全文获取类型
收费全文 | 412323篇 |
免费 | 4920篇 |
国内免费 | 1562篇 |
专业分类
电工技术 | 7841篇 |
综合类 | 413篇 |
化学工业 | 61697篇 |
金属工艺 | 16369篇 |
机械仪表 | 12255篇 |
建筑科学 | 10231篇 |
矿业工程 | 1727篇 |
能源动力 | 11512篇 |
轻工业 | 35478篇 |
水利工程 | 3806篇 |
石油天然气 | 6155篇 |
武器工业 | 39篇 |
无线电 | 51357篇 |
一般工业技术 | 79763篇 |
冶金工业 | 78658篇 |
原子能技术 | 8707篇 |
自动化技术 | 32797篇 |
出版年
2021年 | 3452篇 |
2020年 | 2475篇 |
2019年 | 3128篇 |
2018年 | 5244篇 |
2017年 | 5244篇 |
2016年 | 5427篇 |
2015年 | 3741篇 |
2014年 | 6497篇 |
2013年 | 18759篇 |
2012年 | 10397篇 |
2011年 | 14412篇 |
2010年 | 11557篇 |
2009年 | 13296篇 |
2008年 | 13746篇 |
2007年 | 13511篇 |
2006年 | 11874篇 |
2005年 | 10715篇 |
2004年 | 10264篇 |
2003年 | 10265篇 |
2002年 | 9693篇 |
2001年 | 10126篇 |
2000年 | 9388篇 |
1999年 | 10010篇 |
1998年 | 25720篇 |
1997年 | 17971篇 |
1996年 | 13847篇 |
1995年 | 10451篇 |
1994年 | 9149篇 |
1993年 | 9044篇 |
1992年 | 6438篇 |
1991年 | 6198篇 |
1990年 | 5985篇 |
1989年 | 5793篇 |
1988年 | 5616篇 |
1987年 | 4873篇 |
1986年 | 4764篇 |
1985年 | 5309篇 |
1984年 | 4896篇 |
1983年 | 4601篇 |
1982年 | 4287篇 |
1981年 | 4288篇 |
1980年 | 4053篇 |
1979年 | 3908篇 |
1978年 | 3697篇 |
1977年 | 4501篇 |
1976年 | 6009篇 |
1975年 | 3160篇 |
1974年 | 3119篇 |
1973年 | 3127篇 |
1972年 | 2696篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Suetsugu T. Kazimierczuk M.K. 《IEEE transactions on circuits and systems. I, Regular papers》2006,53(7):1468-1476
Design equations for satisfying the off-nominal operating condition [i.e., only the zero-voltage switching (ZVS) condition] of the Class-E amplifier with a linear shunt capacitance at a duty ratio D=0.5 are derived. A new parameter s (V/s), called the slope of switch voltage when the switch turns on is introduced to obtain an image of the distance from the nominal conditions. By examining off-nominal Class-E operation degree of the design freedom of the Class-E amplifier increases by one. In addition various amplifier parameters such as operating frequency, output power, and load resistance range can be set as design specifications. For example, the peak switch voltage and switch current can be taken into account in the design procedure. Examples of a design procedure of the Class-E amplifier for off-nominal operation are given. The theoretical results were verified with PSpice simulation and experiments. 相似文献
52.
Starting from a microscopic Hamiltonian defined on a semi-infinite cubic lattice, and employing a mean-field approximation, the surface parameters relevant for wetting in confined ternary mixtures are derived. These are found in terms of the microscopic coupling constants, and yield a physical interpretation of their origins. In comparison with the standard expression for the surface free-energy density, several new terms arising from the derivation are identified. The influence of the surface parameters on a predicted unbinding transition in a mixture of oil, water, and amphiphile demonstrate that existing results are robust to the addition of the extra surface terms. 相似文献
53.
