全文获取类型
收费全文 | 23939篇 |
免费 | 1042篇 |
国内免费 | 32篇 |
专业分类
电工技术 | 322篇 |
综合类 | 38篇 |
化学工业 | 5128篇 |
金属工艺 | 377篇 |
机械仪表 | 471篇 |
建筑科学 | 1307篇 |
矿业工程 | 99篇 |
能源动力 | 619篇 |
轻工业 | 1846篇 |
水利工程 | 229篇 |
石油天然气 | 61篇 |
无线电 | 1792篇 |
一般工业技术 | 4458篇 |
冶金工业 | 4548篇 |
原子能技术 | 196篇 |
自动化技术 | 3522篇 |
出版年
2023年 | 199篇 |
2022年 | 118篇 |
2021年 | 502篇 |
2020年 | 338篇 |
2019年 | 431篇 |
2018年 | 536篇 |
2017年 | 463篇 |
2016年 | 632篇 |
2015年 | 559篇 |
2014年 | 749篇 |
2013年 | 1420篇 |
2012年 | 1161篇 |
2011年 | 1511篇 |
2010年 | 1078篇 |
2009年 | 1015篇 |
2008年 | 1149篇 |
2007年 | 1087篇 |
2006年 | 945篇 |
2005年 | 762篇 |
2004年 | 745篇 |
2003年 | 657篇 |
2002年 | 540篇 |
2001年 | 390篇 |
2000年 | 306篇 |
1999年 | 352篇 |
1998年 | 706篇 |
1997年 | 515篇 |
1996年 | 409篇 |
1995年 | 399篇 |
1994年 | 373篇 |
1993年 | 350篇 |
1992年 | 262篇 |
1991年 | 189篇 |
1990年 | 267篇 |
1989年 | 258篇 |
1988年 | 215篇 |
1987年 | 219篇 |
1986年 | 227篇 |
1985年 | 262篇 |
1984年 | 220篇 |
1983年 | 221篇 |
1982年 | 205篇 |
1981年 | 194篇 |
1980年 | 170篇 |
1979年 | 192篇 |
1978年 | 162篇 |
1977年 | 185篇 |
1976年 | 232篇 |
1975年 | 160篇 |
1974年 | 123篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Sy Thomas; Shore Lynn M.; Strauss Judy; Shore Ted H.; Tram Susanna; Whiteley Paul; Ikeda-Muromachi Kristine 《Canadian Metallurgical Quarterly》2010,95(5):902
On the basis of the connectionist model of leadership, we examined perceptions of leadership as a function of the contextual factors of race (Asian American, Caucasian American) and occupation (engineering, sales) in 3 experiments (1 student sample and 2 industry samples). Race and occupation exhibited differential effects for within- and between-race comparisons. With regard to within-race comparisons, leadership perceptions of Asian Americans were higher when race–occupation was a good fit (engineer position) than when race–occupation was a poor fit (sales position) for the two industry samples. With regard to between-race comparisons, leadership perceptions of Asian Americans were low relative to those of Caucasian Americans. Additionally, when race–occupation was a good fit for Asian Americans, such individuals were evaluated higher on perceptions of technical competence than were Caucasian Americans, whereas they were evaluated lower when race–occupation was a poor fit. Furthermore, our results demonstrated that race affects leadership perceptions through the activation of prototypic leadership attributes (i.e., implicit leadership theories). Implications for the findings are discussed in terms of the connectionist model of leadership and leadership opportunities for Asian Americans. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
992.
Ng Thomas W. H.; Feldman Daniel C.; Lam Simon S. K. 《Canadian Metallurgical Quarterly》2010,95(4):744
This study examined the relationships among psychological contract breaches, organizational commitment, and innovation-related behaviors (generating, spreading, implementing innovative ideas at work) over a 6-month period. Results indicate that the effects of psychological contract breaches on employees are not static. Specifically, perceptions of psychological contract breaches strengthened over time and were associated with decreased levels of affective commitment over time. Further, increased perceptions of psychological contract breaches were associated with decreases in innovation-related behaviors. We also found evidence that organizational commitment mediates the relationship between psychological contract breaches and innovation-related behaviors. These results highlight the importance of examining the nomological network of psychological contract breaches from a change perspective. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
994.
995.
996.
