全文获取类型
收费全文 | 434篇 |
免费 | 47篇 |
出版年
2022年 | 3篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 13篇 |
2014年 | 15篇 |
2013年 | 24篇 |
2012年 | 31篇 |
2011年 | 24篇 |
2010年 | 12篇 |
2009年 | 15篇 |
2008年 | 26篇 |
2007年 | 24篇 |
2006年 | 17篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 17篇 |
2000年 | 13篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1971年 | 2篇 |
1970年 | 4篇 |
1967年 | 2篇 |
1932年 | 4篇 |
1931年 | 2篇 |
排序方式: 共有481条查询结果,搜索用时 15 毫秒
51.
Additivity in the circadian phototransduction system of the mouse has not been tested directly. Because of this, accurate prediction of circadian phase shifts elicited by polychromatic light stimuli cannot be derived from the results of studies using monochromatic light stimuli. This limitation also makes it impossible to deduce the relative contributions of the photoreceptive mechanisms (rods, cones and melanopsin-containing retinal ganglion cells) underlying circadian phototransduction in the mouse. Using nearly monochromatic light stimuli of different spectral composition, and combinations thereof, we demonstrated that murine circadian phototransduction exhibits additivity. Based on the locomotor activity phase shifts elicited by these stimuli, we developed the first quantitative assessment of the relative contributions of conventional and novel photoreceptive mechanisms for circadian functioning in the mouse. 相似文献
52.
53.
Orsomando G de la Garza RD Green BJ Peng M Rea PA Ryan TJ Gregory JF Hanson AD 《The Journal of biological chemistry》2005,280(32):28877-28884
gamma-Glutamyl hydrolase (GGH, EC 3.4.19.9) catalyzes removal of the polyglutamyl tail from folyl and p-aminobenzoyl polyglutamates. Plants typically have one or a few GGH genes; Arabidopsis has three, tandemly arranged on chromosome 1, which encode proteins with predicted secretory pathway signal peptides. Two representative Arabidopsis GGH proteins, AtGGH1 and AtGGH2 (the At1g78660 and At1g78680 gene products, respectively) were expressed in truncated form in Escherichia coli and purified. Both enzymes were active as dimers, had low K(m) values (0.5-2 microm) for folyl and p-aminobenzoyl pentaglutamates, and acted as endopeptidases. However, despite 80% sequence identity, they differed in that AtGGH1 cleaved pentaglutamates, mainly to di- and triglutamates, whereas AtGGH2 yielded mainly monoglutamates. Analysis of subcellular fractions of pea leaves and red beet roots established that GGH activity is confined to the vacuole and that this activity, if not so sequestered, would deglutamylate all cellular folylpolyglutamates within minutes. Purified pea leaf vacuoles contained an average of 20% of the total cellular folate compared with approximately 50 and approximately 10%, respectively, in mitochondria and chloroplasts. The main vacuolar folate was 5-methyltetrahydrofolate, of which 51% was polyglutamylated. In contrast, the principal mitochondrial and chloroplastic forms were 5-formyl- and 5,10-methenyltetrahydrofolate polyglutamates, respectively. In beet roots, 16-60% of the folate was vacuolar and was again mainly 5-methyltetrahydrofolate, of which 76% was polyglutamylated. These data point to a hitherto unsuspected role for vacuoles in folate storage. Furthermore, the paradoxical co-occurrence of GGH and folylpolyglutamates in vacuoles implies that the polyglutamates are somehow protected from GGH attack. 相似文献
54.
55.
Lizabeth Bowen Brian Aldridge Kimberlee Beckmen Tom Gelatt Lorrie Rea Kathy Burek Ken Pitcher Jeffrey L. Stott 《EcoHealth》2006,3(2):109-113
Characterization of the polygenic and polymorphic features of the Steller sea lion major histocompatibility complex (MHC) provides an ideal window for evaluating immunologic vigor of the population and identifying emergence of new genotypes that reflect ecosystem pressures. MHC genotyping can be used to measure the potential immunologic vigor of a population. However, since ecosystem-induced changes to MHC genotype can be slow to emerge, measurement of differential expression of these genes can potentially provide real-time evidence of immunologic perturbations. MHC DRB genes were cloned and sequenced using peripheral blood mononuclear leukocytes derived from 10 Steller sea lions from Southeast Alaska, Prince William Sound, and the Aleutian Islands. Nine unique DRB gene sequences were represented in each of 10 animals. MHC DRB gene expression was measured in a subset of six sea lions. Although DRB in genomic DNA was identical in all individuals, relative levels of expressed DRB mRNA was highly variable. Selective suppression of MHC DRB genes could be indicative of geographically disparate environmental pressures, thereby serving as an immediate and sensitive indicator of population and ecosystem health. 相似文献
56.
