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Isotope fractionation has been used with increasing frequency as a tool to quantify degradation of chlorinated aliphatic
pollutants in the environment. The objective of this research was to determine if the electron donor present in enrichment
cultures prepared from uncontaminated sediments influenced the extent of isotope fractionation of tetrachloroethylene (PCE),
either directly, or through its influence on microbial community composition. Two PCE-degrading enrichment cultures were prepared
from Duck Pond (DP) sediment and were incubated with formate (DPF) or H2 (DPH) as electron donor. DPF and DPH were significantly different in both product distribution and extent of isotope fractionation.
Chemical and isotope analyses indicated that electron donors did not directly affect the product distribution or the extent
of isotope fractionation for PCE reductive dechlorination. Instead, restriction fragment length polymorphism (RFLP) and sequence
analysis of the 16S rRNA clone libraries of DPF and DPH identified distinct microbial communities in each enrichment culture,
suggesting that differences in microbial communities were responsible for distinct product distributions and isotope fractionation
between the two cultures. A dominant species identified only in DPH was closely related to known dehalogenating species (Sulfurospirillum multivorans and Sulfurospirillum halorespirans) and may be responsible for PCE degradation in DPH. Our study suggests that different dechlorinators exist at the same site
and can be preferentially stimulated by different electron donors, especially over the long-term (i.e., years), typical of
in-situ ground water remediation. 相似文献
65.
Recognizing the forest for the trees: testing temporal patterns of cladogenesis using a null model of stochastic diversification 总被引:2,自引:1,他引:1
Computer simulations are developed and employed to examine the expected
temporal distributions of nodes under a null model of stochastic lineage
bifurcation and extinction. These Markovian models of phylogenetic process
were constructed so as to permit direct comparisons against empirical
phylogenetic trees generated from molecular or other information available
solely from extant species. For replicate simulated phylads with n extant
species, cumulative distribution functions (cdf's) of branching times were
calculated, and compared (using the Kolmogorov-Smirnov test statistic D) to
those from three published empirical trees. Molecular phylogenies for
columbine plants and avian cranes showed statistically significant
departures from the null expectations, in directions indicating recent and
ancient species' radiations, respectively, whereas a molecular phylogeny
for the Drosophila virilis species group showed no apparent historical
clustering of branching events. Effects of outgroup choice and phylogenetic
frame of reference were investigated for the columbines and found to have a
predictable influence on the types of conclusions to be drawn from such
analyses. To enable other investigators to statistically test for
nonrandomness in temporal cladogenetic pattern in empirical trees generated
from data on extant species, we present tables of mean cdf's and associated
probabilities under the null model for expected branching times in phylads
of varying size. The approaches developed in this report complement and
extend those of other recent methods for employing null models to assess
the statistical significance of pattern in evolutionary trees.
相似文献
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An exercise for medical students was designed to illustrate one method of setting up a clinical trial and incidentally to demonstrate some effects of placebos. Twelve groups of four students participated: one in each group was the “recorder”, the other three (volunteers) were randomly assigned to the treatment A, treatment B, or untreated groups. Subjects performed seven psychomotor or mental tests before taking medication and 30 and 60 minutes after medication. The time taken for the tests and the errors made were recorded. Treatment A was one green and yellow gelatin capsule filled with lactose, taken with water; treatment B was a red and white capsule containing lactose; untreated subjects received a drink of water. No large changes in performance occurred and no evidence of fatigue or learning was noted, although the B''s took significantly longer to perform the arithmetic test after medication than before. Treated subjects were instructed to check any of 29 listed side effects that they experienced. A total of 44 side effects was reported: 8 of 12 in A group and 10 of 12 in B checked one or more symptoms. Indications are that the results of the trial will not soon be forgotten. 相似文献
68.
Cyclin-dependent kinases (Cdks) control cytoskeleton polarization in yeast morphogenesis. However, the target and mechanism remain unclear. Here, we show that the Candida albicans Cdk Cdc28, through temporally controlled association with two cyclins Ccn1 and Hgc1, rapidly establishes and persistently maintains phosphorylation of the septin cytoskeleton protein Cdc11 for hyphal development. Upon hyphal induction, Cdc28-Ccn1 binds to septin complexes and phosphorylates Cdc11 on Ser394, a nonconsensus Cdk target. This phosphorylation requires prior phosphorylation on Ser395 by the septin-associated kinase Gin4. Mutating Ser394 or Ser395 blocked Cdc11 phosphorylation on Ser394 and impaired hyphal morphogenesis. Reconstitution experiments using purified Cdc28-Ccn1, Gin4, and septins reproduced phosphorylations on the same residues. Transient septin-Cdc28 associations were also detected prior to bud and mating-projection emergence in S. cerevisiae. Our study uncovers a direct link between the cell-cycle engine and the septin cytoskeleton that may be part of a conserved mechanism underlying polarized morphogenesis. 相似文献
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Chris A. Smethurst Nicola Bevan Carl Brooks Amanda Emmons Peter J. Gough Claudette Mookherjee Kitty Moores Simon Peace Joanne Philp Val Piercy Steve P. Watson Mara Zippoli 《Bioorganic & medicinal chemistry letters》2012,22(23):7252-7255
Optimisation of a series of biaryl sulphonamides resulted in the identification of compound 7 which demonstrated dose-dependent and strain-specific inhibition of monocyte recruitment in a thioglycollate-induced peritonitis model of inflammation. 相似文献
70.
Phase-Variable Surface Structures Are Required for Infection of Campylobacter jejuni by Bacteriophages 下载免费PDF全文
Chris Coward Andrew J. Grant Craig Swift Jennifer Philp Rebecca Towler Mohammad Heydarian Jennifer A. Frost Duncan J. Maskell 《Applied microbiology》2006,72(7):4638-4647
This study characterizes the interaction between Campylobacter jejuni and the 16 phages used in the United Kingdom typing scheme by screening spontaneous mutants of the phage-type strains and transposon mutants of the sequenced strain NCTC 11168. We show that the 16 typing phages fall into four groups based on their patterns of activity against spontaneous mutants. Screens of transposon and defined mutants indicate that the phage-bacterium interaction for one of these groups appears to involve the capsular polysaccharide (CPS), while two of the other three groups consist of flagellatropic phages. The expression of CPS and flagella is potentially phase variable in C. jejuni, and the implications of these findings for typing and intervention strategies are discussed. 相似文献