全文获取类型
收费全文 | 827篇 |
免费 | 90篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 15篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 26篇 |
2014年 | 37篇 |
2013年 | 48篇 |
2012年 | 70篇 |
2011年 | 51篇 |
2010年 | 37篇 |
2009年 | 35篇 |
2008年 | 36篇 |
2007年 | 48篇 |
2006年 | 29篇 |
2005年 | 38篇 |
2004年 | 44篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 13篇 |
2000年 | 22篇 |
1999年 | 17篇 |
1998年 | 10篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 20篇 |
1991年 | 14篇 |
1990年 | 20篇 |
1989年 | 8篇 |
1988年 | 8篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1981年 | 3篇 |
1978年 | 2篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 6篇 |
1972年 | 5篇 |
1971年 | 2篇 |
1969年 | 2篇 |
1968年 | 10篇 |
1967年 | 4篇 |
1966年 | 3篇 |
排序方式: 共有917条查询结果,搜索用时 593 毫秒
71.
We report a kinetic study on thermal aggregation process of the model protein bovine serum albumin (BSA) in low concentration regime. Aim of this study is to provide information on relationship between conformational changes and initial step of aggregation. The experimental approach is based on steady-state fluorescence spectra of the two tryptophans located in two different domains, in way to study conformational changes in the surrounding of these residues. We also follow emission spectra of Fluorescein-5-Maleimide dye bound to the single free cysteine of BSA. Complementary information on the extent of aggregation and on the structural changes is obtained by Rayleigh scattering and circular dichroism measurements. These data contribute to clarify the connection between conformational changes at tertiary and secondary structure level during the aggregation and how the different domains are involved. We also discuss the relevant role played by cysteine 34 in the aggregation pathways. 相似文献
72.
Battino M Bompadre S Leone L Pugnaloni A Rubini C Ferreiro MS Gallardo I Bullon P 《BioFactors (Oxford, England)》2003,18(1-4):271-275
Cyclosporine A (CsA) plays a pivotal role in controlling Ca2+ movement in the cell modulating also the mitochondrial permeability transition pore. We investigated if chronic administration of CsA may have some effects on the lipophilic and hydrophilic antioxidant pattern of rat liver mitochondria and on their morphological structure. It seems that CsA administration does not statistically affect the redox status of the antioxidants investigated and their amounts (vitamin E, CoQ9, CoQ10, glutathione, uric acid and ascorbic acid) despite the variety of effects that this treatment produces at physiological and morphological levels. However, some kind of derangement could occur in the liver biochemical machinery since CsA treatment induces a markedly increased variability in antioxidant contents. 相似文献
73.
74.
Regulator of G protein signaling (RGS) proteins are GTPase-activating proteins for heterotrimeric G proteins. One of the best-studied RGS proteins, RGS4, accelerates the rate of GTP hydrolysis by all G(i) and G(q) alpha subunits yet has been shown to exhibit receptor selectivity. Although RGS4 is expressed primarily in brain, its effect on modulating the activity of serotonergic receptors has not yet been reported. In the present study, transfected BE(2)-C human neuroblastoma cells expressing human 5-HT(1B) receptors were used to demonstrate that RGS4 can inhibit the coupling of 5-HT(1B) receptors to cellular signals. Serotonin and sumatriptan were found to stimulate activation of extracellular signal-regulated kinase. This activation was attenuated, but not completely inhibited, by RGS4. Similar inhibition by RGS4 of the protein kinase Akt was also observed. As RGS4 is expressed at high levels in brain, these results suggest that it may play a role in regulating serotonergic pathways. 相似文献
75.
HMW1 Is Required for Cytadhesin P1 Trafficking to the Attachment Organelle in Mycoplasma pneumoniae 总被引:2,自引:0,他引:2 下载免费PDF全文
Mycoplasma pneumoniae proteins HMW1-HMW3 collectively are essential for cytadherence, but the function or requirement for each has not been defined. Cytadherence mutant M6 lacks HMW1 because of a frameshift in hmw1 and produces a truncated adherence-associated protein P30 because of a deletion at the 3′ end of p30. Genetic manipulation of this mutant was used to evaluate the role of HMW1 in cytadherence. Mutant M6 was transformed with a recombinant transposon containing a wild-type p30 allele. Transformants synthesized both truncated and full-length P30, from the resident and recombinant alleles, respectively. However, these transformants remained hemadsorption negative, suggesting that HMW1 is required for cytadherence. Wild-type M. pneumoniae cells are generally elongated, tapering to form the attachment organelle at one end of the cell. The cytadhesin protein P1 is normally densely clustered on the mycoplasma surface at this differentiated terminal structure. However, both mutant M6 and M6 transformed with recombinant p30 had a striking ovoid morphology with no tapering at the tip structure, making the attachment organelle indistinguishable. Furthermore, protein P1 was randomly distributed on the mycoplasma surface rather than clustered at a polar location. In contrast, mutant M6 transformed with a recombinant transposon expressing the wild-type hmw1 allele exhibited a near-normal morphology and localized P1 to the attachment organelle. Significantly, M6 transformed with an hmw1 gene truncated slightly at the 3′ end failed to restore proper morphology or P1 localization to the attachment organelle, suggesting a functional importance to the C-terminal domain of HMW1. 相似文献
76.
