全文获取类型
收费全文 | 270篇 |
免费 | 30篇 |
专业分类
300篇 |
出版年
2022年 | 3篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 20篇 |
2012年 | 20篇 |
2011年 | 22篇 |
2010年 | 12篇 |
2009年 | 17篇 |
2008年 | 19篇 |
2007年 | 11篇 |
2006年 | 11篇 |
2005年 | 9篇 |
2004年 | 18篇 |
2003年 | 13篇 |
2002年 | 13篇 |
2001年 | 5篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有300条查询结果,搜索用时 15 毫秒
81.
Maija K. Pietilä Nina S. Atanasova Hanna M. Oksanen Dennis H. Bamford 《Environmental microbiology》2013,15(6):1674-1686
Extremophiles are found in all three domains of cellular life. However, hyperthermic and hypersaline environments are typically dominated by archaeal cells which also hold the records for the highest growth temperature and are able to grow even at saturated salinity. Hypersaline environments are rich of virus‐like particles, and spindle‐shaped virions resembling lemons are one of the most abundant virus morphotypes. Spindle‐shaped viruses are archaea‐specific as all the about 15 such virus isolates infect either hyperthermophilic or halophilic archaea. In the present work, we studied spindle‐shaped virus His1 infecting an extremely halophilic euryarchaeon, Haloarcula hispanica. We demonstrate that His1 tolerates a variety of salinities, even lower than that of seawater. The detailed analysis of the structural constituents showed that the His1 virion is composed of only one major and a few minor structural proteins. There is no lipid bilayer in the His1 virion but the major structural protein VP21 is most likely lipid modified. VP21 forms the virion capsid, and the lipid modification probably enables hydrophobic interactions leading to the flexible nature of the virion. Furthermore, we propose that euryarchaeal virus His1 may be related to crenarchaeal fuselloviruses, and that the short‐tailed spindle‐shaped viruses could form a structure‐based viral lineage. 相似文献
82.
Endoplasmic reticulum remains continuous and undergoes sheet-to-tubule transformation during cell division in mammalian cells 总被引:4,自引:1,他引:3 下载免费PDF全文
The endoplasmic reticulum (ER) is a multifaceted cellular organelle both structurally and functionally, and its cell cycle–dependent morphological changes are poorly understood. Our quantitative confocal and EM analyses show that the ER undergoes dramatic reorganization during cell division in cultured mammalian cells as mitotic ER profiles become shorter and more branched. 3D modeling by electron tomography reveals that the abundant interphase structures, sheets, are lost and subsequently transform into a branched tubular network that remains continuous. This is confirmed by observing the most prominent ER subdomain, the nuclear envelope (NE). A NE marker protein spreads to the mitotic ER tubules, although it does not show a homogenous distribution within the network. We mimicked the mitotic ER reorganization using puromycin to strip the membrane-bound ribosomes from the interphase ER corresponding to the observed loss of ribosomes normally occurring during mitosis. We propose that the structural changes in mitotic ER are linked to ribosomal action on the ER membranes. 相似文献
83.
Gints Kalnins Janis Kuka Solveiga Grinberga Marina Makrecka-Kuka Edgars Liepinsh Maija Dambrova Kaspars Tars 《The Journal of biological chemistry》2015,290(35):21732-21740
CutC choline trimethylamine-lyase is an anaerobic bacterial glycyl radical enzyme (GRE) that cleaves choline to produce trimethylamine (TMA) and acetaldehyde. In humans, TMA is produced exclusively by the intestinal microbiota, and its metabolite, trimethylamine oxide, has been associated with a higher risk of cardiovascular diseases. Therefore, information about the three-dimensional structures of TMA-producing enzymes is important for microbiota-targeted drug discovery. We have cloned, expressed, and purified the CutC GRE and the activating enzyme CutD from Klebsiella pneumoniae, a representative of the human microbiota. We have determined the first crystal structures of both the choline-bound and choline-free forms of CutC and have discovered that binding of choline at the ligand-binding site triggers conformational changes in the enzyme structure, a feature that has not been observed for any other characterized GRE. 相似文献
84.
