全文获取类型
收费全文 | 2113篇 |
免费 | 226篇 |
国内免费 | 156篇 |
专业分类
化学 | 291篇 |
晶体学 | 16篇 |
力学 | 201篇 |
综合类 | 61篇 |
数学 | 1324篇 |
物理学 | 602篇 |
出版年
2025年 | 5篇 |
2024年 | 26篇 |
2023年 | 28篇 |
2022年 | 28篇 |
2021年 | 50篇 |
2020年 | 65篇 |
2019年 | 72篇 |
2018年 | 58篇 |
2017年 | 62篇 |
2016年 | 65篇 |
2015年 | 54篇 |
2014年 | 92篇 |
2013年 | 107篇 |
2012年 | 102篇 |
2011年 | 85篇 |
2010年 | 90篇 |
2009年 | 112篇 |
2008年 | 130篇 |
2007年 | 115篇 |
2006年 | 146篇 |
2005年 | 92篇 |
2004年 | 82篇 |
2003年 | 94篇 |
2002年 | 91篇 |
2001年 | 89篇 |
2000年 | 92篇 |
1999年 | 79篇 |
1998年 | 83篇 |
1997年 | 47篇 |
1996年 | 52篇 |
1995年 | 36篇 |
1994年 | 20篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 22篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有2495条查询结果,搜索用时 0 毫秒
71.
Several recent works have established dynamical localization for Schrödinger operators, starting from control on the localization length of their eigenfunctions, in terms of their centers of localization. We provide an alternative way to obtain dynamical localization, without resorting to such a strong condition on the exponential decay of the eigenfunctions. Furthermore, we illustrate our purpose with the almost Mathieu operator, H
, , =–+ cos(2(+x)), 15 and with good Diophantine properties. More precisely, for almost all , for all q>0, and for all functions 2(
) of compact support, we show that
The proof applies equally well to discrete and continuous random Hamiltonians. In all cases, it uses as input a repulsion principle of singular boxes, supplied in the random case by the multi-scale analysis. 相似文献
72.
Bentian Zhang Gengtao Fu Yutao Li Lecheng Liang Nicholas S. Grundish Yawen Tang John B. Goodenough Zhiming Cui 《Angewandte Chemie (International ed. in English)》2020,59(20):7857-7863
Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions, but still remains arduous. Herein, we demonstrate a novel and general hydrogel‐freeze drying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt3M (M=Mn, Cr, Fe, Co, etc.) intermetallic NPs (Pt3M/rGO‐HF) with ultrasmall particle size (about 3 nm) and dramatic monodispersity. The formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while a freeze‐drying can retain the hydrogel derived three‐dimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt3M intermetallic NPs (≈3 nm) due to confinement effect of 3D porous structure. Such Pt3M intermetallic NPs exhibit the smallest particle size among the reported ordered Pt‐based intermetallic catalysts. A detailed study of the synthesis of ordered intermetallic Pt3Mn/rGO catalyst is provided as an example of a generally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt‐based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies. 相似文献
73.
Ramsés Djidjou-Demasse Gbenga J. Abiodun Abiodun M. Adeola Joel O. Botai 《Studies in Applied Mathematics》2020,144(4):389-411
In this paper, we develop and analyze a malaria model with seasonality of mosquito life-history traits: periodic-mosquitoes per capita birth rate, -mosquitoes death rate, -probability of mosquito to human disease transmission, -probability of human to mosquito disease transmission, and -mosquitoes biting rate. All these parameters are assumed to be time dependent leading to a nonautonomous differential equation system. We provide a global analysis of the model depending on two threshold parameters and (with ). When , then the disease-free stationary state is locally asymptotically stable. In the presence of the human disease-induced mortality, the global stability of the disease-free stationary state is guarantied when . On the contrary, if , the disease persists in the host population in the long term and the model admits at least one positive periodic solution. Moreover, by a numerical simulation, we show that a sub-critical (backward) bifurcation is possible at . Finally, the simulation results are in accordance with the seasonal variation of the reported cases of a malaria-epidemic region in Mpumalanga province in South Africa. 相似文献
74.
Ming Dai Peter Schiavone Cun‐Fa Gao 《ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik》2016,96(11):1374-1380
We develop a new method to construct periodic inclusions with uniform internal hydrostatic stress in an elastic plane subjected to uniform remote in‐plane loading. The method is based on two particular conformal mappings which lead to a system of nonlinear equations from which the inclusion shapes are determined. We illustrate our results with several examples. In particular, we show that the ratio of the inclusion size to the period of the inclusion‐matrix system changes with the inclusion aspect ratio and, in the specific case of uniform remote shear loading, the orientation of the inclusions is also altered. Finally, we show that if the period of the inclusion‐matrix system exceeds roughly six times the inclusion size, such periodic inclusions can be treated approximately as periodic elliptical inclusions with specific aspect ratio and orientation determined by the corresponding elastic constants and uniform remote loading. 相似文献
75.
Yoshinori Ohmasa Susumu Shimomura Ayano Chiba 《Journal of Applied Crystallography》2016,49(3):835-844
In small‐angle X‐ray scattering from highly oriented pyrolytic graphite, radial streak patterns are observed. The streaks change their direction with sample rotation and appear and disappear in pairs. This streak pattern can be explained by double Bragg scattering. The directions of the streaks calculated as functions of the rotation angle are in good agreement with experiment. In addition, asymmetry in the intensity of the streaks and a small deviation from the radial pattern are observed, and they can be explained by the finite sample‐size effect. The necessity of taking double Bragg scattering into account in small‐angle X‐ray scattering studies of crystalline materials is emphasized. 相似文献
76.
