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排序方式: 共有729条查询结果,搜索用时 15 毫秒
61.
Hugues Ouellet Shenheng Guan Jonathan B. Johnston Eric D. Chow Petrea M. Kells Alma L. Burlingame Jeffery S. Cox Larissa M. Podust Paul R. Ortiz De Montellano 《Molecular microbiology》2010,77(3):730-742
The infectivity and persistence of Mycobacterium tuberculosis requires the utilization of host cell cholesterol. We have examined the specific role of cytochrome P450 CYP125A1 in the cholesterol degradation pathway using genetic, biochemical and high‐resolution mass spectrometric approaches. The analysis of lipid profiles from cells grown on cholesterol revealed that CYP125A1 is required to incorporate the cholesterol side‐chain carbon atoms into cellular lipids, as evidenced by an increase in the mass of the methyl‐branched phthiocerol dimycocerosates. We observed that cholesterol‐exposed cells lacking CYP125A1 accumulate cholest‐4‐en‐3‐one, suggesting that this is a physiological substrate for this enzyme. Reconstitution of enzymatic activity with spinach ferredoxin and ferredoxin reductase revealed that recombinant CYP125A1 indeed binds both cholest‐4‐en‐3‐one and cholesterol, efficiently hydroxylates both of them at C‐27, and then further oxidizes 27‐hydroxycholest‐4‐en‐3‐one to cholest‐4‐en‐3‐one‐27‐oic acid. We determined the X‐ray structure of cholest‐4‐en‐3‐one‐bound CYP125A1 at a resolution of 1.58 Å. CYP125A1 is essential for growth of CDC1551 in media containing cholesterol or cholest‐4‐en‐3‐one. In its absence, the latter compound is toxic for both CDC1551 and H37Rv when added with glycerol as a second carbon source. CYP125A1 is a key enzyme in cholesterol metabolism and plays a crucial role in circumventing the deleterious effect of cholest‐4‐en‐3‐one. 相似文献
62.
Díaz-Lezama N Hernández-Elvira M Sandoval A Monroy A Felix R Monjaraz E 《Biochemical and biophysical research communications》2010,403(1):24-29
Ghrelin is a multifunctional peptide hormone with roles in growth hormone release, food intake and cell proliferation. With ghrelin now recognized as important in neoplastic processes, the aim of this report is to present findings from a series of in vitro studies evaluating the cellular mechanisms involved in ghrelin regulation of proliferation in the PC-3 human prostate carcinoma cells. The results showed that ghrelin significantly decreased proliferation and induced apoptosis. Consistent with a role in apoptosis, an increase in intracellular free Ca(2+) levels was observed in the ghrelin-treated cells, which was accompanied by up-regulated expression of T-type voltage-gated Ca(2+) channels. Interestingly, T-channel antagonists were able to prevent the effects of ghrelin on cell proliferation. These results suggest that ghrelin inhibits proliferation and may promote apoptosis by regulating T-type Ca(2+) channel expression. 相似文献
63.
Peña Messina E Tapia Varela R Velázquez Abunader JI Orbe Mendoza AA Velazco Arce JM 《Revista de biología tropical》2010,58(4):1577-1586
Tilapia production has increased in Aguamilpa Reservoir, in Nayarit, Mexico, in the last few years and represents a good economic activity for rural communities and the country. We determined growth parameters, mortality and reproductive aspects for 2413 specimens of blue tilapia Oreochromis aureus in this reservoir. Samples were taken monthly from July 2000 through June 2001, of which 1 371 were males and 1 042 were females. Standard length (SL) and total weight (TW) were measured in each organism. The SL/TW relationships through power models for sexes were determined. The growth parameters L infinity k, and t0 of the von Bertalanffy equation were estimated using frequency distribution of length through ELEFAN-I computer program. Finally the reproductive cycle and size of first maturity were established using morph chromatic maturity scale. The results suggested that the males and females had negative allometric growth (b < 3). Significant differences were found between SL/TW model for the sexes, suggesting separate models for males and females. Results indicate that there are no differences in growth rates between sexes; the proposed parameters were L infinity = 43.33 cm standard length, k = 0.36/year and t0 = -0.43 years. Natural and fishing mortality coefficients were 0.83/year and 1.10/year, respectively. The estimated exploitation rate (0.57/year) suggested that during the study period the fishery showed signs of overfishing. Blue tilapia reproduces year-round; the highest activity occurs from January through May and size of first maturity was 23 cm SL. We conclude that it is necessary to establish a minimum catch size in this reservoir based on the reproductive behavior of this species. 相似文献
64.
