全文获取类型
收费全文 | 2303篇 |
免费 | 128篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 42篇 |
综合类 | 4篇 |
化学工业 | 563篇 |
金属工艺 | 50篇 |
机械仪表 | 85篇 |
建筑科学 | 80篇 |
矿业工程 | 1篇 |
能源动力 | 116篇 |
轻工业 | 186篇 |
水利工程 | 34篇 |
石油天然气 | 44篇 |
无线电 | 292篇 |
一般工业技术 | 488篇 |
冶金工业 | 99篇 |
原子能技术 | 16篇 |
自动化技术 | 342篇 |
出版年
2024年 | 8篇 |
2023年 | 49篇 |
2022年 | 94篇 |
2021年 | 134篇 |
2020年 | 97篇 |
2019年 | 103篇 |
2018年 | 135篇 |
2017年 | 109篇 |
2016年 | 131篇 |
2015年 | 84篇 |
2014年 | 135篇 |
2013年 | 218篇 |
2012年 | 124篇 |
2011年 | 155篇 |
2010年 | 105篇 |
2009年 | 86篇 |
2008年 | 67篇 |
2007年 | 55篇 |
2006年 | 63篇 |
2005年 | 35篇 |
2004年 | 44篇 |
2003年 | 27篇 |
2002年 | 19篇 |
2001年 | 26篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 18篇 |
1997年 | 9篇 |
1996年 | 20篇 |
1995年 | 15篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 16篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 10篇 |
1975年 | 6篇 |
1974年 | 5篇 |
排序方式: 共有2442条查询结果,搜索用时 15 毫秒
11.
A novel approach is presented to calculate the sensitivities of the scattering parameters of microwave filters obtained with the full‐wave mode‐matching (MM) technique. Using only the MM simulation of the original network, the sensitivities of the scattering parameters with respect to all designable parameters are obtained. The adjoint network method (ANM) is applied to the generalized scattering matrices of the different filter components. This guarantees good accuracy of the calculated sensitivities. The implementation details are discussed for N‐resonator ridge waveguide filters. Excellent agreement is obtained between the sensitivities calculated using ANM and those obtained using the expensive central differences. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. 相似文献
12.
Fadwa T. Eljack Ahmed F. Abdelhady Mario R. Eden Frederico B. Gabriel Xiaoyun Qin Mahmoud M. El-Halwagi 《Computers & Chemical Engineering》2005,29(11-12):2304
Decoupling the constitutive equations from the balance and constraint equations allows for reformulating a conventional forward problem into two reverse problems. The first reverse problem is the reverse of a simulation problem, where the process model is solved in terms of the constitutive (synthesis/design) variables instead of the process variables, thus providing the synthesis/design targets. The second reverse problem (reverse property prediction) solves the constitutive equations to identify unit operations, operating conditions and/or products by matching the synthesis/design targets. Visualization of the problem is achieved by employing recently developed property clustering techniques, which allows a high-dimensional problem to be visualized in two or three dimensions. The clusters by definition satisfy intra-stream and inter-stream conservation through linear “mixing” rules, which allows for the development of consistent additive rules along with their ternary representation. 相似文献
13.
Mahmoud Mollabashi R. M. Lees Li-Hong Xu M. Bakota 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(12):2569-2582
The microwave spectrum of CD3OH has been studied over the 8 to 58 GHz region, and numerousb-type transitions have been assigned. Many of these belong toP subbranches which descend to the microwave region from subband origins lying much higher in the far-infrared, pass through zero frequency, and return upward again. Others are members ofb-typeQ branches which extend across the region. As well, variousa-typeK-doublet lines arising as transitions directly across the split levels of asymmetry doublets have been identified. 相似文献
14.
Mahmoud Abu-Zeid 《国际水资源开发杂志》2001,17(4):527-538
Access to water is viewed as a basic human right, a social necessity and a critical environmental resource in spite of the fact that water also has its own financial and economic values. Thus, the selection of set prices and pricing mechanisms addressing these contradicting views is remarkably complicated. On the other hand, water pricing is typically viewed as a good means to cover initial costs and sustain resources invested in water systems development, especially irrigated agriculture. Additionally, the cost of water services needs to be reasonable enough and linked to the amount of water consumed to encourage conservation. This paper illustrates criteria for equitable cost sharing, which include economic justification, efficiency and equity as well as users' acceptance. Elements of agricultural water pricing are also discussed. These elements comprise: the cost of water services, which is the total cost associated with irrigated agricultural systems development; the value of water, which reflects water's economic, social, environmental, cultural and religious values in the society; and the cost recovery mechanisms, which are the organizational and administrative measures to implement agreed upon policies to value water and services and make the collections. 相似文献
15.
