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71.
Manuel Rico Jorge Santoro Carlos González Marta Bruix José Luis Neira José Luis Nieto José Herranz 《Journal of biomolecular NMR》1991,1(3):283-298
Summary A method is proposed to generate initial structures in cases where the distance geometry method may fail, such as when the set of1H NMR NOE-based distance constraints is small in relation to the size of the protein. The method introduces an initial correlation between the and backbone angles (based on empirical observations) which is relaxed in later stages of the calculation. The obtained initial structures are refined by well-established methods of energy minimization and restrained molecular dynamics. The method is applied to determine the solution structure of Ribonuclease A (124 residues) from a NOE basis consisting of 467 NOE cross-correlations (97 intra-residue, 206 sequential, 23 medium-range and 141 long-range) obtained at 360 MHz. The global shape and backbone overall fold of the eight final refined structures are close to those shown by the crystal structure. A meaningful difference in the positioning of the catalytically important His119 side chain in the solution and crystal structures has been detected. 相似文献
72.
Intrinsic protein phosphorylation was studied in synaptosomal membrane fragments made from cerebral cortex tissue taken from the following species: human (biopsy specimens), ox, rat, rabbit, guinea pig and mouse. Membrane fragments from all species exhibited a qualitatively similar range of protein acceptors phosphorylated by cyclic AMP-dependent protein kinase activity; contrary to a previous report, no evidence for cyclic GMP-dependent protein kinase activity was found in the human material. With the exception of membrane fragments prepared from ox brain, all the preparations exhibited the same range of Ca2+-dependent protein kinase activity. Ox brain obtained from a slaughterhouse yielded membranes containing no Ca2+-dependent protein kinase activity, but this may have been due to unavoidable postmortem losses. 相似文献
73.
Angela M. Otto Marie-Odile Ulrich Luis Jimenez de Asua 《Journal of cellular physiology》1981,108(2):145-153
Epidermal growth factor (EGF) stimulates the initiation of DNA synthesis in Swiss 3T3 cells after a constant prereplicative period of 14–15 hours. The final rate of initiation follows apparent first-order kinetics and can thus be quantified by a rate constant k. The value of k can be changed by later additions during the prereplicative period: When cells stimulated by a very low concentration of EGF, alone or with insulin, which results in a relatively low value of k, receive a saturating amount of EGF at 15 hours, then k is markedly increased after 4–6 hours. Insulin alone (up to 200 ng/ml) is unable to set the lag phase, but does have a synergistic effect on the value of k given by EGF. When added at 15 hours, insulin also increases k, but after a delay of 4–6 hours. In contrast, both hydrocortisone and prostaglandin E1 (PGE1) inhibit the stimulation of DNA synthesis by EGF only during the first 8 hours of the prereplicative period of decreasing the value of k. Prostaglandin F2α (PGF2α), which stimulates DNA synthesis in a similar mode as EGF, when added with EGF has a synergistic effect on DNA synthesis. This suggests that EGF and PGF2α, nevertheless, act through different regulatory events. 相似文献
74.
Minnie K. O''Farrell Dorothie Clingan Philip S. Rudland Luis Jimenez De Asua 《Experimental cell research》1979,118(2):311-321
The ability of prostaglandin F2α (PGF2α) and other prostaglandins to stimulate the initiation of DNA synthesis in quiescent cultures of various mouse fibroblastic cell types has been investigated. PGF2α was found to be more effective than the other prostaglandins. Most cell types, with the exception of BALB/c 3T3, responded to PGF2α. Addition of PGF2α in combination with insulin resulted in a synergistic increase in the proportion of cells synthesizing DNA. The effect of nutrients on the stimulation of the initiation of DNA synthesis has been examined in detail; it was found that Swiss 3T3 cells showed a requirement for hypoxanthine and vitamin B12 whereas Swiss 3T6 cells demonstrated a stringent requirement for vitamin B12 only. The effect of prostaglandin precursors, synthetic analogues of the prostaglandin endoperoxides and inhibitors of prostaglandin synthesis was also examined in two cell types. The effect of PGF2α was compared with that of two polypeptide growth factors, epidermal growth factor (EGF) and fibroblast growth factor (FGF) in Swiss 3T6 cells grown in 0.0025% (v/v) serum. In combination with insulin each of these three growth factors stimulated the initiation of DNA synthesis in approximately the same number of cells. 相似文献
75.
JoséLuis Avila Antonio Bretaña María Argelia Casanova Angela Avila Francisco Rodríguez 《Experimental parasitology》1979,48(1):27-35
A liquid medium was developed for the continuous cultivation of Trypanosoma cruzi. Among the several highly purified macromolecules tested only bovine liver catalase, horseradish peroxidase, lactoperoxidase, and bovine hemoglobin supported the continuous growth, at high yield, of mice-virulent Trypanosoma cruzi; other hemoproteins were inactive. Bovine liver catalase showed optimal Trypanosoma cruzi growth-promoting activity, parasites reaching 20 × 106 parasites/ml (95% epimastigotes) at about 10 days in most of the 45 subpassages to date. Furthermore, this protein in the incubation medium provided all the amino acid requirements of actively growing parasites, thus eliminating the need for exogeneous free amino acids. Additional experiments revealed that the hemoprotein's growth-promoting activity was independent of any enzymatic activity and that reconstituting the exact protein composition by means of exogeneous amino acids did not support parasite multiplication, suggesting the importance of the primary structure of the active proteins for growth-promoting activity. These active macromolecules supported the multiplication of five different strains of Trypanosoma cruzi, but did not support Leishmania brasiliensis or Leishmania mexicana proliferation, suggesting species specificity. 相似文献
76.
Rat liver ribosome treatment with ethanol and 1 M NH4Cl releases some 31–33 ribosomal proteins. This split protein fraction binds Phe-tRNA, Ac-Phe-tRNA, Met-tRNAM and f-Met-tRNAF in the absence of K+ and Mg++ ions. When the split protein fraction is passed through Sephadex G-100 only six proteins are retained in the column: S10, S14, S15, S19, L35, and L36. The aminoacyl-tRNA binding activity of this protein fraction retained in the Sephadex G-100 column is similar to that of the total split protein fraction, suggesting that the above six proteins, or only some of them, are involved in the binding reaction. 相似文献
77.
Murine egasyn, a protein which stabilizes the binding of β-glucuronidase to microsomal membranes, was induced 1.9 fold in liver by phenobarbital treatment. Accompanying this increase was an alteration of the subcellular distribution of liver β-glucuronidase, although total glucuronidase activity remained constant. In control mice 32.6 ± 4.6% of the activity was microsomal, while after four days of phenobarbital treatment 50.5 ± 3.1% was microsomal. Thus, the availability of egasyn appears to be an important factor in determining the proportion of glucuronidase distributed to either microsomes or lysosomes. 相似文献
78.
Circular dichroism studies on synthetic peptides related to the C-terminal region of yeast iso-1-cytochrome c were carried out and compared with conformational studies on horse cytochrome c fragments. Evidence is presented for a weaker predisposition for ordered structure in the former peptides when compared with the corresponding region in horse cytochrome c. These findings agree with theoretical predictions and with observations that yeast and other mammalian type cytochromes c differ in several minor respects. 相似文献
79.
80.
María T. Domínguez Cristina Aponte Ignacio M. Pérez-Ramos Luis V. García Rafael Villar Teodoro Marañón 《Plant and Soil》2012,357(1-2):407-424