全文获取类型
收费全文 | 22958篇 |
免费 | 1054篇 |
国内免费 | 315篇 |
专业分类
电工技术 | 484篇 |
综合类 | 543篇 |
化学工业 | 4342篇 |
金属工艺 | 564篇 |
机械仪表 | 798篇 |
建筑科学 | 922篇 |
矿业工程 | 188篇 |
能源动力 | 677篇 |
轻工业 | 2435篇 |
水利工程 | 260篇 |
石油天然气 | 205篇 |
武器工业 | 27篇 |
无线电 | 2503篇 |
一般工业技术 | 3174篇 |
冶金工业 | 3847篇 |
原子能技术 | 190篇 |
自动化技术 | 3168篇 |
出版年
2023年 | 129篇 |
2022年 | 411篇 |
2021年 | 571篇 |
2020年 | 332篇 |
2019年 | 418篇 |
2018年 | 469篇 |
2017年 | 449篇 |
2016年 | 496篇 |
2015年 | 414篇 |
2014年 | 619篇 |
2013年 | 1221篇 |
2012年 | 952篇 |
2011年 | 1152篇 |
2010年 | 882篇 |
2009年 | 948篇 |
2008年 | 916篇 |
2007年 | 918篇 |
2006年 | 804篇 |
2005年 | 652篇 |
2004年 | 721篇 |
2003年 | 950篇 |
2002年 | 1230篇 |
2001年 | 1041篇 |
2000年 | 610篇 |
1999年 | 546篇 |
1998年 | 1378篇 |
1997年 | 899篇 |
1996年 | 662篇 |
1995年 | 449篇 |
1994年 | 325篇 |
1993年 | 367篇 |
1992年 | 203篇 |
1991年 | 162篇 |
1990年 | 148篇 |
1989年 | 135篇 |
1988年 | 136篇 |
1987年 | 117篇 |
1986年 | 116篇 |
1985年 | 155篇 |
1984年 | 88篇 |
1983年 | 93篇 |
1982年 | 86篇 |
1981年 | 104篇 |
1980年 | 99篇 |
1979年 | 63篇 |
1978年 | 53篇 |
1977年 | 100篇 |
1976年 | 195篇 |
1975年 | 51篇 |
1973年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
探讨了激光与电弧相互作用后,焊缝中心上部和下部晶粒大小不同的原因,在此基础上研究了焊接速度的改变对6009铝合金接头的微观组织、拉伸性能、显微硬度的影响。结果表明:6009铝合金激光-MIG焊焊接接头的抗拉强度和延伸率随着焊接速度的增加而增加,拉伸试样的断裂位置由焊缝区转移到热影响区,断口呈现均匀分布的韧窝形貌,断裂机制为微孔聚集形断裂;焊缝中心上部晶粒小于焊缝中心下部,而且尺寸分布均匀。焊缝中心上部的显微硬度则高于焊缝下部。接头热影响区存在软化区,宽度为4~6 mm。 相似文献
992.
Soraya Mendes de Souza Lineu Jose Pedroso Paulo Marcelo Vieira Ribeiro 《土木工程与建筑:英文版》2013,(9):1111-1117
Problems of fluid structure interactions are governed by a set of fundamental parameters. This work aims at showing through simple examples the changes in natural vibration frequencies and mode shapes for wall-cavity systems when the structural rigidity is modified. Numerical results are constructed using ANSYS software with triangular finite elements for both the fluid (2D acoustic elements) and the solid (plane stress) domains. These former results are compared to proposed analytical expressions, showing an alternative benchmark tool for the analyst. Very rigid wall structures imply in frequencies and mode shapes almost identical to those achieved for an acoustic cavity with Neumann boundary condition at the interface. In this case, the wall behaves as rigid and fluid-structure system mode shapes are similar to those achieved for the uncoupled reservoir case. 相似文献
993.
994.
T. Wambecq A. Fenu K. De Gussem G. Parmentier G. De Gueldre B. Van De Steene 《Water and Environment Journal》2013,27(2):247-252
This study quantifies the impact of the oxidation ditch horizontal water velocity on the energy consumption of a full‐scale wastewater treatment plant (WWTP). A WWTP was modelled by means of the ASM2d platform, showing very good correlation with reference operational data. As to reduce the energy requirements of the plant while guarantying the same nutrient removal performance, two approaches were used. A classical aeration control optimization, yielding a 4% energy reduction, was compared with an increase of the oxidation ditch propelling power. The horizontal water velocity in the oxidation ditches was estimated at only 0.15 m/s. By increasing the horizontal water velocity to 0.3 m/s, an 8% energy reduction could be achieved. Moreover, a synergistic effect for classic control optimization and oxidation ditch water velocity optimization resulted in a 14% energy reduction. Energy spent in propelling power counteracts the aeration energy gain derived by an increase in the oxidation ditch horizontal velocity. An optimum in the water velocity was quantified at 0.3 m/s, comparably with its design value. 相似文献
995.
