收费全文 | 234篇 |
免费 | 86篇 |
320篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2016年 | 3篇 |
2013年 | 3篇 |
2012年 | 6篇 |
2011年 | 4篇 |
2009年 | 5篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 3篇 |
1998年 | 13篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1967年 | 2篇 |
1966年 | 2篇 |
1960年 | 2篇 |
1959年 | 9篇 |
1958年 | 11篇 |
1957年 | 16篇 |
1956年 | 17篇 |
1955年 | 19篇 |
1954年 | 11篇 |
1953年 | 15篇 |
1952年 | 17篇 |
1951年 | 9篇 |
1950年 | 11篇 |
1949年 | 6篇 |
1948年 | 6篇 |
These results indicate that all hop varieties and pollinator clones can be made available to the industry free from HLVd and that the chances of infection can be reduced by avoiding early-season cultural operations that cut into hop shoots. 相似文献
The integration of biotechnology into chemical manufacturing has been recognized as a key technology to build a sustainable society. However, the practical applications of biocatalytic chemical conversions are often restricted due to their complexities involving the unpredictability of product yield and the troublesome controls in fermentation processes. One of the possible strategies to overcome these limitations is to eliminate the use of living microorganisms and to use only enzymes involved in the metabolic pathway. Use of recombinant mesophiles producing thermophilic enzymes at high temperature results in denaturation of indigenous proteins and elimination of undesired side reactions; consequently, highly selective and stable biocatalytic modules can be readily prepared. By rationally combining those modules together, artificial synthetic pathways specialized for chemical manufacturing could be designed and constructed.
ResultsA chimeric Embden-Meyerhof (EM) pathway with balanced consumption and regeneration of ATP and ADP was constructed by using nine recombinant E. coli strains overproducing either one of the seven glycolytic enzymes of Thermus thermophilus, the cofactor-independent phosphoglycerate mutase of Pyrococcus horikoshii, or the non-phosphorylating glyceraldehyde-3-phosphate dehydrogenase of Thermococcus kodakarensis. By coupling this pathway with the Thermus malate/lactate dehydrogenase, a stoichiometric amount of lactate was produced from glucose with an overall ATP turnover number of 31.
ConclusionsIn this study, a novel and simple technology for flexible design of a bespoke metabolic pathway was developed. The concept has been testified via a non-ATP-forming chimeric EM pathway. We designated this technology as “synthetic metabolic engineering”. Our technology is, in principle, applicable to all thermophilic enzymes as long as they can be functionally expressed in the host, and thus would be potentially applicable to the biocatalytic manufacture of any chemicals or materials on demand.
相似文献Previous impressions that the size of ammonite aptychi is unusually large, thereby posing a problem to their interpretation as part of the jaw apparatus, are shown to be incorrect. The relative length of the aptychus for at least the Jurassic ammonite groups studied, at approximately 15% of the length of the body chamber, is remarkably constant in different taxonomic groups and sizes. This is well within the range for buccal mass length as percentage of mantle length of living cephalopods, being most similar to Octopus and Sepia and much smaller than Nautilus. The height and width of aptychi relative to whorl height and width are larger but again ammonites are probably not significantly different from modern cephalopods. The size and design, with no obvious structures for biting or crushing, suggest that ammonites were adapted to a particular type of relatively unspecialised feeding in which mostly small animals were ingested, possibly with some external digestion. The large shovel-like lower jaw may have functioned like a scoop for collecting large quantities of water and small prey, and movement of the buccal complex with the upper jaw almost closed against the lower jaw could have expelled water while retaining captured prey. Calcification of aptychi may have been protective, but more likely acted to weight the buccal mass for nektobenthic feeding and to make it more rigid. 相似文献