Brian T. Pittner Melisa W. Mullins Suzanna Reid E. Charles Snow 《In vitro cellular & developmental biology. Animal》1998,34(5):421-429
Summary Because isolation of sufficient numbers of cycling, germinal center B cells from mice for biochemical characterization of
BCR-derived signals can be problematic, we have designed an experimental approach for generating large numbers of cycling
B cells for further study. In the experiments reported here, small, resting B cells were polyclonally stimulated with lipopolysaccharide
(LPS), and cycling B cells isolated as two bands on three-step Percoll gradients. Cycling B cells isolated at Days 2, 4, or
6 of preactivation showed an increased expression of Fas receptor and peanut agglutinin binding, with a concomitant decrease
in sIgD positivity. These cells phenotypically resembled extrafollicular or early germinal center B cells. These cycling B
cells were used to study the functional consequences of differential signaling through the BCR. Strong cross-linking of BCR,
by restimulation of cycling normal B cells with either immobilized or soluble F(ab’)2 anti-μ and cycling hen egg lysozyme (HEL) transgenic B cells with either soluble or immobilized HEL, extended cellular proliferation
by 2–3 d. In contrast, cycling B cells either restimulated with soluble, whole anti-μ (to mimic binding of soluble immune
complexes) or cultured in the absence of restimulation (to mimic cycling B cells not competitive for antigen) resulted in
the rapid exit of the cells from cycle. This system will enable the molecular and biochemical characterization of signal delivery
to cycling B cells. 相似文献
77.
78.
79.
Wild Sicilian Rosemary: Phytochemical and Morphological Screening and Antioxidant Activity Evaluation of Extracts and Essential Oils 下载免费PDF全文
Edoardo M. Napoli Laura Siracusa Antonella Saija Antonio Speciale Domenico Trombetta Teresa Tuttolomondo Salvatore La Bella Mario Licata Giuseppe Virga Raffaele Leone Claudio Leto Laura Rubino Giuseppe Ruberto 《化学与生物多样性》2015,12(7):1075-1094
To identify the best biotypes, an extensive survey of Sicilian wild rosemary was carried out by collecting 57 samples from various sites, followed by taxonomic characterization from an agronomic perspective. All the biotypes collected were classified as Rosmarinus officinalis L. A cluster analysis based on the morphological characteristics of the plants allowed the division of the biotypes into seven main groups, although the characteristics examined were found to be highly similar and not area‐dependent. Moreover, all samples were analyzed for their phytochemical content, applying an extraction protocol to obtain the nonvolatile components and hydrodistillation to collect the essential oils for the volatile components. The extracts were characterized by LC‐UV‐DAD/ESI‐MS, and the essential oils by GC‐FID and GC/MS analyses. In the nonvolatile fractions, 18 components were identified, namely, 13 flavones, two organic acids, and three diterpenes. In the volatile fractions, a total of 82 components were found, with as predominant components α‐pinene and camphene among the monoterpene hydrocarbons and 1,8‐cineole, camphor, borneol, and verbenone among the oxygenated monoterpenes. Cluster analyses were carried out on both phytochemical profiles, allowing the separation of the rosemary samples into different chemical groups. Finally, the total phenol content and the antioxidant activity of the essential oils and extracts were determined with the Folin–Ciocalteu (FC) colorimetric assay, the UV radiation‐induced peroxidation in liposomal membranes (UV‐IP test), and the scavenging activity of the superoxide radical (O$\rm{{_{2}^{{^\cdot} -}}}$ ). The present study confirmed that the essential oils and organic extracts of the Sicilian rosemary samples analyzed showed a considerable antioxidant/free radical‐scavenging activity. 相似文献
80.
Peter Aitken Richard Charles Franklin Jenine Lawlor Rob Mitchell Kerrianne Watt Jeremy Furyk Niall Small Leone Lovegrove Peter Leggat 《PloS one》2015,10(6)