全文获取类型
收费全文 | 2211篇 |
免费 | 8篇 |
国内免费 | 19篇 |
专业分类
电工技术 | 24篇 |
综合类 | 7篇 |
化学工业 | 436篇 |
金属工艺 | 11篇 |
机械仪表 | 17篇 |
建筑科学 | 6篇 |
矿业工程 | 2篇 |
能源动力 | 1429篇 |
轻工业 | 14篇 |
石油天然气 | 1篇 |
武器工业 | 1篇 |
无线电 | 29篇 |
一般工业技术 | 80篇 |
冶金工业 | 4篇 |
原子能技术 | 142篇 |
自动化技术 | 35篇 |
出版年
2023年 | 78篇 |
2022年 | 122篇 |
2021年 | 130篇 |
2020年 | 123篇 |
2019年 | 81篇 |
2018年 | 62篇 |
2017年 | 60篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 122篇 |
2013年 | 104篇 |
2012年 | 129篇 |
2011年 | 258篇 |
2010年 | 217篇 |
2009年 | 153篇 |
2008年 | 138篇 |
2007年 | 140篇 |
2006年 | 58篇 |
2005年 | 43篇 |
2004年 | 27篇 |
2003年 | 25篇 |
2002年 | 26篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 16篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有2238条查询结果,搜索用时 15 毫秒
81.
The cross-linkable sulfonated ploy(arylene ether)s derived from 3,3′-diallyl-4,4′-dihydroxybiphenyl, bisphthalazinone, 4,4′-difluorobenzophenone (DFBP) and sulfonated 4,4′-diflourobenzophenone (SDFBP) were synthesized over a wide range of DFBP/SDFBP molar ratios. The resulting sulfonated poly(arylene ether)s with high inherent viscosity (1.02–1.29 dL g−1) are soluble in polar organic solvents and can form flexible and transparent membranes by casting from their solution. Cross-linking reaction was carried out using the thermal activated radical cross-linking agent (TARC) at 140 °C. The comprehensive properties of the virgin and the cross-linked membranes were compared accordingly. The results showed that the cross-linked membranes revealed the better mechanical, oxidative and dimensional stabilities together with high proton conductivity (9.675 × 10−3 S cm−1) at 25 °C under 100% relative humidity. 相似文献
82.
A self-humidifying membrane based on sulfonated poly(ether ether ketone) (SPEEK) hybrid with sulfated zirconia (SO42−/ZrO2, SZ) supported platinum catalyst (Pt-SZ catalyst) was synthesized for fuel cell applications. The SZ, a solid state superacid with hygroscopic properties and proton-conductive properties, was employed to synthesize the Pt-SZ catalyst. The self-humidifying membrane (SPEEK/Pt-SZ) was characterized by TEM, FT-IR, TGA and SEM coupled with EDX. The SPEEK/Pt-SZ membrane exhibited higher water uptake and proton conductivity than the plain SPEEK membrane. Consequently, the SPEEK/Pt-SZ self-humidifying membrane under dry operation showed a higher open circuit voltage (OCV) of 1.015 V and a maximum power density of 0.95 W cm−2, relative to 0.96 V and 0.54 W cm−2 for the plain SPEEK membrane. The incorporation of the catalytic, hygroscopic and proton-conductive Pt-SZ catalyst in the SPEEK matrix facilitated water balance and proton conduction, accordingly improved the single cell performance under dry operation. In addition, the enhanced OCV and the decreased area ohmic resistance confirmed the effect of Pt-SZ catalyst in the self-humidifying membrane on suppressing reactant crossover and the membrane self-humidification. 相似文献
83.
