全文获取类型
收费全文 | 14955篇 |
免费 | 1002篇 |
国内免费 | 47篇 |
专业分类
电工技术 | 248篇 |
综合类 | 18篇 |
化学工业 | 3265篇 |
金属工艺 | 629篇 |
机械仪表 | 891篇 |
建筑科学 | 269篇 |
矿业工程 | 3篇 |
能源动力 | 708篇 |
轻工业 | 1280篇 |
水利工程 | 51篇 |
石油天然气 | 19篇 |
武器工业 | 2篇 |
无线电 | 2718篇 |
一般工业技术 | 3247篇 |
冶金工业 | 881篇 |
原子能技术 | 215篇 |
自动化技术 | 1560篇 |
出版年
2024年 | 7篇 |
2023年 | 148篇 |
2022年 | 116篇 |
2021年 | 406篇 |
2020年 | 314篇 |
2019年 | 348篇 |
2018年 | 454篇 |
2017年 | 427篇 |
2016年 | 538篇 |
2015年 | 408篇 |
2014年 | 641篇 |
2013年 | 1027篇 |
2012年 | 1020篇 |
2011年 | 1233篇 |
2010年 | 856篇 |
2009年 | 985篇 |
2008年 | 835篇 |
2007年 | 691篇 |
2006年 | 585篇 |
2005年 | 560篇 |
2004年 | 435篇 |
2003年 | 440篇 |
2002年 | 397篇 |
2001年 | 328篇 |
2000年 | 314篇 |
1999年 | 282篇 |
1998年 | 434篇 |
1997年 | 290篇 |
1996年 | 237篇 |
1995年 | 210篇 |
1994年 | 146篇 |
1993年 | 152篇 |
1992年 | 99篇 |
1991年 | 82篇 |
1990年 | 75篇 |
1989年 | 72篇 |
1988年 | 58篇 |
1987年 | 46篇 |
1986年 | 40篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 14篇 |
1976年 | 22篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 22 毫秒
41.
42.
S H Yoon J H Collins D Musale S Sundararajan S P Tsai G A Hallsby J F Kong J Koppes P Cachia 《Water science and technology》2005,51(6-7):151-157
A newly developed membrane performance enhancer (MPE) was used to prevent membrane fouling in a membrane bioreactor (MBR) process. It transpired that 1,000 mg/l of MPE reduced polysaccharide levels from 41 mg/I to 21 mg/I on average under the experimental condition. Repeated experiments also confirmed that 50-1,000 mg/l of MPE could reduce membrane fouling significantly and increase the intervals between membrane cleanings. Depending on MPE dosages and experimental conditions, trans-membrane pressure (TMP) increase was suppressed for 20-30 days, while baseline TMP surged within a few days. In addition, MPE allowed MBR operation even at 50,000 mg/l of total solid and reduced permeate COD. However, no evidence of toxicity for sludge was found from respiratory works. 相似文献
43.
Oh Kee Kwon Kang Ho Kim Eun Deok Sim Jong Hoi Kim Hyun Soo Kim Kwang Ryong Oh 《Photonics Technology Letters, IEEE》2005,17(3):537-539
Tunable external-cavity lasers with low power variation over a broad tuning range are demonstrated using asymmetric multiple quantum-wells with a wide and flat gain. For a 2.8-/spl mu/m-wide ridge waveguide laser of cavity length 380 /spl mu/m, when used in a grating external cavity and with an antireflection coating on one facet of laser diode chip, the power variation of less than -1 dB is obtained over a range of 80 nm. This extremely low power variation is a direct result of the spectrally flat gain. 相似文献
44.
Dielectric reliability in Al2O3(2–3.1nm)–HfO2(3nm) stack capacitor with Metal–Insulator–Si(MIS) structure is investigated in this paper. We propose an optimized capacitor process through the Time–Dependent Dielectric Breakdown (TDDB) data under various process conditions. Furthermore, due to asymmetric current at both negative and positive voltage stress polarities, we show different lifetime extrapolation by a fluence–driven model. As a result, the maximum allowed operating voltage is projected to be 1.7V (failure rate 10ppm during 10year @ 85°C) for Data “0” retention lifetime. 相似文献
45.
Ho Nam Kwon Man Geun Kim Il-Han Hwang Young Kab Yun Seon-Ju Kim Jong-Hyun Lee 《Photonics Technology Letters, IEEE》2005,17(4):774-776
We developed a micromachined X-type 2/spl times/4 optical add-drop module (OADM) featuring no difference in propagation length. Four pairs of lensed fibers are aligned in "X" position, and four micromirrors are located between the pairs of optical fibers. The OADM was fabricated utilizing a silicon-on-insulator process. Electrostatic comb actuators can be driven up to 90 /spl mu/m to change the light path within 1 ms. The insertion loss and the on-off ratio were less than 3 and 70 dB, respectively. The loss uniformity in every channel was 1.5 dB. 相似文献
46.
