全文获取类型
收费全文 | 271396篇 |
免费 | 2815篇 |
国内免费 | 664篇 |
专业分类
电工技术 | 5083篇 |
综合类 | 229篇 |
化学工业 | 38031篇 |
金属工艺 | 14466篇 |
机械仪表 | 11459篇 |
建筑科学 | 6168篇 |
矿业工程 | 2014篇 |
能源动力 | 5777篇 |
轻工业 | 18255篇 |
水利工程 | 3336篇 |
石油天然气 | 5365篇 |
武器工业 | 8篇 |
无线电 | 29845篇 |
一般工业技术 | 58721篇 |
冶金工业 | 42919篇 |
原子能技术 | 6079篇 |
自动化技术 | 27120篇 |
出版年
2021年 | 1607篇 |
2019年 | 1578篇 |
2018年 | 10868篇 |
2017年 | 11460篇 |
2016年 | 7394篇 |
2015年 | 2320篇 |
2014年 | 3171篇 |
2013年 | 9006篇 |
2012年 | 7630篇 |
2011年 | 15127篇 |
2010年 | 13340篇 |
2009年 | 12981篇 |
2008年 | 12819篇 |
2007年 | 14858篇 |
2006年 | 5664篇 |
2005年 | 8722篇 |
2004年 | 6943篇 |
2003年 | 6510篇 |
2002年 | 5175篇 |
2001年 | 4726篇 |
2000年 | 4722篇 |
1999年 | 4758篇 |
1998年 | 11434篇 |
1997年 | 8158篇 |
1996年 | 6448篇 |
1995年 | 4700篇 |
1994年 | 4318篇 |
1993年 | 4115篇 |
1992年 | 3244篇 |
1991年 | 3107篇 |
1990年 | 2873篇 |
1989年 | 2955篇 |
1988年 | 2844篇 |
1987年 | 2407篇 |
1986年 | 2318篇 |
1985年 | 2727篇 |
1984年 | 2521篇 |
1983年 | 2354篇 |
1982年 | 2099篇 |
1981年 | 2211篇 |
1980年 | 2039篇 |
1979年 | 2132篇 |
1978年 | 2129篇 |
1977年 | 2375篇 |
1976年 | 3201篇 |
1975年 | 1837篇 |
1974年 | 1771篇 |
1973年 | 1778篇 |
1972年 | 1448篇 |
1971年 | 1342篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 1, pp. 25–28, January, 1993. 相似文献
992.
JL Banyer S Goldwurm L Cullen B van der Griend A Zournazi DJ Smit LW Powell EC Jazwinska 《Canadian Metallurgical Quarterly》1998,9(3):235-239
We have examined acetaminophen (paracetamol) dosing for outpatient management of posttonsillectomy pain in children. Forty children, 5-15 years of age, undergoing tonsillectomy and their parents were randomly assigned to use a scheduled administration of acetaminophen in weight appropriate doses, 60 mg.kg-1.24h-1 orally, 90 mg.kg-1.24h-1 rectally, or to use acetaminophen 'as needed' according to present standards (control group). Postoperative pain was assessed by the child using the poker chip tool for the first three days after discharge. The prevalence of pain amongst all the children was high. The second day after discharge 22%-64% of the children in the study group and 36%-73% of the children in the control group rated severe pain. Recommended dose ranges of acetaminophen do not provide sufficient pain relief in children following tonsillectomy. Further studies are required to determine, whether higher doses of acetaminophen or analgesics with different analgesic properties will lead to improved analgesia in children following tonsillectomy. 相似文献
993.
There is great interest today in massively parallel analytical strategies as a way to accelerate the rate of discovery in biological research; among them being 'biochips' and 'laboratories-on-a-chip'. The concept in the 'chip' approach is that minaturization will allow large numbers of operations to be performed in parallel in a small space, as in electronics. Proceeding with the semiconductor analogy, this paper demonstrates that in situ micromachining can be used to simultaneously fabricate millions of micrometer size, particle like structures in multiple liquid chromatography columns on a single wafer. Reduction of this widely used bioanalytical tool to the nanoliter volume, parallel processing, chip format is a significant step toward laboratories-on-a-chip. 相似文献
994.
Data compiled by the American Psychological Association (APA) revealed that 7%–10% of ethics complaints filed were against custody evaluators. Comparative data from various state and provincial psychology boards remain too sketchy to permit an accurate appraisal of this problem at the local level. Nevertheless, vulnerability to ethics complaints remains an occupational hazard for the private practitioner who engages in custody assessment. This article offers practitioners who conduct custody evaluations suggestions for reducing their risk of incurring an ethics complaint and discusses variables to consider when responding to a review board inquiry. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
996.
997.
B Schmidt 《Canadian Metallurgical Quarterly》1996,45(10):370-374
Giving a case example of an male adolescent with radical right-wing attitudes, the lack of male identification as well as in unresolved dyadic fixation to the mother will be shown. Though the radical right-wing orientation the adolescent tries on the basis of a phallic narcissistic conflict to establish bordes against an unresolved dyadic fixation to his mother. 相似文献
998.
N. V. Filimonova A. B. Ivanov Z. V. Tret'yakova 《Refractories and Industrial Ceramics》1996,37(10):348-351
Inflammation of a mixture of Furnon-3KhP refractory mortar prepared using a binary reducer consisting of metallic Al and Mg powders is considered. It is shown that the inflammation temperature can be decreased by 100 – 150°C. Mechanical characteristics of refractory bricks joined by the mortar are determined.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 10, pp. 16 – 19, October, 1996. 相似文献
999.
Neusser S. Nijhuis J. Spaanenburg L. Hoefflinger B. Franke U. Fritz H. 《Micro, IEEE》1993,13(1):57-66
A solution to autonomous lateral vehicle guidance using a neurocontroller that can learn from measured human-driving data without knowledge of the physical car parameters is discussed. Simulations and practical tests confirm that a small-size feedforward autonomous neural network (21 neurons) can learn to steer a vehicle at high speeds only from looking at human-driving examples. In this way, the network learns the total closed-loop behavior, including the nonlinear dynamics of the vehicle and the driver's individual driving style. The main result of practical investigations is that the neutral controller trained on human-driving examples exhibits an aperiodic behavior that does not vanish at higher speeds (tests performed up to 130 km/h) and produces fewer lateral deviations than the linear state controller 相似文献
1000.
Gronningsaeter A. Angelsen B.A.J. Heimdal A. Torp H.G. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(3):359-369
Scattering from blood limits the contrast between the vessel wall and the lumen in intravascular ultrasound imaging. This makes it difficult to localize the vessel wall, especially on still images. This paper presents a method for automatic detection of vessel walls and reduction of blood noise based on correlation of the RF-signal between adjacent frames. The ultrasound RF-signal is quadrature demodulated, digitized, stored in memory, and transferred to a computer for processing and analysis. The absolute value of the cross-correlation coefficient between two adjacent frames is used to differentiate between stationary and fluctuating signals. Models and numerical calculations presented in this work indicate that the cross-correlation coefficient obtained from a radially dilating vessel wall will be larger than 0.8 under standard 20 MHz imaging conditions. The corresponding value from blood is less than 0.2 for blood velocities exceeding 0.5 cm s-1 . The blood-noise filter is based on detecting this difference in correlation and displays vessel wall regions with no modifications, while regions detected as blood are rejected. A simplified vessel-wall detector that is suitable for real-time implementation is proposed. The performance of this detector and the blood noise filter are demonstrated by in vitro experiments 相似文献