全文获取类型
收费全文 | 62859篇 |
免费 | 4163篇 |
国内免费 | 1515篇 |
专业分类
电工技术 | 1197篇 |
综合类 | 7639篇 |
化学工业 | 5070篇 |
金属工艺 | 2761篇 |
机械仪表 | 1377篇 |
建筑科学 | 30342篇 |
矿业工程 | 1670篇 |
能源动力 | 1371篇 |
轻工业 | 339篇 |
水利工程 | 5691篇 |
石油天然气 | 3091篇 |
武器工业 | 221篇 |
无线电 | 381篇 |
一般工业技术 | 4240篇 |
冶金工业 | 2316篇 |
原子能技术 | 235篇 |
自动化技术 | 596篇 |
出版年
2024年 | 115篇 |
2023年 | 389篇 |
2022年 | 1108篇 |
2021年 | 1277篇 |
2020年 | 1368篇 |
2019年 | 930篇 |
2018年 | 1029篇 |
2017年 | 1391篇 |
2016年 | 1585篇 |
2015年 | 1944篇 |
2014年 | 4098篇 |
2013年 | 2692篇 |
2012年 | 4294篇 |
2011年 | 4739篇 |
2010年 | 3828篇 |
2009年 | 4423篇 |
2008年 | 4020篇 |
2007年 | 4938篇 |
2006年 | 4233篇 |
2005年 | 3697篇 |
2004年 | 2985篇 |
2003年 | 2668篇 |
2002年 | 2366篇 |
2001年 | 1873篇 |
2000年 | 1539篇 |
1999年 | 1135篇 |
1998年 | 826篇 |
1997年 | 701篇 |
1996年 | 573篇 |
1995年 | 473篇 |
1994年 | 369篇 |
1993年 | 229篇 |
1992年 | 213篇 |
1991年 | 132篇 |
1990年 | 77篇 |
1989年 | 83篇 |
1988年 | 46篇 |
1987年 | 35篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 5篇 |
1980年 | 25篇 |
1979年 | 5篇 |
1975年 | 2篇 |
1964年 | 5篇 |
1959年 | 8篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
A problem of deformation of a curved shell loaded by internal pressure, axial force, and temperature difference is discussed. Physical equations are derived whereby the displacements and angles of rotation of the line of centers of mass of cross sections of a shell are related to loading parameters. A general constitutive set of equations for a curved element during its deformation is given. Using a method of initial parameters, an analytical solution is obtained for the differential equations for displacements and angles of rotation of the center line allowing for the action of distributed forces and moments. 相似文献
82.
街面水电站混凝土面板堆石坝主要技术问题探讨 总被引:1,自引:1,他引:0
街面水电站拦河坝为混凝土面板堆石坝,在面板止水结构型式、面板防裂措施、上游面的施工方法、趾板开挖处理及趾板灌浆等方面,根据工程实际情况,结合国内外的新技术新工艺进行了探讨。 相似文献
83.
Peter H. Bischoff 《Canadian Metallurgical Quarterly》2007,11(1):4-14
Fundamental concepts of tension stiffening are used to explain why Branson’s equation for the effective moment of inertia Ie does not predict deflection well for fiber reinforced polymer (FRP) reinforced concrete beams. The tension stiffening component in Branson’s equation is shown to depend on the ratio of gross-to-cracked moment of inertia (Ig/Icr), and gives too much tension stiffening for beams with an Ig/Icr ratio greater than 3. FRP beams typically have an Ig/Icr ratio greater than 5, leading to a much stiffer response and underprediction of computed deflections as observed by others in the past. One common approach to computing deflection of FRP reinforced concrete beams has been to use a modified form of the Branson equation. This paper presents a rational development of appropriate modification factors needed to reduce the tension stiffening component in Branson’s original expression to realistic levels. Computed deflections using this approach give reasonable results with the right modification factor, and compare well with a more general unified approach that incorporates a realistic tension stiffening model. Comparison is made with the existing and past correction factors recommended by ACI 440 for predicting deflection of FRP beams. The method presently used by ACI 440 gives reasonable estimates of deflection for glass and carbon FRP reinforced beams. However, this method underestimates deflection of aramid FRP reinforced beams and is restricted to rectangular sections. A proposal is made for adoption of a simple modification factor that works well for all types of FRP bar and beam cross-sectional shape. 相似文献
84.
William D. Tape John B. Kennedy Murty K. S. Madugula 《Canadian Metallurgical Quarterly》2007,11(1):91-98
The current methods of connecting the flanges of precast double tee members, and their respective short comings in specific situations, are described. A new carbon fiber-reinforced polymer (CFRP) flange-to-flange connection is proposed to eliminate the problems associated with repair requirements for the current connections. Design expressions for the currently used mechanical anchorage and the proposed CFRP connection are presented. A comparative calculation for the two systems is given. 相似文献
85.
Juan D. Manrique Mohamed Al-Hussein Avi Telyas Geoff Funston 《Canadian Metallurgical Quarterly》2007,133(3):208-216
This paper focuses on the procedure utilized in the construction of tilt-up irregular concrete panels that are constructed on-site using concrete slabs and wooden formwork. The case study required high-quality concrete finishing. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often 90° joints between panels. To meet precision requirements, the casting slabs were leveled and flattened with laser screed technology and smoothed with chemical solutions. To ensure that the final result met expectations, a mock-up model was built using different types of materials and to simulate site constraints. The architectural design is a composition of precast concrete panels like “Lego” pieces assembled similarly to a jigsaw puzzle. The unique construction process required a state-of-the-art analysis to produce the set quality. Quality conditions as set by the owner included creating a smooth concrete surface on all panels while avoiding damages and reducing equipment and material costs. The proposed methodology is described through its implementation on the case study, which is also described in this paper. 相似文献
86.
混凝土早期收缩开裂是加剧混凝土劣化并导致最终失效的一个重要因素.分析混凝土早期的自由收缩量值是进行收缩开裂研究的基础。为此,基于湿度扩散理论建立了混凝士早期的自生收缩与干燥收缩计算分析模型,经实例验证,计算结果与试验结果有较好的一致性。 相似文献
87.
88.
高 2 7m的水塔建于 193 4年 ,其顶部水罐由 12根钢筋混凝土柱支撑。在倒向侧 7根立柱上形成不同高度的爆破切口 ,背向侧倾倒中心线上的一根立柱上形成小爆破切口 ,其余 4根立柱底部打贯通孔 ,使水塔准确定向倾倒。文中讨论了立柱切口高度的计算 ,爆破参数的确定 ,并介绍了所采用的安全措施。 相似文献
89.
本文比较全面地考虑了钢筋混凝土梁板结构实际设计时的全部必要约束,给出了一套(单跨矩形和T形梁、单向板、按弹性理论计算的双向板和矩形等截面连续梁)简单实用的近优化设计的解析公式,为编制其优化设计的实用程序和图表提供了根据. 相似文献
90.