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81.
The biological cycle of mercury in the terrestrial isopod Porcellio scaber was investigated. Testing the possibility of in vivo Hg(2+) methylation was divided into two methodologically different parts. Firstly, concentrations of total mercury and MeHg in isopods P. scaber and their environment from a Hg-unpolluted area were measured by the use of validated methods (CV AAS, CV AFS). The data obtained show that the percentage of MeHg in leaves, soil and faeces was less than 1%. In contrast, the percentage of MeHg in gut and hepatopancreas was increased to 14 and 77%, respectively, indicating methylation of Hg(2+) in the gut and its further accumulation in glands. To confirm this assumption, the second methodology was applied-a radiotracer technique with 203Hg(2+) of high specific activity. There are few radiotracer techniques for Hg-methylation assays; for our work we chose the method of Czuba et al. which includes alkaline leaching of Hg species, their extraction into dithizone-toluene, followed by specific separation of Hg dithizonates by thin-layer chromatography and gamma counting. All steps of the analytical protocol were checked and optimised by the use of aqueous solutions of 203Hg(2+) and Me(203)Hg(+). The most important finding was that cleaning-up the extract through a florisil column is not appropriate, because the column retains different percentages of Hg(2+) and MeHg(+) and consequently affects the accuracy of the final result. This optimised protocol was then applied to Hg transformation studies in the terrestrial isopod P. scaber. Leaching Hg species from P. scaber fed with 203Hg(2+) or Me(203)Hg(+) dosed food was completely efficient only at elevated temperatures. Preliminary results of methylation/demethlytion studies are rather variable but they show that both processes (Hg(2+)<-->MeHg(+)) take place in the isopod P. scaber. Additionally, an assessment of the mass balance of Hg in isopods P. scaber exposed to 203Hg(2+) indicates that volatile Hg species are also formed. 相似文献
82.
A gas sensor for application in water analysis was developed by combination of a mid-infrared (MIR) hollow waveguide with a Fourier transform infrared (FT-IR) spectrometer and coupling of the hollow waveguide gas sensor module to a supported capillary membrane sampler (SCMS) for continuous liquid-gas extraction. Different hollow waveguides have been characterized in this study for developing an optimized optical configuration. Analysis of industrially relevant compounds has been performed, investigating chlorinated hydrocarbons (CHCs), such as dichloromethane and chloroform, representing highly volatile analytes, and 1,4-dioxane as an example of target compounds with low volatility. The suitability of this spectroscopic IR sensing system for industrial applications is demonstrated under simulated real-world conditions with limits of detection in the ppb (v/v) and ppm (v/v) concentration range for CHCs and 1,4-dioxane, respectively. 相似文献
83.
A sub-sea deployable fiber-optic sensor system for the continuous determination of a range of environmentally relevant volatile organic compounds in seawater has been developed. The prototype of a robust, miniaturized Fourier transform infrared (FT-IR) spectrometer for in situ underwater pollution monitoring was designed, developed, and built in our research group. The assembled instrument is enclosed in a sealed aluminium pressure vessel and is capable of maintenance-free operation in an oceanic environment down to depths of at least 300 m. The whole system can be incorporated either in a tow frame or a remotely operated vehicle (ROV). A suitable fiber-optic sensor head was developed, optimized in terms of sensitivity and hydrodynamics, and connected to the underwater FT-IR spectrometer. Due to a modular system design, various other sensor head configurations could be realized and tested, ensuring facile adaptation of the instrument to future tasks. The sensor system was characterized in a series of laboratory and simulated field tests. The sensor proved to be capable of quantitatively detecting a range of chlorinated hydrocarbons and monocyclic aromatic hydrocarbons in seawater down to the low ppb (microg/L) concentration range, including mixtures of up to 6 components. It has been demonstrated that varying amounts of salinity, turbidity, or humic acids, as well as interfering seawater pollutants, such as aliphatic hydrocarbons or phenols, do not significantly influence the sensor characteristics. In addition, the sensor exhibits sufficient long-time stability and a low susceptibility to sensor fouling. 相似文献
84.
