全文获取类型
收费全文 | 154782篇 |
免费 | 11966篇 |
国内免费 | 11602篇 |
专业分类
化学 | 56434篇 |
晶体学 | 2039篇 |
力学 | 9635篇 |
综合类 | 1500篇 |
数学 | 45933篇 |
物理学 | 62809篇 |
出版年
2023年 | 826篇 |
2022年 | 1222篇 |
2021年 | 2007篇 |
2020年 | 2373篇 |
2019年 | 2659篇 |
2018年 | 2289篇 |
2017年 | 2268篇 |
2016年 | 2294篇 |
2015年 | 2165篇 |
2014年 | 3770篇 |
2013年 | 7018篇 |
2012年 | 4430篇 |
2011年 | 5488篇 |
2010年 | 5645篇 |
2009年 | 11292篇 |
2008年 | 12687篇 |
2007年 | 11365篇 |
2006年 | 10216篇 |
2005年 | 7619篇 |
2004年 | 7134篇 |
2003年 | 7237篇 |
2002年 | 7266篇 |
2001年 | 5936篇 |
2000年 | 5588篇 |
1999年 | 5148篇 |
1998年 | 4520篇 |
1997年 | 3599篇 |
1996年 | 3286篇 |
1995年 | 3620篇 |
1994年 | 3466篇 |
1993年 | 2833篇 |
1992年 | 2244篇 |
1991年 | 1701篇 |
1990年 | 1376篇 |
1989年 | 1230篇 |
1988年 | 1134篇 |
1987年 | 902篇 |
1986年 | 675篇 |
1985年 | 1516篇 |
1984年 | 1130篇 |
1983年 | 749篇 |
1982年 | 1101篇 |
1981年 | 1264篇 |
1980年 | 1092篇 |
1979年 | 981篇 |
1978年 | 855篇 |
1977年 | 734篇 |
1976年 | 704篇 |
1974年 | 432篇 |
1973年 | 574篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
On Regularization of a Source Identification Problem in a Parabolic PDE and its Finite Dimensional Analysis 下载免费PDF全文
Subhankar Mondal & M. Thamban Nair 《偏微分方程(英文版)》2021,34(3):240-257
We consider the inverse problem of identifying a general source term, which is a function of both time variable and the spatial variable, in a parabolic PDE from the knowledge of boundary measurements of the solution on some portion of the lateral boundary. We transform this inverse problem into a problem of solving a compact linear operator equation. For the regularization of the operator equation with noisy data, we employ the standard Tikhonov regularization, and its finite dimensional realization is done using a discretization procedure involving the space $L^2(0,\tau;L^2(Ω))$. For illustrating the specification of an a priori source condition, we have explicitly obtained the range space of the adjoint of the operator involved in the operator equation. 相似文献
2.
Khoder Makkawi Nourdine Ait-Tmazirte Maan El Badaoui El Najjar Nazih Moubayed 《Entropy (Basel, Switzerland)》2021,23(4)
When applying a diagnostic technique to complex systems, whose dynamics, constraints, and environment evolve over time, being able to re-evaluate the residuals that are capable of detecting defaults and proposing the most appropriate ones can quickly prove to make sense. For this purpose, the concept of adaptive diagnosis is introduced. In this work, the contributions of information theory are investigated in order to propose a Fault-Tolerant multi-sensor data fusion framework. This work is part of studies proposing an architecture combining a stochastic filter for state estimation with a diagnostic layer with the aim of proposing a safe and accurate state estimation from potentially inconsistent or erroneous sensors measurements. From the design of the residuals, using α-Rényi Divergence (α-RD), to the optimization of the decision threshold, through the establishment of a function that is dedicated to the choice of α at each moment, we detail each step of the proposed automated decision-support framework. We also dwell on: (1) the consequences of the degree of freedom provided by this α parameter and on (2) the application-dictated policy to design the α tuning function playing on the overall performance of the system (detection rate, false alarms, and missed detection rates). Finally, we present a real application case on which this framework has been tested. The problem of multi-sensor localization, integrating sensors whose operating range is variable according to the environment crossed, is a case study to illustrate the contributions of such an approach and show the performance. 相似文献
3.
