全文获取类型
收费全文 | 1980篇 |
免费 | 82篇 |
国内免费 | 67篇 |
专业分类
化学 | 332篇 |
晶体学 | 14篇 |
力学 | 345篇 |
综合类 | 2篇 |
数学 | 77篇 |
物理学 | 1359篇 |
出版年
2024年 | 4篇 |
2023年 | 29篇 |
2022年 | 25篇 |
2021年 | 47篇 |
2020年 | 38篇 |
2019年 | 23篇 |
2018年 | 30篇 |
2017年 | 30篇 |
2016年 | 37篇 |
2015年 | 50篇 |
2014年 | 46篇 |
2013年 | 268篇 |
2012年 | 86篇 |
2011年 | 137篇 |
2010年 | 73篇 |
2009年 | 114篇 |
2008年 | 116篇 |
2007年 | 99篇 |
2006年 | 94篇 |
2005年 | 74篇 |
2004年 | 55篇 |
2003年 | 58篇 |
2002年 | 57篇 |
2001年 | 54篇 |
2000年 | 61篇 |
1999年 | 39篇 |
1998年 | 53篇 |
1997年 | 15篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 29篇 |
1993年 | 21篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 16篇 |
1989年 | 22篇 |
1988年 | 27篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1982年 | 7篇 |
1981年 | 15篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 4篇 |
排序方式: 共有2129条查询结果,搜索用时 15 毫秒
71.
目的评估胰岛素联合沙格列汀治疗2型糖尿病的有效性和安全性。方法回顾性对照研究50例2型糖尿病患者胰岛素加用沙格列汀或阿卡波糖治疗(48±8)周后血糖水平和血糖波动等指标的变化。结果治疗(48±8)周后,两组血糖、Hb A1c、MAGE均明显下降(P均≤0.001),其中沙格列汀组MAGE的降幅明显大于阿卡波糖组(P=0.024),胃肠道不良反应发生率显著低于阿卡波糖组。结论沙格列汀联合胰岛素具有更强的控制血糖波动的疗效,胃肠道不良反应发生率更低。 相似文献
72.
1.引 言 数值求解不可压缩流体流动问题可以采用原始变量的方程作为控制方程,也可以用涡量一流函数方程作为控制方程.直接求解原始变量的不可压缩 Navier—Stokes方程存在一个主要困难:速度向量在每一时刻都必须满足零散度约束条件,即不可压缩性连续方程.用涡量一流函数方程求解时,连续方程自动满足,所以不存在约束条件的问题,但涡量的边界条件比较难处理,且不易应用于三维问题和带有自由表面或其它流体交界面的问题. 解决上述速度向量必须满足零散度约束条件的困难的方法有:人工压缩法[3,17];压力Pois… 相似文献
73.
74.
波纹板式空冷器阻力与传热特性实验研究 总被引:5,自引:0,他引:5
在可改变风量和热水流量的实验条件下,对波纹板式空冷器的阻力与传热特性进行实验研究。得到了空气侧的阻力降关联式以及两侧的对流换热系数关联式,其适用于热水雷诺数在2000-8000之间、空气雷诺数在2000-10000之间。在相同工况下,比较了波纹板式、光管式和翅片管式空冷器的性能指标,结果表明:迎面风速在2.45-4.1 m/s之间,波纹板式空冷器传热系数达到100-160 W/m2/℃;约比光管式提高70%,但只有以管束外表面为基准的翅片管式传热系数的六分之一;板式空冷器单位体积换热量约是翅片管式空冷器的1.5倍,是光管式的15倍;板式空冷器单位功耗换热量约是光管式空冷器的5.5倍,而翅片管式空冷器与光管式空冷器则相差不大。 相似文献
75.
LI Hong-fei JIANG Shi-chun AN Li-jia YU Dong-hong 《高等学校化学研究》2007,23(5):613-621
The calculations presented in this paper are based on the Sanchez-Lacombe(SL)lattice fluid theory.The interaction energy parameter,g12/k,required in this approach was obtained by fitting the cloud points of polystyrene(PS)/methylcyclohexane(MCH)polymer solutions under pressure.The SL lattice fluid theory was used to calculate the spinodals,the binodals,and the Flory-Huggins(FH)interaction parameter of the solutions.The calculated results show that the SL lattice fluid theory can describe the dependences of thermodynamics of PS/MCH solutions on temperature and pressure very well.However,the calculated enthalpy and the excess volume changes indicate that the Clausius-Clapeyron equation cannot be suitable to describe pressure effect on PS/MCH solutions.Further analysis on the thermodynamics of this system under pressure shows that the role of entropy is more important than the excess volume in the present case. 相似文献
76.
77.
F. Thibault K.A. Grabow C.I. Marcus L.A. Robertson M.C. Stoffel 《Journal of Molecular Spectroscopy》2009,256(1):17-2081
Theoretical and experimental values have been determined for the pressure broadening of the ν1 + ν3 band of acetylene by hydrogen and deuterium at 195 K, and experimental values of the pressure shifts have been determined. Theoretical values have been calculated on the basis of a recent potential energy surface using the close coupling scheme. We discuss the detailed contribution of the various rotational angular momenta of the perturbing gas and the ortho and para contribution to the total pressure broadening cross-sections. We give routes to circumvent the computational cost of such calculations. Experimental values have been measured using a tunable diode laser spectrometer assuming a Voigt line shape. These pressure broadening parameters are compared with measurements performed recently at room temperature and with present measurements performed at 195 K in the ν1 + ν3 band of acetylene. A satisfactory agreement is obtained with the present results and available ones at 295 K. 相似文献
78.
Simone Melchionna 《Journal of computational physics》2011,230(10):3966-3976
A method to simulate bodies suspended in a Lattice Boltzmann solvent is proposed. It is based on a generalized reaction force that enforces no-slip boundary conditions at the fluid–body interface as the limiting case of an iterative procedure. A smooth version of the Heaviside function allows to treat spherical particles of arbitrary size and produces smooth hydrodynamic forces as particles move in the continuum. Numerical tests demonstrate the accuracy of the method in reproducing the hydrodynamic field around a single particle and the fluid-mediated forces between pairs of particles. The drag force experienced by a particle moving in a straight channel and at various Reynolds numbers is studied as a non-trivial testcase. 相似文献
79.
The influence of several factors (amplitude of ultrasonic waves, external static pressure, temperature and viscosity of medium) acting, either individually or in combination, on the amount of power transferred to a liquid medium during ultrasonication (power output) was measured by calorimetry. At constant amplitude (150 microns) and pressure (200 kPa), the power output decreased as the temperature was raised. The effect of temperature could be compensated by increasing pressure. The magnitude of the increase in power output due to raising the pressure depended on the pressure range and the treatment temperature. At all temperatures and pressures studied, the power output increased exponentially when the amplitude was increased linearly. The magnitude of this power output did not depend on the temperature or pressure of treatment. At 40 degrees C the magnitude of the increase in power output due to increasing the pressure was not influenced by the amplitude of sonic waves. The power output increased as the viscosity of the medium was increased. The magnitude of this effect did not depend on the amplitude but on the static pressure. 相似文献
80.
R. J. Emrich 《Shock Waves》1996,5(6):327-339
Recollections of activities in the Physics Department of Princeton University leading to the construction and use of the SHOCK
TUBE are recorded. Walker Bleakney was the leader of these activities from 1940 to 1979, and his methods and attitude are
described. Original interferograms made at Princeton show some results obtained. 相似文献