54.
du Burck F. Lopez O. El Basri A. 《IEEE transactions on instrumentation and measurement》2003,52(2):288-291
We have developed a narrow-band controller in the MHz range, based on a field-programmable gate array. It is used to control the probe beam intensity in frequency-modulated spectroscopy experiments with an acoustooptic modulator. The residual amplitude modulation at the modulation frequency (2.5 MHz) is reduced by 50 dB. The first-harmonic detection of the signals is operated in saturation spectroscopy of I/sub 2/ at 514.5 nm and 501.7 nm. A reduction of the background noise and a large increase in the signal-to-noise ratio are obtained. 相似文献
55.
Web Services Architecture 总被引:1,自引:0,他引:1
K Mockford 《BT Technology Journal》2004,22(1):19-26
The underlying need for Web Services has been demonstrated by their early adoption and rapid evolution during the last few
years. This evolution has resulted in a number of specifications being proposed that at first glance seem independent of one
another. The current immaturity of the base technology and the growing number and diversity of specifications related to Web
Services is sometimes seen as a barrier to developers attempting to combine them to create a working piece of software. For
some, the apparent lack of stability and coherence in the specifications even raises the question of the real long-term viability
and value of the technology. This document puts those specifications into perspective by describing the set of interoperable
XML protocols that are the foundation of building interoperable systems, middleware, and applications.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
56.
In order to ascertain the metastable phase relation in the Cr2O3-Fe2O3 system, the existing phases were investigated by X-ray analysis using samples obtained by heating the coprecipitated powders for 1 h at 600–1000°C. There was a metastable two-phase region of Cr2O3-rich (CC) and Fe2O3-rich (FC) phases below about 940°C. Equilibrium state of 1:1 composition at 600–900°C was considered to be a single phase of the corundum solid solution. The metastable two-phase CC + FC region was suggested to appear probably due to the compositional inhomogeneity in the coprecipitated powders. 相似文献
57.
Dispersion-relation-preserving FDTD algorithms for large-scale three-dimensional problems 总被引:1,自引:0,他引:1
We introduce dispersion-relation-preserving (DRP) algorithms to minimize the numerical dispersion error in large-scale three-dimensional (3D) finite-difference time-domain (FDTD) simulations. The dispersion error is first expanded in spherical harmonics in terms of the propagation angle and the leading order terms of the series are made equal to zero. Frequency-dependent FDTD coefficients are then obtained and subsequently expanded in a polynomial (Taylor) series in the frequency variable. An inverse Fourier transformation is used to allow for the incorporation of the new coefficients into the FDTD updates. Butterworth or Chebyshev filters are subsequently employed to fine-tune the FDTD coefficients for a given narrowband or broadband range of frequencies of interest. Numerical results are used to compare the proposed 3D DRP-FDTD schemes against traditional high-order FDTD schemes. 相似文献
58.
59.
The main objective of this present study was to evaluate, for a standard mortar, the drying effect on its mechanical behaviour. Numerous uniaxial compression tests were thus performed with loading-unloading cycles. They were carried out on different samples previously preserved under various conditions of conservation: preserved from desiccation, air drying and rapid drying at 60°C. The obtained results showed significant influences of these conditions on the material behaviour (increase in strength, decrease in Young's modulus and Poisson's ratio) and the necessity of taking into account the coupling effects between mechanical—poromechanical behaviours and drying. 相似文献
60.
This article reviews state-of-the-art in transport adaptation techniques for mobile networks. It discusses the mechanisms for rate adaptation to combat quality degradations of speech caused by the radio links. It begins with a review of dynamic schemes for adaptation of speech encoders in cellular networks where we observe two distinct approaches to rate adaptation: network controlled and source controlled. The issues associated with adaptive voice over IP (VoIP) mechanisms are considered next. Here, the encoder detects some form of network congestion to judge how to behave itself for the good of the network. It is noted that this altruistic behavior will only benefit coordinated IP networks such as private intranets and its application to the public Internet is improbable. 相似文献