全文获取类型
收费全文 | 3766篇 |
免费 | 448篇 |
国内免费 | 250篇 |
专业分类
化学 | 1181篇 |
晶体学 | 55篇 |
力学 | 608篇 |
综合类 | 51篇 |
数学 | 1501篇 |
物理学 | 1068篇 |
出版年
2024年 | 4篇 |
2023年 | 42篇 |
2022年 | 81篇 |
2021年 | 107篇 |
2020年 | 98篇 |
2019年 | 97篇 |
2018年 | 96篇 |
2017年 | 117篇 |
2016年 | 152篇 |
2015年 | 124篇 |
2014年 | 173篇 |
2013年 | 275篇 |
2012年 | 211篇 |
2011年 | 208篇 |
2010年 | 201篇 |
2009年 | 242篇 |
2008年 | 220篇 |
2007年 | 225篇 |
2006年 | 193篇 |
2005年 | 171篇 |
2004年 | 162篇 |
2003年 | 160篇 |
2002年 | 159篇 |
2001年 | 112篇 |
2000年 | 104篇 |
1999年 | 82篇 |
1998年 | 89篇 |
1997年 | 81篇 |
1996年 | 67篇 |
1995年 | 44篇 |
1994年 | 49篇 |
1993年 | 44篇 |
1992年 | 41篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 10篇 |
1988年 | 21篇 |
1987年 | 24篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1975年 | 3篇 |
排序方式: 共有4464条查询结果,搜索用时 46 毫秒
1.
就标准厚度卡片在霍尔传感器的定标方面的应用作了有益的探讨。在纵向测量微小长度时,霍尔片处于磁场边缘位置,其对磁场的梯度更大,即灵敏度更高,且靠中心位置的线性更好。 相似文献
2.
The magnetic skyrmion transport driven by pure voltage-induced strain gradient is proposed and studied via micromagnetic simulation. Through combining the skyrmion with multiferroic heterojunction, a voltage-induced uniaxial strain gradient is adjusted to move skyrmions. In the system, a pair of short-circuited trapezoidal top electrodes can generate the symmetric strain. Due to the symmetry of strain, the magnetic skyrmion can be driven with a linear motion in the middle of the nanostrip without deviation. We calculate the strain distribution generated by the trapezoidal top electrodes pair, and further investigate the influence of the strain intensity as well as the strain gradient on the skyrmion velocity. Our findings provide a stable and low-energy regulation method for skyrmion transport. 相似文献
3.
4.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
Y. Wardi 《Journal of Optimization Theory and Applications》1989,61(3):473-485
A stochastic algorithm for finding stationary points of real-valued functions defined on a Euclidean space is analyzed. It is based on the Robbins-Monro stochastic approximation procedure. Gradient evaluations are done by means of Monte Carlo simulations. At each iteratex
i
, one sample point is drawn from an underlying probability space, based on which the gradient is approximated. The descent direction is against the approximation of the gradient, and the stepsize is 1/i. It is shown that, under broad conditions, w.p.1 if the sequence of iteratesx
1,x
2,...generated by the algorithm is bounded, then all of its accumulation points are stationary. 相似文献
6.
Venansius Baryamureeba 《Numerical Linear Algebra with Applications》2002,9(2):93-106
A sequence of least‐squares problems of the form miny∥G1/2(AT y?h)∥2, where G is an n×n positive‐definite diagonal weight matrix, and A an m×n (m?n) sparse matrix with some dense columns; has many applications in linear programming, electrical networks, elliptic boundary value problems, and structural analysis. We suggest low‐rank correction preconditioners for such problems, and a mixed solver (a combination of a direct solver and an iterative solver). The numerical results show that our technique for selecting the low‐rank correction matrix is very effective. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
7.
线性分式规划最优解集的求法 总被引:5,自引:0,他引:5
薛声家 《应用数学与计算数学学报》2002,16(1):90-96
本文使用多面集的表示定理,导出了线性分式规划最优解集的结构,并给出确定全部最优解的计算步骤。 相似文献
8.
9.
讨论了求解无约束线性最小二乘问题的一种并行单纯形法以及对它的改进算法并行共轭梯度—单纯形法 .算法本身具有很强的并行机制 ,能够充分地发挥并行机快速省时的特点 .本文也对算法做了理论分析 ,对算法的收敛性给予了证明 (在二维情形下 ) .最后做了数值实验 (由于软硬件条件的限制 ,并行算法未能在并行计算机上实现 ,鉴于这种情况 ,我们所做的数值实验均是在串行机上完成的 ) 相似文献
10.
Donghyun Cho Taihyun Chang Apostolos Avgeropoulos Nikos Hadjichristidis 《European Polymer Journal》2003,39(11):2155-2160
Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species. 相似文献