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排序方式: 共有515条查询结果,搜索用时 15 毫秒
1.
分泌型磷脂酶PLA2G5属于磷脂酶A2超家族的一员,在免疫细胞和非免疫细胞中均有表达.研究表明,PLA2G5参与生物学事件的发生发展,在特定的病理条件下具有诱导作用.本文简要阐述了PLA2G5的来源、结构特征、生物学功能和在疾病中的作用,以及现有或潜在的PLA2G5抑制剂,以期探索基于PLA2G5的治疗新靶标. 相似文献
2.
Alkaptonuria has been diagnosed in a laboratory born, five year old, female orangutan. In man, this relatively rare amino acid metabolic disorder is characterized by arthritis, pigmentation of cartilage, and darkening of the urine upon standing. The color change is due to oxidation of homogentisic acid not normally found in the urine. The condition in man is a simple Mendelian recessive trait characterized by the absence of homogentisic acid oxidase activity. At two years of age, the affected orangutan was noted to void urine of normal color, which upon standing turned a very dark maroon color. Clinically the animal appeared normal; and the results of a urinalysis, hemogram, and survey radiographs confirmed this evaluation. Nonspecific laboratory determinations used to diagnose alkaptonuria in man were positive. Homogentisic acid in the urine was confirmed by paper chromatography, and a quantitative evaluation was made by a commercial laboratory. The orangutan has shown no clinical change or evidence of ochronosis during the past three years, and quarterly survey radiographs show no evidence of osteoarthropathy. The affected orangutan has half brothers and sisters in the colony but no full sibling. Both parents are young, however, and are being paired in an attempt to produce siblings. It is hoped that additional animals with this metabolic defect will become available for use as potential models for studying this inborn error of metabolism. 相似文献
3.
Starch Biosynthesis in Developing Wheat Grain : Evidence against the Direct Involvement of Triose Phosphates in the Metabolic Pathway 总被引:16,自引:8,他引:8 下载免费PDF全文
We have used 13C-labeled sugars and nuclear magnetic resonance (NMR) spectrometry to study the metabolic pathway of starch biosynthesis in developing wheat grain (Triticum aestivum cv Mardler). Our aim was to examine the extent of redistribution of 13C between carbons atoms 1 and 6 of [1-13C] or [6-13C]glucose (or fructose) incorporated into starch, and hence provide evidence for or against the involvement of triose phosphates in the metabolic pathway. Starch synthesis in the endosperm tissue was studied in two experimental systems. First, the 13C sugars were supplied to isolated endosperm tissue incubated in vitro, and second the 13C sugars were supplied in vivo to the intact plant. The 13C starch produced by the endosperm tissue of the grain was isolated and enzymically degraded to glucose using amyloglucosidase, and the distribution of 13C in all glucosyl carbons was quantified by 13C-NMR spectrometry. In all of the experiments, irrespective of the incubation time or incubation conditions, there was a similar pattern of partial (between 15 and 20%) redistribution of label between carbons 1 and 6 of glucose recovered from starch. There was no detectable increase over background 13C incidence in carbons 2 to 5. Within each experiment, the same pattern of partial redistribution of label was found in the glucosyl and fructosyl moieties of sucrose extracted from the tissue. Since it is unlikely that sucrose is present in the amyloplast, we suggest that the observed redistribution of label occurred in the cytosolic compartment of the endosperm cells and that both sucrose and starch are synthesized from a common pool of intermediates, such as hexose phosphate. We suggest that redistribution of label occurs via a cytosolic pathway cycle involving conversion of hexose phosphate to triose phosphate, interconversion of triose phosphate by triose phosphate isomerase, and resynthesis of hexose phosphate in the cytosol. A further round of triose phosphate interconversion in the amyloplast could not be detected. These data seriously weaken the argument for the selective uptake of triose phosphates by the amyloplast as part of the pathway of starch biosynthesis from sucrose in plant storage tissues. Instead, we suggest that a hexose phosphate such as glucose 1-phosphate, glucose 6-phosphate, or fructose 6-phosphate is the most likely candidate for entry into the amyloplast. A pathway of starch biosynthesis is presented, which is consistent with our data and with the current information on the intracellular distribution of enzymes in plant storage tissues. 相似文献
4.
