全文获取类型
收费全文 | 58747篇 |
免费 | 2938篇 |
国内免费 | 200篇 |
专业分类
电工技术 | 888篇 |
综合类 | 94篇 |
化学工业 | 11360篇 |
金属工艺 | 2153篇 |
机械仪表 | 3271篇 |
建筑科学 | 1286篇 |
矿业工程 | 54篇 |
能源动力 | 2285篇 |
轻工业 | 4258篇 |
水利工程 | 258篇 |
石油天然气 | 212篇 |
武器工业 | 1篇 |
无线电 | 10366篇 |
一般工业技术 | 11769篇 |
冶金工业 | 5878篇 |
原子能技术 | 661篇 |
自动化技术 | 7091篇 |
出版年
2023年 | 524篇 |
2022年 | 677篇 |
2021年 | 1467篇 |
2020年 | 1054篇 |
2019年 | 1106篇 |
2018年 | 1409篇 |
2017年 | 1414篇 |
2016年 | 1743篇 |
2015年 | 1399篇 |
2014年 | 2155篇 |
2013年 | 3668篇 |
2012年 | 3399篇 |
2011年 | 4153篇 |
2010年 | 3129篇 |
2009年 | 3304篇 |
2008年 | 3063篇 |
2007年 | 2559篇 |
2006年 | 2343篇 |
2005年 | 2029篇 |
2004年 | 1931篇 |
2003年 | 1786篇 |
2002年 | 1711篇 |
2001年 | 1338篇 |
2000年 | 1235篇 |
1999年 | 1225篇 |
1998年 | 2235篇 |
1997年 | 1463篇 |
1996年 | 1225篇 |
1995年 | 977篇 |
1994年 | 737篇 |
1993年 | 696篇 |
1992年 | 502篇 |
1991年 | 501篇 |
1990年 | 427篇 |
1989年 | 414篇 |
1988年 | 329篇 |
1987年 | 284篇 |
1986年 | 258篇 |
1985年 | 237篇 |
1984年 | 202篇 |
1983年 | 155篇 |
1982年 | 152篇 |
1981年 | 131篇 |
1980年 | 128篇 |
1979年 | 102篇 |
1978年 | 94篇 |
1977年 | 123篇 |
1976年 | 160篇 |
1975年 | 80篇 |
1974年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
941.
Zhen-Xue Liu Jung-Nam Park S. H. R. Abdi Seung-Kyu Park Yong-Ki Park Chul Wee Lee 《Topics in Catalysis》2006,39(3-4):221-226
In this paper, the ethylene adsorption capacities of the nano-sized carbon hollow spheres (CNB) and active carbon (AC), the
Pd (PdCl2) impregnated CNB or AC (Pd/CNB, Pd/AC) and heat treatment under various conditions, were studied at different ethylene concentrations
from 64 to 1060 ppm. The results indicated that AC had a good ethylene adsorption capacity at high ethylene concentration.
Pd impregnation decreased the ethylene adsorption capacity of AC. Heat treatment and H2 activation could increase the ethylene adsorption capacity, but also lowered than AC itself. CNB had lower ethylene adsorption
capacity than AC, but heat treatment and H2 activation could increase its ethylene adsorption capacity markedly. With activating condition from heat treatment in N2 at 300 °C to activation in H2/N2 at 100 °C, to activation in H2 at 200 °C, and to activation in H2 at 300 °C, the ethylene adsorption capacity of Pd/CNB was increased regularly. At low ethylene concentration, viz., 64 ppm,
the ethylene adsorption quantities (q
a) by Pd/CNB activated in H2 at 200 or 300 °C were higher than any other adsorbents. So, activated in H2 atmosphere at higher than 100 °C, Pd/CNB is particularly advantaged for adsorbing low concentration of ethylene. Amongst
all the adsorbents used, Pd/CNB activated in H2 atmosphere at 300 °C for 2 h has the highest ethylene adsorption capacity at lower concentration than 125 ppm. In addition,
all the CNB, Pd/CNB, AC, and Pd/AC samples can be easily regenerated in airflow for more than 3 h. 相似文献
942.
Mun-Soo Yun Ki-Young Jeong Eui-Wan Lee Bong-Soo Jin Seong-In Moon Chil-Hoon Doh 《Korean Journal of Chemical Engineering》2006,23(2):230-236
The aim of this paper is to study the electrochemical behavior of Si-C material synthesized by heating a mixture of silicon
and polyvinylidene fluoride (PVDF) in the ratios of 5, 20, and 50 wt%. The particle size of the synthesized material was found
to be increased with increase in the PVDF ratio. The coexistence of silicon with carbon was confirmed from the XRD analysis.
