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21.
Coe John G. S. Murray Lois E. Dawes Ian W. 《Molecular genetics and genomics : MGG》1994,245(6):661-674
Transposition of a new Drosophila retrotransposon was investigated. Total genomic Southern analysis and polytene in situ hybridizations in D. buzzatii strains and other related species using a 6 kb D. buzzatii clone (cDb314) showed a dispersed, repetitive DNA pattern, suggesting that this clone contains a transposable element (TE). We have sequenced the cDb314 clone and demonstrated that it contains all the conserved protein sequences and motifs typical of retrovirus-related sequences. Although cDb314 does not include the complete TE, the protein sequence alignment demonstrates that it includes a defective copy of a new long terminal repeat (LTR) retrotransposon, related to the gypsy family, which we have named Osvaldo. Using a D. buzzatii inbred line in which all insertion sites are known, we have measured Osvaldo transposition rates in hybrids between this D. buzzatii line and its sibling species D. koepferae. The results show that Osvaldo transposes in bursts at high rate, both in the D. buzzatii inbred line and in species hybrids. 相似文献
22.
Synopsis We have examined the concentrations of reproductively-related steroid hormones in 5 species of carcharhinid sharks, marine fishes possessing the unique attribute of placental viviparity. Measurements of serum estradiol, testosterone, progesterone, dihydrotestosterone, and corticosterone have provided baseline data for these hormones in both immature and adult male and female placental sharks. Our studies include: (1) changes in hormonal levels during maturation, (2) concentrations of circulating steroid hormones during peak breeding season, and (3) hormonal levels during gestation, including the collection of serial samples through and beyond birth from free-ranging lemon sharks. Our data suggest that steroids, important in regulating reproduction in higher mammals, are also essential in these cartilaginous fishes. 相似文献
23.
The sialidase superfamily and its spread by horizontal gene transfer 总被引:15,自引:1,他引:14
Peter Roggentin Roland Schauer Lois L. Hoyer † Eric R. Vimr 《Molecular microbiology》1993,9(5):915-921
Sialidases (neuraminidases, EC 3.2.1.18) belong to a class of glycosyl hydrolases that release terminal N-acylneuraminate (slalic acid) residues from glycoproteins, glycolipids, and polysaccharides. These enzymes are common in animals of the deuterostomate lineage (Echinodermata through Mammalia) and also in diverse microorganisms that mostly exist as animal commensals or pathogens. Sialidases, and their sialyl substrates, appear to be absent from plants and most other metazoans. Even among bacteria, sialidase is found irregularly so that related species or even strains of one species differ in this property. This unusual phylogenetic distribution makes sialidases interesting for evolutionary studies. The biochemical diversity among bacterial sialidases does not indicate close relationships. However, at the molecular level, homologies are detectable, supporting the hypothesis of a common sialidase origin and thus of a sialidase super family. Some findings indicate that sialidase genes were recently transferred via phages among bacteria. The proposal of a sialidase origin in higher animals is suggested by the presence of apparently homologous enzymes in this kingdom, supporting the idea that some microbes may have acquired the genetic information during association with their animal hosts. 相似文献
24.
Baculovirus recombinants expressing a neurotoxin gene,tox34,from the straw itch mitePyemotes triticihave been previously shown to paralyze or kill insects approximately 50% faster than wild-type. We constructed a series of recombinants of the baculovirusAutographa californicanucleopolyhedrovirus which expressedtox34with different signal sequences or were controlled by different promoters to evaluate their influence on toxin expression in cell culture and in insects. Heterologous signal sequences provided no significant increase in the overall levels of the maturetox34gene product, Tox34, secreted into the tissue culture media from infected cells and no improvement in the time required for paralysis of insect hosts. The time required for paralysis was promoter-dependent; the late 6.9K DNA binding protein gene promoter was generally the most effective promoter, although an insect HSP70 promoter was equally or more effective in one of the species. 相似文献
25.
Extracellular polysaccharide of Nostoc commune (Cyanobacteria) inhibits fusion of membrane vesicles during desiccation 总被引:6,自引:0,他引:6
Donna R. Hill Thomas W. Keenan Richard F. Helm Malcolm Potts Lois M. Crowe John H. Crowe 《Journal of applied phycology》1997,9(3):237-248
Cells of the cyanobacterium Nostoc commune secrete a complex, high molecular weight, extracellular polysaccharide (EPS) which
accumulates to more than 60% of the dry weight of colonies. The EPS was purified from the clonal isolate N. commune DRH1.
