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41.
A number of spraying experiments showed that the virus cannot enter a plant unless some of the cells are injured. It is not essential that such injury should be brought about in the presence of the virus. The chances of infection fall off rapidly in the first few minutes after injury, but infection occurs occasionally as long as half an hour after the cell is damaged.
Inoculations by micropipette into single cells of the host plant yielded only about one-tenth of the expected number of infections. This suggests differences in the susceptibility of the cells to virus attack. 相似文献
Inoculations by micropipette into single cells of the host plant yielded only about one-tenth of the expected number of infections. This suggests differences in the susceptibility of the cells to virus attack. 相似文献
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Rajasekhar Ramakrishnan Janak D. Ramakrishnan 《Bulletin of mathematical biology》2010,72(8):2019-2046
Tracer studies are analyzed almost universally by multicompartmental models where the state variables are tracer amounts or
activities in the different pools. The model parameters are rate constants, defined naturally by expressing fluxes as fractions
of the source pools. We consider an alternative state space with tracer enrichments or specific activities as the state variables,
with the rate constants redefined by expressing fluxes as fractions of the destination pools. Although the redefinition may
seem unphysiological, the commonly computed fractional synthetic rate actually expresses synthetic flux as a fraction of the
product mass (destination pool). We show that, for a variety of structures, provided the structure is linear and stationary,
the model in the enrichment state space has fewer parameters than that in the activities state space, and is hence better
both to study identifiability and to estimate parameters. The superiority of enrichment modeling is shown for structures where
activity model unidentifiability is caused by multiple exit pathways; on the other hand, with a single exit pathway but with
multiple untraced entry pathways, activity modeling is shown to be superior. With the present-day emphasis on mass isotopes,
the tracer in human studies is often of a precursor, labeling most or all entry pathways. It is shown that for these tracer
studies, models in the activities state space are always unidentifiable when there are multiple exit pathways, even if the
enrichment in every pool is observed; on the other hand, the corresponding models in the enrichment state space have fewer
parameters and are more often identifiable. Our results suggest that studies with labeled precursors are modeled best with
enrichments. 相似文献
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W. F. LOOMIS C. KLEIN PH. BRACKET 《Differentiation; research in biological diversity》1979,12(1-3):83-89
Following the initiation of development, amoebae of Dictyostelium discoideum aggregate chemotactically toward cyclic AMP (cAMP). Adenyl cyclase, cAMP phosphodiesterase, and cAMP binding sites all increase 20–40 fold during the first few hours of development. It has been shown that addition of 1 mM EDTA and 5 mM MgCl2 accelerates the aggregation process. Likewise, the calcium ionophore, A23187, leads to precocious aggregation while 4 × 10−5 M progesterone considerably delays it These treatments have now been shown to result in increased accumulation of adenyl cyclase in the case of EDTA and Mg2+ or the ionophore and greatly decreased accumulation in the case of the steroid.
Treatment with EDTA and Mg2+ or the ionophore has been shown not only to accelerate aggregation in wild-type amoebae but to overcome complete blocks to aggregation in certain mutant strains. We have found that addition of Mn2+ will also permit aggregation of mutant cells otherwise unable to aggregate. This divalent ion, unlike EDTA and Mg2+ or the ionophore, was shown to directly stimulate adenyl cyclase. Calcium ions were also found to affect the enzyme such that at Ca2+ concentrations found within the cells the great majority of the activity is inhibited. Manganese ions can overcome the inhibition by Ca2+ .
These findings show that conditions which stimulate aggregation result in increased activity of adenyl cyclase either by increased accumulation of the enzyme or by increased activity of the available enzyme, and support the proposed central role of adenyl cyclase in aggregation. 相似文献
Treatment with EDTA and Mg
These findings show that conditions which stimulate aggregation result in increased activity of adenyl cyclase either by increased accumulation of the enzyme or by increased activity of the available enzyme, and support the proposed central role of adenyl cyclase in aggregation. 相似文献
50.
Dilip K. Tosh Janak Padia Daniela Salvemini Kenneth A. Jacobson 《Purinergic signalling》2015,11(3):371-387
We reported that 2-(3,4-difluorophenylethynyl)-N6-3-chlorobenzyl (N)-methanocarba adenosine derivative 1 (MRS5698) binds selectively to human and mouse A3 adenosine receptors (A3ARs, Ki 3 nM). It is becoming an important pharmacological tool for defining A3AR effects and is orally active in a chronic neuropathic pain model. Here, we introduce a new synthetic route for MRS5698 from d-ribose, suitable for a scale-up on a multi-gram scale, and we measure in vitro and in vivo ADME-Tox parameters. MRS5698 was very stable in vitro, failed to inhibit CYPs at <10 μM, and was largely bound to plasma proteins. It was well tolerated in the rat at doses of ≤200 mg/kg i.p. A 1 mg/kg i.p. dose in the mouse displayed t1/2 of 1.09 h and plasma Cmax of 204 nM at 1 h with an AUC of 213 ng × h/mL. CACO-2 bidirectional transport studies suggested intestinal efflux of MRS5698 (efflux ratio 86). Although the oral %F is only 5 %, the beneficial effect to reverse pain lasted for at least 2 h in the CCI model in rats, using the same vehicle for oral administration of a high dose. The stability, low toxicity, lack of CYP interaction, pharmacokinetic half-life, and in vivo efficacy suggest that MRS5698 is a preferred compound for further consideration as a treatment for neuropathic pain.