A field emission scanning electron microscope (FESEM) study performed with the material proved the improvement in coating
efficiency with increase in the PVDF ratio. Coin cells of the type 2025 were made by using the synthesized material, and the
electrochemical properties were studied. An electrode was prepared by using the developed Si-C material. Si-C|Li cells were
made with this electrode. A charge|discharge test was performed for 20 cycles at 0.1 C hour rate. Initial charge and discharge
capacities of Si-C material derived from 20 wt% of PVDF was found to be 1,830 and 526 mAh|g, respectively. Initial charge/discharge
characteristics of the electrode were analyzed. The level of reversible specific capacity was about 216mAh/g at Si-C material
derived from 20 wt% of PVDF, initial intercalation efficiency (IIE), intercalation efficiency at initial charge/discharge,
was 68%. Surface irreversible specific capacity was 31 mAh/g, and average specific resistance was 2.6 ohm * g. 相似文献
943.
Joon‐Seop Kim Min‐Chul Hong Yeon Hwa Nah Yeonhee Lee Seunghee Han Hyun Eui Lim 《应用聚合物科学杂志》2002,83(11):2500-2504
The wetting properties of polystyrene‐based ionomers treated with plasma source ion implantation (PSII) were investigated by the measurement of water contact angles. When sulfonated ionomers were aged for a few days, the hydrophobic recovery for the ionomers became much slower than that for the nonionic polymers. However, when the samples were aged over 20 days, the water contact angle of the ionomers converged with that of the nonionic polymer. Thus, it was concluded that the ionic interaction between the ionic groups and the presence of ionic groups together resulted in the slow hydrophobic recovery and that the aging effect was significant for the ionomers. For the methacrylate ionomer of low ion content, on the other hand, it was found that the PSII treatment produced only a small change in hydrophobic recovery behavior. Thus, it was suggested that the low ionic content coupled with the small size of the ionic unit might cause changes only of a very insignificant degree in hydrophobic recovery behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2500–2504, 2002 相似文献
944.
Chlorinated poly(vinyl chloride) (CPVC)/poly(vinyl pyrrolidone) (PVP) membranes were prepared by using the solvent system tetrahydrofuran (THF)/n‐butyl alcohol (n‐BA) to investigate the possibility of pore size and pore‐size distribution control. The coagulation of CPVC/PVP solution was induced by the exposure to water vapor at 25 (±0.5)°C. The average pore diameter, dp, and the size distribution of pores on the surface of the membrane were quantified through the image analyzer from the images visualized by field emission scanning electron microscope (FE‐SEM). Surface pore size and distribution of the prepared CPVC/PVP membrane were strongly affected by the relative humidity (RH) in the environment and the content of PVP used as an additive. Particularly, in the case of CPVC membrane without PVP, the mean pore size was 0.15–0.2 μm, depending on the RH. The pore distribution became broad with the increase of the RH. The membranes had open pores as confirmed by the hydraulic permeation experiment. In addition, the water flux and membrane resistance (Rm) were greatly affected by the composition of polymer solution and the RH. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1195–1202, 2002 相似文献
945.
The utilization of waste glass in concrete can cause cracking and weakening due to expansion by alkali-silica reaction (ASR). In this study, ASR expansion and properties of strength were analyzed in terms of waste glass content, glass color (brown, green), fibers (steel fiber, polypropylene fiber) and fiber content, in anticipation of reducing ASR expansion.Results showed that green waste glass was more usable than brown because its expansion was less than that of brown glass. Using the accelerated ASTM C 1260 test of waste glass, no pessimum content was found. Furthermore, when fibers and waste glass were combined, there was an effect on the reduction of expansion and strength loss due to ASR between the alkali in the cement paste and the silica in the waste glass. In particular, adding 1.5 vol.% of steel fiber to concrete containing 20% waste glass reduced the expansion ratio by 40% and increased flexural strength by up to 110%, a vast improvement when compared with using only waste glass (80 °C H2O curing) by itself. 相似文献
946.
