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881.
Paweł Wiśniewski Justyna Szklarczyk Marcin Maciaga Andrzej Paszkowski 《Acta Physiologiae Plantarum》2006,28(6):577-588
The occurrence of four l-alanine:2-oxoglutarate aminotransferase (AOAT) isoenzymes (AOAT-like proteins): alanine aminotransferase 1 and 2 (AlaAT1
and AlaAT2, EC 2.6.1.2) and l-glutamate:glyoxylate aminotransferase 1 and 2 (GGAT1 and GGAT2, EC 2.6.1.4) was demonstrated in Arabidopsis thaliana leaves. These enzymes differed in their substrate specificity, susceptibility to pyridoxal phosphate inhibitors and behaviour
during molecular sieving on Zorbax SE-250 column. A difference was observed in the electrostatic charge values at pH 9.1 between
GGAT1 and GGAT2 as well as between AlaAT1 and AlaAT2, despite high levels of amino acid sequence identity (93 % and 85 %,
respectively). The unprecedented evidence for the monomeric structure of both AlaAT1 and AlaAT2 is presented. The molecular
mass of each enzyme estimated by molecular sieving on Sephadex G-150 and Zorbax SE-250 columns and SDS/PAGE was approximately
60 kDa. The kinetic parameters: Km (Ala)=1.53 mM, Km (2-oxoglutarate)=0.18 mM, kcat=124.6 s−1, kcat/Km=8.1 × 104 M−1·s−1 of AlaAT1 were comparable to those determined for other AlaATs isolated from different sources. The two studied GGATs also
consisted of a single subunit with molecular mass of 47.3–70 kDa. The estimated Km values for l-glutamate (1.2 mM) and glyoxylate (0.42 mM) in the transamination catalyzed by putative GGAT1 contributed to indentification
of the enzyme. Based on these results we concluded that each of four AOAT genes in Arabidopsis thaliana leaves expresses different AOAT isoenzyme, functioning in a native state as a monomer. 相似文献
882.
Increase in d-tagatose Production Rate by Site-directed Mutagenesis of l-arabinose Isomerase from Geobacillus thermodenitrificans 总被引:2,自引:0,他引:2
Among single-site mutations of l-arabinose isomerase derived from Geobacillus thermodenitrificans, two mutants were produced having the lowest and highest activities of d-tagatose production. Site-directed mutagenesis at these sites showed that the aromatic ring at amino acid 164 and the size
of amino acid 475 were important for d-tagatose production. Among double-site mutations, one mutant converted d-galactose into d-tagatose with a yield of 58% whereas the wild type gave 46% d-tagatose conversion after 300 min at 65 °C.
Received 31 August 2005; Revisions requested 27 September 2005; Revisions received 8 November 2005; Accepted 8 November 2005 相似文献
883.
Carol M. Berman Consuel S. Ionica Meredith Dorner Jinhua Li 《International journal of primatology》2006,27(3):827-854
We describe basic patterns of postconflict affiliation between former opponents within a group of wild, provisioned Tibetan macaques Macaca thibetana on Mt. Huangshan, China. Like most primates studied to date, Tibetan macaques reconciled, i.e., overall they engaged in affiliative interaction with opponents at higher rates immediately after an aggressive conflict than at other times. Probabilities of affiliation were enhanced ≤30 s after the end of hostilities. However when we examined sex partner combinations separately, we found unequivocal evidence for reconciliation only for male-male dyads. Tolerant interaction among other partner combinations apparently was not disrupted after a conflict, presumably obviating the need to reconcile. One aspect of reconciliation among males was consistent with other indications of a despotic dominance style: aggressors initiated a higher proportion of affiliative interactions after a conflict than at other times. Another aspect of reconciliation was more typical of relaxed dominance styles: males used specialized behaviors (embraces and same-sex mounts) disproportionately to reconcile. We also found inconsistent evidence for the valuable relationship hypothesis; probabilities of reconciliation were enhanced for male-male dyads with the closest affiliative relationships, but not for those that displayed the most tolerance or mutual agonistic support. We discuss reconciliation and other aspects of conflict management among males in the context of a group with nearly even sex ratios and high male-male mating competition. 相似文献
884.
