全文获取类型
收费全文 | 2606篇 |
免费 | 97篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 24篇 |
综合类 | 12篇 |
化学工业 | 576篇 |
金属工艺 | 130篇 |
机械仪表 | 46篇 |
建筑科学 | 44篇 |
矿业工程 | 7篇 |
能源动力 | 193篇 |
轻工业 | 168篇 |
水利工程 | 34篇 |
石油天然气 | 23篇 |
无线电 | 320篇 |
一般工业技术 | 585篇 |
冶金工业 | 299篇 |
原子能技术 | 31篇 |
自动化技术 | 220篇 |
出版年
2024年 | 13篇 |
2023年 | 47篇 |
2022年 | 73篇 |
2021年 | 116篇 |
2020年 | 80篇 |
2019年 | 99篇 |
2018年 | 122篇 |
2017年 | 109篇 |
2016年 | 107篇 |
2015年 | 57篇 |
2014年 | 111篇 |
2013年 | 244篇 |
2012年 | 127篇 |
2011年 | 171篇 |
2010年 | 104篇 |
2009年 | 120篇 |
2008年 | 123篇 |
2007年 | 73篇 |
2006年 | 63篇 |
2005年 | 54篇 |
2004年 | 46篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 30篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 49篇 |
1997年 | 38篇 |
1996年 | 38篇 |
1995年 | 35篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 16篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 14篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 11篇 |
1982年 | 12篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有2712条查询结果,搜索用时 15 毫秒
81.
82.
Rowdra Ghatak Dipak R. Poddar Rabindra K. Mishra 《AEUE-International Journal of Electronics and Communications》2009,63(4):279-286
This article compares input impedances and radiation characteristics of half wavelength Koch fractal V–electric dipoles having included angles 60°, 90° and 120°. The study considers three structures. In the 1st structure the Koch arms open into the V-region, in 2nd structure they open away from the V-region and in the third structure, one arm opens into and the other away from the V-region. A first iteration, structure 1 of V-Koch electric dipole antenna with included angle of 120° was fabricated and the experimental return loss was in good agreement with simulation. At their first resonances the antennas’ gain and input resistance decrease with decrease in included angles, an observation synonymous to Euclidian electric dipoles. In terms of gain, the first structure is found to give better performance than the other two. For this structure, the pattern distortion at the second resonance was also less compared to the other structures. 相似文献
83.
Role of boron in low carbon aluminum-killed cold rolled batch annealed steels has been critically examined. It was found that
it is not the absolute boron but B/N ratio that controls the forming properties. Pancake shaped grains (high grain shape anisotropy)
are highly desirable for improving the desirable {111} texture, normal anisotropy, and draw ability of the steel sheets. Microstructural
analysis showed that the extent of pancaking decreases with increase in B/N atomic ratio and reaches ultimately to formation
of equiaxed grains. Low B/N ratio (upto 0.3) resulted in improved mean plastic anisotropy ratio (r
m) value and high grain shape anisotropy, which has been characterized through grain aspect ratio. The desirable orientation
in steel with low B/N ratio is attributed to sufficient availability of Al and N to precipitate during batch annealing. Optimum
amount of boron, aluminum, and nitrogen in steel has resulted in coarse pancake structure, which is ideally suited for improved
formability. 相似文献
84.
Sediment TMDL Development for the Amite River 总被引:1,自引:0,他引:1
The Amite River is recognized as one of the 15 water bodies impaired by sediments in Louisiana, USA. Based on US EPA’s Protocol
sediment TMDL (Total Maximum Daily Load) development is conducted for the Amite River and described in this paper. The TMDL
development consists of four components: (1) development of a new model for cohesive sediment transport, (2) estimation of
sediment loads (sources) due to watershed erosion, (3) river flow computation, and (4) determination of sediment TMDL for
the Amite River. Using the mass conservation principle and Reynolds transport theorem a new 1-D model has been developed for
computation of suspended cohesive sediment transport. Sediment erosion in the Amite River Basin is calculated by combining
the USLE (Universal Soil Loss Equation) model with GIS and the digital elevation model of the Amite River Basin. Digital elevation
data was imported into the GIS which generated inputs for USLE. The calculated average annual rate of soil erosion in the
Amite River Basin is 13.368 tons per ha, producing a nonpoint sediment load of 103 mg/L to the Amite River. The flow computation
is performed using the HEC-RAS software. The computed sediment concentration in the Amite River varies in the range of 3–114 mg/L
and sediment TMDL is 281.219 tons/day. The reduction necessary to support beneficial uses of the river is 55% or 275.946 tons/day.
Results indicate that the combined application of the new 1-D sediment transport model, GIS, USLE model, and HEC-RAS is an
efficient and effective approach to sediment TMDL development. 相似文献
85.
