全文获取类型
收费全文 | 3485篇 |
免费 | 89篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 41篇 |
综合类 | 6篇 |
化学工业 | 878篇 |
金属工艺 | 124篇 |
机械仪表 | 80篇 |
建筑科学 | 48篇 |
矿业工程 | 3篇 |
能源动力 | 299篇 |
轻工业 | 185篇 |
水利工程 | 22篇 |
石油天然气 | 7篇 |
无线电 | 340篇 |
一般工业技术 | 803篇 |
冶金工业 | 470篇 |
原子能技术 | 25篇 |
自动化技术 | 265篇 |
出版年
2023年 | 38篇 |
2022年 | 81篇 |
2021年 | 109篇 |
2020年 | 86篇 |
2019年 | 86篇 |
2018年 | 142篇 |
2017年 | 77篇 |
2016年 | 84篇 |
2015年 | 77篇 |
2014年 | 112篇 |
2013年 | 217篇 |
2012年 | 159篇 |
2011年 | 195篇 |
2010年 | 157篇 |
2009年 | 143篇 |
2008年 | 121篇 |
2007年 | 117篇 |
2006年 | 93篇 |
2005年 | 78篇 |
2004年 | 67篇 |
2003年 | 81篇 |
2002年 | 50篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 68篇 |
1998年 | 154篇 |
1997年 | 99篇 |
1996年 | 93篇 |
1995年 | 50篇 |
1994年 | 53篇 |
1993年 | 54篇 |
1992年 | 36篇 |
1991年 | 40篇 |
1990年 | 34篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 39篇 |
1985年 | 28篇 |
1984年 | 36篇 |
1983年 | 41篇 |
1982年 | 24篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 32篇 |
1978年 | 22篇 |
1977年 | 16篇 |
1976年 | 23篇 |
1975年 | 9篇 |
1973年 | 11篇 |
排序方式: 共有3596条查询结果,搜索用时 0 毫秒
1.
2-D symmetry: theory and filter design applications 总被引:1,自引:0,他引:1
In this comprehensive review article, we present the theory of symmetry in two-dimensional (2-D) filter functions and in 2-D Fourier transforms. It is shown that when a filter frequency response possesses symmetry, the realization problem becomes relatively simple. Further, when the frequency response has no symmetry, there is a technique to decompose that frequency response into components each of which has the desired symmetry. This again reduces the complexity of two-dimensional filter design. A number of filter design examples are illustrated. 相似文献
2.
The global market for liquid mixed‐metal stabilizers is migrating toward heavy‐metal‐free products, Historically, these systems have not been performance and cost competitive. High efficiency calcium‐zinc stabilizers have the potential to replace heavy‐metal‐based products. The intrinsic value of non‐phenolic lubricating calcium intermediates and calcium‐zinc stabilizers is discussed. 相似文献
3.
A. Sadananda Chary S. Narender Reddy T. Chiranjivi 《Journal of Materials Science》1989,24(6):2199-2202
Dielectric properties, dielectric constant (k), dielectric loss (tan δ) and a.c. conductivity (σ) in the solution-grown single crystals of RbNO3 are presented from room temperature to about 200°C covering the frequency range 102 to 105 Hz. A broad peak observed in tan δ-frequency data between 103 and 105Hz is thought to be due to impurity-vacancy dipoles. The sudden rise of three parameters near 160°C is attributed to the known
phase transition from trigonal to CsCl structure. 相似文献
4.
The aim of the present paper is to review the recent progress in the synthesis of in situ particle reinforced aluminum composites
using thermal, mechanical and combined mechanical-thermal activation of aluminothermic reduction reactions. The combination
of combustion synthesis (CS) and mechanosynthesis (MS) is the most recent development in the processing of advanced materials
like micro and nano aluminum based composites. The combined mechanical thermal synthesis (MTS) has widened the possibilities
for both CS and MS. MTS holds great potential for commercial viability and offers exciting processing route for the synthesis
of advanced materials. Enhanced reaction kinetics and extended concentration limits in MTS are demonstrated by illustrating
the synthesis of aluminum based nanocomposite involving Al–CeO2. 相似文献
5.