Yong K. Park Ho K. Lee Nong M. Hwang Houk C. Kwon Jong C. Park Duk N. Yoon 《Journal of the American Ceramic Society》1988,71(6):297-C
Microstructures of Y-Ba-Cu-O superconductor were observed using a polarized microscope. Orthorhombic and tetragonal phases were easily distinguished by the optical etching with cross-polarized light. In the specimen cooled rapidly in oxygen, it was possible to see the path of oxygen diffusion by observing the variation of the twin concentration. At the boundary between transformed and untransformed materials, evidence for diffusion-driven transformation could be clearly seen. 相似文献
947.
Highly Efficient Overall Water Splitting Through Optimization of Preparation and Operation Conditions of Layered Perovskite Photocatalysts 总被引:1,自引:0,他引:1
Jindo Kim Dong Won Hwang Hyun Gyu Kim Sang Won Bae Jae Sung Lee Wei Li Se Hyuk Oh 《Topics in Catalysis》2005,35(3-4):295-303
The layered perovskite materials were found to give the high photocatalytic activity in water splitting reaction under UV
irradiation, where the electronic structure of perovskite slab constructing the layered structure (the total cation valency)
was the most crucial factor to the high photocatalytic activity. Both the excessive cation valency and the layered structure
were required for active photocatalysts, while the slab thickness of layered perovskites had an insignificant effect on water-splitting
activity. In order to identify key variables that affected photocatalytic activity and to optimize the performance of (110)
layered perovskite, La2Ti2O7 was modified by various methods. The optimum amount of loaded nickel had a great effect and the amount depended on the surface
area of the perovskite phase. When an alkaline-earth element such as Ba, Sr, and Ca was doped on La2Ti2O7, the photocatalytic activity was enhanced markedly. Introduction of an alkaline hydroxide into the reaction system as an
external additive enhanced the activity further showing extremely high quantum yields close to 50%. 相似文献
948.
Jae-Keun Lee Hee-Soo Shin Chan-Jung Park Chang-Geon Lee Jung-Eun Lee Young-Whan Kim 《Korean Journal of Chemical Engineering》2002,19(1):41-45
A laboratory-scale electrodewatering system, incorporating an electric field as an additional driving force to conventional
pressure dewatering, has been developed to decrease the water content of sludges generated in wastewater treatment. Consisting
of a piston-type filter press, a power supply and a data acquisition system, the electrodewatering system’s performance was
evaluated as a function of applied pressure, applied voltage, sludge type and filtration time. Experiments were carried out
using sewage sludges with the electric field up to 120 V/cm and pressure ranging from 98.1 to 392.4 kPa. Electrodewatering
involving a combination of electric field and pressure enhances both the dewatering rate and final dewatered volume. The final
water content of sewage sludges in the electrodewatering system can be reduced to 62 wt%, as compared to 78 wt% achieved with
the pressure filtration alone. The electrodewatering system shows the potential to be an effective method for reducing the
water content in sludges. 相似文献
949.
Towards an Environmentally Acceptable Heterogeneous Catalytic Method of Producing Adipic Acid by the Oxidation of Hydrocarbons in Air 总被引:1,自引:0,他引:1
Raja Robert Lee Sang-Ok Sanchez-Sanchez Manuel Sankar Gopinathan Harris Kenneth D.M. Johnson Brian F.G. Thomas John Meurig 《Topics in Catalysis》2002,20(1-4):85-88
A survey is given of the catalytic methods potentially available for the production of adipic acid by the oxidation of readily available hydrocarbon precursors under environmentally benign conditions. Encouraging results are reported using H2O2 as oxidant and microporous FeAlPO-5 as catalyst at moderate temperatures. 相似文献
950.
Poly(amide imide)–epoxysilane (coupling agent) composites were reacted with silica, a condensation product of tetraethylorthosilicate (TEOS), by a sol–gel process and were then cast into films. After this procedure, the chemical characteristics and mechanical and thermal properties were measured. Fourier transform infrared showed that silica existed in the poly(amide imide) matrix. When a proper amount of silica was added to the poly(amide imide) matrix, the tensile strength, elongation, and toughness increased greatly. A poly(amide imide)/30 wt % epoxysilane composite with 20 wt % TEOS had the best mechanical properties. Thermogravimetric analysis under nitrogen and oxygen atmospheres indicated that the char contents increased with the amount of silica. The glass‐transition temperatures of the poly(amide imide)–silica nanocomposites were observed around 170–180°C with differential scanning calorimetry. This approach may be a new method for the low‐temperature thermal curing of poly(amide imide). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1780–1788, 2004 相似文献