全文获取类型
收费全文 | 783篇 |
免费 | 11篇 |
国内免费 | 1篇 |
专业分类
化学 | 365篇 |
晶体学 | 11篇 |
力学 | 21篇 |
数学 | 58篇 |
物理学 | 340篇 |
出版年
2024年 | 7篇 |
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 17篇 |
2015年 | 14篇 |
2014年 | 29篇 |
2013年 | 68篇 |
2012年 | 42篇 |
2011年 | 48篇 |
2010年 | 41篇 |
2009年 | 32篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 23篇 |
2005年 | 29篇 |
2004年 | 16篇 |
2003年 | 18篇 |
2002年 | 19篇 |
2001年 | 12篇 |
2000年 | 7篇 |
1999年 | 6篇 |
1998年 | 6篇 |
1994年 | 12篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1976年 | 4篇 |
1975年 | 6篇 |
1974年 | 11篇 |
1973年 | 12篇 |
1971年 | 5篇 |
1959年 | 5篇 |
排序方式: 共有795条查询结果,搜索用时 359 毫秒
81.
The present study was conducted to evaluate the adsorption efficiency of synthesized nano zinc oxide (n-ZnO) for the removal of hexavalent chromium (Cr6+). The synthesized sample was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. Batch experiment results revealed that low dose (4 g L?1) of n-ZnO was highly efficient at the initial metal concentration of 9 mg L?1 in acidic conditions (pH 2) at 50 °C for the contact time of 90 min. A Langmuir adsorption isotherm model was found to be best fitted indicating a homogeneous surface and the adsorption followed pseudo-second order kinetics. Intra-particle diffusion was not a rate limiting factor in the present study. Thermodynamic study revealed that the adsorption process was endothermic and spontaneous at all the studied temperatures with increasing randomness. 相似文献
82.
This paper reports on the change in the magnetic and the structural properties of Pt/Cr/Co multilayers due to 1 MeV N+-ion irradiation at room temperature. We observe irradiation induced formation of the CoCrPt ternary alloy phase at a fluence of 1×1016 ions cm?2. Phase formation is accompanied by an enhancement in the coercivity. The enhancement in the coercivity is attributed to inhomogeneous alloying and possible mixing-induced strain. These findings are explained in the light of ion beam induced recoil mixing and ionization events. 相似文献
83.
R. Brajpuriya S. Tripathi S.M. Chaudhari D.M. Phase T. Shripathi U. Pietsch 《Applied Surface Science》2007,253(21):8584-8587
In situ temperature dependent energy-dispersive structural and magnetic study of electron beam evaporated Fe/Al multilayer sample (MLS) has been investigated. The structural studies show the formation of an intermixed FeAl transition layer of a few nanometers thick at the interface during deposition, which on annealing at 300 °C transforms to B2FeAl intermetallic phase. Magnetization decreases with increase in temperature and drops to minimum above 300 °C due to increase in anti-ferromagnetic interlayer coupling and formation of nonmagnetic FeAl phase at the interface. The Curie temperature (Tc) is found to be 288 °C and is much less than that of bulk bcc Fe. 相似文献
84.
We revisit the well-known topics of self- and induced-screening in an otherwise isotropic neutral plasma/colloid. It is pointed out that the standard Debye-Hückel (DH) theory (ignoring finite size effects) suffers from many ambiguities related to net ionic numbers, total charge of the system, role of the electrostatic Gauss law, short-distance behaviour of the potential and incorrectly normalized pair correlation functions. We give a new formulation (incorporating finite size effects) such that ionic numbers are maintained, the total charge of the system has physically correct value, the Gauss law boundary conditions are rigorously obeyed, short-distance behaviour of the potential is guaranteed automatically, and correlation functions are correctly normalized. Numerical differences between the two approaches show up if the screening length μ−1 becomes comparable to the size R of the system. 相似文献
85.
For a given set M of positive integers, a problem of Motzkin asks for determining the maximal density μ(M) among sets of nonnegative integers in which no two elements differ by an element of M. The problem is completely settled when |M|?2, and some partial results are known for several families of M for |M|?3, including the case where the elements of M are in arithmetic progression. We consider some cases when M either contains an arithmetic progression or is contained in an arithmetic progression. 相似文献
86.
Retailers often conduct non-overlapping sequential online auctions as a revenue generation and inventory clearing tool. We build a stochastic dynamic programming model for the seller’s lot-size decision problem in these auctions. The model incorporates a random number of participating bidders in each auction, allows for any bid distribution, and is not restricted to any specific price-determination mechanism. Using stochastic monotonicity/stochastic concavity and supermodularity arguments, we present a complete structural characterization of optimal lot-sizing policies under a second order condition on the single-auction expected revenue function. We show that a monotone staircase with unit jumps policy is optimal and provide a simple inequality to determine the locations of these staircase jumps. Our analytical examples demonstrate that the second order condition is met in common online auction mechanisms. We also present numerical experiments and sensitivity analyses using real online auction data. 相似文献
87.
计及管道边界条件滑移的影响,研究微极流体蠕动泵,经由圆柱形管道输运的Stokes流动.壁面运动的控制方程为正弦波方程.使用润滑理论,得到了轴向速度、微转动向量、流函数、压力梯度、摩擦力和机械效率的解析数值解.用图形表示出构成参数,如像耦合参数、微极参数和表征蠕流泵特性的滑移参数、摩擦力和俘获现象的影响.数值计算表明,当耦合参数较大时,需要蠕动泵的压力更大,而微极参数和滑移参数正相反.俘获团块的大小随耦合参数和微极参数的减小而缩小,而随滑移参数的增大而缩小. 相似文献
88.
In the present paper, photovoltaic studies of dye-sensitized solar cells (DSSCs) based on betacyanin/TiO2 and betacyanin/WO3–TiO2 have been done. The cell performances were compared through I–V curves and wavelength dependant photocurrent measurements for the two new types of DSSCs. The TiO2-coated DSSC showed the photovoltage and photocurrent of 300 mV and 4.96 mA/cm2, whereas the cell employing WO3–TiO2 photoelectrode showed the values 435 mV and 9.86 mA/cm2, respectively. The conversion efficiency of TiO2 based dye-sensitized solar cell was found to be 0.69 %, while WO3–TiO2-based cell exhibited a higher conversion efficiency of 2.2 %. The better performance of the WO3–TiO2 dye-sensitized solar cell photoelectrode is thought to be due to an inherent energy barrier at the electrode/electrolyte interface leading to the reduced recombination of photoinduced electrons. 相似文献
89.
G. K. Singh A. P. Singh V. K. Sharma A. Kapoor K. N. Tripathi 《Optics & Laser Technology》2002,34(3):219-223
A general expression for the change in extraordinary refractive index of the annealed proton exchanged LiNbO3 waveguide has been deduced. The expression deduced explains the experimental results of decrease in change of extraordinary refractive index with annealing. The effect of annealing time has also been incorporated following Cao's model (Cao, Ramaswamy, Srivastava, J. Lightwave Technol. 10 (1992) 1302–1313). The concentration profile of protons in the annealed waveguide has been deduced theoretically, which is consistent with the previous results. The spontaneous polarization has been considered as the central mechanism for change in extraordinary refractive index due to proton exchange with annealing. 相似文献
90.
H. P. Singh D. D. Tripathi R. B. Mishra 《International Journal of Theoretical Physics》1987,26(9):861-872
The equations of magnetohydrodynamics of a perfect fluid are classified with respect to the Coriolis parameter, and all essentially different solutions of rank one are indicated. The geometry of streamlines is discussed. 相似文献