全文获取类型
收费全文 | 259287篇 |
免费 | 77033篇 |
国内免费 | 50978篇 |
专业分类
电工技术 | 33943篇 |
技术理论 | 2篇 |
综合类 | 27357篇 |
化学工业 | 34854篇 |
金属工艺 | 29141篇 |
机械仪表 | 11414篇 |
建筑科学 | 17827篇 |
矿业工程 | 15276篇 |
能源动力 | 10219篇 |
轻工业 | 27598篇 |
水利工程 | 9189篇 |
石油天然气 | 15596篇 |
武器工业 | 4502篇 |
无线电 | 38701篇 |
一般工业技术 | 37686篇 |
冶金工业 | 9413篇 |
原子能技术 | 2109篇 |
自动化技术 | 62471篇 |
出版年
2024年 | 3213篇 |
2023年 | 6021篇 |
2022年 | 8272篇 |
2021年 | 10090篇 |
2020年 | 11741篇 |
2019年 | 20168篇 |
2018年 | 21741篇 |
2017年 | 23303篇 |
2016年 | 22756篇 |
2015年 | 22767篇 |
2014年 | 22338篇 |
2013年 | 22265篇 |
2012年 | 22384篇 |
2011年 | 19178篇 |
2010年 | 17356篇 |
2009年 | 14157篇 |
2008年 | 12056篇 |
2007年 | 11054篇 |
2006年 | 9528篇 |
2005年 | 8550篇 |
2004年 | 10088篇 |
2003年 | 8064篇 |
2002年 | 7638篇 |
2001年 | 6635篇 |
2000年 | 5914篇 |
1999年 | 5368篇 |
1998年 | 4540篇 |
1997年 | 4035篇 |
1996年 | 3817篇 |
1995年 | 3787篇 |
1994年 | 3108篇 |
1993年 | 2845篇 |
1992年 | 2726篇 |
1991年 | 1998篇 |
1990年 | 1546篇 |
1989年 | 1431篇 |
1988年 | 1093篇 |
1987年 | 353篇 |
1986年 | 311篇 |
1985年 | 217篇 |
1984年 | 147篇 |
1982年 | 166篇 |
1981年 | 152篇 |
1980年 | 111篇 |
1978年 | 106篇 |
1976年 | 238篇 |
1975年 | 213篇 |
1972年 | 237篇 |
1971年 | 128篇 |
1960年 | 205篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
原油中含有大量的高分子有机固相物质,因此,要准确地描述油气体系相平衡,必须对气液固三相相平衡进行研究,在对高分子有机烃类沥青沉降机理有了一定的认识的基础上,提出了大的交互作用系数,可以描述沥青与原油中轻质不相容性的程度。根据对油气烃类混合物体系的一般性认识与提出的沥青组分特征化方法,导出了与之相应的有其自身特殊性的气液沥青三相相平衡物料平衡方程组,用考虑沥青沉降三相闪蒸数值算法,对沥青沉降进行有效的理化模拟计算,此外,结合实例分析,给出了沥青质参考逸度的计算,饱和压力和沉降量的拟合方法。 相似文献
93.
We have investigated the effect of extended dislocations (0.5-3 μm) on charge distribution in GaN epilayer grown by metalorganic chemical vapor deposition on (0001) sapphire using atomic force microscopy (AFM) and scanning surface potential microscopy (SSPM). It has been observed for the surface at the extended dislocations present in undoped GaN film to be negatively charged showing 0.04-0.2 V higher potential relative to regions that contain no dislocations. In addition to the higher potential at the dislocation core, the surrounding surfaces, including the edge of the dislocations, are also negatively charged in a symmetric way around the dislocations revealing crater-shaped higher potential regions (∼0.04 V) relative to surrounding dislocation-free area. The experimental results show that the protrusion-type of dislocation is also negatively charged and its potential is dependent on the size of dislocation. 相似文献
94.
