全文获取类型
收费全文 | 459370篇 |
免费 | 29297篇 |
国内免费 | 10023篇 |
专业分类
电工技术 | 23004篇 |
技术理论 | 70篇 |
综合类 | 27537篇 |
化学工业 | 72120篇 |
金属工艺 | 26561篇 |
机械仪表 | 26568篇 |
建筑科学 | 30130篇 |
矿业工程 | 12488篇 |
能源动力 | 11745篇 |
轻工业 | 29002篇 |
水利工程 | 8145篇 |
石油天然气 | 24238篇 |
武器工业 | 2816篇 |
无线电 | 50366篇 |
一般工业技术 | 57476篇 |
冶金工业 | 21239篇 |
原子能技术 | 4455篇 |
自动化技术 | 70730篇 |
出版年
2025年 | 926篇 |
2024年 | 7929篇 |
2023年 | 7402篇 |
2022年 | 10555篇 |
2021年 | 14826篇 |
2020年 | 12417篇 |
2019年 | 10340篇 |
2018年 | 23478篇 |
2017年 | 23628篇 |
2016年 | 20065篇 |
2015年 | 15019篇 |
2014年 | 18225篇 |
2013年 | 21348篇 |
2012年 | 25735篇 |
2011年 | 34030篇 |
2010年 | 29987篇 |
2009年 | 26246篇 |
2008年 | 27066篇 |
2007年 | 27198篇 |
2006年 | 20259篇 |
2005年 | 18861篇 |
2004年 | 13064篇 |
2003年 | 11850篇 |
2002年 | 10457篇 |
2001年 | 8911篇 |
2000年 | 8950篇 |
1999年 | 9492篇 |
1998年 | 7276篇 |
1997年 | 6199篇 |
1996年 | 5884篇 |
1995年 | 4809篇 |
1994年 | 3922篇 |
1993年 | 2648篇 |
1992年 | 2124篇 |
1991年 | 1616篇 |
1990年 | 1253篇 |
1989年 | 1018篇 |
1988年 | 850篇 |
1987年 | 546篇 |
1986年 | 421篇 |
1985年 | 270篇 |
1984年 | 226篇 |
1983年 | 174篇 |
1982年 | 137篇 |
1981年 | 82篇 |
1980年 | 102篇 |
1968年 | 46篇 |
1965年 | 45篇 |
1955年 | 65篇 |
1954年 | 70篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
World oil production and reserve additions heavily depend on giant oilfields. Currently, there are more than 4,000 producing oilfields in the world, producing around 68 million barrels of oil per day. Most oilfields in the world are minor ones, with oil production below 20,000 barrels per day; only 3% (about 120) oilfields in the world produce over 100,000 barrels per day with overall daily production exceeding 32 million barrels, which accounts for 47% of the total world oil supply . The scales of the oilfields heavily influence economic indices like investment, production and life spans of the oilfields. Therefore, giant oilfields have always been the dream of oil finders and targets of geologists' researches . 相似文献
3.
Shi-Jin Ding Hang Hu Lim H.F. Kim S.J. Yu X.F. Chunxiang Zhu Li M.F. Byung Jin Cho Chan D.S.H. Rustagi S.C. Yu M.B. Chin A. Dim-Lee Kwong 《Electron Device Letters, IEEE》2003,24(12):730-732
For the first time, we successfully fabricated and demonstrated high performance metal-insulator-metal (MIM) capacitors with HfO/sub 2/-Al/sub 2/O/sub 3/ laminate dielectric using atomic layer deposition (ALD) technique. Our data indicates that the laminate MIM capacitor can provide high capacitance density of 12.8 fF//spl mu/m/sup 2/ from 10 kHz up to 20 GHz, very low leakage current of 3.2 /spl times/ 10/sup -8/ A/cm/sup 2/ at 3.3 V, small linear voltage coefficient of capacitance of 240 ppm/V together with quadratic one of 1830 ppm/V/sup 2/, temperature coefficient of capacitance of 182 ppm//spl deg/C, and high breakdown field of /spl sim/6 MV/cm as well as promising reliability. As a result, the HfO/sub 2/-Al/sub 2/O/sub 3/ laminate is a very promising candidate for next generation MIM capacitor for radio frequency and mixed signal integrated circuit applications. 相似文献
4.
Code-division multiple-access (CDMA) implemented with direct-sequence spread spectrum (DS/SS) signaling is a promising multiplexing technique for cellular telecommunications services. The efficiency of a direct-sequence spread-spectrum code-division multiple-access (DS-CDMA) system depends heavily on the shape of the spectrum of the spread signal. Maximum efficiency is obtained with an ideal brick-wall bandpass spectrum. There are two approaches toward achieving such a spectrum. One is to use a simple spreader that produces a broad spectrum and then follow it with a precise, high order filter to band limit the spectrum. A second approach, which is the approach taken in this paper, is to use a spreader that produces a spectrum close to the ideal spectrum and then employ a simple filter to control the out-of-band power. The proposed spreader/despreader is based on a simple hybrid function and can be easily implemented. An analysis provides a compact expression for the signal-to-noise ratio (SNR) of a RAKE receiver. The expression includes the effects of baseband, intermediate frequency (IF) and RF filtering as well as the effects of the spectral densities of the spreading/despreading functions. The analysis shows that the proposed spreader/despreader yields superior performance over a conventional pseudo noise (PN) spreading/despreading mechanism 相似文献
5.
Network fault identification is an important network management function, which is closely related to fault management and has an impact on other network management functions such as configuration management, and performance management. This paper investigates fault surveillance and fault identification mechanisms for a transparent optical network in which data travels optically from the source node to the destination node without going through any optical-to-electrical (O/E) or electrical-to-optical (E/O) conversion. Mechanisms and algorithms are proposed to detect and isolate faults such as fiber cuts, laser, receiver, or router failures. These mechanisms allow nonintrusive device monitoring without requiring any prior knowledge of the actual protocols being used in the data transmission 相似文献
6.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
7.
8.
Introduction
Owing to long-time running, more facilities including stations, pipelines, vessels have become corrosive and aged ,some process has grown old, it has exert more burden for the maintenance and repair.Simultaneously, the fluid production rate, oil production rate and water injection rate has changed greatly so that the inflicts and problems from the established surface systems will become more obvious. Energy cost of production and running has increasing continuously. Capacity has been unbalance in systems and areas.
…… 相似文献
9.
10.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献