全文获取类型
收费全文 | 9160篇 |
免费 | 1226篇 |
国内免费 | 1321篇 |
专业分类
化学 | 5694篇 |
晶体学 | 85篇 |
力学 | 1351篇 |
综合类 | 62篇 |
数学 | 499篇 |
物理学 | 4016篇 |
出版年
2024年 | 25篇 |
2023年 | 115篇 |
2022年 | 271篇 |
2021年 | 288篇 |
2020年 | 381篇 |
2019年 | 324篇 |
2018年 | 292篇 |
2017年 | 378篇 |
2016年 | 390篇 |
2015年 | 366篇 |
2014年 | 473篇 |
2013年 | 742篇 |
2012年 | 588篇 |
2011年 | 639篇 |
2010年 | 484篇 |
2009年 | 549篇 |
2008年 | 514篇 |
2007年 | 566篇 |
2006年 | 477篇 |
2005年 | 495篇 |
2004年 | 420篇 |
2003年 | 351篇 |
2002年 | 312篇 |
2001年 | 310篇 |
2000年 | 248篇 |
1999年 | 227篇 |
1998年 | 203篇 |
1997年 | 170篇 |
1996年 | 154篇 |
1995年 | 149篇 |
1994年 | 122篇 |
1993年 | 90篇 |
1992年 | 82篇 |
1991年 | 73篇 |
1990年 | 65篇 |
1989年 | 41篇 |
1988年 | 46篇 |
1987年 | 33篇 |
1986年 | 31篇 |
1985年 | 31篇 |
1984年 | 31篇 |
1983年 | 11篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 10篇 |
1977年 | 22篇 |
1976年 | 13篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
It is shown that in-situ
166mHo (I = 7) in a spherical single crystal of HoF3 can be used as sensitive internal thermometer to thermally detect NMR (NMR-TDNO) from the 100% abundant stable 165Ho (I = 7/2) nuclei. In addition, new 166mHo NMRON results are reported. Both the 166mHo NMRON and 165Ho NMR-TDNO spectra show three distinct quadrupolar split sub-resonances, in zero applied field. The data is used to make
estimates of the Ho magnetic moments and quadrupole parameters for the 166mHo and 166mHo sites. 相似文献
62.
An algorithm for a time accurate incompressible Navier–Stokes solver on an unstructured grid is presented. The algorithm uses a second order, three‐point, backward difference formula for the physical time marching. For each time step, a divergence free flow field is obtained based on an artificial compressibility method. An implicit method with a local time step is used to accelerate the convergence for the pseudotime iteration. To validate the code, an unsteady laminar flow over a circular cylinder at a Reynolds number of 200 is calculated. The results are compared with available experimental and numerical data and good agreements are achieved. Using the developed unsteady code, an interaction of a Karman vortex street with an elliptical leading edge is simulated. The incident Karman vortex street is generated by a circular cylinder located upstream. A clustering to the path of the vortices is achieved easily due to flexibility of an unstructured grid. Details of the interaction mechanism are analysed by investigating evolutions of vortices. Characteristics of the interactions are compared for large‐ and small‐scale vortex streets. Different patterns of the interaction are observed for those two vortex streets and the observation is in agreement with experiment. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
63.
In order to study cross flow induced vibration of heat exchanger tube bundles, a new fluid–structure interaction model based on surface vorticity method is proposed. With this model, the vibration of a flexible cylinder is simulated at Re=2.67 × 104, the computational results of the cylinder response, the fluid force, the vibration frequency, and the vorticity map are presented. The numerical results reproduce the amplitude‐limiting and non‐linear (lock‐in) characteristics of flow‐induced vibration. The maximum vibration amplitude as well as its corresponding lock‐in frequency is in good agreement with experimental results. The amplitude of vibration can be as high as 0.88D for the case investigated. As vibration amplitude increases, the amplitude of the lift force also increases. With enhancement of vibration amplitude, the vortex pattern in the near wake changes significantly. This fluid–structure interaction model is further applied to simulate flow‐induced vibration of two tandem cylinders and two side‐by‐side cylinders at similar Reynolds number. Promising and reasonable results and predictions are obtained. It is hopeful that with this relatively simple and computer time saving method, flow induced vibration of a large number of flexible tube bundles can be successfully simulated. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
64.
65.
I. Jánossy 《Pramana》2003,61(2):435-445
It is suggested that liquid crystal—polymer interfaces are coupled systems, in which the components mutually influence the
orientational state of each other. The photo-orientation process at liquid crystal-polymer interfaces provides a striking
example of such a coupling. Experiments show that the anisotropic structure generated by polarised light at a polymer surface
is strongly affected by the phase of the liquid crystal covering the polymer. Photo-orientation is significantly more efficient
when the liquid crystal is in the isotropic phase than when it exhibits orientational order. The observations are interpreted
by assuming that in the smectic and nematic phases the liquid crystal stabilises to a large extent polymer chain-segments
aligned parallel to the director, while it blocks the photo-induced formation of chain-segments in the perpendicular direction.
Other situations, in which the coupling between the liquid crystal and the polymer can be important, are also discussed briefly. 相似文献
66.
67.
本文采用二维Ffowcs Williams&Hawkings(FW-H)方程对平行剪切层远声场辐射特性进行了研究。近流场时间精确数据通过计算气动声学(Computational Aeroacoustics,CAA)技术数值模拟获得,声远场信息则通过FW-H方程对近流场内的可穿透积分面进行积分获得。该方法首先采用具有解析解的涡/尾缘干涉问题进行了校核,进一步采用CAA/FW-H匹配技术对二维平行剪切层声辐射问题进行了预测,计算结果表明,积分解与计算域内的CAA数值解吻合较好。 相似文献
68.
We have studied isospin symmetry violation in nuclear reactions by measuring simultaneously the cross-section of the following
two reactionsp +d →3H π+ andp +d →3He π0. The experiment was perfomed at the cooler synchrotron accelerator COSY, Jülich at several beam energies close to the correspondingη production threshold. We also have ongoing programmes onη-nucleus final-state interaction studies viap+6 Li →7 Be +η reactions, high resolution search for dibaryonic resonances and lambda-proton final state interaction studies. The experimental
details and results obtained so far are presented here 相似文献
69.
70.
提出了一种制备偶数个多原子Greenberger-Horne-Zerlinger态的方案,它是基于原子-腔场相互作用.首先n个分离的腔初始时处于真空态,通过双光子转移,把n个腔制备成数态|2>和真空态|o>的缠结态.随后,与腔场发生共振相互作用的2n个等同的原子被分别送入n个腔,通过相互作用后,2n个原子处于GHZ态,而n个腔仍然处于真空态. 相似文献