全文获取类型
收费全文 | 189篇 |
免费 | 26篇 |
出版年
2019年 | 2篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2010年 | 3篇 |
2008年 | 4篇 |
2007年 | 6篇 |
2006年 | 5篇 |
2005年 | 9篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 9篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 6篇 |
1971年 | 9篇 |
1970年 | 2篇 |
1969年 | 4篇 |
1968年 | 7篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
1903年 | 2篇 |
排序方式: 共有215条查询结果,搜索用时 296 毫秒
71.
72.
73.
Calculation of binding isotherms for heterogenous polymers 总被引:30,自引:0,他引:30
D M Crothers 《Biopolymers》1968,6(4):575-584
The matrix method of statistical mechanics is used to calculate equilibria for the binding of small molecules to polymers. When there is only one kind of binding site the problem is simple; some examples are given for illustrative purposes. If, however, the binding sites are not all equivalent and the bound molecules interact or interfere with each other, the problem is no longer trivial, being formally analogous with calculation of the helix–coil transition equilibrium in a heterogeneous polypeptide. Particular difficulties arise when the sequence of binding sites is aperiodic; most naturally occurring materials fall in this class. The purpose of this paper is to point out that problems of this type are readily solved with good accuracy by use of random-number methods on a high-speed digital computer. One such calculation is presented for illustration. The methods developed are applicable to such systems as the binding of actinomycin, Hg–, and acridine dyes to DNA. 相似文献
74.
75.
76.
77.
Aposematic signals represent one of the most accessible traits to evaluate the interaction of natural and sexual selection on signal evolution. Here we investigate the contributions of these two selective forces on the aposematic signal evolution of the highly polytypic strawberry poison frog, Oophaga pumilio, of Bocas del Toro, Panama. Previous research has shown that the brightness of O. pumilio warning coloration can inform predators of the toxicity levels associated with different populations of the archipelago. Other studies suggest that sexual selection may be influencing warning signal brightness within populations via female mate choice (Isla Solarte, Isla Bastimentos, and Aquacate Peninsula populations) and male–male competition (Isla Solarte). Here we present two non-exclusive scenarios for how natural and sexual selection interact to drive phenotypic variation across this archipelago: (1) predators impose a selective regime whereby populations above a toxicity-brightness threshold are at liberty to diversify via sexual selection and below which populations are constrained to maintain a stricter resemblance to a more cryptic population mean, and (2) synergistic/additive effects of inter- and intrasexual selection drive the evolution of brighter males within populations above this toxicity threshold. We investigate whether aposematic patterns of divergence across the archipelago relative to the common mainland phenotype meet these predictions using existing data on O. pumilio morph toxicity measures and overall conspicuousness estimates to an avian predator. Using standardized z-scores to evaluate the range of trait values, we find that indeed the population representative of the common mainland phenotype (Almirante) represents an intermediate level of both toxicity and conspicuousness, and that derived Bocas del Toro populations vary in each of those components in directions predicted by the proposed scenarios. Furthermore, we find greater divergence towards conspicuousness than crypsis, a pattern suggestive of sexual and natural selection acting synergistically in morphs with high toxicity. 相似文献
78.
Jay B. Patel Adam D. Wright Kilian B. Lohmann Kun Peng Chelsea Q. Xia James M. Ball Nakita K. Noel Timothy W. Crothers Jenny Wong‐Leung Henry J. Snaith Laura M. Herz Michael B. Johnston 《Liver Transplantation》2020,10(10)
The production of highly efficient single‐ and multijunction metal halide perovskite (MHP) solar cells requires careful optimization of the optical and electrical properties of these devices. Here, precise control of CH3NH3PbI3 perovskite layers is demonstrated in solar cell devices through the use of dual source coevaporation. Light absorption and device performance are tracked for incorporated MHP films ranging from ≈67 nm to ≈1.4 µm thickness and transfer‐matrix optical modeling is utilized to quantify optical losses that arise from interference effects. Based on these results, a device with 19.2% steady‐state power conversion efficiency is achieved through incorporation of a perovskite film with near‐optimum predicted thickness (≈709 nm). Significantly, a clear signature of photon reabsorption is observed in perovskite films that have the same thickness (≈709 nm) as in the optimized device. Despite the positive effect of photon recycling associated with photon reabsorption, devices with thicker (>750 nm) MHP layers exhibit poor performance owing to competing nonradiative charge recombination in a “dead‐volume” of MHP. Overall, these findings demonstrate the need for fine control over MHP thickness to achieve the highest efficiency cells, and accurate consideration of photon reabsorption, optical interference, and charge transport properties. 相似文献
79.
80.
Viktorian Miok Saskia M Wilting Mark A van de Wiel Annelieke Jaspers Paula I van Noort Ruud H Brakenhoff Peter JF Snijders Renske DM Steenbergen Wessel N van Wieringen 《BMC bioinformatics》2014,15(1)