全文获取类型
收费全文 | 10846篇 |
免费 | 854篇 |
国内免费 | 6篇 |
出版年
2023年 | 67篇 |
2022年 | 161篇 |
2021年 | 281篇 |
2020年 | 155篇 |
2019年 | 282篇 |
2018年 | 310篇 |
2017年 | 276篇 |
2016年 | 402篇 |
2015年 | 625篇 |
2014年 | 633篇 |
2013年 | 822篇 |
2012年 | 954篇 |
2011年 | 900篇 |
2010年 | 557篇 |
2009年 | 537篇 |
2008年 | 649篇 |
2007年 | 660篇 |
2006年 | 560篇 |
2005年 | 501篇 |
2004年 | 444篇 |
2003年 | 400篇 |
2002年 | 368篇 |
2001年 | 94篇 |
2000年 | 60篇 |
1999年 | 84篇 |
1998年 | 93篇 |
1997年 | 67篇 |
1996年 | 61篇 |
1995年 | 67篇 |
1994年 | 62篇 |
1993年 | 42篇 |
1992年 | 55篇 |
1991年 | 43篇 |
1990年 | 28篇 |
1989年 | 43篇 |
1988年 | 25篇 |
1987年 | 28篇 |
1986年 | 28篇 |
1985年 | 31篇 |
1984年 | 19篇 |
1983年 | 27篇 |
1982年 | 14篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 15篇 |
1977年 | 15篇 |
1974年 | 15篇 |
1972年 | 11篇 |
1968年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
291.
Marco I. Ries Hazrat Ali Peter P. Lankhorst Thomas Hankemeier Roel A. L. Bovenberg Arnold J. M. Driessen Rob J. Vreeken 《The Journal of biological chemistry》2013,288(52):37289-37295
Metabolic profiling and structural elucidation of novel secondary metabolites obtained from derived deletion strains of the filamentous fungus Penicillium chrysogenum were used to reassign various previously ascribed synthetase genes of the roquefortine/meleagrin pathway to their corresponding products. Next to the structural characterization of roquefortine F and neoxaline, which are for the first time reported for P. chrysogenum, we identified the novel metabolite roquefortine L, including its degradation products, harboring remarkable chemical structures. Their biosynthesis is discussed, questioning the exclusive role of glandicoline A as key intermediate in the pathway. The results reveal that further enzymes of this pathway are rather unspecific and catalyze more than one reaction, leading to excessive branching in the pathway with meleagrin and neoxaline as end products of two branches. 相似文献
292.
Tiago G. Santos Flavio H. Beraldo Glaucia N. M. Hajj Marilene H. Lopes Martin Roffe Fernanda C. S. Lupinacci Valeriy G. Ostapchenko Vania F. Prado Marco A. M. Prado Vilma R. Martins 《Journal of neurochemistry》2013,124(2):210-223
Prion protein (PrPC) is a cell surface glycoprotein that is abundantly expressed in nervous system. The elucidation of the PrPC interactome network and its significance on neural physiology is crucial to understanding neurodegenerative events associated with prion and Alzheimer's diseases. PrPC co‐opts stress inducible protein 1/alpha7 nicotinic acetylcholine receptor (STI1/α7nAChR) or laminin/Type I metabotropic glutamate receptors (mGluR1/5) to modulate hippocampal neuronal survival and differentiation. However, potential cross‐talk between these protein complexes and their role in peripheral neurons has never been addressed. To explore this issue, we investigated PrPC‐mediated axonogenesis in peripheral neurons in response to STI1 and laminin‐γ1 chain‐derived peptide (Ln‐γ1). STI1 and Ln‐γ1 promoted robust axonogenesis in wild‐type neurons, whereas no effect was observed in neurons from PrPC‐null mice. PrPC binding to Ln‐γ1 or STI1 led to an increase in intracellular Ca2+ levels via distinct mechanisms: STI1 promoted extracellular Ca2+ influx, and Ln‐γ1 released calcium from intracellular stores. Both effects depend on phospholipase C activation, which is modulated by mGluR1/5 for Ln‐γ1, but depends on, C‐type transient receptor potential (TRPC) channels rather than α7nAChR for STI1. Treatment of neurons with suboptimal concentrations of both ligands led to synergistic actions on PrPC‐mediated calcium response and axonogenesis. This effect was likely mediated by simultaneous binding of the two ligands to PrPC. These results suggest a role for PrPC as an organizer of diverse multiprotein complexes, triggering specific signaling pathways and promoting axonogenesis in the peripheral nervous system. 相似文献
293.