We earlier found that seleno-l-methionine (L-SeMet) as a food source of selenium (Se) is directly converted to methylselenol (CH3SeH), α-ketobutyrate, and ammonia by the mouse hepatic cystathionine γ-lyase. The purpose of this study was to clarify the
biological role of cystathionine γ-lyase in Se detoxification and cytosolic glutathione peroxidase (cGPx) biosynthesis because
another metabolic pathway to CH3SeH via seleno-l-cystathionine and seleno-l-cysteine (l-SeCyH) from l-SeMet has been shown by several enzymatic reactions. When mice were treated with either toxic doses of l-SeMet or a Se-deficient diet, the cystathionine γ-lyase activity for l-SeMet was invariable, suggesting that this enzyme was effective in both detoxification and biotransformation of Se. Concerning
Se biotransformation into cGPx, production of H2Se as the possible precursor was not observed by the in vitro reaction of the liver cytosol with CH3SeH. When l-SeMet was administered at the nutritional dose to mice fed a Se-deficient diet, levels of both cGPx mRNA and cGPx protein
were significantly restored. This recovery was not comparatively suppressed by coadministration of periodate-oxidized adenosine,
an inhibitor of S-adenosylhomo-cystenase, where the conversion of l-SeMet to l-SeCyH is inhibited. However, the recovery was strongly suppressed when propargylglycine, an inhibitor of cystathioine γ-lyase
that catalyzes the α,γ-elimination reaction of both l-SeMet and seleno-l-cystathionine, was treated. These results suggest that cystathionine γ-lyase is a notable enzyme, in SeMet metabolism and
that CH3SeH produced by the enzymatic reaction is utilized for cGPx biosynthesis. 相似文献
885.
Three Chl–protein complexes were isolated from thylakoid membranes of Bryopsis maxima and Ulva pertusa, marine green algae that inhabit the intertidal zone of the Pacific Ocean off the eastern coast of Japan by dodecyl-β-d-maltoside polyacrylamide gel electrophoresis. The slowest-moving fractions showed low Chl a/b and Chl/P-700 ratios, indicating that this fraction corresponds to complexes in PS I, which is large in both algae. The intermediate and fastest-moving fractions showed the traits of PS II complexes, with some associated Chl a/b–protein complexes and LHC II, respectively. The spectral properties of the separated Chl–proteins were also determined. The absorption spectra showed a shallow shoulder at 540 nm derived from siphonaxanthin in Bryopsis maxima, but not in Ulva pertusa. The 77 K emission spectra showed a single peak in Bryopsis maxima and two peaks in Ulva pertusa. Besides the excitation spectra indicated that the excitation energy transfer to the PS I complexes differed quite a lot higher plants. This suggested that the mechanisms of energy transfer in both of these algae differ from those of higher plants. Considering the light environment of this coastal area, the large size of the antennae of PS I complexes implies that the antennae are arranged so as to balance light absorption between the two photosystems. In addition, we discuss the relationships among the photosystem stoichiometry, the energy transfer, and the distribution between the two photosystems. 相似文献
886.
Cloning and Sequencing Analysis of Alginate Lyase Genes from the Marine Bacterium Vibrio sp. O2 总被引:1,自引:0,他引:1
Kawamoto H Horibe A Miki Y Kimura T Tanaka K Nakagawa T Kawamukai M Matsuda H 《Marine biotechnology (New York, N.Y.)》2006,8(5):481-490
We isolated a new marine bacteria, which displayed alginate-depolymerizing activity in plate assays, from seawater in Mihonoseki
Harbor, Japan. Analysis of the 16S ribosomal RNA gene sequence of one of the isolates proved that this alginate-depolymerizing
bacterium belonged to the genus Vibrio and it was named Vibrio sp. O2. The alginate lyase genes of Vibrio sp. O2 were cloned and expressed in Escherichia
coli. Two alginate lyase-producing clones, pVOA-A4 and pVOA-B5, were obtained. The alginate lyase gene alyVOA from pVOA-A4 was composed of an 858-bp open reading frame (ORF) encoding 285 amino acid residues, while alyVOB from pVOA-B5 was composed of an 828-bp ORF encoding 275 amino acid residues. The degree of identity between the deduced amino
acid sequences of AlyVOA or AlyVOB and Photobacterium sp. ATCC43367 alginate poly(ManA)lyase AlxM was 92.3% or 32.6%, respectively. Alginate lyase consensus regions corresponding
to the sequences YFKAGXYXQ and RXELR were observed in all three of these sequences. AlyVOA and AlyVOB both degraded polymannuronate
in plate assays and were therefore confirmed to be poly(β-D-mannuronate)lyases. 相似文献
887.