85.
Nongrowing season methane emissions–a significant component of annual emissions across northern ecosystems 下载免费PDF全文
Wetlands are the single largest natural source of atmospheric methane (CH4), a greenhouse gas, and occur extensively in the northern hemisphere. Large discrepancies remain between “bottom‐up” and “top‐down” estimates of northern CH4 emissions. To explore whether these discrepancies are due to poor representation of nongrowing season CH4 emissions, we synthesized nongrowing season and annual CH4 flux measurements from temperate, boreal, and tundra wetlands and uplands. Median nongrowing season wetland emissions ranged from 0.9 g/m2 in bogs to 5.2 g/m2 in marshes and were dependent on moisture, vegetation, and permafrost. Annual wetland emissions ranged from 0.9 g m?2 year?1 in tundra bogs to 78 g m?2 year?1 in temperate marshes. Uplands varied from CH4 sinks to CH4 sources with a median annual flux of 0.0 ± 0.2 g m?2 year?1. The measured fraction of annual CH4 emissions during the nongrowing season (observed: 13% to 47%) was significantly larger than that was predicted by two process‐based model ensembles, especially between 40° and 60°N (modeled: 4% to 17%). Constraining the model ensembles with the measured nongrowing fraction increased total nongrowing season and annual CH4 emissions. Using this constraint, the modeled nongrowing season wetland CH4 flux from >40° north was 6.1 ± 1.5 Tg/year, three times greater than the nongrowing season emissions of the unconstrained model ensemble. The annual wetland CH4 flux was 37 ± 7 Tg/year from the data‐constrained model ensemble, 25% larger than the unconstrained ensemble. Considering nongrowing season processes is critical for accurately estimating CH4 emissions from high‐latitude ecosystems, and necessary for constraining the role of wetland emissions in a warming climate. 相似文献
86.
Parikka K Leppänen AS Xu C Pitkänen L Eronen P Osterberg M Brumer H Willför S Tenkanen M 《Biomacromolecules》2012,13(8):2418-2428
Carboxylated, anionic polysaccharides were selectively prepared using a combination of enzymatic and chemical reactions. The galactose-containing polysaccharides studied were spruce galactoglucomannan, guar galactomannan, and tamarind galactoxyloglucan. The galactosyl units of the polysaccharides were first oxidized with galactose oxidase (EC 1.1.3.9) and then selectively carboxylated, resulting in the galacturonic acid derivatives with good conversion and yield. The degrees of oxidation (DO) of the products were determined by gas chromatography-mass spectrometry (GC-MS). A novel feasible electrospray ionization-mass spectrometry (ESI-MS) method was also developed for the determination of DO. The solution properties and charge densities of the products were investigated. The interaction of the products with cellulose was studied by two methods, bulk sorption onto bleached birch kraft pulp and adsorption onto nanocellulose ultrathin films by quartz crystal microbalance with dissipation (QCM-D). To study the effect of the location of the carboxylic acid groups on the physicochemical properties, polysaccharides were also oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated reaction producing polyuronic acids. The chemo-enzymatically oxidized galacturonic polysaccharides with an unmodified backbone had a better ability to interact with cellulose than the TEMPO-oxidized products. The selectively carboxylated polysaccharides can be further exploited, as such, or in the targeted functionalization of cellulose surfaces. 相似文献
87.
