全文获取类型
收费全文 | 8690篇 |
免费 | 646篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 158篇 |
综合类 | 11篇 |
化学工业 | 2449篇 |
金属工艺 | 150篇 |
机械仪表 | 230篇 |
建筑科学 | 329篇 |
矿业工程 | 20篇 |
能源动力 | 337篇 |
轻工业 | 1263篇 |
水利工程 | 60篇 |
石油天然气 | 23篇 |
无线电 | 544篇 |
一般工业技术 | 1879篇 |
冶金工业 | 399篇 |
原子能技术 | 43篇 |
自动化技术 | 1450篇 |
出版年
2024年 | 24篇 |
2023年 | 121篇 |
2022年 | 340篇 |
2021年 | 466篇 |
2020年 | 250篇 |
2019年 | 262篇 |
2018年 | 352篇 |
2017年 | 307篇 |
2016年 | 422篇 |
2015年 | 310篇 |
2014年 | 460篇 |
2013年 | 768篇 |
2012年 | 587篇 |
2011年 | 697篇 |
2010年 | 516篇 |
2009年 | 418篇 |
2008年 | 465篇 |
2007年 | 374篇 |
2006年 | 269篇 |
2005年 | 204篇 |
2004年 | 163篇 |
2003年 | 168篇 |
2002年 | 126篇 |
2001年 | 90篇 |
2000年 | 85篇 |
1999年 | 84篇 |
1998年 | 64篇 |
1997年 | 50篇 |
1996年 | 74篇 |
1995年 | 47篇 |
1994年 | 54篇 |
1993年 | 45篇 |
1992年 | 52篇 |
1991年 | 34篇 |
1990年 | 27篇 |
1989年 | 30篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 41篇 |
1984年 | 52篇 |
1983年 | 38篇 |
1982年 | 37篇 |
1981年 | 45篇 |
1980年 | 37篇 |
1979年 | 33篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1972年 | 17篇 |
排序方式: 共有9345条查询结果,搜索用时 31 毫秒
91.
Poly[3-3′(vinylcarbazole)] (PVK) was synthetized with N-vinylcarbazole as monomer by oxidative polymerization with ferric chloride. The resulting polymer was then deposited on various solid supports by using Langmuir-Schaefer (LS) method. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at air-water interface. Different layers of PVK were doped with iodine vapours. Both scanning probe microscopy and optical microscopy images indicated a good uniformity of the films. The morphology and the thickness of PVK films were investigated using atomic force microscopy. The voltammetric investigation of I2 doped PVK showed a distinctive electrochemical behaviour. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the photoelectrochemical properties of the composite LS films. 相似文献
92.
The polyesterification and isomerization reaction of 1,6-hexane diol and maleic anydride in a melt without catalyst was studied by 13C and 1H n.m.r. spectroscopy. The structure and concentration of oligoester species during the polyesterification and isomerization were determined depending on the reaction temperature and time. According to the number and configuration of repeating units determined from 1H n.m.r. spectra kinetics of both reactions were also considered. The degree of isomerization is continuously increasing in the investigated reaction range. 相似文献
93.
A model employing the correction factors of Marek and Standart, but using a concentration-dependent liquid phase association factor of Jenkins—Robinson, has been used to model vapour—liquid equilibrium data for mixtures of acetic acid with benzene, toluene, o-xylene and p-xylene. With the aim to use systems of acetic acid—benzene and acetic acid—toluene as the test mixtures for distillation columns, the examination of the systems of acetic acid—aromatic hydrocarbons was undertaken. The model promises to be useful in modelling isobaric and isothermal data of acetic acid—benzine, acetic acid—toluene, acetic acid-p-xylene and acetic acid-o-xylene systems. Deviation plots show that the isothermal and isobaric data are represented well. 相似文献
94.
The underpotential deposition of Bi on Au has been investigated by specular reflectance spectroscopy and linear sweep voltammetry. The spectral dependance of ΔR/R caused by Bi adatoms has been determined and compared with the calculated spectrum. A satisfactory agreement between experimental and calculated spectra was found. ΔR/R values have been used to determine the surface concentration of Biad which then has been used to calculate the electrosorption valence of Biad. It has been found that γBi = 2.6. The optical evidence of interaction of Bi ions with gold oxide has been obtained. 相似文献
95.
Irena Orović Milica Orlandić Srdjan Stanković 《Multimedia Tools and Applications》2014,70(3):1503-1519
An image watermarking technique based on the concept of JPEG2000 algorithm is proposed. Biorthogonal wavelet 9/7 transform is used to provide a set of coefficients suitable for watermark embedding. The statistical properties of different subbands are analyzed in order to choose the number of decomposition levels and position of subbands, which will assure the best compromise between the watermark transparency and robustness. The JPEG2000 quantization is applied to avoid insignificant wavelet coefficients, while the remaining ones are used for watermarking. The optimal and blind watermark detection is based on the nonlinear score function and appropriate model of coefficients distribution. The performance of the proposed procedure is tested on examples with various images, showing robustness under different attacks, while maintaining high image quality. 相似文献
96.