Application of mid-infrared spectroscopy: measuring hydrogen peroxide concentrations in bleaching baths 总被引:1,自引:0,他引:1
The presented work applies mid-infrared attenuated total reflection (ATR) spectroscopy to the measurment of hydrogen peroxide in aqueous matrices. The performance of different ATR crystals mounted in flow cells was investigated in the presence of aqueous hydrogen peroxide solutions. Quantitative determination has been achieved by evaluation of specific OH stretching and deformation vibrations with linear correlation between peak areas or peak heights and hydrogen peroxide concentration in the range of 1-10% (weight in water). Important aspects such as chemical stability of the waveguide material and influences of pH and ionic strength on the performance are discussed. Feasibility for the investigation of real world samples is demonstrated by measuring industrial bleaching solutions with known concentrations of hydrogen peroxide fitting well with calibration graphs established with neat hydrogen peroxide solutions. The presented sensor system is capable of determining hydrogen peroxide within complex matrices and clearly corroborates the potential of providing an in situ measurement concept for on-line hydrogen peroxide detection. 相似文献
85.
Natalia Y. Ermolova Boris Makarevitch 《Wireless Communications, IEEE Transactions on》2007,6(2):433-437
The problem of low complexity sub-optimal power and subcarrier allocation for OFDMA systems is addressed in the paper. We propose a heuristic non-iterative method that is an extension of the ordered subcarrier selection algorithm recently proposed for a single user case to the OFDMA systems. The suggested method improves the average BER-performance of the system and it also provides fairness between the users in terms of the bit rates. Both the theoretical analysis and simulation results confirm efficiency of the proposed technique. Based on the proven lemma about inversion of power gains, we strengthen the suggested method by low complexity power loading that consists in equalization of the received signal-to-noise ratios of each user 相似文献
86.
新型电磁式电压互感器 总被引:1,自引:0,他引:1
介绍了一种新型电磁式电压互感器,阐述了电磁式和电容式电压互感器技术特性的区别. 相似文献
87.
The article introduces, as a result of further development of the first-order scheme NICE, a simple and efficient higher-order explicit numerical scheme for the integration of a system of ordinary differential equations which is constrained by an algebraic condition (DAE). The scheme is based on the truncated Taylor expansion of the constraint equation with order h of the scheme being determined by the highest exponent in the truncated Taylor series. The integration scheme thus conceived will be named NICE h , considering both principal premises of its construction. In conjunction with a direct solution technique used to solve the boundary value problem, the NICE h scheme is very convenient for integrating constitutive models in plasticity. The plasticity models are defined mostly by a system of algebraic and differential equations in which the yield criterion represents the constraint condition. To study the properties of the new integration scheme, which, like the forward-Euler scheme, is characterised by its implementation simplicity due to the explicitness of its formulations, a damage constitutive model (Gurson–Tvergaard–Needleman model) is considered. The general opinion that the implicit backward-Euler scheme is much more accurate than the thus-far known explicit schemes is challenged by the introduction of the NICE h scheme. The accuracy of the higher-order explicit scheme in the studied cases is significantly higher than the accuracy of the classical backward-Euler scheme, if we compare them under the condition of a similar CPU time consumption. 相似文献
89.
Boris Mahltig Dr. 《真空研究与实践》2010,22(2):25-28
Vacuum impregnation of porous metal materials with inorganic nanosol The sealing of porous metal pieces is possible by application of inorganic nanosols. For suitable sealing it is necessary that the nansols are applied by vacuum impregnation. For sealing useful nanosols contain particles of silicon/aluminium‐oxide with a modification of organic methyl groups. The nanosol particles are smaller than 100nm and the maximum of the particle size distribution is around 10nm. Beside sealing of the metal pieces, also their stability against corrosion can be improved by this nanosol application. The further development of this technology is especially promising for applications in machine factory or automobile. 相似文献
90.