全文获取类型
收费全文 | 12734篇 |
免费 | 760篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 171篇 |
综合类 | 15篇 |
化学工业 | 2681篇 |
金属工艺 | 449篇 |
机械仪表 | 939篇 |
建筑科学 | 230篇 |
矿业工程 | 3篇 |
能源动力 | 439篇 |
轻工业 | 1101篇 |
水利工程 | 83篇 |
石油天然气 | 13篇 |
无线电 | 2349篇 |
一般工业技术 | 2744篇 |
冶金工业 | 708篇 |
原子能技术 | 167篇 |
自动化技术 | 1443篇 |
出版年
2024年 | 13篇 |
2023年 | 163篇 |
2022年 | 232篇 |
2021年 | 438篇 |
2020年 | 282篇 |
2019年 | 326篇 |
2018年 | 367篇 |
2017年 | 421篇 |
2016年 | 457篇 |
2015年 | 379篇 |
2014年 | 554篇 |
2013年 | 825篇 |
2012年 | 834篇 |
2011年 | 1015篇 |
2010年 | 735篇 |
2009年 | 781篇 |
2008年 | 723篇 |
2007年 | 570篇 |
2006年 | 495篇 |
2005年 | 446篇 |
2004年 | 413篇 |
2003年 | 368篇 |
2002年 | 383篇 |
2001年 | 293篇 |
2000年 | 261篇 |
1999年 | 245篇 |
1998年 | 363篇 |
1997年 | 237篇 |
1996年 | 179篇 |
1995年 | 123篇 |
1994年 | 111篇 |
1993年 | 91篇 |
1992年 | 65篇 |
1991年 | 56篇 |
1990年 | 50篇 |
1989年 | 57篇 |
1988年 | 30篇 |
1987年 | 39篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 16篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
991.
The low cycle fatigue tests of Ni-base superalloy Hastelloy X have been carried out in the temperature range of 650 - 870 °C with various total strain ranges. A change of slope in the Coffin-Manson (C-M) plot was found at 870 °C: the fatigue life significantly decreased at the total strain range less than 0.6%. The fatigue cracks initiated at the surface of the specimens and propagated transgranularly, regardless of test condition. However, the fatigue crack initiation site on the surface shifted from grain interior to grain boundary (GB) predominantly when the discontinuity of slope in the C-M plot began to occur. The fatigue crack tended to initiate preferentially at the oxidized GB rather than grain interior at 870 °C with total strain range below 0.6%. Under this condition, cyclic stability was pronounced, while cyclic hardening occurred at the rest of test conditions. The dislocation structures responsible for the cyclic stress response may partly account for the determination of major fatigue crack initiation site. 相似文献
992.
In this paper, low-velocity impact response and damage of composite laminates is analytically investigated. A modified displacement field of the plate considering initially loaded in-plane strain is proposed. From the displacement field, a finite element equation on the structural behavior of composite laminate is newly induced and a computational program is coded. Numerical results using the FEM code is compared with the numerical ones from reference. Additional numerical analysis is performed on another impact condition, and the effect of initial in-plane load is investigated. Potential delamination damage area in the first inter-ply surface from the bottom of the laminate is approximately estimated, and the effect of the initial in-plane load and the impact condition are also investigated. Consequently, it may be concluded that the initial in-plane load of the laminate does not affect so much on the impact damage area of the laminate. 相似文献
993.
Won-Yong Choi Sun-Mog Hong 《International Journal of Control, Automation and Systems》2009,7(6):922-929
The local search in tracking with a phased array radar can be characterized in terms of the events that can occur in the search
and the probabilities of those events. In predicting the event probabilities, it is required to evaluate the expectation of
a product of target detection probabilities for repeated beam-positioning in the local search. In this paper, we present a
model of the local search and derive an expression for the expectation of the detection-probability product. An expression
of angular measurement accuracy of target detection is also presented. Evaluation of the expressions requires numerical integration,
which is computationally expensive. Approximations to the expressions are presented in analytic form, which are fairly accurate. 相似文献
994.
A self-biasing magnetostrictive element for a magnetomechanical Electronic Article Surveillance (EAS) marker is fabricated
by annealing a ribbon of ferromagnetic amorphous material (Co47.4Fe31.6Si2Bi19) in a presence of magnetic field applied in a transverse direction relative to the ribbon’s longitudinal axis, and then annealing
in a presence of magnetic field applied in the direction of the longitudinal axis. The two-step annealed ribbon exhibits remanent
magnetization along the longitudinal axis and has plural magnetic domains situated along the longitudinal axis. The magnetic
orientation of each domain is canted by ± 03B8; < 90° from the ribbon axis with the direction of canting alternating from
domain to domain. To obtain such a canted anisotropy, theoretical background for the calculation of the field strength (H)
and canted angle (θ) is described. 相似文献
995.
