全文获取类型
收费全文 | 450篇 |
免费 | 83篇 |
出版年
2018年 | 3篇 |
2016年 | 10篇 |
2015年 | 14篇 |
2014年 | 12篇 |
2013年 | 15篇 |
2012年 | 17篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 13篇 |
2007年 | 24篇 |
2006年 | 22篇 |
2005年 | 14篇 |
2004年 | 18篇 |
2003年 | 23篇 |
2002年 | 13篇 |
2001年 | 26篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 7篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 10篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 18篇 |
1991年 | 12篇 |
1990年 | 23篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1967年 | 4篇 |
1966年 | 3篇 |
1965年 | 5篇 |
1964年 | 2篇 |
排序方式: 共有533条查询结果,搜索用时 15 毫秒
121.
N-acetylmuramyl-L-alanine amidase of Bacillus licheniformis and its L-form 总被引:19,自引:10,他引:9 下载免费PDF全文
A cell wall lytic enzyme has been demonstrated to be a component of the membrane of Bacillus licheniformis NCTC 6346 and an l-form derived from it. The lytic enzyme, characterized as an N-acetylmuramyl-l-alanine amidase, is solubilized from membranes by nonionic detergents. Ionic detergents inactivate the enzyme. In the bacterium the specific activities of amidase and d-alanine carboxypeptidase in mesosomes are approximately 65% of those in membranes. Selective transfer of lytic enzyme from nongrowing L-forms, L-form membranes, and protoplasts to added walls occurred after mixing, and 31 to 77% of the enzyme lost from L-form membranes was recovered on the walls. Membranes isolated from L-forms growing in the presence of added walls contained as little as 13% of the amidase found in membranes of a control culture. These results have been interpreted as showing that in vivo the amidase is "bound" to the surface of the bacterial cell membrane in such a location that it can be readily accessible to the cell wall. 相似文献
122.
123.
Characteristics of the endoglucanase encoded by a cel gene from Bacteroides succinogenes expressed in Escherichia coli 总被引:2,自引:0,他引:2
K A Taylor B Crosby M McGavin C W Forsberg D Y Thomas 《Applied and environmental microbiology》1987,53(1):41-46
A cel gene from Bacteroides succinogenes inserted into the vector pUC8 coded for an enzyme which exhibited high hydrolytic activity on carboxymethylcellulose, p-nitrophenylcellobioside, and lichenan and low activity on laminarin and xylan. The enzyme was not synthesized by the Escherichia coli host when cells were cultured in complex medium containing added glucose. In the absence of added glucose, the endoglucanase and cellobiosidase activities synthesized were partitioned into the periplasmic space during growth, and practically all enzyme was located in the periplasm when the stationary phase of growth was reached. The enzyme exhibited 17- and sixfold higher Km values for the hydrolysis of carboxymethylcellulose and lichenan, respectively, than did the extracellular endoglucanase complex from B. succinogenes. The Cel endoglucanase had a pH optimum similar to that of the B. succinogenes enzyme except that the range was narrower, and the Cel endoglucanase was more readily inactivated on exposure to high temperature, detergents, and certain metals. Its activity was stimulated by calcium and magnesium. Nondenaturing polyacrylamide gel electrophoresis at different acrylamide concentrations revealed the presence of three endoglucanase components, two with molecular weights of 43,000 and one with a molecular weight of 55,000. 相似文献
124.
Molecular cloning of a xylanase gene from Bacteroides succinogenes and its expression in Escherichia coli 总被引:4,自引:0,他引:4
A Sipat K A Taylor R Y Lo C W Forsberg P J Krell 《Applied and environmental microbiology》1987,53(3):477-481
A gene coding for xylanase synthesis in Bacteroides succinogenes was isolated by cloning, with Escherichia coli HB101 as the host. After partial digestion of B. succinogenes DNA with Sau3A, fragments were ligated into the BamHI site of pBR322 and transformed into E. coli HB101. Of 14,000 colonies screened, 4 produced clear halos on Remazol brilliant blue-xylan agar. Plasmids from two stable clones recovered exhibited identical restriction enzyme patterns, with the same 9.4-kilobase-pair (kbp) insert. The plasmid was designated pBX1. After subcloning of restriction enzyme fragments, a 3-kbp fragment was found to code for xylanase activity in either orientation when inserted into pUC18 and pUC19. The original clone possessed approximately 10-fold higher xylanase activity than did clones harboring the 3-kbp insert in pUC18, pUC19, or pBR322. The enzyme was partially secreted into the periplasmic space of E. coli. The periplasmic enzyme of the BX1 clone had 2% of the activity on carboxymethyl cellulose and less than 0.2% of the activity on p-nitrophenyl xyloside and a range of other substrates that it exhibited on xylan. The xylanase gene was not subject to catabolite repression by glucose or induction by either xylan or xylose. The xylanase activity migrated as a single broad band on nondenaturing polyacrylamide gels. The Km of the pBX1-encoded enzyme was 0.22% (wt/vol) of xylan, which was similar to that for the xylanase activity in an extracellular enzyme preparation from B. succinogenes. Based on these data it appears that the xylanase gene expressed in E. coli is fully functional and codes for an enzyme with properties similar to the B. succinogenes enzyme(s). 相似文献
125.