磁处理技术是利用磁场对非铁磁性流体作用.使被作用物的性质产生某些期望的变化,从而改善生产效果和使用效益。磁处理对常规钻井液流变性能的影响研究结果表明,磁化能明显改善钻井液性能。通过研究磁化后泡沫钻井液的性质.测定与控制钻井液的电导率,以便从电测曲线上取得更好的地层特性评价。泡沫钻井液的电导率与密度基本呈线性关系,电导率随密度的升高而变大;磁处理后泡沫钻井液的性质发生明显改变.泡沫钻井液的电导率有不同程度的下降,在磁场强度为100mT、蜂数为2的磁场条件下泡沫钻井液的电导率变化率降低最大,电导率平均下降16%左右。 相似文献
95.
可持续发展战略指导下的轨道交通规划与评价 总被引:9,自引:0,他引:9
提出了轨道交通规划与评价在实施可持续发展战略过程中需要研究的问题,研究重点是轨道交通规划与评价方法体系和环境对策,研究了轨道交通规划目标的变化、轨道交通规划优化决策理论与方法、轨道交通规划中的环境影响评价、城市轨道交通网络的合理规划、城际轨道交通——客运专线/高速铁路线路基本走向的规划、轨道交通规划可持续发展的评价指标体系概念框架、轨道交通系统可持续发展的能力建设问题等,并通过实例验证了所建立的理论方法体系和模型体系;不仅进行了有关理论和方法的探讨,而且以面向实际应用为目标,开发了相应的软件系统,为轨道交 相似文献
96.
The requirements on an object-oriented DBMS for management of information in a large, complex enterprise are presented. These requirements aid in the achievement of an environment characterized by data sharing, open architectures, application and data portability, and assurance of data integrity. They were defined from the point of view of a user of the DBMS; therefore they describe the expected functionality of the DBMS and do not specify the method of implementation to achieve this functionality. They encompass requirements on the data model, query and data manipulation languages, the system architecure, interfaces to the system, change management, and transaction management. 相似文献
97.
Timothy Thomasma Kurt Hilbrecht 《International Journal of Flexible Manufacturing Systems》1991,3(3-4):231-250
Good methods are needed to specify, test, and debug material-handling control logic. This article surveys a number of representative methods for defining and describing control algorithms for programmable material-handling equipment used in flexible manufacturing systems. The methods are evaluated with regard to their suitability for communication between people and as bases for interfaces to automatic program generators. It is concluded that no single method is entirely satisfactory. Three methods (position diagrams, function block diagrams, and operation networks) have potential to be combined into an effective hybrid approach that minimizes the need for the user to switch between various conceptual models. 相似文献
98.
P. V. Zrelov V. V. Ivanov 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1991,310(3):623-630
The statistical method of identification of relativistic charged particles by measurements of ionization losses or time-of-flights simultaneously in some detectors of an experimental plant on the basis of the new goodness-of-fit ωn3-criterion is considered. The method proposed has been used for the secondary particles identification from the high energy -particles fragmentation on target nuclei. The efficiency of the method is excellently illustrated by reliable separation of events (rare events as well), connected with the appearence of 1- and 2-charged particles. The comparison of the ωn3-method with the traditional methods and with the method based on the ωn2-criterion shows that the new method outperforms the ωn2-method and most of the traditional ones in efficiency, but compares unfavourably with the likelihood method in power, however, the former has a number of advantages as compared with the latter. 相似文献
99.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC 总被引:1,自引:0,他引:1
Min Gyu Kim Gil-Cho Ahn Hanumolu P.K. Sang-Hyeon Lee Sang-Ho Kim Seung-Bin You Jae-Whui Kim Temes G.C. Un-Ku Moon 《Solid-State Circuits, IEEE Journal of》2008,43(5):1195-1206
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation. 相似文献
100.
This paper examines Total Quality Management (TQM) as defined by Dr. W. Edwards Deming including Deming's fourteen points and explains how the United States' Department of Defense (DOD) defines TQM and why TQM is necessary. It also covers how the DOD is planning on implementing TQM and the policy that has been established as guidance in the implementation process. 相似文献