全文获取类型
收费全文 | 467826篇 |
免费 | 7356篇 |
国内免费 | 1901篇 |
专业分类
电工技术 | 9888篇 |
综合类 | 1274篇 |
化学工业 | 74558篇 |
金属工艺 | 19021篇 |
机械仪表 | 13620篇 |
建筑科学 | 12128篇 |
矿业工程 | 1479篇 |
能源动力 | 12539篇 |
轻工业 | 42592篇 |
水利工程 | 3820篇 |
石油天然气 | 4489篇 |
武器工业 | 19篇 |
无线电 | 58726篇 |
一般工业技术 | 88998篇 |
冶金工业 | 87652篇 |
原子能技术 | 8125篇 |
自动化技术 | 38155篇 |
出版年
2021年 | 4126篇 |
2020年 | 3141篇 |
2019年 | 3730篇 |
2018年 | 5781篇 |
2017年 | 5572篇 |
2016年 | 6066篇 |
2015年 | 4631篇 |
2014年 | 7358篇 |
2013年 | 22121篇 |
2012年 | 11270篇 |
2011年 | 15422篇 |
2010年 | 12892篇 |
2009年 | 14524篇 |
2008年 | 14937篇 |
2007年 | 14797篇 |
2006年 | 13234篇 |
2005年 | 12068篇 |
2004年 | 11608篇 |
2003年 | 11829篇 |
2002年 | 11369篇 |
2001年 | 11644篇 |
2000年 | 10648篇 |
1999年 | 11523篇 |
1998年 | 28824篇 |
1997年 | 20254篇 |
1996年 | 15871篇 |
1995年 | 12015篇 |
1994年 | 10690篇 |
1993年 | 10480篇 |
1992年 | 7615篇 |
1991年 | 7421篇 |
1990年 | 6910篇 |
1989年 | 6687篇 |
1988年 | 6546篇 |
1987年 | 5594篇 |
1986年 | 5550篇 |
1985年 | 6246篇 |
1984年 | 5667篇 |
1983年 | 5310篇 |
1982年 | 4931篇 |
1981年 | 4904篇 |
1980年 | 4666篇 |
1979年 | 4411篇 |
1978年 | 4164篇 |
1977年 | 5158篇 |
1976年 | 7287篇 |
1975年 | 3612篇 |
1974年 | 3468篇 |
1973年 | 3553篇 |
1972年 | 2916篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Performance study of iSCSI-based storage subsystems 总被引:9,自引:0,他引:9
iISCSI is emerging as an end-to-end protocol for transporting storage I/O block data over IP networks. By exploiting the ubiquitous Internet infrastructure, iSCSI greatly facilitates remote storage, remote backup, and data mirroring. This article evaluates the performance of two typical iSCSI storage subsystems by measuring and analyzing block-level I/O access performance and file-level access performance. In the file-level performance study, we compare file access performance in an NAS scheme with that in an iSCSI-based SAN scheme. Our test results show that Gigabit Ethernet-based iSCSI can reach very high bandwidth, close to that of a direct FC disk access in block I/O access. However, when the iSCSI traverses through longer distance, throughput relies heavily on the available bandwidth between the initiator and the target. On the other hand, the file-level performance shows that iSCSI-based file access (SAN scheme) provides higher performance than using NFS protocol in Linux and SMB protocol in Windows (NAS scheme). However, the advantage of using iSCSI-based file accesses decreases as the file size increases. The obtained experimental results shed some light on the performance of applications based on iSCSI storage. 相似文献
22.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
23.
The In-site of Ba2In2O5 with Brownmillerite structure was partially substituted for Ce4+ ions in order to examine the doping effect on the order-disorder transition. Ba2In2 – x
Ce
x
O5 + x/2 (x = 0.1, 0.2, 0.3, 0.5, 1.0, and 1.5) were prepared by solid state reaction. X-Ray diffraction analyses of these powder samples demonstrated that Ba2In2 – x
Ce
x
O5 + x/2 (x = 0.1 and 0.2) possesses Brownmillerite structure. With increasing content of Ce4+ ion the crystal system of Ba2In2 – x
Ce
x
O5 + x/2 (x = 0.3, 0.5, and 1.0) changed to cubic perovskite structure above the order-disorder transition temperature of Ba2In2O5. Arrhenius plots of the electrical conductivities of Ba2In2 – x
Ce
x
O5 + x/2 (x = 0.2, 0.3, and 1.0) exhibited no discontinuity. These compounds had high transference numbers of oxide ion above 973 k. 相似文献
24.
The basic methods of verifying continuous automatic belt weighers are described. A comparative analysis of these methods on the basis of experimental studies is made and ways of implementing the results in industry are recommended. 相似文献
25.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
26.
Yu. I. Golovin D. V. Lopatin R. K. Nikolaev A. V. Umrikhin 《Technical Physics Letters》2004,30(5):426-428
The effect of crystal orientation on the photogeneration of free charge carriers was studied for C60 single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with
respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C60 crystal. 相似文献
27.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations. 相似文献
28.
Popular biorthogonal wavelet filters via a lifting scheme and its application in image compression 总被引:2,自引:0,他引:2
Cheng L. Liang D.L. Zhang Z.H. 《Vision, Image and Signal Processing, IEE Proceedings -》2003,150(4):227-232
A technique using a lifting scheme is presented for constructing compactly supported wavelets whose coefficients are composed of free variables locating in an interval. An efficient approach-based wavelet for image compression is developed by selecting the coefficients of the 9-7 wavelet filter and associated lifting scheme. Furthermore, the rationalised coefficients wavelet filter that can be implemented with simple integer arithmetic is achieved and its characteristic is close to the well known original irrational coefficients 9-7 wavelet filters developed by A. Cohen et al. (Commun. Pure Appl. Maths., vol.45, no.1, p.485-560, 1992). To reduce the computational cost of image coding applications further, an acceleration technique is proposed for the lifting steps. Software and hardware simulations show that the new method has very low complexity, and simultaneously preserves the high quality of the compressed image. 相似文献
29.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
30.
E. Griese Prof. Dr.-Ing. 《e & i Elektrotechnik und Informationstechnik》2003,120(6):186-191
Optical interconnection technology on the printed circuit board level is a key technology for future microelectronic equipment. The consideration of functional, technological, and economical requirements results in a hybrid solution, where electrical and optical interconnects are integrated into one substrate called electrical optical printed circuit board. The significant part of the entire design process for electrical optical printed circuit boards is marked by the design supporting modelling and simulation of optical interconnects. Based on an abstract model for an entire optical interconnect a simulation model for optical multimode-waveguides is presented, taking into account all significant waveguide properties. Apart from that, the modeling of active components (laser- and photo-diodes) is addressed. 相似文献