全文获取类型
收费全文 | 163495篇 |
免费 | 22738篇 |
国内免费 | 7010篇 |
专业分类
电工技术 | 8703篇 |
技术理论 | 5篇 |
综合类 | 11098篇 |
化学工业 | 35849篇 |
金属工艺 | 7426篇 |
机械仪表 | 8940篇 |
建筑科学 | 10940篇 |
矿业工程 | 2904篇 |
能源动力 | 4273篇 |
轻工业 | 17062篇 |
水利工程 | 2878篇 |
石油天然气 | 5420篇 |
武器工业 | 1014篇 |
无线电 | 21673篇 |
一般工业技术 | 24765篇 |
冶金工业 | 5856篇 |
原子能技术 | 1714篇 |
自动化技术 | 22723篇 |
出版年
2024年 | 447篇 |
2023年 | 1601篇 |
2022年 | 3090篇 |
2021年 | 4527篇 |
2020年 | 4516篇 |
2019年 | 5701篇 |
2018年 | 5886篇 |
2017年 | 6569篇 |
2016年 | 6953篇 |
2015年 | 8370篇 |
2014年 | 9663篇 |
2013年 | 12035篇 |
2012年 | 10901篇 |
2011年 | 11368篇 |
2010年 | 10991篇 |
2009年 | 10508篇 |
2008年 | 10130篇 |
2007年 | 9558篇 |
2006年 | 9246篇 |
2005年 | 7785篇 |
2004年 | 6403篇 |
2003年 | 5942篇 |
2002年 | 6735篇 |
2001年 | 5767篇 |
2000年 | 4462篇 |
1999年 | 3145篇 |
1998年 | 1998篇 |
1997年 | 1679篇 |
1996年 | 1495篇 |
1995年 | 1307篇 |
1994年 | 1041篇 |
1993年 | 783篇 |
1992年 | 593篇 |
1991年 | 469篇 |
1990年 | 366篇 |
1989年 | 260篇 |
1988年 | 236篇 |
1987年 | 158篇 |
1986年 | 96篇 |
1985年 | 93篇 |
1984年 | 74篇 |
1983年 | 49篇 |
1982年 | 42篇 |
1981年 | 44篇 |
1980年 | 36篇 |
1979年 | 22篇 |
1977年 | 13篇 |
1976年 | 23篇 |
1975年 | 13篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
通过试验,分析比较了江西Sb2O3、南宁Sb2O3和大连Sb(Ac)3三种缩聚催化剂对聚酯切片质量的影响。试验结果表明,Sb(Ac)3是优良的缩聚催化剂。 相似文献
82.
Qin‐Tao Liu Malcolm R Clench Judith L Kinderlerer 《Journal of the science of food and agriculture》2002,82(5):553-558
Structural isomers of monoacylglycerols (monoglycerides, MAGs) were identified and compared after degradation of butter oil by two strains of Penicillium roquefortii and a commercial lipase from P roquefortii (EC 3.1.1.3) at pH 7.0 and 10 °C. The conditions were selected as they were comparable with those used in the manufacture of blue mould‐ripened cheese. The commercial lipase was selected to compare with the fungal strains in terms of acyl migration. Results showed that the main isomers formed by lipolysis with the commercial lipase were sn‐2 MAGs (64 mol%), whilst spores and emerging mycelia of P roquefortii produced mainly sn‐1(3) MAGs (83–90 mol%). The work reported here may lead to further assessment of different MAG structural isomers as natural preservatives in foods and dairy products. © 2002 Society of Chemical Industry 相似文献
83.
The reduction of calcium sulfate to produce calcium sulfide is a part of the cyclic process for converting sulfur dioxide
to elemental sulfur that is described in Part I. The kinetics of the hydrogen reduction of nickel-catalyzed calcium-sulfate
pellets were investigated using a thermogravimetric analysis (TGA) technique at reaction temperatures between 1023 and 1088
K and hydrogen partial pressures between 12.9 and 86.1 kPa. The reactivity of nickel-catalyzed calcium-sulfate pellets was
demonstrated by the conversion of 70 pct fresh nickel-catalyzed calcium sulfate to calcium sulfide in 20 minutes at 1073 K
under a hydrogen partial pressure of 86.1 kPa. Furthermore, the reactivity remained relatively intact after ten cycles of
reactions and regenerations. This observed characteristic of the pellets is important because the solids must be reusable
for repeated cycles to avoid generating secondary pollutants. The nucleation and growth rate expression was found to be useful
in describing the kinetics of the reaction, which had an activation energy of about 167 kJ/mol (∼40 kcal/mol) in all reaction
cycles except for the first regenerated samples that were lower at 146 kJ/mol (35 kcal/mol). The reaction order with respect
to hydrogen partial pressure was 0.22 in all cycles with the exception of the first regenerated sample for which it was 0.37. 相似文献
84.