Recently, alpha-L-arabinofuranosidases (EC3.2.1.55) have received increased attention primarily due to their role in the degradation of lignocelluloses as well as their positive effect on the activity of other enzymes acting on lignocelluloses. As a result, these enzymes are used in many biotechnological applications including wine industry, clarification of fruit juices, digestion enhancement of animal feedstuffs and as a natural improver for bread. Moreover, these enzymes could be used to improve existing technologies and to develop new technologies. The production, mechanisms of action, classification, synergistic role, biochemical properties, substrate specificities, molecular biology and biotechnological applications of these enzymes have been reviewed in this article. 相似文献
888.
Enzymatic synthesis of l-ascorbyl linoleate in organic media 总被引:1,自引:0,他引:1
A novel l-ascorbyl fatty acid ester, l-ascorbyl linoleate was successfully prepared by enzymatic esterification and transesterification in a non-aqueous medium using immobilized lipase as biocatalyst. Changes in enzymatic activity and product yield were studied for the following variable: the nature of the fatty acid, the fatty acid concentration and water content. The yield of synthesis for the C18 unsaturated fatty acids were higher than for the C18 saturated fatty acid. Initial enzyme concentration does not affect the equilibrium of the reaction. And the product yield (33.5%) in the transesterification was higher than that of the esterification (21.8%) at a high-substrate concentration 0.3 M. The medium water content was found to have a distinct influence on the l-ascorbyl linoleate synthesis.These authors contributed equally to the article. 相似文献
889.
Navtej Kaur Pratap Kumar Pati Madhu Sharma P. S. Ahuja 《In vitro cellular & developmental biology. Plant》2006,42(2):124-127
Summary A protocol for the inducton of somatic embryogenesis from immature zygotic embryos of Rosa bourboniana, a scented rose species, was established. Somatic embryos were induced after 8wk of inoculation of zygotic embryos on MS
medium supplemented with different concentrations of 2,4-dichlorophenoxy acetic acid (5–15 μM). In addition to 2,4-dichlorophenoxy acetic acid concentrations, somatic embryogenesis was also influenced by the month of
collection of the explant and the stage of maturity of the hip. Maximum embryogenic response (16.6%) was observed using 2,4-dichlorophenoxy
acetic acid (15 μM), from green hips in the month of September. The use of l-proline (800 mg l−1) was found to be optimum for secondary embryogenesis. On periodic subculturing, the cultures formed somatic embryos sustainably
over a period of 18 mo. For somatic embryo germination, 6-benzylaminopurine (5 μM) was found to be most suitable. Rooted plants were transferred successfully to soil and appear morphologically normal under
greenhouse conditions. Transfer of plants for hardening was most suitable during the active growth period between June and
September.
IHBT Publication No: 0447 相似文献
890.
A strategy, termed alanine-scanning mutagenesis, was used to identify the amino acid residues which are critical to the antigenicity
of Escherichia coli
l-asparaginase (l-ASP). Three continuous alkaline residues, 195RKH197, were mutated to Ala selectively. Four mutant recombinant l-ASPs were constructed and expressed in E. coli, and then purified. The purified mutants showed a single band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis
and were more than 95% pure by reverse high-perfomance liquid chromatography. The activities of wild-type and m l-ASPs in the fermentative medium were all about 130 U/mL. The change from 195RKH 197 to 195AAA 197 reduced the antigenicity
ofhe enzyme greatly as shown in competition enzyme-linked immunosorbent assay using polyclonal antibodies raised against the
wild-type l-ASP from rabbits. The results show that residues 195RKH197 of E. coli
l-ASP are critical to its antigenicity.
These authors contributed equally to this work. 相似文献