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1.
- 1.
- 1. The plasma membrane has been isolated from rat myometrium using a single step density gradient centrifugation without any salt extraction. A new kind of continuous sucrose density gradient was prepared using an Instrumentation Specialities Co. (ISCO) density gradient former. Other subcellular fractions were also obtained by this technique. 相似文献
2.
Escherichia coli and Bacillus megaterium rendered permeable to ribonucleoside triphosphates by toluene treatment retain the capacity to synthesize discrete ribonucleic acid species. 相似文献
3.
The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
相似文献
4.
Stimulation of tissue plasminogen activator by denatured proteins and fibrin clots: A possible additional role for plasminogen activator? 总被引:1,自引:0,他引:1
Purified plasminogen activator from pig heart displays weak activity toward plasminogen, with or without detergents present. The activation rate is enhanced at least 50 times upon addition of low concentrations (1 μg/ml) of many proteins following their denaturation by acid, base, or heat. No native proteins, at concentrations up to 10 mg/ ml, enhanced plasminogen activator activity. The degree of enhancement by many denatured proteins was as great as that caused by the presence of a fibrin clot, and occurred at lower protein concentrations. Similar observations with activators from human vena cava and cadaver perfusate suggest that the effect is probably general to tissue activators. None of the denatured proteins examined enhanced the activity of urokinase, streptokinase, staphylokinase, or plasmin. Small proteins known to renature rapidly, such as RNAse, and highly ordered structural proteins, such as collagen and keratin, could not be converted to stimulators of plasminogen activators by treatment with acid or base. If, as appears likely, plasminogen activator can indeed recognize and be stimulated by misfolded proteins, a possible role in selective catabolism of damaged protein in general, not solely fibrin clots, is evident. If the nature of the stimulatory peptide grouping can be elucidated, plasminogen activator may also be a valuable tool both for study of protein denaturation and clarification of the clot stimulatory effect in fibrinolysis. 相似文献
5.
Radcliffe CE Drucker DB Boote V Fletcher-Williams G Claydon MA 《Canadian journal of microbiology》2001,47(1):96-101
Species of Peptostreptococcus cause a variety of infections, primarily abscesses of soft tissues, joints, and mucous membranes. The aim of this study was to compare the phospholipid analogue profiles of Peptostreptococcus species, represented by P. anaerobius, P. asaccharolyticus, P. indolicus, P. lacrimalis, and P. prevotii; Micromonas micros (P. micros) and Finegoldia magna (P. magnus). After anaerobic growth on blood-FAA, lipids extracted by chloroform-methanol (2:1 v/v) were purified, then analysed by fast atom bombardment mass spectrometry (FAB-MS) in negative ion mode. The major peaks with mass to charge (m/z) 719, 721, and 749, corresponded to phosphatidylglycerol analogues, namely PG (32:1), PG (32:0), and PG (34:0), which have been found previously in Lactobacillus spp., Clostridium difficile, and Staphylococcus spp. Other major peaks observed, with m/z 619, 647, 665, 675, 677, 687, 691, 693, 701, 703, 707, 733, and 746 have also been reported in one or more of these three species. However, other major peaks found here in Peptostreptococcus, Micromonas, and Finegoldia have not been described elsewhere; these are 501, 514, 515, 618, 659, 673, 676, 688, 690, 692, 694, 700, 706, 715, 718, 722, and 750. We conclude that Peptostreptococcus, Micromonas, and Finegoldia isolates are chemically unique. 相似文献
6.
In multi-cellular organisms, failure to properly regulate cell-cycle progression can result in inappropriate cell death or uncontrolled cell division leading to tumor formation. To guard against such events, conserved regulatory mechanisms called "checkpoints" block progression into mitosis in response to DNA damage and incomplete replication, as well as in response to other signals. Checkpoint mutants in organisms as diverse as yeast and humans are sensitive to various chemical agents that inhibit DNA replication or cause DNA damage. This phenomenon is the primary rationale for chemotherapy, which uses drugs that preferentially target tumor cells with compromised checkpoints. In this study, we demonstrate the use of Drosophila checkpoint mutants as a system for assaying the effects of various DNA-damaging and anti-cancer agents in a developing multicellular organism. Dwee1, grp and mei-41 are genes that encode kinases that function in the DNA replication checkpoint. We tested zygotic mutants of each gene for sensitivity to the DNA replication inhibitor hydroxyurea (HU), methyl methanosulfonate (MMS), ara-C, cisplatin, and the oxygen radical generating compound paraquat. The mutants show distinct differences in their sensitivity to each of the drugs tested, suggesting an underlying complexity in the responses of individual checkpoint genes to genotoxic stress. 相似文献
7.
