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111.
Sulfate-Reducing Bacteria Methylate Mercury at Variable Rates in Pure Culture and in Marine Sediments 总被引:2,自引:6,他引:2 下载免费PDF全文
Jeffrey K. King Joel E. Kostka Marc E. Frischer F. Michael Saunders 《Applied microbiology》2000,66(6):2430-2437
Differences in methylmercury (CH3Hg) production normalized to the sulfate reduction rate (SRR) in various species of sulfate-reducing bacteria (SRB) were quantified in pure cultures and in marine sediment slurries in order to determine if SRB strains which differ phylogenetically methylate mercury (Hg) at similar rates. Cultures representing five genera of the SRB (Desulfovibrio desulfuricans, Desulfobulbus propionicus, Desulfococcus multivorans, Desulfobacter sp. strain BG-8, and Desulfobacterium sp. strain BG-33) were grown in a strictly anoxic, minimal medium that received a dose of inorganic Hg 120 h after inoculation. The mercury methylation rates (MMR) normalized per cell were up to 3 orders of magnitude higher in pure cultures of members of SRB groups capable of acetate utilization (e.g., the family Desulfobacteriaceae) than in pure cultures of members of groups that are not able to use acetate (e.g., the family Desulfovibrionaceae). Little or no Hg methylation was observed in cultures of Desulfobacterium or Desulfovibrio strains in the absence of sulfate, indicating that Hg methylation was coupled to respiration in these strains. Mercury methylation, sulfate reduction, and the identities of sulfate-reducing bacteria in marine sediment slurries were also studied. Sulfate-reducing consortia were identified by using group-specific oligonucleotide probes that targeted the 16S rRNA molecule. Acetate-amended slurries, which were dominated by members of the Desulfobacterium and Desulfobacter groups, exhibited a pronounced ability to methylate Hg when the MMR were normalized to the SRR, while lactate-amended and control slurries had normalized MMR that were not statistically different. Collectively, the results of pure-culture and amended-sediment experiments suggest that members of the family Desulfobacteriaceae have a greater potential to methylate Hg than members of the family Desulfovibrionaceae have when the MMR are normalized to the SRR. Hg methylation potential may be related to genetic composition and/or carbon metabolism in the SRB. Furthermore, we found that in marine sediments that are rich in organic matter and dissolved sulfide rapid CH3Hg accumulation is coupled to rapid sulfate reduction. The observations described above have broad implications for understanding the control of CH3Hg formation and for developing remediation strategies for Hg-contaminated sediments. 相似文献
112.
Whole-Cell versus Total RNA Extraction for Analysis of Microbial Community Structure with 16S rRNA-Targeted Oligonucleotide Probes in Salt Marsh Sediments 总被引:2,自引:1,他引:2 下载免费PDF全文
Marc E. Frischer Jean M. Danforth Michele A. Newton Healy F. Michael Saunders 《Applied microbiology》2000,66(7):3037-3043
rRNA-targeted oligonucleotide probes have become powerful tools for describing microbial communities, but their use in sediments remains difficult. Here we describe a simple technique involving homogenization, detergents, and dispersants that allows the quantitative extraction of cells from formalin-preserved salt marsh sediments. Resulting cell extracts are amenable to membrane blotting and hybridization protocols. Using this procedure, the efficiency of cell extraction was high (95.7% ± 3.7% [mean ± standard deviation]) relative to direct DAPI (4′,6′-diamidino-2-phenylindole) epifluorescence cell counts for a variety of salt marsh sediments. To test the hypothesis that cells were extracted without phylogenetic bias, the relative abundance (depth distribution) of five major divisions of the gram-negative mesophilic sulfate-reducing delta proteobacteria were determined in sediments maintained in a tidal mesocosm system. A suite of six 16S rRNA-targeted oligonucleotide probes were utilized. The apparent structure of sulfate-reducing bacteria communities determined from whole-cell and RNA extracts were consistent with each other (r2 = 0.60), indicating that the whole-cell extraction and RNA extraction hybridization approaches for describing sediment microbial communities are equally robust. However, the variability associated with both methods was high and appeared to be a result of the natural heterogeneity of sediment microbial communities and methodological artifacts. The relative distribution of sulfate-reducing bacteria was similar to that observed in natural marsh systems, providing preliminary evidence that the mesocosm systems accurately simulate native marsh systems. 相似文献
113.
114.
