全文获取类型
收费全文 | 6524篇 |
免费 | 1078篇 |
国内免费 | 732篇 |
专业分类
化学 | 4575篇 |
晶体学 | 72篇 |
力学 | 379篇 |
综合类 | 38篇 |
数学 | 785篇 |
物理学 | 2485篇 |
出版年
2024年 | 15篇 |
2023年 | 129篇 |
2022年 | 179篇 |
2021年 | 214篇 |
2020年 | 235篇 |
2019年 | 263篇 |
2018年 | 208篇 |
2017年 | 198篇 |
2016年 | 294篇 |
2015年 | 314篇 |
2014年 | 349篇 |
2013年 | 424篇 |
2012年 | 564篇 |
2011年 | 628篇 |
2010年 | 390篇 |
2009年 | 337篇 |
2008年 | 395篇 |
2007年 | 369篇 |
2006年 | 373篇 |
2005年 | 291篇 |
2004年 | 228篇 |
2003年 | 207篇 |
2002年 | 155篇 |
2001年 | 154篇 |
2000年 | 155篇 |
1999年 | 175篇 |
1998年 | 146篇 |
1997年 | 129篇 |
1996年 | 122篇 |
1995年 | 116篇 |
1994年 | 111篇 |
1993年 | 75篇 |
1992年 | 76篇 |
1991年 | 86篇 |
1990年 | 53篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 19篇 |
1984年 | 9篇 |
1983年 | 19篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有8334条查询结果,搜索用时 15 毫秒
991.
ZnO nanoparticles were prepared by a simple chemical synthesis route. Subsequently, SiO2 layers were successfully coated onto the surface of ZnO nanoparticles to modify the photocatalytic activity in acidic or alkaline solutions. The obtained particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS) and zeta potential. It was found that ultrafine core/shell structured ZnO/SiO2 nanoparticles were successfully obtained. The photocatalytic performance of ZnO/SiO2 core/shell structured nanoparticles in Rhodamine B aqueous solution at varied pH value were also investigated. Compared with uncoated ZnO nanoparticles, core/shell structured ZnO/SiO2 nanoparticles with thinner SiO2 shell possess improved stability and relatively better photocatalytic activity in acidic or alkaline solutions, which would broaden its potential application in pollutant treatment. 相似文献
992.
In this paper, we investigate the permutation behavior of a class of quadrinomials. Each term of these quadrinomials has a Niho-type exponent, and two sets of coefficient triples making the quadrinomials to be permutations are obtained. We use a substitution to transform the permutation problem into the root distribution problem in the unit circle of certain quadratic and cubic equations. 相似文献
993.
Kaikai Cao Jinru Wang Xiaochen Zeng 《Mathematical Methods in the Applied Sciences》2020,43(2):808-821
Using compactly supported wavelets, Chaubey et al consider L2-risk estimation for mixed density under multiplicative censoring (Chaubey YP, Chesneau C, Doosti H. Adaptive wavelet estimation of a density from mixtures under multiplicative censoring. Statistics, 2015, 49: 638-659). In this paper, we try to discuss Lp-risk (1 ≤ p<∞) estimation for that statistical model of the linear and nonlinear wavelet estimators respectively. Our results can be seen as an extension of the work of Chaubey et al. 相似文献
994.
995.
曾庆怡 《纯粹数学与应用数学》2018,(1):26-41
结合ACS环和p.q-Baer环的定义,本文将p.q-Baer环推广到PCS环,这样在p.q-Baer环和ACS环之间存在一类新的环,PCS环.环R称为PCS-环,如果R的每个主理想的右零化子作为右理想在一个由幂等元生成的右理想中是本质的.PCS-环包括所有的右p.q-Baer环,所有的右FI-扩展环,以及所有的交换的ACS-环.通过研究环主右理想的零化子的性质和模的本质子模的性质,研究了三种环之间的关系,推广了p.q-Baer环的结果,得到了ACS环所没有的结果,同时研究了环的扩张问题,证明了强PCS性质是Morita等价性质. 相似文献
996.
In this paper, we study Hamilton–Souplet–Zhang's gradient estimates for positive solutions to the nonlinear parabolic equation on noncompact Riemannian manifolds, where are two real constants. As an application, we obtain a Liouville-type theorem. 相似文献
997.
Studying the geometric flow plays a powerful role in mathematics and physics. In this paper, we introduce the mean curvature flow on Finsler manifolds and give a number of examples of the mean curvature flow. For Minkowski spaces, a special case of Finsler manifolds, we prove the short time existence and uniqueness for solutions of the mean curvature flow and prove that the flow preserves the convexity and mean convexity. We also derive some comparison principles for the mean curvature flow. 相似文献
998.
本文用预处理Legendre-Galerkin-Chebyshev配置方法来求解二阶变系数Burgers方程,该方法首先对方程进行预处理,然后在空间方向应用Legendre-Galerkin-Chebyshev配置方法,对时间方向采用leap-frog/Crank-Nicolson格式进行离散,这样可使得变系数项和非线性项能够显式计算.我们对该方法进行了误差估计,并通过数值算例验证了算法的有效性和理论分析的正确性. 相似文献
999.
Scanning tunneling microscopy (STM) and spectroscopy (STS) are used in this work to investigate the charge-transfer effect at the molecule-substrate interface of substituted metal phthalocyanines. STS results revealed that the apparent energy gaps for both fluorinated phthalocyanines and unsubstituted phthalocyanines are essentially the same, which agree with the hybrid density functional calculations. More interestingly, there is a systematic shift of the energy level of valence bands, possibly as the result of charge-transfer effect at the molecule-substrate interface. 相似文献
1000.
We report first-principles calculations on the electrical transport properties of two kinds of one-dimensional nanowires: (a) a carbon nanowire (CNW) with alternating single and triple bonds and (b) a boron-nitrogen nanowire (BNNW) with equidistant bonds. We demonstrate the similarity and difference between the carbon nanowire and its boron-nitrogen analogue in the molecular orbital and transport properties, and then explore the potential innovations. The effects of molecular orbitals and nanowire-electrode coupling on the transport properties are analyzed. The cases of the nanowires sandwiched between both nanoscale and bulk electrodes are considered. It suggests that the characteristics of the transmission spectra and the current-voltage characteristics (I-V curves) are determined both by the electrodes and by the molecule as well as their coupling. In particular, the negative differential resistance (NDR) phenomenon is more apparent when the nanowires are positioned between two nanoscale electrodes. The tuning of the transport properties is also probed through the changes of nanowire-electrode separation and the inclusion of a gate voltage. These lead to dramatic variations in the equilibrium conductance, which can be understood from the shift and alignment of the molecular orbital relative to the Fermi level of the electrodes. In the analysis of the effects of nanowire-electrode separation, it shows that the equilibrium conductance has the same variation behavior as that of the projected density of states (PDOS) for CNW, while the localized molecular orbitals of BNNW result in its conductance varies differently from its PDOS. The different molecular orbital characteristics near the Fermi level of these two kinds of nanowires underlie their different transport properties. 相似文献