全文获取类型
收费全文 | 324342篇 |
免费 | 3339篇 |
国内免费 | 1275篇 |
专业分类
电工技术 | 5955篇 |
综合类 | 260篇 |
化学工业 | 46533篇 |
金属工艺 | 18426篇 |
机械仪表 | 13119篇 |
建筑科学 | 6379篇 |
矿业工程 | 3136篇 |
能源动力 | 6748篇 |
轻工业 | 19216篇 |
水利工程 | 4509篇 |
石油天然气 | 10132篇 |
武器工业 | 61篇 |
无线电 | 32928篇 |
一般工业技术 | 73555篇 |
冶金工业 | 49435篇 |
原子能技术 | 9507篇 |
自动化技术 | 29057篇 |
出版年
2021年 | 2656篇 |
2019年 | 2602篇 |
2018年 | 11455篇 |
2017年 | 11902篇 |
2016年 | 9227篇 |
2015年 | 3403篇 |
2014年 | 5094篇 |
2013年 | 11784篇 |
2012年 | 9617篇 |
2011年 | 16199篇 |
2010年 | 14225篇 |
2009年 | 14007篇 |
2008年 | 14168篇 |
2007年 | 15643篇 |
2006年 | 7414篇 |
2005年 | 9407篇 |
2004年 | 7801篇 |
2003年 | 7486篇 |
2002年 | 6261篇 |
2001年 | 5685篇 |
2000年 | 5418篇 |
1999年 | 5337篇 |
1998年 | 13217篇 |
1997年 | 9228篇 |
1996年 | 7011篇 |
1995年 | 5491篇 |
1994年 | 4802篇 |
1993年 | 5039篇 |
1992年 | 3805篇 |
1991年 | 3880篇 |
1990年 | 3781篇 |
1989年 | 3688篇 |
1988年 | 3619篇 |
1987年 | 3181篇 |
1986年 | 3256篇 |
1985年 | 3579篇 |
1984年 | 3310篇 |
1983年 | 3163篇 |
1982年 | 2841篇 |
1981年 | 2816篇 |
1980年 | 2866篇 |
1979年 | 2883篇 |
1978年 | 2882篇 |
1977年 | 3136篇 |
1976年 | 3711篇 |
1975年 | 2652篇 |
1974年 | 2513篇 |
1973年 | 2609篇 |
1972年 | 2327篇 |
1971年 | 2118篇 |
排序方式: 共有10000条查询结果,搜索用时 254 毫秒
81.
Automation and Remote Control - A linear-quadratic positional differential game of three persons is considered. Coefficient criteria are established under which there is no Nash equilibrium... 相似文献
82.
Tarasova E. A. Khazanova S. V. Golikov O. L. Puzanov A. S. Obolensky S. V. Zemlyakov V. E. 《Semiconductors》2021,55(12):895-898
Semiconductors - The paper presents the results of modeling the electrophysical parameters of AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures via... 相似文献
83.
Nefedov E. I. Zayarnyi V. P. Ponomarev I. N. 《Journal of Communications Technology and Electronics》2021,66(4):420-426
Journal of Communications Technology and Electronics - Mathematical models are developed for planar symmetric slot antennas (SAs) with constant slot width using a tensor Green function that takes... 相似文献
84.