Use of chromosomal integration in the establishment and expression of blaZ, a Staphylococcus aureus beta-lactamase gene, in Bacillus subtilis 总被引:7,自引:12,他引:7 下载免费PDF全文
C W Saunders B J Schmidt M S Mirot L D Thompson M S Guyer 《Journal of bacteriology》1984,157(3):718-726
With several different vectors, attempts were made to establish blaZ, a Staphylococcus aureus beta-lactamase gene, in Bacillus subtilis. Stable establishment of blaZ in B. subtilis was achieved by use of a vector that allowed the integration of a single copy of the gene into the chromosome of that host. blaZ was expressed in the heterologous host since B. subtilis strains carrying integrated blaZ produced beta-lactamase and were more resistant to ampicillin than was wild-type B. subtilis. blaZ was stably inherited in such strains, as no loss of the ability to produce beta-lactamase was observed after growth in nonselective liquid medium or on solid medium. In contrast, a blaZ-containing restriction fragment could not be established in B. subtilis with either pUB110- or pC194-based vectors. Similarly, a pC194-based shuttle vector (pGX318) containing the 5' end of blaZ (including the promoter and the coding region for the signal sequence and the first few amino acids of the mature protein) was unable to transform B. subtilis. Two derivatives of pGX318 that could be stably established in B. subtilis were isolated. The structures of these derivatives suggested that inactivation of the blaZ promoter was associated with the acquisition of the ability to be established. 相似文献
115.
James Saunders Joseph Bastian 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1984,154(2):199-209
Summary Previous anatomical and physiological studies of the gymnotoid electrosensory lateral line lobe (ELLL) suggest that the anatomically identified basilar and non-basilar pyramidal cells correspond to the physiologically defined E and I cells. Intracellular injection of horseradish peroxidase (HRP) into physiologically identified E and I cells confirms this hypothesis. The morphologies and physiological responses of the basilar and non-basilar pyramidal cells were compared. Both types of pyramidal cells have extensive apical dendritic trees that interact with a parallel fiber network in the ELLL. The apical dendritic trees of the non-basilar pyramidal cells have a wider spread along the rostrocaudal axis of the ELLL than those of the basilar pyramidal cells. This difference is discussed in reference to the interaction of these cell types with the parallel fibers of the ELLL. The density of apical dendritic branches was measured and related to the distance of these branches from the cell body. No obvious differences were seen between the dendritic density patterns of basilar and non-basilar pyramidal cells. An interesting correlation, however, exists between the atypical physiological characteristics of two basilar pyramidal cells and their dendritic density patterns. Two cells of the medial (ampullary) segment of the ELLL were analyzed. Like the pyramidal cells of the three lateral (tuberous) regions of the ELLL, the physiology of these cells appears to be related to the presence of an extended basilar process. The ampullary cells, however, have apical dendritic trees that are oriented orthogonally to the dendritic trees of the pyramidal cells.Abbreviations
AM
amplitude modulation
-
DML
dorsal molecular layer
-
ELLL
electrosensory lateral line lobe
-
EOD
electric organ discharge
-
HRP
horseradish peroxidase
-
LC
lobus caudalis
-
Npd
nucleus praeeminentialis dorsalis
-
PSTH
post stimulus time histogram 相似文献
116.
R J Buist R Deslauriers J K Saunders G W Mainwood 《Canadian journal of physiology and pharmacology》1991,69(11):1663-1669
23Na nuclear magnetic resonance spectroscopy (NMR) is increasingly being used to study Na+ gradients and fluxes in biological tissues. However, the quantitative aspects of 23Na NMR applied to living systems remain controversial. This paper compares sodium concentrations determined by 23Na NMR in intact rat hindlimb (n = 8) and excised rat gastrocnemius muscle (n = 4) with those obtained by flame photometric methods. In both types of samples, 90% of the sodium measured by flame photometry was found to be NMR-visible. This is much higher than previously reported values. The NMR measurements for intact hindlimb correlated linearly with the flame photometric measurements, implying that one pool of sodium, predominantly extracellular, is 100% visible. From measurements on excised muscle, in which extracellular space is more clearly defined, the NMR visibility of intracellular Na+ was calculated to be 70%, assuming an extracellular space of 12% of the total tissue water volume and an extracellular NMR visibility of 100%. 23Na transverse relaxation measurements were carried out using a Hahn spin echo on both intact hindlimb (n = 1) and excised muscle (n = 2) samples. These showed relaxation curves that could each be described adequately using two relaxation times. The rapidly relaxing component showed a T2 value of 3-4 ms and the slowly relaxing component a T2 of 21-37 ms. A spin lattice relaxation (T1) measurement on intact hindlimb yielded a value of 51 ms. These relatively long relaxation times show that the quadrupolar relaxation effect of Na+ complexing to large macromolecules or being otherwise motionally restricted is relatively weak. This is consistent with the high NMR visibilities reported here. 相似文献
117.