The midpoint of the membrane phase transition (Tm) of desiccated cells of N. commune CHEN was low (Tm
dry = 8 °C) and was comparable to the Tm of rehydrated cells((Tm)H20 = 6 °C). The EPS was not responsible for the depression of Tm. However, the EPS, at low concentrations, inhibited specifically the fusion of phosphatidylcholine membrane vesicles when
they were dried in vitro at0% relative humidity (−400 MPa). Low concentrations of a trehalose:sucrose mixture, in a molar
ratio which corresponded with that present in cells in vivo, together with small amounts of the EPS, were efficient in preventing
leakage of carboxyfloroscein (CF) from membrane vesicles. Freeze-fracture electron microscopy resolved complex changes in
the structure of the EPS and the outer membrane in response to rehydration of desiccated cells. The capacity of the EPS to
prevent membrane fusion, the maintenance of a low Tm
dry in desiccated cells, and the changes in rheological properties of the EPS in response to water availability, constitute what
are likely important mechanisms for desiccation tolerance in this cyanobacterium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
26.
Jerzy K. Kulski Silvana Gaudieri Matthew Bellgard Lois Balmer Keith Giles Hidetoshi Inoko Roger L. Dawkins 《Journal of molecular evolution》1997,45(6):599-609
Sequence analysis of a 237 kb genomic fragment from the central region of the MHC has revealed that the HLA-B and HLA-C genes
are contained within duplicated segments peri-B (53 kb) and peri-C (48 kb), respectively, and separated by an intervening
sequence (IF) of 30 kb. The peri-B and peri-C segments share at least 90% sequence homology except when interrupted by insertions/deletions
including Alu, L1, an endogenous retrovirus, and pseudogenes. The sequences of peri-B, IF, and peri-C were searched for the
presence of Alu elements to use as markers of evolution, chromosomal rearrangements, and polymorphism. Of 29 Alu elements,
14 were identified in peri-B, 11 in peri-C, and 4 in IF. The Alu elements in peri-B and peri-C clustered phylogenetically
into two clades which were classified as ``preduplication' and ``postduplication' clades. Four Alu J elements that are shared
by peri-B and peri-C and are flanked by homologous sequences in their paralogous locations, respectively, clustered into a
``preduplication' clade. By contrast, the majority of Alu elements, which are unique to either peri-B or peri-C, clustered
into a postduplication clade together with the Alu consensus subfamily members ranging from platyrrhine-specific (Spqxcg)
to catarrhine-specific Alu sequences (Y). The insertion of platyrrhine-specific Alu elements in postduplication locations
of peri-B and peri-C implies that these two segments are the products of a duplication which occurred in primates prior to
the divergence of the New World primate from the human lineage (35–44 mya). Examination of the paralogous Alu integration
sites revealed that 9 of 14 postduplication Alu sequences have produced microsatellites of different length and sequence within
the Alu 3′-poly A tail. The present analysis supports the hypothesis that HLA-B and HLA-C genes are products of an extended
segmental duplication between 44 and 81 million years ago (mya), and that subsequent diversification of both genomic segments
occurred because of the mobility and mutation of retroelements such as Alu repeats.
Received: 21 May 1997 / Accepted: 9 July 1997 相似文献
27.
Infrared spectroscopic studies on interactions of water and carbohydrates with a biological membrane
John H. Crowe Lois M. Crowe Dennis Chapman 《Archives of biochemistry and biophysics》1984,232(1):400-407
Infrared spectroscopy was used to investigate the changes in bands assigned to phospholipids and proteins in dehydrated and rehydrated sarcoplasmic reticulum. The changes in CH2 and CH3 stretching bands, amide bands, and phosphate stretching bands are similar to shifts in frequency seen for those bands in phospholipid and protein preparations during thermotropic phase transitions and hydration. IR studies on dry trehalose-sarcoplasmic reticulum mixtures show similar results; with increasing trehalose concentration in the dry mixtures, amide and phosphate bands shift to frequencies characteristic of hydrated samples. Changes in bands assigned to OH deformations in the trehalose suggest that the interaction between the carbohydrate and membrane is by means of hydrogen bonding between these OH groups and membrane components. 相似文献
28.
29.
John H. Collins Bliss Forbush Lois K. Lane Eleanor Ling Arnold Schwartz Anita Zot 《生物化学与生物物理学报:生物膜》1982,686(1):7-12
Highly purified lamb kidney (Na++K+)-ATPase was photoaffinity labeled with the tritiated 2-nitro-5-azidobenzoyl derivative of ouabain (NAB-ouabain). The labeled (Na++K+)-ATPase was mixed with unlabeled carrier enzyme. Two proteolipid (γ1 and γ2) fractions were then isolated by chromatography on columns of Sepharose CL-6B and Sephadex LH-60. The two fractions were interchangeable when rechromatographed on the LH-60 column, suggesting that γ1 is an aggregated form of γ2. The total yield was 0.8–1.5 mol of γ component per mol of catalytic subunit recovered. This indicates that the γ component is present in stoichiometric amounts in the (Na++K+)-ATPase. The proteolipids that were labeled with NAB-ouabain copurified with the unlabeled proteolipids. 相似文献
30.