全文获取类型
收费全文 | 5624篇 |
免费 | 184篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 39篇 |
综合类 | 7篇 |
化学工业 | 1158篇 |
金属工艺 | 86篇 |
机械仪表 | 79篇 |
建筑科学 | 215篇 |
矿业工程 | 20篇 |
能源动力 | 166篇 |
轻工业 | 366篇 |
水利工程 | 35篇 |
石油天然气 | 36篇 |
武器工业 | 2篇 |
无线电 | 431篇 |
一般工业技术 | 805篇 |
冶金工业 | 1659篇 |
原子能技术 | 14篇 |
自动化技术 | 697篇 |
出版年
2023年 | 32篇 |
2022年 | 72篇 |
2021年 | 91篇 |
2020年 | 59篇 |
2019年 | 72篇 |
2018年 | 88篇 |
2017年 | 91篇 |
2016年 | 89篇 |
2015年 | 88篇 |
2014年 | 129篇 |
2013年 | 363篇 |
2012年 | 222篇 |
2011年 | 298篇 |
2010年 | 191篇 |
2009年 | 221篇 |
2008年 | 220篇 |
2007年 | 238篇 |
2006年 | 197篇 |
2005年 | 157篇 |
2004年 | 124篇 |
2003年 | 120篇 |
2002年 | 133篇 |
2001年 | 100篇 |
2000年 | 81篇 |
1999年 | 103篇 |
1998年 | 374篇 |
1997年 | 258篇 |
1996年 | 164篇 |
1995年 | 141篇 |
1994年 | 96篇 |
1993年 | 108篇 |
1992年 | 50篇 |
1991年 | 56篇 |
1990年 | 68篇 |
1989年 | 54篇 |
1988年 | 50篇 |
1987年 | 38篇 |
1986年 | 43篇 |
1985年 | 60篇 |
1984年 | 58篇 |
1983年 | 46篇 |
1982年 | 44篇 |
1981年 | 42篇 |
1980年 | 46篇 |
1979年 | 46篇 |
1978年 | 50篇 |
1977年 | 70篇 |
1976年 | 94篇 |
1975年 | 36篇 |
1973年 | 35篇 |
排序方式: 共有5815条查询结果,搜索用时 15 毫秒
91.
Lisa Anthony Quincy Brown Berthel Tate Jaye Nias Robin Brewer Germaine Irwin 《Personal and Ubiquitous Computing》2014,18(6):1471-1483
In next-generation classrooms and educational environments, interactive technologies such as surface computing, natural gesture interfaces, and mobile devices will enable new means of motivating and engaging students in active learning. Our foundational studies provide a corpus of over 10,000 touch interactions and nearly 7,000 gestures collected from nearly 70 adults and children aged 7 years and above, which can help us understand the characteristics of children’s interactions in these modalities and how they differ from adults. Based on these data, we identify key design and implementation challenges of supporting children’s touch and gesture interactions, and we suggest ways to address them. For example, we find children have more trouble successfully acquiring onscreen targets and having their gestures recognized than do adults, especially the youngest age group (7–10 years old). The contributions of this work provide a foundation that will enable touch-based interactive educational apps that increase student success. 相似文献
92.
Damage Mechanisms and the Mechanical Properties of a Laminated 0/90 Ceramic/Matrix Composite 总被引:2,自引:0,他引:2
Douglas S. Beyerle S. Mark Spearing Anthony G. Evans 《Journal of the American Ceramic Society》1992,75(12):3321-3330
The tensile properties of a 0/90 laminated CAS matrix composite reinforced with Nicalon fibers have been measured. Some effects of notches have also been explored. Changes in modulus and permanent strain caused by matrix cracking have been measured and compared with available models. For this comparison, independent measurements have been made of the constituent properties and the residual stress. The ultimate tensile strength has also been measured and compared with a global load-sharing model. It is concluded that lower-bound matrix cracking models provide good predictability of the stresses at which various matrix cracking mechanisms first operate. Also, the ultimate tensile strength is found to be consistent with a global load-sharing model, based on the in situ strength properties of the fibers. Conversely, the evolution of matrix cracks at stresses above the lower bound has yet to be adequately modeled. In addition, a need is identified for improved models relating elastic properties and permanent strains to matrix crack spacing. 相似文献
93.
William A. Levinson Anthony Arnold Ofelia Dehodgins 《Polymer Engineering and Science》1993,33(15):980-988
Experimental data confirm the utility of the following simple equation in predicting the spin coating behavior of polyimide precursor solutions: in which . 相似文献
94.
A semitheoretical correlation based on an extension of the random length, random angle statistical model of Davidson (1959) is developed which predicts liquid film mass transfer coefficients in a column packed with partially wetted Raschig rings. The method takes into account the ring size and the mixing which occurs at the packing junctions and allows an estimation of the effective length of a packing piece for a particular liquid viscosity. Predicted values of mass transfer coefficients are in good agreement with the experimental values obtained for the carbon dioxide-water and carbon dioxide-aqueous glycerol systems at 25°C reported by Mangers and Ponter (1980b) and other systems reported by Sherwood and Holloway (1940). 相似文献
95.
