全文获取类型
收费全文 | 46008篇 |
免费 | 6794篇 |
国内免费 | 4284篇 |
专业分类
电工技术 | 5147篇 |
综合类 | 4433篇 |
化学工业 | 4486篇 |
金属工艺 | 1519篇 |
机械仪表 | 2405篇 |
建筑科学 | 247篇 |
矿业工程 | 319篇 |
能源动力 | 2229篇 |
轻工业 | 334篇 |
水利工程 | 57篇 |
石油天然气 | 124篇 |
武器工业 | 371篇 |
无线电 | 14957篇 |
一般工业技术 | 5057篇 |
冶金工业 | 442篇 |
原子能技术 | 251篇 |
自动化技术 | 14708篇 |
出版年
2024年 | 268篇 |
2023年 | 1930篇 |
2022年 | 2133篇 |
2021年 | 2286篇 |
2020年 | 2604篇 |
2019年 | 1984篇 |
2018年 | 2044篇 |
2017年 | 2969篇 |
2016年 | 3054篇 |
2015年 | 3017篇 |
2014年 | 3788篇 |
2013年 | 3851篇 |
2012年 | 4781篇 |
2011年 | 4368篇 |
2010年 | 3357篇 |
2009年 | 3313篇 |
2008年 | 2063篇 |
2007年 | 2527篇 |
2006年 | 1931篇 |
2005年 | 922篇 |
2004年 | 528篇 |
2003年 | 415篇 |
2002年 | 439篇 |
2001年 | 387篇 |
2000年 | 322篇 |
1999年 | 309篇 |
1998年 | 134篇 |
1997年 | 99篇 |
1996年 | 99篇 |
1995年 | 92篇 |
1994年 | 64篇 |
1993年 | 54篇 |
1992年 | 55篇 |
1991年 | 59篇 |
1990年 | 48篇 |
1989年 | 63篇 |
1988年 | 118篇 |
1987年 | 236篇 |
1986年 | 203篇 |
1985年 | 62篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1971年 | 7篇 |
1970年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
131.
Recently, there has been much interest in wide band-gap wurtzite semiconductors such as group-III nitrides (GaN, AlGaN, and InGaN) and ZnO. Ion-beam-defect processes are considerably more complex in these wurtzite semiconductors than in the case of both elemental and group-III-V cubic semiconductors. This brief review focuses on our recent studies of the following aspects of ion-beam-defect processes: (i) effects of implanted species and the density of collision cascades, (ii) the nature of ion-beam-produced planar defects in GaN, (iii) defect production in GaN by swift heavy ions, (iv) blistering of H-implanted GaN, (v) electrical isolation of GaN and ZnO, (vi) the effect of Al and In content on defect processes in III-nitrides, and (vii) structural damage in ZnO with an intriguing effect of the formation of an anomalous defect peak. Emphasis is given to unusual ion-beam-defect processes and to the physical mechanisms underlying them. 相似文献
132.
A.M. Efremov 《Vacuum》2004,75(2):133-142
In this work, we carried out investigations aimed at understanding the effect of gas mixing ratio on plasma parameters, gas phase composition and etch rate in CF4/Ar inductively coupled plasma. For this purpose, a combination of experimental methods and modelling was used. Experiments showed that electron temperature and electron density are not very sensitive to variations of Ar content in CF4/Ar plasma. From a zero-dimensional plasma model, the densities of both neutral and charged particles change monotonically. The analysis of surface kinetics based on an ion-assisted etching mechanism showed the possibility of non-monotonic etch rate behaviour due to a concurrence of chemical and physical etching pathways. 相似文献
133.
134.
135.
