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161.
Ligand/receptor internalization: a kinetic, flow cytometric analysis of the internalization of N-formyl peptides by human neutrophils 总被引:3,自引:0,他引:3
Fluorescence flow cytometry was used to measure the internalization of the fluorescent ligand N-formyl-nle-leu-phe-nle-tyr-lys-fluorescein by human neutrophils. The internalization process was monitored by the accessibility of the receptor-bound fluorescent ligand to quenching following a change in the pH of the extracellular medium from 7.4 to 3.0. In such a pH change, extracellular ligand or fluorescein are quenched immediately (excitation 488 nm). In contrast, intracellular fluorescein (derived from fluorescein diacetate) or intracellular ligand are quenched with half-times of approximately 20 or approximately 40 sec, respectively, at 37 degrees C. The fraction of internalized ligand is calculated by resolving the fast and slow components of the quenching process. Temporal resolution of the internalization process in this system depends upon two factors. We have previously shown that it is possible to examine essentially continuously the kinetics of ligand binding in the nM concentration range without removing the free ligand (Sklar LA, Finney DA, Cytometry 3:161, 1982). We have now modified a Becton Dickinson FACS IV sample head assembly to permit direct addition of reagents into the cell suspension while on-line. This enables us to change the suspension pH and evaluate internalization with a time resolution of a few seconds. We observe that internalized ligand can be detected within 1 min and that the rate is proportional to the number of receptors occupied. The rate is essentially linear over the first few minutes and approximately 60% of the receptor-bound ligand is internalized after 3 min. 相似文献
162.
Using laser Raman spectroscopy, we are able to study conformational changes that occur as previously-dried hen egg-white lysozyme is sequentially rehydrated. Parallel n.m.r. exchangeability studies enable us to monitor flexibility changes also during this rehdyration. The results are consistent with a general loosening up of the protein at a water content of ~0.08 g water/g protein, followed by (probably small) local conformational changes. The enzyme regains its activity only after both these processes have gone to completion; thus these solvent-related changes may be necessary before activity can recommence. 相似文献
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164.
Myth, Experiment, and the Reinvention of Polynesian Voyaging 总被引:1,自引:0,他引:1
Experimental canoe voyages between Hawai'i, Tahiti, and Aotearoa (New Zealand) indicate that proponents of the "mythical" view of voyaging traditions cannot casually dismiss their historical basis because they believe it impossible for canoes navigated without instruments to have been intentionally sailed over such long distances. Furthermore, the key role of Hawaiians in this reinvention of Polynesian voyaging, and in particular their efforts to extend the sailing and navigational trials far beyond the original experimental plan, point toward a more Polynesian interpretation of voyaging traditions than one developed solely through Western analytical approaches. 相似文献
165.
When aggregating amoebas of the cellular slime mold Dictyostelium discoideum are disaggregated and morphogenesis is reinitiated, the amoebas will reaggregate in less than the original time. When aggregating amoebas are disaggregated and resuspended either in full nutrient medium or in buffered salts solution containing dextrose, they retain this developmentally acquired capacity to rapidly reaggregate for approximately 1 hr and then lose it completely in a synchronous and discrete step which we have referred to as the “erasure event.” In this report, it is demonstrated that micromolar concentrations of cAMP completely block this transition from the developmental to vegetative state, and that other cyclic nucleotides also inhibit it, but they do so at 20-fold higher concentrations. Neither the hydrolysis products of cAMP nor the vegetative chemoattractant folic acid inhibit dedifferentiation at concentrations as high as 10?3M, demonstrating a specificity for cyclic nucleotides and cAMP in particular. The addition of cAMP at any time during the lag period preceding the erasure event inhibits it and addition immediately after the erasure event reverses it. Since cAMP may inhibit the transition from the developmental to vegetative state intracellularly or extracellularly, we have also examined the intracellular concentration of cAMP and the levels of cAMP binding sites on the cell surface during the erasure process. Evidence is presented that the majority of cAMP binding sites on the cell surface are not necessary for the inhibition of erasure by cAMP. The results of these latter studies are discussed in terms of alternative models for the involvement of cAMP in the transition from the developing to vegetative state. 相似文献
166.
Numerous pollen records provide evidence for the widespread range expansion of Alnus throughout Alaska and adjacent Canada during the middle Holocene. Because Alnus can fix atmospheric N2, this vegetational change probably had a profound effect on N availability and cycling. To assess this effect, we analyzed
a sediment core from Grandfather Lake in southwestern Alaska for a suite of geochemical indicators, including elemental composition,
biogenic silica (BSi) content, and carbon (C) and nitrogen (N) isotopes of organic matter. These data, in conjunction with
a pollen record from the same site, are used to infer biogeochemical processes associated with the mid-Holocene Alnus expansion. The increase in Alnus pollen percentages from 10% to 70% circa 8000-7000 BP (14C years before present) suggests the rapid spread of Alnus shrub thickets on mountain slopes and riparian zones in the Grandfather Lake region. Coincident with this vegetational change,
the mean value of the sediment BSi content increases from 20.4 to 106.2 mg/g, reflecting increased diatom productivity within
the lake as a result of Alnus N2 fixation in the watershed soils and the associated N flux to the lake. Elevated aquatic productivity at this time is also
supported by increased percentages of organic C and N, decreased C:N ratios, and decreased values of δ
13C. Furthermore, the δ
15N values of sediments increase substantially with the establishment of Alnus shrub thickets, suggesting enhanced N availability and accelerated N cycling within the lake and its watershed. Superimposed
on a general trend of soil acidification throughout the postglacial period, soil acidity probably increased as a result of
the Alnus expansion, as can be inferred from decreasing ratios of authigenic base cations to allogenic silica (Si) and increasing ratios
of authigenic aluminum (Al) to allogenic Si. The ultimate cause of these mid-Holocene ecosystem changes was an increase in
effective moisture in the region.
Received 21 July 2000; accepted 3 January 2001. 相似文献
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169.
D Raimunda T Khare C Giometti S Vogt JM Argüello L Finney 《Metallomics : integrated biometal science》2012,4(9):921-927
Metals are critical and dynamic components of biochemistry. To understand their roles, we greatly need tools to identify the ligands that bind them within the complexity of natural systems. This work describes the development of methods that not only detect and distinguish metals, but also characterize the proteins that bind them. We describe an approach to expose, identify and quantify metalloproteins in complex mixtures by sequential non-denaturing 2D-gel electrophoresis (2D GE)/X-ray Fluorescence (XRF) and tandem mass spectrometry (MS/MS) in the same spot of a sample. We first apply the development of 2D GE/XRF to Shewanella oneidensis MR-1, a well-studied system, and verify our electrophoretic approach. Then, we identified a novel periplasmic zinc protein in Pseudomonas aeruginosa PAO1 through 2D GE/XRF followed by MS/MS. The identity and function of this protein was verified through a gene mutation experiment. 相似文献
170.
Iryna Schlackow A. Sarah Walker Kate Dingle David Griffiths Sarah Oakley John Finney Ali Vaughan Martin J. Gill Derrick W. Crook Tim E. A. Peto David H. Wyllie 《PLoS medicine》2012,9(7)