996.
R. H. Charlier C. P. De Meyer 《The International journal of environmental studies》2013,70(4):249-265
Processing municipal and industrial wastes on land and particularly near inhabited centra has met with increased opposition. An apparent remedy to the problem is the establishment of such facilities offshore, hence various projects to build them on artificial islands. The paper examines a concrete proposal to locate such an island offshore from the Belgian Coast. Oceanographic and environmental aspects of the site are discussed, construction methods reviewed, erosion and corrosion effects looked at. The possibility of utilizing ocean power to provide the necessary operation energy is likewise considered. 相似文献
997.
N. De la Cruz L. Esquius D. Grandjean A. Magnet A. Tungler L.F. de Alencastro C. Pulgarín 《Water research》2013
This study focuses on the removal of 22 selected micropollutants in an effluent from a municipal wastewater treatment plant (MWTP) at pilot scale. A reactor of 37 L with five low pressure mercury lamps emitting at 254 nm (UV254) was used. The 22 micropollutants include 15 pharmaceuticals, 2 X-Ray contrast medias, 1 corrosion inhibitor and 4 biocides/pesticides. Five of these 22 compounds were used as indicative substances as proposed by the Swiss Federal Office for the Environment (FOEN) (carbamazepine, diclofenac, sulfamethoxazole, benzotriazole and mecoprop). 相似文献
998.
999.
Christopher D. Sinigalliano Jared S. Ervin Laurie C. Van De Werfhorst Brian D. Badgley Elisenda Ballesté Jakob Bartkowiak Alexandria B. Boehm Muruleedhara Byappanahalli Kelly D. Goodwin Michèle Gourmelon John Griffith Patricia A. Holden Jenny Jay Blythe Layton Cheonghoon Lee Jiyoung Lee Wim G. Meijer Rachel Noble Meredith Raith Hodon Ryu Michael J. Sadowsky Alexander Schriewer Dan Wang David Wanless Richard Whitman Stefan Wuertz Jorge W. Santo Domingo 《Water research》2013
Here we report results from a multi-laboratory (n = 11) evaluation of four different PCR methods targeting the 16S rRNA gene of Catellicoccus marimammalium originally developed to detect gull fecal contamination in coastal environments. The methods included a conventional end-point PCR method, a SYBR® Green qPCR method, and two TaqMan® qPCR methods. Different techniques for data normalization and analysis were tested. Data analysis methods had a pronounced impact on assay sensitivity and specificity calculations. Across-laboratory standardization of metrics including the lower limit of quantification (LLOQ), target detected but not quantifiable (DNQ), and target not detected (ND) significantly improved results compared to results submitted by individual laboratories prior to definition standardization. The unit of measure used for data normalization also had a pronounced effect on measured assay performance. Data normalization to DNA mass improved quantitative method performance as compared to enterococcus normalization. The MST methods tested here were originally designed for gulls but were found in this study to also detect feces from other birds, particularly feces composited from pigeons. Sequencing efforts showed that some pigeon feces from California contained sequences similar to C. marimammalium found in gull feces. These data suggest that the prevalence, geographic scope, and ecology of C. marimammalium in host birds other than gulls require further investigation. This study represents an important first step in the multi-laboratory assessment of these methods and highlights the need to broaden and standardize additional evaluations, including environmentally relevant target concentrations in ambient waters from diverse geographic regions. 相似文献
1000.
The objective of this study is to show that the core competence approach has validity when applied to construction. The focus is on the analysis of the fit between market strategies of firms in the building industry and their core capabilities. Certain strategies require specific core capabilities and key external and internal conditions supporting these capabilities. The resource-based approach focuses on the conditions in a firm, the internal capabilities, and supports a core capability that is demanded. The network literature will be related to external conditions that support a core capability of a firm active in a certain market. In a multiple case study, firms are analysed that are involved in different stages of the building process. The case studies demonstrate firms with consistent patterns of market strategies, core capabilities, and supporting internal and external conditions. The specific core capability of the firm under investigation determines the types of external and internal conditions that are critical. 相似文献