全文获取类型
收费全文 | 69981篇 |
免费 | 4103篇 |
国内免费 | 152篇 |
专业分类
电工技术 | 674篇 |
综合类 | 255篇 |
化学工业 | 13756篇 |
金属工艺 | 1318篇 |
机械仪表 | 1410篇 |
建筑科学 | 2305篇 |
矿业工程 | 177篇 |
能源动力 | 1752篇 |
轻工业 | 11449篇 |
水利工程 | 724篇 |
石油天然气 | 310篇 |
武器工业 | 9篇 |
无线电 | 4094篇 |
一般工业技术 | 11044篇 |
冶金工业 | 14885篇 |
原子能技术 | 390篇 |
自动化技术 | 9684篇 |
出版年
2024年 | 137篇 |
2023年 | 572篇 |
2022年 | 1072篇 |
2021年 | 1901篇 |
2020年 | 1491篇 |
2019年 | 1624篇 |
2018年 | 2461篇 |
2017年 | 2401篇 |
2016年 | 2536篇 |
2015年 | 1931篇 |
2014年 | 2522篇 |
2013年 | 4833篇 |
2012年 | 3873篇 |
2011年 | 4079篇 |
2010年 | 3134篇 |
2009年 | 2965篇 |
2008年 | 2940篇 |
2007年 | 2650篇 |
2006年 | 1940篇 |
2005年 | 1768篇 |
2004年 | 1751篇 |
2003年 | 1605篇 |
2002年 | 1516篇 |
2001年 | 1219篇 |
2000年 | 965篇 |
1999年 | 1089篇 |
1998年 | 4826篇 |
1997年 | 3171篇 |
1996年 | 2087篇 |
1995年 | 1233篇 |
1994年 | 987篇 |
1993年 | 1074篇 |
1992年 | 393篇 |
1991年 | 438篇 |
1990年 | 372篇 |
1989年 | 349篇 |
1988年 | 362篇 |
1987年 | 311篇 |
1986年 | 288篇 |
1985年 | 324篇 |
1984年 | 238篇 |
1983年 | 166篇 |
1982年 | 219篇 |
1981年 | 248篇 |
1980年 | 228篇 |
1979年 | 148篇 |
1978年 | 134篇 |
1977年 | 333篇 |
1976年 | 628篇 |
1975年 | 139篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
Lorena Rodríguez-López Myriam Rincón-Fontán Xanel Vecino Ana B. Moldes Jose M. Cruz 《Journal of surfactants and detergents》2020,23(1):79-90
Over the last few years, the global biosurfactant market has raised due to the increasing awareness among consumers, for the use of biological or bio-based products. Because of their composition, it can be speculated that these are more biocompatible and more biodegradable than their chemical homologous. However, at the moment, no studies exist in the literature about the biodegradability of biosurfactants. In this work, a biosurfactant contained in a crude extract, obtained from a corn wet-milling industry stream that ferments spontaneously in the presence of lactic acid bacteria, was subjected to a biodegradation study, without addition of external microbial biomass, under different conditions of temperature (5–45 °C), biodegradation time (15–55 days), and pH (5–7). For that, a Box–Behnken factorial design was applied, which allowed to predict the percentage of biodegradation for the biosurfactant contained in the crude extract, between the range of the independent variables selected in the study, obtaining biodegradation values between 3 and 80%. The percentage of biodegradation for the biosurfactant was calculated based on the increase in the surface tension of samples of the crude extract. Furthermore, it was also possible to predict the variation in t1/2 for the biosurfactant (time to achieve the 50% of biodegradation) under different conditions. 相似文献
72.
73.
Luca Pietrobon Lorenzo Fallarino Andreas Berger Andrey Chuvilin Flix Casanova Luis E. Hueso 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(47):6295-6301
Graphene has been predicted to develop a magnetic moment by proximity effect when placed on a ferromagnetic film, a promise that could open exciting possibilities in the fields of spintronics and magnetic data recording. In this work, the interplay between the magnetoresistance of graphene and the magnetization of an underlying ferromagnetic insulating film is studied in detail. A clear correlation between both magnitudes is observed but through a careful modeling of the magnetization and the weak localization measurements, that such correspondence can be explained by the effects of the magnetic stray fields arising from the ferromagnetic insulator is found. The results emphasize the complexity arising at the interface between magnetic and 2D materials. 相似文献
74.
