全文获取类型
收费全文 | 41642篇 |
免费 | 4924篇 |
国内免费 | 2974篇 |
专业分类
电工技术 | 8090篇 |
综合类 | 4361篇 |
化学工业 | 2334篇 |
金属工艺 | 3100篇 |
机械仪表 | 2872篇 |
建筑科学 | 7285篇 |
矿业工程 | 1799篇 |
能源动力 | 1674篇 |
轻工业 | 484篇 |
水利工程 | 1535篇 |
石油天然气 | 3353篇 |
武器工业 | 428篇 |
无线电 | 1370篇 |
一般工业技术 | 5873篇 |
冶金工业 | 1438篇 |
原子能技术 | 224篇 |
自动化技术 | 3320篇 |
出版年
2024年 | 180篇 |
2023年 | 568篇 |
2022年 | 1141篇 |
2021年 | 1316篇 |
2020年 | 1453篇 |
2019年 | 1235篇 |
2018年 | 1216篇 |
2017年 | 1491篇 |
2016年 | 1518篇 |
2015年 | 1707篇 |
2014年 | 2564篇 |
2013年 | 2322篇 |
2012年 | 2998篇 |
2011年 | 3309篇 |
2010年 | 2456篇 |
2009年 | 2569篇 |
2008年 | 2456篇 |
2007年 | 2795篇 |
2006年 | 2582篇 |
2005年 | 2211篇 |
2004年 | 1760篇 |
2003年 | 1584篇 |
2002年 | 1347篇 |
2001年 | 1136篇 |
2000年 | 949篇 |
1999年 | 863篇 |
1998年 | 621篇 |
1997年 | 619篇 |
1996年 | 509篇 |
1995年 | 407篇 |
1994年 | 342篇 |
1993年 | 233篇 |
1992年 | 192篇 |
1991年 | 173篇 |
1990年 | 209篇 |
1989年 | 158篇 |
1988年 | 107篇 |
1987年 | 48篇 |
1986年 | 34篇 |
1985年 | 31篇 |
1984年 | 27篇 |
1983年 | 31篇 |
1982年 | 30篇 |
1981年 | 7篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1975年 | 2篇 |
1957年 | 1篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
介绍了垫层上载荷试验的类型,通过工程实例对不同类型垫层上的载荷试验应注意的问题进行了分析和探讨,这对通过载荷试验确定双层地基承载力具有一定的实际意义,可供同类工程参考借鉴。 相似文献
92.
Performance analysis of IEEE 802.11 ad hoc networks in the presence of exposed terminals 总被引:1,自引:0,他引:1
The paper evaluates the performance effects of exposed terminals in IEEE 802.11 ad hoc networks in finite load conditions. It derives analytical models for the estimation of channel utilization and media access delay for IEEE 802.11 ad hoc networks in finite load conditions with and without exposed terminals. The simulation results show that the analytical estimated channel utilization and media access delay metrics are fairly accurate. 相似文献
93.
利用测井资料预测塔河油田地层破裂压力 总被引:7,自引:1,他引:6
针对塔河油田奥陶系碳酸盐岩油藏 ,介绍了地层破裂压力预测和地层裂缝高度预测的基本原理 ,选择了塔河油田 4口井的资料进行了破裂压力和裂缝高度预测的成果处理。为塔河油田奥陶系碳酸盐岩储层改造提供了较为可靠的施工参数 相似文献
94.
This paper presents an adaptive Hopfield neural network (AHNN) based methodology, where the slope of the activation function is adjusted, for finding approximate Pareto solutions for the multi-objective optimization problem of emission and economic load dispatch (EELD). We have placed emphasis on finding solutions quickly, rather than the global Pareto solutions, so that our algorithm can be employed in large on-line power systems where variations in load are quite frequent. To enable faster convergence, adaptive learning rates have been developed by using energy function and applied to the slope adjustment method. The proposed algorithm has been tested on selected IEEE bus benchmark systems. The convergence of AHNN is found to be nearly 50% faster than the non-adaptive version. 相似文献
95.
96.
