全文获取类型
收费全文 | 16448篇 |
免费 | 1238篇 |
国内免费 | 728篇 |
专业分类
电工技术 | 1498篇 |
综合类 | 1020篇 |
化学工业 | 4120篇 |
金属工艺 | 1639篇 |
机械仪表 | 847篇 |
建筑科学 | 878篇 |
矿业工程 | 484篇 |
能源动力 | 1384篇 |
轻工业 | 1716篇 |
水利工程 | 344篇 |
石油天然气 | 403篇 |
武器工业 | 53篇 |
无线电 | 882篇 |
一般工业技术 | 1482篇 |
冶金工业 | 994篇 |
原子能技术 | 142篇 |
自动化技术 | 528篇 |
出版年
2024年 | 61篇 |
2023年 | 228篇 |
2022年 | 372篇 |
2021年 | 495篇 |
2020年 | 527篇 |
2019年 | 464篇 |
2018年 | 393篇 |
2017年 | 526篇 |
2016年 | 532篇 |
2015年 | 511篇 |
2014年 | 867篇 |
2013年 | 903篇 |
2012年 | 1018篇 |
2011年 | 1314篇 |
2010年 | 982篇 |
2009年 | 998篇 |
2008年 | 862篇 |
2007年 | 1165篇 |
2006年 | 1035篇 |
2005年 | 836篇 |
2004年 | 704篇 |
2003年 | 609篇 |
2002年 | 543篇 |
2001年 | 459篇 |
2000年 | 381篇 |
1999年 | 305篇 |
1998年 | 255篇 |
1997年 | 198篇 |
1996年 | 154篇 |
1995年 | 149篇 |
1994年 | 145篇 |
1993年 | 96篇 |
1992年 | 73篇 |
1991年 | 55篇 |
1990年 | 42篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 11篇 |
1983年 | 12篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1964年 | 1篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Hajime Arai Masayuki Tsuda Masahiko Hayashi Hideaki Ohtsuka Yoji Sakurai 《Electrochimica acta》2005,50(9):1821-1828
Several polymorphs of layered nickel dioxide were prepared by using the chemical insertion of alkaline ions into Li0.10NiO2. We used aqueous AOH (A = Li, Na, K) solutions as reducing agents. Sodium and potassium insertion resulted in hydrated layered compounds that can be classified as γ-NiOOH with high crystallinity, while lithium insertion occurred without hydration. We discuss the coordination environment around the A+ ions for these inserted compounds. The thermal behavior, analyzed using high temperature (HT) X-ray diffraction (XRD) and thermogravimetric (TG) measurements, indicated that heating the hydrate at 150 °C yielded its dehydrate. The electrode performance of the nickelate was studied in lithium cells. We discuss the effect of interlayer water on cell rechargeability and the similarity between these nickelate and hydrated manganese dioxide (birnessite). 相似文献
102.
Crystallization of palm oil with and without solvent was carried out over a temperature range of 10–25°C. The yields of olein,
the diglyceride contents, and compositions of the stearin and olein phases were determined by thin-layer and gas-liquid chromatography.
The three major diglycerides, analyzed as C32, C34, and C36, are mainly dipalmitoyl glycerol, palmitoyloleoyl glycerol, and dioleoyl glycerol. In crystallization without solvent, C32 (PP) had a strong affinity for the stearin fraction and C36 diglycerides concentrated in the olein phase. The partition coefficient of diglycerides between the olein and stearin phases
was temperature-dependent and was influenced by the type of solvent used. Although solvent enhances the diglyceride partition
into the olein phase, partitioning is more effective at low temperatures and with acetone as the solvent for fractionation. 相似文献
103.
The membrane electrode assembly (MEA) studied was constituted with a gas diffusion electrode (E-TEK) impregnated with Nafion® solution which was assembled with a Nafion® 117 cation exchange membrane under heat and pressure. The MEA was used as anode in a membrane electrolysis (ME) cell with the objective to regenerate HCl and NaOH from NaCl. Current efficiency for hydrogen oxidation was determined and its value is 100%, which indicates that the only reaction occurring at the anode is the oxidation of hydrogen. Current-potential curves, recorded in different conditions, showed a linear variation in the range 0-3000 A m−2 when hydrochloric acid concentration is below 2 mol dm−3. In this case, the overvoltage was shown to be mainly due to the ohmic drop in the membrane and in the layer where Nafion® impregnation was performed. MEA overvoltage necessary to reach 3000 A m−2 current density was about 0.12 V. For high HCl concentration (6-8 mol dm−3), the MEA overvoltage increased sharply with current density due to the adsorption of chloride anions on platinum catalyst. 相似文献
104.
We present a simple glue method for fabricating membrane electrode assemblies (MEA) for direct methanol fuel cells (DMFC). Rather than the conventional “dry” hot-pressing method that relies solely on hot-pressing at a high pressure and temperature to form a MEA, the “wet” method developed in this work introduces a binding agent, consisting of Nafion® solution, between a polymer electrolyte membrane (PEM) and an anode/cathode. The introduced binding agent can provide a better adhesion and stronger binding force between a membrane and an electrode, thereby facilitating a better interfacial contact between the electrode and the Nafion® membrane, which has been proved by scanning electron microscopy (SEM) analyses to the cross-sectional morphology of the MEA after long-term operation. The cell performance characterization showed the MEA fabricated by the glue method was more stable in cell performance than that fabricated by the conventional hot-pressing method. Cyclic voltammetry (CV) results also demonstrated the MEA fabricated by the glue method exhibited a higher electrochemical surface area (ESA) as a result of the improved interfacial contact between the Nafion® membrane and the electrodes. Finally, the DMFC with the MEA fabricated by the glue method was characterized by the electrochemical impedance spectroscopy (EIS). 相似文献
105.