A regular solution model for the difference of the chemical free energy between γ and ε phases during γ→ε martensitic transformation in the Fe-Mn binary system has been reexamined and partly modified based on many articles concerning
the M
s
and A
s
temperatures of Fe-Mn alloys. Using the regular solution model, the measured M
s
temperatures, and a thermodynamic model for the stacking fault energy (SFE) of austenite (γ), the driving force for γ→ε martensitic transformation, and the SFE of γ have been calculated. The driving force for γ→ε martensitic transformation increases linearly from − 68 to − 120 J/mole with increasing Mn content from 16 to 24 wt pct.
The SFE of γ decreases to approximately 13 at. pct Mn and then increases with increasing Mn content, which is in better agreement with
Schumann’s result rather than Volosevich et al.’s result. 相似文献
996.
Young Soon Chang In Su Choi Do Sun Bai 《Quality and Reliability Engineering International》2002,18(5):383-393
This paper proposes a new method of constructing process capability indices (PCIs) for skewed populations. It is based on a weighted standard deviation method which decomposes the standard deviation of a quality characteristic into upper and lower deviations and adjusts the value of the PCI using decomposed deviations in accordance with the skewness estimated from sample data. For symmetric populations, the proposed PCIs reduce to standard PCIs. The performance of the proposed PCIs is compared with those of standard and other PCIs, and finite sample properties of the estimates are investigated using Monte Carlo simulation. Numerical studies indicate that considerable improvements over existing methods can be achieved by the use of the weighted standard deviation method when the underlying distribution is skewed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
997.
K. H. Eom Y. J. Choi H. Sirisena 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2002,6(6):436-440
We propose a method of pattern classification of electromyographic (EMG) signals using a set of self- organizing feature
maps (SOFMs). The proposed method is simple to apply in that the EMG signals are directly input to the SOFMs without preprocessing.
Experimental results are presented that show the effectiveness of the SOFM based classifier for the recognition of the hand
signal version of the Korean alphabet from EMG signal patterns. 相似文献
998.
Jianjun Gao Choi Look Law Hong Wang Sheel Aditya 《Journal of Infrared, Millimeter and Terahertz Waves》2002,23(11):1611-1626
An improved equivalent circuit model under pinchoff condition for extracting parasitic model parameters for Double Heterojunction δ-doped PHEMTs is presented. Good prediction for S parameters and noise performance are obtained up to 40GHz. A modified parameter extraction technique based on this new model was use to determine a PHEMT equivalent circuit model. Signification improvements of the accuracy of S parameters are obtained by using the new pinchoff model. 相似文献
999.
Mi-Youn Lim Ju-Hyun JeonEun-Young Jeong Chi-Hoon LeeHoi-Seon Lee 《Food chemistry》2007,100(3):1254-1258
The methanol extract of Caesalpinia sappan heartwoods was tested for the growth effects toward five intestinal microorganisms. The biologically active constituent of the C. sappan extract was characterized as 5-hydroxy-1,4-naphthoquinone (C10H6O3). The growth responses varied depending on the bacterial species and dose tested. In the test with Clostridium perfringens, 5-hydroxy-1,4-naphthoquinone produced the strong (+++) inhibition at 5 and 2 mg/disk and moderate (++) inhibition at 1, 0.5, and 0.25 mg/disk. Furthermore, this isolate revealed a weak (+) growth inhibition against Lactobacillus casei at 5 and 2 mg/disk. In comparison of naphthoquinone derivatives, 5-hydroxy-2-methyl-1,4-naphthoquinone had moderate growth inhibition against C. perfringens at 5 and 2 mg/disk, whereas 1,4-naphthoquinone at 5 mg/disk significantly inhibited the growth of all bacteria tested. 1,2-Naphthoquinone had growth inhibition against all bacteria tested at 1 mg/disk. The structure-activity relationship revealed that 5-hydroxy-1,4-naphthoquinone had selective growth inhibition against C. perfringens. These results indicate that hydroxyl functional group of naphthoquinone seems to be required for selective growth-inhibiting activity against C. perfringens. Accordingly, as naturally occurring antimicrobial agents, C. sappan heartwood-derived material could be useful as a preventive agent against diseases caused by C. perfringens. 相似文献
1000.
Polymer blend (poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)) systems with two different mole ratios, complexed with LiCF3SO3 salt, have been characterized at various temperatures and compositions using a thermo‐optical analysis (TOA) technique. We also developed a new melting point depression theory based on the modified perturbed hard sphere chain model to interpret phase behavior of polymer blend electrolyte systems. The obtained results show that the eutectic points move toward higher Tm and lower weight fraction of salt with decreasing PEO mole ratio and also indicate that the mole ratio of PEO–PPO for each polymer blend plays an important role in determining the eutectic point of the polymer blend system. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2314–2319, 2005 相似文献