Shinsook Yoon Mi-Kyoung Kim In-Young Lee Mikyung Yun Jeong E. Nam Shin 《Journal of Industrial and Engineering Chemistry》2008,14(6):759-764
We have developed a mutant strain derived from Agrobacterium sp. ATCC 31750, which produces a water-soluble polysaccharide having potential utility to the food, feed, pharmaceutical and cosmetic industries. A high concentration of product (15 g/L) is obtained by 48 h cultivation of the mutant strain under optimized fermentation conditions. The water-soluble polysaccharide obtained from cultures of the mutant strain beta82 has Glc:Man:Gal in approximate molar ratios of 5.8:6.7:1.0. The molecular weight of the polysaccharide was determined to be approximately 1000 kDa by HPSEC analysis. Linkage analysis contained 3-Glcp, 3-Manp, terminal Glcp and terminal Manp, as well as a small proportion of 3- and 3,4-Galp, and 4,6-Manp residues. Based on analyses using FT-IR and 13C NMR spectrometers, most glycosidic bonds joining these sugar residues are of the α-type, and acetyl groups are apparently attached to the polymer chain at random. 相似文献
47.
Yong Bae Park Keum Cheol Hwang Ikmo Park 《Microwave and Wireless Components Letters, IEEE》2008,18(3):152-154
A tapered coaxial tip in a parallel plate waveguide is investigated. A boundary-value problem of electromagnetic scattering from a tapered coaxial monopole is solved rigorously based on the Fourier transform, eigenfunction expansion, and mode matching. Scattering parameters are represented in a series and computed to understand the behavior of the scattering in terms of the coaxial tip geometry. 相似文献
48.
Optimal and reinforced robustness designs of fuzzy variable structure tracking control for a piezoelectric actuator system 总被引:1,自引:0,他引:1
In this paper, a piezoelectric actuator (PEA) system is approximated by N subsystems, which are described by pulse transfer functions. The approximation error between the PEA system and the fuzzy linear pulse transfer function system is represented by additive nonlinear time-varying uncertainties in every subsystem. First, a dead-beat to the switching surface for every ideal subsystem is designed. It is called the "variable structure tracking control". The output disturbance of the ith subsystem is caused by the approximation error of fuzzy-model and the interaction dynamics resulting from other subsystems. In general, it is not small. Then, the H/sup /spl infin//-norm of the sensitivity function between the switching surface and the output disturbance is minimized. It is the "optimal robustness". Although the effect of the output disturbance is attenuated, a better performance can be reinforced by a switching control which is based on the Lyapunov redesign. This is the final step for the robustness design of control, which is "reinforced robustness". The stability of the overall system is verified by Lyapunov stability theory. Experimental work of a PEA system was carried out to confirm the validity of the proposed control. 相似文献
49.
Sun-Jung Kim Pyeong-Seok Cho Jong-Heun Lee Chong-Yun Kang Jin-Sang Kim Seok-Jin Yoon 《Ceramics International》2008,34(4):827-831
Various compositions of gas sensing films were prepared by the combinatorial deposition of SnO2, ZnO, and WO3 sol solutions and their gas sensing behaviors were investigated. The film composition could be manipulated conveniently via the alternate dropping of different oxide sol solutions. From the correlation between film compositions and gas sensitivities, the selective detection of C2H5OH and CH3COCH3 in the presence of CO, C3H8, H2, and NO2 could be attained. In addition, the discrimination between C2H5OH and CH3COCH3, which is a challenging issue due to their similar chemical nature, becomes possible. This research demonstrates the precise design of the sensor-material composition for the selective gas detection via the combinatorial approach. 相似文献
50.
Gwan-Hwan Hwang Sheng-Jen Chang Huey-Der Chu 《IEEE transactions on pattern analysis and machine intelligence》2004,30(1):59-77
The execution of a client/server application involving database access requires a sequence of database transaction events (or, T-events), called a transaction sequence (or, T-sequence). A client/server database application may have nondeterministic behavior in that multiple executions thereof with the same input may produce different T-sequences. We present a framework for testing all possible T-sequences of a client/server database application. We first show how to define a T-sequence in order to provide sufficient information to detect race conditions between T-events. Second, we design algorithms to change the outcomes of race conditions in order to derive race variants, which are prefixes of other T-sequences. Third, we develop a prefix-based replay technique for race variants derived from T-sequences. We prove that our framework can derive all the possible T-sequences in cases where every execution of the application terminates. A formal proof and an analysis of the proposed framework are given. We describe a prototype implementation of the framework and present experimental results obtained from it. 相似文献