全文获取类型
收费全文 | 569篇 |
免费 | 82篇 |
国内免费 | 2篇 |
专业分类
653篇 |
出版年
2021年 | 10篇 |
2020年 | 4篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 18篇 |
2015年 | 22篇 |
2014年 | 24篇 |
2013年 | 22篇 |
2012年 | 31篇 |
2011年 | 28篇 |
2010年 | 24篇 |
2009年 | 21篇 |
2008年 | 36篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 29篇 |
2004年 | 22篇 |
2003年 | 16篇 |
2002年 | 22篇 |
2001年 | 18篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1994年 | 4篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 7篇 |
1969年 | 4篇 |
1966年 | 4篇 |
排序方式: 共有653条查询结果,搜索用时 15 毫秒
91.
PB1-F2 protein, expressed from an alternative reading frame of most influenza A virus (IAV) PB1 segments, may possess specific residues associated with enhanced inflammation (L62, R75, R79, and L82) and cytotoxicity (I68, L69, and V70). These residues were shown to increase the pathogenicity of primary viral and secondary bacterial infections in a mouse model. In contrast to human seasonal influenza strains, virulence-associated residues are present in PB1-F2 proteins from pandemic H1N1 1918, H2N2 1957, and H3N2 1968, and highly pathogenic H5N1 strains, suggesting their contribution to viruses'' pathogenic phenotypes. Non-human influenza strains may act as donors of virulent PB1-F2 proteins. Previously, avian influenza strains were identified as a potential source of inflammatory, but not cytotoxic, PB1-F2 residues. Here, we analyze the frequency of virulence-associated residues in PB1-F2 sequences from IAVs circulating in mammalian species in close contact with humans: pigs, horses, and dogs. All four inflammatory residues were found in PB1-F2 proteins from these viruses. Among cytotoxic residues, I68 was the most common and was especially prevalent in equine and canine IAVs. Historically, PB1-F2 from equine (about 75%) and canine (about 20%) IAVs were most likely to have combinations of the highest numbers of residues associated with inflammation and cytotoxicity, compared to about 7% of swine IAVs. Our analyses show that, in addition to birds, pigs, horses, and dogs are potentially important sources of pathogenic PB1-F2 variants. There is a need for surveillance of IAVs with genetic markers of virulence that may be emerging from these reservoirs in order to improve pandemic preparedness and response. 相似文献
92.
Between 1991 and 1993, Alaska harbor porpoise ( Phocoena phocoena ) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km2 , or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km2 , or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km2 , or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km2 and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km2 and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km2 , resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number. 相似文献
93.
94.
A study of GDP binding to purified thermogenin protein from brown adipose tissue. 总被引:1,自引:0,他引:1 下载免费PDF全文
1. The binding of GDP to purified thermogenin protein was studied by using fluorescence spectroscopy and equilibrium dialysis. 2. GDP binding to thermogenin diminished fluorescence emission in a concentration-dependent manner that exhibited saturation. 3. Kd values for binding of nucleoside di- and tri-phosphates were lower than those for nucleoside monophosphates. 4. The GDP-induced fluorescence quenching was decreased by increasing pH, but the apparent Kd was unaltered by pH changes. 5. Equilibrium dialysis showed a Kd change from 3 to 6 microM when the pH was increased from 6.6 to 8.5. 6. The apparent pK of the fluorescence changes induced by pH (8.3) was identical with the apparent pK of the GDP-binding response. 7. The data are consistent with the existence of protonated and non-protonated forms of thermogenin protein that both bind GDP. 相似文献
95.
Jrme Goudeau Catherine S Sharp Jonathan Paw Laura Savy Manuel D Leonetti Andrew G York Dustin L Updike Cynthia Kenyon Maria Ingaramo 《Genetics》2021,217(4)
We create and share a new red fluorophore, along with a set of strains, reagents and protocols, to make it faster and easier to label endogenous Caenorhabditis elegans proteins with fluorescent tags. CRISPR-mediated fluorescent labeling of C. elegans proteins is an invaluable tool, but it is much more difficult to insert fluorophore-size DNA segments than it is to make small gene edits. In principle, high-affinity asymmetrically split fluorescent proteins solve this problem in C. elegans: the small fragment can quickly and easily be fused to almost any protein of interest, and can be detected wherever the large fragment is expressed and complemented. However, there is currently only one available strain stably expressing the large fragment of a split fluorescent protein, restricting this solution to a single tissue (the germline) in the highly autofluorescent green channel. No available C. elegans lines express unbound large fragments of split red fluorescent proteins, and even state-of-the-art split red fluorescent proteins are dim compared to the canonical split-sfGFP protein. In this study, we engineer a bright, high-affinity new split red fluorophore, split-wrmScarlet. We generate transgenic C. elegans lines to allow easy single-color labeling in muscle or germline cells and dual-color labeling in somatic cells. We also describe a novel expression strategy for the germline, where traditional expression strategies struggle. We validate these strains by targeting split-wrmScarlet to several genes whose products label distinct organelles, and we provide a protocol for easy, cloning-free CRISPR/Cas9 editing. As the collection of split-FP strains for labeling in different tissues or organelles expands, we will post updates at doi.org/10.5281/zenodo.3993663 相似文献
96.
