全文获取类型
收费全文 | 18518篇 |
免费 | 3530篇 |
国内免费 | 2488篇 |
专业分类
化学 | 13712篇 |
晶体学 | 263篇 |
力学 | 969篇 |
综合类 | 220篇 |
数学 | 2058篇 |
物理学 | 7314篇 |
出版年
2024年 | 51篇 |
2023年 | 467篇 |
2022年 | 689篇 |
2021年 | 847篇 |
2020年 | 943篇 |
2019年 | 909篇 |
2018年 | 744篇 |
2017年 | 693篇 |
2016年 | 946篇 |
2015年 | 1055篇 |
2014年 | 1200篇 |
2013年 | 1427篇 |
2012年 | 1789篇 |
2011年 | 1742篇 |
2010年 | 1174篇 |
2009年 | 1163篇 |
2008年 | 1321篇 |
2007年 | 1168篇 |
2006年 | 1009篇 |
2005年 | 839篇 |
2004年 | 601篇 |
2003年 | 460篇 |
2002年 | 446篇 |
2001年 | 364篇 |
2000年 | 366篇 |
1999年 | 297篇 |
1998年 | 271篇 |
1997年 | 216篇 |
1996年 | 223篇 |
1995年 | 189篇 |
1994年 | 147篇 |
1993年 | 139篇 |
1992年 | 113篇 |
1991年 | 79篇 |
1990年 | 81篇 |
1989年 | 59篇 |
1988年 | 51篇 |
1987年 | 48篇 |
1986年 | 45篇 |
1985年 | 50篇 |
1984年 | 25篇 |
1983年 | 17篇 |
1982年 | 17篇 |
1981年 | 8篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
研究了应用于锂二次电池正极的新型高能量密度存贮材料Li(AlxCo1-x)O2 (x=01—05)的磁性.发现Al3+的掺杂可导致Co3+中d电子自旋态发生变化,即有部分d电子进入高自旋态.伴随Co3+中电子状态的改变,材料结构演化也发生了相应变化,表现为c/a比增大明显减缓,较好地解释了材料结构对Vegard定律的正偏离.这对材料的微观结构与性能设计具有重要意义.
关键词:
锂电池材料
Li(AlxCo1-x)O2
磁性
自旋态
结构演化 相似文献
62.
新型微球板电子倍增器和微通道板相比具有高增益、无离子反馈、制备简单、造价低廉等优点。介绍了微球板电子倍增器的工作原理、特点和广阔的应用前景。由于微球板基体的形成技术是微球板制备的关键技术,论文从理论上研究了微球板基体烧结过程中的烧结速率。并采用自行设计组分的高铅玻璃,用立式炉成珠设备进行了玻璃微珠的制备。探索了微球板制备过程中玻璃微珠的分级技术、微球板电子倍增器基体成型工艺和技术。制备出基本满足要求的微球板电子倍增器基体。给出了制造的样品和文献上样品结构的SEM对比照片,最后对实验过程中的一些现象进行了分析,并给出了实验的结论。 相似文献
63.
Because of package, a single FBG has dual Bragg wavelength. One is sensitive to stress and the other is sensitive to temperature. By using the special mechanism, the wavelengths can be tuned by stress and temperature respectively. 相似文献
64.
65.
With the advances in pulsed laser systems, microscopic imaging techniques such as multiphoton and pump-probe fluorescence microscopy have developed into effective tools for investigating intensity and time-resolved phenomena inside biological systems. However, pulsed lasers used in these techniques usually are commercial systems with repetition frequencies of around 80 MHz. While these systems have proven to be adequate for multiphoton and pump-probe microscopic imaging applications, the temporal separation of the laser pulse train (around 12.5 ns) is long compared to the fluorescence lifetimes of many common fluorescence species. In this work, we present the designs of repetition rate multipliers based on passive optical components that can be used to increase the efficiency in multiphoton and pump-probe fluorescence microscopy. Depending on the lifetime of fluorescence molecules under investigation, the passive repetition rate multiplier can increase the duty cycle of multiphoton or pump-probe microscopy up to fourfold. 相似文献
66.
I. El-Kady R. Biswas Y. Ye M. F. Su I. Puscasu Martin Pralle E. A. Johnson J. Daly A. Greenwald 《Photonics and Nanostructures》2003,1(1):69-77
In this work, we present both the theoretical basis as well as supporting experimental measurements for development of a novel mid-infrared thermally stimulated narrow band emitter with a spectral bandwidth of less than 10%. To achieve this, we utilize a metallized-surface 2D photonic crystal of air voids in a silicon background with hexagonal structure symmetry. Our results are based on the generation of discrete surface plasmon (SP) modes in the thin metallized layer residing on the top surface. This yields a series of adequately spaced discrete peaks in the reflection spectrum, dominated by a single sharp feature corresponding to the lowest plasmon order, in an otherwise uniform highly reflective spectrum (>90%) over most of the IR spectrum. This, in turn, gives rise to a sharp absorption feature with a correspondingly narrow thermal emission peak in the emission spectrum. Transfer matrix calculations simulate well both the position and strengths of the absorption peaks. By altering the period of the surface photonic lattice, the SP peak and emissive band can be tuned to the desired wavelength. These devices promise a new class of tunable infrared emitters with high power in a narrow spectral bandwidth. Such narrow band sources are critical to achieving high efficiency gas sensors. 相似文献
67.
68.
A glass fiber piezooptical optical bistability device is reported.Basing on pho-toelastic and strain effects of single-mode fiber,we have realized piezooptical modulation andperformed experiments of optical bistability. 相似文献
69.
Characteristics and structures of weak efficient surfaces of production possibility sets 总被引:1,自引:0,他引:1
Quanling Wei Hong Yan Gang Hao 《Journal of Mathematical Analysis and Applications》2007,327(2):1055-1074
This paper studies the characteristics and structure of the weak surface of the production possibility set. We apply techniques and methods of transferring a polyhedral cone from its intersection form to its sum form, identify an intersection representation of the production possibility set. We give the structure theorem of weak surface of the production possibility set, which includes three complementary slackness conditions. We define the input weak efficiency and output weak efficiency for different DEA models according to the representation of the intersection form. It investigates the characteristics of the weak surfaces, and proves the structure theorems of input weak DEA efficiency and output weak DEA efficiency. The structure theorems establish weighted combination of inputs and outputs that are weak DEA efficient. Numerical examples are provided for illustration. 相似文献
70.
药用植物化学分类法与红外指纹图谱的相关性研究 总被引:27,自引:6,他引:21
本文首次采用傅里叶变换红外光谱法(FTIR)对五加科、桔梗科、木兰科、樟科、豆科、蕨类等科目中的典型药用植物进行了系统研究,比较了各科内植物的异同,并且讨论了相同植物不同药用部位、不同采药时间对其红外谱图的影响。结合药典中关于药物主体有效成分的记载,分析了各药用植物谱图中主要成分的特征基团,对主要吸收峰进行了指认。在传统形态比较分类方法的基础上,FTIR可以成为一种快速、可靠、客观、有效的化学分类学的补充方法。 相似文献