One approach for solving Constraint Satisfaction Problems (CSP) (and related Constraint Optimization Problems (COP)) involving integer and Boolean variables is reduction to propositional satisfiability problem (SAT). A number of encodings (e.g., direct, log, support, order) for this purpose exist as well as specific encodings for some constraints that are often encountered (e.g., cardinality constraints, global constraints). However, there is no single encoding that performs well on all classes of problems and there is a need for a system that supports multiple encodings. We present a system that translates specifications of finite linear CSP problems into SAT instances using several well-known encodings, and their combinations. We also present a methodology for selecting a suitable encoding based on simple syntactic features of the input CSP instance. Thorough evaluation has been performed on large publicly available corpora and our encoding selection method improves upon the efficiency of existing encodings and state-of-the-art tools used in comparison. 相似文献
97.
The hydrophobic-polar (HP) model has been widely studied in the field of protein structure prediction both for theoretical purposes and as a benchmark for new optimization strategies. In this work we present results of the recently proposed Hybrid Monte Carlo Ant Colony Optimization heuristic in the HP model using a fragment assembly-like strategy. Moreover we extend that method introducing a general framework for optimization in the HP model, called Local Landscape Mapping, and we test it using the pull moves set to generate solutions. We describe the heuristic and compare results obtained on well known HP instances in the 3-dimensional cubic lattice to those obtained with standard Ant Colony optimization and Simulated Annealing. Fragment assembly-like tests were performed using a modified objective function to prevent the creation of overlapping walks. Results show that our method performs better than the other heuristics in all benchmark instances when the fragment assembly-like strategy is used while in the case of pull moves-based neighborhood its performance is comparable to that of simulated annealing. 相似文献
98.
The Alder ene functionalization reaction of double bonds containing macromolecules such as polyisobutene oligomer (PIB) and a styrene-butadiene-styrene triblock copolymer (SBS) samples with maleic anhydride (MAH) or diethyl maleate (DEM) as enophiles is described. The analysis of the products by means of different techniques assesses the addition of the polar molecules to the reactive vinylidene units of the polymer with functional degrees (FD) depending on the type of enophile and polymer reactivity. The role of the reaction conditions and the use as Lewis acids as catalysts are discussed in terms of their influence on the addition reaction extent and on the polymer molecular weight. 相似文献
99.
The electrochemical deposition and dissolution of aluminium on glassy carbon, platinum and gold electrodes in chloraluminate melts have been investigated using linear sweep voltammetry and potentiostatic pulse techniques. It was shown that deposition of aluminium on the glassy carbon electrode at low overpotentials takes place by 3-D progressive nucleation and growth, with the incorporation of atoms in the crystal lattice as the rate-determining step. At overpotentials higher than –100 mV vs Al, in the melts containing more than 52 mol % of AlCl3, diffusion of Al2Cl
7
–
, takes over the control of deposition of aluminium. Alloying of platinum and gold electrodes with aluminium from the melt occurs in the underpotential region. 相似文献
100.
An aerosol dynamics model, AERO2, is presented, which describes the formation of H2SO4-H2O aerosol in a smog chamber. The model is used to analyse how the uncertainties on four input parameters are propagated through an aerosol dynamics model. The input parameters are: the rate of the reaction between SO2 and OH (k1), the ratio between the nucleation rate used in AERO2 and that derived from classical nucleation theory (tn), the H2SO4 mass accommodation coefficient () and a measure of the turbulence intensity in the reactor (ke). Uncertainties for these parameters are taken from the literature. One of the results of the analysis is that AERO2 and aerosol dynamics models in general can only predict upper bounds for the total number (Ntot) and total volume (Vtot) concentrations of the particles. The uncertainties on Ntot and Vtot are mainly due to the uncertainties on k1, and tn. An uncertainty factor of 20–100 still remains when the uncertainty on k1, is reduced to ±5%. Aerosol measurements from three smog chamber experiments have therefore been used, in an attempt to reduce the uncertainty on k1 and tn. Values for k1 are obtained in the reduced range 7.8 × 10−13 to 1.0 × 10−12 cm3 s−1, which is within the range found in the literature. For tn, values in the range 104–107 are obtained, which is close to the upper bound of the range in literature. These values for tn are in marked contrast with a recent set of experiments on nucleation in H2SO4-H2O mixtures, which suggests a value for tn of at most 10−5. 相似文献