全文获取类型
收费全文 | 3558篇 |
免费 | 261篇 |
国内免费 | 330篇 |
专业分类
化学 | 2091篇 |
晶体学 | 25篇 |
力学 | 303篇 |
综合类 | 15篇 |
数学 | 348篇 |
物理学 | 1367篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 67篇 |
2021年 | 70篇 |
2020年 | 70篇 |
2019年 | 95篇 |
2018年 | 80篇 |
2017年 | 116篇 |
2016年 | 118篇 |
2015年 | 99篇 |
2014年 | 158篇 |
2013年 | 301篇 |
2012年 | 162篇 |
2011年 | 229篇 |
2010年 | 171篇 |
2009年 | 235篇 |
2008年 | 243篇 |
2007年 | 229篇 |
2006年 | 214篇 |
2005年 | 195篇 |
2004年 | 142篇 |
2003年 | 120篇 |
2002年 | 114篇 |
2001年 | 99篇 |
2000年 | 92篇 |
1999年 | 91篇 |
1998年 | 68篇 |
1997年 | 87篇 |
1996年 | 63篇 |
1995年 | 71篇 |
1994年 | 50篇 |
1993年 | 42篇 |
1992年 | 24篇 |
1991年 | 28篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 14篇 |
1981年 | 16篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1974年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有4149条查询结果,搜索用时 31 毫秒
1.
2.
Since the outbreak of the COVID-19 pandemic, most countries have recommended their citizens to adopt social distance, hand hygiene, and face mask wearing. However, wearing face masks has not been well adopted by many citizens. While the reasons are complex, there is a general perception that the evidence to support face mask wearing is lacking, especially for the general public in a community setting. Face mask wearing can block or filter airborne virus-carrying particles through the working of colloid and interface science. This paper assesses current knowledge behind the design and functioning of face masks by reviewing the selection of materials, mask specifications, relevant laboratory tests, and respiratory virus transmission trials, with an overview of future development of reusable masks for the general public. This review highlights the effectiveness of face mask wearing in the prevention of COVID-19 infection. 相似文献
3.
G.E. Farr 《Discrete Mathematics》2019,342(5):1510-1519
This paper continues the study of combinatorial properties of binary functions — that is, functions such that , where is a finite set. Binary functions have previously been shown to admit families of transforms that generalise duality, including a trinity transform, and families of associated minor operations that generalise deletion and contraction, with both these families parameterised by the complex numbers. Binary function representations exist for graphs (via the indicator functions of their cutset spaces) and indeed arbitrary matroids (as shown by the author previously). In this paper, we characterise degenerate elements – analogues of loops and coloops – in binary functions, with respect to any set of minor operations from our complex-parameterised family. We then apply this to study the relationship between binary functions and Tutte’s alternating dimaps, which also support a trinity transform and three associated minor operations. It is shown that only the simplest alternating dimaps have binary representations of the form we consider, which seems to be the most direct type of representation. The question of whether there exist other, more sophisticated types of binary function representations for alternating dimaps is left open. 相似文献
4.
Heinrich Saller 《International Journal of Theoretical Physics》2002,41(8):1491-1509
Unstable particles, together with their stable decay products, constitute probability collectives that are defined as Hilbert spaces with dimension higher than one, nondecomposable in a particle basis. Their structure is considered in the framework of Birkhoff-von Neumann's Hilbert subspace lattices. Bases with particle states are related to bases with a diagonal scalar product by a Hilbert-bein involving the characteristic decay parameters (in some analogy to the n-bein structures of metrical manifolds). Probability predictions as expectation values, involving unstable particles, have to take into account all members of the higher dimensional collective. For example, the unitarity structure of the S-matrix for an unstable particle collective can be established by a transformation with its Hilbert-bein. 相似文献
5.
We present a general scheme for entangling any degree of freedom of two uncorrelated identical particles from independent
sources by a combination of two-particle interferometry and which-way detection. We show that this entanglement generation
procedure works for completely random initial states of the variable to be entangled. We also demonstrate a curious complementarity
exhibited by our scheme and its applications in estimating the generated entanglement as a function of wave packet overlap
at the beamsplitter. 相似文献
6.
7.
8.
A sample of 1233 events is used to study the general characteristics of {}^{16}O-Em interactions at 4.5 A GeV/c. Multiplicity and angular distributions of slow particles and correlations among them are discussed. The present data are compared with the corresponding results from the interactions of other projectiles at the same energy and also the same projectile at different energies. The results indicate that black particle production is independent of the energy and mass of the projectile, but for grey particles it is dependent on the mass of projectile. 相似文献
9.
用Quantum Sutton-Chen多体势对Ag6Cu4和CuNi液态金属凝固过程进行了分子动力学模拟研究.在冷却速率2×1012到2×1014K/s范围内,CuNi总是形成fcc晶体结构,而Ag6Cu4总是形成非晶态结构.考虑到CuNi及AgCu中原子半径之比分别为1.025和1.13,那么模拟结果证实了原子的尺寸差别是非晶态合金形成的一个主要影响因素.此外采用键对及原子多面体类型指数法对凝固过程中微观结构组态变化的分析,不但能说明二十面体结构在非晶态合金形成和稳定性中所起的关键作用,又有助于对液态金属的凝固过程、非晶态结构特征的深入理解. 相似文献
10.
In different regimes of exposure of metals to pulsed laser radiation, we show the role played by the liquid-drop phase formed from the target material in a laser-induced erosion plume due to bulk vaporization, in the dynamics of this plume. For some metals, the ranges of power densities of the acting laser radiation, at which the condensed-phase particles influence the passage of laser radiation to the target surface, have been determined experimentally. The mechanism of realization of a low-threshold breakdown has been revealed. 相似文献