全文获取类型
收费全文 | 16704篇 |
免费 | 2868篇 |
国内免费 | 2447篇 |
专业分类
化学 | 12352篇 |
晶体学 | 299篇 |
力学 | 985篇 |
综合类 | 177篇 |
数学 | 1798篇 |
物理学 | 6408篇 |
出版年
2024年 | 73篇 |
2023年 | 329篇 |
2022年 | 614篇 |
2021年 | 620篇 |
2020年 | 634篇 |
2019年 | 704篇 |
2018年 | 576篇 |
2017年 | 563篇 |
2016年 | 756篇 |
2015年 | 790篇 |
2014年 | 1006篇 |
2013年 | 1329篇 |
2012年 | 1521篇 |
2011年 | 1670篇 |
2010年 | 1156篇 |
2009年 | 1130篇 |
2008年 | 1147篇 |
2007年 | 1104篇 |
2006年 | 911篇 |
2005年 | 805篇 |
2004年 | 655篇 |
2003年 | 509篇 |
2002年 | 483篇 |
2001年 | 428篇 |
2000年 | 390篇 |
1999年 | 296篇 |
1998年 | 231篇 |
1997年 | 186篇 |
1996年 | 193篇 |
1995年 | 158篇 |
1994年 | 171篇 |
1993年 | 126篇 |
1992年 | 126篇 |
1991年 | 105篇 |
1990年 | 99篇 |
1989年 | 86篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 43篇 |
1984年 | 30篇 |
1983年 | 19篇 |
1982年 | 11篇 |
1981年 | 14篇 |
1980年 | 8篇 |
1979年 | 14篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
BAHADURASYMPTOTICEFFICIENCYINASEMIPARAMETRICREGRESSIONMODEL¥LIANGHUA;CHENGPINGAbstract:TheauthorSgiveMLEθ1MLofθ1inthemodelY=θ... 相似文献
192.
We present in this paper a model study on the “order-by-disorder” process in the cyclic phase of spin-2 condensate, which forms a family of incommensurable, spiral degenerate ground states. On the basis of the ordering mechanism of entropic splitting, it is demonstrated that the energy corrections resulting from quantum fluctuations of disorder lift the accidental degeneracy of the cyclic configurations and thus lead to an eventual spiral order called the cyclic order. The order-by-disorder phenomenon is then realized even if the magnetic field exists. Finally, we show that our theoretic observations can be verified experimentally by direct detection of the cyclic order in the 87Rb condensate of a spin-2 manifold with a weak magnetic field. 相似文献
193.
Wenkai Liang Zheng Chen Fan Yang Huiqiang Zhang 《Proceedings of the Combustion Institute》2013,34(1):695-702
The effects of Soret diffusion on premixed syngas/air flames at normal and elevated temperatures and pressures are investigated numerically including detailed chemistry and transport. The emphasis is placed on assessing and interpreting the influence of Soret diffusion on the unstretched and stretched laminar flame speed and Markstein length of syngas/air mixtures. The laminar flame speed and Markstein length are obtained by simulating the unstretched planar flame and positively-stretched spherical flame, respectively. The results indicate that at atmospheric pressure the laminar flame speed of syngas/air is mainly reduced by Soret diffusion of H radical while the influence of H2 Soret diffusion is negligible. This is due to the facts that the main reaction zone and the Soret diffusion for H radical (H2) are strongly (weakly) coupled, and that Soret diffusion reduces the H concentration in the reaction zone. Because of the enhancement in the Soret diffusion flux of H radical, the influence of Soret diffusion on the laminar burning flux increases with the initial temperature and pressure. Unlike the results at atmospheric pressure, at elevated pressures the laminar flame speed is shown to be affected by the Soret diffusion of H2 as well as H radical. For stretched spherical flame, it is shown that the Soret diffusion of both H and H2 should be included so that the stretched flame speed can be accurately predicted. Similar to the laminar flame speed, the Markstein length is also reduced by Soret diffusion. However, the reduction is found to be mainly caused by Soret diffusion of H2 rather than that of H radical. Moreover, the influence of Soret diffusion on the Markstein length is demonstrated to decrease with the initial temperature and pressure. 相似文献
194.