The proper folding of tubulins and their incorporation into microtubules consist of a series of reactions, in which evolutionarily conserved proteins, cofactors A to E, play a vital role. We have cloned a fission yeast gene (alp41(+)) which encodes a highly conserved small GTP-binding protein homologous to budding yeast CIN4 and human ARF-like Arl2. alp41(+) is essential, disruption of which results in microtubule dysfunction and growth polarity defects. Genetic analysis indicates that Alp41 plays a crucial role in the cofactor-dependent pathway, in which it functions upstream of the cofactor D homologue Alp1(D) and possibly in concert with Alp21(E). 相似文献
8.
The proper folding of tubulins prior to their incorporation into microtubules requires a group of conserved proteins called
cofactors A to E. In fission yeast, homologues of these cofactors (at least B, D and E) are necessary for the biogenesis of
microtubules and for cell viability. Here we show that the temperature-sensitive alp11-924 mutant, which is defective in the cofactor B homologue, contains an opal nonsense mutation, which results in the production
of a truncated Alp11B protein (Alp111–118). We isolated a tRNATrp gene as a multicopy suppressor of this mutation, which rescues alp11-924 by read-through of the nonsense codon. The truncated Alp111–118 protein lacks the C-terminal half of Alp11B, consisting of a central coiled-coil region and the distal CLIP-170 domain found in a number of proteins involved in microtubule
functions. Both of these domains are required for the maintenance of microtubule architecture in vivo. Detailed functional
analyses lead us to propose that Alp11B comprises three functional domains: the N-terminal half executes the essential function, the central coiled-coil region is
necessary for satisfactory maintenance of cellular α-tubulin levels, and the C-terminal CLIP-170 domain is required for efficient
binding to α-tubulin.
Received: 29 November 1999 / Accepted: 18 April 2000 相似文献
9.
Applications of supercritical fluid extraction and chromatography in forensic science 总被引:2,自引:0,他引:2
Radcliffe C Maguire K Lockwood B 《Journal of biochemical and biophysical methods》2000,43(1-3):261-272
Supercritical fluid technology is a rapidly expanding analytical technique. Here we give a brief insight into the background of supercritical fluid technology and how supercritical fluid extraction and supercritical fluid chromatography work in analysis. The applications of these two techniques in forensic science are known to be important. The main area of forensic use of supercritical fluid technology is in the sample preparation and separation of drugs of abuse particularly opiates, cannabinoids, cocaine and sedatives. Supercritical fluid technology can be used for both time-of-death-related drug analysis and for obtaining information relating to long term drug abuse. We also give a review of the use of supercritical fluids in two other major forensic areas, fingerprinting and the extraction and separation of explosives from both bombing events and gunshot residues. Overall we show that supercritical fluid technology is fast becoming a major part of forensic investigations and that it is an invaluable analysis technique. 相似文献
10.
A wide-ranging examination of plastid (pt)DNA sequence homologies within
higher plant nuclear genomes (promiscuous DNA) was undertaken. Digestion
with methylation-sensitive restriction enzymes and Southern analysis was
used to distinguish plastid and nuclear DNA in order to assess the extent
of variability of promiscuous sequences within and between plant species.
Some species, such as Gossypium hirsutum (cotton), Nicotiana tabacum
(tobacco), and Chenopodium quinoa, showed homogenity of these sequences,
while intraspecific sequence variation was observed among different
cultivars of Pisum sativum (pea), Hordeum vulgare (barley), and Triticum
aestivum (wheat). Hypervariability of plastid sequence homologies was
identified in the nuclear genomes of Spinacea oleracea (spinach) and Beta
vulgaris (beet), in which individual plants were shown to possess a unique
spectrum of nuclear sequences with ptDNA homology. This hypervariability
apparently extended to somatic variation in B. vulgaris. No sequences with
ptDNA homology were identified by this method in the nuclear genome of
Arabidopsis thaliana.
相似文献