全文获取类型
收费全文 | 3856篇 |
免费 | 66篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 32篇 |
综合类 | 11篇 |
化学工业 | 505篇 |
金属工艺 | 76篇 |
机械仪表 | 53篇 |
建筑科学 | 49篇 |
能源动力 | 89篇 |
轻工业 | 142篇 |
水利工程 | 4篇 |
石油天然气 | 8篇 |
无线电 | 437篇 |
一般工业技术 | 442篇 |
冶金工业 | 1675篇 |
原子能技术 | 16篇 |
自动化技术 | 387篇 |
出版年
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 55篇 |
2020年 | 20篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 50篇 |
2015年 | 56篇 |
2014年 | 80篇 |
2013年 | 173篇 |
2012年 | 117篇 |
2011年 | 145篇 |
2010年 | 142篇 |
2009年 | 167篇 |
2008年 | 137篇 |
2007年 | 144篇 |
2006年 | 102篇 |
2005年 | 80篇 |
2004年 | 81篇 |
2003年 | 66篇 |
2002年 | 72篇 |
2001年 | 48篇 |
2000年 | 44篇 |
1999年 | 83篇 |
1998年 | 584篇 |
1997年 | 334篇 |
1996年 | 224篇 |
1995年 | 113篇 |
1994年 | 107篇 |
1993年 | 103篇 |
1992年 | 31篇 |
1991年 | 48篇 |
1990年 | 31篇 |
1989年 | 40篇 |
1988年 | 32篇 |
1987年 | 33篇 |
1986年 | 27篇 |
1985年 | 30篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 15篇 |
1980年 | 14篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 29篇 |
1976年 | 49篇 |
1975年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有3926条查询结果,搜索用时 15 毫秒
221.
By computer simulation, random samples were drawn from underlying Gaussian, uniform, and negative exponential distributions which differed in terms of their mean and variance. The conditional probability of an observation of a given magnitude, or higher, was computed for each of 2 distributions. Resulting conditional probabilities for the 2 distributions trace out a receiver operating characteristic (ROC) curve. The area under the ROC-curve, which provides a distribution-free measure of performance, was calculated over a wide range of possible performances. It is shown that the sampling variability of the area measure is dependent upon its mean value and is relatively independent of the complex of conditions which lead to the given mean value. A similar conclusion is reached for the sampling variability of the intersection of the ROC-curve with the negative diagonal. This measure leads to an estimate of the sampling variability of the measure d'e, an index of O performance, often employed in the signal detectability approach to performance measurement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
222.
Biomedical waveforms, such as electrocardiogram (ECG) and arterial pulse, always possess a lot of important clinical information in medicine and are usually recorded in a long period of time in the application of telemedicine. Due to the huge amount of data, to compress the biomedical waveform data is vital. By recognizing the strong similarity and correlation between successive beat patterns in biomedical waveform sequences, an efficient data compression scheme mainly based on pattern matching is introduced in this paper. The waveform codec consists mainly of four units: beat segmentation, beat normalization, two-stage pattern matching and template updating and residual beat coding. Three different residual beat coding methods, such as Huffman/run-length coding, Huffman/run-length coding in discrete cosine transform domain, and vector quantization, are employed. The simulation results show that our compression algorithms achieve a very significant improvement in the performances of compression ratio and error measurement for both ECG and pulse, as compared with some other compression methods. 相似文献
223.
Macromodelling is a new area of circuit theory which has gained importance with the advent of large scale integration for semiconductor chips. These integrated circuits require an analysis capability which far exceeds presently available computer-aided network analysis programs. This paper gives an overview of work which pertains to the area of macromodelling. Also, recent progress in macroanalysis is discussed, such as the latent approach, which is a method which takes advantage of the natural small activity in large systems. 相似文献
224.
Tribological properties of electroless Ni-P-SiC composite coatings in rolling/sliding contact under boundary lubrication 总被引:1,自引:0,他引:1
Wei-Long Liu Shu-Hue Hsieh Shen-Jenn Hwang Ting-Kan Tsai Wen-Jauh Chen 《北京科技大学学报(英文版)》2007,14(2):167-172
Ni-P-SiC composite coatings were prepared under a given bath composition and operation parameters of electroless plating. The tribological properties of the Ni-P-SiC composite coatings after annealing at 400℃ for 1 h were tested in rolling/sliding contact under boundary lubrication condition using a two-roller tribometer. The measurement contained friction coefficient, contact surface temperature, contact electrical resistance, and wear rate of the Ni-P-SiC composite coatings under various slide to roll ratios, loads, and rolling speeds. For the simultaneous examination of the effect of the chosen parameters on the tribological properties of the Ni-P-SiC composite coatings, an orthogonal regression experimental design method was used. 相似文献
225.
An active snubber dc/dc converter to achieve zero voltage switching (ZVS) on power switch is presented. In the proposed converter, the primary windings of two transformers are connected in series so that the primary currents of the two transformers are equal. The secondary sides of the isolated zeta converters are connected in the parallel to share the load current and reduce the current stresses on the secondary windings of the two transformers. A boost type of active snubber is connected in parallel with the main switch to recycle the energy stored in transformer leakage and magnetizing inductors and to limit voltage stress of the main switch. During the transition interval between the active switch and the auxiliary switch, the resonance based on the resonant inductor and the output capacitor of the power switch will allow the switch to turn on at ZVS. The principle of operation, steady-state analysis and design consideration of the proposed converter are provided. Finally, experimental results for a 360 W (12 V/30 A) prototype circuit with 150 kHz switching frequency were given to demonstrate the circuit performance and verify the feasibility of the proposed converter. 相似文献
226.
