全文获取类型
收费全文 | 2221篇 |
免费 | 147篇 |
国内免费 | 153篇 |
专业分类
2521篇 |
出版年
2024年 | 5篇 |
2023年 | 29篇 |
2022年 | 36篇 |
2021年 | 62篇 |
2020年 | 68篇 |
2019年 | 63篇 |
2018年 | 74篇 |
2017年 | 48篇 |
2016年 | 61篇 |
2015年 | 67篇 |
2014年 | 94篇 |
2013年 | 154篇 |
2012年 | 88篇 |
2011年 | 95篇 |
2010年 | 56篇 |
2009年 | 119篇 |
2008年 | 120篇 |
2007年 | 122篇 |
2006年 | 114篇 |
2005年 | 103篇 |
2004年 | 91篇 |
2003年 | 88篇 |
2002年 | 97篇 |
2001年 | 58篇 |
2000年 | 60篇 |
1999年 | 42篇 |
1998年 | 60篇 |
1997年 | 44篇 |
1996年 | 42篇 |
1995年 | 36篇 |
1994年 | 39篇 |
1993年 | 43篇 |
1992年 | 34篇 |
1991年 | 29篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 20篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1977年 | 8篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
排序方式: 共有2521条查询结果,搜索用时 15 毫秒
151.
优良的甘蔗原料是生产高品质红糖的基础,筛选营养价值丰富的甘蔗种质资源,是选育红糖加工型甘蔗品种的基础.本研究以全国广泛种植、当前普遍用于红糖加工以及历史上较早应用于制作红糖等具有代表性的16份甘蔗种质为试验材料,通过分析蔗汁的蛋白质、总游离氨基酸、总多酚、蔗糖、还原糖、灰分、氯化物、胶体含量等营养、品质指标,采用因子分... 相似文献
152.
Sugar constituents of fucose-containing polysaccharides from various Japanese brown algae 总被引:3,自引:0,他引:3
Sugar constituents of the fucose-containing polysaccharides (FCPs) from 21 species of brown algae were analyzed. FCPs were extracted with hot water (100 °C, 4 h), separated by precipitation with 20% (v:v) ethanol in the presence of 0.05 M MgCl2 to remove contaminating soluble alginate, and purified by DEAE-Sephadex column chromatography. The samples were hydrolyzed with HCI, and neutral sugar and uronic acid were separated by anion exchange chromatography. Their amounts were determined by gas-liquid chromatography. The neutral sugars in the FCPs from Ishige okamurae, Laminaria ochotensis, Myelophycus simplex, Padina arborescens and Sargassum thunbergii all contained arabinose, fucose, galactose, glucose, mannose, rhamnose and xylose residues. The FCPs from Ishige okamurae, Padina arborescens, Sargassum hemiphyllum, S. patents and S. sagamianum contained the four uronic acids, galacturonic acid, glucuronic acid, guluronic acid and mannuronic acid. 相似文献
153.
Sylvia Lindberg 《Physiologia plantarum》1990,79(2):275-282
Three cultivars of sugar beet (Beta vulgaris L.), which are sensitive to aluminium (Al) in the order Primahill > Monohill > Regina, were grown in water culture for 2 weeks. Nutrients were supplied at 15% increase of amounts daily, corresponding to the nutrient demand for maximal growth. The 2.4-dinitrophenol (DNP)-sensitive (metabolic) and DNP-insensitive (non-metabolic) uptake of aluminium, phosphate. 45Ca2+ and K+(86Rb+) in roots were measured as well as transport to shoots of intact plants. All 3 cultivars absorbed more aluminium if DNP was present during the aluminium treatment than in its absence. It is suggested that sugar beets are able to extrude aluminium activity or that they possess an active mechanism to keep Al outside the cell. The presence of Al in the medium during the 1-h experiment affected the metabolic and non-metabolic fluxes of 45Ca2+ and K+(86Rb+) in different ways. In the presence of DNP, the influx of both 45Ca2+ and K+(86Rb+) and the efflux of 45Ca2+ were inhibited by Al in a competitive way. At inhibition of 45Ca2+ influx, 2 Al ions are probably bound per Ca2+ uptake site in cv. Regina (Al-tolerant), but in cvs Primahill and Monohill only one Al ion is bound (more Al sensitive). Aluminium competitively inhibited the active efflux of 45Ca2+ (absence of DNP) in almost the same way in the 3 cultivars. In contrast, aluminium stimulated the influx of K+(86Rb+) in cvs Primahill, Monohill and Regina in the absence of DNP. Thus, the Al effects on active and passive K+(86Rb+) influx are different. The total influx of K+(86Rb+) increased in the presence of Al and might be connected to an active exclusion of Al. Regina is the least Al-sensitive cultivar, probably because Al interferes less with the Ca2+ fluxes and because this cultivar actively excludes phosphate in the presence of Al. Thus Al-phosphate precipitation within the plant could be avoided. 相似文献
154.
Kiyoshi Isono Junsaku Nagatsu Kimie Kobinata Kazuya Sasaki Saburo Suzuki 《Bioscience, biotechnology, and biochemistry》2013,77(2):190-199
Seven additional components, polyoxins C, D, E, F, G, H and I were isolated from polyoxin complex. They have molecular formulae corresponding to C11H15N3O8, C17H23N5O14, C17H23N5O13, C23H30N6O15, C17H25N5O12, C23H32N6O13 and C19H24N4O12, respectively. These polyoxins except inactive polyoxins C and I were highly active against various kinds of phytopathogenic fungi. The close structural similarity among them including polyoxins A and B is also discussed. 相似文献
155.
