全文获取类型
收费全文 | 1552篇 |
免费 | 33篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 58篇 |
综合类 | 1篇 |
化学工业 | 319篇 |
金属工艺 | 30篇 |
机械仪表 | 12篇 |
建筑科学 | 69篇 |
矿业工程 | 2篇 |
能源动力 | 55篇 |
轻工业 | 88篇 |
水利工程 | 11篇 |
石油天然气 | 5篇 |
无线电 | 114篇 |
一般工业技术 | 209篇 |
冶金工业 | 395篇 |
原子能技术 | 20篇 |
自动化技术 | 203篇 |
出版年
2023年 | 13篇 |
2022年 | 16篇 |
2021年 | 22篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 30篇 |
2017年 | 22篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 31篇 |
2013年 | 101篇 |
2012年 | 42篇 |
2011年 | 76篇 |
2010年 | 48篇 |
2009年 | 53篇 |
2008年 | 60篇 |
2007年 | 71篇 |
2006年 | 57篇 |
2005年 | 41篇 |
2004年 | 46篇 |
2003年 | 32篇 |
2002年 | 33篇 |
2001年 | 20篇 |
2000年 | 19篇 |
1999年 | 31篇 |
1998年 | 74篇 |
1997年 | 41篇 |
1996年 | 40篇 |
1995年 | 33篇 |
1994年 | 20篇 |
1993年 | 32篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 26篇 |
1989年 | 22篇 |
1988年 | 20篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 18篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 21篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 13篇 |
1973年 | 15篇 |
排序方式: 共有1591条查询结果,搜索用时 0 毫秒
81.
Towa RT Miller RJ Frizzell LA Zachary JF O'Brien WD 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(10):1411-1420
Attenuation coefficient and propagation speed of intercostal tissues were estimated as functions of temperature (22, 30, and 37 degrees C) from fresh chest walls from eight 10- to 11-week-old female Sprague-Dawley (SD) rats, eight 21- to 24-week-old female Long-Evans (LE) rats, and ten 6- to 10-week-old mixed sex Yorkshire (York) pigs. The primary purpose of the study was to estimate the temperature dependence of the intercostal tissue's attenuation coefficient so that accurate estimates of the in situ (at the pleural surface) acoustic pressure levels could be made for our ultrasound-induced lung hemorrhage studies. The attenuation coefficient of intercostal tissue for both species was independent of the temperature at the discrete frequencies of 3.1 MHz (-0.0076, 0.0065, and 0.016 dB/cm/degrees C for SD rats, LE rats, and York pigs, respectively) and 6.2 MHz (-0.015, 0.014, and 0.014 dB/cm/degrees C for SD rats, LE rats, and York pigs, respectively). However, the temperature-dependent regressions yielded a significant temperature dependency of the intercostal tissue attenuation coefficients in SD and LE rats (over the 3.1 to 9.6 MHz frequency range); there was no temperature dependency in York pigs (over the 3.1 to 8.6 MHz frequency range). There was no significant temperature dependency of the intercostal tissue propagation speed in SD rats; there was a temperature dependency in LE rats and York pigs (-0.59, -1.6, and -2.9 m/s/degrees C for SD rats, LE rats, and York pigs, respectively). Even though the attenuation coefficient's temperature dependency was significant from the linear regression functions, the differences were not very great (-0.040 to -0.13, 0.011 to 0.18, and 0.055 to 0.10 dB/cm/degrees C for SD rats, LE rats, and York pigs, respectively, over the data frequency range). These findings suggest that it is not necessary to determine the attenuation coefficient of intercostal tissue at body temperature (37 degrees C), but rather it is sufficient to determine the attenuation coefficient at room temperature (22 degrees C), a much easier experimental procedure. 相似文献
82.
The postmortem examination of failed IT projects reveals that long before the failure there were significant symptoms or “early warning signs.” This article describes the top 12 people-related and project-related IT project risks, based on “early warning sign” data collected from a panel of 19 experts and a survey of 55 IT project managers. 相似文献
83.
V. Cheutet C.E. Catalano J.P. Pernot B. Falcidieno F. Giannini J.C. Leon 《Computers & Graphics》2005,29(6):916-930
This paper addresses the designers’ activity and in particular the way designers express an object shape in 2D sketches through character lines and how these lines form a basis for sketching shapes in 3D. The tools currently available in commercial CAS/CAD systems to manipulate the digital models are still not sufficiently suited to support design. In this paper, the so-called fully free-form deformation features (δ-F4) are introduced as a modelling method to take into account the curve-oriented stylists’ way of working. Both the advantages of a free-form surface deformation method and a feature-based approach are merged to define these high-level modelling entities allowing for a direct manipulation of surfaces through a limited number of intuitive parameters. Such features incorporate several characteristics designed to handle the uncertainties and/or inconsistencies of the designer's input during a sketching activity. In addition, a δ-F4 classification is proposed to enable a fast access to the desired shape according to its semantics and characteristics. 相似文献
84.
