全文获取类型
收费全文 | 43020篇 |
免费 | 2622篇 |
国内免费 | 723篇 |
专业分类
化学 | 22101篇 |
晶体学 | 313篇 |
力学 | 1102篇 |
综合类 | 55篇 |
数学 | 3471篇 |
物理学 | 8150篇 |
无线电 | 11173篇 |
出版年
2023年 | 478篇 |
2022年 | 506篇 |
2021年 | 1024篇 |
2020年 | 905篇 |
2019年 | 917篇 |
2018年 | 847篇 |
2017年 | 814篇 |
2016年 | 1391篇 |
2015年 | 1174篇 |
2014年 | 1675篇 |
2013年 | 2496篇 |
2012年 | 2814篇 |
2011年 | 3045篇 |
2010年 | 2078篇 |
2009年 | 2053篇 |
2008年 | 2799篇 |
2007年 | 2523篇 |
2006年 | 2492篇 |
2005年 | 2243篇 |
2004年 | 1965篇 |
2003年 | 1756篇 |
2002年 | 1604篇 |
2001年 | 1157篇 |
2000年 | 1002篇 |
1999年 | 779篇 |
1998年 | 598篇 |
1997年 | 523篇 |
1996年 | 556篇 |
1995年 | 425篇 |
1994年 | 421篇 |
1993年 | 400篇 |
1992年 | 331篇 |
1991年 | 285篇 |
1990年 | 264篇 |
1989年 | 201篇 |
1988年 | 169篇 |
1987年 | 150篇 |
1986年 | 95篇 |
1985年 | 141篇 |
1984年 | 109篇 |
1983年 | 83篇 |
1982年 | 111篇 |
1981年 | 118篇 |
1980年 | 81篇 |
1979年 | 101篇 |
1978年 | 93篇 |
1977年 | 82篇 |
1976年 | 78篇 |
1975年 | 68篇 |
1974年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
71.
72.
采用Cundari和Stevens等推导的有效芯势对镧系金属一氢化物进行了理论计算,以探讨镧系金属元素与氢的相互作用。结果表明所有镧系金属一氢化物基态时理论上是稳定的,最稳定的是SmH,最不稳定的是DyH;键长计算结果显示,基态时镧系金属一招兵买马花物有独立王国 收缩现象发生;红外振动频率理论计算值与实验结果一致;成键轨道中,金属原子轨道的贡献主要是s轨道和d轨道:从CeH至ErH(GdH)例外)随着外层电子的增加s轨道成分逐渐增大d轨道成分逐渐减小;从TmH和LuH(包括GdH),成键轨道中金属原子轨道的贡献主要是d轨道,约为90%;约大多数镧系金属一氧化物的成键轨道中金属原子轨道f成分小于1%。 相似文献
73.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
74.
Gauss periods give an exponentiation algorithm that is fast for many finite fields but slow for many other fields. The current paper presents a different method for construction of elements that yield a fast exponentiation algorithm for finite fields where the Gauss period method is slow or does not work. The basic idea is to use elements of low multiplicative order and search for primitive elements that are binomial or trinomial of these elements. Computational experiments indicate that such primitive elements exist, and it is shown that they can be exponentiated fast. 相似文献
75.
Neodymium-substituted Bi4Ti3O12 (BNdT) thin films were prepared by a chemical solution deposition technique on platinum- coated silicon substrates. All of
the samples were annealed at the relatively low temperature of 600 °C by a rapid thermal annealing process in different atmospheres,
such as O2, air, and nitrogen, and vacuum. Irrespective of different annealing atmospheres, all of the BNdT thin films exhibit good
ferroelectric properties, such as a saturated hysteresis loop, good fatigue endurance, and low leakage current density. A
large remanent polarization (Pr) of ∼48 μC/cm2 with an electric field of 240 kV/cm was observed from the BNdT thin film annealed in O2 atmosphere. The BNdT thin films annealed in nitrogen and vacuum, at reduced oxygen partial pressures, exhibit smaller Pr than that annealed in oxygen. The difference of Pr of the BNdT thin films annealed in different atmospheres may originate from differences in the grain sizes and the number
of oxygen vacancies.
PACS 77.55.+f; 77.80.-e; 77.80.Fm; 81.15.-z 相似文献
76.
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
77.
78.
Taekyun Kim 《Journal of Mathematical Analysis and Applications》2002,273(1):236-242
The purpose of this paper is to give a proof of Kummer type congruence for the q-Bernoulli numbers of higher order, which is an answer to a part of the problem in a previous publication (see Indian J. Pure Appl. Math. 32 (2001) 1565-1570). 相似文献
79.
We report on the Langmuir-Blodgett film deposition and plasma etching of cadmium distearate on n-Gao.47Ino.53As to form a high-barrier-height Schottky barrier. Using this technique to form the gate electrode, we fabricated a 1?m-gate-length inverted InP-GalnAs modulation-doped field-effect transistor (MODFET) with an extrinsic transconductance of 170mS/mm and a cutoff frequencyfT of 19 GHz. 相似文献
80.