全文获取类型
收费全文 | 1593篇 |
免费 | 182篇 |
国内免费 | 126篇 |
专业分类
化学 | 275篇 |
晶体学 | 4篇 |
力学 | 191篇 |
综合类 | 44篇 |
数学 | 871篇 |
物理学 | 516篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 25篇 |
2021年 | 31篇 |
2020年 | 34篇 |
2019年 | 39篇 |
2018年 | 40篇 |
2017年 | 43篇 |
2016年 | 56篇 |
2015年 | 41篇 |
2014年 | 113篇 |
2013年 | 132篇 |
2012年 | 73篇 |
2011年 | 97篇 |
2010年 | 77篇 |
2009年 | 105篇 |
2008年 | 110篇 |
2007年 | 96篇 |
2006年 | 88篇 |
2005年 | 81篇 |
2004年 | 65篇 |
2003年 | 70篇 |
2002年 | 57篇 |
2001年 | 45篇 |
2000年 | 37篇 |
1999年 | 38篇 |
1998年 | 42篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有1901条查询结果,搜索用时 734 毫秒
991.
Production processes in a wide range of industries rely on modern mixed-model assembly systems, which allow an efficient manufacture of various models of a common base product on the same assembly line. In order to facilitate a just-in-time supply of materials, the literature proposes various sequencing problems under the term “level scheduling”, which all aim at evenly smoothing the part consumption induced by the production sequence over time. Among these approaches, the popular product rate variation (PRV) problem is considered to be an appropriate approximate model, if either (i) all products require approximately the same number and mix of parts or (ii) part usages of all products are (almost completely) distinct. These statements are (iii) further specified by analytical findings, which prove the equivalence of product and material oriented level scheduling under certain conditions. These three prerequisites commonly cited in the literature when justifying the practical relevance of the PRV are evaluated by means of three simple computational experiments and are then discussed with regard to their relevance in practical settings. It is concluded that the PRV is in fact inappropriate for use in today’s real world mixed-model assembly systems. 相似文献
992.
基于模糊距离总变差的模糊识别模型及径流预报应用 总被引:1,自引:0,他引:1
根据待识别样本的加权广义欧氏权距离,基于模糊距离总变差为最小的目标函数,提出了一种新的计算模糊聚类中心矩阵、模糊模式识别矩阵与目标权重的模糊识别模型.该模型具有较好的稳定性,径流中长期预报实例说明是可行的. 相似文献
993.
The total variation model of Rudin, Osher, and Fatemi for image denoising is considered to be one of the best denoising models. Recently, by using the Bregman method, Goldstein and Osher obtained a very efficient algorithm for the solution of the ROF model. In this paper, we give a rigorous proof for the convergence of the Bregman method. We also indicate that a combination of the Bregman method with wavelet packet decomposition often enhances performance for certain texture rich images. 相似文献
994.
Polyaniline (PANI)/glycidyl ether of bisphenol A (SU-8) composite film is elaborated in order to detect ammonia gas. These composite films are characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The sensitivity to ammonia is measured by optical absorption changes. The ammonia sensing properties of PANI/SU-8 composite films are studied, and then are compared to pure PANI films elaborated by chemical way. Experimental results show that the PANI/SU-8 optical sensor has simultaneously a rapid response to ammonia gas and regenerates easily, that is advantageous compared to pure PANI films. 相似文献
995.
996.
We analyze the asymptotic behavior of solutions to nonlinear elliptic equation Δu±|u|q=b(x)f(u) in Ω, subject to the singular boundary condition u(x)=∞ as , where Ω is a smooth bounded domain in RN, for some , and . Our approach employs Karamata regular variation theory combined with the method of lower and supper solution. 相似文献
997.
Let Ω⊂RN(N?3) be a bounded domain with smooth boundary. We show the asymptotic behavior of boundary blowup solutions to non-linear elliptic equation Δu±|∇u|q=b(x)f(u) in Ω, subject to the singular boundary condition u(x)=∞ as dist(x,∂Ω)→0,f is Γ-varying at ∞. Our analysis is based on the Karamata regular variation theory combined with the method of lower and supper solution. 相似文献
998.
999.
By the Karamata regular variation theory and the method of lower and upper solutions, we establish the asymptotic behavior of boundary blow-up solutions of the quasilinear elliptic equation div(|u|p−2u)=b(x)f(u) in a bounded ΩRN subject to the singular boundary condition u(x)=∞, where the weight b(x) is non-negative and non-trivial in Ω, which may be vanishing on the boundary or go to unbounded, the nonlinear term f is a Γ-varying function at infinity, whose variation at infinity is not regular. 相似文献
1000.
遥感方法定量监测植被与气候变化的关系已经成为全球变化研究的一个重要领域。攀西地区是我国长江上游重要的生态屏障,对维持四川乃至我国整体生态环境的稳定具有重要作用。基于攀西地区多年MODIS多光谱数据和气象数据对植被动态变化以及该变化与气候因子的关系进行了探讨。结果显示,NDVI变化和气温、降水呈正相关,其中降水是影响攀西地区植被生长的主要气候因子,NDVI变化与秋季降水量变化呈现出良好的一致性;研究区植被长势与气温和降水存在一定的时滞性,主要体现在前1个月气温和降水对植被长势的影响上。 相似文献