全文获取类型
收费全文 | 26626篇 |
免费 | 773篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 329篇 |
综合类 | 13篇 |
化学工业 | 5867篇 |
金属工艺 | 516篇 |
机械仪表 | 463篇 |
建筑科学 | 1159篇 |
矿业工程 | 332篇 |
能源动力 | 650篇 |
轻工业 | 1725篇 |
水利工程 | 226篇 |
石油天然气 | 245篇 |
无线电 | 1707篇 |
一般工业技术 | 4078篇 |
冶金工业 | 6147篇 |
原子能技术 | 265篇 |
自动化技术 | 3709篇 |
出版年
2022年 | 201篇 |
2021年 | 410篇 |
2020年 | 266篇 |
2019年 | 345篇 |
2018年 | 422篇 |
2017年 | 367篇 |
2016年 | 485篇 |
2015年 | 390篇 |
2014年 | 614篇 |
2013年 | 1651篇 |
2012年 | 937篇 |
2011年 | 1201篇 |
2010年 | 922篇 |
2009年 | 971篇 |
2008年 | 1149篇 |
2007年 | 1063篇 |
2006年 | 973篇 |
2005年 | 881篇 |
2004年 | 743篇 |
2003年 | 711篇 |
2002年 | 705篇 |
2001年 | 485篇 |
2000年 | 390篇 |
1999年 | 446篇 |
1998年 | 440篇 |
1997年 | 427篇 |
1996年 | 473篇 |
1995年 | 443篇 |
1994年 | 451篇 |
1993年 | 436篇 |
1992年 | 431篇 |
1991年 | 271篇 |
1990年 | 410篇 |
1989年 | 387篇 |
1988年 | 336篇 |
1987年 | 404篇 |
1986年 | 348篇 |
1985年 | 441篇 |
1984年 | 463篇 |
1983年 | 398篇 |
1982年 | 375篇 |
1981年 | 297篇 |
1980年 | 298篇 |
1979年 | 357篇 |
1978年 | 299篇 |
1977年 | 238篇 |
1976年 | 217篇 |
1975年 | 245篇 |
1974年 | 217篇 |
1973年 | 224篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
961.
962.
Marlene Charbonnier Maurice Romand Hilmar Esrom Robert Seeb ck 《The Journal of Adhesion》2001,75(4):381-404
New approaches for electroless plating of nonconductive polymers or polymer-based materials are described. In this work, polyimide substrates were surface-functionalized (i) in nitrogenated (ammonia at reduced pressure) and oxygenated (air at atmospheric pressure) atmospheres under assistance of vacuum-ultraviolet (VUV) irradiation (use of a xenon silent discharge excimer source) or (ii) directly in air at atmospheric pressure using a dielectric-barrier discharge (DBD) device. After functionalization, the substrates were “activated” by dipping in a dilute acidic PdCl2 solution or by spin-coating of a thin metal-organic film (from a solution of palladium acetate (PdAc) in chloroform). The catalytic activity of the so-deposited palladium species toward the electroless deposition of nickel was studied before and after a VUV post-irradiation (in air at atmospheric or reduced pressure) with a view to understanding better the role of the reducer (sodium hypophosphite) within the electroless bath.
This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl2 route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl2 and PdCl2 solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered. 相似文献
This work confirms the specific interest of grafting nitrogenated functionalities onto polymer surfaces for attaching covalently the palladium-based catalyst (in particular in the case of the PdCl2 route), forming thus strong Pd - N - C bonds at the metal/polymer interface. This results from the strong chemical affinity of palladium toward nitrogen. On the other hand, when oxygenated functionalities are surface-grafted, the conventional two-step procedure using SnCl2 and PdCl2 solutions can be proposed due to the strong chemical affinity of tin toward oxygen. The Ni deposits obtained under these different conditions pass the standard Scotch®-tape test and, therefore, exhibit a good practical adhesion. For this same purpose, it is interesting to note that the DBD treatment operating in air at atmospheric pressure causes an increase of the surface roughness and, therefore, an improvement in adhesion of metallic films when their initiation is catalyzed through the PdAc route. In addition, this work demonstrates that extensive research still has to be performed to understand and improve the Ni/polymer adhesion when the PdAc route associated with a VUV irradiation is considered. 相似文献
963.