A kind of complex additive mainly containing Al, Mg, F, and O was prepared. The synthetical performances of the property-modified prebaked anodes containing additives were tested in laboratory. On the basis of ideal testing results obtained, a large number of industrial prebaked property-modified anodes are prepared in a large-scale aluminum company. Further more, they are all used in 160 kA prebaked anode aluminum electrolysis cells. The statistic result show that, compared with common anodes, the property-modified ones enhance current by 11.6 kg per ton aluminum averagely. 相似文献
85.
Analysis on the effectiveness of the 20-H rule for printed-circuit-board layout to reduce edge-radiated coupling 总被引:1,自引:0,他引:1
Montrose M.I. Er-Ping Li Hong-Fang Jin Wei-Liang Yuan 《Electromagnetic Compatibility, IEEE Transactions on》2005,47(2):227-233
This paper presents the quantified study of the electromagnetic radiation mechanism of the 20-H rule using a numerical approach that has not yet been systematically addressed. The 20-H rule is a rule-of-thumb layout technique recommended to minimize radiated fields propagating from the edges of a printed circuit board (PCB) coupling onto nearby structures. Propagating electromagnetic fields may corrupt adjacent cable assemblies, sheet metal enclosures, and aperture openings. The magnitude of this design rule is investigated using the full-wave finite-difference time-domain (FDTD) method. An analysis on whether benefits exist from use of this rule is examined and under what conditions the rule is valid when correctly implemented. The purpose of this paper is to provide insight into the validity of the 20-H rule, recognizing that every PCB will have different simulation results. FDTD is used to capture a snapshot view of field propagation. This view allows one to determine the validity of the 20-H rule at a single point of time within a dynamic structure and what may be expected when digital components are finally added to a PCB assembly, which generally negates simulated results. 相似文献
86.
Hong Wang Rong Zeng Xiuping Li 《Microwave Theory and Techniques》2005,53(2):564-570
In this paper, RF noise in 0.18-mum NMOSFETs concerning the contribution of carrier heating and hot carrier effect is characterized and analyzed in detail via a novel approach that modulates the channel carrier heating and number of hot carriers using body bias. We confirm qualitatively a negligible role of hot carrier effect on the channel noise in deep-submicrometer MOSFETs. For a device under reverse body bias (Vb), even though the increase in hot carrier population is clearly characterized by dc measurements, the device high-frequency noise is found to be irrelevant to the increase in the channel hot carriers. Experimental results show that the high-frequency noise is slightly reduced with the increase in |Vb|, and can be qualitatively explained by secondary effects such as the suppression of nonequilibrium channel noise and substrate induced noise. The reduction of NFmin and Rn with the increase in |Vb| may provide a possible methodology to finely adjust the device high-frequency noise performance for circuit design 相似文献
87.
88.
Yu‐Qing Cao Zhan Zhang Yan‐Xin Guo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1441-1444
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry 相似文献
89.
The cooling and solidification of melted drops during their movement in an immiscible cooling medium is widely employed for granulation in the chemical industry, and a study of these processes to provides a basis for the design of the granulation tower height and the temperature of the cooling medium is reported. A physical model of the cooling and solidification of the drop is established and the numerical calculation is performed. The influences of the key factors in the solidification, i.e., Bi number, drop diameter, temperature of the cooling medium, etc. are presented. The cooling and solidification during wax granulation in a water‐cooling tower and during urea granulation in an air‐cooling tower (spraying tower) are described in detail. Characteristics of the solidification and temperature distribution within the particle at different times are shown. The model and calculations can be used for structure design of the granulation tower and optimization of the operation parameters. 相似文献
90.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献