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排序方式: 共有4012条查询结果,搜索用时 15 毫秒
71.
Hassan Elhadidy Jan Franc Eduard Belas Pavel Hlídek Pavel Moravec Roman Grill Pavel Hoschl 《Journal of Electronic Materials》2008,37(9):1219-1224
Thermoelectric effect spectroscopy and photoluminescence techniques were used to study the defect levels in samples from three
crystals of CdTe:In grown by the vertical gradient freeze method. The main goal of the investigation was to study defects,
which strongly trap charge carriers or act as recombination centers in order to eliminate them from the technological process.
The main difference among detecting and non-detecting samples was the absence of electron traps with a very high capture cross-section
and energy 0.6 eV to 0.7 eV, which act as lifetime killers even at low concentrations. Recently published ab initio calculations show a complex of Te antisite and Cd vacancy within this energy range. 相似文献
72.
High-gain observers have been used in non-linear control to estimate derivatives of the output. In this paper, we study discrete-time implementation of high-gain observers and their use as numerical differentiators, in noise-free as well as noisy measurements. We show that discretization using the bilinear transformation method gives better results than other discretization methods. We also show that many of the available numerical differentiators are special cases of the bilinear discrete-time equivalents of full-order or reduced-order high-gain observers. 相似文献
73.
74.
S. Ouendadji S. Ghemid N. Bouarissa H. Meradji F. El Haj Hassan 《Journal of Materials Science》2011,46(11):3855-3861
Based on the self-consistent ab initio full potential-linearized augmented plane wave method, the structural, electronic, optical, and thermodynamic properties of CdSe x Te1−x ternary semiconductor alloys have been investigated. The exchange–correlation potential was calculated using both the generalized gradient approximation (GGA) by Perdew–Burke–Ernzerhof (PBE) and the GGA by Engel–Vosko (EV-GGA). The ground-state properties are determined for the cubic bulk materials CdSe, CdTe, and their mixed crystals at various concentrations (x = 0.25, 0.5, and 0.75). Deviation of the lattice parameter from Vegard’s law and the bulk modulus from linear concentration dependence has been examined. The microscopic origins of the band-gap bowing parameter have been discussed. Moreover, the refractive index and the optical dielectric constant for CdSe x Te1−x are studied using different models. Besides, the thermodynamic stability of the alloys of interest is investigated by means of the miscibility critical temperature. 相似文献
75.
Hassan HajabdollahiPouria Ahmadi Ibrahim Dincer 《International Journal of Refrigeration》2011,34(4):1066-1076
This paper presents a thermoeconomic optimization of a shell and tube condenser, based on two new optimization methods, namely genetic and particle swarm (PS) algorithms. The procedure is selected to find the optimal total cost including investment and operation cost of the condenser. Initial cost includes condenser surface area and operational cost includes pump output power to overcome the pressure loss. Design parameters are tube number, number of tube pass, inlet and outlet tube diameters, tube pitch ratio and tube arrangements (30, 45, 60 and 90°). Therefore, shell diameter should be selected less than 7 m, tube length should be less than 15 m, and ratio of diameter to tube length should be in the range of 1/12 to 1/3. In addition, it is found that GA provides better results for computer CPU running time, compared to PS algorithm. Finally, a sensitivity analysis of design parameters at the optimal point is conducted. Results show that an increase in the tube number leads to decrease in the objective function first then it leads to a considerable increment in objective function. 相似文献
76.
S. Labidi M. Labidi H. Meradji S. Ghemid F. El Haj Hassan 《Computational Materials Science》2011,50(3):1077-1082
Using first-principle method, we investigate the structural, electronic, optical and thermodynamic properties of the strontium semiconductors Pb1?xSrxS with 25%, 50% and 75% of Sr. The calculations are performed by using the full-potential linearized augmented plane wave (FP-LAPW) method. As exchange–correlation potential we used the generalized gradient approximation (GGA) of Perdew et al. The variation of the calculated equilibrium lattice constant versus concentration shows that a small deviation from Vegard’s law is clearly visible with downward bowing parameter equal to 0.009 Å. The bulk modulus as a function of x for Pb1?xSrxS alloy shows a significant deviation from the linear concentration dependence (LCD) with downward bowing equal to 6.62 GPa. The different roles of structural and chemical effects on the gap bowing and its variation with composition are identified and discussed. In addition, density of states and optical properties were calculated and compared to the available experimental data and previous theoretical works. On the other hand, the thermodynamic stability of these alloys was investigated by calculating the excess enthalpy of mixing ΔHm as well as the phase diagram. 相似文献
77.
