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51.
A ribosome association factor (AF) was isolated from the yeast Sacchharomyces cerevisiae. Partial amino acid sequence of AF was determined from its fragment of 25 kDa isolated by treating AF with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-Bromoindolenine (BNPS-skatole). This sequence has a 86% identity to the product of the single-copy S. cerevisiae STM1 gene that is apparently involved in several events like binding to quadruplex and triplex nucleic acids and participating in apoptosis, stability of telomere structures, cell cycle, and ribosomal function. Here we show that AF and Stm1p share some characteristics: both bind to quadruplex and Pu triplex DNA, associates ribosomal subunits, and are thermostable. These observations suggest that these polypeptides belong to a family of proteins that may have roles in the translation process.  相似文献   
52.
To elucidate the general constraints imposed on the structure of the D- and T-loops in functional tRNAs, active suppressor tRNAs were selected in vivo from a combinatorial tRNA gene library in which several nucleotide positions of these loops were randomized. Analysis of the nucleotide sequences of the selected clones demonstrates that among the randomized nucleotides, the most conservative are nucleotides 54 and 58 in the T-loop. In most cases, they make the combination U54-A58, which allows the formation of the normal reverse Hoogsteen base pair. Surprisingly, other clones have either the combination G54-A58 or G54-G58. However, molecular modeling shows that these purine–purine base pairs can very closely mimic the reverse Hoogsteen base pair U-A and thus can replace it in the T-loop of a functional tRNA. This places the reverse Hoogsteen base pair 54-58 as one of the most important structural aspects of tRNA functionality. We suggest that the major role of this base pair is to preserve the conformation of dinucleotide 59–60 and, through this, to maintain the general architecture of the tRNA L-form.  相似文献   
53.
A ribose residue inserted between the 3′-OH of one nucleotide and the 5′-phosphate group of the next nucleotide, functions as a site-specific cleavage site within DNA. This extra ribose does not interrupt helix formation and it protects duplex DNA against cleavage by restriction enzymes. Cleavage can be obtained with periodate and all ribose fragments can be removed with sodium hydroxide. As a result of this, an intact natural oligodeoxynucleotide is obtained after ligation reaction, which means that site-specific cleavage and recovering of intact DNA occurs without loss of genetic information.  相似文献   
54.
The immunological activity of different vaccines against hepatitis B was evaluated in the Hepatological Center organized on the basis of the Infectious Hospital in Tula. Newborn infants were immunized with the use of the following vaccines: Engerix B (Belgium), Combiotech (Russia), Euvax B (Aventis Pastèur, South Korea). Altogether, after the full course of immunization anti-HBs were detected in 76 children out of 81 (in 93.8%). Vaccine Engerix B, when introduced according to the schedule 0-1-2-12 months, exhibited high immunogenic properties in a group of infants born of women with persistent HBs-antigenemia. Anti-HBs at a concentration exceeding 1000 I.U./I could be detected in 84.6%. In another group of children immunized according to the schedule 0-1-6 months first with vaccine Combiotech at the age of 0 and 1 month, then (at the age of 6 months) with vaccine Euvax, the presence of postvaccinal anti HBs at protective concentration was registered in all children. After immunization against hepatitis B with the use of all above-mentioned vaccines introduced according to both schedules high immunological activity and safety of immunization were noted.  相似文献   
55.
It is often assumed mutant frequencies, as measured in a DNA sample, faithfully represent basic mutation rates associated with these mutations. This paradigm was extremely helpful for in vitro studies of the mechanisms of mutagenesis/repair and causes of mutations. However, in vivo, mutant fractions appear to vary dramatically and randomly from sample to sample. It's unlikely that basic mutational rates vary so much. Such variations are probably caused by clonal expansions of mutants within tissue. Whether a particular tissue sample includes an expansion or not, is a matter of chance, which explains the observed random fluctuations of mutant fractions. Well-known examples of clonal expansions involve pathological conditions such as cancer or mitochondrial disease. It is less appreciated that even in normal tissue, expansions of somatic mutants create local deviations from the "expected" mutant frequencies. The sizes of clonal expansions appear to span a wide range and thus, may affect samples of various sizes, from individual cells to individuals. In conclusion, human body appears to be a sort of a "gambling ground" for clonally expanding mutants. We speculate that expansion of early mutants rather than de novo mutation at old age may be the major source of at least some aging-specific mutants in our bodies.  相似文献   
56.
DNA polymerase mu (pol mu) is a member of the pol X family of DNA polymerases, and it shares a number of characteristics of both DNA polymerase beta (pol beta) and terminal deoxynucleotidyl transferase (TdT). Because pol beta has been shown to perform translesion DNA synthesis past cisplatin (CP)- and oxaliplatin (OX)-GG adducts, we determined the ability of pol mu to bypass these lesions. Pol mu bypassed CP and OX adducts with an efficiency of 14-35% compared to chain elongation on undamaged DNA, which is second only to pol eta in terms of bypass efficiency. The relative ability of pol mu to bypass CP and OX adducts was dependent on both template structure and sequence context. Since pol mu has been shown to be more efficient on gapped DNA templates than on primed single-stranded DNA templates, we determined the ability of pol mu to bypass Pt-DNA adducts on both primed single-stranded and gapped templates. The bypass of Pt-DNA adducts by pol mu was highly error-prone on all templates, resulting in 2, 3, and 4 nt deletions. We postulate that bypass of Pt-DNA adducts by pol mu may involve looping out the Pt-GG adduct to allow chain elongation downstream of the adduct. This reaction appears to be facilitated by the presence of a downstream "acceptor" and a gap large enough to provide undamaged template DNA for elongation past the adduct, although gapped DNA is clearly not required for bypass.  相似文献   
57.
