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11.
Kurt S. Pregitzer 《The New phytologist》2002,154(2):267-270
12.
13.
Liver alcohol dehydrogenase 总被引:3,自引:0,他引:3
G Pettersson 《CRC critical reviews in biochemistry》1987,21(4):349-389
The article deals with the structure and function of liver alcohol dehydrogenase and reviews mainly literature published after 1979, i.e., summarizes progress made in the field since Klinman presented her review on alcohol dehydrogenases. The emphasis will be on high-resolution crystallographic data, results obtained with metal-substituted enzyme derivatives, and on the mechanism and pH dependence of the catalytic reaction. 相似文献
14.
Promoters and processing sites within the transforming region of bovine papillomavirus type 1. 总被引:15,自引:9,他引:6
The mRNAs present in bovine papillomavirus type 1 (BPV-1)-transformed C127 cells were studied by primer extension. The results show that two internal promoters are present in the E region of BPV-1 in addition to the previously identified promoter at coordinate 1 (H. Ahola, A. Stenlund, J. Moreno-López, and U. Pettersson, Nucleic Acids Res. 11:2639-2650, 1983). One, located at coordinate 31, generated a set of mRNAs with heterogeneous 5' ends, which may encode the major transforming protein of BPV-1, the E5 protein. The second promoter, which is located at coordinate 39, generates colinear mRNAs which encode either the E4 protein or a truncated form of the E2 protein. Unlike the cottontail rabbit papillomavirus (O. Danos, E. Georges, G. Orth, and M. Yaniv, J. Virol. 53:735-741, 1985), BPV-1 appears to lack a separate promoter for expression of the E7 protein. The major splice sites in the transforming region (E region) of the BPV-1 genome were also identified by nucleotide sequence analysis. 相似文献
15.
1. A simple model based on rapid-equilibrium assumptions is derived which relates the steady-state activity of the Calvin cycle for photosynthetic carbohydrate formation in C3 plants to the kinetic properties of a single cycle enzyme (fructose bisphosphatase) and of the phosphate translocator which accounts for the export of photosynthate from the chloroplast. Depending on the kinetic interplay of these two catalysts, the model system may exhibit a single or two distinct modes of steady-state operation, or may be unable to reach a steady state. 2. The predictions of the model are analysed with regard to the effect of external orthophosphate on the steady-state rate of photosynthesis in isolated chloroplasts under conditions of saturating light and CO2. Due to the possible existence of two distinct steady states, the model may account for the stimulatory as well as the inhibitory effects of external phosphate observed in experiments with intact chloroplasts. Stability arguments indicate, however, that only the steady-state case corresponding to phosphate inhibition of the rate of photosynthesis could be of physiological interest. 3. It is concluded that chloroplasts under physiological conditions most likely operate in a high-velocity steady state characterized by a negative Calvin cycle flux control coefficient for the phosphate translocator. This means that any factor enhancing the export capacity of the phosphate translocator can be anticipated to decrease the actual steady-state rate of photosynthate export due to a decreased steady-state rate of cyclic photosynthate production. 相似文献
16.
A Phorbol Ester-Sensitive Kinase Catalyzes the Phosphorylation of P0 Glycoprotein in Myelin 总被引:5,自引:4,他引:1
The proposed structural protein of peripheral nerve myelin, P0, has been shown to have several covalent modifications. In addition to being glycosylated, sulfated, and acylated, P0 is phosphorylated, with the intracellular site of this latter addition being in question. By employing nerve injury models that exhibit different levels of P0 biosynthesis in the absence and presence of myelin assembly, we have examined the cellular location of P0 phosphorylation. It is demonstrated that there is comparable P0 phosphorylation in both normal and crush-injured adult rat sciatic nerves, although the level of biosynthesis of P0 differs between these myelin maintaining and actively myelinating nerve models, respectively. The glycoprotein does not appear to be phosphorylated readily in the transected adult sciatic nerve, a preparation in which P0 biosynthesis is observed but that lacks myelin membrane. These observations suggest that the modification is not associated with the biosynthesis or maturation of P0 in the endoplasmic reticulum or Golgi, but that it instead occurs after myelin assembly. That P0 phosphorylation occurs in the normal nerve even when translation is inhibited by cycloheximide treatment lends further support to this conclusion. P0 is shown to be phosphorylated on one or more serine residues, with all or most of the phosphate group(s) being labile as evidenced by pulse-chase analysis. Addition of a biologically active phorbol ester, 12-O-tetradecanoylphorbol-13-acetate or 4 beta-phorbol 12,13-dibutyrate, substantially increases the extent of [32P]orthophosphate incorporation into the glycoprotein of normal and crushed nerve but not transected nerve. Biologically inactive 4 alpha-phorbol 12,13-didecanoate has no effect on P0 phosphorylation. Similarly, the addition of the cyclic AMP analog 8-bromo-cyclic AMP causes no appreciable changes in P0 labeling. These findings indicate that the phorbol ester-sensitive enzyme, protein kinase C, may be responsible for the phosphorylation of P0 within the myelin membrane. 相似文献
17.