A. G. ATKINS Z. CHEN B. COTTERELL 《Fatigue & Fracture of Engineering Materials & Structures》2003,26(1):67-77
In this paper, energy dissipation rate D vs. Δa curves in ductile fracture are predicted using a ‘conversion’ between loads, load‐point displacements and crack lengths predicted by NLEFM and those found in real ELPL propagation. The NLEFM/ELPL link was recently discovered for the DCB testpiece, and we believe it applies to other cracked geometries. The predictions for D agree with experimental results. The model permits a crack tip toughness R(Δa) which rises from Jc and saturates out when (if) steady state propagation is reached after a transient stage in which all tunnelling, crack tip necking and shear lip formation is established. JR is always greater than the crack tip R(Δa) and continues to rise even after R(Δa) levels off. The analysis is capable of predicting the usual D vs. Δa curves in the literature which have high initial values and fall monotonically to a plateau at large Δa. It also predicts that D curves for CCT testpieces should be higher than those for SENB/CT, as found in practice. The possibility that D curves at some intermediate Δa may dip to a minimum below the levelled‐off value at large Δa is predicted and confirmed by experiment. Recently reported D curves that have smaller initial D than the D‐values after extensive propagation can also be predicted. The testpiece geometry and crack tip R(Δa) conditions required to produce these different‐shaped D vs. Δa curves are established and confirmed by comparison with experiment. The energy dissipation rate D vs. Δa is not a transferable property as it depends on geometry. The material characteristic R(Δa) may be the ‘transferable property’ for scaling problems in ELPL fracture. How it can be deduced from D vs. Δa curves (and by implication, JR vs. Δa curves) is established. 相似文献
97.
通过高炉鼓风机扩压叶片断裂事故,从化学分析、物理检验,结合使用情况对扩压叶片断裂原因进行了详细分析,并提出了改进措施。 相似文献
98.
变压器有载合闸过程中故障分闸后铁心剩磁分析 总被引:3,自引:0,他引:3
通过有载合闸变压器模型,分析了变压器有载合闸过程中由于副边突然短路导致主保护动作时电流和磁通的暂态过程,并对变压器铁心内的剩磁作了定性的分析。 相似文献
99.
In this work we present the discrete models for dynamic fracture of structures built of brittle materials. The models construction is based on Voronoi cell representation of the heterogeneous structure, with the beam lattice network used to model the cohesive and compressive forces between the neighboring cells. Each lattice component is a geometrically exact shear deformable beam which can describe large rigid body motion and the most salient fracture mechanisms. The latter can be represented through the corresponding form of the beam constitutive equations, which are derived either at microscale with random distribution of material properties or at a mesoscale with average deterministic values. The proposed models are also placed within the framework of dynamics, where special attention is paid to constructing the lattice network mass matrix as well as the corresponding time-stepping schemes. Numerical simulations of compression and bending tests is given to illustrate the models performance. 相似文献
100.
The correlation between the crack resistance measured from dynamic and quasi-static J-R tests has been investigated based on test data from instrumented Charpy impact tests and quasi-static single edge notched bend (SENB) J-R tests.The method originally proposed by Aurich et al. [Analyse und Weiterentwicklung Bruchmechanischer versagenskonzepte--Lokales Risswachstum, Ermittlung des Risswiderstandsverhaltens aus der Kerbslagarbeit. BAM Forschungsbericht 192, Berlin 1993, ISBN 3-89429-329-2], to develop a correlation coefficient between the net fracture resistance of Charpy V-notch (ISO) and quasi-static compact tension tests, was extended to establish correlations between so-called ductile-brittle transition fracture resistance curves obtained from instrumented Charpy V-notched (ISO) and fatigue precracked impact tests and quasi-static SENB J-R fracture resistance tests.The correlation between the dynamic and quasi-static crack resistance with regard to practical application to fracture assessments appears to be reasonably consistent, bearing in mind the inherent scatter in crack resistance data in general. The findings of the present research project from testing of ship grade NVE 36 and pressure vessel steel to ASTM A516 Gr. 70 as well as two weldments in the NVE 36 steel, are in excellent agreement with the results of the research conducted by Aurich et al. [Analyse und Weiterentwicklung Bruchmechanischer versagenskonzepte--Lokales Risswachstum, Ermittlung des Risswiderstandsverhaltens aus der Kerbslagarbeit. BAM Forschungsbericht 192, Berlin 1993, ISBN 3-89429-329-2] for structural and pressure vessel steels to the German DIN standard steels including St 52-3, StE 355 and StE 460. 相似文献