全文获取类型
收费全文 | 459篇 |
免费 | 16篇 |
专业分类
林业 | 39篇 |
农学 | 26篇 |
基础科学 | 7篇 |
77篇 | |
综合类 | 20篇 |
农作物 | 50篇 |
水产渔业 | 36篇 |
畜牧兽医 | 169篇 |
园艺 | 11篇 |
植物保护 | 40篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 16篇 |
2017年 | 8篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 13篇 |
2013年 | 31篇 |
2012年 | 47篇 |
2011年 | 46篇 |
2010年 | 22篇 |
2009年 | 19篇 |
2008年 | 24篇 |
2007年 | 20篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 14篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1996年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有475条查询结果,搜索用时 0 毫秒
471.
The effect of block sequence on the self-assembly of ABC-type triblock copolymers in the ordered state is investigated using
an isothermal-isobaric molecular dynamics simulation. The block sequence has an important effect on the morphology of ABC
triblock copolymers. Different morphologies are observed depending on the block sequence as well as the block composition.
The triblock copolymers with the volume fraction of 1:1:1 (f
A=f
B=f
C=0.33) show the three phase and four layered lamellar structures irrespective of the block sequence. The A32B16C32 triblock copolymer withf
B=0.2 shows a morphology in which cylinders of midblock B are formed at the interface between A and C lamellae, whereas the
morphology of triblock copolymer B16C32A32 and C32A32B16 show a cylindrical core-shell structure and a lamellar type morphology, respectively. The A20B40C20 triblock copolymer with the block B as a major component shows a tricontinuous structure, whereas both B40C20A20 and C20A20B40 triblock copolymers exhibit the lamellar structures. When the block B has larger volume fraction withf
B=0.75, the matrix is composed of block B, and other two blocks A and C form spherical domains. 相似文献
472.
Antioxidant activities and phenolic compositions of the active fractions of Salvia virgata Jacq. (Lamiaceae) from Turkey were examined. The aerial part of S. virgata was extracted with different solvents in an order of increasing polarity such as hexane, ethyl acetate, methanol, and 50% aqueous methanol using a Soxhlet apparatus. Water extract was also prepared from S. virgata by reflux. All solvent fractions were investigated for their total phenolic contents, total flavonoids, flavonols, qualitative-quantitative compositions (by HPLC-PDA analysis), iron(III) reductive activities, free radical scavenging activities (using DPPH*), and effect upon linoleic acid peroxidation activities; also, the peroxidation level was determined by the TBA method. The results of activity tests given as IC50 values were estimated from nonlinear algorithm and compared with standards, viz., butylated hydroxytoluene, ascorbic acid, and gallic acid. Polar fractions were found to be more active for free radical activity whereas nonpolar fractions protected the peroxidation of linoleic acid. Rosmarinic acid was the most abundant component in the extracts, followed by caffeic acid and lutelin-7- O-glycoside. 相似文献
473.
Key message
Liming, an ameliorative method for acidified forest soils, affected the relative abundance of prey of ground-hunting spiders and consequently reduced densities of functionally similar species of these predators.Context
Liming, an ameliorative method for acidified forest soils, may modify the structure of an arthropod community by altering the soil characteristics and/or the availability of food resources.Aims
We investigated the effect of liming on the community structure of ground-hunting spiders in a birch forest.Methods
We established six experimental birch stand plots. Each stand was exposed to one of three experimental treatments: control, 1.5 t/ha, or 3 t/ha of dolomitic limestone. We collected spiders using pitfall traps during 5 years. We characterized the community in terms of activity density, species richness, community-weighted mean body size, and functional diversity and evenness in body size. We further investigated the potential links through which the liming might affect spiders, namely soil characteristics, effect of liming on birch, and densities of potential prey.Results
The commonly used dosage of 3 t/ha reduced densities of functionally similar species which led to the reduced functional evenness in body size and increased functional divergence in body size. Liming increased soil pH only slightly but decreased the densities of spiders’ preferred prey.Conclusion
The liming affected the community of ground-hunting spiders, at least partially, through reduced densities of their preferred prey.474.
Seong-Hee Ko YoonHee Lim Eun Jae Kim Young Wook Ko In-Sun Hong Sanghee Kim YunJae Jung 《Marine drugs》2022,20(9)
The intestine and skin provide crucial protection against the external environment. Strengthening the epithelial barrier function of these organs is critical for maintaining homeostasis against inflammatory stimuli. Recent studies suggest that polar marine algae are a promising bioactive resource because of their adaptation to extreme environments. To investigate the bioactive properties of polar marine algae on epithelial cells of the intestine and skin, we created extracts of the Antarctic macroalgae Himantothallus grandifolius, Plocamium cartilagineum, Phaeurus antarcticus, and Kallymenia antarctica, analyzed the compound profiles of the extracts using gas chromatography-mass spectrometry, and tested the protective activities of the extracts on human intestinal and keratinocyte cell lines by measuring cell viability and reactive oxygen species scavenging. In addition, we assessed immune responses modulated by the extracts by real-time polymerase chain reaction, and we monitored the barrier-protective activities of the extracts on intestinal and keratinocyte cell lines by measuring transepithelial electrical resistance and fluorescence-labeled dextran flux, respectively. We identified bioactive compounds, including several fatty acids and lipid compounds, in the extracts, and found that the extracts perform antioxidant activities that remove intracellular reactive oxygen species and scavenge specific radicals. Furthermore, the Antarctic marine algae extracts increased cell viability, protected cells against inflammatory stimulation, and increased the barrier integrity of cells damaged by lipopolysaccharide or ultraviolet radiation. These results suggest that Antarctic marine algae have optimized their composition for polar environments, and furthermore, that the bioactive properties of compounds produced by Antarctic marine algae can potentially be used to develop therapeutics to promote the protective barrier function of the intestine and skin. 相似文献
475.
缅甸是东南亚林业大国,尽管近年来森林资源总量下降,但竹资源丰富,发展空间十分巨大,竹产业被列为该国政府发展农村经济的重要方向.但是缅甸竹产业整体开发水平落后,且面临竹材综合利用率不高、产品附加值低及资源浪费严重等问题,亟待以科技为主的全方位提升.中国在竹林经营和产业开发方面经验丰富,但也存在资源短缺、与周边国家交流不足... 相似文献