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排序方式: 共有282条查询结果,搜索用时 15 毫秒
1.
Determination of steady state and nonsteady-state glycerol kinetics in humans using deuterium-labeled tracer 总被引:1,自引:0,他引:1
Using deuterium-labeled glycerol as tracer and gas-liquid chromatography-mass spectrometry techniques for the determination of isotopic enrichment, we have developed a simple and ethically acceptable method of determining glycerol appearance rate in humans under steady-state and nonsteady-state conditions. In normal subjects, the appearance rate of glycerol in the post-absorptive state was 2.22 +/- 0.20 mumol X kg-1 X min-1, a value in agreement with those reported in studies with radioactively labeled tracers. The ratio nonesterified fatty acid (NEFA) appearance rate/glycerol appearance rate ranged from 1.95 to 3.40. In insulin-dependent diabetic patients with a mild degree of metabolic control, the appearance rate of glycerol was 2.48 +/- 0.29 mumol X kg-1 X min-1. The volume of distribution of glycerol, determined by the bolus injection technique, was (mean) 0.306 l X kg-1 in normal subjects and 0.308 l X kg-1 in insulin-independent diabetic patients. To evaluate the usefulness of the method for determination of glycerol kinetics in nonsteady-state conditions, we infused six normal subjects with natural glycerol and calculated the isotopically determined glycerol appearance rate using a single compartment model (volume of distribution 0.31 l X kg-1). During these tests, the expected glycerol appearance rates were successively 5.03 +/- 0.33, 7.48 +/- 0.39, 9.94 +/- 0.34, 7.48 +/- 0.39, and 5.03 +/- 0.33 mumol +/- kg-1 X min-1, whereas the corresponding isotopically determined appearance rates were 4.62 +/- 0.45, 6.95 +/- 0.56, 10.85 +/- 0.51, 7.35 +/- 0.34, and 5.28 +/- 0.12 mumol X kg-1 X min-1.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
2.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4 下载免费PDF全文
Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
3.
Extreme differences in rates of molecular evolution of foraminifera revealed by comparison of ribosomal DNA sequences and the fossil record 总被引:5,自引:3,他引:5
Pawlowski J; Bolivar I; Fahrni JF; de Vargas C; Gouy M; Zaninetti L 《Molecular biology and evolution》1997,14(5):498-505
Foraminifera have one of the best known fossil records among the
unicellular eukaryotes. However, the origin and phylogenetic relationships
of the extant foraminiferal lineages are poorly understood. To test the
current paleontological hypotheses on evolution of foraminifera, we
sequenced about 1,000 base pairs from the 3' end of the small subunit rRNA
gene (SSU rDNA) in 22 species representing all major taxonomic groups.
Phylogenies were derived using neighbor- joining, maximum-parsimony, and
maximum-likelihood methods. All analyses confirm the monophyletic origin of
foraminifera. Evolutionary relationships within foraminifera inferred from
rDNA sequences, however, depend on the method of tree building and on the
choice of analyzed sites. In particular, the position of planktonic
foraminifera shows important variations. We have shown that these changes
result from the extremely high rate of rDNA evolution in this group. By
comparing the number of substitutions with the divergence times inferred
from the fossil record, we have estimated that the rate of rDNA evolution
in planktonic foraminifera is 50 to 100 times faster than in some benthic
foraminifera. The use of the maximum-likelihood method and limitation of
analyzed sites to the most conserved parts of the SSU rRNA molecule render
molecular and paleontological data generally congruent.
相似文献
4.
Jolanda?HM?van Bilsen Josée?PA?Wagenaar-Hilbers Maarten?JF?van der Cammen Mariska?EA?van Dijk Willem?van Eden Marca?HM?WaubenEmail author 《Arthritis research & therapy》2002,4(4):R2
We have recently found that matrix metalloproteinases (MMPs) are targets for T-cell and B-cell reactivity in experimental
arthritis. In the present article, we investigate whether modulation of MMP-specific T-cell responses could influence the
course of adjuvant arthritis (AA). Lewis rats were treated nasally with MMP peptides prior to or after AA induction. Administration
of the MMP-10 or the MMP-16 peptide prior to AA induction reduced the arthritic symptoms. In contrast, administration of the
MMP-10 peptide after AA induction aggravated the arthritic symptoms. The present study shows the possible usefulness of MMP
peptides for immunotherapy. However, a clear understanding of proper timing of peptide administration is crucial for the development
of such therapies. 相似文献
5.