Chung-Ru Wu Hsieh-Hung Hsieh Liang-Hung Lu 《Microwave Theory and Techniques》2007,55(4):625-632
In this paper, a distributed circuit topology for active mixers suitable for ultra-wideband operations is presented. By employing nonuniform artificial transmission lines with the complementary transconductance stages in the Gilbert-cell multiplier, the proposed mixer demonstrates broadband characteristics at microwave frequencies while maintaining a high conversion gain (CG) with improved gain flatness. Using a 0.18-mum CMOS process, the proposed circuit is implemented, exhibiting a -3-dB bandwidth of 28 GHz. With a local-oscillator power of 3 dBm and an IF frequency of 10 MHz, the fabricated circuit has a CG of 12.5plusmn1 dB and an average input third-order intercept point (IIP3) of 0 dBm within the entire frequency range. The fully integrated wideband mixer occupies a chip area of 0.87times0.82 mm2 and consumes a dc power of 20 mW from a 2-V supply voltage 相似文献
227.
The realisation of a microwave filter is presented by using the asymmetrical compact microstrip resonator and floating plate coupling structures. The filter demonstrates the properties of low insertion loss, wide pass bandwidth and two controllable transmission zeros, which results in fast roll-off responses near to the corner frequencies of the passband. It also has the advantages of compact size, ease of fabrication and absence of via holes. An X-band prototype with 34% fractional bandwidth was designed and fabricated to verify the proposed design concept. Good agreement between simulation and measurement was obtained. 相似文献
228.
Hung-Tse Chen Hsieh S.-I. Chrong-Jung Lin Ya-Chin King 《Electron Device Letters, IEEE》2007,28(6):499-501
A new NAND-type nonvolatile memory with a field-enhancing tip structure embedded in low-temperature polycrystalline silicon (LTPS) panel was demonstrated on a glass substrate for the first time. A thin-film transistor (TFT) metal-oxide-nitride-oxide-silicon (MONOS) device based on sequential lateral solidification crystallization with a fully depleted poly-Si channel, an oxide-nitride-oxide stack gate dielectric, and a metal gate is integrated into a NAND array. A NAND test array based on p-channel LTPS TFTs exhibits good cycling endurance and data retention properties and negligible program and read disturbance. These results strongly support the claim that this TFT-MONOS device is a promising candidate for use in embedded nonvolatile memory for system-on-panel and 3-D IC applications 相似文献
229.
Shu-Han Chen Sheng-Yu Wang Rei-Jay Hsieh Jen-Inn Chyi 《Electron Device Letters, IEEE》2007,28(8):679-681
This letter investigates the dc characteristics of a double heterojunction bipolar transistor (DHBT) with a compressively strained InGaAsSb base, which is grown by solid-source molecular beam epitaxy. The novel InP/InGaAsSb HBT has a lower base/emitter (B/E) junction turn-on voltage, a lower offset voltage, and a junction ideality factor closer to unity than the conventional InP/InGaAs composite collector DHBT. These characteristics are attributed to the transistor's type-I B/E junction and type-II base/collector junction, which facilitates carrier transport for low power, high current density, and high-speed operation. Heterojunction bipolar transistors (HBTs), InP/InGaAsSb, molecular beam epitaxy (MBE). 相似文献
230.
Wang Y.-Y. Hsieh T.-E.. Chen I.-C.. Chen C.-H.. 《Advanced Packaging, IEEE Transactions on》2007,30(3):421-427
Direct encapsulation of organic light-emitting devices (OLEDs) was realized by using highly transparent, photo-curable co-polyacrylate/silica nanocomposite resin. Feasibility of such a resin for OLED encapsulation was evaluated by physical/electrical property analysis of resins and driving voltage/luminance/lifetime measurement of OLEDs. Electrical property analysis revealed a higher electrical insulation of photocured nanocomposite resin film at 3.20times1012 Omega in comparison with that of oligomer film at 1.18times1012 Omega at 6.15 V to drive the bare OLED. This resulted a lower leakage current and the device driving voltage was efficiently reduced so that the nanocomposite-encapsulated OLED could be driven at a lower driving voltage of 6.09 V rather than 6.77 V for the oligomer-encapsulated OLED at the current density of 20 mA/cm2. Luminance measurement revealed a less than 1.0% luminance difference of OLEDs encapsulated by various types of resins, which indicates that the photo-polymerization takes very little effect on the light-emitting property of OLEDs. Lifetime measurement of OLEDs found that , the time span for the normalized luminance of device drops to 80%, for nanocomposite-encapsulated OLED is 350.17 h in contrast to 16.83 h for bare OLED and 178.17 h for the oligomer-encapsulated OLED. This demonstrates that nanocomposite resin with optimum properties is feasible to OLED packaging and a compact device structure could be achieved via the method of direct encapsulation. 相似文献