全文获取类型
收费全文 | 605篇 |
免费 | 29篇 |
出版年
2023年 | 8篇 |
2022年 | 17篇 |
2021年 | 29篇 |
2020年 | 42篇 |
2019年 | 40篇 |
2018年 | 26篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 24篇 |
2014年 | 35篇 |
2013年 | 57篇 |
2012年 | 52篇 |
2011年 | 45篇 |
2010年 | 22篇 |
2009年 | 23篇 |
2008年 | 28篇 |
2007年 | 25篇 |
2006年 | 16篇 |
2005年 | 19篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有634条查询结果,搜索用时 15 毫秒
611.
612.
ABSTRACT: BACKGROUND: Metagenomics approaches provide access to environmental genetic diversity for biotechnology applications, enabling the discovery of new enzymes and pathways for numerous catalytic processes. Discovery of new glycoside hydrolases with improved biocatalytic properties for the efficient conversion of lignocellulosic material to biofuels is a critical challenge in the development of economically viable routes from biomass to fuels and chemicals. RESULTS: Twenty-two putative ORFs (open reading frames) were identified from a switchgrass-adapted compost community based on sequence homology to related gene families. These ORFs were expressed in E. coli and assayed for predicted activities. Seven of the ORFs were demonstrated to encode active enzymes, encompassing five classes of hemicellulases. Four enzymes were over expressed in vivo, purified to homogeneity and subjected to detailed biochemical characterization. Their pH optima ranged between 5.5 - 7.5 and they exhibit moderate thermostability up to ~60-70degreesC. CONCLUSIONS: Seven active enzymes were identified from this set of ORFs comprising five different hemicellulose activities. These enzymes have been shown to have useful properties, such as moderate thermal stability and broad pH optima, and may serve as the starting points for future protein engineering towards the goal of developing efficient enzyme cocktails for biomass degradation under diverse process conditions. 相似文献
613.
José Martín Gallardo Sayyed Mohammad Hadi Alavi Zdeněk Adámek Bořek Drozd 《Reviews in Fish Biology and Fisheries》2010,20(3):403-408
The effect of keeping female tench in two different types of keepnets for 24 h after landing was tested. The first type, fine
knotted nylon mesh, was placed in two different positions in the edge: (a) anglers position, anchored on one side and (b)
stretch position, anchored on both ends of the keepnets. The second type was made of dense fine and soft textile net in black
color and anchored on both ends in a stretch position. After capture by rod the fish were landed by hand, the hook was removed
and the damage to the body and fins checked before confining the fish inside the keepnets. After confinement, blood samples
were collected and the number, disposition and extent of wounds checked. The retention in the keepnets did not produce significant
changes in plasma cortisol, glucose and osmolality. Fine knotted nets caused more injuries than the soft textile one. As a
consequence, the use of this latter type is recommended for tench retention. 相似文献
614.
615.
616.
Hadi N Yehia Rockford K Draper Carole Mikoryak Erin Kate Walker Pooja Bajaj Inga H Musselman Meredith C Daigrepont Gregg R Dieckmann Paul Pantano 《Journal of nanobiotechnology》2007,5(1):8-17
This work concerns exposing cultured human epithelial-like HeLa cells to single-walled carbon nanotubes (SWNTs) dispersed
in cell culture media supplemented with serum. First, the as-received CoMoCAT SWNT-containing powder was characterized using
scanning electron microscopy and thermal gravimetric analyses. Characterizations of the purified dispersions, termed DM-SWNTs,
involved atomic force microscopy, inductively coupled plasma – mass spectrometry, and absorption and Raman spectroscopies.
Confocal microRaman spectroscopy was used to demonstrate that DM-SWNTs were taken up by HeLa cells in a time- and temperature-dependent
fashion. Transmission electron microscopy revealed SWNT-like material in intracellular vacuoles. The morphologies and growth
rates of HeLa cells exposed to DM-SWNTs were statistically similar to control cells over the course of 4 d. Finally, flow
cytometry was used to show that the fluorescence from MitoSOX™ Red, a selective indicator of superoxide in mitochondria, was
statistically similar in both control cells and cells incubated in DM-SWNTs. The combined results indicate that under our
sample preparation protocols and assay conditions, CoMoCAT DM-SWNT dispersions are not inherently cytotoxic to HeLa cells.
We conclude with recommendations for improving the accuracy and comparability of carbon nanotube (CNT) cytotoxicity reports. 相似文献
617.
Hadi Nazem-Bokaee Dayue Chen Sean Michael O'Donnell Andrew L. Zydney 《Biotechnology and bioengineering》2019,116(8):2010-2017
Virus filtration remains a critical step in the downstream process for the production of monoclonal antibodies and other mammalian cell-derived biotherapeutics. Recent studies have shown large differences in virus capture behavior of different virus filters, although the origin of these differences is still unclear. The objective of this study was to use confocal and scanning electron microscopy to directly evaluate the capture of virus-size nanoparticles in Planova 20N and BioEX hollow-fiber virus filters. Confocal images of fluorescent nanoparticles were quantified using ImageJ image processing software based on the measured fluorescence intensity of the labeled nanoparticles. Nanoparticle capture by the Planova BioEX was independent of transmembrane pressure from 10 to 45 psi. In contrast, the Planova 20N showed significant differences in nanoparticle capture profile at low pressure, consistent with literature data showing virus breakthrough under these conditions. Images obtained after a process interruption show significant migration of previously captured nanoparticles in the Planova 20N filters but not in the BioEX. These results provide important insights into the nature of virus capture in different virus filters and its dependence on the underlying structure of the virus filtration membranes. 相似文献
618.
The EcoP15 restriction endonuclease forms complexes at specific sites on unmodified DNA both in the presence and in the absence of S-adenosyl-l-methionine. ATP acts as an allosteric effector of EcoP15 and induces DNA cleavage followed by release of the enzyme from the DNA. The efficiency of endonucleolytic scission varies from site to site. The nucleotide sequences at sites that are cleaved at a high frequency were compared. 相似文献
619.
620.