全文获取类型
收费全文 | 7737篇 |
免费 | 731篇 |
国内免费 | 1283篇 |
专业分类
化学 | 4927篇 |
晶体学 | 53篇 |
力学 | 1078篇 |
综合类 | 59篇 |
数学 | 357篇 |
物理学 | 3277篇 |
出版年
2024年 | 25篇 |
2023年 | 173篇 |
2022年 | 165篇 |
2021年 | 192篇 |
2020年 | 219篇 |
2019年 | 163篇 |
2018年 | 184篇 |
2017年 | 291篇 |
2016年 | 320篇 |
2015年 | 269篇 |
2014年 | 360篇 |
2013年 | 649篇 |
2012年 | 408篇 |
2011年 | 498篇 |
2010年 | 392篇 |
2009年 | 497篇 |
2008年 | 521篇 |
2007年 | 536篇 |
2006年 | 469篇 |
2005年 | 439篇 |
2004年 | 402篇 |
2003年 | 298篇 |
2002年 | 295篇 |
2001年 | 250篇 |
2000年 | 217篇 |
1999年 | 217篇 |
1998年 | 188篇 |
1997年 | 173篇 |
1996年 | 151篇 |
1995年 | 128篇 |
1994年 | 138篇 |
1993年 | 92篇 |
1992年 | 78篇 |
1991年 | 65篇 |
1990年 | 41篇 |
1989年 | 51篇 |
1988年 | 33篇 |
1987年 | 29篇 |
1986年 | 18篇 |
1985年 | 17篇 |
1984年 | 20篇 |
1983年 | 3篇 |
1982年 | 28篇 |
1981年 | 18篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有9751条查询结果,搜索用时 31 毫秒
1.
2.
Gustavo A.Carri 《高分子科学》2015,33(4):523-539
We revisit the Simha-Somcynsky model of polymer fluids with the purpose of developing novel theoretical and computational approaches to simplify and speed up its solution as well as the fitting of experimental data, and decrease its level of mathematical complexity. We report a novel method that allows us to solve one of the two equations of the model exactly, thus putting the level of mathematical difficulty on a par with the one of other models for polymer fluids. Moreover, we describe a computational algorithm capable of fitting all five parameters of the model in an unbiased way. The results obtained reproduce literature results and fit experimental pressure-volume-temperature and solubility parameter data for three polymers very accurately. Moreover, the new techniques allow for the investigation of the model at very low temperatures. Unexpectedly, the model predicts behaviors that could be interpreted as a glass transition, as routinely observed in dilatometry and differential scanning calorimetry, and a glass phase. We compared the predicted and experimental T g’s for cis poly(1,4-butadiene) and found an excellent quantitative agreement. 相似文献
3.
Demixing during film casting of blends of polystyrene, polymethylmethacrylate, and a symmetric diblock copolymer of styrene and methylmethacrylate is discussed. The concentration fluctuations in the homogeneous solutions were calculated in mean field approximation. The structures in the homogeneous and demixed solutions and in the dry films were measured by small-angle x-ray scattering, and the morphologies of the dry films were characterized by transmission electron microscopy. The structure of the dry blends is evidently already pre-formed in solution. 相似文献
4.
A new unified electroweak model is proposed in this paper. In this unified electroweak model, Higgsmechanism is not used, so no Higgs particle exists in the model. In order to keep the masses of intermediate gaugebosons non-zero, two sets of gauge fields will be introduced. In order to introduce symmetry breaking and to help tointroduce the masses of all fields, a vacuum potential is needed. Except for those terms concerning Higgs particle, thefundamental dynamical properties of this model are similar to those of the standard model. And in a proper limit, thismodel will approximately return to the standard model. The purpose of this paper is not to say that the Higgs particledoes not exist in Nature, it is only to prove that, without a Higgs particle, we can also set up a unified electroweak modelwhich is consistent with present experiments. 相似文献
5.
6.
Wei Shi Yujie J. Ding Changshui Fang Qiwei Pan Qingtian Gu 《Optics and Lasers in Engineering》2002,38(6):361-371
Mode-matching and effective index methods are used to analyze single-mode operation of optical rib polymer waveguides. Their single-mode waveguiding conditions are determined. Single-mode rib waveguides fabricated from guest–host polyetherketone are presented. The estimated propagation loss of straight rib-waveguides is 0.7 dB/cm at 1.55 μm. Furthermore, by using the mode field-transfer matrix method, 2×2 and 4×4 polymer Mach–Zehnder interference switch operating at 1.55 μm wavelength has been designed based on optical multi-mode interference. 相似文献
7.
束晕-混沌的复杂性理论与控制方法及其应用前景 总被引:18,自引:0,他引:18
本文系统论述涉及强流加速器等强流离子束装置中产生的束晕-混沌的复杂性理论与控制方法及其应用前景。强流离子束在核材料生产与增殖、洁净核能、放射性废物嬗变、放射性药物生产、重离子聚变、高能物理、核科学与工程、国防与民用工业和医疗等许多方面都有极其重要的应用潜力和诱人的发展前景。尤其是,近年来强流加速器驱动的放射性洁净核能系统是国内外关注的热门课题,因为它比常规核电更安全、更干净、更便宜。但是,强流离子束形成的束晕-混沌的复杂性现象已引起了国内外广泛关注,需要加以抑制、控制和消除这类现象,解决这一难题已经成为强流离子束应用中的关键问题之一。目前不仅必须深入研究这类束晕-混沌的复杂特性及其产生的物理机制,而且需要研究如何实现对束晕-混沌的有效控制,并寻求和发展其新理论、新方法和新技术。这就向强流离子束物理和非线性-复杂性科学及其技术提出了一系列极富挑战性的新课题。本文结合国内外的研究概况,根据我们多年来的研究成果,特别是我们首创性地提出了一些束晕-混沌的有效控制方法,它们包括:非线性反馈控制法,小波反馈控制法,变结构控制法,延迟反馈控制法,参数自适应控制法等,进行重点的介绍。对上述课题当前的主要进展及相关问题进行系统的总结和比较全面综述的评论。最后,指出该领域今后的研究方向,以推动这个崭新领域的深入研究和应用发展。 相似文献
8.
The transport of monodisperse as well as polydisperse colloid suspensions in a two-dimensional, water saturated fracture with spatially variable and anisotropic aperture is investigated with a particle tracking model. Both neutrally buoyant and dense colloid suspensions are considered. Although flow and transport in fractured subsurface formations have been studied extensively by numerous investigators, the transport of dense, polydisperse colloid suspensions in a fracture with spatially variable and anisotropic aperture has not been previously explored. Simulated snapshots and breakthrough curves of ensemble averages of several realizations of a log-normally distributed aperture field show that polydisperse colloids exhibit greater spreading than monodisperse colloids, and dense colloids show greater retardation than neutrally buoyant colloids. Moreover, it is demonstrated that aperture anisotropy oriented along the flow direction substantially increases colloid spreading; whereas, aperture anisotropy oriented transverse to the flow direction retards colloid movement. 相似文献
9.
10.