Progressive sheet-to-tubule transformation is a general mechanism for endoplasmic reticulum partitioning in dividing mammalian cells 总被引:1,自引:0,他引:1
Puhka M Joensuu M Vihinen H Belevich I Jokitalo E 《Molecular biology of the cell》2012,23(13):2424-2432
The endoplasmic reticulum (ER) is both structurally and functionally complex, consisting of a dynamic network of interconnected sheets and tubules. To achieve a more comprehensive view of ER organization in interphase and mitotic cells and to address a discrepancy in the field (i.e., whether ER sheets persist, or are transformed to tubules, during mitosis), we analyzed the ER in four different mammalian cell lines using live-cell imaging, high-resolution electron microscopy, and three dimensional electron microscopy. In interphase cells, we found great variation in network organization and sheet structures among different cell lines. In mitotic cells, we show that the ER undergoes both spatial reorganization and structural transformation of sheets toward more fenestrated and tubular forms. However, the extent of spatial reorganization and sheet-to-tubule transformation varies among cell lines. Fenestration and tubulation of the ER correlates with a reduced number of membrane-bound ribosomes. 相似文献
88.
Kirsi H. Pietilinen Jaakko Kaprio Maija Rsnen Aila Rissanen Richard J. Rose 《Obesity (Silver Spring, Md.)》2002,10(9):875-884
Objective: This study identified genetic and environmental influences on the tracking of body size from birth to 16 to 18.5 years of age. Research Methods and Procedures: Longitudinal information was collected from a nationally representative sample of Finnish twin adolescents (birth cohorts 1975 to 1979) and their parents through questionnaires mailed when the twins were ages 16 and 18.5 years old. The sample included 702 monozygotic, 724 same‐sex dizygotic, and 762 opposite‐sex dizygotic sets of twins. The measures used were length, weight, ponderal index (kilograms per cubic meters), and gestational age at birth, and height, weight, and body mass index (kilograms per square meters) at 16 to 18.5 years of age. The changes in genetic and environmental influences on body size from birth to early adulthood were analyzed by quantitative genetic modeling. Results: The twins who had a higher weight or ponderal index at birth were taller and heavier in early adulthood, whereas those who were longer at birth were taller, but not heavier, later in life. Adult height was affected more by the birth size than body mass index. In the genetic modeling analyses, the genetic factors accounting for the variation of body size became more apparent with age, and both genetic and environmental influences on stature had a sizable carry‐over effect from birth to late adolescence, whereas for relative weight, the influences were more age‐specific. Discussion: The genetic and environmental architecture of body size changes from birth to adulthood. Even in monozygotic twins who share their genetic background, the initially larger twin tended to remain larger, demonstrating the long‐lasting effects of fetal environment on final body size. 相似文献
89.
Koutaniemi S Guillon F Tranquet O Bouchet B Tuomainen P Virkki L Petersen HL Willats WG Saulnier L Tenkanen M 《Planta》2012,236(2):739-751
Immunolabeling can be used to locate plant cell wall carbohydrates or other components to specific cell types or to specific regions of the wall. Some antibodies against xylans exist; however, many partly react with the xylan backbone and thus provide limited information on the type of substituents present in various xylans. We have produced a monoclonal antibody which specifically recognizes glucopyranosyl uronic acid (GlcA), or its 4-O-methyl ether (meGlcA), substituents in xylan and has no cross-reactivity with linear or arabinofuranosyl-substituted xylans. The UX1 antibody binds most strongly to (me)GlcA substitutions at the non-reducing ends of xylan chains, but has a low cross-reactivity with internal substitutions as well, at least on oligosaccharides. The antibody labeled plant cell walls from both mono- and dicotyledons, but in most tissues an alkaline pretreatment was needed for antibody binding. The treatment removed acetyl groups from xylan, indicating that the vicinity of glucuronic acid substituents is also acetylated. The novel labeling patterns observed in the xylem of tree species suggested that differences within the cell wall exist both in acetylation degree and in glucuronic acid content. 相似文献
90.
Jukka Jokinen Hanna Rinta-Kokko Lotta Siira Arto A. Palmu Mikko J. Virtanen Hanna Nohynek Anni Virolainen-Julkunen Maija Toropainen J. Pekka Nuorti 《PloS one》2015,10(3)