全文获取类型
收费全文 | 2704篇 |
免费 | 221篇 |
出版年
2023年 | 6篇 |
2022年 | 27篇 |
2021年 | 49篇 |
2020年 | 28篇 |
2019年 | 47篇 |
2018年 | 64篇 |
2017年 | 52篇 |
2016年 | 78篇 |
2015年 | 137篇 |
2014年 | 137篇 |
2013年 | 207篇 |
2012年 | 198篇 |
2011年 | 206篇 |
2010年 | 120篇 |
2009年 | 124篇 |
2008年 | 149篇 |
2007年 | 152篇 |
2006年 | 114篇 |
2005年 | 123篇 |
2004年 | 113篇 |
2003年 | 106篇 |
2002年 | 98篇 |
2001年 | 43篇 |
2000年 | 43篇 |
1999年 | 41篇 |
1998年 | 32篇 |
1997年 | 32篇 |
1996年 | 31篇 |
1995年 | 21篇 |
1994年 | 20篇 |
1993年 | 24篇 |
1992年 | 37篇 |
1991年 | 31篇 |
1990年 | 24篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1986年 | 23篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1969年 | 6篇 |
1968年 | 8篇 |
排序方式: 共有2925条查询结果,搜索用时 628 毫秒
31.
Paiva R. P. Munita C. J. S. Cunha I. I. L. Romano J. Alonso C. D. 《Biological trace element research》1990,(1):231-242
Two nuclear techniques, Energy-Dispersive X-Ray Fluorescence Analysis (EDXRF) and Instrumental Neutron Activation Analysis (INAA), were used to analyze aerosol samples collected in the city of São Paulo, Brazil. Na, Cl, Mn, V, Al, Sm, Mo, W, La, As, Br, Sb, K, Ba, Se, Th, Cr, Rb, Ca, Fe, Ce, and Sc were determined by INAA, and Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Hg, and Pb were determined by EDXRF. A preliminary identification of the main source of the atmospheric aerosol was performed based on enrichment factor and correlation coefficient calculations.
相似文献32.
Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years
in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative
of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different
vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination.
Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient
to determine the key allergenic thresholds in the studied area. 相似文献
33.
Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination. Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient to determine the key allergenic thresholds in the studied area. 相似文献
34.
Angelo De Milito Marinunzia Catucci Francesco Iannelli Laura Romano Maurizio Zazzi Pier Egisto Valensin 《Molecular biotechnology》1995,3(2):166-169
A reliable selective PCR procedure that combines the use of additionally mutated primers with the specificity-enhancing properties
of a commercial preparation (Perfect Match, Stratagene) is described. The human immunodeficiency virus type 1pol gene point mutations known to confer in vitro resistance to azidothymidine were examined as a model for optimization of the
assay. The usual strategy of deliberately introducing an additional mismatch 1 residue from the 3′ end in the wild-type and
mutant primers did not allow reproducible discrimination between wild-type and mutant target sequences. Addition of minimal
amounts of Perfect Match to the same PCR mixtures resulted in a significantly enlarged range of selective annealing temperatures,
providing a valuable and cost-effective means for reliable detection of known mutations by selectivePCR. 相似文献
35.
Giuliano Callaini Maria Giovanna Riparbelli Marcella Cintorino Sergio Antonio Tripodi Giorgio Bianciardi Piero Tosi Romano Dallai 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):39-45
Summary— Immunofluorescence and immunoelectron microscopy indicated that the antibody raised against the nuclear antigen Ki-67 of mammalian cells recognized antigenic determinants of early Drosophila embryos, localized on the outside of the nuclear envelope. Hence, the nuclear envelope of Drosophila appears to share a similar epitope with the chromosome scaffold of mitotic mammalian cells. With the progression of mitosis the antigen persisted around the mitotic spindle region and was also found in the pole regions at metaphase and anaphase. The antibody also stained the equatorial regions of the spindles from anaphase to late telophase. The antibody may therefore be used as a biochemical marker of the nuclear envelope for studying nuclear membrane biogenesis and behavior during the mitotic divisions of the Drosophila embryo. 相似文献
36.
