全文获取类型
收费全文 | 389120篇 |
免费 | 30263篇 |
国内免费 | 16469篇 |
专业分类
电工技术 | 23120篇 |
技术理论 | 59篇 |
综合类 | 24568篇 |
化学工业 | 63839篇 |
金属工艺 | 21760篇 |
机械仪表 | 25087篇 |
建筑科学 | 30522篇 |
矿业工程 | 13040篇 |
能源动力 | 11325篇 |
轻工业 | 22877篇 |
水利工程 | 6790篇 |
石油天然气 | 25589篇 |
武器工业 | 3519篇 |
无线电 | 43477篇 |
一般工业技术 | 44704篇 |
冶金工业 | 20756篇 |
原子能技术 | 3999篇 |
自动化技术 | 50821篇 |
出版年
2024年 | 1615篇 |
2023年 | 6106篇 |
2022年 | 10934篇 |
2021年 | 15349篇 |
2020年 | 11866篇 |
2019年 | 9539篇 |
2018年 | 10903篇 |
2017年 | 12296篇 |
2016年 | 11000篇 |
2015年 | 14913篇 |
2014年 | 19098篇 |
2013年 | 23002篇 |
2012年 | 24819篇 |
2011年 | 27306篇 |
2010年 | 23623篇 |
2009年 | 22532篇 |
2008年 | 22130篇 |
2007年 | 21090篇 |
2006年 | 21686篇 |
2005年 | 19000篇 |
2004年 | 12239篇 |
2003年 | 10383篇 |
2002年 | 9302篇 |
2001年 | 8487篇 |
2000年 | 8909篇 |
1999年 | 10341篇 |
1998年 | 8545篇 |
1997年 | 7126篇 |
1996年 | 6704篇 |
1995年 | 5632篇 |
1994年 | 4587篇 |
1993年 | 3248篇 |
1992年 | 2642篇 |
1991年 | 2048篇 |
1990年 | 1584篇 |
1989年 | 1282篇 |
1988年 | 1066篇 |
1987年 | 713篇 |
1986年 | 564篇 |
1985年 | 355篇 |
1984年 | 252篇 |
1983年 | 212篇 |
1982年 | 207篇 |
1981年 | 143篇 |
1980年 | 144篇 |
1979年 | 71篇 |
1978年 | 37篇 |
1977年 | 39篇 |
1976年 | 58篇 |
1975年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Writing and debugging concurrent (shared-variable) programs is notoriously difficult. This motivated the development of numerous static analysis and run-time analysis techniques designed to (help) ensure that concurrent programs satisfy common correctness requirements for concurrent programs, such as absence of race conditions and absence of deadlocks. This paper focuses on another common correctness requirement for concurrent programs, namely, atomicity, which requires that any set of concurrent invocations of designated procedures is equivalent to performing those invocations serially in some order. Run-time analysis algorithms for detecting violations of atomicity are presented. The algorithms vary in cost and precision. 相似文献
992.
As the design trend of modern cellular phones evolves to be miniaturization and versatile sound in quality, the electro-mechanical components including the micro-speaker are essential toward size reduction and broad frequency range of sound. To reduce size, a diaphragm type micro-speaker is commonly employed in industry, while to broaden the sound frequency range corrugations on the diaphragm are adopted. The corrugations are generally capable of leading to fairly flat response over a broad range since diaphragm stiffness is decreased in axial direction. To confirm the aforementioned capability, the modeling on a corrugated diaphragm is performed first using finite element method (FEM) to obtain the associated dynamic equations in terms of modal coordinates; then the equations are next combined with the magneto-electrical model of the voice coil motor (VCM) that is attached to the bottom side of the diaphragm. Finally, the acoustic effects of the air inertia on the diaphragm and vents of the outer case are modeled using basic acoustic theories. Assembling all derived system equations and solving them, the frequency response of the micro-speaker in sound pressure level (SPL) can be simulated. It shows that the diaphragm corrugation in fact helps flatten the SPL response of the micro-speaker (especially in high frequency range) to lessen sound distortion. Furthermore, the corrugation angle approximately below 45° is favored over other angles or flatter SPL response. Experiments are also conducted to verify the theoretical findings. 相似文献
993.
经对胜利油田近三年来典型井例测试资料分析评价及其增产措施效果分析认为,有三类地层压裂增油效果很好:地层物性相对较好的常压系统且存在严重堵塞的储层;物性较好的常压地层;高压低渗透储层。有两类地层酸化效果很好:灰岩、白云岩裂缝、低产低渗透储层;物性较好且存在严重污染堵塞的储层。其它地层压裂、酸化一般是无效的。 相似文献
994.