Porous glass packing materials have been used for gel permeation chromatography using an aqueous phosphate buffer. Elution volumes were determined for polystyrene sulfonates, dextrans, and small neutral and charged molecules at three different ionic strengths, viz., 0.01M, 0.1M, and 1.0M phosphate, pH 7.0. The pore diameters of the glasses studied were 75, 240, 700, and 2000 Å. Elution volumes of nonionic species were unaffected by changing the solvent ionic strength. Elution volumes of charged species were markedly affected by the ionic strength of the solvent. This was attributed to a combination of decreased polymer dimensions and decreased ionic exclusion with increasing buffer concentration. The use of low ionic strength solvents may be exploited to tailor the separating range for polyelectrolytes with porous glass packings. This is particularly useful in the low molecular weight range where the lowest pore size available is 75 Å. 相似文献
96.
Ritesh Rawal Antonio Feteira Alberto Arenas Flores Neil C. Hyatt Anthony R. West Derek C. Sinclair Kumaravinothan Sarma Neil McN. Alford 《Journal of the American Ceramic Society》2006,89(1):336-339
The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba8 Nb4 Ti3 O24 are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O2 at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛr ∼44–48, quality factor, Q × f r ∼21 000–23 500 GHz (at f r ∼5.5 GHz) and temperature coefficient of resonant frequency, TC f ,∼+115 ppm/K. 相似文献
97.
Guttamindapalli A. Ravi Feridoon Azough Robert Freer Robert J. Cernik Anthony M. T. Bell 《Journal of the American Ceramic Society》2007,90(12):3947-3952
Mixed-oxide prepared Ca0.7 Ti0.7 La0.3 Al0.3 O3 (CTLA) ceramics (≈96% dense), grain size 6–7 μm, with dielectric properties (at 4 GHz) of ɛr ≈46, Q × f ≈38 000 GHz, and τf +13 ppm/°C, were studied at 25°–1300°C using synchrotron X-ray powder diffraction. At room temperature, CTLA exhibits a distorted orthorhombic structure, with two tilt systems: a =5.40383 (4) Å, b =5.41106 (6) Å, and c =7.64114 (7) Å with space group Pbnm . At 1050°±25°C, there is a transition from orthorhombic ( Pbnm ) to tetragonal ( I 4/ mcm ), with a simpler tilt arrangement. The lattice parameters at 1100°C were: a =5.44285 (4) Å and c =7.68913 (8) Å. 相似文献
98.
Anthony E. Hughes 《Journal of the American Ceramic Society》1995,78(2):369-378
X-ray photoelectron spectroscopy (XPS) has been used to study surface segregation in 9.5 mol% single-crystal Y2 O3 -ZrO2 which has been subjected to air anneals at temperatures ranging from 900° to 1500°C. The kinetics of segregation reveal an enrichment of Y, Si, Na, and Fe at short times; however, at longer times surface equilibrium is reached. The heats of segregation for Y, Si, Na and Fe, determined from Arrhenius plots, were 9.3 ± 3.0, 59.0 ± 7.0, –23.5 ± 11.5, –18.0 ± 6.0 kJ/mol, respectively. XPS analysis of the equilibrium states at all temperatures revealed a distinct surface layer which, given the positive heats of segregation for Si and Y, is quite stable. 相似文献
99.
Induced Defensive Response of Myrtle Oak to Foliar Insect Herbivory in Ambient and Elevated Co2 总被引:2,自引:0,他引:2
The rising level of atmospheric CO2 has stimulated several recent studies attempting to predict the effects of increased CO2 on ecological communities. However, most of these studies have been conducted in the benign conditions of the laboratory and in the absence of herbivores. In the current study, we utilized large octagonal chambers, which enclosed portions of an intact scrub-oak community to investigate the interactive effects of CO2 and insect herbivory on myrtle oak, Quercus myrtifolia. Specifically, we assessed the effects of ambient and elevated CO2 (2x current concentrations) on percent foliar nitrogen, C:N ratio, total relative foliar tannin content, and the presence of leaf damage caused by leaf mining and leaf chewing insects that feed on myrtle oak. Total foliar N declined and C:N ratios increased significantly in oaks in elevated CO2 chambers. The percentages of leaves damaged by either leafminers or leaf chewers tended to be lower in elevated compared to ambient chambers, but they co-occurred on leaves less than expected, regardless of CO2 treatment. Leaves that had been either mined or chewed exhibited a similar wounding or defensive response; they had an average of 25 and 21% higher protein binding ability, which is correlated with tannin concentration, compared to nondamaged control leaves, respectively. While the protein-binding ability (expressed as total percent tannin) of leaves from elevated CO2 was slightly higher than from leaves grown in ambient chambers, this difference was not significant. 相似文献
100.
Responses of fig wasps to host plant volatile cues 总被引:4,自引:0,他引:4
Fig wasps (Chalcidoidea; Agaonidae) are intimately associated with the 750 or so species of fig trees (Ficus, Moraceae). Each tree species is usually pollinated by a single species of wasp belonging to the subfamily Agaoninae, while other wasps of the family are parasitoids or seed predators. Previous experiments have shown that the wasps are attracted to the trees by volatiles emanating from the figs. Using fig-bearing trees and arrays of sticky traps baited with figs, we investigated the specificity of wasp attraction and its timing. The pollinators of two closely relatedFicus species were specifically attracted to figs of their host species and only at the time when figs were ready to be pollinated. Some nonpollinating fig wasps appear to respond to the same volatile cues. 相似文献