Abdelkader Outzourhit Ali Naziripour John U. Trefny Tomoko Kito Baki Yarar Robert Yandrofski 《组合铁电体》2013,141(4):227-241
Abstract Ba1?x Sr x TiO3 thin film capacitors have been successfully prepared using rf-sputtering and a metal organic deposition (MOD) method. The structure, microstructure and composition of the BSTO films are presented. Films grown on lanthanum aluminate LAO(100) showed c-axis preferred growth orientation. Broad paraelectric-to-ferroelectric transitions were observed in films prepared by both methods. The tunability of the capacitance by means of an appplied electric field is examined using various capacitor geometries. A decrease in the capacitance exceeding 75% at 77 K was obtained from the MOD deposited films under an electric field strength of 0.3 MV/cm. On the other hand, the tunability of the capacitance in the rf-sputtered films ranged from 5 to 10% at 77 K and at 20 kV/cm, while it exceeds 50% in some films. The results are compared with the predictions of Devonshire's phenomenological theory. 相似文献
964.
965.
Fahhad Alharbi John D. Bass Abdelmajid Salhi Ahmed Alyamani Ho-Cheol Kim Robert D. Miller 《Renewable Energy》2011,36(10):2753-2758
Presented are the results of a comparative analysis to identify abundant, non-toxic binary materials with potential applicability for photovoltaics. Materials other than the conventional Si, CdTe, and Cu(In,Ga)Se2 (CIGS) are examined. The screening is based on the materials’ bulk properties and a set of environmental, physical, and chemical criteria. The screening process is detailed and the properties and applicability of the screened materials are discussed. 相似文献
966.
Use of Sb spray for improved performance of InAs/GaAs quantum dots for novel photovoltaic structures
Stephen P. Bremner Latha NatarajSylvain G. Cloutier Conan WeilandAnup Pancholi Robert Opila 《Solar Energy Materials & Solar Cells》2011,95(7):1665-1670
Photoluminescence output from InAs/GaAs quantum dots has been improved by a Sb treatment immediately prior to capping with GaAs. Spectra taken at 300 and 80 K show a significant increase in output intensity when the quantum dots are exposed for 15 s under a Sb flux of approximately 0.1 monolayers per second, but this improvement is lost when the Sb exposure is extended to 30 s. There is no significant shift in the emission energies between samples indicating strain relief due to the cap layer is not responsible for the improvement. Analysis of temperature dependent photoluminescence taken between 80 and 300 K show increased activation energies at lower temperatures when an Sb spray is used, suggesting passivation of deep defect levels. For the higher temperature activation energy, corresponding to carrier escape from the QD to the barrier, whilst a 15 s Sb spray gives a substantial increase, the longer 30 s Sb spray sees the activation energy decrease, a result deduced to be due to Sb segregation providing shallow defect levels. A band structure including a very thin GaAsSb layer adjacent to the quantum dots is used to explain these results, with the 30 s Sb spray leading to shallow Sb segregation related defects and a lower activation energy. Depth dependent X-ray photoelectron spectroscopy data support the band structure proposed to explain the photoluminescence results and also reveals the highest concentration of Sb at the sample surface suggesting a ‘floating layer’ of Sb during growth of the GaAs cap. Some of the implications of these results, for growth of quantum dot samples and for two novel solar cell proposals, the intermediate band and hot carrier solar cells, are discussed. 相似文献
967.
Practical aspects of implementing surfactant mass balance computation in finite elements models, where the model geometry
shape change is captured by utilizing the arbitrary Lagrange–Eulerian method are discussed briefly. The discussion and the
reported simulations are carried out in two-dimensional Cartesian coordinates. Two alternative approaches to formulating the
governing equation of surfactant mass balance for solving it computationally are presented and discussed. One of the approaches
is based on computing the boundary curvature and boundary tangential velocity, as well as their differentials on the boundary,
directly. The other approach is based on reformulating the governing equation in order to track the proportional rate of change
of local surface area. As a conclusion, it is found that though both of the presented approaches can be configured to perform
adequately in terms of surfactant mass conservation, surface differentials that are necessary to compute the surface curvature
and surface tangential velocity in the first one of the methods evoke numerical oscillations near those points of the boundary
where it is not smooth. The text is accompanied by example simulations and figures. 相似文献
968.
