全文获取类型
收费全文 | 1675篇 |
免费 | 61篇 |
国内免费 | 78篇 |
专业分类
化学 | 286篇 |
晶体学 | 2篇 |
力学 | 146篇 |
综合类 | 3篇 |
数学 | 1040篇 |
物理学 | 337篇 |
出版年
2023年 | 19篇 |
2022年 | 17篇 |
2021年 | 27篇 |
2020年 | 22篇 |
2019年 | 40篇 |
2018年 | 35篇 |
2017年 | 42篇 |
2016年 | 42篇 |
2015年 | 44篇 |
2014年 | 89篇 |
2013年 | 206篇 |
2012年 | 59篇 |
2011年 | 121篇 |
2010年 | 101篇 |
2009年 | 134篇 |
2008年 | 108篇 |
2007年 | 128篇 |
2006年 | 66篇 |
2005年 | 69篇 |
2004年 | 59篇 |
2003年 | 46篇 |
2002年 | 41篇 |
2001年 | 24篇 |
2000年 | 26篇 |
1999年 | 29篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 22篇 |
1995年 | 30篇 |
1994年 | 14篇 |
1993年 | 22篇 |
1992年 | 10篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有1814条查询结果,搜索用时 0 毫秒
21.
Let ∑, Г be two n-by-n diagonal matrices with σi,γi as their diagonals. For the inverse eigenvalue problem: look for y∈Rn such that Г + yyT is similar to ∑, we prove thatu also the sufficient condition for the solvability of this inverse problem. Its solution (set) is given explicitly. In some case, the problem is unstable. But we prove that the sums of the square of some contigious components keep stable, i.e., small sum keeps small, large sum has a small relative perturbation, see Theorem 3. 相似文献
22.
本文利用奇异积分方程理论,对于具有非零边界条件的球对称模型的散射裂为函数,给出了直接求妥方法并给出了解的明显表达式。 相似文献
23.
We make first report on inverse chaos synchronization between bidirectionally non-linearly and linearly coupled variable multiple time delay laser systems governed by the Ikeda model. The results are of certain importance in secure chaos-based communication systems. 相似文献
24.
Ki Wan Kim Seung Wook Baek 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,108(3):423-439
An inverse radiation problem was considered to estimate boundary conditions such as temperature distribution and emissivity in axisymmetric absorbing, emitting, and scattering medium, given the measured incident radiative heat fluxes. The finite-volume method was employed to solve a direct radiative transfer equation for a two-dimensional axisymmetric geometry. Various parameter estimators, such as conjugate-gradient method, hybrid genetic algorithm, and finite-difference Newton method, were employed to solve the inverse problems, while discussing their performances in terms of estimation accuracy and computational efficiency. Based on this, we proposed, as a best inverse analysis tool, a new combined method that adopted the hybrid genetic algorithm as an initial value selector and used the finite-difference Newton method as a parameter estimator. 相似文献
25.
26.
设计了一款用于医疗方面的视场为74°的电子内镜物镜.电子内镜外径为8 mm从而实现无麻醉,内镜前端可弯曲来实现无盲区检测.物镜有效焦距为4 mm,后工作距为4.8 mm.系统的畸变最大值少于4%,场曲最大值为0.27 mm.为了提高成像质量,将非球面引入此五片镜系统.所设计的光学系统尤其适用于0.25英寸CCD像传感器,且显示模式为SVGA. 相似文献
27.
C.E. Siewert 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,72(4):299-313
Analytical techniques are used to solve a class of inverse radiative-transfer problems relevant to finite and semi-infinite plane-parallel media. While the assumption of isotropic scattering is made, diffuse reflection is allowed at the surface, for the semi-infinite case, and at both surfaces for the case of a finite layer. For the general case based on a semi-infinite medium, a cubic algebraic equation is used to define the basic result, but for the specific case of a semi-infinite medium illuminated by a constant incident distribution of radiation, very simple exact expressions are developed for the albedo for single scattering ? and the coefficient for diffuse reflection ρ. Analytical results are also developed (again in terms of a cubic algebraic equation) for the case of a finite layer with equal reflection coefficients relevant to the two surfaces. For the general case of a finite layer with unequal reflection coefficients, two specific formulations are given. The first algorithm is based on a system of three quadratic algebraic equations for the two reflection coefficients ρ1 and ρ2 and the single-scattering albedo ?. Secondly, an elimination between these three algebraic equations is carried out to yield two coupled algebraic equations for ρ1 and ρ2 plus an explicit expression for ? in terms of ρ1 and ρ2. In addition, an exact expression for τ0, the optical thickness of the finite layer, is developed in terms of ?, ρ1 and ρ2. As is typical with the considered class of inverse problems in radiative transfer, all surface quantities are either specified or considered available from experimental measurements. All basic results are tested numerically. 相似文献
28.
Hongwu Fan Bingxi LiLidan Yang Ruzhu Wang 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(1):75-83
A new inverse radiation analysis is presented for estimating the heat rate and temperature distributions in the combustion region from the information of the temperature and heat flux profiles of wall elements in the system. The Monte Carlo method is employed to solve the radiative heat transfer equation. The inverse radiation problem is posed as a minimization problem of the least squares criterion, which is solved by the conjugate gradient method. The performance of the present technique of inverse analysis is evaluated and the effects of the errors of the absorption coefficient, emissivity and convective heat transfer coefficient on the inverse analysis are investigated. The results show that the present technique is robust and yields accurate estimation even with noisy measurement. 相似文献
29.
Huai-Chun Zhou Yu-Bo HouDong-Lin Chen Chu-Guang Zheng 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(5):605-620
A parallel-plane space filled with absorbing, emitting, isotropically scattering, gray medium is studied in this paper. The boundary intensity and boundary temperature profiles are calculated for the inverse analysis. For the simultaneous estimation of temperature, absorption and scattering coefficient profiles in the medium, the sum of residuals of boundary intensity and temperature after being weighted by a balance factor is minimized through using a Newton-type iteration algorithm and the least-squares method. To avoid over-updating for the parameters, the relative updating magnitude during the iteration process is constrained not to be >0.5. It is shown that the boundary intensity measurement alone is not enough to estimate simultaneously the temperature (source) and the radiative properties (both absorption and scattering coefficients) when the measurement data contain sensitive random errors. The boundary temperature measurement can serve as a necessary supplementation to the boundary intensity to make this kind of inverse radiative transfer problem resolvable. It was shown that a compensation relationship between absorption and scattering coefficients makes it difficult to fix them accurately. Parabolic profiles for the three parameters are used to validate the estimation method. When the optical thickness approaches 4.0, the results for the radiative properties are not acceptable, although the result for temperature profile is reasonable. This means the method needs further improvements. 相似文献
30.
Bjorn Fritzell 《Journal of voice》1992,6(2)
Inverse filtering is a noninvasive method of producing a glottogram thought to reflect the vibratory motions of the vocal fold. The flow glottogram provides information related to the type of phonation, the sound pressure level, the regularity of vocal fold vibrations, and to the presence or absence of vocal fold closure. Limited data, speech samples, filter tuning, and lack of unanimity on waveform display and interpretation have contributed to slow application of the techniques to the clinical population. The author argues the technique has utility in both diagnosis and treatment 相似文献