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排序方式: 共有196条查询结果,搜索用时 78 毫秒
1.
Cloning and characterization of a gene which determines osmotic stability in Saccharomyces cerevisiae. 总被引:3,自引:2,他引:1
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The srb1-1 mutation of Saccharomyces cerevisiae is an ochre allele which renders the yeast dependent on an osmotic stabilizer for growth and gives the cells the ability to lyse on transfer to hypotonic conditions. A DNA fragment which complements both of these phenotypic effects has been cloned. This clone contains a functional gene which is transcribed into a 2.3-kb polyadenylated mRNA molecule. Transformation of yeast strains carrying defined suppressible alleles demonstrated that the cloned fragment does not contain a nonsense suppressor. Integrative transformation and gene disruption experiments, when combined with classical genetic analysis, confirmed that the cloned fragment contained the wild-type SRB1 gene. The integrated marker was used to map SRB1 to chromosome XV by Southern hybridization and pulsed-field gel electrophoresis. A disruption mutant created by the insertion of a TRP1 marker into SRB1 displayed only the lysis ability phenotype and was not dependent on an osmotic stabilizer for growth. Lysis ability was acquired by growth in (or transfer to) an osmotically stabilized environment, but only under conditions which permitted budding. It is inferred that budding cells lyse with a higher probability and that weak points in the wall at the site of budding are involved in the process. The biotechnological potential of the cloned gene and the disruption mutant is discussed. 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
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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.
The structure and growth of the polyplacophoran shell, characteristically consisting of eight plates surrounded by a girdle, is examined in the light of current views on the relationships of mantle and shell in the Bivalvia. The periostracum and outer and inner calcareous layers of the shell of the latter group are homologous with the cuticle, tegmentum and articulamentum respectively of the shell of the Polyplacophora. The margin of the mantle consists of a large marginal fold, which secretes the cuticular girdle, and a small accessory fold bearing mucous cells. These are functionally comparable with all three folds of the mantle margin found in other molluscs, although anatomically the marginal fold of the chitons probably represents only the inner surface of the outer fold of the mantle margin.
The cuticle not only forms the girdle, which bears calcified spines or spicules, but also extends between the shell plates. The principal part of the cuticle consists largely of mucopolysaccharide material but there is also a thin discrete inner region which is similar chemically to the periostracum of other molluscs. The cuticle, possibly without spines, probably covered the entire dorsal surface of a primitive placophoran and beneath this, plates developed. As these grew the cuticle became worn away except marginally and between the plates. It is suggested that a covering of mucus over the visceropallium may have been the forerunner of the molluscan shell and the possible evolutionary relationships of the shell throughout the Mollusca are discussed. 相似文献
The cuticle not only forms the girdle, which bears calcified spines or spicules, but also extends between the shell plates. The principal part of the cuticle consists largely of mucopolysaccharide material but there is also a thin discrete inner region which is similar chemically to the periostracum of other molluscs. The cuticle, possibly without spines, probably covered the entire dorsal surface of a primitive placophoran and beneath this, plates developed. As these grew the cuticle became worn away except marginally and between the plates. It is suggested that a covering of mucus over the visceropallium may have been the forerunner of the molluscan shell and the possible evolutionary relationships of the shell throughout the Mollusca are discussed. 相似文献
4.
The structure and growth of the polyplacophoran shell, characteristically consisting of eight plates surrounded by a girdle, is examined in the light of current views on the relationships of mantle and shell in the Bivalvia. The periostracum and outer and inner calcareous layers of the shell of the latter group are homologous with the cuticle, tegmentum and articulamentum respectively of the shell of the Polyplacophora. The margin of the mantle consists of a large marginal fold, which secretes the cuticular girdle, and a small accessory fold bearing mucous cells. These are functionally comparable with all three folds of the mantle margin found in other molluscs, although anatomically the marginal fold of the chitons probably represents only the inner surface of the outer fold of the mantle margin.
