全文获取类型
收费全文 | 21357篇 |
免费 | 3715篇 |
国内免费 | 2822篇 |
专业分类
化学 | 10079篇 |
晶体学 | 246篇 |
力学 | 1043篇 |
综合类 | 365篇 |
数学 | 1694篇 |
物理学 | 6562篇 |
无线电 | 7905篇 |
出版年
2024年 | 95篇 |
2023年 | 531篇 |
2022年 | 799篇 |
2021年 | 946篇 |
2020年 | 789篇 |
2019年 | 763篇 |
2018年 | 685篇 |
2017年 | 758篇 |
2016年 | 901篇 |
2015年 | 1022篇 |
2014年 | 1208篇 |
2013年 | 1482篇 |
2012年 | 1761篇 |
2011年 | 1745篇 |
2010年 | 1457篇 |
2009年 | 1465篇 |
2008年 | 1447篇 |
2007年 | 1332篇 |
2006年 | 1300篇 |
2005年 | 1172篇 |
2004年 | 809篇 |
2003年 | 642篇 |
2002年 | 652篇 |
2001年 | 554篇 |
2000年 | 546篇 |
1999年 | 450篇 |
1998年 | 331篇 |
1997年 | 310篇 |
1996年 | 311篇 |
1995年 | 253篇 |
1994年 | 227篇 |
1993年 | 176篇 |
1992年 | 157篇 |
1991年 | 143篇 |
1990年 | 122篇 |
1989年 | 107篇 |
1988年 | 87篇 |
1987年 | 54篇 |
1986年 | 57篇 |
1985年 | 49篇 |
1984年 | 31篇 |
1983年 | 27篇 |
1982年 | 26篇 |
1981年 | 11篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1975年 | 8篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 24 毫秒
41.
Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications 总被引:1,自引:0,他引:1
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly. 相似文献
42.
43.
C.-C. WANGZ. YE 《Journal of sound and vibration》2002,250(4):723-744
The oscillation of a bubble has many vibrational modes, contributing to different portions in acoustic scattering. Without approximations a priori, an hydrodynamic approach is applied to investigate acoustic scattering by a bubble in water, taking into account the heat exchange and viscosity. The scattering function is derived for a wide range of frequencies. Examples are shown to illustrate the thermal and viscous effects on sound scattering. Comparison is made with three existing models. While these models are known not to be applicable for high frequencies, it is shown here that even in the low-frequency region, there are also noticeable discrepancies between the exact solution and the three existing models with regard to the scattering properties such as the scattering cross-section, and the quality factor of resonant peaks. By numerical simulation, we claim that the discrepancies may be due to the incomplete consideration of the thermal exchange process in the previous models. The approach presented here is valid for any other fluid enclosure in liquids. 相似文献
44.
运用群论及原子分子反应静力学方法,推导了XY(H,Li,Na)分子基态的电子态及相应的离解极限.并采用密度泛函方法(B3LYP)和二次组态相互作用方法(QCISD)优化计算了XY(H,Li,Na)分子基态的平衡结构、振动频率和离解能.使用QCISD/6-311++G(3df,3pd)方法,对XY(H,Li,Na)分子基态进行了单点能扫描计算,采用最小二乘法拟合Murrell-Sorbie函数得到了相应的势能函数和与该基态相对应的光谱常数(Be,αe,ωe和ωexe),计算结果与实验数据符合得相当好. 相似文献
45.
不完全信息群体决策专家权重的集结 总被引:8,自引:5,他引:3
本文对于属性权重信息和属性效用信息都不完全的群体多属性决策问题,通过构造属性值区间和运用系统聚类分析法,对群体决策中的专家进行分类,并确定每位专家的权重. 相似文献
46.
Newton-Leibniz integration rule only applies to commuting functions of continuum variables, while operators made of Dirac’s symbols (ket versus bra, e.g., |q〉〈q| of continuous parameter q) in quantum mechanics are usually not commutative. Therefore, integrations over the operators of type |〉〈| cannot be directly performed by Newton-Leibniz rule. We invented an innovative technique of integration within an ordered product (IWOP) of operators that made the integration of non-commutative operators possible. The IWOP technique thus bridges this mathematical gap between classical mechanics and quantum mechanics, and further reveals the beauty and elegance of Dirac’s symbolic method and transformation theory. Various applications of the IWOP technique, including constructing the entangled state representations and their applications, are presented. 相似文献
47.
Mingxi Fan Kai-Yeung Siu 《Selected Areas in Communications, IEEE Journal on》2002,20(2):303-309
We introduce a dual-mode multiuser detector that dynamically switches its detection mode between matched-filter and decorrelator operations based on the channel characteristics. This detector significantly reduces the overall computational requirement while maintaining similar performance as that of the decorrelator. The switching mechanism of our dual-mode detector is designed by exploiting the performance-complexity tradeoff between the decorrelator and the matched-filter. Extensions of this idea to other types of multiuser detectors are also proposed 相似文献
48.
本文首先将文[1]中的BLD映射推广为弱(L1,L2)-BLD映射,并证明了如下正则性结果:存在两个可积指数 P1=P1(n,L1,L2)<n<q1=q1(n,L1,L2),使得对任意弱(L1,L2)-BLD映射f∈(Ω,Rn),都有f∈(Ω,Rn),即f为(L1,L2)-BLD映射. 相似文献
49.
50.
本文提出了一种基于电子现金的新型支付协议,该协议通过第三方实时核算客户拥有的电子现金,但不进行实时转账。协议模型较好地克服了现有在线支付的交易瓶颈问题以及离线支付中电子现金容易被重用、伪造或篡改的问题,在交易过程中有效地保证了安全性,并且实现了电子现金的原子性、匿名性、可分割性和可验证性。 相似文献