156.
The impact of salinity on three arboreal mangrove plants, Sonneratia apetala (Sa), S. caseolaris (Sc) and Rhizophora stylosa (Rs), was studied. The three mangrove species were treated with different salinity levels over a three-month period. The response and adaptation of these three mangrove species to salinity were shown to be different. Net photosynthesis rate, stomata conductance and transpiration rate of leaves decreased and soluble sugar content in leaves increased, with salt concentration in all three mangrove species. The malondial dehyde (MDA) content in stems and leaves of Sa and Sc somewhat decreased when the salinity was lower than 10, but rapidly increased with increasing salt concentration. The MDA content in stems and leaves of Rs increased only when salinity was greater than 40. No changes were observed in the MDA content of roots in the three mangrove species. The adaptabilities of Sa and Sc to salt tolerance were limited. The more salt tolerant the mangrove Rs, the more likely the free oxygen radicals were eliminated through the increase in activity of superoxide dismutase (SOD). Results of this experiment identified salinity levels best suited for the growth and metabolism of the species, which provides information necessary for maintaining mangrove forestation along the South China coast. 相似文献
157.
The impact of salinity on three arboreal mangrove plants, Sonneratia apetala (Sa), S. caseolaris (Sc) and Rhizophora stylosa (Rs), was studied. The three mangrove species were treated with different salinity levels over a three-month period. The response and adaptation of these three mangrove species to salinity were shown to be different. Net photosynthesis rate, stomata conductance and transpiration rate of leaves decreased and soluble sugar content in leaves increased, with salt concentration in all three mangrove species. The malondial dehyde (MDA) content in stems and leaves of Sa and Sc somewhat decreased when the salinity was lower than 10, but rapidly increased with increasing salt concentration. The MDA content in stems and leaves of Rs increased only when salinity was greater than 40. No changes were observed in the MDA content of roots in the three mangrove species. The adaptabilities of Sa and Sc to salt tolerance were limited. The more salt tolerant the mangrove Rs, the more likely the free oxygen radicals were eliminated through the increase in activity of superoxide dismutase (SOD). Results of this experiment identified salinity levels best suited for the growth and metabolism of the species, which provides information necessary for maintaining mangrove forestation along the South China coast. 相似文献
158.
Effects of salinity and temperature stress on Ecophysiological characteristics of exotic cordgrass, Spartina alterniflora 下载免费PDF全文
Salintiy and temperature are two important ecological factors which affect the distribution and abundance of Spartina alerniflora Loisel. To find out how cordgrass adapts to the environmental conditions in the introduced range, we studied the dynamics of a series of important physiological components including superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), malondialdehyde (MDA), soluble sugar and free proline under different salinity and temperature stresses. The results showed that low NaCl concentration (lower than 100 mmol·L−1) enhanced the growth of S. alterniflora. On the contrary, high NaCl concentration (higher than 100 mmol·L−1) inhibited the growth of S. alterniflora. To a certain extent, S. alterniflora was able to be acclimated to the osmotic pressure created by external solution concentration by adjusting the activities of POD, SOD and CAT, and the contents of free proline and soluble sugar. S. alterniflora varied in its responses to environment in different parts of the plant under 5°C and 38°C temperature stress. Compared with roots, leaves accumulated more soluble sugar, and CAT activities in leaves were higher, whereas SOD and POD activities in leaves were much lower than those in roots. 相似文献
159.
A. L. P. Freitas D. I. A. Teixeira F. H. F. Costa W. R. L. Farias A. S. C. Lobato A. H. Sampaio N. M. B. Benevides 《Journal of applied phycology》1997,9(6):495-501
Aqueous protein extracts from 30 Brazilian marine algae were examined for haemagglutinating activity using native and enzyme-treated
rabbit, chicken, sheep and human erythrocytes. Most extracts agglutinated at least one of the blood cells used. Sheep and
rabbit erythrocytes were more suitable for detection of the agglutinating activity. The minimum protein concentration necessary
to produce positive agglutination was usually lower with enzyme-treated erythrocytes than native ones. The five algal protein
extracts showing the greatest haemagglutination titre were tested for sugar-binding specificity. Only the activity present
in the green alga Cauler pacupressoides was inhibited by simple sugars and not by the glycoproteins tested. The activity of
the other four extracts was inhibited by at least one of the glycoproteins utilised.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
160.
Stem cells intrigue. They have the ability to divide exponentially, recreate the stem cell compartment, as well as create differentiated cells to generate tissues. Therefore, they should be natural candidates to provide a renewable source of cells for transplantation applied in regenerative medicine. Stem cells have the capacity to generate specific tissues or even whole organs like the blood, heart, or bones. A subgroup of stem cells, the neural stem cells (NSCs), is characterized as a self-renewing population that generates neurons and glia of the developing brain. They can be isolated, genetically manipulated and differentiated in vitro and reintroduced into a developing, adult or a pathologically altered central nervous system. NSCs have been considered for use in cell replacement therapies in various neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. Characterization of genes with tightly controlled expression patterns during differentiation represents an approach to understanding the regulation of stem cell commitment. The regulation of stem cell biology by the ATP-binding cassette (ABC) transporters has emerged as an important new field of investigation. As a major focus of stem cell research is in the manipulation of cells to enable differentiation into a targeted cell population; in this review, we discuss recent literatures on ABC transporters and stem cells, and propose an integrated view on the role of the ABC transporters, especially ABCA2, ABCA3, ABCB 1 and ABCG2, in NSCs' proliferation, differentiation and regulation, along with comparisons to that in hematopoietic and other stem cells. 相似文献