The cuticle not only forms the girdle, which bears calcified spines or spicules, but also extends between the shell plates. The principal part of the cuticle consists largely of mucopolysaccharide material but there is also a thin discrete inner region which is similar chemically to the periostracum of other molluscs. The cuticle, possibly without spines, probably covered the entire dorsal surface of a primitive placophoran and beneath this, plates developed. As these grew the cuticle became worn away except marginally and between the plates. It is suggested that a covering of mucus over the visceropallium may have been the forerunner of the molluscan shell and the possibleevolutionary relationships of the shell throughout the Mollusca are discussed. 相似文献
The cuticle not only forms the girdle, which bears calcified spines or spicules, but also extends between the shell plates. The principal part of the cuticle consists largely of mucopolysaccharide material but there is also a thin discrete inner region which is similar chemically to the periostracum of other molluscs. The cuticle, possibly without spines, probably covered the entire dorsal surface of a primitive placophoran and beneath this, plates developed. As these grew the cuticle became worn away except marginally and between the plates. It is suggested that a covering of mucus over the visceropallium may have been the forerunner of the molluscan shell and the possibleevolutionary relationships of the shell throughout the Mollusca are discussed. 相似文献
5.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
6.
Macadamia racemes were cross-pollinated and had flowers removedto determine whether manipulation of initial fruit set wouldaffect final fruit set or yield. Examination of flowers collected7 d after pollination indicated that the cross-pollination treatmentgenerally induced a small (13-19%) but significant increasein the number of pollen grains per stigma. All flowers possessedsome pollen grains, but in all cases cross-pollination approximatelydoubled the percentage of flowers with a pollen tube at thebase of the style (42-68% of flowers on cross-pollinated racemescompared with 21-35% of flowers on control racemes). Fruit setafter 14 d was always improved by cross-pollination, and thistranslated into increased final fruit numbers on two out offour occasions. In these two cases, kernel weights were increasedby 24 and 31% in the cross-pollinated treatments. This indicatesa possible xenic (paternal parent) effect in macadamia. Flowerremoval resulted in retention of a greater percentage of flowersas fruits, so that only severe reductions in flower number decreasedfinal fruit numbers. Improved efficiency of cross-pollinationin macadamia may increase both nut numbers and nut size.Copyright1994, 1999 Academic Press Macadamia integrifolia Maiden and Betche, Macadamia tetraphylla L. A. S. Johnson, Proteaceae, macadamia, pollination, pollen tube growth, flower number, fruit drop, fruit set, xenia 相似文献
7.
8.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
9.
Napier R.M.; Trueman S.; Henderson J.; Boyce J.M.; Hawes C.; Fricker M.D.; Venis M.A. 《Journal of experimental botany》1995,46(10):1603-1613
The most abundant proteins in the lumen of the endoplasmic reticulum(ER) are thought to be molecular chaperones, some of which mightalso be involved in calcium storage and release. We have purifiedcalreticulin from maize by ion exchange and reverse-phase chromatography.Identity with plant and animal calreticulins was confirmed byN-terminal amino acid sequencing and it was shown to bind calciumwith a calcium overlay technique. An antiserum raised to thepurified protein was used to screen an expression library andthe full coding sequence for maize calreticulin was determinedfrom the clones selected. The sequence shows 96% identity tobarley calreticulin and 55% identity to animal calreticulins.The three major functional regions are conserved, as are targetingand retention features. When visualized by indirect immunofluorescencemicroscopy, calreticulin was found to be confined to the ERand nuclear envelope of maize root cells. It was distributedthroughout the ER compartment and we found no evidence of calreticulin-enriched areas of ER, such as might be associated with specializedcalcium storage domains. Increasing or decreasing extracellularcalcium did not induce measurable changes in calreticulin levels.In addition, maize calreticulin, as well as other recognizedchaperones, was shown to bind to denatured protein and couldbe eluted specifically by nucleoside trisphosphates. Key words: Endoplasmic reticulum, calcium-binding protein, immunofluorescence, targeting, Zea mays L 相似文献
10.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献