全文获取类型
收费全文 | 690篇 |
免费 | 59篇 |
出版年
2021年 | 11篇 |
2020年 | 4篇 |
2019年 | 4篇 |
2018年 | 4篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 43篇 |
2012年 | 63篇 |
2011年 | 50篇 |
2010年 | 23篇 |
2009年 | 25篇 |
2008年 | 34篇 |
2007年 | 26篇 |
2006年 | 38篇 |
2005年 | 31篇 |
2004年 | 23篇 |
2003年 | 23篇 |
2002年 | 26篇 |
2001年 | 22篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 7篇 |
1986年 | 13篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有749条查询结果,搜索用时 31 毫秒
1.
2.
This paper describes the functional characterization of the xyloside transporter, XylP, of Lactobacillus pentosus with the aid of a spectroscopy-based assay system. In order to monitor the transport reaction, the natural xyloside isoprimeverose, a building block of hemicellulose, and the analogue methyl-isoprimeverose were chemically synthesized by a new and efficient procedure. The XylP protein was purified by metal affinity chromatography, following high level expression in Lactococcus lactis from the nisin-inducible promoter. The purified XylP protein was incorporated into liposomes, in which the glucose dehydrogenase from Acinetobacter calcoaceticus (sGDH) was entrapped. sGDH can oxidize aldose sugars in the presence of dichlorophenol-indophenol as electron acceptor. The coupled assay thus involves XylP-mediated isoprimeverose uptake followed by internal oxidation of the sugar by sGDH, which can be monitored from the reduction of 2,6-dichlorophenol-indophenol at 600 nm. The uptake of isoprimeverose was stimulated by the presence of the non-oxidizable methyl-isoprimeverose on the trans-side of the membrane, indicating that exchange transport is faster than unidirectional downhill uptake. Unlike other members of the galactoside-pentoside-hexuronide family, XylP does not transport monosaccharides (xylose) but requires a glycosidic linkage at the anomeric carbon position. Consistent with a proton motive force-driven mechanism, the uptake was stimulated by a membrane potential (inside negative relative to outside) and inhibited by a pH gradient (inside acidic relative to outside). The advantages of the here-described transport assay for studies of carbohydrate transport are discussed. 相似文献
3.
4.
5.
To complement the role of primary care teams working with patients with HIV disease and AIDS within greater London and to ease the load on the special hospital units a home support team was developed. It comprises six specialist nurses, a general practitioner trained medical officer, and a receptionist and is funded from regional and district sources and charities. A nurse is available for out of hours and emergency weekend calls, with support from the patient''s general practitioner or the attached medical officer. During the first 18 months 249 patients were seen; the mean duration of care was five months. Nearly a third (18/50, 30%) of patients who were terminally ill died at home. The team''s activities included practical nursing care, emotional support for carers and patients, and advice and guidance to primary care teams. Problems in providing care in patients'' homes included issues relating to confidentiality and 24 hour cover. With the increasing incidence of HIV infection the home support team may be a useful model for care of large numbers of patients with symptomatic HIV disease, especially in large urban areas. 相似文献
6.
A degradation pathway for dl--phenylhydracrylic, phenylacetic, 3- and 4-hydroxyphenylacetic acid by a Flavobacterium is presented. Experiments with washed cells and enzyme studies revealed that dl--phenylhydracrylic acid in an initial reaction was oxidatively decarboxylated to phenylacetaldehyde. Whole cells oxidized both stereoisomers of phenylhydracrylic acid at different rates. The product phenylacetaldehyde in turn was oxidized to phenylacetic acid. No hydroxylation of phenylacetic acid was detected in cell extracts, but on the basis of experiments with washed cells it is assumed that phenylacetic acid is mainly metabolized via 3-hydroxyphenylacetic acid. This latter product was subsequently hydroxylated yielding the ring-cleavage substrate homogentisate. 4-Hydroxyphenylacetic acid was also degraded via homogentisate. Ringcleavage of homogentisate gave maleylacetoacetate which was further degraded through a glutathione-dependent pathway. Homoprotocatechuate was not an intermediate in the metabolism of dl-phenylhydracrylic acid, phenylacetic, 3- and 4-hydroxyphenylacetic acid metabolism, but it could be hydroxylated aspecifically to 2,4,5-trihydroxyphenylacetic acid by the action of the 3-hydroxyphenylacetic acid-6-hydroxylase.Abbreviations HPLC
high-performance liquid chromatography
- PHA
phenylhydracrylic acid
- PA
phenylacetic acid
- HPA
hyxdroxyphenylacetic acid
- PMS
phenazine methosulphate
- PMA
phenylmalonic acid
- GSH
glutathione 相似文献
7.
Induction of anchorage-independent growth of human embryonic fibroblasts with a deletion in the short arm of chromosome 11 by human papillomavirus type 16 DNA. 总被引:5,自引:3,他引:2 下载免费PDF全文
H L Smits E Raadsheer I Rood S Mehendale R M Slater J van der Noordaa J ter Schegget 《Journal of virology》1988,62(12):4538-4543
8.
9.
Wolterbeek, H. Th. and De Bruin, M. 1986. Xylem and phloem importof Na+, K+ , Rb+, Cs+ and in tomato fruits: differential contributions from stem and leaf.J.exp. Bot. 37: 928939. The transport of Na+, K+, Rb+, Cs+ and into developing fruits of tomato (an inbred lineof Lycopersicon esculentum Mill. cv. Tiny Tim) was measured.Element solutions were introduced into the transpiration streamthrough the cut stem bases of plant parts consisting of a stempart with single green fruit, both with and without attachedfully expanded leaf. Measurements were carried out of the accumulationin the fruit of the gamma-ray emitting radiotracers 24Na+, 42K+,86Rb+, 134Cs+ and The transport into the fruit was expressed by a single parameter taking intoaccount volume flows varying with time and experiments. Xylemto phloem transfer in the stem as a source of fruit elementsupply was shown to be inversely related with the velocity offlow of the stem xylem. The results also indicated that thetransfer system in the stem was more rapidly equilibrated thanit was in the leaf. Stem loading of the phloem is suggested as a possible mechanismregulating the solute influx in fruits under varying flow velocitiesof the stem xylem, while fruit influx of phloem solutes, whichwere loaded in the leaf, may play a major role in influx regulationunder conditions of varying solute concentrations. Key words: Alkali ions, tomato fruits, stem and leaf phloem loading 相似文献
10.
Prevost, I. and Le PageDegivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.J.exp. Bot. 36: 19001905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radioimmunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability 相似文献