全文获取类型
收费全文 | 4075篇 |
免费 | 104篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 75篇 |
综合类 | 17篇 |
化学工业 | 929篇 |
金属工艺 | 113篇 |
机械仪表 | 187篇 |
建筑科学 | 110篇 |
矿业工程 | 11篇 |
能源动力 | 688篇 |
轻工业 | 130篇 |
水利工程 | 33篇 |
石油天然气 | 64篇 |
无线电 | 317篇 |
一般工业技术 | 625篇 |
冶金工业 | 76篇 |
原子能技术 | 73篇 |
自动化技术 | 738篇 |
出版年
2024年 | 5篇 |
2023年 | 42篇 |
2022年 | 43篇 |
2021年 | 63篇 |
2020年 | 125篇 |
2019年 | 154篇 |
2018年 | 134篇 |
2017年 | 262篇 |
2016年 | 368篇 |
2015年 | 276篇 |
2014年 | 474篇 |
2013年 | 429篇 |
2012年 | 259篇 |
2011年 | 234篇 |
2010年 | 163篇 |
2009年 | 178篇 |
2008年 | 51篇 |
2007年 | 97篇 |
2006年 | 99篇 |
2005年 | 72篇 |
2004年 | 48篇 |
2003年 | 39篇 |
2002年 | 62篇 |
2001年 | 62篇 |
2000年 | 44篇 |
1999年 | 99篇 |
1998年 | 25篇 |
1997年 | 25篇 |
1996年 | 20篇 |
1995年 | 21篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 22篇 |
1987年 | 27篇 |
1986年 | 31篇 |
1985年 | 23篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1965年 | 1篇 |
排序方式: 共有4186条查询结果,搜索用时 15 毫秒
81.
Modeling of the Effect of pH on the Calcite Dissolution Kinetics 总被引:2,自引:0,他引:2
I. V. Dolgaleva I. G. Gorichev A. D. Izotov V. M. Stepanov 《Theoretical Foundations of Chemical Engineering》2005,39(6):614-621
The kinetics and mechanism of calcite dissolution at various pH are investigated. A scheme of the ion distribution in various states of the medium is presented. The kinetic curves of dissolution are modeled, taking into account the structure of the electrical double layer and the acid-base characteristics of calcite. 相似文献
82.
Malaysia has seen tremendous growth in the standard of living and household per capita income. The demand for a more systematic and efficient planning has become increasingly more important, one of the keys to achieving a high standard in healthcare. In this paper, a Maximal Covering Location Problem (MCLP) is used to study the healthcare facilities of one of the districts in Malaysia. We address the limited capacity of the facilities and the problem is formulated as Capacitated MCLP (CMCLP). We propose a new solution approach based on genetic algorithm to examine the percentage of coverage of the existing facilities within the allowable distance specified/targeted by Malaysian government. The algorithm was shown to generate good results when compared to results obtained using CPLEX version 12.2 on a medium size problem consisting of 179 nodes network. The algorithm was extended to solve larger network consisting of 809 nodes where CPLEX failed to produce non-trivial solutions. We show that the proposed solution approach produces significant results in determining good locations for the facility such that the population coverage is maximized. 相似文献
83.
In this paper, the similarity of moment vectors between the test and the reference image blocks together with the result from the block classification are used in the formulation of an image quality metric (IQM). First, the reference and the test images are divided into non-overlapping 8×8 blocks and transformed into moment domain using Discrete Tchebichef Transform. The moment features are then used in two operations: the local quality index calculation and the image content (block) classification. The local quality index is obtained from the similarity measure of moment vectors between the reference and the test image blocks. Next, the content of each reference image block is classified into three types: “plain”, “edge” and “texture”, based on its moment energy level and moment energy distribution. The local quality indices obtained from all the image blocks are then averaged based on the block types to obtain three mean quality scores for each test image. The performance of these three mean quality scores and their combinations are studied using the LIVE database. The results show that the performance of the metric is significantly improved by combining the mean quality scores from the edge and texture image region. The best combination (the proposed metric) is then compared with five other IQMs using the LIVE database and four other independent databases. The results show that the proposed metric performs comparatively well for all the databases. 相似文献
84.
Bridges are the most useful part in the transportation network. Any disruption of the bridge structures may hamper the whole transportation system. In the last recent tsunamis, numerous number of bridges were structurally damaged by the tsunami waves. Lack of proper provisions of tsunami forces in the design guidelines also contributes to the augmentations of the damage level. Therefore, proper evaluation of the tsunami forces on the bridge girder should be introduced in the design promptly. In this study, laboratory experiments were carried out to reveal the damage mechanism of the bridge girder by assessing the exerted tsunami forces. Both broken and unbroken waves were considered for the analysis. The results showed that measured forces were larger for broken waves than those of unbroken waves. Maximum force of the broken waves was 4.59 times as large as the hydrostatic pressure. Also, waves reached the peak value more rapidly for larger wave heights than those of smaller ones. Additionally, a girder that is placed at a higher position is much vulnerable to tsunami hazard. 相似文献
85.
