全文获取类型
收费全文 | 4680篇 |
免费 | 390篇 |
国内免费 | 191篇 |
专业分类
化学 | 1903篇 |
晶体学 | 36篇 |
力学 | 185篇 |
综合类 | 104篇 |
数学 | 1463篇 |
物理学 | 1570篇 |
出版年
2023年 | 39篇 |
2022年 | 70篇 |
2021年 | 92篇 |
2020年 | 132篇 |
2019年 | 104篇 |
2018年 | 76篇 |
2017年 | 90篇 |
2016年 | 143篇 |
2015年 | 151篇 |
2014年 | 151篇 |
2013年 | 277篇 |
2012年 | 173篇 |
2011年 | 356篇 |
2010年 | 307篇 |
2009年 | 434篇 |
2008年 | 395篇 |
2007年 | 366篇 |
2006年 | 305篇 |
2005年 | 192篇 |
2004年 | 185篇 |
2003年 | 157篇 |
2002年 | 156篇 |
2001年 | 132篇 |
2000年 | 108篇 |
1999年 | 86篇 |
1998年 | 89篇 |
1997年 | 68篇 |
1996年 | 68篇 |
1995年 | 52篇 |
1994年 | 40篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 30篇 |
1990年 | 22篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 17篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1976年 | 5篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 6篇 |
1967年 | 3篇 |
排序方式: 共有5261条查询结果,搜索用时 15 毫秒
51.
The most promising 3D display technology lies in holographic display system. Kinform, whose theoretical diffraction efficiency is 100%, is the promising type of hologram. It is found that one of the greatest obstacles to the practical application of kinoform is the computational speed. A new model to increase the computational speed is proposed to solve the problem. In the proposed model named horizontal parallax only (HPO) kinoform, the vertical parallax is omitted because the human visual system cannot perceive the vertical parallax. Therefore, the computational speed for HPO kinform is many times faster than that for full parallax kinform. In this paper, both the theoretical basis and the experimental results of HPO kinoform are discussed. 相似文献
52.
Randall Claywell Laszlo Nadai Imre Felde Sina Ardabili Amirhosein Mosavi 《Entropy (Basel, Switzerland)》2020,22(11)
The accurate prediction of the solar diffuse fraction (DF), sometimes called the diffuse ratio, is an important topic for solar energy research. In the present study, the current state of Diffuse irradiance research is discussed and then three robust, machine learning (ML) models are examined using a large dataset (almost eight years) of hourly readings from Almeria, Spain. The ML models used herein, are a hybrid adaptive network-based fuzzy inference system (ANFIS), a single multi-layer perceptron (MLP) and a hybrid multi-layer perceptron grey wolf optimizer (MLP-GWO). These models were evaluated for their predictive precision, using various solar and DF irradiance data, from Spain. The results were then evaluated using frequently used evaluation criteria, the mean absolute error (MAE), mean error (ME) and the root mean square error (RMSE). The results showed that the MLP-GWO model, followed by the ANFIS model, provided a higher performance in both the training and the testing procedures. 相似文献
53.
We study the statistical properties of wave transport in a disordered waveguide. We first derive the properties of a “building block” (BB) of length δL starting from a potential model consisting of thin potential slices. We then find a diffusion equation—in the space of transfer matrices that describe our system—which governs the evolution with the length L of the disordered waveguide of the transport properties of interest. The latter depend only on the mean free paths and on no other property of the slice distribution. The universality that arises demonstrates the existence of a generalized central-limit theorem. We have developed a numerical simulation in which the universal statistical properties of the BB found analytically are first implemented numerically, and then the various BBs are combined to construct the full waveguide. The reported results thus obtained are in good agreement with microscopic calculations, for both bulk and surface disorder. 相似文献
55.
In this paper, we present a novel local-world model of wireless sensor networks (WSN) with two kinds of nodes: sensor nodes and sink nodes, which is different from other models with identical nodes and links. The model balances energy consumption by limiting the connectivity of sink nodes to prolong the life of the network. How the proportion of sink nodes, different energy distribution and the local-world scale would affect the topological structure and network performance are investigated. We find that, using mean-field theory, the degree distribution is obtained as an integral with respect to the proportion of sink nodes and energy distribution. We also show that, the model exhibits a mixed connectivity correlation which is greatly distinct from general networks. Moreover, from the perspective of the efficiency and the average hops for data processing, we find some suitable range of the proportion p of sink nodes would make the network model have optimal performance for data processing. 相似文献
56.
57.
58.
Note on Generalized Quantum Gates and Quantum Operations 总被引:1,自引:0,他引:1
Yue-Qing Wang Hong-Ke Du Yan-Ni Dou 《International Journal of Theoretical Physics》2008,47(9):2268-2278
Recently, Gudder proved that the set of all generalized quantum gates coincides the set of all contractions in a finite-dimensional
Hilbert space (S. Gudder, Int. J. Theor. Phys. 47:268–279, 2008). In this note, we proved that the set of all generalized
quantum gates is a proper subset of the set of all contractions on an infinite dimensional separable Hilbert space ℋ. Meanwhile,
we proved that the quantum operation deduced by an isometry is an extreme point of the set of all quantum operations on ℋ.
This subject is supported by NSF of China (10571113). 相似文献
59.
D. Basanta H. Hatzikirou A. Deutsch 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):393-397
Tumour cells have to acquire a number of capabilities if a neoplasm is to become a cancer. One of these key capabilities is
increased motility which is needed for invasion of other tissues and metastasis. This paper presents a qualitative mathematical
model based on game theory and computer simulations using cellular automata. With this model we study the circumstances under
which mutations that confer increased motility to cells can spread through a tumour made of rapidly proliferating cells. The
analysis suggests therapies that could help prevent the progression towards malignancy and invasiveness of benign tumours. 相似文献
60.
One of the challenges of cellular automaton research is finding models with a low complexity and at the same time a rich dynamics. A measure of low complexity is the number of states in the model and the number of transition rules to switch between those states. In this paper, we propose a 2-dimensional 2-state cellular automaton that-though governed by a single simple transition rule-has a sufficiently rich dynamics to be computationally universal. According to the transition rule, a cell’s state is determined by the sum of the states of the cells at orthogonal or diagonal distances one or two from the cell (distance-2 Moore neighbourhood), but not by the previous state of the cell itself. Notwithstanding its simplicity, this model is able to generate a great variety of patterns, including several types of stable configurations, oscillators and patterns that move over cellular space (gliders). We prove the computational universality of the model by constructing a universal set of logic gates (NOT and AND) from these patterns. A key element in this proof is the shifting of phases and positions of signals such that they meet the input requirements of the logic gates. Similarities of the model with classical spin systems are also discussed. 相似文献