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951.
It has been suggested that catalase-peroxidase plays an important role in several aspects of mycobacterial metabolism and is a virulence factor in the main pathogenic mycobacteria. In this investigation, we studied genes encoding for this protein in the fast-growing opportunistic pathogen Mycobacterium fortuitum. Nucleotide sequences of two different catalase-peroxidase genes (katGI and katGII) of M. fortuitum are described. They show only 64% homology at the nucleotide level and 55% identity at the amino acid level, and they are more similar to catalases-peroxidases from different bacteria, including mycobacteria, than to each other. Both proteins were found to be expressed in actively growing M. fortuitum, and both could also be expressed when transformed into Escherichia coli and M. aurum. We detected the presence of a copy of IS6100 in the neighboring region of a katG gene in the M. fortuitum strain in which this element was identified (strain FC1). The influence of each katG gene on isoniazid (isonicotinic acid hydrazide; INH) susceptibility of mycobacteria was checked by using the INH-sensitive M. aurum as the host. Resistance to INH was induced when katGI was transformed into INH-sensitive M. aurum, suggesting that this enzyme contributes to the natural resistance of M. fortuitum to the drug. This is the first report showing two different genes encoding same enzyme activity which are actively expressed within the same mycobacterial strain. 相似文献
952.
Incomplete activation of Escherichia coli hemolysin (HlyA) due to mutations in the 3' region of hlyC. 下载免费PDF全文
Mutational analysis of the carboxy-terminal region of Escherichia coli HlyC was performed by site-directed mutagenesis. Replacement of residue Val-127 or Lys-129 reduced the activity of HlyC to about 30 or 60%, respectively, of that of the wild type, while replacement of Gly-128 reduced the activity to less than 1% of the wild-type level. Complete inactivation of HlyC was caused by a double mutation, replacement of Gly-128 with valine and of Lys-129 with isoleucine. Analysis of culture supernatants from mutants with reduced hemolytic activity by two-dimensional gel electrophoresis revealed the production and simultaneous secretion of nonacylated, monoacylated, and fully acylated HlyA forms, demonstrating impairment of the acylation reaction, possibly due to a decreased affinity of HlyC for the individual HlyA acylation sites. 相似文献
953.
Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA 总被引:10,自引:0,他引:10
Miguel A. Aranda Aurora Fraile Joaquín Dopazo José M. Malpica Fernando García-Arenal 《Journal of molecular evolution》1997,44(1):81-88
The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected
tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and
was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from
0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic
positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly
different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing
were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure
may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two
subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA
variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs
by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination
events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural
populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our
knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA
replicon to be estimated.
Received: 14 May 1996 / Accepted: 17 July 1996 相似文献
954.
Maria Manuela M. Caniça Chang Y. Lu Rajagopal Krishnamoorthy Gérard C. Paul 《Journal of molecular evolution》1997,44(1):57-65
The molecular diversity of inhibitor-resistant TEM (IRT) enzymes was explored using a strategy which involved DNA amplification
by polymerase chain reaction (PCR), analysis of restriction fragment length polymorphism (RFLP), and direct nucleotide sequencing.
The study of plasmid-borne genes from 27 strains, resistant to amoxicillin and β-lactamase-inhibitor combinations, identified
mutations resulting in amino acid change at positions 69, 244, 275, and 276 known to be associated with the IRT phenotype
and a mutation at nucleotide position 162 in the promoter region. These mutations were found to lie on two different gene
sequences, described here as ``TEM-1B like' and ``TEM-2 like' restriction linkage groups. Further analysis, of nucleotide
sequences of promoter and coding regions of the β-lactamases, confirmed that a given mutation causing IRT phenotype could
be associated with two different gene sequence frameworks and two different causal mutations could lie on identical gene sequence
framework. These data argue in favor of convergent phenotypic evolution of IRT enzymes under the selective pressure imposed
by the intensive clinical use of β-lactam–β-lactamase inhibitor combinations.
