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1.
Jeffrey R. Lehman 《School science and mathematics》1995,95(2):69-77
Science teacher educators from 205 colleges/universities completed a questionnaire concerning the nature and extent of microcomputer offerings in their secondary science teacher preparation programs. These data are reported and compared to a similar sample surveyed in 1984. Seventy-seven percent of reporting institutions now require either a microcomputer course or completion of a microcomputer competency within their secondary science certification program. The most common applications in these courses are simulations, word processing, databases, and spreadsheet use. Chi-square analysis revealed that more institutions in 1992 were requiring a microcomputer course than in 1984. However, only 23.4% of the institutions offered a microcomputer course designed solely for secondary science majors, and 10.6% of the institutions offered such a course taught by a science teacher educator. Preservice science teachers were also more likely in 1992 than in 1984 to be using microcomputers in instruction during supervised field experiences in secondary schools. Finally, college/university science teacher educators perceived that microcomputer use in secondary science classrooms has increased during the past five years. 相似文献
2.
Exact rotamer optimization for protein design 总被引:1,自引:0,他引:1
Computational methods play a central role in the rational design of novel proteins. The present work describes a new hybrid exact rotamer optimization (HERO) method that builds on previous dead-end elimination algorithms to yield dramatic performance enhancements. Measured on experimentally validated physical models, these improvements make it possible to perform previously intractable designs of entire protein core, surface, or boundary regions. Computational demonstrations include a full core design of the variable domains of the light and heavy chains of catalytic antibody 48G7 FAB with 74 residues and 10(128) conformations, a full core/boundary design of the beta1 domain of protein G with 25 residues and 10(53) conformations, and a full surface design of the beta1 domain of protein G with 27 residues and 10(60) conformations. In addition, a full sequence design of the beta1 domain of protein G is used to demonstrate the strong dependence of algorithm performance on the exact form of the potential function and the fidelity of the rotamer library. These results emphasize that search algorithm performance for protein design can only be meaningfully evaluated on physical models that have been subjected to experimental scrutiny. The new algorithm greatly facilitates ongoing efforts to engineer increasingly complex protein features. 相似文献
3.
[reaction: see text]. The potent oxidant, peroxynitrite, will oxidize 8-oxo-7,8-dihydroguanosine to give several products. In the presence of a thiol agent, the major final product has been determined to be a spiroiminodihydantoin compound. Additionally, we have found that the spiroiminodihydantoin, and not the previously reported 4-hydroxy-8-oxo-4,8-dihydroguanosine, is the major final product formed during the methylene blue-mediated photooxidation of guanosine. 相似文献
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Highlights? Recycling of genetic material is important for the origins of life ? Simulation studies show recycling leads to the selection of genotypes from a pool ? Recycling can lead to the sudden emergence of a high-fitness RNA genotype ? Experimental studies with the Azoarcus ribozyme show fragment recycling 相似文献
6.
Schroedinger's equation with separable n-p (3S1) and potentials solved to obtain a three-body model of the 6Li ground-state wave function. This model predicts the α-n-p binding energy of 6Li to be 4.67 MeV [Exp.: 4.53 MeV = 3.697 + 0.834 (Coulomb)], the asymptotic normalization constant of the d-α tail to be 2.39, and the amount of d+α component to be 65%. The 6Li→α+d vertex function is slightly more momentum dependent than present experiments suggest. 相似文献
7.
Oded Goldreich Shafi Goldwasser Eric Lehman Dana Ron Alex Samorodnitsky 《Combinatorica》2000,20(3):301-337
at arguments of its choice, the test always accepts a monotone f, and rejects f with high probability if it is ε-far from being monotone (i.e., every monotone function differs from f on more than an ε fraction of the domain). The complexity of the test is O(n/ε).
The analysis of our algorithm relates two natural combinatorial quantities that can be measured with respect to a Boolean
function; one being global to the function and the other being local to it. A key ingredient is the use of a switching (or sorting) operator on functions.
Received March 29, 1999 相似文献
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A contour map of the minimum values for three-body rate constants and for equilibrium constants has been constructed for the initial three-body clustering of gas molecules to positive ions. The map was constructed from laboratory measurements of the clustering of gas molecules to alkali ions and consolidates into a readily useful form several recent measurements. Use of the map shows that labile clustering can be extremely important in laboratory experiments and in the earth's upper atmosphere. 相似文献
10.
Partridge SC Singer L Sun R Wilmes LJ Klifa CS Lehman CD Hylton NM 《Magnetic resonance imaging》2011,29(9):1215-1221
Promising recent investigations have shown that breast malignancies exhibit restricted diffusion on diffusion-weighted imaging (DWI) and may be distinguished from normal tissue and benign lesions in the breast based on differences in apparent diffusion coefficient (ADC) values. In this study, we assessed the influence of intravoxel fat signal on breast diffusion measures by comparing ADC values obtained using a diffusion-weighted single shot fast spin-echo sequence with and without fat suppression. The influence of breast density on ADC measures was also evaluated. ADC values were calculated for both tumor and normal fibroglandular tissue in a group of 21 women with diagnosed breast cancer. There were systematic underestimations of ADC for both tumor and normal breast tissue due to intravoxel contribution from fat signal on non–fat-suppressed DWI. This ADC underestimation was more pronounced for normal tissue values (mean difference=40%) than for tumors (mean difference=27%, P<.001) and was worse in women with low breast tissue density vs. those with extremely dense breasts (P<.05 for both tumor and normal tissue). Tumor conspicuity measured by contrast-to-noise ratio was significantly higher on ADC maps created with fat suppression and was not significantly associated with breast density. In summary, robust fat suppression is important for accurate breast ADC measures and optimal lesion conspicuity on DWI. 相似文献