Richmond JP Burns JM Rea LD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(6):535-545
Two key factors influence the diving and hence foraging ability of marine mammals: increased oxygen stores prolong aerobic metabolism and decreased metabolism slows rate of fuel consumption. In young animals, foraging ability may be physiologically limited due to low total body oxygen stores and high mass specific metabolic rates. To examine the development of dive physiology in Steller sea lions, total body oxygen stores were measured in animals from 1 to 29 months of age and used to estimate aerobic dive limit (ADL). Blood oxygen stores were determined by measuring hematocrit, hemoglobin, and plasma volume, while muscle oxygen stores were determined by measuring myoglobin concentration and total muscle mass. Around 2 years of age, juveniles attained mass specific total body oxygen stores that were similar to those of adult females; however, their estimated ADL remained less than that of adults, most likely due to their smaller size and higher mass specific metabolic rates. These findings indicate that juvenile Steller sea lion oxygen stores remain immature for more than a year, and therefore may constrain dive behavior during the transition to nutritional independence. 相似文献
57.
Six phenological series were available for ‘Golden Delicious’ apple blooming at six sites in Trentino, an alpine fruit-growing region. Several models were tested to predict flowering dates, all involving a “chilling and forcing” approach. In many cases, application of the models to different climatic conditions results in low accuracy of prediction of flowering date. The aim of this work is to develop a model with more general validity, starting from the six available series, and to test it against five other phenological series outside the original area of model development. A modified version of the “Utah” model was the approach that performed best. In fact, an algorithm using “chill units” for rest completion and a thermal sum for growing-degree-hours (GDH), whose efficiency changes over time depending on the fraction of forcing attained, yielded a very good prediction of flowering. Results were good even if hourly temperatures were reconstructed from daily minimum and maximum values. Errors resulting from prediction of flowering data were relatively small, and root mean square errors were in the range of 1–6 days, being <2 days for the longest phenological series. In the most general form of the model, the summation of GDH required for flowering is not a fixed value, but a function of topoclimatic variables for a particular site: slope, aspect and spring mean temperature. This approach allows extension of application of the model to sites with different climatic features outside the test area. 相似文献
58.
Mukherjee A Bilton PR Mackay L Janoschka A Zhu H Rea D Langridge-Smith PR Campopiano DJ Teschner T Trautwein AX Schünemann V Sadler PJ 《Journal of biological inorganic chemistry》2012,17(4):573-588
Isothermal calorimetric studies of the binding of iron(III) citrate to ferric ion binding protein from Neisseria gonorrhoeae suggested the complexation of a tetranuclear iron(III) cluster as a single step binding event (apparent binding constant K(app) (ITC) = 6.0(5) × 10(5) M(-1)). High-resolution Fourier transform ion cyclotron resonance mass spectrometric data supported the binding of a tetranuclear oxo(hydroxo) iron(III) cluster of formula [Fe(4)O(2)(OH)(4)(H(2)O)(cit)](+) in the interdomain binding cleft of FbpA. The mutant H9Y-nFbpA showed a twofold increase in the apparent binding constant [K(app) (ITC) = 1.1(7) × 10(6) M(-1)] for the tetranuclear iron(III) cluster compared to the wild-type protein. M?ssbauer spectra of Escherichia coli cells overexpressing FbpA and cultured in the presence of added (57)Fe citrate were indicative of the presence of dinuclear and polynuclear clusters. FbpA therefore appears to have a strong affinity for iron clusters in iron-rich environments, a property which might endow the protein with new biological functions. 相似文献
59.
Rea M Zheng W Chen M Braud C Bhangu D Rognan TN Xiao W 《The Plant journal : for cell and molecular biology》2012,71(5):776-786
Imprinting, i.e. parent-of-origin expression of alleles, plays an important role in regulating development in mammals and plants. DNA methylation catalyzed by DNA methyltransferases plays a pivotal role in regulating imprinting by silencing parental alleles. DEMETER (DME), a DNA glycosylase functioning in the base-excision DNA repair pathway, can excise 5-methylcytosine from DNA and regulate genomic imprinting in Arabidopsis. DME demethylates the maternal MEDEA (MEA) promoter in endosperm, resulting in expression of the maternal MEA allele. However, it is not known whether DME interacts with other proteins in regulating gene imprinting. Here we report the identification of histone H1.2 as a DME-interacting protein in a yeast two-hybrid screen, and confirmation of their interaction by the in vitro pull-down assay. Genetic analysis of the loss-of-function histone h1 mutant showed that the maternal histone H1 allele is required for DME regulation of MEA, FWA and FIS2 imprinting in Arabidopsis endosperm but the paternal allele is dispensable. Furthermore, we show that mutations in histone H1 result in an increase of DNA methylation in the maternal MEA and FWA promoter in endosperm. Our results suggest that histone H1 is involved in DME-mediated DNA methylation and gene regulation at imprinted loci. 相似文献
60.
Jacob F Ukegjini K Nixdorf S Ford CE Olivier J Caduff R Scurry JP Guertler R Hornung D Mueller R Fink DA Hacker NF Heinzelmann-Schwarz VA 《PloS one》2012,7(2):e31885