全文获取类型
收费全文 | 1479篇 |
免费 | 24篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 9篇 |
综合类 | 7篇 |
化学工业 | 241篇 |
金属工艺 | 282篇 |
机械仪表 | 26篇 |
建筑科学 | 30篇 |
矿业工程 | 9篇 |
能源动力 | 12篇 |
轻工业 | 201篇 |
水利工程 | 8篇 |
石油天然气 | 5篇 |
无线电 | 45篇 |
一般工业技术 | 175篇 |
冶金工业 | 150篇 |
原子能技术 | 1篇 |
自动化技术 | 305篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 77篇 |
2017年 | 74篇 |
2016年 | 78篇 |
2015年 | 83篇 |
2014年 | 33篇 |
2013年 | 47篇 |
2012年 | 52篇 |
2011年 | 628篇 |
2010年 | 47篇 |
2009年 | 39篇 |
2008年 | 46篇 |
2007年 | 25篇 |
2006年 | 18篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 11篇 |
2001年 | 3篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 6篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 6篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1971年 | 2篇 |
排序方式: 共有1506条查询结果,搜索用时 15 毫秒
81.
Describes a university 66-credit professional diploma sequence that includes 1 yr of internship experience for the training of school psychologists to work with bilingual/bicultural populations. Competence for working with these populations involves 3 general areas: language, cross-cultural expertise, and assessment. An integrated curriculum and faculty offers linguistics, cultural-urban studies, and bilingual education courses in addition to the core courses in professional school psychology. Bilingual students and faculty have been recruited. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
82.
This work explores the potential use of a member of the periplasmic family of binding proteins, the phosphate binding protein (PBP), as the biorecognition element in a sensing scheme for the detection of inorganic phosphate (Pi). The selectivity of this protein originates from its natural role which, in Escherichia coli, is to serve as the initial receptor for the highly specific translocation of Pi to the cytoplasm. The single polypeptide chain of PBP is folded into two similar domains connected by three short peptide linkages that serve as a hinge. The Pi binding site is located deep within the cleft between the two domains. In the presence of the ligand, the two globular domains engulf the former in a hinge-like manner. The resultant conformational change constitutes the basis of the sensor development. A mutant of PBP (MPBP), where an alanine was replaced by a cysteine residue, was prepared by site-directed mutagenesis using the polymerase chain reaction (PCR). The mutant was expressed, from plasmid pSD501, in the periplasmic space of E. coli and purified in a single chromatographic step on a perfusion anion-exchange column. Site-specific labeling was achieved by attaching the fluorophore, N-[2-(1-maleimidyl)ethyl]-7-(diethylamino)coumarin-3-carboxamide (MDCC), to the protein through the sulfhydryl group of the cysteine moiety. Steady-state fluorescence studies of the MPBP-MDCC conjugate showed a change in the intensity of the signal upon addition of Pi. Calibration curves for Pi were constructed by relating the intensity of the fluorescence signal with the amount of analyte present in the sample. The sensing system was first developed and optimized on a spectrofluorometer using ml volumes of sample. It was then adapted to be used on a microtiter plate arrangement with microliter sample volumes. The system's versatility was finally proven by developing a fiber optic fluorescence-based sensor for monitoring Pi. In all three cases the detection limits for the analyte were in the sub-microMolar range. It was also demonstrated that the sensing system was selective for phosphate over other structurally-similar anions, paving the way for the design and development of a new family of biosensors utilizing the specific binding properties of periplasmic proteins. 相似文献
83.
84.
85.