In the paper, the characters and fields were introduced for utilizing the Series/Parallel Switch (SPS). The circuit principle of the SPS technology was analyzed in detailed, explained and illuminated. We understood clearly the difference between SPS and single-phase transformator by the figure and table. Finally, it summarized that the main characters of SPS. 相似文献
106.
In this study, multi-wall carbon nanotubes (MWCTs) is evaluated as a transducer, stabilizer and immobilization matrix for the construction of amperometric sensor based on iron-porphyrin. 5,10,15,20-Tetraphenyl-21H,23H-porphine iron(III) chloride (Fe(III)P) adsorbed on MWCNTs immobilized on the surface of glassy carbon electrode. Cyclic voltammograms of the Fe(III)P-incorporated-MWCNTs indicate a pair of well-defined and nearly reversible redox couple with surface confined characteristics at wide pH range (2-12). The surface coverage (Γ) and charge transfer rate constant (ks) of Fe(III)P immobilized on MWCNTs were 7.68 × 10−9 mol cm−2 and 1.8 s−1, respectively, indicating high loading ability of MWCNTs for Fe(III)P and great facilitation of the electron transfer between Fe(III)P and carbon nanotubes immobilized on the electrode surface. Modified electrodes exhibit excellent electrocatalytic activity toward reduction of ClO3−, IO3− and BrO3− in acidic solutions. The catalytic rate constants for catalytic reduction of bromate, chlorate and iodate were 6.8 × 103, 7.4 × 103 and 4.8 × 102 M−1 s−1, respectively. The hydrodynamic amperometry of rotating-modified electrode at constant potential versus reference electrode was used for detection of bromate, chlorate and iodate. The detection limit, linear calibration range and sensitivity for chlorate, bromate and iodate detections were 0.5 μM, 2 μM to 1 mM, 8.4 nA/μM, 0.6 μM, 2 μM to 0.15 mM, 11 nA/μM, and 2.5 μM, 10 μM to 4 mM and 1.5 nA/μM, respectively. Excellent electrochemical reversibility of the redox couple, good reproducibility, high stability, low detection limit, long life time, fast amperometric response time, wide linear concentration range, technical simplicity and possibility of rapid preparation are great advantages of this sensor. The obtained results show promising practical application of the Fe(III)P-MWCNTs-modified electrode as an amperometric sensor for chlorate, iodate and bromate detections. 相似文献
107.
串联式干气密封在液态烃泵上的应用 总被引:4,自引:0,他引:4
从理论上对干气密封的作用机理及影响干气密封性能的主要参数进行了研究。对液态烃泵用串联式干气密封的结构进行优化,设计制造出了适合轻烃类介质的串联式干气密封及控制系统,工业运行获得成功,极大地提高了液态烃泵的性能及可靠性。 相似文献
108.
Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy.
The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique
on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried
out in aqueous electrolyte solutions of 0.5 M Na2
SO
4 + 5 mM K3[Fe(CN)6]/K4[Fe(CN)6]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials
in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk
conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation
dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge
transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond
surface was obtained by SECM measurements. 相似文献
109.
The catalysts of air electrode were prepared by sintering the active carbon loaded with manganese nitrate and potassium permanganate
at 360 °C The air electrode was made up of a catalyst layer, a waterproof and gas-permeable layer, a current collecting substrate
and a second waterproof and gas-permeable layer. The cell was assembled by the air electrode, pure magnesium anode and 10%
NaCl solution used as electrolyte. The microstructures of air electrodes before and after discharging were characterized by
SEM. The electrochemical behaviors of the air electrodes were determined by means of polarization curves, volt-ampere curves
and constant current discharge curves. The polarization voltage of air electrode is—173 mV (vs SCE) at the current density of 50 mA/cm2. The air electrodes exhibits good activity and stability in neutral electrolyte. The magnesium-air cell could work at 5 W
for more than 7 h. 相似文献
110.
Surface performance of workpieces processed by electrical discharge machining in gas 总被引:1,自引:0,他引:1
The surface performance of workpieces processed by electrical discharge machining in gas(dry EDM)was studied in this paper.Firstly,the composition,micro hardness and recast layer of electrical discharge machined(EDMed)surface of 45 carbon steels in air were investigated through different test analysis methods.The results show that the workpiece surface EDMed in air contains a certain quantity of oxide,and oxidation occurs on the workpiece surface.Compared with the surface of workpieces processed in kerosene,fewer cracks exist on the dry EDMed workpiece surface,and the surface recast layer is thinner than that obtained by conventional EDM.The micro hardness of workpieces machined by dry EDM method is lower than that machined in kerosene,and higher than that of the matrix.In addition,experiments were conducted on the surface wear resistance of workpieces processed in air and kerosene using copper electrode and titanium alloy electrode.The results indicate that the surface wear resistance of workpieces processed in air can be improved,and it is related with tool material and dielectric. 相似文献