全文获取类型
收费全文 | 5157篇 |
免费 | 440篇 |
国内免费 | 579篇 |
专业分类
化学 | 1689篇 |
晶体学 | 13篇 |
力学 | 86篇 |
综合类 | 101篇 |
数学 | 2754篇 |
物理学 | 719篇 |
无线电 | 814篇 |
出版年
2024年 | 7篇 |
2023年 | 69篇 |
2022年 | 128篇 |
2021年 | 142篇 |
2020年 | 150篇 |
2019年 | 152篇 |
2018年 | 168篇 |
2017年 | 193篇 |
2016年 | 203篇 |
2015年 | 134篇 |
2014年 | 277篇 |
2013年 | 498篇 |
2012年 | 264篇 |
2011年 | 308篇 |
2010年 | 239篇 |
2009年 | 286篇 |
2008年 | 313篇 |
2007年 | 358篇 |
2006年 | 320篇 |
2005年 | 285篇 |
2004年 | 245篇 |
2003年 | 226篇 |
2002年 | 208篇 |
2001年 | 141篇 |
2000年 | 164篇 |
1999年 | 124篇 |
1998年 | 122篇 |
1997年 | 74篇 |
1996年 | 77篇 |
1995年 | 51篇 |
1994年 | 43篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 11篇 |
1989年 | 22篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 20篇 |
1984年 | 9篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有6176条查询结果,搜索用时 21 毫秒
871.
The classical AtiyahHirzebruch spectral sequence relates the ordinary homology with coefficients in h_*(*) to h*(-). We study a spectral sequence converging to h*(F(-)) where F is a (reasonable) functor on spaces. We determine precisely when this spectral sequence collapses and we develop the basic elementary theory of such functors. When F is a reduced homotopy exact functor, H*(F(-)) is a homology theory and this reduces to the classical case of Atiyah–Hirzebruch. We calculate various examples to show that the theory is nontrivial. 相似文献
872.
The non-commutative neutrix convolution product of the functions x
r cos–(x) and x
s cos+(x) is evaluated. Further similar non-commutative neutrix convolution products are evaluated and deduced. 相似文献
873.
Zhanfeng Huang Dan Ouyang Ruiman Ma Wei Wu Vellaisamy A. L. Roy Wallace C. H. Choy 《Advanced functional materials》2019,29(45)
Solution‐process fine metal‐oxide nanoparticles are promising carrier transport layer candidates for unlocking the full potential of solution process in solar cells, due to their low cost, good stability, and favorable electrical/optical properties. However, exotic organic ligands adopted for achieving small size and monodispersion can mostly cause poor conductivity, which thus impedes their electrical application. In this work, a concept of constructing a hypocrystalline intermediate is proposed to develop a general method for synthesizing various ternary metal oxide (TMO) nanoparticles with a sub‐ten‐nanometer size and good dispersibility without exotic ligands. Particularly, a guideline is summarized based on the understandings about the impact of metal ion intercalation as well as water and anion coordination on the hypocrystalline intermediate. A general method based on the proposed concept is developed to successfully synthesize various sub‐ten‐nanometer TMO nanoparticles with excellent ability for forming high‐quality (smooth and well‐coverage) films. As an application example, the high‐quality films are used as hole transport layers for achieving high‐performance (stability and efficiency) organic/perovskite solar cells. Consequently, this work will contribute to the development of TMO for large‐scale and high‐performance optoelectronic devices and the concept of tailoring intermediate can leverage the fundamental understandings of synthesis strategies for other metal oxides. 相似文献
874.
钱岭 《电信工程技术与标准化》2020,(5):1-7
人工智能技术在各个行业的应用均体现出爆发趋势,但是AI技术的性能局限同时约束着相关产品的应用场景。在感知方面,识别算法的准确率无法达到100%,召回率更低;在认知方面,知识难以100%覆盖业务场景,因此如何开展商业化应用就需要精心规划。本文首先介绍几项AI产品研发应用,并总结相关的经验和问题。在此基础上,按照面向任务关键应用(MCA)和非任务关键应用(NMCA)2个维度,针对4个应用类型(决策支持与增强、智能代理、决策自动化、智慧产品),围绕3类商业价值和2类应用假设,分析AI类应用产品的战略规划决策要素,为AI应用领域决策者提供帮助。 相似文献
875.
