全文获取类型
收费全文 | 2090篇 |
免费 | 66篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 10篇 |
综合类 | 3篇 |
化学工业 | 609篇 |
金属工艺 | 72篇 |
机械仪表 | 64篇 |
建筑科学 | 34篇 |
矿业工程 | 3篇 |
能源动力 | 181篇 |
轻工业 | 138篇 |
水利工程 | 13篇 |
石油天然气 | 7篇 |
无线电 | 144篇 |
一般工业技术 | 507篇 |
冶金工业 | 132篇 |
原子能技术 | 10篇 |
自动化技术 | 237篇 |
出版年
2024年 | 7篇 |
2023年 | 16篇 |
2022年 | 72篇 |
2021年 | 88篇 |
2020年 | 67篇 |
2019年 | 52篇 |
2018年 | 91篇 |
2017年 | 68篇 |
2016年 | 75篇 |
2015年 | 57篇 |
2014年 | 80篇 |
2013年 | 161篇 |
2012年 | 103篇 |
2011年 | 132篇 |
2010年 | 104篇 |
2009年 | 101篇 |
2008年 | 111篇 |
2007年 | 94篇 |
2006年 | 58篇 |
2005年 | 62篇 |
2004年 | 41篇 |
2003年 | 36篇 |
2002年 | 36篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 39篇 |
1998年 | 25篇 |
1997年 | 21篇 |
1996年 | 28篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 26篇 |
1992年 | 25篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1975年 | 2篇 |
1974年 | 2篇 |
排序方式: 共有2164条查询结果,搜索用时 15 毫秒
61.
Suresh Dhaniyala Richard C. Flagan Karena A. McKinney Paul O. Wennberg 《Aerosol science and technology》2013,47(10):828-840
A novel inlet has been designed for selective sampling of gas and aerosol phases of volatile species from high-speed aircraft. A multistage flow system brings the flow nearly isokinetically towards the sampling port. Two small airfoil-shaped "blades" are placed close to the sample port to provide the flow conditions required for aerosol and gas sampling. Aerosols are sampled when these blades are positioned to operate the inlet as a counterflow virtual impactor (CVI). The design enables sampling of particles as small as 0.1 w m from a high-speed aircraft under stratospheric conditions, a substantial improvement over that possible with previous CVI designs. For gas sampling, one of the blades is moved by a stepper motor to occlude the inlet opening and gas is sampled perpendicular to the bulk flow. Boundary layer suction is used to prevent the sampled gas from coming in contact with the impactor walls. This is one of the first designs of an inlet that enables gas sampling free of wall contact. The inlet was flown on the NASA ER-2 aircraft during the SOLVE 2000 campaign to study aerosol/gas partitioning of nitric acid in the lower stratosphere. Data from the flight tests show that the inlet flow characteristics are broadly in agreement with computational fluid dynamics (CFD) simulations. 相似文献
62.
Arantzazu Eiguren-Fernandez Edward L. Avol Suresh Thurairatnam Mahnaz Hakami John R. Froines Antonio H. Miguel 《Aerosol science and technology》2013,47(4):438-446
Ambient concentrations of 15 vapor-and particle-phase (PM 2.5 ) polycyclic aromatic hydrocarbons (PAHs), listed by the US EPA as priority pollutants, were measured between July 2002 and November 2003 in six Southern California communities participating in a multi-year chronic respiratory health study of schoolchildren. The communities were geographically distributed over two hundred kilometers, extending from Long Beach in coastal Los Angeles, to high mountain areas to the north and west of the Los Angeles basin, and south into Eastern San Diego County. Seasonal and spatial variation in the atmospheric concentrations of PAHs is of interest because this class of compounds includes potent mutagens, carcinogens, and species capable of generating reactive oxygen species (ROS) that may lead to oxidative stress. Naphthalene accounted for 95% of the total PAH mass; annual averages ranged from 89 to 142 ng m ? 3 . Benzo[ghi]perylene (BGP) and the pro-carcinogen benzo[a]pyrene (BAP), present almost exclusively in the particle-phase, ranged respectively from 38 to 231 pg m ?3 and 75 and 111 pg m ? 3 , with the highest values observed in Long Beach, a community with a high volume of seaport-related activities, and Lancaster, a commuter dormitory community. A considerable increase in the particle-phase PAH concentration, relative to the vapor-phase, was observed as ambient temperature decreased. Cold/hot season ratios for PAHs in PM 2.5 averaged 5.7, reaching 54 at Long Beach. The presented data underscore the importance of seasonal variations on atmospheric PAH concentrations. These observations are relevant to future interpretation and analysis of community-scale human health effects research. 相似文献
63.
