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991.
Ernst Freese 《Molecular & general genetics : MGG》1957,88(3):388-406
Summary In crosses involving three allelic pab markers of the same cistron, the recombination frequencies between any two of the markers were such, that a consistent order of the three markers could be established. In these crosses two closely linked markers (0,9% distance, on each side) were also present. The segregation of the pab independent types showed, with respect to the outside markers, a frequent appearance of all four types of outside marker combinations, which in the crossing-over theory would belong to one crossover between the pab markers and 0, 1, or 2 crossovers in the adjacent regions. This deviation from ordinary crossingover expectations, called correlation effect, is confined to very small dimensions of the genome. In the present case to regions of about 0,05% map units.-Inspite of this effect, which sometimes nearly equals out the four types of outside marker combinations, the two recombinant types were, in all present crosses, significantly different, such that the pab markers could be ordered with respect to the outside markers. This ordering is in agreement with that established independently from recombination frequencies. Thus the frequencies of the different types of outside marker combinations are in agreement with the assumption, that the linear genes are built lengthwise into the chromosomal thread, and in disagreement with the assumption that genes or even larger chromosomal parts are sidechains of the chromosome.For this work a subdividing technique has been used by which it was relatively easy to obtain the double mutants between close markers. The same technique can also be applied for the partial selection of double mutants of allelic markers, provided that relatively close markers are available. In determining the linkage relationships it has been found, that me-3 seems to involve a fairly large deletion.
Mit 8 Textabbildungen
Diese Arbeit wurde unterstützt durch Stipendium und Sachbeihilfe der Deutschen Forschungsgemeinschaft und durch ein Stipendium des Damon Runyon Memorial Funds for Cancer Research. Die experimentelle Arbeit wurde ermöglicht durch die Gastfreundlichkeit von Herrn Prof. J. Straub und die großzügige Unterstützung von Herrn Dr. C. Bresch (Botanisches Institut Köln). 相似文献
Mit 8 Textabbildungen
Diese Arbeit wurde unterstützt durch Stipendium und Sachbeihilfe der Deutschen Forschungsgemeinschaft und durch ein Stipendium des Damon Runyon Memorial Funds for Cancer Research. Die experimentelle Arbeit wurde ermöglicht durch die Gastfreundlichkeit von Herrn Prof. J. Straub und die großzügige Unterstützung von Herrn Dr. C. Bresch (Botanisches Institut Köln). 相似文献
992.
993.
Ernst M Kaup B Müller M Bringer-Meyer S Sahm H 《Applied microbiology and biotechnology》2005,66(6):629-634
A whole-cell biotransformation system for the reduction of prochiral carbonyl compounds, such as methyl acetoacetate, to chiral hydroxy acid derivatives [methyl (R)-3-hydroxy butanoate] was developed in Escherichia coli by construction of a recombinant oxidation/reduction cycle. Alcohol dehydrogenase from Lactobacillus brevis catalyzes a highly regioselective and enantioselective reduction of several ketones or keto acid derivatives to chiral alcohols or hydroxy acid esters. The adh gene encoding for the alcohol dehydrogenase of L. brevis was expressed in E. coli. As expected, whole cells of the recombinant strain produced only low quantities of methyl (R)-3-hydroxy butanoate from the substrate methyl acetoacetate. Therefore, the fdh gene from Mycobacterium vaccae N10, encoding NAD+-dependent formate dehydrogenase, was functionally coexpressed. The resulting two-fold recombinant strain exhibited an in vitro catalytic alcohol dehydrogenase activity of 6.5 units mg–1 protein in reducing methyl acetoacetate to methyl (R)-3-hydroxy butanoate with NADPH as the cofactor and 0.7 units mg–1 protein with NADH. The in vitro formate dehydrogenase activity was 1.3 units mg–1 protein. Whole resting cells of this strain catalyzed the formation of 40 mM methyl (R)-3-hydroxy butanoate from methyl acetoacetate. The product yield was 100 mol% at a productivity of 200 mol g–1 (cell dry weight) min–1. In the presence of formate, the intracellular [NADH]/[NAD+] ratio of the cells increased seven-fold. Thus, the functional overexpression of alcohol dehydrogenase in the presence of formate dehydrogenase was sufficient to enable and sustain the desired reduction reaction via the relatively low specific activity of alcohol dehydrogenase with NADH, instead of NADPH, as a cofactor. 相似文献
994.
Consumption of herbal medicines is widespread and increasing. Harvesting from the wild, the main source of raw material, is causing loss of genetic diversity and habitat destruction. Domestic cultivation is a viable alternative and offers the opportunity to overcome the problems that are inherent in herbal extracts: misidentification, genetic and phenotypic variability, extract variability and instability, toxic components and contaminants. The use of controlled environments can overcome cultivation difficulties and could be a means to manipulate phenotypic variation in bioactive compounds and toxins. Conventional plant-breeding methods can improve both agronomic and medicinal traits, and molecular marker assisted selection will be used increasingly. There has been significant progress in the use of tissue culture and genetic transformation to alter pathways for the biosynthesis of target metabolites. Obstacles to bringing medicinal plants into successful commercial cultivation include the difficulty of predicting which extracts will remain marketable and the likely market preference for what is seen as naturally sourced extracts. 相似文献
995.
