全文获取类型
收费全文 | 311143篇 |
免费 | 5140篇 |
国内免费 | 1765篇 |
专业分类
电工技术 | 6208篇 |
综合类 | 1768篇 |
化学工业 | 49991篇 |
金属工艺 | 12910篇 |
机械仪表 | 9659篇 |
建筑科学 | 8254篇 |
矿业工程 | 2265篇 |
能源动力 | 7299篇 |
轻工业 | 29572篇 |
水利工程 | 3691篇 |
石油天然气 | 7810篇 |
武器工业 | 152篇 |
无线电 | 33422篇 |
一般工业技术 | 59433篇 |
冶金工业 | 52421篇 |
原子能技术 | 7739篇 |
自动化技术 | 25454篇 |
出版年
2021年 | 3127篇 |
2019年 | 2624篇 |
2018年 | 4401篇 |
2017年 | 4449篇 |
2016年 | 4642篇 |
2015年 | 3582篇 |
2014年 | 5666篇 |
2013年 | 13786篇 |
2012年 | 8842篇 |
2011年 | 11358篇 |
2010年 | 9400篇 |
2009年 | 10389篇 |
2008年 | 10573篇 |
2007年 | 10337篇 |
2006年 | 9047篇 |
2005年 | 8219篇 |
2004年 | 7409篇 |
2003年 | 6996篇 |
2002年 | 6990篇 |
2001年 | 6755篇 |
2000年 | 6381篇 |
1999年 | 6412篇 |
1998年 | 14982篇 |
1997年 | 11199篇 |
1996年 | 8683篇 |
1995年 | 6609篇 |
1994年 | 5983篇 |
1993年 | 5845篇 |
1992年 | 4527篇 |
1991年 | 4474篇 |
1990年 | 4315篇 |
1989年 | 4323篇 |
1988年 | 4276篇 |
1987年 | 3619篇 |
1986年 | 3611篇 |
1985年 | 4182篇 |
1984年 | 3979篇 |
1983年 | 3632篇 |
1982年 | 3429篇 |
1981年 | 3577篇 |
1980年 | 3431篇 |
1979年 | 3371篇 |
1978年 | 3449篇 |
1977年 | 3931篇 |
1976年 | 5057篇 |
1975年 | 3160篇 |
1974年 | 3008篇 |
1973年 | 3026篇 |
1972年 | 2653篇 |
1971年 | 2474篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
J. B. Quinn G. E. Schumacher L. W. Schultheis 《Journal of Failure Analysis and Prevention》2004,4(1):41-46
Several days after heart surgery, a patient discovered his upper right canine tooth had broken at the root. Such tooth damage,
recognized post-operatively, is usually assumed to be caused by blunt mechanical force from an instrument used by the anesthesiologist
during placement of a breathing tube at the start of surgery.
In this case, the patient had saved the crown portion of the broken tooth, and it was possible to examine the root fracture
characteristics. The curvature and direction of the crack path and natural tooth situation suggested that failure could be
described through a cantilever beam model. This was confirmed when a whole extracted sample tooth was embedded and broken
by a measured force in a manner consistent with the model. The resulting fracture surface matched that of the patient’s broken
canine tooth. However, the high load and force direction necessary to fracture the root was inconsistent with forces applied
during the anesthesia procedure. The failure analysis and further investigation indicated tooth clenching on the breathing
tube during recovery was the likely cause of fracture.
This paper presents an alternate explanation for intubation-related dental injury, demonstrates the practicality of fractographic
analysis of biological materials, and introduces a methodology for simulating in vitro tooth settings for mechanical testing. 相似文献
53.
Mathematical models of thermomechanical processes which are based on the laws of rational thermodynamics of irreversible processes are treated. Singular features of the unsteady-state behavior of a continuous medium are demonstrated within different models, such as a medium with internal parameters of state, a medium with memory, and a medium of the velocity type. 相似文献
54.
Managing sewerage systems is a highly complex task due to the dynamic nature of the facilities. Their performance strongly depends on the know-how applied by the operators. In order to define optimal operational settings, two decision support tools based on mathematical models have been developed. Moreover, easy-to-use interfaces have been created as well, aiding operators who presumably do not have the necessary skills to use modelling software. The two developed programs simulate the behaviour of both wastewater treatment plants (WWTP) and sewer network systems, respectively. They have essentially the same structure, including raw data management and statistical analysis, a simulation layer using the application programming interface of the applied software and a layer responsible for the representation of the obtained results. Four user modes are provided in the two software including the simulation of historical data using the applied and novel operational settings, as well as modes concerning prediction of possible operation periods and updates. Concerning the WWTP software, it was successfully installed in Nantes (France) in June 2004. Moreover, the one managing sewer networks has been deployed in Saint-Malo (France) in January 2005. This paper presents the structure of the developed software and the first results obtained during the commissioning phase. 相似文献
55.
56.
57.
A method is given for calculating the monitoring reliability parameters (MRP) for an engineering system with allowance for the drift in the measurement error of the means of measurement (MM). The approach is based on introducing a biased MM error distribution into the traditional formulas for the conditional probabilities of spurious and unobserved failure. The bias at the center of the distribution is determined by the systematic error at the given instant. An example is given to illustrate the performance in MRP calculation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–13, January, 1994. 相似文献
58.
Montanari D. Van Houdt J. Groeseneken G. Maes H.E. 《Solid-State Circuits, IEEE Journal of》1998,33(7):1090-1095
This paper presents a high-speed, small-area circuit specifically designed to identify the levels in the read out operation of a flash multilevel memory. The circuit is based on the analog computation of the Euclidean distance between the current read out from a memory cell and the reference currents that represent the different logic levels. An experimental version of the circuit has been integrated in a standard double-metal 0.7-μm CMOS process with a die area of only 140×100 μm2. Operating under a 5-V power supply, this circuit identifies the read-out current of a memory cell, and associates it with the appropriate logic level in 9 ns 相似文献
59.
A modification to the `shape-invariant' sinusoidal speech model is proposed, whereby the phases of the component sinewaves used for the excitation are made to add coherently at each glottal closure. Applied to pitch and time-scale modification, higher quality synthetic speech is produced when large changes are required 相似文献
60.
The authors report the design of a new current-mode A/D converter, based on a modified successive-approximations model, in 1.2 μm CMOS technology. The proposed circuit is characterised by good accuracy and fast dynamic performance, low power consumption and small occupation area. SPICE simulations allow the design approach to be validated and the electrical performance of the ADC to be predicted 相似文献