全文获取类型
收费全文 | 7655篇 |
免费 | 1605篇 |
国内免费 | 943篇 |
专业分类
化学 | 5452篇 |
晶体学 | 116篇 |
力学 | 445篇 |
综合类 | 92篇 |
数学 | 866篇 |
物理学 | 3232篇 |
出版年
2024年 | 32篇 |
2023年 | 240篇 |
2022年 | 387篇 |
2021年 | 370篇 |
2020年 | 448篇 |
2019年 | 419篇 |
2018年 | 349篇 |
2017年 | 323篇 |
2016年 | 437篇 |
2015年 | 447篇 |
2014年 | 479篇 |
2013年 | 653篇 |
2012年 | 724篇 |
2011年 | 704篇 |
2010年 | 507篇 |
2009年 | 463篇 |
2008年 | 441篇 |
2007年 | 393篇 |
2006年 | 329篇 |
2005年 | 300篇 |
2004年 | 252篇 |
2003年 | 205篇 |
2002年 | 181篇 |
2001年 | 154篇 |
2000年 | 111篇 |
1999年 | 137篇 |
1998年 | 105篇 |
1997年 | 90篇 |
1996年 | 91篇 |
1995年 | 75篇 |
1994年 | 64篇 |
1993年 | 44篇 |
1992年 | 35篇 |
1991年 | 46篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 14篇 |
1985年 | 13篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1978年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
931.
An arc of a digraph is called universal if and are in a common cycle for any vertex of . In this paper we characterize local tournaments whose every arc is universal. 相似文献
932.
Rui Shen Zhiqing Meng Chuangyin Dang Min Jiang 《Numerical Functional Analysis & Optimization》2017,38(11):1473-1489
In this paper, an algorithm of barrier objective penalty function for inequality constrained optimization is studied and a conception–the stability of barrier objective penalty function is presented. It is proved that an approximate optimal solution may be obtained by solving a barrier objective penalty function for inequality constrained optimization problem when the barrier objective penalty function is stable. Under some conditions, the stability of barrier objective penalty function is proved for convex programming. Specially, the logarithmic barrier function of convex programming is stable. Based on the barrier objective penalty function, an algorithm is developed for finding an approximate optimal solution to an inequality constrained optimization problem and its convergence is also proved under some conditions. Finally, numerical experiments show that the barrier objective penalty function algorithm has better convergence than the classical barrier function algorithm. 相似文献
933.
934.
将层板横截面分为含裂纹区与不含裂纹区,在每一区内,根据夏变函数理论与特征函数展开法,得到了各自区内满足所有支配方程、裂纹表面边界条件与层间连续条件的位移与应力的特征展开式,然后利用分区广义变分原理满足裂纹表面边界以外的边界条件以及两区之间的交界条件,并由此求得奇异场控制量(广义应力强度因子)。 相似文献
935.
Characteristics of elemental carbon and organic carbon in PM10 during spring and autumn in Chongqing, China 总被引:2,自引:0,他引:2
Di Ye Qi Zhao Changtan Jiang Jun Chen Xiaoxing Meng 《中国颗粒学报》2007,5(4):255-260
PM10 (particulate matter with aerodynamic diameter less than 10 μm) samples were collected simultaneously at nine urban sites and one urban background site during two intensive observation campaigns in 2006. Concentrations of elemental carbon (EC) and organic carbon (OC) in PM10 were analyzed using an element analyzer. The characteristics regarding spatial and seasonal distribution patterns of OC and EC concentrations and their contributions to PM10 mass, as well as correlation between OC and EC, were investigated in detail. The average OC and EC concentrations for urban sites were 57.5 ± 20.8 and 8.3 ± 3.9 μg/m^3, respectively, both being around three times higher than those for urban background site. As a whole, EC concentrations did not show distinct seasonal variations, though OC concentrations were generally higher in autumn than in spring. For urban sites, total carbonaceous aerosol (TCA) accounted for 33.2% in spring and 35.0% in autumn of PM10 mass. The OC and EC concentrations were found significantly correlated to each other both in spring and in autumn, implying the existence of similar emission sources such as coal combustion. The OC/EC ratios generally exceeded 2.0, indicating the presence of secondary organic carbon (SOC), whose estimated concentration for urban Chongqing was 26.7 and 39.4μg/m^3, accounting for 48.9 and 61.9% of the total OC observed in the samples, in spring and in autumn, respectively. 相似文献
936.
润滑剂边界滑移及其对弹流润滑特性的影响 总被引:4,自引:7,他引:4
基于润滑剂在弹性流体动力润滑状态下表现出类似塑件固体的非牛顿特性,根据塑性屈服和流体动力润滑理论,建立了考虑润滑剂在固液界面滑移的线接触弹流润滑失效预测模型。计算结果显示:载荷和滑滚比对润滑油膜厚度影响显著;在一定载荷和滑滚比下,润滑油膜将丧失承载能力而破裂。与现有理论及实验数据对比,线接触弹流润滑失效预测模型的计算结果与实验结果具有较好的一致性。 相似文献
937.
The cusped field thruster is a kind of newly developed electric propulsion device. The electric field at the channel exit and the low frequency oscillation were measured by former experiments. While the formation mechanism of them have not been fully interpreted yet. Through studying two distinguishing typical electron paths in the thrusters, a fluid model is built up along two electron paths, and then the model is completed by synthetically analyzing the effect of two electron paths. Time‐averaged electric potential distribution, anode current oscillation curve and time‐synchronized atom density and ion density distribution are obtained by simulation. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
938.
近年来, 自组装纳米结构因为其容易制备、稳定、环保以及与各种功能基团、粒子等的多样结合能力吸引了科学家们的目光, 成为人们研究的热点课题, 在光电池、光催化、水凝胶、药物缓释等方面的实验科学领域得到了广泛的应用. 尤其是光催化方面, 自组装结构的重复性为激子的传递创造了比较良好的条件, 成为众多激子传递平台中的佼佼者. 本文报道了一种以苯丙氨酸二肽纳米管和羧基石墨烯为基础的自组装光吸收催化平台, 对其结构进行研究, 并使用该体系进行了烟酰胺腺嘌呤二核苷酸到它的还原态的催化实验. 该体系的微观结构由纳米管和石墨烯膜复合而成, 羧基石墨烯的存在能够降低纳米管直径, 实现纳米管的形态操控, 石墨烯与多肽纳米管复合纳米结构的存在实现了多通道协同激子传递, 降低了激子传递的距离, 极大增强了催化中心对于激子的接受和使用效率. 在复合了光敏剂和催化中心之后, 该体系具有较高的稳定性, 均一的分散性, 很强的光能吸收和转化能力等性质. 对于从NADP+往NADPH转变的催化实验表明, 该体系有较高的反应速率和催化效率, 并且比两种单一结构催化平台效果之和更好, 实现了一加一大于二的效应, 展现了复合纳米结构光吸收催化平台的巨大潜力和广阔应用前景. 相似文献
939.
940.