Treatment of azoxybenzene and its derivatives with acids is known to result in the Wallach rearrangement, which leads to 2- or4-hydroxyazobenzenes. Starting in the 1960s, experimental findings have lead to the proposal of several mechanisms for this rearrangement. In this work, molecular orbital theory employing the semiempirical AM1 method is used to locate and discuss the energetics of the intermediates and the transition states for this rearrangement. Based on the results of AM1 calculations in vacuum and in solution, the most plausible mechanistic pathways are proposed and discussed. 相似文献
876.
Seung Hwan Son 《Proceedings of the American Mathematical Society》1998,126(10):2895-2902
In his first and second letters to Hardy, Ramanujan made several assertions about the Rogers-Ramanujan continued fraction . In order to prove some of these claims, G. N. Watson established two important theorems about that he found in Ramanujan's notebooks. In his lost notebook, after stating a version of the quintuple product identity, Ramanujan offers three theta function identities, two of which contain as special cases the celebrated two theorems of Ramanujan proved by Watson. Using addition formulas, the quintuple product identity, and a new general product formula for theta functions, we prove these three identities of Ramanujan from his lost notebooks.
877.
Claudia Miller 《Proceedings of the American Mathematical Society》1998,126(1):53-60
This paper concerns the notion of complexity, a measure of the growth of the Betti numbers of a module. We show that over a complete intersection the complexity of the tensor product of two finitely generated modules is the sum of the complexities of each if for . One of the applications is simplification of the proofs of central results in a paper of C. Huneke and R. Wiegand on the tensor product of modules and the rigidity of Tor.
878.
通过化学自催化反应在半导体晶圆I/O铝或铜金属垫上沉积具有可焊接性的镍金/镍钯金层,此工艺已在MOSFET、IGBT、RFID、SAW Filter等产品上得到广泛应用。着重阐述了在新产品设计和工程评估阶段,对于晶圆产品本身应予以考量的因素,如钝化层种类及厚度,I/O金属垫的成分及结构,切割轨道上金属图形的大小及钝化层的覆盖,不同I/O pad的电势等。其中一些因素导致的问题会直接影响化学镍金/镍钯金后产品的性能应用。在化镀工艺过程中,要充分了解产品本身结构以及可能造成的相应缺陷及问题,并且应综合考虑这些因素的影响。 相似文献
879.
基于紫铜填充中间层的黄铜激光焊接气孔控制 总被引:1,自引:0,他引:1
采用中间过渡层的新方法研究了黄铜焊接气孔的控制,对比分析了以紫铜为中间层的黄铜激光焊接和常规激光焊接获得的焊缝的气孔率,结果表明:在中间层条件下,焊缝表面和内部的气孔率均大幅降低;随着焊接速率增大,气孔率逐渐减小,当焊接速率为2.2 mm/s时,气孔率几乎为零;当焊接参数相同时,中间层条件下的焊缝气孔率仅为常规激光焊接的1/3,焊接接头的力学性能优于常规激光焊接。在焊缝成形良好的前提下,验证了采用紫铜为中间层的焊接方法控制黄铜激光焊接气孔缺陷的有效性。 相似文献
880.
By the reduction in the size of transistors and the development of submicron technology, as well as the construction of more integrated circuits on chips, leakage power has become one of the main concerns of electronic circuit designers. In this article, we first review techniques presented in recent years to reduce leakage power and then present a new technique based on the gate-level body biasing technique and the multi-threshold CMOS technique to minimize leakage power in digital circuits. Afterward, we develop another new method by improving the first proposed technique to achieve higher efficiency and simultaneously reduce leakage power and propagation delay in digital circuits. In the proposed technique, we use two dynamic threshold MOSFET transistors to reduce leakage current. In this paper, the body biasing generator structure is applied to reduce propagation delay. The proposed technique has been successfully validated and verified by post-layout simulation with Cadence Virtuoso based on the 32 nm process technology.We evaluate the efficiency of the proposed techniques by examining factors including power, delay, area, and the power delay product. The simulation results using HSPICE software and performance analysis to process corner variations based on the 32 nm process technology show that the proposed technique, in addition to having proper performance in different corners of the technology, significantly reduces leakage power and propagation delay in logic CMOS circuits. In general, the proposed technique has a very successful performance compared to previous techniques. 相似文献