《Materials Research Bulletin》2006,41(8):1437-1446
Yttria stabilised zirconia has been prepared using a simple sol-powder coating technique. The polymeric yttria sol, which was prepared using 1,3 propanediol as a network modifier, was homogeneously mixed with nanocrystalline zirconia powder and it showed a dual function: as a binder which promoted densification and a phase modifier which stabilised zirconia in the tetragonal and cubic phases. Thermal analysis and X-ray diffraction revealed that the polymeric yttria sol which decomposed at low temperature into yttrium oxide could change the m → t phase transformation behaviour of the zirconia, possibly due to the small particle size and very high surface area of both yttria and zirconia particles allowing rapid alloying. The sintered samples exhibited three crystalline phases: monoclinic, tetragonal and cubic, in which cubic and tetragonal are the major phases. The weight fractions of the individual phases present in the selected specimens were determined using quantitative Rietveld analysis. 相似文献
86.
《Materials Research Bulletin》2006,41(11):2070-2079
The production of magnesium–chromium oxides by solution combustion synthesis was investigated using glycine and urea for the first time. Ammonium dichromate, urea/glycine and ammonium nitrate aqueous solutions were used as the precursors of the oxides. The effect of different reaction parameters, such as fuel richness, stoichiometry and fuel leanness was evaluated; such parameters were modified by changing the reagents and the fuel/oxidant ratio. The results suggest that glycine is an interesting complexing/combustible agent for ammonium dichromate to produce chromite spinel. Addition of extra ammonium nitrate to stoichiometric compositions improved the specific surface area and reduced the crystallite size. The highest specific surface area (153.40 m2/g) was obtained for the stoichiometric fuel/oxidant mixtures containing glycine as combustible in combination with ammonium nitrate; however, the smallest crystallite size (approximately 9 nm) of Pirochromite (MgCr2O4) was synthesized using urea as combustible. 相似文献
87.
《Materials Research Bulletin》2006,41(12):2260-2267
Ce1−xGdxO2−1/2x nanopowder were successfully synthesized by microwave-induced combustion process. For the preparation, cerium nitrate, gadolinium nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only 30 min to obtain Ce1−xGdxO2−1/2x powders. The exo-endo temperature, phase identification, and morphology of resultant powders were investigated by TG/DTA, XRD, and SEM. The as-received Ce1−xGdxO2−1/2x powders showed that the average particle size ranged from 18 to 50 nm, crystallite dimension varied from 11 to 20 nm, and the specific surface area was distribution from 16 to 46 m2/g. As for Ce1−xGdxO2−1/2x ceramics sintered at 1450 °C for 3 h, the bulk density of Ce1−xGdxO2−1/2x ceramics were over 91% of the theoretical density, the maximum electrical conductivity, σ700 °C = 0.017 S/cm with minimum activation energy, Ea = 0.869 eV was found at Ce0.80Gd0.20O1.90 ceramic. 相似文献
88.
A. Haque B. H. Lim A. S. M. A. Haseeb H. H. Masjuki 《Journal of Materials Science: Materials in Electronics》2012,23(1):115-123
Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers.
Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga
solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment
was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame,
CuZn4, Cu5Zn8 and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al3Ni2 IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn3 IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with
a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about
45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the
Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength
was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard
Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output
voltage after 1,000 thermal cycles was found 12.1%. 相似文献
89.
Nonclassical light and collapse-revival dynamics are consequences of dynamical quantum interference in transient photon-atom interaction. We study the time evolution of atom and photons in a high quality cavity for time-dependent atom-field coupling, with different initial field states and initial atomic states. The inversion for initial superposed atomic state seems to be independent of initial classical fields but can be stimulated by the Schrodinger cat field. Interesting effects of the transient coupling are found through analysis of the collapse-revival in population inversion and the features in the Wigner function. Oscillatory coupling coefficient can prolong the occurrence of collapse, in analogy to the Zeno effect. The intensity atom-field coupling duration is an important parameter for controlling atomic inversion and producing frozen nonclassical light in the cavity after the atom-field coupling ceases. 相似文献
90.
《Fusion Engineering and Design》2014,89(7-8):1126-1130
Europe is currently developing two reference breeder blankets concepts for DEMO reactor specifications that will be tested in ITER under the form of Test Blanket Modules (TBMs): the Helium-Cooled Lithium-Lead (HCLL) concept which uses the eutectic Pb-16Li as both breeder and neutron multiplier; the Helium-Cooled Pebble-Bed (HCPB) concept which features lithiated ceramic pebbles as breeder and beryllium pebbles as neutron multiplier. Each TBM is associated with several sub-systems required for their operation; together they form the Test Blanket System (TBS). This paper presents the state of HCLL and HCPB TBS instrumentation design. The discussion is based on the systems functional analysis, from which three main categories of instrumentation are defined: those relevant to safety functions; those relevant to interlock functions; those designed for the control and scientific exploitation of the devices based on the TBM program objectives. 相似文献