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21.
Cellulolytic bacteria became established 12 days after birth in the caecum and colon of conventionally-reared mice fed a diet containing 5 p. 100 crude cellulose (Weende). Their population reached a level between 10(6) and 10(7) bacteria per gram of digestive contents in 25-day-old animals. However, variations between animals were very large; 20 to 50% of the individuals were free of cellulolytic bacteria. A low cellulolytic population was observed in adult mice fed a cellulose-free diet. The amount of cellulose in the diet and its nature (crude or pure cellulose) affected the number of cellulolytic bacteria: the higher the percentage of cellulose in the diet, the higher the number of cellulolytic bacteria, in particular with crude cellulose-containing diet. 相似文献
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23.
Structural variants of mercury reductase containing the N-terminal domain, which is easily cleaved by trypsin, have been found in Gram-positive bacteria with a low genomic G + C content (Bacillus, Staphylococcus and, possibly, some other genera). Mercury reductases without the N-terminal domain and relatively resistant to limited proteolysis are typical for Gram-positive bacteria with a high genomic G + C content (Arthrobacter, Citreobacterium, Micrococcus, Mycobacterium, Rhodococcus). Both types of mercury reductase genes may be located on plasmids. 相似文献
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26.
Wilkinson 《Ecology letters》1999,2(4):207-209
The evolution of antibiotic resistance in bacteria is well known. Here I describe possible mechanisms by which an increased rate of re-colonization of vertebrate guts by microbes caused by antibiotic use could lead to selection for increased virulence in currently mutualistic or benign microbes. The importance of understanding both the source and the frequency of colonization in such mutualisms is stressed and the possible importance of pseudo-vertical transmission in the evolution of these systems is discussed. A number of areas requiring experimental investigation are identified. 相似文献
27.
Werner Eckert 《Biogeochemistry》1987,4(1):15-26
The process of H2S oxidation by the phototrophic bacteriaThiocapsa roseopersicina andChlorobium phaeobacteroides, respectively, was monitored using a Pt-glass-Ag0, Ag2S electrode combination without liquid junction. Due to the resulting pe(pH) and pH2S plottings three steps can be distinguished: oxidation of H2S to an S(0) state, oxidation of S (0) to SO4
2–, and oxidation of the remaining H2S directly to SO4
2–. Differences between the investigated bacteria exist with respect to their individual oxidation strategies.Thiocapsa apparently stops oxidizing H2S at pH2S 7.5 (e.g. 10–7.5M H2S) and shifts to the utilization of the intracellularly stored S (0). In contrastChlorobium utilizes its extracellularly stored sulfur parallel to the extracellular H2S fraction. The corresponding Pt-sensor responses (pe7 values) were found to be similar to the corresponding partial redox equilibria (p7 values) of H2S oxidation stoichiometries as proposed by Van Niel (1931) and Trüper (1964). It is concluded that the recording of pe enables investigators to understand (and control) in situ redox processes, independent of their thermodynamic equilibration, only bound to changes of electroactivity vs. sensor. 相似文献
28.
Michel Fons Brigitte Cami Jean-Claude Patte Marc Chippaux 《Molecular & general genetics : MGG》1987,206(1):141-143
Summary A library of Deusulfovibrio desulfuricans Norway genomic DNA was constructed in Escherichia coli with pBR322 as vector and plasmids able to complement the proA and leuB mutations of the host were screened. It was observed that all the plasmids studied were highly unstable, the insert DNA being rapidely lost under non-selective growth conditions. A 2.75 kb DNA fragment of D. desulfuricans Norway was found to complement E. coli ProA, ProB and ProC deficiencies. From the results of restriction analysis and Southern hybridization, it is proposed that the genes involved in proline and leucine biosynthesis are clustered on the chromosome of D. desulfuricans Norway. 相似文献
29.
A continuous nutrient flow system has been developed to measure microbial activity in soil with various concentrations of
added substrate. The system consists of a thin soil layer through which substrate was added continuously over periods up to
4.5 days. Substrate utilization was determined by effluent analysis. Respiration was measured manually by injecting a sample
into a gas chromatograph or automatically by coupling the growth chamber to a computer-controlled gas sampling valve. This
permitted respiratory CO2 to be measured by the gas chromatograph at intervals selected by the investigator. Software controlling the valve and gas
chromatograph not only automated gas phase sampling, but also provided a scan of CO2 evolution and a preliminary data summary. This included the date and time of sample, peak height, and percent CO2 in the gas phase. Data for growth on glucose using a microbial population native to a California annual grassland soil demonstrated
that the direct cell count and respiratory techniques for biomass estimation give comparable results. This procedure provides
the potential for detailed analyses of substrate utilization in studies of the growth and maintenance of soil microorganisms. 相似文献
30.
Azra Tufail 《Hydrobiologia》1987,148(3):245-255
Sediment cores were set up to study microbial colonisation and interactions on marine sand grains under enrichment conditions. Cores were enriched with photosynthetic media in the light and dark (PL, PD) and heterotrophic media in the light and dark (HL, HD), and were incubated for 25 days. Sediment chlorophylls were then measured by acetone extraction, viable heterotrophic bacteria by plate counts, and numbers of cells mm–2 sand grain surface by s.e.m. Chlorophyll a occurred in all sediments but was highest in the PL sediment. Bacteriochlorophyll a was only observed in the HL sediment. Heterotrophic viable counts were high in the HL and HD sediments. Dense growth of diatoms and blue-green algae, and a marine fungal Thraustochytrid sp. occurred on PL grains. The blue-green alga Schizothrix was often associated with the diatom Amphora on PL grains. Many different bacteria grew on HL and HD grains and some unusual colony and cell morphologies were recorded (Caulobacter, Flexibacter, polymer strands). Characteristic flakey material sometimes occurred in hollows on grains. The results are discussed in relation to microbial communities in low energy sedimentary environments. 相似文献