全文获取类型
收费全文 | 1159篇 |
免费 | 81篇 |
出版年
2023年 | 5篇 |
2022年 | 4篇 |
2021年 | 19篇 |
2020年 | 13篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 22篇 |
2016年 | 34篇 |
2015年 | 55篇 |
2014年 | 65篇 |
2013年 | 89篇 |
2012年 | 103篇 |
2011年 | 88篇 |
2010年 | 58篇 |
2009年 | 64篇 |
2008年 | 79篇 |
2007年 | 89篇 |
2006年 | 74篇 |
2005年 | 75篇 |
2004年 | 60篇 |
2003年 | 53篇 |
2002年 | 59篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 8篇 |
1998年 | 10篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1971年 | 3篇 |
1965年 | 1篇 |
1964年 | 2篇 |
1927年 | 2篇 |
排序方式: 共有1240条查询结果,搜索用时 15 毫秒
91.
92.
Helen B. Anderson Jesper Madsen Eva Fuglei Gitte H. Jensen Sarah J. Woodin René van der Wal 《Polar Biology》2015,38(2):153-162
Pink-footed geese Anser brachyrhynchus nest in two contrasting but commonly found habitats: steep cliffs and open tundra slopes. In Svalbard, we compared nest densities and nesting success in these two environments over ten breeding seasons to assess the impact of spring snow cover, food availability to nesting adults and arctic fox Vulpes lagopus (main terrestrial predator) abundance. In years with extensive spring snow cover, fewer geese at both colonies attempted to breed, possibly because snow cover limited pre-nesting feeding opportunities, leaving adults in poor breeding condition. Nesting success at the steep cliff colony was lower with extensive spring snow cover; such conditions force birds to commit to repeated and prolonged recess periods at far distant feeding areas, leaving nests open to predation. By contrast, nesting success at the open tundra slope was not affected by spring snow cover; even if birds were apparently in poor condition they could feed immediately adjacent to their nests and defend them from predators. Foxes were the main nest predator in the open tundra slopes but avian predators likely had a larger impact at the steep cliffs colony. Thus, the relative inaccessibility of the cliffs habitat may bring protection from foxes but also deprives geese from readily accessing feeding areas, with the best prospects for successful nesting in low spring snow cover years. Our findings indicate that spring snow cover, predator abundance and food proximity did not uniformly influence nesting success of this herbivore, and their effects were dependent on nesting habitat choice. 相似文献
93.
94.
95.
Enzymatic degradation of lignin‐carbohydrate complexes (LCCs): Model studies using a fungal glucuronoyl esterase from Cerrena unicolor 下载免费PDF全文
96.
Engineering temporal accumulation of a low recalcitrance polysaccharide leads to increased C6 sugar content in plant cell walls 下载免费PDF全文
Miguel E. Vega‐Sánchez Dominique Loqué Jeemeng Lao Michela Catena Yves Verhertbruggen Thomas Herter Fan Yang Jesper Harholt Berit Ebert Edward E. K. Baidoo Jay D. Keasling Henrik V. Scheller Joshua L. Heazlewood Pamela C. Ronald 《Plant biotechnology journal》2015,13(7):903-914
Reduced cell wall recalcitrance and increased C6 monosaccharide content are desirable traits for future biofuel crops, as long as these biomass modifications do not significantly alter normal growth and development. Mixed‐linkage glucan (MLG), a cell wall polysaccharide only present in grasses and related species among flowering plants, is comprised of glucose monomers linked by both β‐1,3 and β‐1,4 bonds. Previous data have shown that constitutive production of MLG in barley (Hordeum vulgare) severely compromises growth and development. Here, we used spatio‐temporal strategies to engineer Arabidopsis thaliana plants to accumulate significant amounts of MLG in the cell wall by expressing the rice CslF6 MLG synthase using secondary cell wall and senescence‐associated promoters. Results using secondary wall promoters were suboptimal. When the rice MLG synthase was expressed under the control of a senescence‐associated promoter, we obtained up to four times more glucose in the matrix cell wall fraction and up to a 42% increase in saccharification compared to control lines. Importantly, these plants grew and developed normally. The induction of MLG deposition at senescence correlated with an increase of gluconic acid in cell wall extracts of transgenic plants in contrast to the other approaches presented in this study. MLG produced in Arabidopsis has an altered structure compared to the grass glucan, which likely affects its solubility, while its molecular size is unaffected. The induction of cell wall polysaccharide biosynthesis in senescing tissues offers a novel engineering alternative to enhance cell wall properties of lignocellulosic biofuel crops. 相似文献
97.
Johansson AS Haeggström JZ Palmblad J 《Prostaglandins, leukotrienes, and essential fatty acids》2011,84(3-4):109-112
Leukotriene B4 (LTB4), a potent chemotactic and immune-modulating lipid mediator, signals via two receptors, BLT1 and BLT2, leading to pro-inflammatory responses in phagocytes. Recently, we reported that BLT1 is the predominating BLT on human umbilical vein endothelial cells (HUVEC) and transmits a variety of functional responses. Here, we demonstrate that, in HUVEC, two BLT1 antagonists (U75302, CP105696) and one BLT2 antagonist (LY255283) possess intrinsic but varying agonist activity for adhesion of neutrophils, up-regulation of E-selectin, ICAM-1 and VCAM-1, and release of MCP-1. These effects were observed after exposure of HUVEC for the drugs for 0.25-6h, persisted for several hours, and were less potent in magnitude as those elicited by LPS. Our findings may have consequences for interpretation of in vitro BLT blockade experiments. 相似文献
98.
Jensen TB Henriksen JR Rasmussen BE Rasmussen LM Andresen TL Wengel J Pasternak A 《Bioorganic & medicinal chemistry》2011,19(16):4739-4745
Thrombin binding aptamer is a DNA 15-mer which forms a G-quadruplex structure and possess promising anticoagulant properties due to specific interactions with thrombin. Herein we present the influence of a single 2'-C-piperazino-UNA residue and UNA residues incorporated in several positions on thermodynamics, kinetics and biological properties of the aptamer. 2'-C-Piperazino-UNA is characterized by more efficient stabilization of quadruplex structure in comparison to regular UNA and increases thermodynamic stability of TBA by 0.28-0.44 kcal/mol in a position depending manner with retained quadruplex topology and molecularity. The presence of UNA-U in positions U3, U7, and U12 results in the highest stabilization of G-quadruplex structure (ΔΔG(37)(°)=-1.03kcal/mol). On the contrary, the largest destabilization mounting to 1.79 kcal/mol was observed when UNA residues were placed in positions U7, G8, and U9. Kinetic studies indicate no strict correlation between thermodynamic stability of modified variants and their binding affinity to thrombin. Most of the studied variants bind thrombin, albeit with decreased affinity in reference to unmodified TBA. Thrombin time assay studies indicate three variants as being as potent as TBA in fibrin clotting inhibition. 相似文献
99.
Lohse B Kristensen JL Kristensen LH Agger K Helin K Gajhede M Clausen RP 《Bioorganic & medicinal chemistry》2011,19(12):3625-3636
Methylated lysines are important epigenetic marks. The enzymes involved in demethylation have recently been discovered and found to be involved in cancer development and progression. Despite the relative recent discovery of these enzymes a number of inhibitors have already appeared. Most of the inhibitors are either previously reported inhibitors of related enzymes or compounds derived from these. Development in terms of selectivity and potency is still pertinent. Several reports on the development of functional assays have been published. 相似文献
100.
Kim H Blomqvist Jesper Lundbom Nina Lundbom Raimo E Sepponen 《Biomedical engineering online》2011,10(1):1-9