全文获取类型
收费全文 | 17191篇 |
免费 | 917篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 169篇 |
综合类 | 19篇 |
化学工业 | 3787篇 |
金属工艺 | 335篇 |
机械仪表 | 327篇 |
建筑科学 | 659篇 |
矿业工程 | 33篇 |
能源动力 | 529篇 |
轻工业 | 2585篇 |
水利工程 | 140篇 |
石油天然气 | 41篇 |
武器工业 | 1篇 |
无线电 | 924篇 |
一般工业技术 | 2845篇 |
冶金工业 | 2871篇 |
原子能技术 | 101篇 |
自动化技术 | 2765篇 |
出版年
2023年 | 113篇 |
2022年 | 144篇 |
2021年 | 592篇 |
2020年 | 356篇 |
2019年 | 399篇 |
2018年 | 656篇 |
2017年 | 613篇 |
2016年 | 649篇 |
2015年 | 457篇 |
2014年 | 653篇 |
2013年 | 1121篇 |
2012年 | 1061篇 |
2011年 | 1200篇 |
2010年 | 860篇 |
2009年 | 811篇 |
2008年 | 829篇 |
2007年 | 717篇 |
2006年 | 604篇 |
2005年 | 524篇 |
2004年 | 405篇 |
2003年 | 374篇 |
2002年 | 336篇 |
2001年 | 245篇 |
2000年 | 248篇 |
1999年 | 232篇 |
1998年 | 1029篇 |
1997年 | 617篇 |
1996年 | 414篇 |
1995年 | 248篇 |
1994年 | 211篇 |
1993年 | 209篇 |
1992年 | 71篇 |
1991年 | 91篇 |
1990年 | 72篇 |
1989年 | 74篇 |
1988年 | 63篇 |
1987年 | 59篇 |
1986年 | 54篇 |
1985年 | 59篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 57篇 |
1981年 | 66篇 |
1980年 | 51篇 |
1979年 | 26篇 |
1978年 | 32篇 |
1977年 | 68篇 |
1976年 | 95篇 |
1975年 | 22篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Tamás Ungár Levente Balogh Gábor Ribárik 《Metallurgical and Materials Transactions A》2010,41(5):1202-1209
Diffraction line broadening is caused by different defects present in crystalline materials: (1) small coherent domains, (2)
dislocations, (3) other types of microstrains, (4) twin boundaries, (5) stacking faults, (6) chemical inhomogeneities, and
(7) grain-to-grain second-order internal stresses. Line profile analysis provides qualitative and quantitative information
about defect types and densities, respectively. Line profiles can broaden, be asymmetric, and be shifted, and these features
can be anisotropic in terms of hkl indices. A few thumb rules help qualitative selection of lattice defect types. If the breadths do not increase globally with
hkl, the defects are of size type, i.e., either the domain size is small or twinning or faulting, or both, is present. Whenever the breadths increase globally, the
defects produce microstrains. Physically based profile functions can be determined for the different defect types and hkl anisotropy. The qualitative input about defect types based on different experimental observations allows adequate quantitative
evaluation of the densities of different defect types by using physically modeled profile functions. 相似文献
992.
Silvia Baena‐Ruano Carlos Jiménez‐Ot Inés M. Santos‐Dueñas Jorge E. Jiménez‐Hornero José L. Bonilla‐Venceslada Carmen Álvarez‐Cáliz Isidoro García‐García 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2010,85(7):908-912
BACKGROUND: The acetification process needs an overall study of the variables influencing it in order to establish their optimum values. Based on industrial experience and available literature, including a recently proposed model by the authors, among the variables most strongly influencing the acetification process are the ethanol concentration at the time the reactor is unloaded, the unloaded volume and the loading rate. To ensure economically efficient industrial production of vinegar, and to check the predictions of the aforementioned model, the influence of the final ethanol concentration at unloading time on the mean acetification rate and on productivity has been studied in this work. RESULTS: An increase in the final ethanol concentration from 0.5 to 3.5% (v/v) increased the mean overall acetification rate and acetic acid production by 38 and 26%, respectively. The increase was established mainly during the loading phase. CONCLUSIONS: The final ethanol concentration is a key variable for process optimization. If a high rate is desired then a product containing much unused substrate will be obtained, which may be industrially unacceptable. These results suggest the necessity to investigate other possibilities when high values for yield and productivity must to be achieved. Copyright © 2010 Society of Chemical Industry 相似文献
993.
Paul-Aymé Toulemonde Julie Diani Pierre Gilormini Nancy Desgardin Robert Nevière 《The Journal of Adhesion》2018,94(8):657-666
The integrity of propellant/liner structures in rocket motors is critical to ensure controlled combustion of the engine. In an effort to improve the bonding between the liner and the propellant, it is necessary to characterize it well. Therefore, a propellant–liner structure, bounded thanks to co-curing, has been submitted to a peel test while recording the macroscopic fracture energy and the local displacement field on the propellant-free surface. The experimental setup includes two cameras in order to record the displacement field on the propellant-free surface. Upon loading, the peel force stabilizes quickly due to a cohesive fracture in the propellant, providing access to the fracture energy. While the crack propagates through the propellant, it is observed that only a small localized area is submitted to strain, and most of the structure remains unstrained. 相似文献
994.