Thomas Arnold Dr. Georg Boehm Inga‐Maria Eichentopf Manuela Janietz Johannes Meister Axel Schindler 《真空研究与实践》2010,22(4):10-16
Plasma Jet Machining (PJM) is a surface figuring technology based on atmospheric plasma assisted chemical etching or deposition, respectively. In both cases a sub‐aperture plasma jet source is used combined with a CNC multi‐axes system for the processing of curved surfaces. It is under development for the surface figuring of a variety of optical materials by IOM for about 15 years. PJM is capable to figure deep aspheric or free‐form substrates with high material removal rate and high spatial resolution. Based on chemical reactions between plasma generated radicals and the surface PJM does not introduce any damage to the processed surface and sub‐surface region in contrast to abrasive techniques. Deterministic deposition of SiOx layers and subsequent proportional transfer using ion beams or polishing is another plasma jet based technique for surface figuring that extends the range of machinable materials. The article gives an overview on the current state of PJM development in IOM and shows examples of its application. 相似文献
997.
Sam Solomon Lovely Jacob H. Padma Kumar K. G. Gopchandran J. K. Thomas 《Journal of Materials Science: Materials in Electronics》2010,21(11):1132-1136
Ln0.9Eu0.1TiNbO6 (Ln = Pr, Nd, Sm, Dy and Y) ceramics have been prepared through the solid state ceramic route. The samples are calcined at
about 1,250 °C and sintered between 1,370 and 1,425 °C for 4 hours. Structure of the samples is analyzed using X-ray diffraction
method. Pr, Nd, Sm and Y based compounds form solid solutions while Dy based compound is a composite. The microstructure is
analyzed using Scanning Electron Microscopy. All the compositions have strong photoluminescence in the visible region. The
dielectric constant (ε
r
), the unloaded quality factor (Q
u
) and the temperature coefficient of resonant frequency (τ
f
) are measured in the microwave frequency region. The samples have relatively high ε
r
, high Q
u
× f and good thermal stability. Hence these materials are suitable for optoelectronic and dielectric resonator applications. 相似文献
998.
H. Padma Kumar Sumesh George J. K. Thomas Sam Solomon 《Journal of Materials Science: Materials in Electronics》2010,21(1):27-32
Bi substituted LnTiTaO6 (Ln = Ce, Pr and Nd) ceramics are prepared using the conventional solid state ceramic route. The materials are calcined at
1,150°C and sintered at 1,375°C. The structure is analysed using X-ray diffraction technique and the microstructure using
scanning electron microscopy. The microwave dielectric properties of the samples are measured using the cavity resonator method.
Substitution of Bi increases the dielectric constant and improves the thermal stability. A number of samples with improved
quality factor are obtained and can be used in practical microwave circuits. 相似文献
999.
Declan J. Curran Thomas J. Fleming Mark R. Towler Stuart Hampshire 《Journal of materials science. Materials in medicine》2010,21(4):1109-1120
Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)–zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0–5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200°C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700°C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000°C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200°C showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200°C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration. 相似文献
1000.
Jacob John R. Suriyakala Selvin Thomas Jude Martin Mendez Anitha Pius Sabu Thomas 《Journal of Materials Science》2010,45(11):2892-2901
Morphology, mechanical properties, thermal stability and gas transport behaviour of interpenetrating polymer networks (IPNs)
based on PI/PMMA have been investigated using various techniques. Crosslinking level of both phases and concentration of PMMA
were found to have noticeable effects on the compatibility of immiscible components during IPN formation. Effect of crosslinking
was studied by preparing IPNs with varying amount of crosslinker concentration in each phase. Crosslinking of both phases
facilitated deeper interpenetrations between both networks, and certain degree of compatibility is attained during IPN formation.
Nanometre-sized domains were observed for highly crosslinked IPN. Lower concentration of PMMA was found to favour phase mixing
more effectively than others. DSC curve of 65/35 IPN showed a broad transition arising from the α and β-relaxations of PMMA
due to the higher flexibility attained by mixing with the highly mobile PI chains. The mechanical properties of the IPNs were
correlated to the morphology of the system and 50/50 composition showed maximum mechanical properties among the studied compositions.
Mode of mechanical failure, thermal stability and gas transport behaviour were also analysed. IPNs having nanometre-sized
domains showed least gas permeability among the studied samples. 相似文献