Rosalba Esquivel-Cote Rosa María Ramírez-Gama Guadalupe Tsuzuki-Reyes Alma Orozco-Segovia Pilar Huante 《Plant and Soil》2010,337(1-2):65-75
In this study we evaluated the ability of two wild strains of Azospirillum, A. lipoferum AZm5 and A. brasilense VS9, to produce ACC deaminase. We tested the effects of a deficiency and medium doses of nitrogenous fertilizers on the growth and physiology of tomato plants (Lycopersicon esculentum Mill cv. ACE VF55) inoculated with both Azospirillum strains independently. Tomato plants were evaluated by root elongation assay and grown in pot soil culture with different nitrogen levels (0 kg N ha–1 and 170 kg N ha–1). The root:shoot ratio (R:S) and some ecophysiological traits were determined after 42 days of plant growth. Results showed very different physiological characteristics in both strains. We found three relevant aspects related to the AZm5 strain: it produces high amounts of cytokinins, it contains the gene acdS, which encodes ACC deaminase, and it promotes plant growth. We conclude that AZm5 maybe useful to increase N uptake in N-deficient soil by production of cytokinins and the promotion of ACC deaminase activity, which favored leaf expansion and higher leaf N investment. Therefore, for tomato culture, a simultaneous biofertilization with AZm5 and a relatively low fertilization with N (170 kg N ha–1) to promote AZm5 activity could be advantageous. 相似文献
65.
66.
Simon MD Chu F Racki LR de la Cruz CC Burlingame AL Panning B Narlikar GJ Shokat KM 《Cell》2007,128(5):1003-1012
Histone lysine residues can be mono-, di-, or trimethylated. These posttranslational modifications regulate the affinity of effector proteins and may also impact chromatin structure independent of their role as adaptors. In order to study histone lysine methylation, particularly in the context of chromatin, we have developed a chemical approach to install analogs of methyl lysine into recombinant proteins. This approach allows for the rapid generation of large quantities of histones in which the site and degree of methylation can be specified. We demonstrate that these methyl-lysine analogs (MLAs) are functionally similar to their natural counterparts. These methylated histones were used to examine the influence of specific lysine methylation on the binding of effecter proteins and the rates of nucleosome remodeling. This simple method of introducing site-specific and degree-specific methylation into recombinant histones provides a powerful tool to investigate the biochemical mechanisms by which lysine methylation influences chromatin structure and function. 相似文献
67.
Martnez-Castillo Violeta Rodrguez-Troncoso Alma Paola de Jess Adolfo Tortolero-Langarica Jos Bautista-Guerrero Eric Padilla-Gamio Jacqueline Cupul-Magaa Amlcar Lev 《Hydrobiologia》2022,849(10):2395-2412
Hydrobiologia - Reef development occurs commonly under oligotrophic conditions that favor corals over competitors. In the Eastern Tropical Pacific (ETP), coral communities develop under highly... 相似文献
68.
69.
Pablo Emilio Vanegas-Espinoza Verónica Ramos-Viveros Antonio Ruperto Jiménez-Aparicio Oliver López-Villegas Francisco José Heredia-Mira Antonio Jesús Meléndez-Martínez Adrián Guillermo Quintero-Gutiérrez Octavio Paredes-López Alma Angélica Del Villar-Martínez 《In vitro cellular & developmental biology. Plant》2011,47(5):596-603
Marigold (Tagetes erecta) flowers are primarily used in industry for their high pigment content. Flower color development implies that chloroplast–chromoplast
transition is associated with carotenoid biosynthesis. We report the recovery of undifferentiated pigmented marigold cells,
various callus tissues, and their analysis by transmission electron microscopy in order to observe accumulating pigment and
development of subcellular structures. Callus was generated from leaf explants and after several rounds of recurrent selection.
Green-, yellow-, and brown-colored callus were obtained that showed distinct carotenoid profiles. For green material, violaxanthin,
lutein, zeaxanthin, and β-carotene were produced, while yellow callus generated mainly lutein, as did the brown callus. Chloroplast–chromoplast
transition was followed by measuring plastid size and shape in undifferentiated marigold cells by digital image analysis.
Cellular alterations were evident in brown callus. Chloroplasts were the main structure in green callus, while yellow callus
clearly showed the formation of plastoglobules, structures that are correlated with chloroplast–chromoplast transition. The
high number of plastoglobules observed in yellow callus is possibly directly related to pigment synthesis and accumulation. 相似文献