Jelena Nikoli Zoran Peri Danijela Aleksi Stefan Tomi Aleksandra Jovanovi 《Entropy (Basel, Switzerland)》2021,23(12)
Driven by the need for the compression of weights in neural networks (NNs), which is especially beneficial for edge devices with a constrained resource, and by the need to utilize the simplest possible quantization model, in this paper, we study the performance of three-bit post-training uniform quantization. The goal is to put various choices of the key parameter of the quantizer in question (support region threshold) in one place and provide a detailed overview of this choice’s impact on the performance of post-training quantization for the MNIST dataset. Specifically, we analyze whether it is possible to preserve the accuracy of the two NN models (MLP and CNN) to a great extent with the very simple three-bit uniform quantizer, regardless of the choice of the key parameter. Moreover, our goal is to answer the question of whether it is of the utmost importance in post-training three-bit uniform quantization, as it is in quantization, to determine the optimal support region threshold value of the quantizer to achieve some predefined accuracy of the quantized neural network (QNN). The results show that the choice of the support region threshold value of the three-bit uniform quantizer does not have such a strong impact on the accuracy of the QNNs, which is not the case with two-bit uniform post-training quantization, when applied in MLP for the same classification task. Accordingly, one can anticipate that due to this special property, the post-training quantization model in question can be greatly exploited. 相似文献
77.
Meng Zhang Dr. Chunxiang Lu Zhihong Bi Xiaolu Xu Xiaodan Ren Xinzhi Li Kuan Lu Shuxia Yuan 《ChemElectroChem》2021,8(5):895-902
A cellulose-based, highly pyrrolic-nitrogen-doped carbon aerogel (PNCA) was successfully prepared by using a facile and ecofriendly in situ dissolution process; the resulting aerogel had a honeycomb-like three-dimensional structure and a highly pyrrole-nitrogen-doped configuration. As the host material of the cathode in lithium-sulfur batteries, PNCA achieved a high sulfur loading up to 76.7 %, owing to the distribution of pyrrole nitrogen and the three-dimensional network structure. As a consequence, this composite cathode exhibits outstanding electrochemical performance, including long-term cycling stability (1292.8 mA h g−1 at 0.2 C over 500 cycles and 540.5 mA h g−1 at 1 C over 1000cycles) and excellent rate performance (1249.9 mA h g−1 at 0.2 C, 1060 mA h g−1 at 0.5 C, 936.3 mA h g−1 at 1 C, and 698 mA h g−1 at 3 C remained). This study aims at providing new insights for the synthesis of highly reactive nitrogen-doped carbon materials and then further proposing a future viewpoint on the design and development of advanced host materials for lithium-sulfur batteries. Furthermore, the key mechanism of the pyrrole-doped nitrogen configuration in the catalytic conversion of polysulfides was revealed for the first time after being combined with DFT theoretical calculations. 相似文献
78.
We address the evaluation of highly oscillatory integrals,with power-law and logarithmic singularities.Such problems arise in numerical methods in engineering.Notably,the evaluation of oscillatory integrals dominates the run-time for wave-enriched boundary integral formulations for wave scattering,and many of these exhibit singularities.We show that the asymptotic behaviour of the integral depends on the integrand and its derivatives at the singular point of the integrand,the stationary points and the endpoints of the integral.A truncated asymptotic expansion achieves an error that decays faster for increasing frequency.Based on the asymptotic analysis,a Filon-type method is constructed to approximate the integral.Unlike an asymptotic expansion,the Filon method achieves high accuracy for both small and large frequency.Complex-valued quadrature involves interpolation at the zeros of polynomials orthogonal to a complex weight function.Numerical results indicate that the complex-valued Gaussian quadrature achieves the highest accuracy when the three methods are compared.However,while it achieves higher accuracy for the same number of function evaluations,it requires signi cant additional cost of computation of orthogonal polynomials and their zeros. 相似文献
79.
Pumpkin seed oil (PSO), which is a valuable compound with high nutritional value used for the prevention of various chronic diseases, is prone to oxidation. In this work, small and uniform (su) ovalbumin (OVA) and pectin (PEC) were used to stabilize PSO in the form of an emulsion. The results showed that suOVA-PEC-PSO emulsion with a droplet size of 9.82 ± 0.05 μm was successfully self-assembled from PSO, PEC, and suOVA solution (with a droplet size of 230.13 ± 14.10 nm) treated with 300 W ultrasound, owing to the formation of a more stable interfacial film on the surface of droplets. The interfacial, rheological, emulsifying, and antioxidant properties of the suOVA-PES-PSO emulsions were excellent, owing to the synergistic effects between PEC and suOVA solution. Moreover, the physical stability of the suOVA-PEC-PSO emulsions to salt stress, a freeze-thaw cycle, and heat treatment was also increased and the oxidation of linolenic acid was notably delayed. These results have extended the food-related applications of OVA and PSO, and provide a promising foundation for further exploration of the self-assembly of composite emulsions by small and uniform proteins. 相似文献
80.
考虑到手性毛细管电泳分离机理的复杂性,提出了不依赖于统计模型的二进制编码遗传算法多目标优化策略。根据实验参数的多少及其重要性,采用均匀设计安排完成初步实验。并用Derringer功效函数作为多指标同时优化的评价指标,以取得较高的分离度和较快分离速度;通过对实验参数给予编码,转化为二进制字符串,根据得到的总功效函数值大小进行遗传算法操作,产生新的一组实验条件。重复上述过程直到得到最佳分离条件为止。此方法成功地应用于华法令对映体的毛细管电泳分离条件优化。 相似文献