David J. Lawrence Brianna L. Smith Cameron D. Collard Keyton A. Elliott Kyle L. Fakhoury Jeffery D. Mangold Anna N. Soyka 《International Journal of Hydrogen Energy》2021,46(2):1642-1655
Monolithically-integrated tandem photoanodes were fabricated on substrates consisting of epitaxial n-GaAs1-xPx (x ? 0.32) grown on n+-GaAs wafers. A p+-n junction photovoltaic (PV) cell was first formed by zinc diffusion into the n-GaAs0.68P0.32 from a deposited ZnO coating. After diffusion the ZnO serves as a transparent electrical contact to the resulting p+-GaAs0.68P0.32 surface layer. Transparent, conducting SnO2:F provides chemical and mechanical protection for the ZnO and the underlying PV cell, and it electrically connects this cell to a top BiVO4 photocatalyst layer. In some photoanodes, a WO3 thin film was interposed between the SnO2:F and BiVO4. All oxide coatings were produced by ultrasonic spray pyrolysis except WO3, which was spin coated. Unassisted (unbiased) solar water splitting was achieved, with a solar-to-hydrogen efficiency approaching 2%, without addition of any co-catalyst to the BiVO4 surface. This work can provide insights to other researchers regarding scalable, low cost approaches for the planar monolithic integration of oxide photoanode materials with PV cells to create new tandem devices. 相似文献
85.
Seyed M. N. GHOREISHI Mahdi FAKOOR Ahmad AZIZI 《Frontiers of Structural and Civil Engineering》2021,15(3):623
In this study, gradual and sudden reduction methods were combined to simulate a progressive failure in notched composite plates using a macro mechanics approach. Using the presented method, a progressive failure is simulated based on a linear softening law prior to a catastrophic failure, and thereafter, sudden reduction methods are employed for modeling a progressive failure. This combination method significantly reduces the computational cost and is also capable of simultaneously predicting the first and last ply failures (LPFs) in composite plates. The proposed method is intended to predict the first ply failure (FPF), LPF, and dominant failure modes of carbon/epoxy and glass/epoxy notched composite plates. In addition, the effects of mechanical properties and different stacking sequences on the propagation of damage in notched composite plates were studied. The results of the presented method were compared with experimental data previously reported in the literature. By comparing the numerical and experimental data, it is revealed that the proposed method can accurately simulate the failure propagation in notched composite plates at a low computational cost. 相似文献
86.
Stepanova L. N. Kuten M. M. Bobrov A. L. 《Russian Journal of Nondestructive Testing》2021,57(9):753-761
Russian Journal of Nondestructive Testing - The results of amplitude analysis of discrete acoustic emission signals from developing sources such as fatigue cracks are presented. The studies were... 相似文献
87.
Blagoveshchenskii D. I. Kozlovskii V. N. Vasin S. A. 《Russian Engineering Research》2021,41(12):1255-1259
Russian Engineering Research - Digital tools for managing improvements in automobile production are developed. An operative tool provides warnings regarding the operational quality of the vehicles... 相似文献
88.
Oglezneva S. A. Kachenyuk M. N. Smetkin A. A. Kul’met’eva V. B. 《Russian Engineering Research》2021,41(5):460-462
Russian Engineering Research - The influence of the parameters of spark plasma sintering on the structural evolution within composites consisting of a superalloy, binder, and a zirconium-oxide... 相似文献
89.
The influence of Newtonian heating/cooling in the presence of heat source/sink has been investigated on laminar free convective flow in a vertical annular permeable region. The mathematical model for the problem has been considered as a boundary value problem consisting of two simultaneous ordinary differential equations. The boundary value problem has been transformed to nondimensional form. This has given rise to a number of parameters representing both geometrical and physical features of the problem. Closed‐form analytical solutions of the governing equations have been obtained for two different cases of internal heat generation/absorption. To assess the effects of governing parameters on the fluid velocity and temperature, a number of profiles of these field variables have been presented. The efficacy of the distinct processes on the field variables has been discussed extensively. The main outcome obtained in this study is that the velocity as well as temperature is enhanced in the case of the Newtonian heating while the opposite behavior occurs in the Newtonian cooling for both cases of source and sink. Furthermore, the influence of the governing parameters has been shown on the skin friction, volume flow rate, and the Nusselt number. 相似文献
90.
Gordenchuk A. D. Kudryashova O. S. 《Theoretical Foundations of Chemical Engineering》2019,53(4):591-595
Theoretical Foundations of Chemical Engineering - Calcium formate is widely used in construction, tanning, and textile manufacture and as an E238 biological additive in cosmetology and the food... 相似文献