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41.
Changes in polyamine content during in vivo maturation and in vitro culture of maize (Zea mays L.) pollen were studied. The endogenous content of free, conjugated and bound polyamines was analyzed during 30 days of pollen evolution, in both developmental pathways (microsporogenesis and androgenesis). The induction of androgenesis from cold-pretreated uninucleate pollen results, in most of cases, in a lower total polyamine content than that of the in vivo uninucleate pollen. These differences indicate that polyamine metabolism is altered during the induction of androgenesis, and this could be a consequence of increased polyamine assimilation. In general, pollen stages that involve cell division (tetrades, pre-anthesis pollen and four-day cultured pollen) are characterized by a predominance of free Spd. The increase of Spd and Spm in 15-day cultured pollen, when the first embryoids are formed, outline the possible implication of these polyamines in embryogenetic processes. Furthermore, these findings may contribute to the improvement of maize androgenesis yield, especially in recalcitrant genotypes, by the exogenous application of polyamines or polyamine-inhibitors to the culture medium.Abbreviations PAs
polyamines
- Put
putrescine
- Spd
spermidine
- Spm
spermine
- S
free polyamine fraction
- SH
conjugated polyamine fraction
- PH
bound polyamine fraction 相似文献
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44.
Marcelo dos Santos Guerra 《Plant Systematics and Evolution》1989,168(1-2):83-86
Azima tetracantha has an asymmetrical karyotype with large chromosomes and a large amount of heterochromatin. The haploid number (n = 11) may represent the base number of the family. However, a possible secondary origin of this base number is also considered. 相似文献
45.
O Lider L M Santos C S Lee P J Higgins H L Weiner 《Journal of immunology (Baltimore, Md. : 1950)》1989,142(3):748-752
We have previously demonstrated that the oral administration of guinea pig myelin basic protein (MBP) protects Lewis rats against the induction of experimental autoimmune encephalomyelitis (EAE) when subsequently immunized with guinea pig MBP in CFA. In addition, animals made orally tolerant to MBP also have diminished proliferative and antibody responses to MBP, but not to other Ag. Nonetheless, the mechanism of oral tolerance to MBP in the EAE model remains undefined. In the present study, we report that T cells isolated from the spleen and mesenteric lymph nodes of MBP orally tolerized animals can adoptively transfer protection against EAE. Furthermore, these T cells are of the CD8+ subclass. In addition, CD8+ T cells from MBP orally tolerized animals also suppress in vitro proliferative responses and antibody responses to MBP in an Ag-specific fashion. These results demonstrate that active cellular mechanisms are initiated after oral administration of an autoantigen that can down-regulate an experimental autoimmune disease and provide the basis for the isolation and characterization of the cells mediating both in vivo and in vitro suppression. 相似文献
46.
A Alvarez U Hidalgo M E Kawada A Munizaga A Zú?iga L Ibánez C S Koenig M J Santos 《Analytical biochemistry》1992,206(1):147-154
This paper shows the successful isolation of peroxisomes from human liver samples that were kept frozen at -70 degrees C. Purification of these peroxisomes was obtained by a combination of two subcellular fractionation techniques: differential centrifugation and isopycnic fractionation in Nycodenz density gradients. Peroxisome integrity was evaluated by latency measurements and by ultrastructural observation. The procedure described here may be useful for the isolation of other subcellular organelles from frozen human samples. 相似文献
47.
Geographic differences in the allele frequencies of the human Y-linked tetranucleotide polymorphism DYS19 总被引:13,自引:0,他引:13
Fabrício R. Santos Tudevdagva Gerelsaikhan Bjamba Munkhtuja Tsendsuren Oyunsuren Jörg T. Epplen Sérgio D. J. Pena 《Human genetics》1996,97(3):309-313
We have studied the allele frequency distribution of the microsatellite locus DYS 19 in several populations with different geographical origins worldwide. Three new alleles were found. In addition, remarkable geographic and ethnic differences were observed in the allele frequency profiles and DNA marker (gene) diversity among populations and major ethnic groups. Amerindians showed an overwhelming predominance of the A allele, while in Caucasians the B allele was modal, and in Greater Asians and Africans allele C became predominant. Even within these geographic regions there were significant gradients, as exemplified by the decreasing frequency profile of the B allele from Great Britain over Germany to Slovakia. Thus, DYS 19 emerges as a useful tool for studying the structure and dynamics of human populations. 相似文献
48.
The magic-bead concept: an integrated approach to nitrogen removal with co-immobilized micro-organisms 总被引:6,自引:0,他引:6
V. A. P. M. dos Santos M. Bruijnse J. Tramper R. H. Wijffels 《Applied microbiology and biotechnology》1996,45(4):447-453
This paper describes both qualitative and quantitative aspects of simultaneous autotrophic nitrification and heterotrophic denitrification by, respectively, the nitrifierNitrisomonas europaea and either of the denitrifiersPseudomonas denitrificans orParacoccus denitrificans co-immobilized in double-layer gel beads. The system is based on the establishment of well-defined oxic and anoxic zones within the cell supports and on physical separation of the nitrifying and denitrifying populations. Nitrification and denitrification rates were obtained from measured bulk concentrations and head-space analysis. The latter analyses showed that ammonia was primarily converted into molecular nitrogen. Nitrous oxide was not detected. High nitrogen removal rates (up to 5.1 mmol N m–3 gel s–1) were achieved in continuous reactors under aerobic conditions. The overall rate of nitrogen removal was controlled by the nitrifying step. The approach followed is, in principle, also suitable to the coupling of other oxidative and reductive bioprocesses having complementary metabolic routes. Two-stage bioconversion processes can be thus conducted as if single-staged, which results in more compact reactor systems. 相似文献
49.
Transfer RNA structural change is a key element in the reassignment of the CUG codon in Candida albicans. 总被引:2,自引:1,他引:1 下载免费PDF全文
The human pathogenic yeast Candida albicans and a number of other Candida species translate the standard leucine CUG codon as serine. This is the latest addition to an increasing number of alterations to the standard genetic code which invalidate the theory that the code is frozen and universal. The unexpected finding that some organisms evolved alternative genetic codes raises two important questions: how have these alternative codes evolved and what evolutionary advantages could they create to allow for their selection? To address these questions in the context of serine CUG translation in C.albicans, we have searched for unique structural features in seryl-tRNA(CAG), which translates the leucine CUG codon as serine, and attempted to reconstruct the early stages of this genetic code switch in the closely related yeast species Saccharomyces cerevisiae. We show that a purine at position 33 (G33) in the C.albicans Ser-tRNA(CAG) anticodon loop, which replaces a conserved pyrimidine found in all other tRNAs, is a key structural element in the reassignment of the CUG codon from leucine to serine in that it decreases the decoding efficiency of the tRNA, thereby allowing cells to survive low level serine CUG translation. Expression of this tRNA in S.cerevisiae induces the stress response which allows cells to acquire thermotolerance. We argue that acquisition of thermotolerance may represent a positive selection for this genetic code change by allowing yeasts to adapt to sudden changes in environmental conditions and therefore colonize new ecological niches. 相似文献
50.