全文获取类型
收费全文 | 2561篇 |
免费 | 209篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 21篇 |
综合类 | 1篇 |
化学工业 | 565篇 |
金属工艺 | 68篇 |
机械仪表 | 100篇 |
建筑科学 | 86篇 |
矿业工程 | 10篇 |
能源动力 | 125篇 |
轻工业 | 423篇 |
水利工程 | 10篇 |
石油天然气 | 18篇 |
无线电 | 419篇 |
一般工业技术 | 454篇 |
冶金工业 | 47篇 |
原子能技术 | 18篇 |
自动化技术 | 408篇 |
出版年
2024年 | 14篇 |
2023年 | 47篇 |
2022年 | 44篇 |
2021年 | 123篇 |
2020年 | 90篇 |
2019年 | 89篇 |
2018年 | 145篇 |
2017年 | 102篇 |
2016年 | 133篇 |
2015年 | 113篇 |
2014年 | 124篇 |
2013年 | 467篇 |
2012年 | 99篇 |
2011年 | 102篇 |
2010年 | 128篇 |
2009年 | 138篇 |
2008年 | 67篇 |
2007年 | 47篇 |
2006年 | 46篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 13篇 |
2002年 | 18篇 |
2001年 | 76篇 |
2000年 | 73篇 |
1999年 | 75篇 |
1998年 | 80篇 |
1997年 | 81篇 |
1996年 | 25篇 |
1995年 | 8篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1973年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有2773条查询结果,搜索用时 15 毫秒
21.
B. J. Mayr ÖVE IEEE H. Weinrichter ÖVE IEEE 《e & i Elektrotechnik und Informationstechnik》1997,114(3):123-130
Modern communication systems offer high speed and reliable data transmission services. The quality of these services is achieved by combining coded multi-level modulation techniques and modern digital signal processing (Viterbi-decoding) in the receiver. In this paper we first present an introduction to Trellis Coded Modulation (TCM) and then some new results on unversal techniques adapted for the AWGN-channel as well as for the fading channel. It is shown that TCM is well suited for communication channels with time variant characteristics (e.g. mobile communication channels), especially when our new codes are applied. 相似文献
22.
S. P. Ashburn M. C. Öztürk J. J. Wortman G. Harris J. Honeycutt D. M. Maher 《Journal of Electronic Materials》1992,21(1):81-86
Titanium and cobalt germanides have been formed on Si (100) substrates using rapid thermal processing. Germanium was deposited
by rapid thermal chemical vapor deposition prior to metal evaporation. Solid phase reactions were then performed using rapid
thermal annealing in either Ar or N2 ambients. Germanide formation has been found to occur in a manner similar to the formation of corresponding silicides. The
sheet resistance was found to be dependent on annealing ambient (Ar or N2) for titanium germanide formation, but not for cobalt germanide formation. The resistivities of titanium and cobalt germanides
were found to be 20 μΩ-cm and 35.3μΩ-cm, corresponding to TiGe2 and Co2Ge, respectively. During solid phase reactions of Ti with Ge, we have found that the Ti6Ge5 phase forms prior to TiGe2. The TiGe2 phase was found to form approximately at 800° C. Cobalt germanide formation was found to occur at relatively low temperatures
(425° C); however, the stability of the material is poor at elevated temperatures. 相似文献
23.
24.
H. Ö. Özbelge T. F. Al-Fariss A. M. Abdulrazik 《Nutrient Cycling in Agroecosystems》1993,34(3):217-222
There is an appreciable amount of carbonaceous sedimentary phosphate deposits in the northern Africa and the Middle East which are expected to gain importance in the near future because of the depletion of the deposits in Florida. In many of the regions where phosphate deposits are found there is a shortage of fresh water, and sea is not very far. The use of sea water instead of fresh water in flotation of carbonaceous phosphate rock is successfully demonstrated. Thus an appreciable reduction in the operating cost and an ample amount of saving in the fresh water resources of the region is expected. 相似文献
25.
26.
