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31.
M. Emmerson 《Helgoland Marine Research》2000,54(2-3):110-116
Increasing concerns over global warming and expected sea level rises have led to the adoption of new coastal management strategies
around the south-east coast of England. This paper explores the role played by the estuarine invertebrate Nereis diversicolor in limiting the colonisation and establishment of the invasive pioneering salt marsh plant, Spartina anglica. The biology of N. diversicolor is briefly reviewed and data from field experiments are presented demonstrating significant negative effects of worm abundance
on transplanted S. anglica biomass. Laboratory-based experiments demonstrated significant negative effects of N. diversicolor abundance on the survival of S. anglica seeds transplanted to sediment cores. The importance of estuarine invertebrates in engineering the mudflat habitat may confound
the foreseen ecosystem services and function provided by saltmarsh management schemes.
Received: 15 February 1999 / Received in revised form: 4 June 1999 / Accepted: 11 June 1999 相似文献
32.
33.
Genotoxicity studies on the preemergence herbicide trifluralin 总被引:4,自引:0,他引:4
M L Garriott E R Adams G S Probst J L Emmerson T J Oberly D E Kindig S B Neal B J Bewsey M A Rexroat 《Mutation research》1991,260(2):187-193
34.
Identification of the Escherichia coli recN gene product as a major SOS protein. 总被引:8,自引:5,他引:3
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The recA+ lexA+-dependent induction of four Escherichia coli SOS proteins was readily observed by two-dimensional gel analysis. In addition to the 38-kilodalton (kDa) RecA protein, which was induced in the greatest amounts and was readily identified, three other proteins of 115, 62, and 12 kDa were seen. The 115-kDa protein is the product of the uvrA gene, which is required for nucleotide excision repair and has previously been shown to be induced in the SOS response. The 62-kDa protein, which was induced to high intracellular levels, is the product of recN, a gene required for recBC-independent recombination. The recA and recN genes were partially derepressed in a recBC sbcB genetic background, a phenomenon which might account for the recombination proficiency of such strains. The 12-kDa protein has yet to be identified. 相似文献
35.
R. J. Phillips D. C. Hickleton P. E. Boehmer P. T. Emmerson 《Molecular & general genetics : MGG》1997,254(3):319-329
To investigate the role that the individual subunits play in the ATP-dependent helicase activity of the RecBCD protein we
have investigated the ability of the RecB, RecC and RecD proteins to displace various 20-mer oligonucleotides annealed to
either end or to the centre of an oligonucleotide 60 bases long. The results show that the only subunit which can displace
the 20-mers in the absence of the other subunits is the RecB protein. Moreover, the 20-mer is displaced only if it is annealed
to the 60-mer at the 5′ end or the middle, suggesting that the RecB protein translocates along the 60-mer in the 3′ to 5′
direction, displacing annealed 20-mers as it proceeds. We have shown that reconstituted RecBC and RecBCD complexes displace
the 20-mers but, unlike RecB, they do not require a 3′-ended single-stranded region for helicase action, but can displace
the 20-mers from either end of the 60-mer. The level of helicase activity of the RecBC complex is considerably greater than
that of RecB alone, and the activity of the RecBCD complex appears to be greater still. This hierarchy of activity is also
shown by DNA binding studies, but is not reflected in the ATPase activities of the enzymes. We have also shown that the ability
of trypsin to cleave various sites on the RecB molecule is modified by the presence of ATP or ATP-γ-S, suggesting that conformational
changes may be induced in RecB upon ATP binding. We discuss a model for the ATP-driven, unidirectional motion of the RecB
translocase along single-stranded DNA. In this model, the RecB molecule binds to single-stranded DNA and then translocates
along it, one base at a time, in the 3′ to 5′ direction, by a `ratchet' mechanism in which repeated stretching and contraction
of the protein is coupled to ATP hydrolysis. The RecC protein in the RecBC complex is proposed to act as a `sliding clamp'
which increases processivity by preventing dissociation.
Received: 10 September 1996 / Accepted: 18 November 1996 相似文献
36.