R Tomazin A B Hill P Jugovic I York P van Endert H L Ploegh D W Andrews D C Johnson 《The EMBO journal》1996,15(13):3256-3266
The herpes simplex virus (HSV) ICP47 protein inhibits the MHC class I antigen presentation pathway by inhibiting the transporter associated with antigen presentation (TAP) which translocates peptides across the endoplasmic reticulum membrane. At present, ICP47 is the only inhibitor of TAP. Here, we show that ICP47 produced in bacteria can block human, but not mouse, TAP, and that heat denaturation of ICP47 has no effect on its ability to block TAP. ICP47 inhibited peptide binding to TAP without affecting ATP binding, consistent with previous observations that the peptide binding and ATP binding sites of TAP are distinct. ICP47 bound to TAP with a higher affinity (KD approximately 5 x 10(-8) M) than did peptides, and ICP47 did not dissociate from TAP. ICP47 was not transported by TAP and remained sensitive to proteases added from the cytosolic surface of the membrane. Peptides acted as competitive inhibitors of ICP47 binding to TAP, and this inhibition required a 100- to 1000-fold molar excess of peptide. These results demonstrate that ICP47 binds to a site which includes the peptide binding domain of TAP and remains bound to this site in a stable fashion. 相似文献
97.
George M. Giambaşu Tyler Luchko Daniel Herschlag Darrin M. York David A. Case 《Biophysical journal》2014
The ionic atmosphere around nucleic acids remains only partially understood at atomic-level detail. Ion counting (IC) experiments provide a quantitative measure of the ionic atmosphere around nucleic acids and, as such, are a natural route for testing quantitative theoretical approaches. In this article, we replicate IC experiments involving duplex DNA in NaCl(aq) using molecular dynamics (MD) simulation, the three-dimensional reference interaction site model (3D-RISM), and nonlinear Poisson-Boltzmann (NLPB) calculations and test against recent buffer-equilibration atomic emission spectroscopy measurements. Further, we outline the statistical mechanical basis for interpreting IC experiments and clarify the use of specific concentration scales. Near physiological concentrations, MD simulation and 3D-RISM estimates are close to experimental results, but at higher concentrations (>0.7 M), both methods underestimate the number of condensed cations and overestimate the number of excluded anions. The effect of DNA charge on ion and water atmosphere extends 20–25 Å from its surface, yielding layered density profiles. Overall, ion distributions from 3D-RISMs are relatively close to those from corresponding MD simulations, but with less Na+ binding in grooves and tighter binding to phosphates. NLPB calculations, on the other hand, systematically underestimate the number of condensed cations at almost all concentrations and yield nearly structureless ion distributions that are qualitatively distinct from those generated by both MD simulation and 3D-RISM. These results suggest that MD simulation and 3D-RISM may be further developed to provide quantitative insight into the characterization of the ion atmosphere around nucleic acids and their effect on structure and stability. 相似文献
98.
Annemarie MM Vlaar Angela EP Bouwmans Marinus JPG van Kroonenburgh Werner H Mess Selma C Tromp Piet GWM Wuisman Alfons GH Kessels Ania Winogrodzka Wim EJ Weber 《BMC neurology》2007,7(1):28
Background
Parkinson's disease (PD) is the second most common neurodegenerative disorder. As there is no definitive diagnostic test, its diagnosis is based on clinical criteria. Recently transcranial duplex scanning (TCD) of the substantia nigra in the brainstem has been proposed as an instrument to diagnose PD. We and others have found that TCD scanning of substantia nigra duplex is a relatively accurate diagnostic instrument in patients with parkinsonian symptoms. However, all studies on TCD so far have involved well-defined, later-stage PD patients, which will obviously lead to an overestimate of the diagnostic accuracy of TCD. 相似文献99.
M Moniruzzaman S W York L O Ingram 《Journal of industrial microbiology & biotechnology》1998,20(5):281-286
Escherichia coli KO11 was previously constructed for the production of ethanol from both hexose and pentose sugars in hemicellulose hydrolysates
by inserting the Zymomonas mobilis genes encoding pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adhB). This biocatalyst appears relatively resistant to potential process errors during fermentation. Antibiotics were not required
to maintain the maximum catabolic activity of KO11 even after deliberate contamination with up to 10% soil. Fermentations
exposed to extremes of temperature (2 h at 5°C or 50°C) or pH (2 h at pH 3 or pH 10) recovered after re-adjustment to optimal
fermentation conditions (35°C, pH6) although longer times were required for completion in most cases. Ethanol yields were
not altered by exposure to extremes in temperature but were reduced by exposure to extremes in pH. Re-inoculation with 5%
(by volume) from control fermentors reduced this delay after exposure to pH extremes.
Received 24 July 1997/ Accepted in revised form 16 April 1998 相似文献
100.
Simple and efficient generation in vitro of nested deletions and inversions: Tn5 intramolecular transposition. 总被引:2,自引:0,他引:2 下载免费PDF全文
We have exploited the intramolecular transposition preference of the Tn 5 in vitro transposition system to test its effectiveness as a tool for generation of nested families of deletions and inversions. A synthetic transposon was constructed containing an ori, an ampicillin resistance (Ampr) gene, a multi-cloning site (MCS) and two hyperactive end sequences. The donor DNA that adjoins the transposon contains a kanamycin resistance (Kanr) gene. Any Amprreplicating plasmid that has undergone a transposition event (Kans) will be targeted primarily to any insert in the MCS. Two different size targets were tested in the in vitro system. Synthetic transposon plasmids containing either target were incubated in the presence of purified transposase (Tnp) protein and transformed. Transposition frequencies (Ampr/Kans) for both targets were found to be 30-50%, of which >95% occur within the target sequence, in an apparently random manner. By a conservative estimate 10(5) or more deletions/inversions within a given segment of DNA can be expected from a single one-step 20 microl transposition reaction. These nested deletions can be used for structure-function analysis of proteins and for sequence analysis. The inversions provide nested sequencing templates of the opposite strand from the deletions. 相似文献