Determination of parameters for enzyme therapy using L-asparaginase entrapped in canine erythrocytes
A Naqi J R DeLoach K Andrews W Satterfield M Keeling 《Biotechnology and applied biochemistry》1988,10(4):365-372
The antitumor agent L-asparaginase was entrapped in canine erythrocytes by a single dialysis encapsulation (efficiency mean = 30%). Concentration of asparaginase in carrier cells was about 240 IU/ml, with an average of 62% cell recovery. Use of a double dialysis procedure increased the L-asparaginase concentration within carrier cells to 530 IU/ml, with an overall cell recovery of 53.9%. In vitro efflux experiments showed L-asparaginase-loaded canine carriers were stable at both 4 and 37 degrees C for an 18-h period. In vivo cell survival studies showed that carrier cells did circulate and that L-asparaginase had a half-life of 6.5 days. No evidence suggesting that the enzyme left the cell was found. Carrier cells prepared with [3H]inulin and [14C]sucrose were stored at 4 degrees C for 2 weeks and began to show signs of deterioration after 2 days. 相似文献
5.
Gastrointestinal transit during mild exercise 总被引:1,自引:0,他引:1
Although exercise is often recommended as therapy for constipation, almost nothing is known of the effects of exercise on rates of movement of material in the gastrointestinal tract. In this study we investigated the influence of mild exercise on transit of a liquid meal from the mouth to the large intestine. Orocecal transit time was determined by a consistent elevation of H2 concentration in a rebreathing apparatus after ingestion of 30 g lactulose; the lactulose was part of a 360-kcal, 350-ml liquid meal. Comparison of transit time was made, in 12 young healthy subjects, between seated rest and a treadmill walk at 5.6 km/h up a 2% grade. The walk elevated heart rate from 64 +/- 4 to 109 +/- 5 beats/min, O2 uptake (VO2) from 0.29 +/- 0.02 to 1.20 +/- 0.07 l/min STPD, and final rectal temperature from 37.0 +/- 0.1 to 38.3 +/- 0.1 degrees C (all P less than 0.01). Exercise speeded transit of the liquid meal, with mean rises in H2 concentration taking place 66 +/- 10 min after ingestion at rest, compared with 44 +/- 6 min after food intake during exercise (P less than 0.02). H2 concentrations in the rebreathing apparatus showed similar base lines in the two experiments, and quantitative increases in H2 concentration, although shifted in time by exercise, were otherwise identical. Subjects with the slowest resting transit rates showed the largest exercise effects (r = 0.79, P less than 0.05). These results indicate that mouth-to-cecum transit of at least the first portion of a liquid meal-based nonabsorbable carbohydrate marker is significantly accelerated during mild exercise. 相似文献
6.
Peggy Keeling Keith Johnson Daryl Sas Kathleen Klukas Peter Donahue Ross Johnson 《The Journal of membrane biology》1983,74(3):217-228
Summary The major membrane protein of the bovine lens fiber cell is a 26-kilodalton (kD) protein (MP26), which appears to be a component
of the extensive junctional specializations found in these cells. To examine the arrangement of MP26 within the junctional
membranes, various proteases were incubated with fiber cell membranes that had been isolated with or without urea and/or detergents.
These membranes were analyzed with electron microscopy and SDS-PAGE to determine whether the junctional specializations or
the proteins were altered by proteolysis. Microscopy revealed no obvious structural changes. Electrophoresis showed that chymotrypsin,
papain, and trypsin degraded MP26 to 21–22 kD species. A variety of protease treatments, including overnight digestions, failed
to generate additional proteolysis. Regions on MP26 which were sensitive to these three proteases overlapped. Smaller peptides
were cleaved from MP26 with V8 protease and carboxypptidases A and B. Protein domains cleaved by these proteases also overlapped
with regions sensitive to chymotrypsin, papain, and trypsin. Specific inhibition of the carboxypeptidases suggested that cleavage
obtained with these preparations was not likely due to contaminating endoproteases. Since antibodies are not thought to readily
penetrate the 2–3 nm extracellular gap in the fiber cell junctions, antibodies to MP26 were used to analyze the location of
the protease-sensitive domains. Antisera were applied to control (26 kD) and proteolyzed (22 kD) membranes, with binding being
evaluated by means of ELISA reactions on intact membranes. Antibody labeling was also done following SDS-PAGE and transfer
to derivatized paper. Both assays showed a significant decrease in binding following proteolysis, with the 22 kD product showing
no reaction with the anti-MP26 sera. These investigations suggest that MP26 is arranged with approximately fourfifths of the
primary sequence “protected” by the lipid bilayer and the narrow extracellular gap. One-fifth of the molecule, including the
C-terminus, appears to be exposed on the cytoplasmic side of the membrane. 相似文献
7.
