全文获取类型
收费全文 | 8992篇 |
免费 | 1079篇 |
国内免费 | 2211篇 |
专业分类
化学 | 4831篇 |
晶体学 | 124篇 |
力学 | 287篇 |
综合类 | 80篇 |
数学 | 1837篇 |
物理学 | 2103篇 |
无线电 | 3020篇 |
出版年
2024年 | 42篇 |
2023年 | 217篇 |
2022年 | 372篇 |
2021年 | 407篇 |
2020年 | 397篇 |
2019年 | 306篇 |
2018年 | 238篇 |
2017年 | 275篇 |
2016年 | 293篇 |
2015年 | 277篇 |
2014年 | 415篇 |
2013年 | 566篇 |
2012年 | 415篇 |
2011年 | 493篇 |
2010年 | 405篇 |
2009年 | 498篇 |
2008年 | 506篇 |
2007年 | 587篇 |
2006年 | 504篇 |
2005年 | 404篇 |
2004年 | 392篇 |
2003年 | 377篇 |
2002年 | 414篇 |
2001年 | 394篇 |
2000年 | 304篇 |
1999年 | 249篇 |
1998年 | 236篇 |
1997年 | 180篇 |
1996年 | 177篇 |
1995年 | 131篇 |
1994年 | 148篇 |
1993年 | 147篇 |
1992年 | 153篇 |
1991年 | 120篇 |
1990年 | 132篇 |
1989年 | 157篇 |
1988年 | 134篇 |
1987年 | 151篇 |
1986年 | 137篇 |
1985年 | 127篇 |
1984年 | 129篇 |
1983年 | 88篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 18篇 |
1977年 | 13篇 |
1975年 | 16篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 594 毫秒
21.
E. C. Ferreira J. A. P. da Costa J. A. K. Freire G. A. Farias V. N. Freire 《Applied Surface Science》2002,190(1-4):191-194
Confined excitons in non-abrupt GaAs/AlxGa1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al0.3Ga0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces. 相似文献
22.
23.
CAS-BUS: A Test Access Mechanism and a Toolbox Environment for Core-Based System Chip Testing 总被引:2,自引:0,他引:2
As System on a Chip (SoC) testing faces new challenges, some new test architectures must be developed. This paper describes a Test Access Mechanism (TAM) named CAS-BUS that solves some of the new problems the test industry has to deal with. This TAM is scalable, flexible and dynamically reconfigurable. The CAS-BUS architecture is compatible with the IEEE P1500 standard proposal in its current state of development, and is controlled by Boundary Scan features.This basic CAS-BUS architecture has been extended with two independent variants. The first extension has been designed in order to manage SoC made up with both wrapped cores and non wrapped cores with Boundray Scan features. The second deals with a test pin expansion method in order to solve the I/O bandwidth problem. The proposed solution is based on a new compression/decompression mechanism which provides significant results in case of non correlated test patterns processing. This solution avoids TAM performance degradation.These test architectures are based on the CAS-BUS TAM and allow trade-offs to optimize both test time and area overhead. A tool-box environment is provided, in order to automatically generate the needed component to build the chosen SoC test architecture. 相似文献
24.
F. F. Maia Jr. J. A. K. Freire G. A. Farias V. N. Freire E. F. da Silva Jr. 《Applied Surface Science》2002,190(1-4):247-251
The excitonic properties of a ZnSe/ZnSxSe1−x strained quantum well (QW) are calculated taking into account interface effects. Numerical results obtained with ZnS0.18Se0.82/ZnSe QWs show that graded interfaces can be responsible for a strong broadening of excitonic spectra. 相似文献
25.
一般来说,新闻直播中镜头是固定的,不需要太多的操作。如今,使用可远程遥控的摄像设备已成为一个热点。本文主要以东方卫视为例,从选型、使用及日常维护等方面,对对AUTOCAM的进行简单介绍。 相似文献
26.
《Fiber and Integrated Optics》2007,26(6):335-342
A fiber-optic chemical sensor (FOCS) for detection of nitrogen dioxide (NO2) molecules is reported. The FOCS presents an optropode structure because of the transmission properties of the sensitive material. The NO2 FOCS is activated by using the semiconductor polymer: regioregular head-to-tail poly(3-octylthiophene-2,5-diyl). The operation wavelength of the sensor is 543.5 nm such that a simple LED and detector can be used for the design of this device. The sensor response decreases after each exposure, demonstrating the reduction in sensitivity as well as irreversibility lower than 5%. However, its properties such as rapid response, high selectivity, high sensitivity (0.43 ± 0.01 muW/ppm), hygroscopic properties, and its operation at room temperature make this kind of FOCS a good alternative for NO2 toxic gas detection. 相似文献
27.
András Vasy 《Journal of Functional Analysis》2004,209(2):468-492
We show the exponential decay of eigenfunctions of second-order geometric many-body type Hamiltonians at non-threshold energies. Moreover, in the case of first-order and small second-order perturbations we show that there are no eigenfunctions with positive energy. 相似文献
28.
29.
30.