全文获取类型
收费全文 | 391篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 127篇 |
金属工艺 | 14篇 |
机械仪表 | 12篇 |
建筑科学 | 15篇 |
能源动力 | 23篇 |
轻工业 | 41篇 |
水利工程 | 4篇 |
石油天然气 | 6篇 |
无线电 | 36篇 |
一般工业技术 | 79篇 |
冶金工业 | 19篇 |
原子能技术 | 2篇 |
自动化技术 | 32篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 11篇 |
2021年 | 19篇 |
2020年 | 12篇 |
2019年 | 17篇 |
2018年 | 14篇 |
2017年 | 17篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 13篇 |
2013年 | 36篇 |
2012年 | 22篇 |
2011年 | 32篇 |
2010年 | 17篇 |
2009年 | 21篇 |
2008年 | 12篇 |
2007年 | 15篇 |
2006年 | 17篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 7篇 |
1998年 | 14篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有414条查询结果,搜索用时 31 毫秒
1.
Shafeeque G. Ansari Mushtaq Ahmad Dar Young-Soon Kim Hyung-Kee Seo Gil-Sung Kim Rizwan Wahab Zubaida A. Ansari Jae-Myung Seo Hyung-Shik Shin 《Korean Journal of Chemical Engineering》2008,25(3):593-598
A comparative study for the nucleation of diamond was carried out using surface treatment like (i) surface scratching with
1 μm diamond paste and (ii) surface etching using chlorine plasma at different RF powers (50, 100 and 150 W). Atomic force
microscopic study shows variation in roughness from 31 nm to 110 nm. Scratching results in random scratches, whereas plasma
etches a surface uniformly. Scanning electron microscopic observations show well faceted crystallites with a predominance
of angular shaped grains corresponding to 〈100〉 and 〈110〉 crystallite surfaces for the scratched as well as plasma etched
substrate. Surface etching at 150 W plasma power results in a better growth in comparison with 50 and 100 W plasma powers.
Chlorine-radical is found responsible for the changes in the growth morphology. Raman spectroscopy shows a sharp peak at 1,332
cm−1 and a peak at ∼1,580 cm−1 for both samples. 相似文献
2.
This paper describes different dynamic tests carried out on three bridges, B14, B15, and B13, over highway E19, which connects Brussels and Antwerpen in Belgium. Different excitation types are considered: a drop weight, a heavy truck on the bridge, and ambient vibrations mainly due to the traffic under the bridge. Finite-element models are constructed to support and verify the dynamic measurements. The modal parameters are extracted from the response time series using the data dependent system approach. A vector autoregressive model is developed and successfully applied to the measured responses in time domain. Good correlation between the finite-element simulations and the experiments is obtained. 相似文献
3.
The effect of N fertilizers on nodulation, nitrogenase, nitrate reductase activities and growth of two cultivars of soybean, Clark and Crauford was evaluated in a field experiment. KNO3 or NH4Cl were applied 27 days after planting at 0,16, 32, 64 and 128 kg N/ha. Nodulation and growth of both cultivars significantly increased when N was applied at low levels whereas specific N2-ase activity (SNA) slightly and insignificantly increased. Cv Crauford showed a greater positive response than cv. Clark. Higher rates of KNO3 and NH4Cl (128 kg N/ha) significantly depressed nodulation and SNA but slightly decreased the plant dry matter. Cv. Crauford was more tolerant to N fertilizers than cv. Clark. The decline in SNA was ascribed to increased nitrate reductase activity (NRA) and higher accumulation of nitrites in nodule cytosol. NRA and nitrate contents in nodules of cv. Clark were greater than that in cv. Crauford. Results showed that NH4
+ is the preferred N source with occasional increases in nodule number and weight. This study provides an evidence for the nodulation and growth variability of soybean cultivars fertilized with different levels of N. The results also suggest that diminishing NRA could contribute to increased N2 fixation and the interaction between NO3
– assimilation and N2 fixation is strongly dependent on the plant cultivar. 相似文献
4.
One of the important aspects in achieving better performance for transient stability assessment (TSA) of power systems employing
computational intelligence (CI) techniques is by incorporating feature reduction techniques. For small power system the number
of features may be small but when larger systems are considered the number of features increased as the size of the systems
increases. Apart from employing faster CI techniques to achieve faster and accurate TSA of power system, feature reduction
techniques are needed in reducing the input features while preserving the needed information so as to make faster training
of the CI technique. This paper presents feature reductions techniques used, namely correlation analysis and principle component
analysis, in reducing number of input features presented to two CI techniques for TSA, namely probabilistic neural network
(PNN) and least squares support vector machines (LS-SVM). The proposed feature reduction techniques are implemented and tested
on the IEEE 39-bus test system and 87-bus Malaysia’s power system. Numerical results are presented to demonstrate the performance
of the feature reduction techniques and its effects on the accuracies and time taken for training the two CI techniques. 相似文献
5.