It has recently been suggested that topoisomerases could be important targets for drugs used in several diseases. This prompted us to purify and characterize the topoisomerases I and II present in the erythrocytes of protozoan parasites of the genus Plasmodium, the causative agent of malaria, in order to later use these enzymatic systems in antimalarial drug assays. The topoisomerases were purified from Plasmodium berghei, a parasite of mouse red cells. The Plasmodium topoisomerase II consists of two subunits with a molecular weight of about 160K. The enzyme is ATP- and Mg2+-dependent. The conditions for the reactions of relaxation, unknotting, decatenation, and catenation were found to be similar to those observed with enzymes from other eukaryotic cells. The Plasmodium topoisomerase I is a monomeric enzyme with a Mr of 70K-100K. It is ATP-independent and K+- or Na-dependent. Mg2+ is not required for relaxation but stimulates the reaction. Topoisomerase II was more sensitive to drug action than topoisomerase I. The most active drugs were the ellipticine derivatives. The antimalarial drugs, currently used in human clinical therapy, were poor inhibitors. Some antitumoral drugs stimulated the double-stranded DNA cleavage activity of Plasmodium topoisomerase II, like that of mammalian topoisomerases II. Antimalarial drugs had no stimulating activity. It is therefore suggested that Plasmodium topoisomerases are not good targets for antimalarial drugs. 相似文献
6.
J F Riou M Umbhauer D L Shi J C Boucaut 《Biology of the cell / under the auspices of the European Cell Biology Organization》1992,75(1):1-9
Tenascin is a large oligomeric extracellular matrix (ECM) glycoprotein whose expression is highly restricted during vertebrate development. It has a characteristic hexameric quaternary structure with six arms linked to a central globular domain. Each arm contains a single polypeptide with the central globular domain formed by the covalent association of the N-terminal ends of the six polypeptides. Tenascin first appears during development, associated with the neural crest cell migration pathways of mammalian, avian and amphibian embryos. During later development, it is observed at sites of cartilage, bone and tendon formation. Tenascin expression also occurs in defined areas in the developing nervous system and in condensing mesenchyme, in response to epithelio-mesenchymal interactions. The function of tenascin in these different morphogenetic processes is not yet clearly understood. Tenascin can promote neurite outgrowth in vitro and can inhibit cell interactions with fibronectin. Results based on antibody mapping and molecular cloning indicate that these properties involve two distinct cell binding sites. Together with its highly regulated expression in the embryo, these properties suggest that tenascin plays a key role in the control of cell migration and differentiation during development. 相似文献
7.
Anne‐Laure Valton Vahideh Hassan‐Zadeh Ingrid Lema Nicole Boggetto Patrizia Alberti Carole Saintomé Jean‐François Riou Marie‐Noëlle Prioleau 《The EMBO journal》2014,33(7):732-746
DNA replication ensures the accurate duplication of the genome at each cell cycle. It begins at specific sites called replication origins. Genome‐wide studies in vertebrates have recently identified a consensus G‐rich motif potentially able to form G‐quadruplexes (G4) in most replication origins. However, there is no experimental evidence to demonstrate that G4 are actually required for replication initiation. We show here, with two model origins, that G4 motifs are required for replication initiation. Two G4 motifs cooperate in one of our model origins. The other contains only one critical G4, and its orientation determines the precise position of the replication start site. Point mutations affecting the stability of this G4 in vitro also impair origin function. Finally, this G4 is not sufficient for origin activity and must cooperate with a 200‐bp cis‐regulatory element. In conclusion, our study strongly supports the predicted essential role of G4 in replication initiation. 相似文献
8.