In this paper, we present a generic mode theory for the three-layer cylindrical waveguides consisting of three arbitrary material mediums. Based on derived eigenvalue equations of the TE, TM, and hybrid modes, the mode conditions of metal/dielectric-coated terahertz hollow waveguides are extracted. In addition, we quantitatively describe both the effective refractive indexes and the loss characteristics of the aurum/polystyrene-coated terahertz hollow waveguides operating at the TE01, TM01, and HE11 modes. It is indicated that the loss coefficient of the TE01 mode can be much lower than that of the TM01, and HE11 modes, and, especially, can tend to that of the terahertz wave in air. So the TE01 mode is very significant for the hollow waveguides in term of low loss propagating of the terahertz wave. We expect these results to enable a variety of new long-distance THz applications in sensing, detecting and communicating. 相似文献
195.
Development of Two‐Channel Phosphorescent Core–Shell Nanoprobe for Ratiometric and Time‐Resolved Luminescence Imaging of Intracellular Oxygen Levels 下载免费PDF全文
196.
Now Ground penetrating radar (GPR) nondestructive testing methods have been applied to many fields of physics. But traditional electromagnetic methods (usually based on least square and local iteration) just roughly give the information of location, level and quality. In this paper we consider inverse electromagnetic problem which is concerned with the estimation of electric conductivity of Maxwell’s equations. A wavelet multilevel representation is proposed to inversion of GPR nondestructive testing. Once we decompose the objective functional onto different levels from the smallest to the largest, there are very few local minimum on the largest level component of the problem. Then local convergent Gauss-Newton method could easily find the global minimum on this level which is close to the global optimization solution on the second largest level. So, Gauss-Newton method with initial value which is solved on the largest level has serious possibility to find the global minimum of the second largest level. Repeating this step one could find the global optimization solution of the original inverse problem. On each level, the stable and fast local convergent Gauss-Newton method is carried out. Results exhibits clear advantages over damping Gauss-Newton method and testify that it is an available method, especially on aspects of wide convergence and precision. 相似文献
197.
Liang Qiu Gang Tang Xianqing Yang Zhipeng Xun Bin Ye Anmin Wang 《International Journal of Theoretical Physics》2014,53(8):2769-2777
The effects of decoherence on quantum discord of two-qutrit system under the influence of multilocal, collective and global depolarising noises are investigated. Sudden change of quantum discord with the decoherence parameter and the initial state parameter occurs for the qutrits being coupled to multilocal or global depolarising noises. On the other hand, decoherence cannot induce sudden change of quantum discord when the system is collectively coupled to the depolarising noise. In addition, the local unitary transformation can alter the region in which the phenomenon of sudden change exists. 相似文献
198.
基于高功率激光装置对脉冲氙灯工程运行可靠性的要求,利用现有的能源模块开展了氙灯放电考核实验。实验结果表明:虽然氙灯运行在安全的能量负载水平,当能源模块单个放电回路的峰值功率超过300 MW时,氙灯石英玻璃管壁存在热损伤风险。肉眼观察到管壁损伤后在反射器对侧的灯管内壁出现乳白色沉积层。经扫描电镜和X射线光电子能谱测试分析,证实热损伤形成的乳白色沉积物为二氧化硅。为探究管壁热损伤机制,采用高速摄影观测了氙灯放电等离子体沟道发展过程。图像显示放大器内金属反射器的几何形状对放电沟道的分布产生了显著影响,尤其是在侧灯箱,灯内电弧沟道会靠近反射器一侧集中分布,因此,导致等离子体对灯管的偏烧。当放电峰值功率超过石英热负载极限时,管壁表面二氧化硅材料会被烧蚀至蒸发、气化,并随后沉积在灯管较冷部位。研究结果表明放电回路的放电峰值功率过高、放大器内金属反射器均会对氙灯造成热损伤。 相似文献
199.
本文建立了B值鞅的极大函数f,平削函数fp^#,fp^#的凸Φ-不等式,反过来用这些不等式刻划了Banach空间的凸性和光滑性,同时给出了超自反空间以及与Hilbert空间同构的Banach空间的特征。本文的结论推广了一些熟知的重要结果。 相似文献
200.
用界面单元法分析复合材料界面力学性能 总被引:11,自引:1,他引:11
本文利用界面单元的固有特性,将其用来模拟复合材料中纤维与基体之间的界面特征,计算了一个沿X轴方向纤维周期排列的单尾板,在横向载荷作用下的应力分布问题.给出了三相(纤维、基体和界面)特性各种配比时应力分布等高线图以及通过界面时径向应力σr的变化情况,反映了界面特性对应力分布的影响. 相似文献