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951.
The barA and sirA genes of Salmonella enterica serovar Typhimurium encode a two-component sensor kinase and a response regulator, respectively. This system increases the expression of virulence genes and decreases the expression of motility genes. In this study, we examined the pathways by which SirA affects these genes. We found that the master regulator of flagellar genes, flhDC, had a positive regulatory effect on the primary regulator of intestinal virulence determinants, hilA, but that hilA had no effect on flhDC. SirA was able to repress flhDC in a hilA mutant and activate hilA in an flhDC mutant. Therefore, although the flhDC and hilA regulatory cascades interact, sirA affects each of them independently. A form of BarA lacking the two N-terminal membrane-spanning domains, BarA198, autophosphorylates in the presence of ATP and transfers the phosphate to purified SirA. Phosphorylated SirA was found to directly bind the hilA and hilC promoters in gel mobility shift assays but not the flhD, fliA, hilD, and invF promoters. Given that the CsrA/csrB system is known to directly affect flagellar gene expression, we tested the hypothesis that SirA affects flagellar gene expression indirectly by regulating csrA or csrB. The sirA gene did not regulate csrA but did activate csrB expression. Consistent with these results, phosphorylated SirA was found to directly bind the csrB promoter but not the csrA promoter. We propose a model in which SirA directly activates virulence expression via hilA and hilC while repressing the flagellar regulon indirectly via csrB. 相似文献
952.
The N-methyl-d-aspartate (NMDA) receptor has four membrane-associated domains, three of which are membrane-spanning (M1, M3, and M4) and one of which is a re-entrant pore loop (M2). The M1-M3 domains have been demonstrated to influence the function of the ion channel, but a similar role for the M4 domain has not been reported. We have identified a methionine residue (Met(823)) in the M4 domain of the NR2A subunit that regulates desensitization and ion channel gating. A tryptophan substitution at this site did not alter the EC(50) for glycine or the peak NMDA EC(50) but decreased the steady-state NMDA EC(50) and markedly increased apparent desensitization, mean open time, and peak current density. Results of rapid solution exchange experiments revealed that changes in microscopic desensitization rates and closing rates could account for the changes in macroscopic desensitization, steady-state NMDA EC(50), and current density. Other amino acid substitutions at this site could increase or decrease the rate of desensitization and mean open time of the ion channel. Both mean open time and desensitization were dependent primarily upon the hydrophobic character of the amino acid at the position. These results demonstrate an important role for hydrophobic interactions at Met(823) in regulation of NMDA receptor function. 相似文献
953.
Increasing cellular G-actin, using latrunculin B, in either intact or permeabilized rat peritoneal mast cells, caused translocation of both actin and an actin regulatory protein, cofilin, into the nuclei. The effect was not associated with an increase in the proportion of apoptotic cells. The major part of the nuclear actin was not stained by rhodamine-phalloidin but could be visualized with an actin antibody, indicating its monomeric or a conformationally distinct state, e.g. cofilin-decorated filaments. Introduction of anti-cofilin into permeabilized cells inhibited nuclear actin accumulation, implying that an active, cofilin-dependent, import exists in this system. Nuclear actin was localized outside the ethidium bromide-stained region, in the extrachromosomal nuclear domain. In permeabilized cells, the appearance of nuclear actin and cofilin was not significantly affected by increasing [Ca(2+)] and/or adding guanosine 5'-O-(3-thiotriphosphate), but was greatly promoted when ATP was withdrawn. Similarly, ATP depletion in intact cells also induced nuclear actin accumulation. In contrast to the effects of latrunculin B, ATP depletion was associated with an increase in cortical F-actin. Our results suggest that the presence of actin in the nucleus may be required for certain stress-induced responses and that cofilin is essential for the nuclear import of actin. 相似文献
954.
Bhave G Nadin BM Brasier DJ Glauner KS Shah RD Heinemann SF Karim F Gereau RW 《The Journal of biological chemistry》2003,278(32):30294-30301
The metabotropic glutamate receptors (mGluRs) have been predicted to have a classical seven transmembrane domain structure similar to that seen for members of the G-protein-coupled receptor (GPCR) superfamily. However, the mGluRs (and other members of the family C GPCRs) show no sequence homology to the rhodopsin-like GPCRs, for which this seven transmembrane domain structure has been experimentally confirmed. Furthermore, several transmembrane domain prediction algorithms suggest that the mGluRs have a topology that is distinct from these receptors. In the present study, we set out to test whether mGluR5 has seven true transmembrane domains. Using a variety of approaches in both prokaryotic and eukaryotic systems, our data provide strong support for the proposed seven transmembrane domain model of mGluR5. We propose that this membrane topology can be extended to all members of the family C GPCRs. 相似文献
955.