S. Salar Behzadi Silvester Ölzant Reinhard Länger Christian Koban Frank M. Unger Helmut Viernstein 《European Food Research and Technology》2006,223(2):238-245
Inversion of sucrose is a stability problem particularly of candies with acidic taste that contain sucrose and small amounts of organic acids such as citric acid, since the free d-fructose produced by hydrolysis is hygroscopic. The following possibilities were investigated for preventing the hydrolysis of sucrose in tablets containing sucrose and citric acid: Adding various amounts of tri-sodium citrate to the formulation to neutralize the citric acid, (Hot) melt coating of citric acid and tri-sodium citrate with a vegetable fat at different coating ratios, variation of the ratio of coated citric acid and tri-sodium citrate in formulations, and compressing the formulations with different compression forces. After tablet processing and storage of tablets, the concentration of d-fructose was determined on the basis of enzymatic reactions. A response surface central composite design was used. The above-mentioned variations were chosen as independent variables and the amount of d-fructose was chosen as response variable. The lowest rates of inversion could be achieved by increasing the content of tri-sodium citrate and the ratio of coating material and decreasing the ratio of coated citric acid and tri-sodium citrate in the tablet formulations. The compression force had no significant effect on the inversion of sucrose. 相似文献
27.
Organo-functional silanes which were able to form chemical bonds with kaolinite and could also have an affinity to the materials of concern here, were studied by the sol-gel process. Polymethacrylate with trialkoxy silyl functional groups were prepared, hydrolysed and co-condensed with kaolinite. The progress of the hydrolysis, which proceeded very slowly, was followed by Karl-Fischer titration. Thermal behavior was investigated by differential thermal analysis. The extent of the reaction leading to network formation was qualitatively followed by Fourier transform-infrared spectroscopy and X-ray diffraction. Free-radical polymerization was carried out ultrasonically in the presence of a catalyst. Trimethoxy silane end-capped silane was found to be covalently bonded to kaolinite. The copolymers, with various amounts of kaolinite, were then hydrolysed and co-condensed in the presence of a catalyst to yield sol-gel materials which have a controllable combination of properties of both the polymer and kaolinite. 相似文献
28.
In comparing our calculated exciton energies with those obtained from pseudopotential calculations (Ref. 27) and from a previous
tight binding calculation (Ref. 30), we stated that the differences between the three semi-empirical calculations arise because
of different treatment of the nanocrystal surfaces. This appears not to be correct. Subsequent calculations with variable
Si-H parameters have shown that the band gap is actually rather insensitive to the actual value of these. Instead, the important
feature appears to be the overall quality of the bulk band structure parameterization. References 27 and 30 use more extensive
and higher quality empirical parameterizations for bulk Si than the sp3s∗ model used by us. Repeating our time dependent calculations with an improved sp3d5 parameterization results in similar values to those of Refs. 27 and 30 for the exciton energies.1 The agreement of the sp3s∗ values with experimental photoluminescence energies (Fig. 7) cannot, therefore, be regarded as well understood at this
time.1,2 相似文献
29.
The effects of an elevated temperature and a 5 wt% silicon addition on the resultant microstructure and inherent phases of Stellite 6 were investigated by using room and high temperature optical microscopy, X-ray diffraction, scanning electron microscopy (SEM) and also bulk hardness and microhardness measurements. It has been observed that exposing Stellite 6 to heat treatments at 1000°C results in a characteristic textured structure and coarsening of interdendritic regions due to bulk diffusion. In addition, both dendritic and interdendritic hardness values increase due to texture formation and increased amounts of carbide and intermetallic phases, respectively. On the other hand, silicon addition to Stellite 6 causes the transformation of the original spongy dendritic microstructure in as-cast Stellite 6 to a eutectic dendritic and skeleton interdendritic structure. Also, when silicon added Stellite 6 was heat treated at 1000°C, particulates emanating from the interdendritic skeleton become irregularly dispersed in the dendritic region. In addition, similarly to Stellite 6; a high temperature heat treatment results in an increase in hardness values of silicon added Stellite 6 due to the presence of an Co2 Si intermetallic phase. 相似文献
30.
M.D. Mikhailov M.N. Özişik 《International Communications in Heat and Mass Transfer》1985,12(4):393-404
A new, powerful method of analysis, involving the combined use of finite integral transform and finite element techniques, is presented for the solution of time dependent heat flow systems composed of many one-dimensional elements connected through the nodes. This method leads to an eigenvalue problem which is not of the conventional Sturm-Liouville type. A procedure for the determination of the eigenvalues is described. The solution obtained is in the form of an infinite series and contains quasi-steady and transient terms. The general solution obtained can be applied in the mathematical modelling of many engineering applications such as the determination of the penetration of the daily temperature cycle into buildings, the analysis of heat transfer in array of extended surfaces in compact heat exchangers, and many others. 相似文献