A mutant rat major histocompatibility haplotype showing a large deletion of class I sequences 总被引:2,自引:2,他引:0
The LEW.1LM1 inbred rat strain, which has been derived from a (LEW×LEW.1W) F2 hybrid, carries a major histocompatibility (RT1) haplotype which is distinct from that of the LEW strain (RT1
1) in that certainRT1.C region-determined class I antigens are not expressed. Here we show that this phenotypic defect is due to genomic deletion
of about 100 kb of theRT1.C region. Certain deleted DNA fragments have been cloned from the wild-type DNA into the EMBL4 vector. Five clones have been
characterized and are shown to possess different restriction maps and to each carry a single stretch of class I cross-hybridizing
sequences. Probes derived from the non-class I coding part of two clones detect fragments which are present in the wild-type
but absent from thelm1 mutant. The type of deletion described here in the rat is discussed in the context ofH-2D/Q deletions in the mouse. 相似文献
18.
19.
G Pettersson 《European journal of biochemistry》1989,184(3):561-566
1. The likely effect of a selective pressure in the direction of higher reaction fluxes on rate parameters for enzyme reactions confirming to Michaelis-Menten kinetics has been analyzed on the basis of relationships which take into account the changes in metabolite concentrations that must be associated with mutational changes of the kinetic properties of enzymes participating in metabolic pathways. 2. Arguments are presented to show that such a pressure should tend to increase kcat, whereas Km may decrease or increase depending on what stage of evolutionary development the enzyme has reached. While the early evolution of enzymes must have been associated with decreasing Km values, an increase of both kcat and Km is mandatory for enhancement of the rate performance of extensively developed enzymes which exhibit kcat/Km ratios approaching the diffusion-control limit. The latter limit is dependent on the equilibrium constant for the catalysed reaction. 3. Enzymes which have reached the diffusion-control limit for their second-order rate performance cannot be considered as perfectly evolved catalysts, but may well undergo further development towards a higher catalytic efficiency in response to the improvement of other enzymes in the metabolic pathway with regard to the criterion of an enhanced reaction flux. Such evolution is associated with an increase of the metabolite levels in the pathway, and a simple model system is examined in order to illustrate the ultimate limits for the metabolite levels and reaction flux that may obtain. 4. The theoretical evidence presented lends no support to previous proposals that certain enzymes (e.g. triosephosphate isomerase), or enzymes showing certain kinetic characteristics (e.g. kcat/Km quotients approaching 10(9) s-1 M-1), have reached the end of their evolutionary development. A claim that any specific enzyme has reached catalytic perfection would provide the unreasonable inference that all enzymes participating in intermediary metabolism have reached catalytic perfection. 相似文献
20.
Metabolites controlling the rate of starch synthesis in the chloroplast of C3 plants 总被引:2,自引:0,他引:2
The extent to which different stromal metabolites affecting ADPglucose pyrophosphorylase control the rate of photosynthetic starch production in the chloroplast of C3 plants has been examined by kinetic model studies. The results indicate that ATP, glucose 1-phosphate, 3-phosphoglycerate, fructose 6-phosphate, and orthophosphate may provide significant contributions to the starch synthesis rate changes induced by variation of the external concentration of orthophosphate, the detailed control situation being dependent on the actual concentration of the external metabolite. 相似文献