Nitrate and phosphate affect cultivability of cyanobacteria from environments with low nutrient levels 总被引:3,自引:0,他引:3
Ernst A Deicher M Herman PM Wollenzien UI 《Applied and environmental microbiology》2005,71(6):3379-3383
Nitrate and phosphate concentrations higher than those found in the natural environment slowed down growth of two strains of non-bloom-forming, phycoerythrin-rich Synechococcus spp. isolated from mesotrophic subalpine lakes. The results make clear why isolation of these picocyanobacteria in standard cultivation media was difficult. At low concentrations, closely related strains exhibited distinct growth characteristics with respect to these two nutrients, possibly explaining differences in their seasonal appearance in the natural environment. 相似文献
996.
997.
Wang J Iwasaki H Krivtsov A Febbo PG Thorner AR Ernst P Anastasiadou E Kutok JL Kogan SC Zinkel SS Fisher JK Hess JL Golub TR Armstrong SA Akashi K Korsmeyer SJ 《The EMBO journal》2005,24(2):368-381
Chromosomal translocations that fuse the mixed lineage leukemia (MLL) gene with multiple partners typify acute leukemias of infancy as well as therapy-related leukemias. We utilized a conditional knockin strategy to bypass the embryonic lethality caused by MLL-CBP expression and to assess the immediate effects of induced MLL-CBP expression on hematopoiesis. Within days of activating MLL-CBP, the fusion protein selectively expanded granulocyte/macrophage progenitors (GMP) and enhanced their self-renewal/proliferation. MLL-CBP altered the gene expression program of GMP, upregulating a subset of genes including Hox a9. Inhibition of Hox a9 expression by RNA interference demonstrated that MLL-CBP required Hox a9 for its enhanced cell expansion. Following exposure to sublethal gamma-irradiation or N-ethyl-N-nitrosourea (ENU), MLL-CBP mice developed myelomonocytic hyperplasia and progressed to fatal myeloproliferative disorders. These represented the spectrum of therapy-induced acute myelomonocytic leukemia/chronic myelomonocytic leukemia/myelodysplastic/myeloproliferative disorder similar to that seen in humans possessing the t(11;16). This model of MLL-CBP therapy-related myeloproliferative disease demonstrates the selectivity of this MLL fusion for GMP cells and its ability to initiate leukemogenesis in conjunction with cooperating mutations. 相似文献
998.
999.
The cDNA for human endo-alpha1,2-mannosidase was reconstructed using two independent EST-clones and its properties characterized. The 2837 bp cDNA construct contained a 1389 bp open reading frame (ORF) encoding for 462 amino acids and an approximately 53.6 kDa protein, respectively. Hydrophobicity analysis of this amino acid sequence, as well as proteolytic degradation studies, indicate that the enzyme is a type II protein, anchored in the membrane via a 19 amino-acid long apolar sequence close to the N-terminus. Human endo-alpha1,2-mannosidase displays a high degree of sequence identity with the catalytic domain of the homologous rat liver endo-enzyme, but differs substantially in the N-terminal peptide region, which includes the transmembrane domain. No sequence similarity exists with other processing alpha-glycosidases. Based on sequence information provided by the 2837 bp construct, the cDNA consisting of the complete 1389 bp ORF was amplified by RT-PCR using human fibroblast RNA. Incubation of E. coli lysates with this cDNA, previously modified for boost translation by codon optimization, resulted in the synthesis of an approximately 52 kDa protein which degraded [(14)C]Glc(3)-Man(9)-GlcNAc(2) efficiently, indicating that the catalytic domain of the enzyme folds correctly under cell-free conditions. Transfection of the endo-alpha1,2-mannosidase wild-type cDNA into COS 1 cells resulted in a moderate (approximately 1.5-fold) but reproducible increase of activity compared with control cells, whereas >18-fold increase in activity was measured after expression of a chimera containing green-fluorescent-protein (GFP) attached to the N-terminus of the endo-alpha1,2-mannosidase polypeptide. This, together with the observation that GFP-endo-alpha1,2-mannosidase is expressed as a Golgi-resident type II protein, points to enzyme-specific parameters directing folding and membrane anchoring, as well as Golgi-targeting, not being affected by fusion of GFP to the endo-alpha1,2-mannosidase N-terminus. 相似文献
1000.
The human gastrointestinal tract is colonized by an abundance of bacteria, which are in constant interaction with the epithelial lining usually leading to an intricate balance between tolerance and immunological response. There is ample evidence that the abundant presence of bacteria thus plays a role in the maintenance of human health, as well as in the induction of chronic inflammatory diseases of the gastrointestinal tract. Research in this field is, however, considerably hampered by the abundance of bacterial species, many of which have not even been characterized, and are difficult to culture specifically. These important limitations may to some extent be overcome by recent molecular biologic methods. Furthermore however, the adherent mucosal flora may differ largely from the luminal flora and that in excreta. These characteristics do not pertain to Helicobacter pylori, which generally colonizes the human stomach as a single strain with stable characteristics. Such colonization is stable throughout life, but can be treated. Furthermore, the association with chronic gastritis is very strong. For these reasons, H. pylori serves as an excellent model for the understanding of the processes involved in bacterial colonization and host response including mediation of immunoregulation, and the mechanisms by which this response can lead to disease. 相似文献