294.
Magdalena Witek Luca Pietro Casacci Francesca Barbero Dario Patricelli Marco Sala Simone Bossi Massimo Maffei Michal Woyciechowski Emilio Balletto Simona Bonelli 《Biological journal of the Linnean Society. Linnean Society of London》2013,109(3):699-709
Myrmica ant colonies host numerous insect species, including the larvae of Maculinea butterflies and Microdon myrmicae hoverflies. Little is known about the interspecific relationships among these social parasites and their host ants occurring in sympatric populations. We investigated communities of social parasites to assess the strategies allowing them to share the same pool of resources (i.e. Myrmica colonies). The present study was carried out at five sites inhabited by different social parasite communities, each comprising varying proportions of Maculinea teleius, Maculinea nausithous, Maculinea alcon, and Microdon myrmicae. We investigated their spatial distributions, host segregation, the degree of chemical similarity between social parasites and hosts, and temporal overlaps in colony resource exploitation. Spatial segregation among social parasites was found in two populations and it arises from microhabitat preferences and biological interactions. Local conditions can drive selection on one social parasite to use a Myrmica host species that is not exploited by other social parasites. Myrmica scabrinodis and Myrmica rubra nests infested by larvae of two social parasite species were found and the most common co‐occurrence was between Ma. teleius and Mi. myrmicae. The successful coexistence of these two species derives from their exploitation of the host colony resources at different times of the year. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 699–709. 相似文献
295.
Marco Fidani Maria C. Gamberini Giuseppe Pompa Francesca Mungiguerra Alessio Casati Francesco Arioli 《Steroids》2013,78(2):121-126
The possibility of an endogenous presence of the glucocorticoid prednisolone has already been demonstrated in bovine and horse urine, with the aim of clarifying its origin in this matrix, which is used by official agencies for the control of illicit treatments. From this point of view, the endogenous nature of prednisolone could be a major topic in doping control of both amateur and professional human athletes. A study was therefore made on 34 human volunteers (13 males and 21 females; aged 22–62) to detect the presence of prednisolone in their urine by HPLC–MS3. One of the volunteers underwent vernal allergy treatment with betamethasone for two subsequent years. An investigation was carried out with the aim of verifying if the suppression, and the circadian rhythm, of cortisol urinary levels could also apply to prednisolone. The results of the study show that prednisolone was present in the urine of all 34 volunteers, with a concentration very close to 100-times lower that of cortisol, with no dependence on gender. The same ratio (1/100) was observed in the prednisolone and cortisol levels detected during the 24 h together with the suppression of prednisolone by betamethasone treatment.These data demonstrate the endogenous nature of low concentrations of prednisolone in human urine, and motivate further studies about the biosynthetic pathways of this corticosteroid and its relationship with stress in humans, as already described in cows. 相似文献
296.
297.
Sabrina Duranti Francesca Turroni Christian Milani Elena Foroni Francesca Bottacini Fabio Dal Bello Alberto Ferrarini Massimo Delledonne Douwe van Sinderen Marco Ventura 《Applied and environmental microbiology》2013,79(1):336-346
In the current work, we describe genome diversity and core genome sequences among representatives of three bifidobacterial species, i.e., Bifidobacterium adolescentis, Bifidobacterium catenulatum, and Bifidobacterium pseudocatenulatum, by employing a polyphasic approach involving analysis of 16S rRNA gene and 16S-23S internal transcribed spacer (ITS) sequences, pulsed-field gel electrophoresis (PFGE), and comparative genomic hybridization (CGH) assays. 相似文献
298.