Received: 18 March 1996 / Accepted: 15 July 1996 相似文献
955.
Juan Cabezas-Herrera María Teresa Moral-Naranjo F. Javier Campoy Cecilio J. Vidal 《Journal of neurochemistry》1997,69(5):1964-1974
Abstract: The distribution and glycosylation of acetylcholinesterase (AChE) forms in vesicles derived from sarcoplasmic reticulum of normal muscle (NMV) were investigated and compared with those from dystrophic muscle vesicles (DMV). AChE activity was similar in NMV and DMV. Most of the AChE in NMV and half in DMV were released with Triton X-100. Asymmetric (A12 ) and globular hydrophilic and amphiphilic (GH 4 , GA 4 , GA 2 , and GA 1 ) AChE species occurred in NMV and DMV, the lighter forms being predominant. The percentage of GH 4 and GA 4 decreased in DMV. A fraction of the AChE that could not be extracted with detergent was detached with collagenase. Most of the detergent-released A12 AChE from NMV and nearly half in DMV failed to bind to Ricinus communis agglutinin (RCA-I). Conversely, the collagenase-detached isoforms bound to RCA, revealing that asymmetric AChE associated with internal membranes or basal lamina differed in glycosylation. Moreover, nearly half of GA 4 AChE in DMV and a few in NMV bound to RCA. Most of the RCA-unreactive GA 4 forms in NMV come from sarcolemma. The results indicate that dystrophy induces minor changes in the distribution and glycosylation of AChE forms in internal membranes of muscle. 相似文献
956.
957.
958.
Consuelo Díaz de la Guardia Roberto Alonso Francisca Alba Francisco Valle 《Aerobiologia》1995,11(1):47-50
We have carried out a study on the annual and daily pollen concentrations from Gramineae over four consecutive years in the atmosphere of Granada (Spain). Samples of pollen grains were collected by the volumetric method with the aid of a Burkard sporetrap. Gramineae, according both to their high sensitizing capacity and to data from allergologists, are responsible for many pollinoses diagnosed in this area. In this work, daily pollen levels from April to July are monitored and the variations identified are interpreted in relation to meteorological conditions. Results indicated that the highest airborne concentrations of Gramineae pollen were found in May and June, although the beginning and intensity of pollination have been variable during these 4 years. 相似文献
959.
Summary A protocol for obtaining regenerated fertile plants from mesophyll protoplasts of three lines of Matthiola incana is described. Protoplasts were isolated from leaves of 21–28 days old Matthiola plants grown in controlled environment. Sustained divisions were achieved when protoplasts were embedded in sodium alginate. Up to 2.0 % of the protoplasts developed into colonies which could be transferred to shoot regeneration media. More than 25 % of the obtained calluses regenerated shoots. About 4 % of these shoots could be rooted and after transfer to soil phenotypically normal plants have been obtained.Abbreviations 2,4-D
2,4-dichlorphenoxyacetic acid
- NAA
naphthalene acetic acid
- IAA
indole-3-acetic acid
- BAP
6-banzylaminopurine
- IPA
isopentenyladenine
- IPAR
isopentenyladenosine
- MES
(2-[N-morpholino]) ethanesulfonic acid 相似文献
960.
Maira Oropeza Palmira Guevara Eva de García José Luis Ramírez 《Plant Molecular Biology Reporter》1995,13(2):182-191
Somaclonal variants resistant to sugarcane mosaic virus (SCMV) were obtained from susceptible sugarcane cv PR62258 through
somatic embryogenesis by increasing the number of subcultures of the embryogenic callus tissue in MS medium with 3 mg/L 2,4-dichlorophenoxyacetic
acid. Transfers were made at 30-day intervals for 1, 2 or 3 subcultures. Two somaclones, namely AT626 and BT627, were selected
by their resistance to SCMV. These subclones have maintained the resistance trait over seven years of testing in the field.
In this report we identified the somaclonal SCMV resistant variants from the maternal line and the nonresistant somaclones,
using the RAPD technique. 相似文献