75.
D. Solís-Cortés E. Navarrete-Astorga J.L. Costa-Krämer J. Salguero-Fernandez R. Schrebler D. Leinen E.A. Dalchiele J.R. Ramos-Barrado F. Martín 《Ceramics International》2019,45(5):5577-5587
C-axis textured thin films of gallium-doped indium zinc oxide (GIZO) with a 2% ratio of Ga/Zn, were obtained via RF-magnetron sputtering with high transparency and electrical conductivity. A Box-Behnken response surface design was used to evaluate the effects of the deposition parameters (In2O3 target power, deposition time, and substrate temperature) on the chemical composition, optical, electrical, and structural properties of the GIZO films. The optical constants and the electrical properties were obtained using optical models. The GIZO stoichiometry, and therefore the In/Zn atomic ratio, affected the crystallinity, crystalline parameters, band gap, and charge carrier mobility of the GIZO films. The charge carrier density was related to the change in the crystalline parameters of the hexagonal structure and the In/Zn atomic ratio. The best electrical conductivity values (1.75?×?103 Ω?1 cm?1) were obtained for GIZO films with In/Zn ratio ≥?1. Several figures of merit (FOM) defined for the visible and solar regions were comparatively used to select the optimal In/Zn atomic ratio that provided the best balance between the conductivity and the transparency. The optimal In/Zn ratio was in a range of 0.85–0.90 for the GIZO films. 相似文献
76.
77.
Chitosan microspheres containing bromocresol green, cresol red, and phenolphthalein for corrosion detection, through pH change, are synthesized in order to be used in protective coatings for aluminium alloys. Microspheres containing corrosion detection species are characterized morphologically (SEM) and physico‐chemically (FTIR, TGA). Release studies (UV–vis) are performed in corrosion‐promoting conditions (pH, NaCl), and detection studies by immersion in media associated with corrosion activity while microspheres' sensing activity is evaluated visually. Electrochemical characterization of AA2024 substrates in the presence of chitosan spheres is performed to understand material performance, and a color change is observed as a result of local pH increase in cathodic areas when corrosion takes place. These findings can be correlated with the results from release studies and seem a promising approach for corrosion sensing purposes, not only because pH increase is possible to detect due to corrosion, but also because chitosan is considered an environmentally friendly material. 相似文献
78.
Pietro Galizia Simone Failla Luca Zoli Diletta Sciti 《Journal of the European Ceramic Society》2018,38(2):403-409
One of the biggest challenges of the materials science is the mutual exclusion of strength and toughness. This issue was minimized by mimicking the natural structural materials. To date, few efforts were done regarding materials that should be used in harsh environments. In this work we present novel continuous carbon fiber reinforced ultra-high-temperature ceramic matrix composites (UHTCMCs) for aerospace featuring optimized fiber/matrix interfaces and fibers distribution. The microstructures – produced by electrophoretic deposition of ZrB2 on unidirectional carbon fibers followed by ZrB2 infiltration and hot pressing – show a maximum flexural strength and fracture toughness of 330 MPa and 14 MPa m1/2, respectively. Fracture surfaces are investigated to understand the mechanisms that affect strength and toughness. The EPD technique allows the achievement of a peculiar salami-inspired architecture alternating strong and weak interfaces. 相似文献
79.
Abraham G. Alvarado Rosaura Hernández-Montelongo Martin Rabelero Lourdes A. Pérez-Carrillo Jorge E. Puig Francisco López-Serrano 《Polymer Engineering and Science》2020,60(2):223-232
A simple but comprehensive model considering homogeneous and micellar nucleation, coagulation, entry of radicals to particles and to micelles and radicals' exit from particles, is presented. The model is validated, in a starved semicontinuous heterophase polymerization of ethyl methacrylate, at three monomer addition rates. The model accurately describes the overall and instantaneous conversion, the average particle density and diameter, and the number and weight average molar masses evolutions over time. It is found that even though the average number of radicals is much smaller than 0.5, the system is not 0-1. An empirical function was used to describe the gel effect. The homogeneous nucleation was the prevailing mechanism for particle formation and large exit rates of radicals were observed. POLYM. ENG. SCI., 60: 223–232, 2019. © 2019 Society of Plastics Engineers 相似文献
80.