Successful implementation of the global poliomyelitis eradication program raises the problem of vaccination against poliomyelitis in the posteradication era. One of the options under consideration envisions completely stopping worldwide the use of the Sabin vaccine. This strategy is based on the assumption that the natural circulation of attenuated strains and their derivatives is strictly limited. Here, we report the characterization of a highly evolved derivative of the Sabin vaccine strain isolated in a case of paralytic poliomyelitis from a 7-month-old immunocompetent baby in an apparently adequately immunized population. Analysis of the genome of this isolate showed that it is a double (type 1-type 2-type 1) vaccine-derived recombinant. The number of mutations accumulated in both the type 1-derived and type 2-derived portions of the recombinant genome suggests that both had diverged from their vaccine predecessors approximately 2 years before the onset of the illness. This fact, along with other recent observations, points to the possibility of long-term circulation of Sabin vaccine strain derivatives associated with an increase in their neurovirulence. Comparison of genomic sequences of this and other evolved vaccine-derived isolates reveals some general features of natural poliovirus evolution. They include a very high preponderance and nonrandom distribution of synonymous substitutions, conservation of secondary structures of important cis-acting elements of the genome, and an apparently adaptive character of most of the amino acid mutations, with only a few of them occurring in the antigenic determinants. Another interesting feature is a frequent occurrence of tripartite intertypic recombinants with either type 1 or type 3 homotypic genomic ends.  相似文献   
58.
The spatial and temporal patterns of post-embryonal cell growth and cell division were characterised in excised cotyledons of vegetable marrow (Cucurbita pepo L. var. giromontia Alef.) incubated in water. The concurrent roles of these two processes in cotyledon growth were determined using paradermal sections of the first palisade layer of developing cotyledons. Tissue specificity was observed in the pattern of cell division. The daughter cells derived from an initial cell, which had already differentiated before imbibition of the seeds, were tightly packed in a cluster, which enabled us to monitor cell division during early cotyledon development. Heterogeneity of cell size was recognised during the process of cell proliferation in the cluster, suggesting that cell division is uncoupled from control of cell size. There was significantly more cell division in the marginal part of the cotyledons than in other parts, suggesting high activity of the marginal meristem. Light enhanced cell and cotyledon enlargement, but had no effect on the number of divisions. This study elucidated the cellular basis of post-germinative Cucurbita cotyledon morphogenesis and development. Electronic Publication  相似文献   
59.
The striped expression pattern of the pair-rule gene even skipped (eve) is established by five stripe-specific enhancers, each of which responds in a unique way to gradients of positional information in the early Drosophila embryo. The enhancer for eve stripe 2 (eve 2) is directly activated by the morphogens Bicoid (Bcd) and Hunchback (Hb). As these proteins are distributed throughout the anterior half of the embryo, formation of a single stripe requires that enhancer activation is prevented in all nuclei anterior to the stripe 2 position. The gap gene giant (gt) is involved in a repression mechanism that sets the anterior stripe border, but genetic removal of gt (or deletion of Gt-binding sites) causes stripe expansion only in the anterior subregion that lies adjacent to the stripe border. We identify a well-conserved sequence repeat, (GTTT)(4), which is required for repression in a more anterior subregion. This site is bound specifically by Sloppy-paired 1 (Slp1), which is expressed in a gap gene-like anterior domain. Ectopic Slp1 activity is sufficient for repression of stripe 2 of the endogenous eve gene, but is not required, suggesting that it is redundant with other anterior factors. Further genetic analysis suggests that the (GTTT)(4)-mediated mechanism is independent of the Gt-mediated mechanism that sets the anterior stripe border, and suggests that a third mechanism, downregulation of Bcd activity by Torso, prevents activation near the anterior tip. Thus, three distinct mechanisms are required for anterior repression of a single eve enhancer, each in a specific position. Ectopic Slp1 also represses eve stripes 1 and 3 to varying degrees, and the eve 1 and eve 3+7 enhancers each contain GTTT repeats similar to the site in the eve 2 enhancer. These results suggest a common mechanism for preventing anterior activation of three different eve enhancers.  相似文献   
60.
A series of biochip readers developed for gel-based biochips includes three imaging models and a novel nonimaging biochip scanner. The imaging readers, ranging from a research-grade versatile reader to a simple portable one, use wide-field objectives and 12-bit digital large-coupled device cameras for parallel addressing of multiple array elements. This feature is valuable for monitoring the kinetics of sample interaction with immobilized probes. Depending on the model and the label used, the sensitivity of these readers approaches 0.3 amol of a labeled sample per gel element. In the selective scanner, both the spot size of the excitation laser beam and the detector field of view match the size of the biochip array elements so that the whole row of the array can be read in a single scan. The portable version reads 50-mm long, 150-element, one-dimensional arrays in 5 s. With a dynamic range of 4000:1, a sensitivity of 1-5 amol of a labeled sample per gel element, and a data format facilitating online processing, the scanner is an attractive, inexpensive solution for biomedical diagnostics. Fluorophores for sample labeling were compared experimentally in terms of detection sensitivity, influence on duplex stability, and suitability for multilabel analysis and thermodynamic studies. Texas Red and tetracarboxyphenylporphyn proved to be the best choice for two-wavelength analysis using the imaging readers.  相似文献   
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