全文获取类型
收费全文 | 199629篇 |
免费 | 2168篇 |
国内免费 | 634篇 |
专业分类
电工技术 | 4072篇 |
综合类 | 127篇 |
化学工业 | 27044篇 |
金属工艺 | 7555篇 |
机械仪表 | 5494篇 |
建筑科学 | 4102篇 |
矿业工程 | 752篇 |
能源动力 | 4702篇 |
轻工业 | 14507篇 |
水利工程 | 1711篇 |
石油天然气 | 2851篇 |
武器工业 | 7篇 |
无线电 | 27473篇 |
一般工业技术 | 37614篇 |
冶金工业 | 45975篇 |
原子能技术 | 3565篇 |
自动化技术 | 14880篇 |
出版年
2021年 | 1263篇 |
2019年 | 1296篇 |
2018年 | 2150篇 |
2017年 | 2128篇 |
2016年 | 2199篇 |
2015年 | 1511篇 |
2014年 | 2653篇 |
2013年 | 8026篇 |
2012年 | 4495篇 |
2011年 | 6170篇 |
2010年 | 4961篇 |
2009年 | 5820篇 |
2008年 | 6193篇 |
2007年 | 6259篇 |
2006年 | 5667篇 |
2005年 | 5339篇 |
2004年 | 5279篇 |
2003年 | 5110篇 |
2002年 | 4932篇 |
2001年 | 5338篇 |
2000年 | 4938篇 |
1999年 | 5476篇 |
1998年 | 15810篇 |
1997年 | 10443篇 |
1996年 | 8005篇 |
1995年 | 5846篇 |
1994年 | 5057篇 |
1993年 | 5066篇 |
1992年 | 3413篇 |
1991年 | 3272篇 |
1990年 | 3238篇 |
1989年 | 3053篇 |
1988年 | 2811篇 |
1987年 | 2280篇 |
1986年 | 2323篇 |
1985年 | 2623篇 |
1984年 | 2340篇 |
1983年 | 2086篇 |
1982年 | 1928篇 |
1981年 | 2064篇 |
1980年 | 1814篇 |
1979年 | 1674篇 |
1978年 | 1673篇 |
1977年 | 2040篇 |
1976年 | 2738篇 |
1975年 | 1433篇 |
1974年 | 1381篇 |
1973年 | 1329篇 |
1972年 | 1137篇 |
1971年 | 962篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
111.
A theoretical expression is derived for the far fields of semiconductor lasers with coated facets. It is shown that the far fields are different for uncoated, antireflection-coated and high-reflection-coated lasers. The correction factor for the far fields is shown to depend on the transmission coefficient of the facets. 相似文献
112.
Asymptotic stability of finite-dimensional linear continuous-time periodic (FDLCP) systems is studied by harmonic analysis. It is first shown that stability can be examined with what we call the harmonic Lyapunov equation. Another necessary and sufficient stability criterion is developed via this generalized Lyapunov equation, which reduces the stability test into that of an approximate FDLCP model whose transition matrix can be determined explicitly. By extending the Gerschgorin theorem to linear operators on the linear space l2, yet another disc-group criterion is derived, which is only sufficient. Stability of the lossy Mathieu equation is analyzed as a numerical example to illustrate the results 相似文献
113.
Field R. D. Hartwig K. T. Necker C. T. Bingert J. F. Agnew S. R. 《Metallurgical and Materials Transactions A》2002,33(13):965-972
The equal-channel angular extrusion (ECAE) technique has been applied to a powder metallurgy (P/M) source Be alloy. Extrusions
have been successfully completed on Ni-canned billets of Be at approximately 425°C. No cracking was observed in the billets,
and significant grain refinement was achieved. In this article, microstructural features and dislocation structures are discussed
for a singlepass extrusion, including evidence of <c> and <c+a> dislocations. Significant crystallographic texture developed during ECAE, which is discussed in terms of this unique deformation
processing technique and the underlying physical processes which sustain the deformation.
S.R. AGNEW, formerly with the Oak Ridge National Laboratory, Oak Ridge, TN 37831-6115
This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals
and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following
ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic
Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee. 相似文献
114.
In this paper, an alternative method of connecting fixed-speed wind turbines, with active pitch mechanisms or variable-slip generators, is proposed and evaluated. Instead of using the conventional soft starter, external resistors are used. The method was evaluated via laboratory tests on a 15-kW machine and theoretically on a 1-MW wind turbine. The proposed method causes smaller grid power quality impact, especially on inductive grids, compared with soft starters. This means that it will be possible to install constant-speed wind turbines to weaker grids using this method. 相似文献
115.
Model-driven development - Guest editor's introduction 总被引:1,自引:0,他引:1
116.
We propose an asynchronous structure for implementation on a SoC. An intersegment topological arrangement preserves parallelization and, through a so-called central arbiter, efficiently organizes communication with high signaling speed in the proposed structure. Researchers proposed the concept of segmenting buses primarily for multicomputer architectures. More recent approaches address on-chip implementation of segmented buses. We present an asynchronous segmented-bus architecture targeted for the modular design of high-performance SoC applications. The structure not only enables faster operation than a conventional bus system but also offers lower power consumption per transferred data item. This is possible because segmentation is realized in such a way that the majority of data transfers in the system are intrasegment transactions on relatively short wires with low or moderate capacitive loads. 相似文献
117.
With the creation of balancing authorities by the North American Reliability Council that span large portions of the North American interconnection, and stringent requirements for real time monitoring of power system evolution, faster and more accurate state estimation algorithms that can efficiently handle systems of very large sizes are needed in the present environment. This paper presents a distributed state estimation algorithm suitable for large-scale power systems. Synchronized phasor measurements are applied to aggregate the voltage phase angles of each decomposed subsystem in the distributed state estimation solution. The aggregated state estimation solution is obtained from the distributed solution using a sensitivity analysis based update at chosen boundary buses. Placement of synchronized phasor measurements in the decomposed subsystems is also investigated in this paper. Test results on the IEEE 118-bus test bed are provided 相似文献
118.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
119.
Yu. A. Chaplygin E. A. Artamonova A. Yu. Krasyukov T. Yu. Krupkina 《Semiconductors》2008,42(13):1522-1526
Heat removal problems, thermal effects, and self-heating phenomena occurring during operation of planar power SOI MOS transistors are considered. Using device-technological simulating methods, the transistor characteristics and safe operation range were studied. It was shown that limitations of the safe operation range are mostly associated with structure self-heating rather than with the parasitic bipolar transistor. 相似文献
120.
Jun Chen Berger T. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(8):3385-3398
We consider a distributed source coding system in which several observations must be encoded separately and communicated to the decoder by using limited transmission rate. We introduce a robust distributed coding scheme which flexibly trades off between system robustness and compression efficiency. The optimality of this coding scheme is proved for various special cases. 相似文献