Vincent Lemiale Yuri Estrin Hyoung Seop Kim Robert O’Donnell 《Metallurgical and Materials Transactions A》2011,42(10):3006-3012
Grain refinement by plastic deformation is becoming increasingly popular as a way of producing metals with improved properties,
such as higher mechanical strength. Surface treatment techniques in which a metallic substrate is bombarded with metallic
particles can generate nanocrystalline layers in the impact zone. Understanding the physical mechanisms underlying this grain
refinement is crucial for achieving an improvement of existing experimental processes. In this article, we propose a numerical
framework combining finite element (FE) simulations with a dislocation-based material model to predict the evolution of the
microstructure under particle impact. A single particle normally impacting on a metallic substrate was simulated at different
initial velocities. The simulations were compared with previously reported numerical and experimental data. The results indicate
that our model accurately captures the grain refinement in the impact zone for a broad range of velocities. This approach
provides valuable information on the formation of nanocrystalline layers in both the substrate and the impacting particle.
Its potential applications include processes involving surface treatment by high velocity particles, such as shot peening,
surface mechanical attrition treatment, kinetic metallization, cold spray, etc. 相似文献
969.
Synthesis and properties of cross‐linked polymers from epoxidized rubber seed oil and triethylenetetramine
下载免费PDF全文
![点击此处可从《应用聚合物科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Muhammad Yusuf Abduh Muhammad Iqbal Francesco Picchioni Robert Manurung Hero J. Heeres 《应用聚合物科学杂志》2015,132(40)
A series of epoxidized oils were prepared from rubber seed, soybean, jatropha, palm, and coconut oils. The epoxy content varied from 0.03 to 7.4 wt %, in accordance with the degree of unsaturation of the oils (lowest for coconut, highest for rubber seed oil). Bulk polymerization/curing of the epoxidized oils with triethylenetetramine (in the absence of a catalyst) was carried out in a batch setup (1 : 1 molar ratio of epoxide to primary amine groups, 100°C, 100 rpm, 30 min) followed by casting of the mixture in a steel mold (180°C, 200 bar, 21 h) and this resulted in cross‐linked resins. The effect of relevant pressing conditions such as time, temperature, pressure, and molar ratio of the epoxide and primary amine groups was investigated and modeled using multivariable nonlinear regression. Good agreement between experimental data and model were obtained. The rubber seed oil‐derived polymer has a Tg of 11.1°C, a tensile strength of 1.72 MPa, and strain at break of 182%. These values are slightly higher than for commercial epoxidized soybean oil (Tg of 6.9°C, tensile strength of 1.11 MPa, and strain at break of 145.7%). However, the comparison highlights the potential for these novel resins to be used at industrial/commercial level. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42591. 相似文献
970.
Investment optimization model for freshwater acquisition and wastewater handling in shale gas production
下载免费PDF全文
![点击此处可从《American Institute of Chemical Engineers》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Linlin Yang Ignacio E. Grossmann Meagan S. Mauter Robert M. Dilmore 《American Institute of Chemical Engineers》2015,61(6):1770-1782
Major challenges of water use in the drilling and fracturing process in shale gas production are large volumes required in a short‐period of time and the nonsteady nature of wastewater treatment. A new mixed‐integer linear programming (MILP) model for optimizing capital investment decisions for water use for shale gas production through a discrete‐time representation of the State‐Task Network is presented. The objective is to minimize the capital cost of impoundment, piping, and treatment facility, and operating cost including freshwater, pumping, and treatment. The goal is to determine the location and capacity of impoundment, the type of piping, treatment facility locations and removal capability, freshwater sources, as well as the frac schedule. In addition, the impact of several factors such as limiting truck hauling and increasing flowback volume on the solution is examined. A case study is optimized to illustrate the application of the proposed formulation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1770–1782, 2015 相似文献