Golestaneh S. Hafez H.M. Mahmoud S.A. 《Vehicular Technology, IEEE Transactions on》1994,43(4):946-954
In FDMA cellular radio systems, the adjacent channel interference (ACI) is suppressed by the IF filter and also by a distance factor. Channels immediately adjacent to each other in frequency are assigned to different cells and, as such, the distance plays a role in reducing their mutual interference. The authors study the feasibility of optimizing the frequency spacing between carriers such that the combined effect of distance and IF filter will be enough to control the interference while allowing the maximum number of channels in a given bandwidth. They also study the decision feedback equalizer (DFE) as a means to reduce any excess ACI that results from reducing the channel spacing. The paper starts with a model that estimates the cumulative probability density of the signal to adjacent channel interference ratio (SIR) as a function of the channel spacing. They then present the results of a computer simulation study to estimate the performance of DFE in mitigating the effect of ACI. The results indicate that, under the conditions of slow flat fading and selection diversity, the DFE is very effective in reducing the effect of excess ACI interference which allows for a considerable reduction in the frequency spacing 相似文献
16.
This paper presents a new massively parallel MIMD architecture, halfway between the Connection Machine and hypercubes based on 32-bit processors. It is built from specific 8-bit processors arranged in a 2-D grid and communicating by message transfers. We discuss the communication problems, the instruction set of the basic processing unit, the programmation of the whole array and the use of a high level data-flow language. 相似文献
17.
The spermatogenesis of Pseudis limellum, from the Southern Pantanal, Brazil, was studied from July 1995 to May 1996, through histological sections of the testis. The cells could be differentiated as: primary spermatogonia, large cells, generally with bilobed nucleus; secondary spermatogonia, smaller cells, with darker cytoplasm, chromatin of radial form; primary and secondary spermatocytes, differentiated according to the different stages of the nucleus during the successive cells divisions. Furthermore, we observed cells in process of morphologic differentiation: rounded spermatids much smaller, with nucleus containing chromatin in compacting process and cytoplasm reduction; elongated spermatids, generally parallel organized in well defined bundles, with the anterior region directed toward the periphery of the seminiferous tubule and the tail directed toward the lumen. Spermatozoa are free in the lumen of the seminiferous tubule. All the cells are organized as cysts, which are supported by a large amount of Sertoli cells. The spermatogenesis in P. limellum is very similar to that of other anurans, but peculiarities were observed regarding the organization of the germ cells, the great amount of free Sertoli cells in the lumen of testis collected in May, and the long cytoplasmatic extensions of the cells bearing pigments and involving the seminiferous tubule. The diameter of the seminiferous tubule (SD) exhibited an annual mean of 251.79 +/- 37.57 microm. Spermatozoa number by seminiferous tubule (SN) exhibited an annual mean of 306.66 +/- 39.83, also with higher and lower values at each month. Variations in SD and SN were not significantly correlated with climatic variables. In this species, reproduction occurs throughout the year in ponds and flooded areas, despite the seasonal climate of the Pantanal. Although males varied in their annual reproductive activity, they were considered potentially reproductive in all months throughout the year. 相似文献
18.
19.
The oil crisis of the 1970s has increased the concern about the continuity of oil imports flow to major oil-importing developed countries. Numerous policy measures including electricity demand-side management (DSM) programs have been adopted in such countries. These measures aim at reducing the growing need for electricity power that increases the dependency on imported foreign oil and damages the environment. On the other hand, the perception that energy can be obtained at very low cost in oil-rich countries led to less attention being paid to the potential of DSM policies in these countries. This paper discusses such potential using the case of the United Arab Emirates (UAE). Since air conditioning is a major source of electric energy consumption, the relationship between climate conditions and electric energy consumption is considered. An electricity demand model is constructed using time series techniques. The fitted model seems to represent these relationships rather well. Forecasts for electricity consumption using the estimated model indicate that a small reduction in cooling degrees requirement might induce a significant reduction in electric energy demand. Hence, a DSM program is proposed with policy actions to include, among others, measures to reduce cooling degrees requirement. 相似文献
20.
Fahd A. Alhaidari Saleh A. Al-Dossary Ilyas A. Salih Abdlrhman M. Salem Ahmed S. Bokir Mahmoud O. Fares Mohammed I. Ahmed Mohammed S. Ahmed 《计算机系统科学与工程》2021,36(1):57-67
Geologists interpret seismic data to understand subsurface properties and subsequently to locate underground hydrocarbon resources. Channels are among the most important geological features interpreters analyze to locate petroleum reservoirs. However, manual channel picking is both time consuming and tedious. Moreover, similar to any other process dependent on human intervention, manual channel picking is error prone and inconsistent. To address these issues, automatic channel detection is both necessary and important for efficient and accurate seismic interpretation. Modern systems make use of real-time image processing techniques for different tasks. Automatic channel detection is a combination of different mathematical methods in digital image processing that can identify streaks within the images called channels that are important to the oil companies. In this paper, we propose an innovative automatic channel detection algorithm based on machine learning techniques. The new algorithm can identify channels in seismic data/images fully automatically and tremendously increases the efficiency and accuracy of the interpretation process. The algorithm uses deep neural network to train the classifier with both the channel and non-channel patches. We provide a field data example to demonstrate the performance of the new algorithm. The training phase gave a maximum accuracy of 84.6% for the classifier and it performed even better in the testing phase, giving a maximum accuracy of 90%. 相似文献