Here we present a high-resolution chromosomal spectral map derived from synchrotron-based soft X-ray spectromicroscopy applied to quinoa species. The label-free characterization of quinoa metaphase chromosomes shows that it consists of organized substructures of DNA-protein complex. The analysis of spectra of chromosomes using the scanning transmission X-ray microscope (STXM) and its superposition of the pattern with the atomic force microscopy (AFM) and scanning electron microscopy (SEM) images proves that it is possible to precisely locate the gene loci and the DNA packaging inside the chromosomes. STXM has been successfully used to distinguish and quantify the DNA and protein components inside the quinoa chromosomes by visualizing the interphase at up to 30-nm spatial resolution. Our study represents the successful attempt of non-intrusive interrogation and integrating imaging techniques of chromosomes using synchrotron STXM and AFM techniques. The methodology developed for 3-D imaging of chromosomes with chemical specificity and temporal resolution will allow the nanoscale imaging tools to emerge from scientific research and development into broad practical applications such as gene loci tools and biomarker libraries. 相似文献
64.
Liquid composite molding (LCM) processes such as resin transfer molding (RTM) and vacuum assisted RTM (VARTM) are used to manufacture high quality and net‐shape fiber reinforced composite parts. All LCM processes impregnate fiber preforms packed in a mold cavity with a thermoset resin. After the preform is fully saturated, the injection is discontinued but the resin continues to cure. Once the curing step is complete, the part is de‐molded. The resin has to be mixed with a curing agent to cure. Typically, the resin and the curing agent are mixed together in a pressure pot before the injection. This has several disadvantages, such as storage of large amounts of hazardous polymerizing resin, wastage, and cleaning of cured resin from the injection line. This paper proposes the implementation and calibration of an alternative to this technique. The approach is to mix the curing agent with the resin as the resin enters the mold through a separate system featuring two feed‐lines. Such a system will enable one to maintain a uniform gel time throughout the part by varying the mixing ratio of resin and the catalyst during the injection. An experimental study of such on‐line mixing to obtain simultaneous curing and to reduce the overall curing time is conducted and presented in this paper. Implementation of a control scheme that varies the curing agent during injection and its effect on cure time is benchmarked with the process in which the percentage of curing agent is held constant. The gel time for the fabricated parts was reduced by 20–25% by continuously varying the percentage of curing agent during injection. POLYM. COMPOS., 26:74–83, 2005. © 2004 Society of Plastics Engineers 相似文献
65.
Silicon - Advances in microelectronics have enabled smaller technical nodes, lower threshold voltages, and greater working frequencies. Even though VLSI circuit performance and power consumption... 相似文献
66.
Ravanamma Rallapalli Muralidhara Reddy Kalimi Ravi Nirlakalla Padma Suvarna Reniguntla 《International Journal of Applied Ceramic Technology》2022,19(4):2053-2063
Structure, morphology, and electrical properties of 10 mol% of Nb2O5-activated yttrium barium titanate (BT) Ba(60-z)Ti(40-x)NbzYxO3 (BTY10Nb10), barium titanate (BT), and 10 mol% of Y2O3-activated BT were explored with calcination and sintering temperatures of 1000°C at 8 h and 1200°C at 6 h, respectively. The thermogravimetric and differential scanning calorimetry (TG–DSC) analysis reported that the total weight loss and residual mass of BT at 1300°C were 16.8 and 83.2%, respectively. The X-ray diffraction (XRD) pattern confirmed that BTY10Nb10 ceramics containing the BaNbO3 phase were developed. A Raman band of BT at 307 cm–1 unveiled a blue shift slightly for BTY10 to 298 cm–1 and for BTY10Nb10 to 306 cm–1. Average pore area of the ferroelectric BTY10Nb10 was found to be 6.96 nm for the total scanning electron microscopy (SEM) image area of 20.31 nm. Formation of BT nanorods analyzed from transmission electron microscopy (TEM) has been reported in three samples that regulate surface roughness. Moreover, Nyquist diagram of BTY10Nb10 shows two overlapping semicircles as a function of frequency. Nanorod structures led to change the morphology and surface roughness. Recoverable energy storage density and energy storage efficiency were estimated as 2.63 µJ/cm3 and 57%, and BTY10Nb10 ferroelectric showed potential for energy storage applications due to changes in surface morphology and porosity. 相似文献
67.