Asperity scattering adds a 'surface lobe' to the usual diffuse, backscatter, and specular lobes of rough surfaces. Although rarely acknowledged, it is an important effect in many materials that are covered with a thin layer of sparse scatterers, such as dust or hairs. In common cases where single scattering predominates, asperity scattering adds important contributions to the structure of the occluding contour and the edge of the body shadow. This is because the bidirectional reflectance distribution function (BRDF) is inversely proportional to the cosines of both the illumination and viewing angles. The BRDF is generally low (and typically negligible) except when either the illuminating rays or visual directions graze the surface. Because asperity scattering selectively influences the edges in the image of an object, it has (as judged by photometric magnitudes) a disproportionally large effect on (human) visual appreciation. We identify it as a neglected but often decisive visual cue in the rendering of human skin. Its effect is to make smooth cheeks look 'velvety' or 'peachy', that is to say, soft (the appearances of both velvet and peachy skin are dominated by asperity scattering). This is a most important aesthetic and emotional factor that is lacking in Lambertian (looks merely dullish and paper-like), 'skin-type' BRDF (looks like glossy plastic), or even translucent (looks 'hard', vitreous) types of rendering.Published online: 8 August 2003 相似文献
86.
Optical and electrical characterization of r.f. sputtered ITO films developed as art protection coatings 总被引:1,自引:0,他引:1
Transparent and conductive tin-doped indium oxide (ITO) films have been prepared by r.f. plasma sputtering technique in Ar and Ar + O2 gas mixture. The influence of the deposition conditions, film thickness, and substrate heating, as well as the post-annealing treatment on the optical and electrical properties of the ITO films has been investigated.The present study has extended the optical behaviour characterization of the ITO films in a wide UV-VIS-IR spectral region in addition to the comprehensive optical studies of this material at shorter wavelengths.The optical constants: refractive index (n), extinction (k) and absorption (α) coefficient, and the optical band gap (Ego) have been calculated for the ITO films in the spectral range between 350 and 2500 nm. A combination of several well-known theoretical models has been applied to describe precisely the complex optical behaviour of ITO films in separate spectral parts. In this approach, a good overlapping between the experimental and the simulated spectra in the whole investigated spectral region has been achieved.The deposition conditions and the optical and electrical properties of the ITO films have been optimized with respect to the requirements for their applications in art protection coatings. 相似文献
87.
The characteristic hypothalamus square-wave secretion and its regulation of the pituitary are essential for the optimal functioning of the menstrual cycle. Here we consider two coupled models, where one mimics the square-wave secretion and the second, a self-replication chemical system, represents a regulated subsystem. We analyse the relation of the period and amplitude of the square-wave oscillations on the secondary oscillator, finding that both period and amplitude shape the secondary oscillations. Furthermore, a combined slow change of both period and amplitude are required for biologically suitable product concentrations of the secondary oscillator. 相似文献
88.
Experimental values of volume and area changes for sweet (Prunus avium) and sour (Prunus cerasus) cherry and rose hips (Rosa rubiginosa) measured in previous works were analyzed to propose generalized correlations for the three fruits which predicted with low
errors. The correlation developed is lineal and the highest errors were observed for fruit water contents corresponding to
storage stability values. The shape factors were measured for the fruits, which were close to spherical values as the fruits
dried. This would enable the assumption of spherical shape to calculate characteristic dimensions used in modeling. Moreover,
the predictions of kinetic models were compared with experimental data for three radii: the initial, assumed constant; variable,
estimating the radius with the correlations published for each fruit; and variable, calculating the radius with the generalized
correlation developed in this work. The RMSE between the experimental data and the predictions by the kinetic model were between
0.321 and 0.562; 0.021 and 0.111; and 0.020 and 0.093, respectively. 相似文献
89.
A. Hundertmark-Zau?kov�� M. Luk��?ov��-Medvid��ov�� F. Prill 《Journal of scientific computing》2011,48(1-3):227-240
We present two new large time step methods within the framework of the well-balanced finite volume evolution Galerkin (FVEG) schemes. The methodology will be illustrated for low Froude number shallow water flows with source terms modeling the bottom topography and Coriolis forces, but results can be generalized to more complex systems of balance laws. The FVEG methods couple a finite volume formulation with approximate evolution operators. The latter are constructed using the bicharacteristics of multidimensional hyperbolic systems, such that all of the infinitely many directions of wave propagation are taken into account explicitly. We present two variants of large time step FVEG method: a semi-implicit time approximation and an explicit time approximation using several evolution steps along bicharacteristic cones. 相似文献
90.