16S rDNA diversity of cultured and uncultured prokaryotes of a mat sample from Lake Fryxell, McMurdo Dry Valleys, Antarctica 总被引:11,自引:0,他引:11
Brambilla E Hippe H Hagelstein A Tindall BJ Stackebrandt E 《Extremophiles : life under extreme conditions》2001,5(1):23-33
The prokaryotic diversity of aerobic and anaerobic bacterial isolates and of bacterial and archaeal 16S rDNA clones was determined for a microbial mat sample from the moated region of Lake Fryxell, McMurdo Dry Valleys, Antarctica. Among the anaerobic bacteria, members of Clostridium estertheticum and some other psychrotolerant strains dominated whereas methanogens and other Archaea were lacking. Isolates highly related to Flavobacterium hibernum, Janthiniobacterium lividum, and Arthrobacter flavus were among the aerobic bacteria most frequently isolated. Assessment of more than 350 partial 16S rDNA clone sequences of libraries generated by Bacteria- and Archaea-specific PCR primers revealed a rich spectrum of bacterial diversity but only two different archaeal clone sequences. Among the Bacteria, representative sequences belonged to the class Proteobacteria, order Verrucomicrobiales, class Actinobacteria, Clostridium/Bacillus subphylum of Gram-positives, and the Cytophaga-Flavobacterium-Bacteroides phylum. The clones formed about 70 higher taxonomy groups (<98% sequence similarity) and 133 potential species, i.e., groups of clones sharing greater than 98% similarity. Only rarely were clone sequences found to be highly related to Lake Fryxell isolates and to strains of described species. Subsequent analysis of ten sequencing batches of 36 individual clones indicated that the diversity might be still higher than had been assessed. 相似文献
956.
Tang Y Shepherd BS Nichols AJ Dunham R Chen TT 《Marine biotechnology (New York, N.Y.)》2001,3(3):205-217
Pituitary growth hormone (GH), prolactin (PRL), and somatolactin (SL) messenger RNA levels in channel catfish (Ictalurus punctatus) were examined under various environmental and physiological conditions. Catfish were sampled following salinity challenge,
during the winter (December) and spring or summer (April or July), and at different sizes (15–18 g, 620–664 g, and 956–1134
g). When catfish (956–1134 g) were transferred from freshwater to saline water containing 8 ppt NaCl, their plasma [Na+] increased significantly above values in the freshwater control group until they were transferred back to freshwater. Pituitary
GH mRNA levels were low for the first 24 hours following transfer to saline water, but thereafter were significantly elevated
above control values until the fish were transferred back to freshwater. Pituitary GH mRNA levels were highest in July and
lowest in December. Growth hormone mRNA levels were also elevated in the size groups 15–18 g and 956–1134 g in July when compared
with December values. Pituitary PRL mRNA levels increased for the first 24 hours following transfer to saline water (956–1134
g), but thereafter were significantly lower than control values until the fish were transferred back to freshwater. Pituitary
PRL mRNA levels were highest in April and July and lowest in December, and were also elevated in the size groups 620–664 g
and 956–1134 g. Pituitary SL mRNA levels were unaffected in catfish transferred to saline water; however, levels were significantly
elevated in catfish of the 956–1134-g size group sampled in April when compared with December. These results suggest the involvement
of GH in adaptation to brackish water and of PRL in adaptation to freshwater in the catfish, and seasonal and size-related
differences in pituitary GH, PRL, and SL mRNA levels.
Received May 17, 2000; accepted October 30, 2000 相似文献
957.
