全文获取类型
收费全文 | 1095篇 |
免费 | 39篇 |
专业分类
化学 | 787篇 |
晶体学 | 8篇 |
力学 | 34篇 |
数学 | 83篇 |
物理学 | 222篇 |
出版年
2023年 | 8篇 |
2022年 | 24篇 |
2021年 | 22篇 |
2020年 | 15篇 |
2019年 | 23篇 |
2018年 | 5篇 |
2017年 | 7篇 |
2016年 | 20篇 |
2015年 | 26篇 |
2014年 | 46篇 |
2013年 | 43篇 |
2012年 | 68篇 |
2011年 | 88篇 |
2010年 | 51篇 |
2009年 | 71篇 |
2008年 | 87篇 |
2007年 | 69篇 |
2006年 | 67篇 |
2005年 | 46篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 15篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 13篇 |
1995年 | 10篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1974年 | 12篇 |
1973年 | 12篇 |
1964年 | 2篇 |
排序方式: 共有1134条查询结果,搜索用时 0 毫秒
91.
Darius H. Torchinsky David Hsieh J.L. Luo Nuh Gedik 《Journal of Physics and Chemistry of Solids》2011,72(5):519-522
We report on band-dependent quasiparticle dynamics in the hole-doped Ba-122 pnictides measured by ultrafast pump-probe spectroscopy. In the superconducting state of the optimal and over hole-doped samples, we observe two distinct relaxation processes: a fast component whose decay rate increases linearly with excitation density and a slow component whose relaxation is independent of excitation strength. We argue that these two components reflect the recombination of quasiparticles in the two hole bands through intraband and interband processes. We also find that the thermal recombination rate of quasiparticles increases quadratically with temperature in all samples. The temperature and excitation density dependence of the decays indicates fully gapped hole bands and nodal or very anisotropic electron bands. 相似文献
92.
Numerical experiments with several variants of the original weighted essentially non‐oscillatory (WENO) schemes (J. Comput. Phys. 1996; 126 :202–228) including anti‐diffusive flux corrections, the mapped WENO scheme, and modified smoothness indicator are tested for the Euler equations. The TVD Runge–Kutta explicit time‐integrating scheme is adopted for unsteady flow computations and lower–upper symmetric‐Gauss–Seidel (LU‐SGS) implicit method is employed for the computation of steady‐state solutions. A numerical flux of the variant WENO scheme in flux limiter form is presented, which consists of first‐order and high‐order fluxes and allows for a more flexible choice of low‐order schemes. Computations of unsteady oblique shock wave diffraction over a wedge and steady transonic flows over NACA 0012 and RAE 2822 airfoils are presented to test and compare the methods. Various aspects of the variant WENO methods including contact discontinuity sharpening and steady‐state convergence rate are examined. By using the WENO scheme with anti‐diffusive flux corrections, the present solutions indicate that good convergence rate can be achieved and high‐order accuracy is maintained and contact discontinuities are sharpened markedly as compared with the original WENO schemes on the same meshes. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
93.
94.
In this paper, we develop a deterministic inventory model for deteriorating items with two warehouses by minimizing the net present value of the total cost. Deterioration rates of items in the two warehouses may be different. In addition, we allow for shortages and complete backlogging. We then prove that the optimal replenishment policy not only exists but also is unique under some condition. Further, the result reveals that the reorder interval based on the average total cost, if it exists, must be longer than that derived using net present value. Finally, we use Yang’s [H.L. Yang, European Journal of Operational Research 157 (2004) 344–356] numerical example to illustrate the model and conclude the paper with suggestions for possible future research. 相似文献
95.
Bi-Zen Hsieh Hung-Yi Chuang Liang Chao Ying-Jie Huang Po-Hao Tseng Tar-Hwa Hsieh Yu-Kai Han Ko-Shan Ho 《Polymer Degradation and Stability》2008,93(5):983-989
The first-order thermal transitions including side-chain melting, crystal-LC, biphasic chimney-like, and isotropic transitions of poly(n-undecyl isocyanate) (PUDIC) were investigated by varying its thermal history. After annealing at 140 °C for different periods of time, it leads to different degrees of backbiting degradation into n-undecyl isocyanurate trimer which behaves as a solvent for the rest non-degraded/rigid PUDIC to change into a lyotropic LC from thermotropic transition. Based on the degree of degradation, various amounts of trimers are present and the PUDIC demonstrates different types of thermal transitions found in DSC thermograms due to the variation of the non-degraded PUDIC concentration in solvent trimers. Finally, a phase diagram includes all types of crystallines, LC, and isotropic regions can be drawn according to the DSC thermograms. 相似文献
96.
97.
Tsai YH Hsieh YH Huang YB Chang JS Huang CT Wu PC 《Chemical & pharmaceutical bulletin》2010,58(11):1461-1465
The objective of this work was to develop a safe and effective delivery vehicle for topical treatment of gemcitabine. The physicochemical properties, drug release rate, drug level in plasma and bladder, and histological changes of tissue after drug administration were investigated. The electrical conductivity, mean size, and viscosity of drug-loaded microemulsions were 0.8-102.0 μS/cm, 116.8-322.5 nm, and 42.9-105.0 cps×103, respectively. Gemcitabine loaded microemulsions showed a slower and sustained release. After intravesical administration of aqueous control and microemulsions treated, the drug concentrations in plasma were 15.11 μg/ml and 2.81-12.82 μg/ml, respectively, and the accumulation in bladder were 18.27 μg and 9.12-64.16 μg, respectively. Microemulsions slightly decreased the systemic absorption and significantly enhanced the accumulation in bladder tissue. Moreover, the preliminary toxicity studies revealed no overt adverse histological changes or tissue irritation by the microemulsion application. Therefore, the microemulsions were suggested to be a promising drug carrier for intravesical chemotherapy. 相似文献
98.
A laser-based measurement system for evaluation of the scraping workpiece quality that can eliminate contact-induced measurement errors and increase measurement accuracy is proposed. The laser-based measurement system comprises a light-scattering-type triangulation laser, a computer numerical control (CNC) machine tool, and an analog-to-digital (A/D) card. The triangulation laser measures the depth of the scraping spots and the CNC machine tool locates their position. The 3D data of the scraping workpiece is then drawn using the least squares method. Cast iron and Turcite workpieces can be measured. Five parameters of the scraping workpiece, namely peak points per square inch, percentage of points, distribution of heights of points or depth of surroundings, edge shape of the grooves, and flatness, can be evaluated. The scanning rate and sampling rate of the laser-based measurement system are 100 mm/s and 10 KHz, respectively. In the future, an appliance machine based on the proposed system will be designed for the on-line detection of scraping workpieces. 相似文献
99.
100.
Po-Hsun Hsieh 《Geometriae Dedicata》2003,97(1):99-113
We study a nonidentity transvection (i.e. (strictly) hyperbolic isometry) or nonidentity Heisenberg translation f of complex hyperbolic space H
n and a Dirichlet polyhedron P of the cyclic group f. We have four main results: (a) If z & in H
n and the axis of a nonidentity transvection are not complex collinear, then, roughly speaking, any two distinct 'naturally arising' geodesics passing through z are not complex collinear. (b) If g is also a transvection or Heisenberg translation of H
n and z & in H
n such that f(z)=g(z) and f
–1(z)=g
–1(z), then f=g. (c) We classify all this kind of polyhedra up to congruence in H
n. (d) We obtain an equivalent condition for P to be cospinal (which means that the complex spines of the two sides of P coincide) in terms of the distance of the spines of the two sides of P. 相似文献