《Journal of Systems Architecture》2007,53(10):751-763
In this paper, a new methodology is presented for topology optimization of networked embedded systems as they occur in automotive and avionic systems as well as wireless sensor networks. By introducing a model which is (1) suitable for heterogeneous networks with different communication bandwidths, (2) modeling of routing restrictions, and (3) flexible binding of tasks onto processors, current design issues of networked embedded systems can be investigated. On the basis of this model, the presented methodology firstly allocates the required resources which can be communication links as well as computational nodes and secondly binds the functionality onto the nodes and the data dependencies onto the links such that no routing restrictions will be violated or capacities on communication links will be exceeded. Due to the often error-prone communication in networks, we allow for routing each data dependency over multiple routes in the networks. With this strategy, our methodology is able to increase the reliability of the entire system. This reliability analysis is based on Binary Decision Diagrams (BDDs) and is integrated in our multi-objective design space exploration. By applying Evolutionary Algorithms, we are able to consider multiple objectives simultaneously during the optimization process and allow for a subsequent unbiased decision making. An experimental evaluation as well as a demonstration of a case study from the field of automotive electronics will show the applicability of the presented approach. 相似文献
136.
《Robotics and Autonomous Systems》2007,55(6):460-469
In this paper, a model-predictive trajectory-tracking control applied to a mobile robot is presented. Linearized tracking-error dynamics is used to predict future system behavior and a control law is derived from a quadratic cost function penalizing the system tracking error and the control effort. Experimental results on a real mobile robot are presented and a comparison of the control obtained with that of a time-varying state-feedback controller is given. The proposed controller includes velocity and acceleration constraints to prevent the mobile robot from slipping and a Smith predictor is used to compensate for the vision-system dead-time. Some ideas for future work are also discussed. 相似文献
137.
138.
《Optical Materials》2005,27(1):99-102
The spin Hamiltonian parameters g∥, g⊥, A∥ and A⊥ for Er3+ ion in LiYF4 are investigated by using the perturbation formulas of these parameters for a 4f11 ion in tetragonal symmetry. In these formulas, the contributions to the spin Hamiltonian parameters from the second-order perturbation terms and the admixtures of different states are considered. The relevant crystal field parameters are calculated from the superposition model and the local structural parameters of the Y3+ site occupied by impurity Er3+. The theoretical optical spectra within 4I15/2 and 4I13/2 states and the spin Hamiltonian parameters obtained in this work are consistent with the observed values. 相似文献
139.
《Diamond and Related Materials》2005,14(8):1353-1360
A high surface area and non-microporous submicrometer-sized β-SiC material was successfully obtained according to the Shape Memory Synthesis (SMS) method. The attack by SiO vapors of a nanodiamond preform with sp3-bound carbon, at 1200–1300 °C under dynamic vacuum, formed β-SiC nanoparticles by carboreduction of the SiO vapors. These β-SiC nanoparticles had a mean size distribution centered at 10 nm and a specific surface area of 140 m2/g. The high carbon to carbide conversion obtained and the location of the remaining unreacted carbon in the core of the β-SiC nanoparticles allowed a direct use of the material as a catalyst support without any stabilizing post-synthesis oxidative treatment. The material showed dispersive properties and a good resistance towards oxidation, due to the presence of a thick and partially oxidized protecting amorphous coating, preventing from the extensive oxidation of SiC into silica. 相似文献
140.
《Thin solid films》2006,515(2):782-785
We present theoretical photoluminescence (PL) and absorption spectra of p-doped InGaN/AlInGaN and AlInGaN/InGaN multiple quantum wells (MQWs). The calculations were performed within the k.p method by means of solving a full eight-band Kane Hamiltonian together with the Poisson equation in a plane wave representation, including exchange–correlation effects within the local density approximation. Strain effects due to the lattice mismatch and an internal electric field are also taken into account. We show that by changing the In and Al composition we can reach short and long emission wavelengths. The trends in the calculated Stokes shift, due to many-body effects within the quasi-two-dimensional hole gas (2DHG), are analyzed as a function of the acceptor doping concentration. Since the studies of optical properties of quantum wells based on nitrides quaternary alloys are at an early stage, the results reported here will provide guidelines for the interpretation of forthcoming experiments. 相似文献