Observations of fatigue-induced slip patterns on the surface of polycrystalline gold (+99.9%) using the scanning tunnelling microscope (STM) are presented. The samples were cycled in four-point bending between zero and 0.0025 strain for 250 and 2500 cycles. STM observations of the sample fatigued for 250 cycles revealed broad slip bands 0.38–0.69 m wide containing narrow slip bands 0.015–0.123 m wide and fine slip lines 0.006 m wide. The depth of these features are 20–57 nm for broad slip bands, 3–7 nm for narrow slip bands, and approximately 2–4 nm for fine slip lines. The sample fatigued for 2500 cycles showed similar values for the width of the slip bands and slip lines except that their depth was increased by a factor of between 2 and 4 times for the narrow slip bands and the fine slip lines. Apparent persistent slip bands (PSBs) spaced 2.4 m, 300–500 nm deep were also observed. These results demonstrate that STM is a significant new tool for observing and distinguishing various types of fatigue-induced surface slip patterns on suitably prepared samples. The vertical resolution obtained with STM is vastly superior to current SEM and TEM methods. 相似文献
6.
A 2-D five-noded finite element which contains a singularity is developed. The new element is compatible with cubic standard isoparametric elements. The main advantage of using cubic isoparametric elements over quadratic elements is to reduce the number of elements required to model a structure for results of comparable accuracy. The element is tested on two different examples. In the first example, an edge crack problem is analyzed using two different meshes. The second example is a crack perpendicular to the interface problem which is solved for two different specific composites. The results obtained using the proposed element are compared with those obtained using other existing elements in the literature. Those comparisons demonstrate the superiority of the present technique in using less number of elements and nodes to produce accurate results. 相似文献
7.
Miscible polymer blends based on various ratios of poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) were prepared in film form by the solution casting technique using benzene as a common solvent. The thermal decomposition behavior of these blends and their individual homopolymers before and after γ‐irradiation at various doses (50–250 kGy) was investigated. The thermogravimetric analysis technique was utilized to determine the temperatures at which the maximum value of the rate of reaction (Tmax) occurs and the kinetic parameters of the thermal decomposition. The rate of reaction curves of the individual homopolymers or their blends before or after γ‐ irradiation displayed similar trends in which the Tmax corresponding to all polymers was found to exist in the same position but with different values. These findings and the visual observations of the blend solutions and the transparency of the films gave support to the complete miscibility of these blends. Three transitions were observed along the reaction rate versus temperature curves; the first was around 100–200°C with no defined Tmax, which may arise from the evaporation of the solvent. The second Tmax was in the 340–380°C range, which depended on the polymer blend and the γ‐irradiation condition. A third transition was seen in the rate of reaction curves only for pure PVAc and its blends with PMMA with ratios up to 50%, regardless of γ‐ irradiation. We concluded that γ‐irradiation improved the thermal stability of PVAc/PMMA blends, even though the PMMA polymer was degradable by γ irradiation. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1773–1780, 2006 相似文献
8.
The influence of HAF carbon black and BaTiO3 ceramic powder contents in SBR vulcanizates on the dielectric constant (ε′) at different frequencies and at fixed temperature of 303 K is studied well in this article. The temperature dependence of the ac conductivity (σac) was also studied. ε′ appreciably decreases as frequency increased for both filled and unfilled SBR vulcanizates. At each frequency, ε′ gradually decreased with BaTiO3 loading, but its change at any fixed frequency with BaTiO3 filler loading is not uniform. For HAF group ε′ (at loading ≥ 40 phr), drops rapidly with frequency. Meanwhile, it increased appreciably beyond a certain HAF filler loading (≈ 20 phr). Experimental values of the dielectric constant of both BaTiO3 and HAF contents were compared with those calculated by using Tsangaris, Clausius and Bruggman models. Tsangaris model with simple modifications was applied and a fairly good agreement was obtained. The HAF particles or aggregates was found to take the shape of oblate ellipsoids with the minor axes parallel to the applied frequency as detected from the decreasing behavior of the depolarizing factor (Y) with HAF contents. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2227–2234, 2007 相似文献
9.
Magdy M. Senna Ateyat M. Yossef Fatma M. Hossam Abdel Wahab M. El‐Naggar 《应用聚合物科学杂志》2007,106(5):3273-3281
Foamy low‐density polyethylene/plasticized starch (LDPE/PLST) blends at different compositions were produced in the presence of azodicarbonamide (ACA) compound as foaming agent. The LDPE/PLST blends before and after electron beam irradiation were investigated in terms of mechanical properties, bulk density, and structure morphology. Moreover, the biodegradability of these materials was evaluated by the soil burial test for 2 months, in which the buried sheets were also examined by scanning electron microscopy (SEM). The results showed that the increase of PLST content from 24 to 30% was accompanied by a decrease in the yield and break stresses of 10 and 20% for the unirradiated blends without the foaming agent, respectively. Further decrease in these mechanical parameters was observed after the foaming process. The bulk density, void fraction, cell size measurements as well as the examination by SEM illustrate clearly the cell growth of the foam structure. The soil burial test and SEM micrographs indicate the growth of microorganisms overall the blend sheets and that the blend was completely damaged after two months of burying. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
10.
SHAFQAT Wahab 《计算机辅助绘图.设计与制造(英文版)》2009,19(1):36-42
A time-resolved numerical computational approach, involving the combustion of double-base propellant is performed on thermal protection material for SRM nozzle. An implicit Navier-Stokes Solver is selected to simulate two-dimensional axial-symmetric unsteady turbulent flow of compressible fluid. The governing equations are discredited by using the finite Volume method. S-A turbulence model is employed. CFD scheme is implemented to investigate the temperature distribution causes at nozzle throat inserts comp... 相似文献