全文获取类型
收费全文 | 24373篇 |
免费 | 2443篇 |
国内免费 | 1597篇 |
专业分类
电工技术 | 1525篇 |
综合类 | 3501篇 |
化学工业 | 4712篇 |
金属工艺 | 2217篇 |
机械仪表 | 1006篇 |
建筑科学 | 1379篇 |
矿业工程 | 706篇 |
能源动力 | 791篇 |
轻工业 | 1076篇 |
水利工程 | 424篇 |
石油天然气 | 966篇 |
武器工业 | 148篇 |
无线电 | 1405篇 |
一般工业技术 | 3214篇 |
冶金工业 | 1855篇 |
原子能技术 | 256篇 |
自动化技术 | 3232篇 |
出版年
2024年 | 82篇 |
2023年 | 286篇 |
2022年 | 475篇 |
2021年 | 641篇 |
2020年 | 719篇 |
2019年 | 683篇 |
2018年 | 591篇 |
2017年 | 790篇 |
2016年 | 836篇 |
2015年 | 888篇 |
2014年 | 1318篇 |
2013年 | 1608篇 |
2012年 | 1734篇 |
2011年 | 1793篇 |
2010年 | 1326篇 |
2009年 | 1433篇 |
2008年 | 1357篇 |
2007年 | 1515篇 |
2006年 | 1472篇 |
2005年 | 1305篇 |
2004年 | 1166篇 |
2003年 | 1043篇 |
2002年 | 869篇 |
2001年 | 686篇 |
2000年 | 590篇 |
1999年 | 487篇 |
1998年 | 373篇 |
1997年 | 374篇 |
1996年 | 327篇 |
1995年 | 306篇 |
1994年 | 296篇 |
1993年 | 192篇 |
1992年 | 183篇 |
1991年 | 152篇 |
1990年 | 123篇 |
1989年 | 92篇 |
1988年 | 73篇 |
1987年 | 48篇 |
1986年 | 25篇 |
1985年 | 20篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1963年 | 4篇 |
1959年 | 4篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Shu-Chu Ren Nelson N. Hsu Donald G. Eitzen 《Journal of research of the National Institute of Standards and Technology》2002,107(5):445-473
Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration. 相似文献
62.
横流均匀环境中三维线源型正负浮力射流特性研究 总被引:2,自引:2,他引:0
本文利用混合有限分析法及交错网格。对横流均匀环境中三维线源型正负浮力射流及负浮力射流的特性进行研究,分析了不同工况下流速,温度和湍动能在断面上的分布及影响射流轨迹线的因素,讨论了轨迹线上温度的变化及浮力射流的贴壁现象。对三维长线源型负浮力射流,分析了流速比,喷口弗汝德数对负浮力射流的影响。 相似文献
63.
Optimal Operation of Reservoir Systems using Simulated Annealing 总被引:5,自引:0,他引:5
A stochastic search technique, simulated annealing (SA), is used to optimize the operation of multiple reservoirs. Seminal application of annealing technique in general to multi-period, multiple-reservoir systems, along with problem representation and selection of different parameter values used in the annealing algorithm for specific cases is discussed. The search technique is improved with the help of heuristic rules, problem-specific information and concepts from the field of evolutionary algorithms. The technique is tested for application to a benchmark problem of four-reservoir system previously solved using a linear programming formulation and its ability to replicate the global optimum solution is examined. The technique is also applied to a system of four hydropower generating reservoirs in Manitoba, Canada, to derive optimal operating rules. A limited version of this problem is solved using a mixed integer nonlinear programming and results are compared with those obtained using SA. A better objective function value is obtained using simulated annealing than the value from a mixed integer non-linear programming model developed for the same problem. Results obtained from these applications suggest that simulated annealing can be used for obtaining near-optimal solutions for multi-period reservoir operation problems that are computationally intractable. 相似文献
64.
求得了带有集中质量的分布质量弹性转轴系统横向自由振动的频率方程和振型函数的精确解析表达式,及其与不转动轴系统自由振动的频率方程和振型函数及转动角速度之间的精确解析关系 相似文献
65.
通过电化学极化曲线和失重实验,研究了氨荒酸盐对铜在氯化钠溶液中的缓蚀性能,并与相应胺的缓蚀性能进行了对比。结果表明:氨荒酸盐对铜具有较好的缓蚀性能。 相似文献
66.
TRT入口方管道爆裂原因剖析 总被引:1,自引:0,他引:1
介绍了鞍钢7#高炉TRT装置入口方管道爆裂事故经过,进行了原因分析,并提出了解决措施。 相似文献
67.
M. Portillo
J. H. Dohr
《Design Studies》1994,15(4):403-416Scholars in design face two central challenges in design methods inquiry: firstly, to integrate process and solution, and secondly, to examine developmental junctures leading to innovation. With these goals in mind, we maintain that design criteria deserve greater attention and illustrate this position with a study of noted designers' use of criteria. The primary finding was that five criteria functions were considered during the design process. The study also explored potential relationships between designer variables (i.e., professional expertise and personality type) and criteria use. 相似文献
68.
本文主要简述与运用AIR-C2H2原子吸收光谱法进行镉镍电池正极浸渍液中钴含量的测定,介绍了钴最佳测定条件及呈良好线性范围的浓度。同时对样品消化处理条件,在测定中样品的干扰因素进行了综合考虑,该方法具有很好的灵敏度,很好的重复性,干扰小,同时具有方法步骤简单,操作容易掌握等特点,对样品钴含量的测定,其相对标准偏差均小于1.0%(n=6),标准加入回收率均在97.0%~102.0%(n=5)范围内,结果表明,运用AIR-C2H2原子吸收光谱法测定镉镍电池正极浸渍液中钴含量的分析,达到了实验室分析质量控制的要求,完全适用于镉镍电池正极浸渍液中钴含量的控制分析和样品系统分析。 相似文献
69.
Angela Altomare Carmelo Giacovazzo Anna Grazia Giuseppina Moliterni Rosanna Rizzi 《Journal of research of the National Institute of Standards and Technology》2004,109(1):125-132
The ab-initio crystal structure solution by powder diffraction data requires great efforts because of the collapse of the experimental information onto the one dimensional 2θ axis of the pattern. Different strategies will be described aiming at improving the process of extraction of the integrated intensities from the experimental pattern in order to make more straightforward the structure solution process by direct methods. Particular attention will be devoted to the EXPO program. Some of its performance will be analysed and results will be shown. 相似文献
70.