Summary Five-day old rats were given a single injection of varying amounts of oestradiol monopropionate (OeM) in propylene glycol (0.5, 5, 30 and 150 g) and 26-day old rats were given a single injection of 5 or 150 g OeM. The rats were sacrificed at varying times after the injection and the changes in the vaginal plate and the vaginal epithelium proper were studied. As indicated by the cornification of the epithelium the reaction to OeM is stronger in the vaginal plate than in the vaginal epithelium proper. The response of the vaginal epithelium to 5 or 150 g OeM is most extensive in the rats injected at 26 days of age. With 150 g OeM a cornification of the vaginal epithelium was obtained in rats injected when 26 days old but not in those injected when 5 days old. The reactions in the vaginal plate were compared with those found previously after injections of testosterone propionate.
Acknowledgement. This investigation was supported by grants from the Swedish Medical Research Council (12 X-579-03, K67-14X-571-03) and from the Swedish Cancer Society (67:46). 相似文献
126.
127.
A sterile germination study with seeds of some common phanerogamic water plants showed almost 100 per cent germination for seeds of Alisma plantago–aquatica, Baldellia ranunculoides and Nymphaea alba. Seeds of Potamogeton lucens could be germinated to about 40 per cent, seeds of Polygonum amphibium germinated sporadically while those of Cladium mariscus could not be germinated at all. Freshly harvested seeds of Alisma and Baldellia showed an ability to germinate at both 20°C and 35°C. A stratification period of one month at +4°C gave germination of all species tested, with the exception of Cladium. Potamogeton germinated in light only, the other species both in light and darkness. Treatment times for surface sterilization in disinfectants are given. 相似文献
128.
Microbial inocula from rumen fluid, soil, and contents of the large intestines of chickens (CLIC) and of swine (SLIC) were tested for their ability to transform deoxynivalenol (vomitoxin) in vitro. Microorganisms in (CLIC) completely transformed pure vomitoxin, and this activity was retained through six serial subcultures. No alteration of the toxin by incubation with SLIC was detected, whereas 35% of the vomitoxin was metabolized in the original culture of rumen fluid and 50% was metabolized by the soil sample, though metabolism was decreased in subsequent subcultures of either sample. A single metabolite was isolated and identified as deepoxy vomitoxin. The increase in concentration of deepoxy vomitoxin in the culture medium corresponded with the decrease in vomitoxin concentration. The vomitoxin transformation rate was not affected by either the ratio of CLIC to vomitoxin (5 to 0.2 g of CLIC per mg of vomitoxin) or the initial concentration of vomitoxin (14 to 1,400 ppm) in the medium. Biotransformation of vomitoxin was completely inhibited when the pH in the medium was lowered to 5.20. Sodium azide at a 0.1% (wt/vol) concentration in the medium blocked the transformation of vomitoxin, suggesting that the deepoxidation of vomitoxin is an energy-dependent process. About 50% of the vomitoxin in moldy corn in culture medium was transformed by microorganisms from CLIC. The vomitoxin transformation rate in moldy corn was not affected when the concentration of CLIC changed from 0.2 to 0.8 g/ml of medium. Vomitoxin in the moldy corn was not transformed when CLIC were added to corn without culture medium.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
129.
Inbred female mice of the NMRI strain were treated subcutaneously with 5 micrograms diethylstilbestrol (DES) in olive oil or vehicle only for the first 5 days after birth. One group of DES-treated females was killed at the age of 8-12 weeks, and the uterine cervix and adjacent parts of the vagina and uterine horns prepared for histological studies. In all preparations, the cervical epithelial lining contained regions with heterotopic columnar epithelium (HCE) along 69-100% of the length of the common cervical canal. Ovaries from neonatally DES-treated females were grafted to 8-week-old ovariectomized control hosts and these hosts were mated to control males 2 weeks later. The hosts gave birth to normal-sized litters. The female offspring from these litters had a normal cervical epithelial lining and, in turn, gave birth to normal-sized litters. These results indicate that treatment of neonatal female mice with DES does not affect the female germ cells as far as concerns factors associated with the development of HCE or reduced fertility in the next generation. 相似文献
130.