全文获取类型
收费全文 | 1032篇 |
免费 | 40篇 |
国内免费 | 54篇 |
专业分类
化学 | 175篇 |
晶体学 | 2篇 |
力学 | 37篇 |
综合类 | 1篇 |
数学 | 641篇 |
物理学 | 270篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 14篇 |
2021年 | 15篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 13篇 |
2017年 | 24篇 |
2016年 | 19篇 |
2015年 | 25篇 |
2014年 | 52篇 |
2013年 | 113篇 |
2012年 | 65篇 |
2011年 | 67篇 |
2010年 | 43篇 |
2009年 | 91篇 |
2008年 | 60篇 |
2007年 | 63篇 |
2006年 | 46篇 |
2005年 | 43篇 |
2004年 | 29篇 |
2003年 | 23篇 |
2002年 | 30篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 21篇 |
1998年 | 24篇 |
1997年 | 19篇 |
1996年 | 20篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有1126条查询结果,搜索用时 15 毫秒
1.
Mark Doyle Susan A. Mulligan Tetsuya Matsuda Gerald M. Pohost 《Magnetic resonance imaging》1992,10(6):887-892
A new “bright blood” strategy, outflow refreshment imaging, is introduced in which a number of overlapping slices are excited in rapid succession. Flowing spins that refresh each overlapped slice portion contribute a bright signal. Additionally, static tissue in each non-overlapped slice portion also yields a bright signal. However, the flow/static contrast is comparable to that produced in inflow refreshment images, and angiograms can be generated by conventional maximum intensity projection processing. The dual ability to visualize angiograms and static tissue images is a major benefit of the strategy. Computer simulations of flow sensitivities and in vivo results are presented which compare the outflow and inflow refreshment imaging strategies. 相似文献
2.
H. Sakuma T. Taniyama K. Ishii Y. Kitamoto Y. Yamazaki 《Journal of magnetism and magnetic materials》2006,300(2):284-292
The order parameter S of Fe–Pt nanoparticles is estimated from X-ray diffraction (XRD) patterns. The total intensity of a diffraction peak is obtained by Rietveld analysis as well as simply integrating the intensity. The Rietveld analysis is found to provide a plausible value of S even for a sample showing an XRD pattern with broad and overlapped peaks. Another order parameter Q, which is obtained from Mössbauer spectra, is introduced, and it is confirmed that Q is equivalent to the probability of Fe atoms being in the L10-type atomic arrangement. The coercivity of Fe–Pt nanoparticles is directly proportional to Q, while it vanishes at S=0.4, indicating that the magnetic property of Fe–Pt nanoparticles has a closer relationship to Q than S. 相似文献
3.
F. Farid 《Linear and Multilinear Algebra》2002,50(3):223-239
An upper bound for the number of components of the numerical range of matrix polynomials is established. We also establish a necessary condition and a sufficient condition for the connectedness of the numerical range of a quadratic selfadjoint matrix polynomial. The boundary of the numerical range of linear matrix polynomials is also considered. 相似文献
4.
Wu Shengjian 《数学年刊B辑(英文版)》1994,15(4):453-462
Suppose that f(z)is a meromorphic function of order λ(0<λ<+∞)and of lower order μ in the plane.Let ρ be a positive number such that μ≤ρ≤λ.(1)If f^(l)(z)(0≤l<+∞)has p(1≤p<+∞)finite nonzero deficient valnes αi(i=1,…,p)with deficiencies δ(αi,f^(l)),then f(z)has a (0,∞)accumulative line of order ≥ρin any angular domain whose vertex is at the origin and whose magnitude is larger than max(π/ρ,2π-4/ρ ∑i=1^p arcsin √δ(αi,f^(l))/2).(2)If f(z) has only p(0<p<+∞)(0,∞),accumulative lines of order≥ρ:arg z=θk(0≤θ1<θ2<…<θp<2π,θp+1=θ1+2π),then λ≤π/ω,where ω=min I≤k≤p(θk+1-θk),provided that f^(l)(z)(0≤l<+∞)has a finite nonzero deficient value. 相似文献
5.
The best-r-point-average (BRPA) estimator of the maximizer of a regression function, proposed in Changchien (in: M.T. Chao, P.E. Cheng (Eds.), Proceedings of the 1990 Taipei Symposium in Statistics, June 28–30, 1990, pp. 63–78) has certain merits over the estimators derived through the estimation of the regression function. Some of the properties of the BRPA estimator have been studied in Chen et al. (J. Multivariate Anal. 57 (1996) 191) and Bai and Huang (Sankhya: Indian J. Statist. Ser. A. 61 (Pt. 2) (1999) 208–217). In this article, we further study the properties of the BRPA estimator and give its convergence rate under some quite general conditions. Simulation results are presented for the illustration of the convergence rate. Some comparisons with existing estimators such as the Müller estimator are provided. 相似文献
6.
High-power operation of diode-pumped fiber lasers at wavelength near 2μm are demonstrated with short length of heavily Tm3 -doped silica glass fibers. With 7-cm long fiber, a laser at near 2 μm is obtained with the threshold of 135 mW, maximum output power of 1.09 W, and slope efficiency of 9.6% with respect to the launched power from a laser diode at 790 nm. The output stability of this fiber laser is within 5%.The dependence of the performance of fiber lasers on the operation temperature and cavity configuration parameters is also investigated. 相似文献
7.
Aleksey K. Alekseev I. Michael Navon 《International Journal of Computational Fluid Dynamics》2013,27(2):113-117
The uncertainty of temperature prediction from the heat flux error is estimated using first and second order adjoint equations. The adjoint codes developed for the inverse heat transfer problems provide the uncertainty estimation for the corresponding forward problems. Numerical tests corroborate the feasibility of fast uncertainty estimation using Hessian maximum eigenvalue obtained via second order adjoint equations. 相似文献
8.
9.
针对环境模拟试验温度控制系统中被控对象存在的非线性、时滞等特点,本文采用区间限幅PID控制算法和模糊PID控制算法对传统控制方法进行了改进。首先为了解决模拟量三通粗调阀调节缓慢的缺点,建立了区间限幅PID控制算法的控制规则表,并将其在PLC中实现。其次提出用模糊PID控制算法来解决电加热器的非线性、大时滞性问题,并结合实际控制经验建立了模糊控制规则表,然后将模糊PID控制算法在PLC中进行实现。最后将限幅PID和模糊PID控制算法应用于某大型环境模拟试验控制系统,实验结果表明利用改进算法对温度控制具有良好的稳定性及精确度。 相似文献
10.
The present paper proposes a new Fin Field Effect Transistor (FinFET) with an amended Channel (AC). The fin region consists of two sections; the lower part which has a rounded shape and the upper part of fin as conventional FinFETs, is cubic. The AC-FinFET devices are proven to have a lower threshold voltage roll-off, reduced DIBL, better subthreshold slope characteristics, and a better gate capacitance in comparison with the C-FinFET. Moreover, the simulation result with three-dimensional and two-carrier device simulator demonstrates an improved output characteristic of the proposed structure due to reduction of self-heating effect. Due to the rounded shape of the lower fin region and decreasing corner effects there, the heat can flow easily, and the device temperature will decrease. Also the gate control over the channel increases due to the narrow upper part of the fin. The paper, thus, attempts to show the advantages of higher performance AC-FinFET device over the conventional one, and its effect on the operation of nanoscale devices. 相似文献