Identification of molecular markers in soybean comparing RFLP,RAPD and AFLP DNA mapping techniques 总被引:16,自引:0,他引:16
Jhy-Jhu Lin Jonathan Kuo Jin Ma James A. Saunders Hunter S. Beard Margaret H. MacDonald William Kenworthy George N. Ude Benjamin F. Matthews 《Plant Molecular Biology Reporter》1996,14(2):156-169
Three different DNA mapping techniques—RFLP, RAPD and AFLP—were used on identical soybean germplasm to compare their ability
to identify markers in the development of a genetic linkage map. Polymorphisms present in fourteen different soybean cultivars
were demonstrated using all three techniques. AFLP, a novel PCR-based technique, was able to identify multiple polymorphic
bands in a denaturing gel using 60 of 64 primer pairs tested. AFLP relies on primers designed in part on sequences for endonuclease
restriction sites and on three selective nucleotides. The 60 diagnostic primer pairs tested for AFLP analysis each distinguished
on average six polymorphic bands. Using specific primers designed for soybean fromEco RI andMse I restriction site sequences and three selective nucleotides, as many as 12 polymorphic bands per primer could be obtained
with AFLP techniques. Only 35% of the RAPD reactions identified a polymorphic band using the same soybean cultivars, and in
those positive reactions, typically only one or two polymorphic bands per gel were found. Identification of polymorphic bands
using RFLP techniques was the most cumbersome, because Southern blotting and probe hybridization were required. Over 50% of
the soybean RFLP probes examined failed to distinguish even a single polymorphic band, and the RFLP probes that did distinguish
polymorphic bands seldom identified more than one polymorphic band. We conclude that, among the three techniques tested, AFLP
is the most useful. 相似文献
118.
A series of observations and an experiment were carried out to test hypotheses about the effects of shade on the densities of spirorbid polychaetes (Neodexiospira spp.) on intertidal pneumatophores (mangrove roots) of Avicennia marina. Densities of spirorbids were greater on pneumatophores surrounded by seagrass (Zostera mucronata) than patches without seagrass. Within patches of seagrass, the density and survivorship of spirorbids on pneumatophores was greater near the substratum (covered by seagrass) than high above the substratum (not covered by seagrass). The model that these patterns of abundance are explained by greater recruitment of spirorbids to shaded surfaces was assessed. This was done by experimentally testing the hypothesis that recruitment to patches without seagrass would not differ between the upper (unshaded) and lower surfaces (unshaded) of clear plastic sheets, but would be greater on the lower surfaces (shaded) than upper surfaces (unshaded) of black plastic sheets. Recruitment was consistent with these predictions and therefore provided evidence that differences in densities of spirorbids between substrata with and without seagrass may be due largely to differences in shading. 相似文献
119.
Anderson IJ Sieprawska-Lupa M Lapidus A Nolan M Copeland A Glavina Del Rio T Tice H Dalin E Barry K Saunders E Han C Brettin T Detter JC Bruce D Mikhailova N Pitluck S Hauser L Land M Lucas S Richardson P Whitman WB Kyrpides NC 《Standards in genomic sciences》2009,1(2):189-196
Methanoculleus marisnigri Romesser et al. 1981 is a methanogen belonging to the order Methanomicrobiales within the archaeal phylum Euryarchaeota. The type strain, JR1, was isolated from anoxic sediments of the Black Sea. M. marisnigri is of phylogenetic interest because at the time the sequencing project began only one genome had previously been sequenced from the order Methanomicrobiales. We report here the complete genome sequence of M. marisnigri type strain JR1 and its annotation. This is part of a Joint Genome Institute 2006 Community Sequencing Program to sequence genomes of diverse Archaea. 相似文献
120.
Schluter C Lam KK Brumm J Wu BW Saunders M Stevens TH Bryan J Conibear E 《Molecular biology of the cell》2008,19(4):1282-1294
Endosomal transport is critical for cellular processes ranging from receptor down-regulation and retroviral budding to the immune response. A full understanding of endosome sorting requires a comprehensive picture of the multiprotein complexes that orchestrate vesicle formation and fusion. Here, we use unsupervised, large-scale phenotypic analysis and a novel computational approach for the global identification of endosomal transport factors. This technique effectively identifies components of known and novel protein assemblies. We report the characterization of a previously undescribed endosome sorting complex that contains two well-conserved proteins with four predicted membrane-spanning domains. Vps55p and Vps68p form a complex that acts with or downstream of ESCRT function to regulate endosomal trafficking. Loss of Vps68p disrupts recycling to the TGN as well as onward trafficking to the vacuole without preventing the formation of lumenal vesicles within the MVB. Our results suggest the Vps55/68 complex mediates a novel, conserved step in the endosomal maturation process. 相似文献