K Madhusudan Reddy Sunkara V Manorama R.D.K Misra 《Materials Research Bulletin》2004,39(10):1491-1498
A comparative study of gas sensing behavior of nanocrystalline nickel ferrite synthesized by micro-emulsion and hydrothermal method to liquefied petroleum gas (LPG) is presented. Nanocrystalline nickel ferrite synthesized by hydrothermal method indicated higher electrical conductivity and gas sensitivity at low operating temperature compared to nanocrystalline nickel ferrite synthesized by reverse micelle technique. This difference in the gas sensing behavior can be attributed to the presence of more oxygen vacancies (i.e. non-stoichiometry) in the hydrothermally synthesized nickel ferrite. Incorporation of palladium had a catalytic effect and the operating temperature was significantly reduced in both the samples. The higher operating temperature of the reverse micelle nickel ferrite material makes the sensor response speed faster (∼10 s) compared to the hydrothermally synthesized material (∼1 min). 相似文献
6.
7.
Autoscan: a scan design without external scan inputs or outputs 总被引:1,自引:0,他引:1
Pomeranz I. Reddy S.M. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2005,13(9):1087-1095
We propose a design-for-testability technique for synchronous sequential circuits called autoscan. Autoscan uses scan chains similar to conventional scan. However, it gives up the external scan inputs and outputs in order to eliminate the test data volume associated with them. Scan operations under autoscan improve the circuit testability by allowing the circuit state to be modified through shifting. Due to the removal of the scan inputs and outputs, synthesis of scan chains under autoscan does not have to satisfy all the constraints imposed on conventional scan chains. We describe a synthesis procedure for autoscan chains, and demonstrate that autoscan allows us to detect almost all the faults that are detectable using conventional scan. We use random sequences in order to show that sequential test generation is not necessary under autoscan. We also describe a test generation procedure, and discuss the effect of autoscan on fault diagnosis. 相似文献
8.
In this paper, we present a method for blind separation of co-channel BPSK signals arriving at an antenna array. This method consists of two parts: the maximum likelihood constellation estimation and assignment. We show that at high SNR, the maximum likelihood constellation estimation is well approximated by the smallest distance clustering algorithm, which we proposed earlier on heuristic grounds. We observe that both these methods for estimating the constellation vectors perform very well at high SNR and nearly attain Cramer-Rao bounds. Using this fact and noting that the assignment algorithm causes negligible error at high SNR, we derive upper bounds on the probability of bit error for the above method at high SNR. These upper bounds fall very rapidly with increasing SNR, showing that our constellation estimation-assignment approach is very efficient. Simulation results are given to demonstrate the usefulness of the bounds 相似文献
9.
EG Mdurvwa JI Alak GE Pimentel-Smith HS Gakou S Kolavala H Abdelrahman PG Reddy 《Canadian Metallurgical Quarterly》1997,43(7):1039-1044
The LP-BM5 murine leukemia virus causes acquired immunodeficiency syndrome in C57BL/6J mice (MAIDS), similar to that of AIDS in humans. The objective of this study was to determine the effect of LP-BM5 viral infection on cellular activation and membrane integrity of splenocytes. Oxidative burst in splenocytes in response to exposure to PMA (20 microg/ml) was significantly higher (p<.02) in infected than in control mice at two weeks post-infection using luminol-enhanced chemiluminescence. By 13 weeks post-infection superoxide anion production in infected mice was significantly lower when compared to controls coinciding with decreased proliferative response to mitogens. The extent of cell membrane damage as indicated by lactic dehydrogenase (LDH) activity in serum was significantly higher in infected than in control mice (p<.001). The results from this study suggests that LP-BM5 virus causes an initial stimulation of cellular activity followed by a decreased cell activation characterized by decreased proliferation of splenocytes and decreased oxygen radical production. Decreased cell membrane integrity indicated by increased LDH activity may partly be responsible for these changes. 相似文献
10.
K. T. Ramakrishna Reddy R. W. Miles 《Journal of Materials Science: Materials in Electronics》2003,14(9):529-532
Small-area polycrystalline CuGa
x
In1–x
Se2-based solar cells produced in the laboratory have been reported with efficiencies up to 18.8%. This success at achieving high-efficiency devices has stimulated a parallel research effort to produce large-area modules based on the use of CuGa
x
In1–x
Se2 with reduced cost of production. One method that has potential to achieve these objectives is chemical spray pyrolysis. Preliminary studies have resulted in devices with efficiencies of 4–5%. Further improvements toward implementing higher-efficiency devices are expected to result from a better understanding of the physical and chemical properties of the chalcopyrite layers produced. In this work we have investigated, for the first time, the properties of these layers using X-ray photoelectron spectroscopy (XPS) to identify the secondary phases and residual impurities present. The layers studied were for In/Ga mole ratios of x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 in CuGa
x
In1–x
Se2. The layers were also profiled by sputter etching away the surface of the layers and repeating the XPS measurements. The effects of annealing the layers in air, vacuum, and selenium vapor were also investigated. 相似文献