Metallic bipolar plates look promising for the replacement of graphite due to higher mechanical strength, better durability to shocks and vibration, no gas permeability, acceptable material cost and superior applicability to mass production. However, the corrosion and passivation of metals in environments of proton exchange membrane fuel cell (PEMFC) cause considerable power degradation. Great attempts were conducted to improve the corrosion resistance of metals while keeping low contact resistance. In this paper, a simple, novel and cost-effective high-energy micro-arc alloying process was employed to prepare compact titanium carbide as coatings for the type 304 stainless steel bipolar plates with a metallurgical bonding between the coating and substrate. It was found that TiC coating increased the corrosion potential of the bare steel in 1 M H2SO4 solution at room temperature by more than 200 mV, and decreased significantly its corrosion current density from 8.3 μA cm−2 for the bare steel to 0.034 μA cm−2 for the TiC-coated steel. No obvious degradation was observed for the TiC coatings after 30-day exposure in solution. 相似文献
84.
Lixin YouHongtan Liu 《International Journal of Heat and Mass Transfer》2002,45(11):2277-2287
A unified two-phase flow mixture model has been developed to describe the flow and transport in the cathode for PEM fuel cells. The boundary condition at the gas diffuser/catalyst layer interface couples the flow, transport, electrical potential and current density in the anode, cathode catalyst layer and membrane. Fuel cell performance predicted by this model is compared with experimental results and reasonable agreements are achieved. Typical two-phase flow distributions in the cathode gas diffuser and gas channel are presented. The main parameters influencing water transport across the membrane are also discussed. By studying the influences of water and thermal management on two-phase flow, it is found that two-phase flow characteristics in the cathode depend on the current density, operating temperature, and cathode and anode humidification temperatures. 相似文献
85.
Junhyun Cho Hwanyeong Oh Jaeman Park Kyoungdoug Min Eunsook Lee Jy-Young Jyoung 《International Journal of Hydrogen Energy》2014
The mass transport characteristics of a gas diffusion layer (GDL) predominantly affect the performance of a proton exchange membrane (PEM) fuel cell. However, studies examining the transient response related to the GDL are insufficient, although the dynamic behavior of a PEM fuel cell is an important issue. In this study, the effects of the design of a micro porous layer (MPL) on the transient response of a PEM fuel cell are investigated. The MPL slurry density and multiple functional layers are treated as the variable design parameter. The results show that the transient response is determined by the capillary pressure gradient through the GDL. The trade-off relation for the PEM fuel cell performance under low and high humidity conditions due to the hydrophobic GDL is mitigated by designing a reverse capillary pressure gradient in the MPL. 相似文献
86.
V. Senthil Velan G. VelayuthamN. Rajalakshmi K.S. Dhathathreyan 《International Journal of Hydrogen Energy》2014
Gas diffusion layer (GDL) is subjected to compressive stress at high temperature along with polymer electrolyte membrane in the fabrication process and in assembling the fuel cell stacks. Compressive stress decreases the thickness of GDL, electrical conductivity, permeability, and affects the pores. Carbon cloth based GDL withstands higher strain level when compared to carbon paper and the pore structure is also disrupted to a greater extent in cloth based GDL. In the present paper, we have addressed the effects of stress on pore structure of cloth based GDL. An optimum GDL must offer low mass transport resistance in an operating PEM fuel cell. The pore size analysis of pristine GDL and GDLs pressed at different pressure levels (200, 600 & 1000 kg cm−2) and their characteristics are evaluated using capillary flow porometry. The compressive stress affects the three types of pores in GDL called bubble point pore, mean flow pore and smallest pore. The change in electrical resistance, wetting behavior and surface morphology is also examined as a function of compressive stress. The fuel cell performances using these GDLs pressed at different compressive stresses are also evaluated and presented. The highest PEMFC performance is achieved at a compressive stress of 200 kg cm−2, which could be attributed to the combined effect of reduced ohmic resistance and optimized pore structure. The order of increasing performance in terms of current density is observed to be j200 > jPristine > j600 > j1000 at 0.15 V. The thicknesses and pore sizes of custom made GDL for optimum fuel cell performance are recommended. 相似文献
87.