8.
The nearly invariant nature of the ''Universal Genetic Code'' attests to its early establishment in evolution and to the difficulty of altering it now, since so many molecules are required for, and depend upon, faithful translation. Nevertheless, variations on the universal code are known in a handful of genomes. We have found one such variant in diplomonads, an early-diverging eukaryotic lineage. Genes for alpha-tubulin, beta-tubulin and elongation factor 1 alpha (EF-1alpha) from two unclassified strains of Hexamitidae were found to contain TAA and TAG (TAR) triplets at positions suggesting a variant code in which TAR codes for glutamine. We found confirmation of this hypothesis by identifying genes encoding glutamine-tRNAs with CUA and UUA anticodons. The alpha-tubulin and EF-1alpha genes from two other diplomonads, Spironucleus muris and Hexamita inflata, were also sequenced and shown to contain no such non-canonical codons. However, tRNA genes with the anticodons UUA and CUA were found in H.inflata, suggesting that this diplomonad also uses these codons, albeit infrequently. The high GC content of these genomes and the presence of two isoaccepting tRNAs compound the difficulty of understanding how this variant code arose by strictly neutral means. 相似文献
9.
Christopher M. Hylton Kay Denyer Peter L. Keeling Ming-Tang Chang Alison M. Smith 《Planta》1996,198(2):230-237
The effects of waxy mutations on starch-granule-bound starch synthases (EC 2.4.1.18) in the developing endosperm of barley (Hordeum vulgare L.) and maize (Zea mays L.) have been investigated. Three granule-bound starch synthases in barley endosperm were identified by use of antibodies to known starch synthases, by reconstitution and assay of individual proteins from sodium dodecyl sulphate-polyacrylamide gels of granule-bound proteins, and by partial purification of proteins released by enzymic digestion of starch. These are proteins of 60, 77 and 90 kDa. Use of antibodies to known starch synthases and partial purification of proteins released by enzymic digestion of starch indicated that there may be at least four granule-bound starch synthases in maize endosperm: proteins of 59, 74, 77 and 83 kDa. Mutations at the waxy loci of both species affected only the 60- (barley) and 59-(maize) kDa isoforms. No evidence was found that other putative isoforms are altered in abundance or activity by the mutations. The contribution of our results to understanding of the starch synthase activity of intact starch granules and the mechanism of amylose synthesis is discussed.We are very grateful to Dr. Roger Ellis (SCRI, Dundee, Scotland) for the gift of barley seeds, and to Drs Roger Ellis, Alan Schulman and Cathie Martin for helpful advice and comments during the course of this work. 相似文献
10.
Association of a 76 kDa polypeptide with soluble starch synthase I activity in maize (cv B73) endosperm 总被引:2,自引:1,他引:1
Chen Mu Chee Harn Yuan-Tih Ko George W. Singletary Peter L. Keeling Bruce P. Wasserman 《The Plant journal : for cell and molecular biology》1994,6(2):151-159
Soluble starch synthase (SSS) I was purified 361-fold from hand-dissected endosperm tissue of inbred maize (Zea mays, cv. B73) to specific activities ranging between 5 and 9 µmol min−1 mg−1. A key to this purification protocol was the introduction of a size-exclusion chromatography step, a size-based fractionation which provided abundant levels of desalted SSS forms I and II. The native molecular masses calculated for SSS forms I and II were 75.5 kDa and 180 kDa, respectively. SSSI was then further purified by hydrophobic interaction chromatography on Phenyl-Superose and by FPLC on Mono Q. Analysis of column peaks by SDS—PAGE and scanning densitometry revealed that a 76 kDa polypeptide is strongly correlated with SSSI activity. Antibodies were then generated against a 76 kDa polypeptide extracted from starch granules. These antibodies, which were monospecific for the soluble 76 kDa polypeptide, neutralized greater than 90% of SSSI activity, and precipitated the 76 kDa protein. These results establish the 76 kDa protein as an SSSI in the B73 line of inbred maize. An immunologically similar 76 kDa protein also appears to be tightly associated with the starch granule. 相似文献