全文获取类型
收费全文 | 376640篇 |
免费 | 4086篇 |
国内免费 | 1144篇 |
专业分类
电工技术 | 7121篇 |
综合类 | 256篇 |
化学工业 | 54419篇 |
金属工艺 | 16541篇 |
机械仪表 | 11738篇 |
建筑科学 | 7615篇 |
矿业工程 | 2709篇 |
能源动力 | 8748篇 |
轻工业 | 25631篇 |
水利工程 | 4335篇 |
石油天然气 | 9517篇 |
武器工业 | 29篇 |
无线电 | 45366篇 |
一般工业技术 | 77252篇 |
冶金工业 | 73536篇 |
原子能技术 | 9490篇 |
自动化技术 | 27567篇 |
出版年
2021年 | 3092篇 |
2019年 | 3059篇 |
2018年 | 5384篇 |
2017年 | 5449篇 |
2016年 | 5738篇 |
2015年 | 3495篇 |
2014年 | 5982篇 |
2013年 | 15709篇 |
2012年 | 9473篇 |
2011年 | 12473篇 |
2010年 | 10083篇 |
2009年 | 11478篇 |
2008年 | 11945篇 |
2007年 | 11838篇 |
2006年 | 10462篇 |
2005年 | 9694篇 |
2004年 | 9233篇 |
2003年 | 9024篇 |
2002年 | 8700篇 |
2001年 | 9052篇 |
2000年 | 8505篇 |
1999年 | 8949篇 |
1998年 | 23519篇 |
1997年 | 16055篇 |
1996年 | 12510篇 |
1995年 | 9233篇 |
1994年 | 8042篇 |
1993年 | 8210篇 |
1992年 | 5922篇 |
1991年 | 5840篇 |
1990年 | 5691篇 |
1989年 | 5478篇 |
1988年 | 5235篇 |
1987年 | 4441篇 |
1986年 | 4549篇 |
1985年 | 5109篇 |
1984年 | 4669篇 |
1983年 | 4290篇 |
1982年 | 3915篇 |
1981年 | 4024篇 |
1980年 | 3874篇 |
1979年 | 3791篇 |
1978年 | 3802篇 |
1977年 | 4243篇 |
1976年 | 5243篇 |
1975年 | 3373篇 |
1974年 | 3227篇 |
1973年 | 3263篇 |
1972年 | 2874篇 |
1971年 | 2547篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A series of novel thermoplastic elastomers, based on poly(dimethylsiloxane) (PDMS) as the soft segment and poly(butylene terephthalate) (PBT) as the hard segment, were synthesized by catalyzed two‐step, melt transesterification reactions of dimethyl terephthalate and methyl esters of carboxypropyl‐terminated poly(dimethylsiloxane)s (M?n = 550–2170 g mol?1) with 1,4‐butanediol. The lengths of both the hard and soft segments were varied while the weight ratio of the hard to soft segments in the reaction mixture was maintained constant (57/43). The molecular structure, composition and molecular weights of the poly(ester–siloxane)s were examined by 1H NMR spectroscopy. The effectiveness of the incorporation of the methyl‐ester‐terminated poly(dimethylsiloxane)s into the copolymer chains was verified by chloroform extraction. The effect of the segment length on the transition temperatures (Tm and Tg) and the thermal and thermo‐oxidative degradation stability, as well as the degree of crystallinity and hardness properties of the synthesized TPESs, were studied. Copyright © 2003 Society of Chemical Industry 相似文献
62.
Scale Up from Small Oven-Drying Tests of Mineral Concentrate to Pilot-Scale Drying with a Heated Pad
While Fickian diffusion models are commonly used in other applications, there are few reports of them being applied to the batch drying of a mineral concentrate. Diffusion coefficients estimated from small-scale oven-drying tests were used to predict the drying behavior of a concentrate sample 1 m × 1 m in area and 50 cm deep, with a heated bottom pad. These pilot-scale tests included both daily turning of the sample and turning every three days. The excellent quantitative agreement between the predicted and observed pilot-scale behavior gives a high level of confidence in the model predictions and suggests that a Fickian diffusion model is adequate to predict the behavior of mineral concentrates at the low moisture contents used here. 相似文献
63.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
64.
M. Kawasaki T. Tsukamoto Y. Kimura T. Iwasaki H. Yamane 《Journal of Materials Science》2003,38(4):739-745
The damage imposed on SiO
x
deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiO
x
layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiO
x
layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiO
x
deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S. 相似文献
65.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献
66.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
67.
A spacecraft in a plasma builds up charge on all the dielectric surfaces and interfaces. Once the net charge exceeds the dielectric breakdown of the material, a discharge occurs. One of the more susceptible pieces of equipment is the antenna/receiver system. The radiated E-field may be strong enough to create an ambiguous signal which may be misinterpreted by the system electronics and cause a system malfunction. A technique is developed to monitor the radiated E-field of materials discharging in an electron environment, using vacuum chambers for measuring the material discharges which are made of highly reflective materials. These chambers affect the radiated E-field due to multiple reflections from the walls. The technique developed defines a method for correcting the effects caused by the measurement facilities. The methodology is: monitor the radiated E-field with a broadband dipole antenna, and digitize the radiated signal as a function of time. Determine the frequency response of the radiated E-field using an FFT algorithm. Measure the transmission and reflection characteristics of the two-port network inside the measurement chamber, and determine the impedance network from the measured E-parameters across the frequency band of interest. Transform the measured E-field frequency response through the impedance network to obtain the frequency response of the actual radiated discharge current. Find the inverse FFT of this response to obtain the actual radiated discharge current response. This technique aids in the prediction of the E-field coupling into receive antennas on-board actual satellites 相似文献
68.
Mine K. Kubota N. Morimoto F. Sanada M. Zhang Qi 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(3):253-255
This short paper discusses the method of effectively canceling equal status normal mode noise not only on a sensor line but also on a transmission line of an optical instrument using a sensor with a sensordummy resistance 相似文献
69.
Crosstalk between microstrip transmission lines 总被引:1,自引:0,他引:1
Hill D.A. Cavcey K.H. Johnk R.T. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):314-321
Methods for prediction of crosstalk between microstrip transmission lines are reviewed and simplified for the weak-coupling case. Classical coupled transmission line theory is used for uniform lines, and potential and induced EMF methods are used for crosstalk between nonuniform lines. It is shown that the potential method is equivalent to classical coupled transmission line theory for the case of uniform lines. An experiment was performed for uniform coupled microstrip lines for frequencies from 50 MHz to 5 GHz, and good agreement between theory and measurement was obtained for both near- and far-end crosstalk 相似文献
70.
Younan N.H. Cox B.I. Taylor C.D. Prather W.D. 《Electromagnetic Compatibility, IEEE Transactions on》1994,36(4):394-398
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz 相似文献