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941.
Ultraviolet Mutagenesis and Its Repair in an ESCHERICHIA COLI Strain Containing a Nonsense Codon 总被引:2,自引:1,他引:1 下载免费PDF全文
Stanley Person John Allen McCloskey Wallace Snipes Richard C. Bockrath 《Genetics》1974,78(4):1035-1049
Ultraviolet mutagenesis and its repair were studied mainly in WU36-10-89, a uvr(-) strain of Escherichia coli containing a UAG mutation in a gene for leucine biosynthesis. Following ultraviolet (UV) irradiation revertants appearing with or without direct photoreactivation (PR) were classified according to the presence and type of suppressor they contained. We find UV mutation production to be quite specific. An analysis of revertants produced by UV indicates they are formed mainly from GC --> AT and that the miscoding is due to a cytosine residue at the site of mutation in a cytosine-thymine (CT) dimer. We propose that the dimer serves as template during some aspects of repair replication and at the time of replication the C in the dimer directs the insertion of A in the complementary strand. We also note that C --> A and T -->G changes caused by a CT dimer occur much less frequently. 相似文献
942.
Dr. John E. Mayfield 《Archives of microbiology》1974,95(1):115-124
Summary A system, utilizing thedwarf andpuff morphological mutants ofSchizophyllum commune, was devised to select specific hyphal segments that were in different stages of septal dissolution and nuclear migration.
These stages were observed with the electron microscope. Direct evidence of the dissolution of complex septal during nuclear
migration was obtained. Initially there was a disruption of the septal swelling, followed by erosion of the remaining cross
wall. Complex septa were therepy converted to simple septa through which nuclei migrated. These septa were covered with secondary
cell wall material. Following nuclear migration only vacuolate hyphae with remnant membrane structures remained. Occasionally,
intact hyphae were observed within these vacuolate hyphae. 相似文献
943.
Kinetics of the activation of rat liver pyruvate kinase by fructose 1,6-disphosphate and methods for characterizing hysteretic transitions 下载免费PDF全文
H. Olin Spivey Wayne Flory Benigno D. Peczon John P. Chandler Roger E. Koeppe 《The Biochemical journal》1974,141(1):119-125
1. Kinetics of fructose 1,6-diphosphate activation of liver pyruvate kinase type I inhibited with MgATP and l-alanine are described as a function of enzyme and fructose 1,6-diphosphate concentrations. These results can be explained by a single pseudo-first-order transition of the enzyme into an active form, independent of the enzyme concentration. This rate constant, k(app.)=0.24s(-1) with 0.02mm-fructose 1,6-diphosphate (t(0.9) approximately 10s where t(0.9) is the time for 90% conversion), is an increasing function of fructose 1,6-diphosphate concentration far beyond that needed to maximally activate enzyme equilibrated with fructose 1,6-diphosphate (about 20mum). 2. The model equations are best analysed with numerical techniques which are described. These techniques are useful in studying similar slow transients frequently observed in stopped-flow studies of enzymes. 3. Shorter transients (t(0.9)=0.5-1.5s) were observed in the kinetic response of the enzyme to the addition of MgATP or phosphoenolpyruvate, but were not further characterized. 相似文献
944.
Interactions of an intact proteoglycan and its fragments with basic homopolypeptides in dilute aqueous solution 下载免费PDF全文
The interactions between a proteoglycan and cationic polypeptides have been investigated by the use of circular-dichroism spectroscopy. The interaction produces an induced conformational change for poly(l-arginine) and poly(l-lysine), similar to the effects previously reported for mucopolysaccharide-polypeptide mixtures. For bovine nasal septum proteoglycan, the interactions are similar to those for chondroitin 4-sulphate, which comprises approximately 63% of the total polysaccharide. The results also suggest that the interactions produce a conformational change in the protein core. Similar studies for the Smith-degradation product show that the protein core can adopt a substantial alpha-helical content and is capable of interactions with poly-(l-arginine). The interactions for chondroitin sulphate ;doublets' are significantly different from those for the separated chains, indicating that the arrangement of the polysaccharide side chains in pairs (and larger groups) along the protein backbone contributes to the interaction properties of the intact proteoglycan. 相似文献
945.
Andrew G. Smith John D. Gilbert W. Arthur Harland Charles J. W. Brooks 《The Biochemical journal》1974,139(3):793-795
Cholest-5-ene-3beta,26-diol, isolated from human brain, was further characterized by oxidation to 3-oxocholest-4-en-26-ol and to 3-oxocholest-4-en-26-oic acid. Identification was achieved by comparison (by t.l.c., g.l.c. and g.l.c.-mass spectrometry) with corresponding reference compounds derived from kryptogenin. 相似文献
946.
The hydrolysis of bradykinin and its higher homologues by angiotensin-converting enzyme has been investigated by using an automated ninhydrin technique. The results show an inverse relationship of hydrolysis rate with size and charge of the peptide, which parallels the inactivation in the pulmonary circulation and offers an explanation for the selectivity of metabolism of these kinins by the lungs. 相似文献
947.
Steady-state kinetics of catecholamine transport by chromaffin-granule `ghosts'' 总被引:9,自引:7,他引:2 下载免费PDF全文
John H. Phillips 《The Biochemical journal》1974,144(2):319-325
Resealed chromaffin-granule ;ghosts' were used to study the steady-state kinetics of catecholamine transport. The pump has a high affinity for (-)-noradrenaline, (-)-adrenaline, tyramine and 5-hydroxytryptamine (serotonin), but a lower affinity for (+)-noradrenaline. The measured rates of incorporation do not conform to Michaelis-Menten kinetics, but affinity constants for the former substrates are in the range 8-18mum. Reserpine is a potent inhibitor. Incorporation as a function of ATP concentration also fails to show simple kinetics; the affinity constant for ATP is deduced to be about 3mm at 1mm-MgCl(2). Adenylyl (betagamma-methylene)diphosphonate is a competitive inhibitor at low concentrations, but inhibits more strongly at high concentrations. The pump has a transition temperature at 29 degrees C and does not seem to be identical with the Mg(2+)-stimulated adenosine triphosphatase of chromaffin granules. 相似文献
948.
949.
950.
The transport of uridine, hypoxanthine, and choline in cultures of Novikoff rat hepatoma cells is competitively inhibited by colcemid with apparent Ki values of 135, 60, and 250 μM respectively, whereas the transport of 2-deoxy-D-glucose is not affected. Ethanol at high concentrations inhibits the transport of all four substrates in an apparent competitive manner. 相似文献