全文获取类型
收费全文 | 1283篇 |
免费 | 107篇 |
国内免费 | 166篇 |
专业分类
化学 | 63篇 |
晶体学 | 2篇 |
力学 | 102篇 |
综合类 | 32篇 |
数学 | 1195篇 |
物理学 | 162篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 15篇 |
2019年 | 26篇 |
2018年 | 31篇 |
2017年 | 39篇 |
2016年 | 39篇 |
2015年 | 31篇 |
2014年 | 59篇 |
2013年 | 111篇 |
2012年 | 89篇 |
2011年 | 75篇 |
2010年 | 73篇 |
2009年 | 83篇 |
2008年 | 95篇 |
2007年 | 96篇 |
2006年 | 97篇 |
2005年 | 61篇 |
2004年 | 55篇 |
2003年 | 71篇 |
2002年 | 57篇 |
2001年 | 48篇 |
2000年 | 37篇 |
1999年 | 41篇 |
1998年 | 40篇 |
1997年 | 33篇 |
1996年 | 25篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 4篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1556条查询结果,搜索用时 578 毫秒
11.
Comparing the volume of the projection body of a double cone and that of the projection body of a ball, we give an explicit counter-example for the Shephard problem of convex bodies in Rn (n ≥ 3) and an affirmative answer to the question of Zhang. 相似文献
12.
13.
This communication considers the steady converging/diverging flow of a non-Newtonian viscous power-law fluid in a round cone. The motion is driven by a sink/source of mass at the origin. It is shown that the problem permits exact similarity solution for a particular value (n=4/3) of the fluid index. In this case a complete set of governing equations can be reduced to an ordinary differential equation, which is solved numerically for different values of the main non-dimensional parameters (the cone angle and the dimensionless sink/source intensity). 相似文献
14.
IntroductionInthispaper,weshallconsiderthefollowingsingularboundaryvalueproblems (BVP)u″ g(t)f(u) =0 , 0 <t<1 ,αu(0 ) -βu′(0 ) =0 , γu(1 ) δu′(1 ) =0 ,(1 )whereα ,β,γ ,δ≥ 0 ,ρ:=βγ αγ αδ>0 ,f∈C([0 ,∞ ) ,[0 ,∞ ) ) ,gmaybesingularatt=0and/ort=1 .Thisproblemarisesnaturallyinthestudyofradiallysymmet… 相似文献
15.
In the United States, the NATO Reference Mobility Model (NRMM) has been used for evaluating military ground vehicle mobility and the Vehicle Cone Index (VCI) has been selected as a mobility metric. VCI represents the minimum soil strength required for a vehicle to consistently make a specific number of passes, usually one or fifty passes. In the United Kingdom, the Mean Maximum Pressure (MMP) has been adopted as a metric for assessing military vehicle cross-country mobility. MMP is the mean value of the maxima occurring under all the wheel stations of a vehicle. Both VCI and MMP are empirically based. This paper presents a review of the basis upon which VCI and MMP were developed, as well as their applications to evaluating vehicle mobility in practice. With the progress in terramechanics and in modelling and simulation techniques in recent years, there is a growing desire to develop physics-based mobility metrics for next generation vehicle mobility models. Based on the review, criteria for selecting physics-based mobility metrics are proposed. Following these criteria, metrics for characterizing military vehicle traction limits and traversability on a given operating area are recommended. 相似文献
16.
17.
János B. Czirok Ákos Tarcsay Pál D. Mezei András Simon László Balázs 《Supramolecular chemistry》2013,25(10-12):722-728
The size limit of substituents allowing O-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R1 on the conformational inversion was investigated by means of 1H NMR. The rotational isomerisation of the parent (R1 = H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies. 相似文献
18.
《先进技术聚合物》2018,29(10):2574-2582
Ternary flame‐retardant modified cyanate ester blends (CEPG and CEPA) are formed by combining triazine compounds (TGIC or TAIC) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide with cyanate ester resin. The curing behaviors, thermal and mechanical properties, and the flame‐retardant properties are investigated. The results show that the CEPG and CEPA blends result in lower curing temperatures and glass transition temperatures than those of neat CE. Both of CEPG and CEPA blends significantly improve the flame‐retardant properties of CE resins, and UL‐94V‐0 rate is achieved for CEPG‐1.0 and CEPA‐0.5. The dielectric constant and loss of CEPA blends are lower than those of CEPG blend with the same phosphors content, and both of them are lower than those of neat CE. Therefore, the ternary flame‐retardant modified cyanate ester blends provide 2 ways for composites of producing printed circuit board with high flame‐retardant property and low dielectric constant and loss. 相似文献
19.
20.
By cone theory and the fixed point index,we study the existence of positive solutions to a three-order boundary value problem with dependence on the first order derivative. 相似文献