Leon Straker Clare Pollock Robin Burgess-Limerick 《International Journal of Industrial Ergonomics》2006,36(12):1045-1053
This paper argues for the systematic development and presentation of evidence-based guidelines for appropriate use of computers by children. The currently available guidelines are characterised and a proposed conceptual model presented. Five principles are presented as a foundation to the guidelines. The paper concludes with a framework for the guidelines, key evidence for and against guidelines, and gaps in the available evidence, with the aim of facilitating further discussion.
Relevance to industry
The current generation of children in affluent countries will typically have over 10 years of computer experience before they enter the workforce. Consequently, the primary prevention of computer-related health disorders and the development of good productivity skills for the next generation of workers needs to occur during childhood. 相似文献
85.
Cuneyt Guzelis Leon O. Chua 《International Journal of Circuit Theory and Applications》1993,21(1):1-33
A rather general class of neural networks, called generalized cellular neural networks (CNNs), is introduced. the new model covers most of the known neural network architectures, including cellular neural networks, Hopfield networks and multilayer perceptrons. Several sets of conditions ensuring the input-output stability and global asymptotic stability of generalized CNNs have been obtained. the conditions for the stability of individual cells are checked in the frequency domain, while the stability of the overall network is analysed in terms of the stability of individual cells and the connectivity characteristics. the results on the global asymptotic stability are useful for the design of a generalized CNN such that the orbit of each state converges to a globally asymptotically stable equilibrium point which depends only on the input and not on the initial state. Such a network defines an algebraic map from the space of external inputs to the space of steady state values of the outputs and hence can accomplish cognitive and computational tasks. 相似文献
86.
LL Judd HS Akiskal JD Maser PJ Zeller J Endicott W Coryell MP Paulus JL Kunovac AC Leon TI Mueller JA Rice MB Keller 《Canadian Metallurgical Quarterly》1998,55(8):694-700
BACKGROUND: Investigations of unipolar major depressive disorder (MDD) have focused primarily on major depressive episode remission/recovery and relapse/recurrence. This is the first prospective, naturalistic, long-term study of the weekly symptomatic course of MDD. METHODS: The weekly depressive symptoms of 431 patients with MDD seeking treatment at 5 academic centers were divided into 4 levels of severity: (1) depressive symptoms at the threshold for MDD; (2) depressive symptoms at the threshold for minor depressive or dysthymic disorder (MinD); (3) subsyndromal or subthreshold depressive symptoms (SSDs), below the thresholds for MinD and MDD; and (4) no depressive symptoms. The percentage of weeks at each level, number of changes in symptom level, and medication status were analyzed overall and for 3 subgroups defined by mood disorder history. RESULTS: Patients were symptomatically ill in 59% of weeks. Symptom levels changed frequently (1.8/y), and 9 of 10 patients spent weeks at 3 or 4 different levels during follow-up. The MinD (27%) and SSD (17%) symptom levels were more common than the MDD (15%) symptom level. Patients with double depression and recurrent depression had more chronic symptoms than patients with their first lifetime major depressive episode (72% and 65%, respectively, vs 46% of follow-up weeks). CONCLUSION: The long-term weekly course of unipolar MDD is dominated by prolonged symptomatic chronicity. Combined MinD and SSD level symptoms were about 3 times more common (43%) than MDD level symptoms (15%). The symptomatic course is dynamic and changeable, and MDD, MinD, and SSD symptom levels commonly alternate over time in the same patients as a symptomatic continuum of illness activity of a single clinical disease. 相似文献
87.
Diagnostic tools in the evaluation of patients with viral hepatitis undergoing liver transplantation
Familiarity with the diagnostic parameters of viral hepatitis is imperative in the liver transplantation arena. Chronic viral hepatitis B and C are among the most common categories of end-stage liver disease. The preoperative diagnosis, determination of recurrent infection, and the assessment of antiviral therapeutic efficacy are dependent on appropriate virological testing. Furthermore, liver transplant personnel are at a high risk for parenterally transmitted viral hepatitis infection. Knowledge and understanding of the serological patterns of acute and chronic viral hepatitis, as well as recognition of the immune status for one or more of these viruses, will facilitate prevention and treatment of viral hepatitis for these health care providers. 相似文献
88.
MK Hong SW Park CW Lee DH Kang JK Song JJ Kim SJ Park MK Hong GS Mintz MB Leon 《Canadian Metallurgical Quarterly》1998,82(5):670-3, A8
We evaluated the role of intravascular ultrasound (IVUS) in 16 patients with unprotected left main coronary artery (LMCA) stenting compared with 80 patients with other (non-LMCA) native coronary artery stenting and found that (1) additional high-pressure or larger size balloon dilations were more frequently performed in LMCA stenting than in non-LMCA stenting (p <0.05) and (2) after IVUS-guided stent implantation, minimum lumen area was > or = 9 mm2 in 88% of patients who underwent LMCA stenting and in 19% of those who underwent non-LMCA stenting (p <0.001). IVUS guidance may be a more important adjunctive imaging modality in the stenting of unprotected LMCA stenoses than in stenting of non-LMCA stenoses. 相似文献
89.
90.