Shipeng Lu Karuna Chourey Marco Reiche Sandor Nietzsche Manesh B. Shah Thomas R. Neu Robert L. Hettich Kirsten Küsel 《Applied and environmental microbiology》2013,79(14):4272-4281
Microbial ferrous iron [Fe(II)] oxidation leads to the formation of iron-rich macroscopic aggregates (“iron snow”) at the redoxcline in a stratified lignite mine lake in east-central Germany. We aimed to identify the abundant Fe-oxidizing and Fe-reducing microorganisms likely to be involved in the formation and transformation of iron snow present in the redoxcline in two basins of the lake that differ in their pH values. Nucleic acid- and lipid-stained microbial cells of various morphologies detected by confocal laser scanning microscopy were homogeneously distributed in all iron snow samples. The dominant iron mineral appeared to be schwertmannite, with shorter needles in the northern than in the central basin samples. Total bacterial 16S rRNA gene copies ranged from 5.0 × 108 copies g (dry weight)−1 in the acidic central lake basin (pH 3.3) to 4.0 × 1010 copies g (dry weight)−1 in the less acidic (pH 5.9) northern basin. Total RNA-based quantitative PCR assigned up to 61% of metabolically active microbial communities to Fe-oxidizing- and Fe-reducing-related bacteria, indicating that iron metabolism was an important metabolic strategy. Molecular identification of abundant groups suggested that iron snow surfaces were formed by chemoautotrophic iron oxidizers, such as Acidimicrobium, Ferrovum, Acidithiobacillus, Thiobacillus, and Chlorobium, in the redoxcline and were rapidly colonized by heterotrophic iron reducers, such as Acidiphilium, Albidiferax-like, and Geobacter-like groups. Metaproteomics yielded 283 different proteins from northern basin iron snow samples, and protein identification provided a glimpse into some of their in situ metabolic processes, such as primary production (CO2 fixation), respiration, motility, and survival strategies. 相似文献
299.
João Vidigal Mafalda M. Dias Fabiana Fernandes Marco Patrone Cláudia Bispo Cláudia Andrade Rui Gardner Manuel J.T. Carrondo Paula M. Alves Ana P. Teixeira 《Journal of biotechnology》2013
Insect cell lines such as Sf9 and High Five™ have been widely used to produce recombinant proteins mostly by the lytic baculovirus vector system. We have recently established an expression platform in Sf9 cells using a fluorescence-based recombinase mediated cassette exchange (RMCE) strategy which has similar development timelines but avoids baculovirus infection. To expedite cell engineering efforts, a robust fluorescence-activated cell sorting (FACS) protocol optimized for insect cells was developed here. The standard sorting conditions used for mammalian cells proved to be unsuitable, resulting in post-sorting viabilities below 10% for both cell lines. We found that the extreme sensitivity to the shear stress displayed by Sf9 and High Five™ cells was the limiting factor, and using Pluronic F-68 in the cell suspension could increase post-sorting viabilities in a dose dependent manner. The newly developed protocol was then used to sort stable populations of both cell lines tagged with a DsRed-expressing cassette. Before sorting, the average fluorescence intensity of the Sf9 cell population was 3-fold higher than that of the High Five™ cell population. By enriching with the 10% strongest DsRed-fluorescent cells, the productivity of both cell populations could be successfully improved. The established sorting protocol potentiates the use of RMCE technology for recombinant protein production in insect cells. 相似文献
300.
Interrogating Biology with Force: Single Molecule High-Resolution Measurements with Optical Tweezers
Single molecule force spectroscopy methods, such as optical and magnetic tweezers and atomic force microscopy, have opened up the possibility to study biological processes regulated by force, dynamics of structural conformations of proteins and nucleic acids, and load-dependent kinetics of molecular interactions. Among the various tools available today, optical tweezers have recently seen great progress in terms of spatial resolution, which now allows the measurement of atomic-scale conformational changes, and temporal resolution, which has reached the limit of the microsecond-scale relaxation times of biological molecules bound to a force probe. Here, we review different strategies and experimental configurations recently developed to apply and measure force using optical tweezers. We present the latest progress that has pushed optical tweezers’ spatial and temporal resolution down to today’s values, discussing the experimental variables and constraints that are influencing measurement resolution and how these can be optimized depending on the biological molecule under study. 相似文献