全文获取类型
收费全文 | 6667篇 |
免费 | 324篇 |
国内免费 | 745篇 |
专业分类
林业 | 789篇 |
农学 | 1055篇 |
基础科学 | 607篇 |
1208篇 | |
综合类 | 1897篇 |
农作物 | 304篇 |
水产渔业 | 257篇 |
畜牧兽医 | 851篇 |
园艺 | 247篇 |
植物保护 | 521篇 |
出版年
2024年 | 18篇 |
2023年 | 75篇 |
2022年 | 201篇 |
2021年 | 287篇 |
2020年 | 234篇 |
2019年 | 256篇 |
2018年 | 164篇 |
2017年 | 237篇 |
2016年 | 233篇 |
2015年 | 302篇 |
2014年 | 274篇 |
2013年 | 315篇 |
2012年 | 443篇 |
2011年 | 409篇 |
2010年 | 434篇 |
2009年 | 357篇 |
2008年 | 384篇 |
2007年 | 363篇 |
2006年 | 346篇 |
2005年 | 354篇 |
2004年 | 149篇 |
2003年 | 177篇 |
2002年 | 91篇 |
2001年 | 120篇 |
2000年 | 152篇 |
1999年 | 212篇 |
1998年 | 176篇 |
1997年 | 148篇 |
1996年 | 137篇 |
1995年 | 104篇 |
1994年 | 101篇 |
1993年 | 88篇 |
1992年 | 88篇 |
1991年 | 60篇 |
1990年 | 72篇 |
1989年 | 51篇 |
1988年 | 47篇 |
1987年 | 26篇 |
1986年 | 14篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 3篇 |
排序方式: 共有7736条查询结果,搜索用时 0 毫秒
51.
北固山湿地野生虉草生物量的研究 总被引:1,自引:0,他引:1
对北固山湿地野生虉草的株高、茎高、叶龄、生物量等进行了研究,结果表明,虉草的株高和茎高的变化呈现出近“S”型的生长曲线,叶龄与株高和茎高均呈一元线性显著的正相关关系,生物量的变化与生育期关系密切。 相似文献
52.
中国对虾育苗时间与温度的关系及其应用 总被引:2,自引:0,他引:2
根据多年的调研和试验资料,利用非线性积温模型,模拟了对虾幼体各发育阶段所需天数与水温的关系。在此基础上研究确定了亲虾产卵孵化期的气候决策模式;并应用模式计算出了我市亲虾产卵孵化的适宜时段。为亲虾适宜产卵孵化期的决策提供了科学方法。 相似文献
53.
Dawei Yu Jiayao Feng Huimin You Shipeng Zhou Yan Bai Jincan He Hua Cao Qishi Che Jiao Guo Zhengquan Su 《Marine drugs》2022,20(1)
Chitosan obtained from abundant marine resources has been proven to have a variety of biological activities. However, due to its poor water solubility, chitosan application is limited, and the degradation products of chitosan oligosaccharides are better than chitosan regarding performance. Chitosan oligosaccharides have two kinds of active groups, amino and hydroxyl groups, which can form a variety of derivatives, and the properties of these derivatives can be further improved. In this review, the key structures of chitosan oligosaccharides and recent studies on chitosan oligosaccharide derivatives, including their synthesis methods, are described. Finally, the antimicrobial and antitumor applications of chitosan oligosaccharides and their derivatives are discussed. 相似文献
54.
55.
56.
Aging is a major risk factor for many chronic diseases, such as cancer, cardiovascular disease, and diabetes. The exact mechanisms underlying the aging process are not fully elucidated. However, a growing body of evidence suggests that several pathways, such as sirtuin, AMP-activated protein kinase, insulin-like growth factor, autophagy, and nuclear factor erythroid 2-related factor 2 play critical roles in regulating aging. Furthermore, genetic or dietary interventions of these pathways can extend lifespan by delaying the aging process. Seaweeds are a food source rich in many nutrients, including fibers, polyunsaturated fatty acids, vitamins, minerals, and other bioactive compounds. The health benefits of seaweeds include, but are not limited to, antioxidant, anti-inflammatory, and anti-obese activities. Interestingly, a body of studies shows that some seaweed-derived extracts or isolated compounds, can modulate these aging-regulating pathways or even extend lifespans of various animal models. However, few such studies have been conducted on higher animals or even humans. In this review, we focused on potential anti-aging bioactive substances in seaweeds that have been studied in cells and animals mainly based on their anti-aging cellular and molecular mechanisms. 相似文献
57.
58.
Root rot symptoms were observed in fields of alfalfa in Chifeng city, Inner Mongolia, China in 2016. Disease incidences of seven alfalfa varieties planted in 2014 ranged from 56% to 95%, while incidence of Gongnong No. 1 planted in 2016 was 8%, 31% and 76% in 2016, 2017 and 2018, respectively. Paraphoma isolates were consistently recovered from black necrotic root tissues of diseased plants with a frequency of 77.1%. Based on morphological characters and phylogenetic analysis of rDNA internal transcribed spacer (ITS), elongation factor 1-α (EF1-α) and β-tubulin (TUB), this fungus was identified as Paraphoma radicina. Glasshouse pathogenicity experiments showed that P. radicina significantly reduced above- and below-ground biomass of alfalfa plants 2 months after inoculation. Paraphoma radicina infected 70% of the plants inoculated with a root dip in conidia, and these symptoms were consistent with the symptoms in the field. Paraphoma radicina was successfully reisolated from disease roots of the inoculated alfalfa plants. This is the first report of P. radicina as the causal agent of alfalfa root rot in China. 相似文献
59.
多段进水一体化污水处理设备处理农村污水研究 总被引:1,自引:0,他引:1
目的根据农村污水的水质特点,基于UCT污水处理工艺设计了多点分段进水一体化处理设备,以提高工艺,提高氮磷去除效率。为相关应用提供了支撑。方法以北京市通州区城郊农村污水为对象,通过模拟试验,研究进水方式对处理污水效果的影响。结果相对于传统单点进水方式,两段和三段进水对处理农村生活污水除污染效果更好,最佳污染去除率在三段进水条件下达到,此时COD、TN和TP去除率分别为93%~97%、82.9%~86.2%和86%~91%,比单点进水和两段进水分别高15%和8%、13%和6%、13%和5%。结论采取多段进水运行方式能够有效提高污水处理系统对氮磷去除效率。 相似文献
60.