Production of Cell Wall-Degrading Enzymes by the Phytopathogenic Fungus Sclerotinia sclerotiorum 总被引:1,自引:1,他引:1 下载免费PDF全文
The range of polysaccharide-degrading enzymes and glycosidases formed by the phytopathogenic fungus Sclerotinia sclerotiorum was monitored following growth on 16 carbohydrate substrates. Endo- and exoenzymes capable of degrading cellulosic, hemicellulosic, and pectinolytic polysaccharides were secreted. Pectinolytic activities were produced constitutively on all of the substrates tested. Cellulolytic enzymes were not induced in simple sugar (i.e., glucose or xylose) media. Polysaccharide growth substrates and cellulase inducers increased all of the enzyme activities tested. Gel filtration analysis revealed the appearance of new molecular forms of pectinase, β-xylosidase, and cellobiosidase during induction on pectin and carboxymethyl cellulose media. 相似文献
9.
Interaction of the bullous pemphigoid antigen 1 (BP230) and desmoplakin with intermediate filaments is mediated by distinct sequences within their COOH terminus 下载免费PDF全文
Fontao L Favre B Riou S Geerts D Jaunin F Saurat JH Green KJ Sonnenberg A Borradori L 《Molecular biology of the cell》2003,14(5):1978-1992
The bullous pemphigoid antigen 1 (BP230) and desmoplakin (DP) are members of the plakin protein family of cytolinkers. Despite their homology, their COOH termini selectively bind distinct intermediate filaments (IFs). We studied sequences within their COOH termini required for their interaction with the epidermal keratins K5/K14, the simple epithelial keratins K8/K18, and type III IF vimentin by yeast three-hybrid, cell transfection, and overlay assays. The results indicate that BP230 interacts with K5/K14 but not with K8/K18 or vimentin via a region encompassing both the B and C subdomains and the COOH extremity, including a COOH-terminal eight-amino-acid stretch. In contrast, the C subdomain with the COOH-terminal extremity of DP interacts with K5/K14 and K8/K18, and its linker region is able to associate with K8/K18 and vimentin. Furthermore, the potential of DP to interact with IF proteins in yeast seems to be regulated by phosphorylation of Ser 2849 within its COOH terminus. Strikingly, BP230 and DP interacted with cytokeratins only when both type I and type II keratins were present. The head and tail domains of K5/K14 keratins were dispensable for their interaction with BP230 or DP. On the basis of our findings, we postulate that (1) the binding specificity of plakins for various IF proteins depends on their linker region between the highly homologous B and C subdomains and their COOH extremity and (2) the association of DP and BP230 with both epidermal and simple keratins is critically affected by the tertiary structure induced by heterodimerization and involves recognition sites located primarily in the rod domain of these keratins. 相似文献
10.
The alpha-like globin gene cluster in rabbits contains embryonic zeta-
globin genes, an adult alpha-globin gene, and theta-globin genes of
undetermined function. The basic arrangement of genes, deduced from
analysis of cloned DNA fragments, is 5'-zeta 0-zeta 1-alpha 1-theta 1- zeta
2-zeta 3-theta 2-3'. However, the pattern of restriction fragments
containing zeta- and theta-globin genes varies among individual rabbits.
Analysis of BamHI fragments of genomic DNA from 24 New Zealand white
rabbits revealed eight different patterns of fragments containing
zeta-globin genes. The large BamHI fragments containing genes zeta 0 and
zeta 1 are polymorphic in length, whereas a 1.9-kb fragment containing the
zeta 2 gene and the 3.5-kb fragment containing the zeta 3 gene do not vary
in size. In contrast to this constancy in the size of the restriction
fragments, the copy number of the zeta 2 and zeta 3 genes does vary among
different rabbits. No length polymorphism was detected in the BamHI
fragments containing the theta-globin genes, but again the copy number
varies for restriction fragments containing the theta 2 gene. The alpha 1-
and theta 1-globin genes are located in a nonpolymorphic 7.2-kb BamHI
fragment. The combined data from hybridization with both zeta and theta
probes shows that the BamHI cleavage pattern does not vary within the
region 5'-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3', but the pattern
genomic blot-hybridization patterns for the progeny of parental rabbits
with different zeta-globin gene patterns shows that the polymorphic
patterns are inherited in a Mendelian fashion. Two different haplotypes
have been mapped based on the genomic blot-hybridization data. The
variation in the alpha-like globin gene cluster in the rabbit population
results both from differences in the copy number of the duplication block
containing the zeta-zeta-theta gene set and from the presence or absence of
polymorphic BamHI sites.
相似文献