Suresh T. Gulati John D. Helfinstine 《International Journal of Applied Glass Science》2011,2(1):39-46
Following a brief history of various tests for measuring edge strength, we present the theory and application of four-point vertical bend test (VBT). The latter is similar to a standard four-point bend test except that the specimen is turned on its edge so as to permit application of uniform tension to a majority of the edge flaws. The article cautions against lateral buckling of the VBT specimen, resulting in failure initiation from the “compression” edge, if its dimensions are not optimized. We provide guidelines for designing the width and thickness of the VBT specimen relative to its length, which obviates the onset of lateral buckling. Three simple inspections to verify the validity of VBT include the shape of load versus deflection curve, location of failure origin, and fracture pattern. Two examples, one involving edge quality of an aluminosilicate glass and the other involving factors that affect edge strength of automotive glass, help illustrate the application of VBT. 相似文献
68.
Environmentally friendly organocatalytic synthesis of aliphatic polyesters was studied. The catalysis investigated is novel, and lends itself well to the potential production of valuable biodegradable products. The reactions were based on an organic acids‐catalyzed ring‐opening polymerization of ε‐caprolactone with fatty acid derivatives as the initiator and were performed in the absence of solvents. The chemical structures of the functionalized polymers were confirmed by 1H and 13C‐NMR spectra. Polymers with different molecular weights, in the range 10,900–15,200 were obtained in the presence of fumaric acid as catalyst. The thermal properties of the functionalized PCLs were determined by modulated differential scanning calorimetry and thermogravimetric analysis. The MDSC results verified that the crystallinity and the melting point of the lipid‐functionalized polymers were lower than that of the unfunctionalized poly(ε‐caprolactone). The hydrolytic degradation of the functionalized polymer was also investigated. The result shows the degradation rate was affected by the presence of oleic acid derivatives in the polymer molecule. The lipid‐functionalized polymers synthesized by the metal‐free polymerization systems seem to be suitable biodegradable polyesters for use in biomedical and pharmacological applications. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
69.
In this work, we report a basic study on the mechanism of lithium ion de-insertion/insertion process from/into LiMn2O4 cathode material in aqueous Li2SO4 solution using electrochemical impedance spectroscopy (EIS). An equivalent circuit distinguishing the kinetic parameters of lithium ion de-insertion/insertion is used to simulate the experimental impedance data. The fitting results are in good agreement with the experimental results and the parameters of the kinetic process of Li+ de-insertion and insertion in LiMn2O4 at different potentials during charge and discharge are obtained using the same circuit. The results indicate that the de-insertion/insertion behavior of lithium ions at LiMn2O4 cathode in Li2SO4 aqueous solution is similar to that reported in the organic electrolytes. The charge transfer resistance (Rct), warburg resistance, double layer capacitance and chemical diffusion coefficient (DLi+) vary with potentials during de-insertion/insertion processes. Rct is lowest at the CV peak potentials and the important kinetic parameter, DLi+ exhibits two distinct minima at potentials corresponding to CV peaks during de-insertion–insertion and it was found to be between 10−8 and 10−10 cm2 s−1during lithium de-insertion/insertion processes. 相似文献
70.
Vankayala Kiran Suresh Babu Kalidindi Balaji Rao Jagirdar Srinivasan Sampath 《Electrochimica acta》2011,(28):10493
Electrochemical oxidation of sodium borohydride (NaBH4) and ammonia borane (NH3BH3) (AB) have been studied on titanium carbide electrode. The oxidation is followed by using cyclic voltammetry, chronoamperometry and polarization measurements. A fuel cell with TiC as anode and 40 wt% Pt/C as cathode is constructed and the polarization behaviour is studied with NaBH4 as anodic fuel and hydrogen peroxide as catholyte. A maximum power density of 65 mW cm−2 at a load current density of 83 mA cm−2 is obtained at 343 K in the case of borhydride-based fuel cell and a value of 85 mW cm−2 at 105 mA cm−2 is obtained in the case of AB-based fuel cell at 353 K. 相似文献