The Kromme is a small estuary in rural eastern Cape, South Africa with a relatively unpopulated and undisturbed catchment. Physical and chemical variables including the major nutrients and E. coli were examined. It was found to be a well oxygenated, well mixed estuary with some stratification in its upper reaches. Nutrient levels were generally low with nitrate values higher in winter than during summer. While no overt seasonality was detected for phosphorus, levels were comparatively high. Faecal E. coli levels were low with a mean count of 26 per 100 ml for the estuary. Along the Kromme, nutrients were highest at the confluence of the Geelhoutboom tributary suggesting it was a major nutrient contributor. At the head of the Kromme, silicate and E. coli were significantly linked to riverflow, while nitrate was correlated with rainfall. In the Geelhoutboom, only nitrate was correlated with riverflow and rainfall. When nutrient gradients (total inorganic nitrogen, total phosphorus and silicate) were correlated against salinity, significant relationships were observed for nitrogen and silicate (Kromme and Geelhoutboom) and for phosphorus along the Geelhoutboom, but not the Kromme, reflecting differences in sub-catchments. An overall N:P atomic ratio of 0.89:1 was found for the system, with more nitrogen relative to phosphorus at the head of the Kromme and vice versa for the Geelhoutboom and mouth. The Kromme is low in nitrogen, conservative in silicate and low in phosphorus while the Geelhoutboom supplies nitrogen, phosphorus and silicate to the system. Although there may be nutrient absorption by sediments in the upper estuary, and by macrophytes in the lower estuary, the Kromme may be classified as a non-conservative mesotrophic marine-dominated estuary which probably exhibits some nutrient recycling. 相似文献
37.
38.
P W Finch A Storey K E Chapman K Brown I D Hickson P T Emmerson 《Nucleic acids research》1986,14(21):8573-8582
The complete nucleotide sequence of the Escherichia coli recB gene which encodes a subunit of the ATP-dependent DNase, Exonuclease V, has been determined. The proposed coding region for the RecB protein is 3543 nucleotides long and would encode a polypeptide of 1180 amino acids with a calculated molecular weight of 133,973. The start of the recB coding sequence overlaps the 3' end of the upstream ptr gene, and the recB termination codon overlaps the initiation codon of the downstream recD gene, suggesting that these genes may form an operon. No sequences which reasonably fit the consensus for an E. coli promoter could be identified upstream of the proposed recB translational start. The predicted RecB amino acid sequence contains regions of homology with ATPases, DNA binding proteins and DNA repair enzymes. 相似文献
39.
Ian D. Hickson Robert L. Gordon Alan E. Tomkinson Peter T. Emmerson 《Molecular & general genetics : MGG》1981,184(1):68-72
Summary The temperature sensitive allele recA200 has been cloned into the multiple copy number plasmid pBR322 and the gene product isolated. The purified RecA200 protein is temperature sensitive in ability to cleave the phage and LexA repressors in vitro and also in ability to promote a successful search for homology between single stranded DNA and a homologous duplex leading to D-loop formation. However, at the non-permissive temperature the RecA200 protein has approximately wild type single stranded DNA dependent ATPase activity and ability to promote pairing between homologous single DNA strands. The demonstration that the temperature sensitivity in vivo can be correlated with the temperature sensitive cleavage of the and LexA repressors in vitro and also with D-loop formation shows that these in vitro reactions, which require large amounts of RecA protein, are not carried out by trace amounts of contaminating proteins. 相似文献
40.
Adult male, Long-Evans rats were exposed 7 h a day for 90 days to continuous wave (CW) 2,450-MHz microwaves at an average power density of 0.5 mW/cm2. Exposures were in a monopole-above-ground radiation chamber with rats in Plexiglas cages. The resulting specific absorption rate (SAR) was 0.14 W/kg (+/- 0.01 SEM). Additional rats served as sham-exposed and home-caged controls. All were evaluated daily for body mass and food and water intakes. Once each 30 days, throughout baseline and exposure phases of the experiment, rats in the sham- and microwave-exposed groups were tested for their sensitivity to footshock. After 90-days of exposure, the rats were evaluated an open field, an active avoidance task and an operant task for food reinforcement. Performance of sham- and microwave-irradiated rats was reliably different on only one measure, the lever-pressing task. The general conclusion reached was that exposure to CW 2,450-MHz microwave radiation at 0.5 mW/cm2 was below the threshold for behavioral effects over a wide range of variables, but did have an effect on a time-related operant task, although the direction of the effect was unpredictable. 相似文献