全文获取类型
收费全文 | 10778篇 |
免费 | 511篇 |
国内免费 | 64篇 |
专业分类
电工技术 | 270篇 |
综合类 | 27篇 |
化学工业 | 2339篇 |
金属工艺 | 234篇 |
机械仪表 | 257篇 |
建筑科学 | 350篇 |
矿业工程 | 11篇 |
能源动力 | 712篇 |
轻工业 | 1047篇 |
水利工程 | 120篇 |
石油天然气 | 218篇 |
武器工业 | 4篇 |
无线电 | 1337篇 |
一般工业技术 | 1928篇 |
冶金工业 | 563篇 |
原子能技术 | 90篇 |
自动化技术 | 1846篇 |
出版年
2024年 | 30篇 |
2023年 | 283篇 |
2022年 | 615篇 |
2021年 | 773篇 |
2020年 | 542篇 |
2019年 | 532篇 |
2018年 | 684篇 |
2017年 | 487篇 |
2016年 | 538篇 |
2015年 | 343篇 |
2014年 | 487篇 |
2013年 | 855篇 |
2012年 | 558篇 |
2011年 | 625篇 |
2010年 | 407篇 |
2009年 | 372篇 |
2008年 | 323篇 |
2007年 | 275篇 |
2006年 | 247篇 |
2005年 | 217篇 |
2004年 | 175篇 |
2003年 | 138篇 |
2002年 | 153篇 |
2001年 | 90篇 |
2000年 | 90篇 |
1999年 | 106篇 |
1998年 | 156篇 |
1997年 | 130篇 |
1996年 | 95篇 |
1995年 | 93篇 |
1994年 | 69篇 |
1993年 | 72篇 |
1992年 | 60篇 |
1991年 | 30篇 |
1990年 | 35篇 |
1989年 | 57篇 |
1988年 | 60篇 |
1987年 | 32篇 |
1986年 | 39篇 |
1985年 | 53篇 |
1984年 | 55篇 |
1983年 | 49篇 |
1982年 | 32篇 |
1981年 | 28篇 |
1980年 | 33篇 |
1979年 | 27篇 |
1978年 | 26篇 |
1977年 | 25篇 |
1976年 | 36篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Intercalation of poly[oligo(oxyethylene) methacrylates] onto sodium montmorillonite (MMT) clay has been investigated. A polymer–clay hybrid has been synthesized through intercalation of the monomer followed by its solution free‐radical polymerization. Eight polymer–clay hybrids were prepared using different weight ratios of clay, different oligo(oxyethylene) lengths and different proportions of crosslinker. Evidence of the development of nanostructures is obtained from scanning electron microscopy, and wide‐angle X‐ray diffraction studies support these results which show disappearance of the peak characteristic to d001 spacing. In this hybrid MMT is dispersed homogeneously in the polymer matrix. © 2003 Society of Chemical Industry 相似文献
22.
Mohammed F. Bain M.F. Ruddell F.H. Linton D. Gamble H.S. Fusco V.F. 《Electron Devices, IEEE Transactions on》2005,52(7):1384-1391
The design and simulation of a novel silicon Schottky diode for nonlinear transmission line (NLTL) applications is discussed in this paper. The Schottky diode was fabricated on a novel silicon-on-silicide-on-insulator (SSOI) substrate for minimized series resistance. Ion implantation technology was used as a low-cost alternative to molecular beam epitaxy to approximate the delta (/spl delta/) doping profile, which results in strong nonlinear CV characteristics. The equivalent circuit model of the Schottky diode under reverse bias conditions was extracted from the S-parameter measurement performed on the diode. The measured CV characteristics show strong nonlinearity, the junction capacitance varies from 182 to 47.5 fF as the reverse bias voltage is varied from 0 to -5 V. A parasitic inductance of 40 pH was measured for the silicon Schottky diode, which is much smaller than a comparable sized GaAs Schottky diode. This small inductance is an advantage for the silicon Schottky diode offering improvement in the silicon NLTL performance. 相似文献
23.
Vibration and damping analysis of beams with composite coats 总被引:1,自引:0,他引:1
Ahmed Abd El-Hamid Hamada 《Composite Structures》1995,32(1-4):33-38
Numerical and experimental investigations of the dynamic behavior for coated laminate composite beams has been presented and discussed in the present work. A numerical technique is utilized to compute the eigen parameters of coated laminated composite beams. An attempt to study the variations in the natural frequencies and damping properties of laminated composite coated beams taking into account different lamina orientation of coat and various kinds of core isotropic material (steel and aluminium) is introduced. The variations of the eigen parameters vs. the code number of the coated layer with the use of various types of isotropic material are measured by utilizing (the frequency response displayed on) an (FFT) analyzer. The experimental and numerical work is carried out on four different fiber orientations, aligned longitudinally, transversely, making 45 ° with the fibers direction and randomly oriented. Comparison between experimental and numerical results shows a tight connection between them. 相似文献
24.
