全文获取类型
收费全文 | 2261篇 |
免费 | 57篇 |
国内免费 | 90篇 |
专业分类
化学 | 535篇 |
晶体学 | 5篇 |
力学 | 354篇 |
综合类 | 12篇 |
数学 | 685篇 |
物理学 | 817篇 |
出版年
2024年 | 6篇 |
2023年 | 31篇 |
2022年 | 19篇 |
2021年 | 30篇 |
2020年 | 35篇 |
2019年 | 46篇 |
2018年 | 27篇 |
2017年 | 42篇 |
2016年 | 52篇 |
2015年 | 55篇 |
2014年 | 109篇 |
2013年 | 182篇 |
2012年 | 147篇 |
2011年 | 176篇 |
2010年 | 123篇 |
2009年 | 141篇 |
2008年 | 97篇 |
2007年 | 112篇 |
2006年 | 101篇 |
2005年 | 86篇 |
2004年 | 72篇 |
2003年 | 66篇 |
2002年 | 50篇 |
2001年 | 50篇 |
2000年 | 34篇 |
1999年 | 48篇 |
1998年 | 40篇 |
1997年 | 50篇 |
1996年 | 48篇 |
1995年 | 20篇 |
1994年 | 40篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 15篇 |
1989年 | 8篇 |
1988年 | 18篇 |
1987年 | 24篇 |
1986年 | 9篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有2408条查询结果,搜索用时 15 毫秒
1.
Multi-quantum well heterostructures (MQWHs) of the novel Ga(NAsP)/GaP material system have been grown, pseudomorphically strained to GaP-substrate. The crystalline perfection is verified by transmission electron microscopy (TEM). For As-concentrations in excess of about 70%, a direct band structure and adequate luminescence efficiency for laser device application is observed. Temperature-dependent photoluminescence (PL) investigations show the influence of carrier localisation and non-radiative recombination processes typical for dilute nitride materials. With rising N content in the active material, the emission wavelength shifts towards longer wavelength, leading to Ga(NAs)/GaP MQW structures with photon energies below the indirect band gap of silicon (Si). At the same time the luminescence intensity drops due to an increase in non-radiative carrier traps and/or structural degradation. 相似文献
2.
3.
Semra Harmandar 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):395-407
A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing-emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing-emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach. 相似文献
4.
5.
郭飞 《应用数学与计算数学学报》1997,11(1):19-26
Wilson,Han和Powell提出的序列二次规划方法(简称SQP方法)是求解非线性规划问题的一个著名方法,这种方法每次迭代的搜索方向是通过求解一个二次规划子问题得到的,本文受[1]启发,得到二次规划子问题的一个近似解,进而给出了一类求解线性约束非线性规划问题的可行方向法,在约束集合满足正则性的条件下,证明了该算法对五种常用线性搜索方法具有全局收敛性。 相似文献
6.
Man Young Kim Seung Wook Baek 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,90(3-4):377-388
Radiative heat transfer in an axisymmetric enclosure with absorbing, emitting, and scattering medium is studied here by using the different methods such as MDOM, FVM, and MFVM with emphasis on the treatment of angular derivative term, which appears in curvilinear coordinates due to angular redistribution. After final discretization equation for MFVM is introduced by using the step scheme and directional weights, the present approach is validated by applying it to three different benchmarking problems with absorbing, emitting, and scattering medium. All of the results presented here support its accuracy as well as moderate efficiency. Finally, the present approaches are applied to a truncated cone-shaped enclosure as a body-fitted geometry case. 相似文献
7.
In this paper we prove existence results for semilinear neutral functional differential inclusions with finite or infinite
delay in Banach spaces. Our theory makes use of analytic semigroups and fractional powers of closed operators, integrated
semigroups and cosine families.
相似文献
8.
9.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
10.
Tetsuro Saeki Takahiro Tamesue Shizuma Yamaguchi Kazuya Sunada 《Applied Acoustics》2004,65(2):203-210
This paper focuses on masking speech with meaningless steady noise as a way of realizing a comfortable sound environment. As a basis for research, meaningless steady noise at minimum sound pressure levels for masking of male or female meaningful speech is considered, based on psychological experiments using a method of adjustment. From the results, band-limited pink noise can be selected as the most effective noise for masking of speech. In the case of speech with a lower sound pressure level, the sound pressure level of the meaningless steady noise needs to be a little higher. 相似文献