A carbon fiber composite gasketless bipolar plate for proton exchange membrane (PEM) fuel cells was developed using the groove of a trapezoidal shape, which develops large contact stresses due to a wedge mechanism. The surface of the composite groove was modified to increase gas tightness without using rubber gaskets. Graphite, polyimide (PI) and polyethylene terephthalate (PET) film were co-cure bonded on the surface of the bipolar plate during the compression molding process to change its surface hardness, which could affect the gas tightness. Additionally, plasma surface treatment and mechanical abrasion were used to modify the surface morphologies. Corrosion and gas tightness tests on the surface modified bipolar plates were performed to verify the reliability of the gasketless sealing method. 相似文献
88.
Electrochromic devices incorporating an electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT) film and a free standing, transparent film of a proton conducting polymer electrolyte with high ambient temperature ionic conductivity of 10−2 S cm−1 have been fabricated with and without the ion storage electrodeposited Prussian blue (PB) counter electrode layer. While coloration efficiency increases as a function of applied potential in the sole PEDOT device with largest values of CE(max,VIS) ∼ 120 cm2 C−1 and CE(max,NIR) ∼ 133 cm2 C−1 attained at Vc = −1.9 V, the PEDOT:PB device shows a digression from this trend. Much higher coloration efficiencies in the visible (247 cm2 C−1 at 570 nm) and NIR (116 cm2 C−1 at 1100 nm) regions are achieved for the PEDOT:PB device at a relatively lower reducing voltage of −0.8 V. The PEDOT:PB device shows fast switching redox process (tc = 2.6 s and tb = 1.3 s for a 50% optical contrast at 632.8 nm) and a highly reversible charge density as the ratio of Qinserted to Qextracted was found to vary between 0.8 and 1.0. When switched between the clear and blue states for 2000 cycles, the insignificant drop in peak current density maxima observed for the PEDOT:PB device, i.e. the good cycling stability, the facile fabrication of device assembly, the ease of scaling up the electrolyte and electrochromic coatings, indicate that this method can be adapted as a simple and inexpensive alternative to conventional electrochromic windows with high cost components. 相似文献
89.
Lili Sun Suli Wang Wei Jin Hongying Hou Luhua Jiang Gongquan Sun 《International Journal of Hydrogen Energy》2010
In this paper, Fe2O3–SO42−/Nafion® composite membranes were prepared by a solution casting method. The physico-chemical properties of composite membranes were characterized by X-ray diffraction (XRD), SEM–EDX and thermogravimetric analysis (TGA). The water uptake ability, proton conductivity, and methanol permeability of the composite membranes were evaluated and compared with the recast Nafion® membrane. The results showed that the proton conductivity and the water uptake of the composite membranes were slightly higher than that of the recast Nafion® membrane. The composite membrane containing 5 wt.% Fe2O3–SO42- showed superior ability to suppress methanol crossover, and it further improved the direct methanol fuel cell (DMFC) performances with both 1 M and 5 M methanol feeding, compared with the recast Nafion® membrane. The preliminary 30 h lifetime test of the DMFC with the composite membrane with 5% Fe2O3–SO42− indicated that the composite membrane is stable working at the real DMFC operating conditions at least during the test. These results suggest the applicability of the composite membranes in DMFCs. 相似文献
90.
F. Trknyi A. Hermanne S. Takcs F. Ditri B. Kirly H. Yamazaki M. Baba A. Mohammadi A.V. Ignatyuk 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(17):2802-2807
Activation cross sections of the natYb(p,xn)169Lu reaction have been measured for the first time up to 70 MeV to investigate the production possibility of the radionuclide 169Yb through decay of its parent 169Lu. The cross sections were measured using the stacked foil irradiation technique and gamma spectrometry. The experimental data were compared with the results of the ALICE-IPPE theoretical model code. Different production routes were compared for the internal radiotherapy related radioisotope 169Yb. Above 30 MeV proton energy the integral yield of the natYb(p,xn)169Lu reaction is higher than that of the earlier investigated 169Tm(p,n)169Yb, 169Tm(d,2n)169Yb, natEr(α,xn)169Yb, natYb(α,x)169Lu and natHf(p,x)169Lu reactions at the equivalent particle energies. 相似文献