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31.
Interaction of four luminescent rhenium(I) diimine complexes, [Re(CO)3(N-N)L]PF6 ((N-N = 2,2-bipyridine, L = py-3-COOH) 1a, (N-N = 2,2-bipyridine, L = py-3-CONH2) 1b, (N-N = 1,10-phenanthroline, L = py-3-COOH) 2a, (N-N = 1,10-phenanthroline, L = py-3-CONH2) 2b with bovine serum albumin (BSA) at physiological pH has been examined using UV-Vis absorption and luminescence spectroscopy, excited state lifetime measurement and circular dichroism (CD). In the presence of BSA, the luminescence of Re(I) complexes is quenched due to the locking-in of the probe into the protein environment. Interestingly the probe is released from the protein environment in the presence of sodium dodecyl sulfate (SDS) resulting in the restoration of the original luminescence along with a red shift in the emission maximum. These observations are explained in terms of binding constants (Ka) of probe with protein and surfactant and the nature of the binding has been investigated from Scatchard plot and Hill’s coefficient (n) value. These studies point out that the interaction between Re(I) complexes and BSA is cooperative in nature. 相似文献
32.
Pagano B Del Vecchio P Mattia CA Graziano G 《International journal of biological macromolecules》2011,49(5):1072-1077
Circular dichroism and differential scanning calorimetry measurements showed that esterase 2 from the thermophilic microorganism Alicyclobacillus acidocaldarius, EST2, and its variant in which the first 35 residues have been deleted, EST2-36del, unfold reversibly on increasing temperature, and possess two cooperative and coupled domains [12]. Structural features of the α/β hydrolase fold of EST2, with nine α-helices packed against the central twisted β-sheet, do not allow a straightforward identification of these two cooperative and coupled domains. Molecular dynamics simulations, each one 20 ns long, have been performed at 300, 400 and 500 K, on both proteins in explicit water. Suitable analysis of MD trajectories has allowed a reliable identification of the two cooperative domains (i.e., the less stable one corresponds to external α-helices, whereas the more stable one corresponds to the central twisted β-sheet) and the attribution of the key coupling role to the last and long α-helix of EST2. 相似文献
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Gabriela K. Hajduk Andrew Cockburn Nicolas Margraf Helen L. Osmond Craig A. Walling Loeske E. B. Kruuk 《Evolution; international journal of organic evolution》2018,72(7):1500-1514
Inbreeding depression plays a major role in shaping mating systems: in particular, inbreeding avoidance is often proposed as a mechanism explaining extra‐pair reproduction in socially monogamous species. This suggestion relies on assumptions that are rarely comprehensively tested: that inbreeding depression is present, that higher kinship between social partners increases infidelity, and that infidelity reduces the frequency of inbreeding. Here, we test these assumptions using 26 years of data for a cooperatively breeding, socially monogamous bird with high female infidelity, the superb fairy‐wren (Malurus cyaneus). Although inbred individuals were rare (~6% of offspring), we found evidence of inbreeding depression in nestling mass (but not in fledgling survival). Mother–son social pairings resulted in 100% infidelity, but kinship between a social pair did not otherwise predict female infidelity. Nevertheless, extra‐pair offspring were less likely to be inbred than within‐pair offspring. Finally, the social environment (the number of helpers in a group) did not affect offspring inbreeding coefficients or inbreeding depression levels. In conclusion, despite some agreement with the assumptions that are necessary for inbreeding avoidance to drive infidelity, the apparent scarcity of inbreeding events and the observed levels of inbreeding depression seem insufficient to explain the ubiquitous infidelity in this system, beyond the mother–son mating avoidance. 相似文献
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37.
《DNA Repair》2014
The O6-alkylguanine DNA alkyltransferase (AGT) is a highly conserved protein responsible for direct repair of alkylated guanine and to a lesser degree thymine bases. While specific DNA lesion-bound complexes in crystal structures consist of monomeric AGT, several solution studies have suggested that cooperative DNA binding plays a role in the physiological activities of AGT. Cooperative AGT–DNA complexes have been described by theoretical models, which can be tested by atomic force microscopy (AFM). Direct access to structural features of AGT–DNA complexes at the single molecule level by AFM imaging revealed non-specifically bound, cooperative complexes with limited cluster length. Implications of cooperative binding in AGT–DNA interactions are discussed. 相似文献
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Carol R. Ember Ian Skoggard Erik J. Ringen Megan Farrer 《Evolution and human behavior》2018,39(4):380-391
Food sharing and (to a lesser extent) labor sharing play central roles in the evolution of cooperation literature. One popular explanation for sharing beyond the family is that it reduces the likelihood of shortages by pooling risk across households. However, the frequency and scope of sharing have never been systematically documented across nonindustrial societies, and the literature is driven by theoretical models, experimental games, and case studies among a few extensively-studied populations. Here we explore the cross-cultural context, frequency, and scope of food and labor sharing customs in relation to resource stress. Using ethnographic data from a worldwide sample of 98 societies in the Standard Cross-Cultural Sample (SCCS), we test the following hypotheses: 1) customary sharing of food and labor beyond the household are cultural universals, 2) societies subject to more resource stress (including unpredictable food-destroying natural hazards) will share more frequently, and 3) the more frequent the resource stress, the broader the geographic and social scope of sharing customs. Hypotheses 1 and 2 are generally supported and are consistent with the theory that extensive beyond-household sharing is adaptive in societies that are subject to more resource stress. Hypothesis 3 was not supported and, contrary to our predictions, there is suggestive evidence that sharing beyond-relatives may be attenuated when resource stress is high. In light of these findings, we consider how resource stress may constitute an important selection pressure for maintaining extensive cooperation and help to explain the ubiquity of beyond-household sharing. 相似文献
40.
Cobra venom cytotoxins (CTX) have been shown to disrupt cells as different as immunocytes, skeletal myocytes, erythrocytes
and tumor cells. Nevertheless, even subpopulations of tumor cells are differentially susceptible to CTX by an order of magnitude.
In the present study, our objective was to compare CTX-specific binding with cytolytic potency for two disparate cell types
in vitro. We investigated the lytic activity of cytotoxin-III from Naja naja atra (NNA, fraction D) using heart cells and human leukemic T-cells (CEM cells). For both cell types, 50% cytolysis, assessed
by tetrazolium dye conversion, occurred with μm concentrations of toxin (EC50= 2.2 μm). We examined the binding of radiolabeled CTX III to both heart cells and CEM cells and found the apparent dissociation constant
(K
Dapp) to be 0.69 μm and 0.75 μm, for CEM and heart cells respectively. The B
max for the CEM cells was 1.0 fmoles/cell and that for heart cells was 5.2 fmoles/cell, both exhibiting positive cooperativity
between the sites (Hill coefficients 1.4, T-cells; 1.6, heart). Relatively modest dissociation constants plus high numbers
of binding sites per cell are consistent with a model of CTX binding to plasma membranes by interaction with phospholipids
in the bilayer. Our results suggest that the lytic activity of this cytotoxin follows its binding to a population of sites
on the cells in a cooperative fashion.
Received: 8 May 1995/Revised: 17 November 1995 相似文献