Acetaldehyde production in Saccharomyces cerevisiae wine yeasts 总被引:1,自引:0,他引:1
Patrizia Romano Giovanna Suzzi Luca Turbanti Mario Polsinelli 《FEMS microbiology letters》1994,118(3):213-218
Abstract Eighty-six strains of Saccharomyces cerevisiae were investigated for their ability to produce acetaldehyde in synthetic medium and in grape must. Acetaldehyde production did not differ significantly between the two media, ranging from a few mg/l to about 60 mg/l, and was found to be a strain characteristic. The fermentation temperature of 30°C considerably increased the acetaldehyde produced. This study allowed us to assign the strains to different phenotypes: low, medium and high acetaldehyde producers. The low and high phenotypes differed considerably also in the production of acetic acid, acetoin and higher alcohols and can be useful for studying acetaldehyde production in S. cerevisiae , both from the technological and genetic point of view. 相似文献
37.
Maria Giovanna Riparbelli Romano Dallai Giuliano Callaini 《Biology of the cell / under the auspices of the European Cell Biology Organization》1993,78(3):223-227
Rhodamine phalloidin-staining was used to study the organization of the cortical actin cytoskeleton of the early Ceratitis capitata embryo. The dynamics of the actin aggregates and their changes in distribution during the formation of the syncytial blastoderm, were followed in detail. It was found that these aggregates formed a shell-like cluster around the interphase nuclei, and concentrated toward the poles of the mitotic apparatus when the nuclei divided. Laser scanning confocal microscopy revealed that aggregates not clustered at the poles of the mitotic apparatus were closely associated with fine fibers of a dense cytoplasmic network of actin filaments. 相似文献
38.
Biometric Study of Acetoin Production in Hanseniaspora guilliermondii and Kloeckera apiculata 下载免费PDF全文
Patrizia Romano Giovanna Suzzi Roberto Zironi Giuseppe Comi 《Applied microbiology》1993,59(6):1838-1841
Gas chromatographic analysis by direct injection of samples yielded quantitative data on acetoin content. Ninety-six strains of Hanseniaspora guilliermondii and Kloeckera apiculata were investigated for the ability to produce acetoin in synthetic medium and in must. High-level production of acetoin was found to be a characteristic of both species. In synthetic medium, the two species were not significantly different with respect to sugar utilization and ethanol or acetoin production. In grape must, the two species were significantly different (P = 0.001) in acetoin production and K. apiculata exhibited a significantly negative correlation between acetoin production and either sugar consumption or ethanol production. Use of selected apiculate yeasts in mixed cultures with Saccharomyces cerevisiae seems promising for optimization of wine bouquet. 相似文献
39.
Annalisa Pezzolo Giorgio Gimelli Amnon Cohen Antonella Lavaggetto Cesare Romano Giuseppina Fogu Orsetta Zuffardi 《Human genetics》1993,92(1):23-27
In situ hybridization of a telomeric (TTA-GGG)
n
sequence to metaphases from three cases of ring chromosome, involving respectively chromosomes 4, 16, and 20, showed the presence of the cognate sequences in all three rings. To investigate whether these ring chromosomes originated by telomere-telomere fusion, we determined, by in situ hybridization, whether telomere-associated sequences and/or specific distal sequences were still present in the ring chromosomes. The finding that these sequences were preserved in all the ring chromosomes strongly indicates that they originated by telomere-telomere fusion. All three subjects carrying the ring chromosomes are affected by the so-called ring syndrome, with failure to thrive, minor dysmorphic signs and no major anomalies. The r(4) patient has the ring in mosaic form with a normal cell line and has normal intelligence. The r(16) and the r(20) patients have moderate mental retardation and suffer from seizures. We conclude that the ring syndrome, even in its more severe manifestation, is caused by ring chromosome instability. 相似文献
40.
Jonathan Reizer Antonio H. Romano Josef Deutscher 《Journal of cellular biochemistry》1993,51(1):19-24
HPr of the Gram-positive bacterial phosphotransferase system (PTS) can be phosphorylated by an ATP-dependent protein kinase on a serine residue or by PEP-dependent Enzyme I on a histidyl residue. Both phosphorylation events appear to influence the metabolism of non-PTS carbon sources. Catabolite repression of the gluconate (gnt) operon of B. subtilis appears to be regulated by the former phosphorylation event, while glycerol kinase appears to be regulated by the latter phosphorylation reaction. The extent of our understanding of these processes will be described. © 1993 Wiley-Liss, Inc. 相似文献