全文获取类型
收费全文 | 18245篇 |
免费 | 1580篇 |
国内免费 | 1462篇 |
专业分类
化学 | 2806篇 |
晶体学 | 135篇 |
力学 | 1826篇 |
综合类 | 177篇 |
数学 | 2763篇 |
物理学 | 3444篇 |
综合类 | 10136篇 |
出版年
2024年 | 59篇 |
2023年 | 167篇 |
2022年 | 341篇 |
2021年 | 396篇 |
2020年 | 453篇 |
2019年 | 376篇 |
2018年 | 380篇 |
2017年 | 547篇 |
2016年 | 600篇 |
2015年 | 666篇 |
2014年 | 983篇 |
2013年 | 1092篇 |
2012年 | 1053篇 |
2011年 | 1113篇 |
2010年 | 817篇 |
2009年 | 1025篇 |
2008年 | 970篇 |
2007年 | 1132篇 |
2006年 | 1078篇 |
2005年 | 968篇 |
2004年 | 813篇 |
2003年 | 772篇 |
2002年 | 683篇 |
2001年 | 581篇 |
2000年 | 542篇 |
1999年 | 516篇 |
1998年 | 446篇 |
1997年 | 383篇 |
1996年 | 356篇 |
1995年 | 339篇 |
1994年 | 242篇 |
1993年 | 236篇 |
1992年 | 224篇 |
1991年 | 190篇 |
1990年 | 167篇 |
1989年 | 166篇 |
1988年 | 127篇 |
1987年 | 77篇 |
1986年 | 50篇 |
1985年 | 44篇 |
1984年 | 35篇 |
1983年 | 5篇 |
1982年 | 19篇 |
1981年 | 16篇 |
1980年 | 4篇 |
1979年 | 9篇 |
1976年 | 3篇 |
1971年 | 4篇 |
1957年 | 5篇 |
1955年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
51.
Q.J. Zhu 《Journal of Mathematical Analysis and Applications》2007,326(1):708-720
Investment systems are studied using a framework that emphasize their profiles (the cumulative probability distribution on all the possible percentage gains of trades) and their log return functions (the expected average return per trade in logarithmic scale as a function of the investment size in terms of the percentage of the available capital). The efficiency index for an investment system, defined as the maximum of the log return function, is proposed as a measure to compare investment systems for their intrinsic merit. This efficiency index can be viewed as a generalization of Shannon's information rate for a communication channel. Applications are illustrated. 相似文献
52.
设Λ={λn}n∞=1为正的实数数列,且当n→∞时,有λn↘0.本文给出了当λn≤Mn-1/2,n=1,2,…,(其中M>0为一正常数)时Müntz系统{xλn}的有理函数在Lp[0,1]空间的逼近速度,主要结论为Rn(f,Λ) Lp≤CMω(f,n-1/2)Lp,1≤p≤∞. 相似文献
53.
李斌 《数学的实践与认识》2006,36(8):25-30
在分析我国房地产自有资本收益率操作中所存在问题的基础上,论述了自有资本收益率的实质是自有资金直接资本化率,并在房地产持有期小于抵押贷款期以及房地产持有期和土地批租年限相同的两种情况下,推导出了与土地有限期使用制度相适应的房地产资本化率和自有资本收益率的计算方法,提出了利用债务保障比率的取值范围检验资本化率合理性的基本公式. 相似文献
54.
55.
壮泰族群的渊源 总被引:1,自引:0,他引:1
覃圣敏 《广西民族大学学报》2005,(2)
壮泰族群的传统文化有许多共同点。这些共同点的形成,因缘于壮泰同源。两个民族的先民原来共同生活在今广西等地,一直到东汉时期。他们分离的时间,主要在三国两晋南北朝时期。分开以后,由于受到不同文化的影响,逐渐形成了两个不同的民族。这种情况,与远古时期生活在中国大陆和东南亚的三大民族集团的发展正相吻合。 相似文献
56.
Existence of a solution for a Signorini contact problem for Maxwell-Norton materials 总被引:1,自引:0,他引:1
The aim of this article is to study the quasistatic evolutionof a MaxwellNorton three-dimensional viscoelastic solidwith contact constraints. After introducing the appropiate functionalframework, we will discretize the problem in time using an implicitscheme whose resultant variational inequality is well posed.By using monotonicity arguments together with compensated compactnesstechniques, we will prove that the corresponding discrete solutionconverges to a solution of the continuous problem. 相似文献
57.
In this paper the effects of surface roughness and annealing temperature (T) of latex coating films on adhesion are discussed for the different stages of the film formation process. The surface free energy of latex films was assessed in terms of practical work of adhesion (W) (or adherence) using a custom-built adhesion-testing device (ATD), atomic force microscopy (AFM), and contact angle measurements. For preannealed latex films surface roughness averages (Ra) were determined from AFM height images and were related to the values of W obtained from ATD measurements at room temperature. The results obtained using these tests exhibiting surface behavior on different length scales indicate a dependence of the measured adhesion on surface roughness and temperature, as well as on the length scale of the measurements.First preannealed samples were studied, which were obtained by heat treatment above the respective glass transition temperatures (Tg). Increasing the temperature of preannealing resulted in a decrease of the adherence observed in ATD experiments at room temperature. However, on the nanoscale, using AFM, no significant variation of the adherence was observed. This observation can be explained by roughness arguments. Preannealing decreases roughness which results in lower adherence values measured by ATD while for essentially single asperity AFM experiments roughness has an insignificant effect. Specimens were also annealed over a constant period of time (90 min) at different temperatures. At the end of the heat treatment, adhesion was measured at the treatment temperature by ATD. The amplified effect of temperature observed in this case on adherence is attributed to the combination of roughness decrease and increasing test temperature. In a third set of experiments completely annealed samples were studied by ATD as well as by AFM as a function of temperature. With increasing T values ATD showed a decrease in adherence, which is attributed to a decreasing surface free energy of the annealed films at elevated T values. AFM, on the other hand, showed an opposite trend which is assigned to increasing penetration of the tip into the tip/wetting polymer samples versus increasing temperature. Finally, annealing isotherms as a function of time were investigated by ATD in situ at different temperatures. This last set of experiments allowed us to optimize annealing time and temperature to achieve complete curing. 相似文献
58.
59.
文中以强化低温固体界面间的接触导热为出发点 ,实验测定了低温环境下两种金属界面在过度加载前后的接触热导值 ,指出过度加载是一种经济有效的强化导热方法 ,对卸载过程接触热导率大于同次加载过程接触热导的“hysteresis”现象产生机理进行了分析 相似文献
60.