The objective of this study was to compare the performance of cellulose acetate (CA) and ethylcellulose (EC)-HPMC combination coatings as semipermeable membranes (SPMs) for osmotic pump tablets (OPTs) of naproxen sodium (NPS) so as to deliver a constant, predetermined amount of drug in solution form over a fixed span of time, independent of external environmental conditions. Osmotic pump tablets were designed with different coating variables and optimized in terms of nature of plasticizer, membrane thickness, and orifice diameter. The effect of insertion of an inner microporous film around the NPS core to minimize deformation of the SPM due to peristaltic movement of the gut was also studied. Osmotic pump tablets composed of membranes with water-soluble plasticizer, propyleneglycol (PG), released drug mainly through diffusion, whereas those designed with CA and EC-HPMC (4:1) coats containing water-insoluble plasticizer, castor oil, released their contents by perfect zero-order kinetics over a prolonged period of time, though the average release rate that could be achieved with the EC-HPMC (4:1) membrane was only about half the rate achieved with the CA membrane for the same membrane thickness. Release rates for both the membranes decreased with increasing membrane thickness and were found to be independent of orifice diameter, agitation intensity, and pH of the dissolution medium. 相似文献
86.
A Nuclear Power Project is being set-up at KudanKulam in the state of Tamil Nadu, India in collaboration with the Russian Federation. The project comprises of two units each of 1000 MWe VVER type reactor. The design of the plant and supply of all the major equipment is in the scope of the Russian Federation while development of infrastructure and project construction is in Indian scope of works. The VVER (Version V-412) reactor that is under construction at KudanKulam site is an advanced PWR, which incorporates all the features of a modern PWR as per the current Russian, Western and IAEA standards. The KudanKulam site in the southern Indian state of Tamil Nadu was one among the several sites evaluated by the Site Selection Committee, which cleared KudanKulam site for setting up an installed capacity up to 6000 MWe. The design, construction and operation of the plant meets the regulatory and licensing requirements of Russian regulatory body “RTN” as also India's Atomic Energy Regulatory Board. The supply of the equipment from the Russian Federation is on schedule and the project construction work by various Indian agencies is also ahead of schedule. The two units of KudanKulam Nuclear Power Project (KKNPP) are scheduled to achieve first criticality in the year 2007–2008. The paper discusses various design features, project construction and management aspects. 相似文献
87.
Harmonic estimation for a signal distorted with additive noise has been an area of interest for researchers in many disciplines of science and engineering. This work presents a new algorithm based on the foraging behavior of E. coli bacteria in our intestine to estimate the harmonic components present in power system voltage/current waveforms. The basic foraging strategy is made adaptive, through a Takagi-Sugeno fuzzy scheme, depending on the operating condition to make the convergence faster. Besides, the harmonic estimation is linear in amplitude and nonlinear in phase. As the proposed algorithm does not rely on Newton-like gradient descent methods, this is used for phase estimation whereas the linear least square scheme estimates the amplitude, thereby presenting the hybrid method. The improvement in %error, as well as the processing time compared with the conventional discrete Fourier transform and genetic algorithm method is demonstrated in this paper. Besides, the performance is quite acceptable even in the presence of decaying dc component as well as to change in amplitude and phase angle of harmonic components. 相似文献
88.
S. K. Mishra P. K. P. Rupa S. K. Das V. Shcherbakov 《Metallurgical and Materials Transactions B》2006,37(4):641-647
A detailed investigation of the effect of alumina diluent on the Al2O3-TiB2/ZrB2 composite by self propagating high temperature synthesis (SHS) dynamic compaction was carried out. A dense composite could
be obtained and microstructure could be tailored and controlled by adding alumina as diluent during the SHS reaction. The
microhardness values decreased for 5 and 10 wt pct additions of alumna but increased for 15 and 20 wt pct additions. Hardness
is influenced by the different phases present and the grain size. 相似文献
89.
The promise of a broadband integrated service digital network has led to the design of mechanisms for efficient transport
of real-time compressed video in packet switching networks. We examine feedback control for video transport in ATM networks
where the available feedback is a single bit of information carried in the cell header. We investigate the performance of
three single-bit schemes for source rate adaptation. Two were originally for congestion control of bursty data traffic and
are modified to control video traffic. The third scheme conveys more information about
the state of queue(s) at the bottleneck. The simulation results show that all three schemes for feedback control of VBR video
streams work remarkably well. During severe network congestion, the signal quality degrades gracefully, but not uniformly
across all connections. Based on insights from the initial simulations, we propose a scheme to improve the fairness of service
and demonstrate its effectiveness. 相似文献
90.