Keystream reuse, also known as the two time pad problem, is a well known weakness in stream ciphers. The implementers of the cryptographic algorithms are still underestimating this threat. The keystream reuse exploitation techniques presented so far assume the underlying plaintext to be textual data and all the heuristics presented previously are based on the language characteristics of the underlying text based data, which fail when compression is applied on the plaintext before encryption. This paper presents exploitation techniques for two time pads in case of stream ciphered digitized and compressed speech signals. In this paper we show that how an adversary can automatically recover the digitized speech signals encrypted under the same keystream provided the language (e.g. English) and digital encoding/compression scheme details of the underlying speech signals are known. Our technique of cryptanalysis is based on the modeling of the speech parameters by exploiting the inter frame correlations between each components of the speech vectors in different frames and then using these models to decode the two speech signals in the keystream reuse scenario. The technique is flexible enough to incorporate all modern speech coding schemes based on parameter or hybrid encoding and compression techniques. The simulation experiments have showed promising results for most of the present day speech digitization and compression techniques. 相似文献
78.
Huang Wei-Ran Yu Cheng-Xin Lu Yi-Ruo Muhammad Hassan Wang Jin-Long Liu Jian-Wei Yu Shu-Hong 《Nano Research》2019,12(6):1483-1488
Nano Research - In the past two decades, the field of surface-enhanced Raman scattering (SERS) has flourished and many rational strategies have been reported for the successful construction of SERS... 相似文献
79.
Mei-Ling Chong Nor' Aini Abdul Rahman Raha Abdul Rahim Suraini Abdul Aziz Yoshihito Shirai Mohd Ali Hassan 《International Journal of Hydrogen Energy》2009,34(17):7475-7482
Clostridium butyricum EB6 successfully produced hydrogen gas from palm oil mill effluent (POME). In this study, central composite design and response surface methodology were applied to determine the optimum conditions for hydrogen production (Pc) and maximum hydrogen production rate (Rmax) from POME. Experimental results showed that the pH, temperature and chemical oxygen demand (COD) of POME affected both the hydrogen production and production rate, both individually and interactively. The optimum conditions for hydrogen production (Pc) were pH 5.69, 36 °C, and 92 g COD/l; with an estimated Pc value of 306 ml H2/g carbohydrate. The optimum conditions for maximum hydrogen production rate (Rmax) were pH 6.52, 41 °C and 60 g COD/l; with an estimated Rmax value of 914 ml H2/h. An overlay study was performed to obtain an overall model optimization. The optimized conditions for the overall model were pH 6.05, 36 °C and 94 g COD/l. The hydrogen content in the biogas produced ranged from 60% to 75%. 相似文献
80.
Building envelope impacts upon energy consumption and indoor environment. The relationship between envelope components and indoor environment has become increasingly important, especially with the new emphasis on visual comfort, thermal comfort and indoor air quality. This paper examines the interaction between occupant thermal comfort and envelope component regulations in the Gulf States. The country chosen for this study is the Kingdom of Bahrain, the smallest country in the Gulf region. Simulation results and comparative studies were employed to investigate the impact of the current envelope component regulations on the internal environment. The paper focuses on residential buildings and concludes that the envelope component regulations contribute positively to the internal thermal performance. Although these envelope components are not generally the primary elements that impact upon internal thermal comfort there are circumstances when the components become very warm and occupants positioned close to them will experience discomfort. This paper shows that the thermal insulation regulation makes a small impact on thermal comfort, whereas the window regulation, particularly glazing, is more influential and that for most window areas, solar impacts are generally large. 相似文献