Frank Nielsen 《Entropy (Basel, Switzerland)》2021,23(4)
We generalize the Jensen-Shannon divergence and the Jensen-Shannon diversity index by considering a variational definition with respect to a generic mean, thereby extending the notion of Sibson’s information radius. The variational definition applies to any arbitrary distance and yields a new way to define a Jensen-Shannon symmetrization of distances. When the variational optimization is further constrained to belong to prescribed families of probability measures, we get relative Jensen-Shannon divergences and their equivalent Jensen-Shannon symmetrizations of distances that generalize the concept of information projections. Finally, we touch upon applications of these variational Jensen-Shannon divergences and diversity indices to clustering and quantization tasks of probability measures, including statistical mixtures. 相似文献
4.
This paper proposes a method for solving optimisation problems involving piecewise quadratic functions. The method provides a solution in a finite number of iterations, and the computational complexity of the proposed method is locally polynomial of the problem dimension, i.e., if the initial point belongs to the sufficiently small neighbourhood of the solution set. Proposed method could be applied for solving large systems of linear inequalities. 相似文献
5.
Dariusz Marek Adam Domaski Joanna Domaska Jakub Szygua Tadeusz Czachrski Jerzy Klamka 《Entropy (Basel, Switzerland)》2021,23(5)
In this article, a way to employ the diffusion approximation to model interplay between TCP and UDP flows is presented. In order to control traffic congestion, an environment of IP routers applying AQM (Active Queue Management) algorithms has been introduced. Furthermore, the impact of the fractional controller and its parameters on the transport protocols is investigated. The controller has been elaborated in accordance with the control theory. The TCP and UDP flows are transmitted simultaneously and are mutually independent. Only the TCP is controlled by the AQM algorithm. Our diffusion model allows a single TCP or UDP flow to start or end at any time, which distinguishes it from those previously described in the literature. 相似文献
6.
We address the problem of telegraphic transport in several dimensions. We review the derivation of two and three dimensional telegrapher’s equations—as well as their fractional generalizations—from microscopic random walk models for transport (normal and anomalous). We also present new results on solutions of the higher dimensional fractional equations. 相似文献
7.
In the assessment of most complex socioeconomic phenomena with the use of multicriteria methods, continuous data are used, the source of which are most often public statistics. However, there are complex phenomena such as quality of life and quality of services in the assessment, for which questionnaire surveys and ordinal measurement scales are used. In this case, the use of classic multicriteria methods is very difficult, taking into account the way of presenting this type of data by official statistics, as well as their permissible transformations and arithmetic operations. Therefore, the main purpose of this study was the presentation of a novel framework which can be applied for assessing socioeconomic phenomena on the basis of survey data. It was assumed that the object assessments may contain positive or negative opinions and an element of uncertainty expressed in the form a “no”, “difficult to say”, or “no opinion” answers. For this reason, the intuitionistic fuzzy TOPSIS (IF-TOPSIS) method is proposed. To demonstrate the potential of this solution, the results of measuring the subjective quality of life of the inhabitants of 83 cities in EU countries, EFTA countries, the UK, the Western Balkans, and Turkey are presented. For most cities, a high level of subjective quality of life was observed using the proposed approach. The highest level of quality of life was observed in Zurich, whereas the lowest was observed in Palermo. 相似文献
8.
In this paper, we consider a scenario where the base station (BS) collects time-sensitive data from multiple sensors through time-varying and error-prone channels. We characterize the data freshness at the terminal end through a class of monotone increasing functions related to Age of information (AoI). Our goal is to design an optimal policy to minimize the average age penalty of all sensors in infinite horizon under bandwidth and power constraint. By formulating the scheduling problem into a constrained Markov decision process (CMDP), we reveal the threshold structure for the optimal policy and approximate the optimal decision by solving a truncated linear programming (LP). Finally, a bandwidth-truncated policy is proposed to satisfy both power and bandwidth constraint. Through theoretical analysis and numerical simulations, we prove the proposed policy is asymptotic optimal in the large sensor regime. 相似文献
9.
Compared with the traditional magnetic bubble, a skyrmion has a smaller size, and better stability and therefore is considered as a very promising candidate for future memory devices. When skyrmions are manipulated, erased and created, the density of skyrmions can be varied, however the relationship between the radii and the densities of skyrmions needs more exploration. In this paper, we study this problem both theoretically and by using the lattice simulation. The average radius of skyrmions as a function of material parameters, the strength of the external magnetic field and the density of skyrmions is obtained and verified. With this explicit function, the skyrmion radius can be easily predicted, which is helpful for the future study of skyrmion memory devices. 相似文献
10.