Steven I. Park Manat Renil Brian Vikstrom Nail Amro Liang-wen Song Bai-ling Xu Kit S. Lam 《Letters in Peptide Science》2001,8(3-5):171-178
Using a `one-bead one-compound' combinatorial library methodand whole cell binding assay, we have identified peptideligands that bind preferentially to human lymphoid malignantcells but not to normal human peripheral lymphocytes. Thesepeptides have a common motif of Leu-Asp-Ile, Leu-Asp-Phe, orLeu-Asp-Val. Anti-4 integrin antibody blocks binding ofcells to these peptides which indicates that the targetreceptor for these peptides is 41 integrin. Thesefindings may have important therapeutic and diagnosticimplications in the treatment of lymphoma, leukemia, andvarious immunologic disorders. 相似文献
958.
The segregation of Nostoc and Anabaena into separate genera has been debated for some time. The nitrogen fixation gene nifD was completely sequenced from representatives of these genera and analyzed phylogenetically, by using the representatives
of other genera of the heterocystous cyanobacteria as outgroups. We were clearly able to differentiate between Nostoc and Anabaena in all analyses used. Our data suggest that Nostoc and Anabaena should remain as separate genera.
Received: 16 November 2001 / Accepted: 14 December 2001 相似文献
959.
Choi KM Zhong Y Hoit BD Grupp IL Hahn H Dilly KW Guatimosim S Lederer WJ Matlib MA 《American journal of physiology. Heart and circulatory physiology》2002,283(4):H1398-H1408
The goal of the study was to determine whether defects in intracellular Ca(2+) signaling contribute to cardiomyopathy in streptozotocin (STZ)-induced diabetic rats. Depression in cardiac systolic and diastolic function was traced from live diabetic rats to isolated individual myocytes. The depression in contraction and relaxation in myocytes was found in parallel with depression in the rise and decline of intracellular free Ca(2+) concentration ([Ca(2+)](i)). The sarcoplasmic reticulum (SR) Ca(2+) store and rates of Ca(2+) release and resequestration into SR were depressed in diabetic rat myocytes. The rate of Ca(2+) efflux via sarcolemmal Na(+)/Ca(2+) exchanger was also depressed. However, there was no change in the voltage-dependent L-type Ca(2+) channel current that triggers Ca(2+) release from the SR. The depression in SR function was associated with decreased SR Ca(2+)-ATPase and ryanodine receptor proteins and increased total and nonphosphorylated phospholamban proteins. The depression of Na(+)/Ca(2+) exchanger activity was associated with a decrease in its protein level. Thus it is concluded that defects in intracellular Ca(2+) signaling caused by alteration of expression and function of the proteins that regulate [Ca(2+)](i) contribute to cardiomyopathy in STZ-induced diabetic rats. The increase in phospholamban, decrease in Na(+)/Ca(2+) exchanger, and unchanged L-type Ca(2+) channel activity in this model of diabetic cardiomyopathy are distinct from other types of cardiomyopathy. 相似文献
960.
Doctor RB Dahl R Fouassier L Kilic G Fitz JG 《American journal of physiology. Cell physiology》2002,282(5):C1042-C1052
The present studies of cholangiocytes used complementary histological, biochemical, and electrophysiological methods to identify a dense population of subapical vesicles, quantify the rates of vesicular trafficking, and assess the contribution of the actin cytoskeleton to membrane trafficking. FM 1-43 fluorescence measured significant basal rates of total exocytosis (1.33 +/- 0.16% plasma membrane/min) in isolated cholangiocytes and apical exocytosis in cholangiocyte monolayers. Cell surface area remained unchanged, indicating that there was a concurrent, equivalent rate of endocytosis. FM 1-43 washout studies showed that 36% of the endocytosed membrane was recycled to the plasma membrane. 8-(4-Chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP; cAMP analog) increased exocytosis by 71 +/- 31%, whereas the Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate (Rp-cAMPS; protein kinase A inhibitor) diminished basal exocytosis by 53 +/- 11%. A dense population of 140-nm subapical vesicles arose, in part, from apical membrane endocytosis. Phalloidin staining showed that a subpopulation of the endocytosed vesicles was encapsulated by F-actin. Furthermore, membrane trafficking was inhibited by disrupting the actin cytoskeleton with cytochalasin D (51 +/- 13% of control) or jasplakinolide (58 +/- 9% of control). These studies indicate that there is a high rate of vesicular trafficking at the apical membrane of cholangiocytes and suggest that both cAMP and the actin cytoskeleton contribute importantly to these events. 相似文献