This article presents an autonomous guide agent that can observe a community of learners on the web, interpret the learners' inputs, and then assess their sharing. The goal of this agent is to find a reliable helper (tutor or other learner) to assist a learner in solving his task. Despite the growing number of Internet users, the ability to find helpers is still a challenging and important problem. Although helpers could have much useful information about courses to be taught, many learners fail to understand their presentations. For that, the agent must be able to deal autonomously with the following challenges: Do helpers have information that the learners need? Will helpers present information that learners can understand? And can we guarantee that these helpers will collaborate effectively with learners? We have developed a new filtering framework, called a pyramid collaborative filtering model, to whittle the number of helpers down to just one. We have proposed four levels for the pyramid. Moving from one level to another depends on three filtering techniques: domain model filtering, user model filtering, and credibility model filtering. A new technique is filtering according to helpers' credibilities. Our experiments show that this method greatly improves filtering effectiveness. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 1065–1082, 2007. 相似文献
25.
Educational research over the past three years has intensified such that the context of learning resources needs to be properly modeled. Many researchers have described and even mandated the use of ontologies in the research being conducted, yet the process of actually connecting one or more ontologies to a learning object has not been extensively discussed. This paper describes a practical model for associating multiple ontologies with learning objects while making full use of the IEEE LOM specification. The model categorizes these ontologies according to five major categories of context based on the most popular fields of study actively being pursued by the educational research community: Thematic context, Pedagogical context, Learner context, Organizational context, and Historical/Statistical context. 相似文献
26.
27.
Lentils, rice and their blend (Koshary) were cooked by traditional Egyptian methods. Cooking resulted in slight changes in the total nitrogen, as well as in the non-protein nitrogen (NPN), ether extract and crude fibre of the three products, compared with raw grains. In contrast, significant decreases were found in the mineral elements, indicating losses through leaching, on washing and cooking. The mineral composition of lentils' cooking liquor confirmed this. 相似文献
28.
Mohammed Nurul Afsar Hua Chi 《Journal of Infrared, Millimeter and Terahertz Waves》1994,15(7):1161-1179
The room temperature application of sapphire as window material at higher frequencies is not feasible since its absorption coefficient increases almost linearly with increasing frequency in the millimeter wavelength region. At cryogenic temperature the absorption coefficient value decreases only by a few factors (factor of 2 to 3) in the 90 – 200 GHz region. The earlier reported temperature squared dependence (decrease) in the absorption coefficient or the loss tangent value is totally absent in our broad band continuous wave data we are reporting here (at 6.5 K, 35K, 77K and 300K) and one we reported at conferences earlier. Our results are verified by another technique. We utilize our precision millimeter wave dispersive Fourier transform spectroscopic techniques at room temperature and at cryogenic temperatures The extra high resistivity single crystal compensated silicon is no doubt the lowest loss material available at room temperature in the entire millimeter wavelength region At higher millimeter wave frequencies an extra high resistivity silicon window or an window made with extra high resistivity silicon coated with diamond film would certainly make a better candidate in the future. A single free standing synthetic diamond window seems to have higher absorption coefficient values at millimeter wavelength region at this time although it is claimed that it possesses good mechanical strength and higher thermal conductivity characteristics. It certainly does not rule out the use of diamond film on a single crystal high resistivity silicon to improve its mechanical strength and thermal conductivity 相似文献
29.
The suppression of the superconductivity by praseodymium in La1−x
Pr
x
CaBaCu3O7 may be explained in terms of the difference in the electronic or crystal structure between these compounds. Three compositions
with x=0.0, 0.5, 1.0 were, therefore, investigated by X-ray diffraction in order to determine the unit-cell dimensions at room temperature
as well as at lower temperatures down to 5 K. The results showed no considerable changes in the orthorhombic unit-cell dimensions
on decreasing the temperature to 5 K. Unit-cell volumes at low temperatures were 0.99 of the room temperature values. The
intensity sequence of reflections in the diffraction pattern was the same for all samples throughout the range of temperature
studied. 相似文献
30.
S. J. C. Irvine A. Stafford M. U. Ahmed A. Brown H. Kheyrandish 《Journal of Electronic Materials》1997,26(6):723-727
The first detailed comparison has been made of the metalorganic vapor phase epitaxy growth rates of CdTe, ZnTe, and ZnSe,
measured in situ with laser reflectometry. The comparison also includes the photo-assisted growth with visible radiation from
an argon ion laser. Using a standard Group II precursor (DMCd or DMZn.TEN) partial pressure of 1.5 × 10−4 atm, VI/II ratio of 1 and DIPM (M = Te, Se) the maximum growth rates are in the region of 10 to 15 AU/ s. Decrease in growth
rates of ZnTe at higher temperatures or higher laser powers have been attributed to the desorption from the substrate of unreacted
Te precursor. The behavior of DTBSe is quite different from DIPSe for both pyrolytic and photo-assisted growth. The maximum
growth rate is around 1 AU/ s with very little photo-enhancement, except at 300°C. Secondary ion mass spectroscopy analysis
of hydrogen concentration in the ZnSe layers shows high concentrations, up to 5.9 × 1019 atoms cm−3 for DTBSe grown ZnSe under pyrolytic conditions. These results show that the growth kinetics play an important part in the
incorporation of hydrogen and passivation of acceptor doped material. 相似文献