516.5mm、6.5°,车轮接地点的侧向滑移量由初始的19.783mm下降为3.2911mm。 相似文献
93.
AIM: To investigate the possible role of endothelin(ET-1) in asthma pathogenesis and the effect of atrial natriuretic factor (ANF) on changes of ET-1. METHODS: Measuring the contents of endothelin-1(ET-1),atrial natriuretic factor(ANF),cGMP in plasma and bronchoalveolar lavage fluid (BALF) of guinea pigs. RESULTS: The contents of ET-1, ANF and cGMP in asthma group were higher than that of the control group; There was a significant negative correlation between ET-1 and ANF( r=-0.638,P <0.05) in plasma of the asthma group, and a significantly negative correlation between ET-1 and ANF( r=-0.921,P <0.01) in BALF of the asthma group. There was a significantly positive correlation between ANF and cGMP( r=0.848,P <0.01) in plasma of the asthma group,and a significantly positive correlation between ANF and cGMP ( r=0.831,P <0.01) in BALF of the asthma group. The levels ET-1 in the asthma+rat ANF(rANF) group were lower than those in the asthma group,and the levels of cGMP in the asthma+rat ANF(rANF) group were higher than those in the asthma group after ceasing to infuse rANF for guinea pigs for 30 minutes.CONCLUSION: ET-1 might play an important role in the pathogenesis of asthma.ANF might inhibit production of ET-1. 相似文献
94.
95.
Jin Yao Haibo Huang Long Mao Zhihan Li Heping Zhu Yuejun Liu 《Fibers and Polymers》2017,18(11):2118-2124
Cellulose nanocrystals (CNC) with high aspect ratio of 80 have been readily prepared from the inexpensive fruit shell of Camellia oleifera Abel (SCOA) for the first time. In this study, SOCA was consecutively subjected to alkali extraction, hydrogen peroxide bleaching and acid hydrolysis to remove non-cellulosic components and release CNC. The derived CNC possesses a needle-shaped structure that in average diameter and length of 6±2 nm and 500±100 nm, respectively. The crystallinity index of CNC increased to 72 % and the initial decomposition temperature raised to 230 oC. The obtained CNC was formed to nanopaper by vacuum filtration showing high visible light transmittance over 90 %. Thus SOCA derived CNC is of great practical potential to apply in the field of biomedicine, energy, packing, etc. Overall, this study is anticipated to offer new possibility for the CNC production from the inexpensive but abundant agricultural wastes. 相似文献
96.
MicroRNAs (miRNAs)are a class of non-coding, endogenous, single-stranded small RNA molecules composed of 19~25 nucleotides. miRNAs are widely involved in the process of human life activities. Recent studies have shown that part of miRNAs regulate the vascular endothelial function and angiogenesis. High expression of miRNA-21 is found to play important roles in the cell proliferation, cell apoptosis, cell growth and death of vascular endothelial cells. This review will focus on the recent progress related to miRNAs in vascular endothelial function and angiogenesis, providing a new insight in cardiovascular disease prevention, clinical diagnosis, prognosis and target therapeutics. 相似文献
97.
为探讨生物菌剂在烤烟上的施用效果,研究了减氮配施生物菌剂对土壤肥力及烟叶产质量影响。结果表明:与常规施肥相比,减氮并配施生物菌剂处理能明显提高烟株各生育时期土壤中有机质、速效磷和速效钾含量,明显增加根际和非根际细菌和放线菌数量,烟叶产量提高172~586 kg/hm~2,产值提高8927~21357元/hm~2。烤后烟叶化学成分分析表明,与常规施肥相比,减氮并配施生物菌剂处理降低了中、上部叶总糖和还原糖含量,除处理T5(众邦)外,中部叶和上部叶烟碱含量均有明显下降,下部叶、中部叶和上部叶烟叶钾含量提高幅度为分别为0.12~0.53、0.03~0.41和0.14~0.65个百分点。不同生物菌剂间相比,以处理T4(人元)和处理T2(时科)在经济性状和烟叶化学成分协调性上表现较好。 相似文献
98.
99.
100.