A Ml (NiCoMnA1)5 hydrogen storage alloys was prepared by double-roller rapid quenching.Its microstructure, electrochemically and kinetic characteristic were studied.A uniform crystal phase with CaCu5 structure could be detected by XRD analyses, whose average grain size is 30 ~ 50 nm and the ratio of c/a of nano-crystal hydrogen storage alloy is larger.The hydrogen absorption/desertion p - C isotherms of alloy show that its fiat-performance is perfect and the magnetic stagnant effect is very little.An simulate cell is used for electrochemical measurement.Electrode is 10C, the capacity decreasing rate via the 450 cycles at 7C is less than 20%. 相似文献
995.
This paper presents a comprehensive set of exact stability criteria for Euler columns with an intermediate elastic restraint. A subset of this class of problem is the buckling problem of columns with an intermediate rigid support where the elastic restraint takes on an infinite stiffness. Also, this study reiterates the existence of a critical elastic restraint stiffness in which the buckled mode switches to a higher-buckling mode of the corresponding column without an intermediate support. It is clear that this critical stiffness value exists only when the restraint is placed at the node of the higher-buckling mode and the buckling load associated with this critical stiffness value is the maximum achievable value that can be attained with an intermediate elastic restraint. 相似文献
996.
La改性的Ag/TS-1催化剂上丙烯选择氧化制环氧丙烷 总被引:1,自引:0,他引:1
在H2 和O2 混合气体存在下 ,在常压固定床、石英反应器上考察了La改性的Ag/TS - 1催化剂催化丙烯环氧化反应。研究结果表明 ,Ag和La负载在TS - 1上的先后顺序对丙烯环氧化反应有影响。H2 在丙烯气相氧化反应体系中起着重要的作用。 相似文献
997.
改性β沸石上合成1,4-二氧六环的研究 总被引:1,自引:0,他引:1
在真空条件下将改性 β沸石用于二甘醇合成 1,4 -二氧六环的反应 ,考察了反应温度、反应时间和催化剂用量对催化剂活性的影响 ,并对该催化剂的稳定性进行了考察。结果表明 ,在最佳反应条件下 ,二甘醇转化率达到 89 6 9% ,1,4 -二氧六环的选择性达到 95 0 1%。 相似文献
998.
三(明)钢烧结厂电除尘灰的气力输送 总被引:1,自引:1,他引:0
三钢烧结厂130m^2烧结机电除尘输灰首次采用了气力输送系统。该系统由气源、输送、管路、灰库及控制五部分组成,本文介绍了系统的工作原理及运行调试情况。系统投产后,运行平稳,达到了设计要求。 相似文献
999.
Xianpeng Wang Lixin Tang 《The International Journal of Advanced Manufacturing Technology》2008,36(5-6):431-441
This paper investigates the hot rolling production scheduling problem in the steel industry and proposes a new mixed integer
programming model for this problem based on the monolithic modeling strategy that integrates batching and scheduling. Using
this strategy, the new model can simultaneously schedule multiple turns and simultaneously determine the production timetable
of these turns in a global optimal view. A long-term tabu search heuristic using frequency-based memory is developed to obtain
near-optimal solutions for this problem. Three kinds of speed-up strategies are developed to accelerate the search procedure
of the proposed tabu search. A practical scheduling system combining the proposed mathematical model and the tabu search heuristic
has been developed and tested on instances collected from practical production data. The experimental results show that the
proposed mathematical model and the tabu search heuristic outperform both the current manual scheduling method and the traditional
serial method. 相似文献
1000.
固体超强酸S_2O_8~(2-)/SnO_2-SiO_2催化合成环己酮1,2-丙二醇缩酮 总被引:3,自引:0,他引:3
采用沉淀-浸渍法制备了固体超强酸S2O28-/SnO2-SiO2,以它为催化剂催化环己酮和1,2-丙二醇合成了环己酮1,2-丙二醇缩酮;考察了带水剂种类及用量、酮醇摩尔比、催化剂用量、反应时间对产品收率的影响,并用正交实验对反应条件进行了优化。实验结果表明,适宜的反应条件为:n(环己酮)∶n(1,2-丙二醇)=1∶1.6、催化剂用量为反应物料总质量的2.0%、带水剂环己烷用量5.0mL、反应时间50min。在此条件下,环己酮1,2-丙二醇缩酮收率达到91.47%;催化剂的稳定性良好,在重复使用5次后环己酮1,2-丙二醇缩酮收率为82.20%,活性下降的主要原因为催化剂表面积碳和吸附了有机物;经傅里叶变换红外光谱和气相色谱质谱分析表明,产物为环己酮1,2-丙二醇缩酮,纯度为100%。 相似文献