Alberto Coz Mercedes Villegas Ana Andrés Javier R. Viguri Dionissios Mantzavinos Nikolaos P. Xekoukoulotakis 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(12):1542-1547
BACKGROUND: Olive oil mill waste is a serious environmental problem in the Mediterranean basin given its particular characteristics of high organic content, seasonal and localized generation, and the type of processing involved. RESULTS: Olive mill waste from a three‐phase mill was characterized by means of total analysis, availability and mobility of the pollutants in order to help the decision‐maker about possible options for its valorization and/or disposal. Water content, loss of ignition, total organic carbon, phenol index and metals concentrations were measured to fully characterize the waste. Three leaching tests (NEN 7341, EN 12457 and UNE CEN‐TS 15364 EX) were carried out to evaluate the environmental hazard of the waste material and the leachates were characterized with respect to electric conductivity, pH, heavy metals, anions and organic pollutants (phenol index and total organic carbon) according to European waste directives. The results were compared with EU regulations for inert, non‐hazardous and hazardous waste disposal. CONCLUSION: It was found that not only organic parameters must be taken into account concerning the fate of this waste material, but also the mobility of heavy metals and anions should be studied. Furthermore, stabilization/solidification processes are recommended before landfill disposal of this kind of agro‐waste material. Copyright © 2011 Society of Chemical Industry 相似文献
995.
996.
Fernando Hernández Sobrino Carlos Rodríguez Monroy José Luís Hernández Pérez 《Renewable & Sustainable Energy Reviews》2010,14(9):3076-3083
For several years the European Union (E.U.) has been promoting the use of biofuels due to their potential benefits such as the reduction of dependence on foreign energy imports (the raw materials can be produced within the E.U.), the more stable fossil fuel prices (they can replace fossil fuels on the market), the greenhouse gas (GHG) reduction (biofuels’ raw materials fix CO2 from the atmosphere) and the fact that they can represent an additional source of income for the primary sector (biofuels’ raw materials are vegetables that can be grown and harvested).Despite the public aids (direct and indirect), biofuels are not competitive with fossil fuels at present, but it is possible that in the future the environment conditions change and biofuels might become competitive. It is difficult to assess whether this will happen or not, but it is possible to make an assessment of a future situation.This article presents two analyses with one objective: to determine if biofuels might become competitive in the future. The first analysis examines the dependencies of two quotations which have a strong relationship with fuels: the crude oil quotation and the CO2 bond quotation. The analysis of these relationships may help to forecast the future competitiveness of biofuels. For instance, biofuels’ future competitiveness will be higher if their raw material costs are not related to crude oil quotations or if they are related in a negative way (the higher the crude oil quotations the lower the raw material biofuels’ cost). The second analysis focuses on the market penetration of biofuels in the Spanish market. There are data related to biofuels monthly consumption in Spain since 2007 and it is possible to know if biofuels are gaining market quota since then. 相似文献
997.
José L. Lerma Miriam Cabrelles Cristina Portalés 《Construction and Building Materials》2011,25(5):2190-2197
It is well known that the content of water does affect materials behaviour and may cause important damages to buildings, including structural deterioration. Thermography is a non-intrusive imaging technique that allows the inspection of different materials based on their surface temperatures. Within an appropriate thermal analysis, moisture and other structural damages can be detected. The present research work deals with multitemporal thermal analysis to detect moisture on buildings, as well as other alterations. Two different approaches are tested to determine the effectiveness on the moisture surveys, one simple based on image differences, and another more sophisticated based on principal components analysis (PCA). The results are tested at the front door of the Arenberg Castle (Leuven, Belgium). Some moisture maps are derived and used to determine the reliability of either the computation of image differences or the PCA to carry out semi-automatically moisture surveys on architectural façades. The latter method is proven to be superior when using thermal imagery acquired at different times. 相似文献
998.
999.
Rogério Cezar de Cerqueira Leite Manoel Regis Lima Verde Leal Luís Augusto Barbosa Cortez W. Michael Griffin Mirna Ivonne Gaya Scandiffio 《Energy》2009
Increasing use of petroleum, coupled with concern for global warming, demands the development and institution of CO2 reducing, non-fossil fuel-based alternative energy-generating strategies. Ethanol is a potential alternative, particularly when produced in a sustainable way as is envisioned for sugarcane in Brazil. We consider the expansion of sugarcane-derived ethanol to displace 5% of projected gasoline use worldwide in 2025. With existing technology, 21 million hectares of land will be required to produce the necessary ethanol. This is less than 7% of current Brazilian agricultural land and equivalent to current soybean land use. New production lands come from pasture made available through improving pasture management in the cattle industry. With the continued introduction of new cane varieties (annual yield increases of about 1.6%) and new ethanol production technologies, namely the hydrolysis of bagasse to sugars for ethanol production and sugarcane trash collection providing renewable process energy production, this could reduce these modest land requirements by 29–38%. 相似文献
1000.
Brian Williams Mark Cummins José Neira Paul Newman Ian Reid Juan Tardós 《Robotics and Autonomous Systems》2009,57(12):1188-1197
Loop closure detection systems for monocular SLAM come in three broad categories: (i) map-to-map, (ii) image-to-image and (iii) image-to-map. In this paper, we have chosen an implementation of each and performed experiments allowing the three approaches to be compared. The sequences used include both indoor and outdoor environments and single and multiple loop trajectories. 相似文献