全文获取类型
收费全文 | 4531篇 |
免费 | 132篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 53篇 |
综合类 | 8篇 |
化学工业 | 647篇 |
金属工艺 | 145篇 |
机械仪表 | 82篇 |
建筑科学 | 168篇 |
能源动力 | 61篇 |
轻工业 | 295篇 |
水利工程 | 9篇 |
石油天然气 | 7篇 |
无线电 | 341篇 |
一般工业技术 | 589篇 |
冶金工业 | 1865篇 |
原子能技术 | 73篇 |
自动化技术 | 321篇 |
出版年
2022年 | 28篇 |
2021年 | 47篇 |
2020年 | 29篇 |
2019年 | 51篇 |
2018年 | 61篇 |
2017年 | 48篇 |
2016年 | 66篇 |
2015年 | 47篇 |
2014年 | 76篇 |
2013年 | 136篇 |
2012年 | 103篇 |
2011年 | 131篇 |
2010年 | 99篇 |
2009年 | 94篇 |
2008年 | 94篇 |
2007年 | 110篇 |
2006年 | 107篇 |
2005年 | 82篇 |
2004年 | 96篇 |
2003年 | 86篇 |
2002年 | 84篇 |
2001年 | 59篇 |
2000年 | 94篇 |
1999年 | 134篇 |
1998年 | 509篇 |
1997年 | 317篇 |
1996年 | 250篇 |
1995年 | 156篇 |
1994年 | 114篇 |
1993年 | 123篇 |
1992年 | 50篇 |
1991年 | 66篇 |
1990年 | 55篇 |
1989年 | 64篇 |
1988年 | 62篇 |
1987年 | 63篇 |
1986年 | 52篇 |
1985年 | 42篇 |
1984年 | 37篇 |
1983年 | 35篇 |
1982年 | 36篇 |
1981年 | 26篇 |
1980年 | 47篇 |
1979年 | 33篇 |
1978年 | 39篇 |
1977年 | 71篇 |
1976年 | 125篇 |
1975年 | 30篇 |
1974年 | 35篇 |
1973年 | 27篇 |
排序方式: 共有4664条查询结果,搜索用时 15 毫秒
1.
Daniela Fogli Antonio Piccinno Stefan Carmien Gerhard Fischer 《Behaviour & Information Technology》2020,39(1):27-46
ABSTRACTThe digital age of the future is ‘not out there to be discovered’, but it needs to be ‘designed’. The design challenge has to address questions about how we want to live, work, and learn (as individuals and as communities) and what we value and appreciate, e.g.: reflecting on quality of life and creating inclusive societies. An overriding design trade-off for the digital age is whether new developments will increase the digital divide or will create more inclusive societies. Sustaining inclusive societies means allowing people of all ages and all abilities to exploit information technologies for personally meaningful activities. Meta-design fosters the design of socio-technical environments that end-user developers can modify and evolve at use time to improve their quality of life and favour their inclusion in the society. This paper describes three case studies in the domain of assistive technologies in which end users themselves cannot act as end-user developers, but someone else (e.g.: a caregiver or a clinician) must accept this role requiring multi-tiered architectures. The design trade-offs and requirements for meta-design identified in the context of the case studies and other researchers’ projects are described to inform the development of future socio-technical environments focused on social inclusion. 相似文献
2.
Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant. 相似文献
3.
Annika Jahn Anton Hoffmann Luisa Blaesing Fabian Kunde Martin Bertau Martina Bremer Steffen Fischer 《化学,工程师,技术》2020,92(11):1733-1740
The enzymatic conversion of lignins, possibly in combination with electrochemical oxidation, makes aromatics such as syringol, guaiacol, vanillin and catechol available in the qualities required by the fragrance industry. The lignins were obtained by soda digestion from wheat straw and Miscanthus, characterized and then converted with laccases. The overall yield amounted up to 9 wt % with a product spectrum confined to four substances. Catechol was the major product, with a fraction of ≈75 %. It can easily be isolated by extraction with acetone. 相似文献
4.
5.
6.
7.
Fischer B. Ghetti A. Selmi L. Bet R. Sangiorgi E. 《Electron Devices, IEEE Transactions on》1997,44(2):288-296
In this paper, new homogeneous hot-electron injection data at 300 K and 77 K is provided covering applied voltages from well below to well above the Si-SiO2 barrier height, and a wide range of oxide fields. We found that, in contrast to the MOSFET case, homogeneous injection shows two different regimes for accelerating voltages below and above the barrier height. A simple interpretation of the data is proposed, and supported by Monte Carlo (MC) simulations of the injection experiment. Essentially, the two regimes are the signature of a marked transition between an electron population mostly heated by the electric field, and a tail population created by additional but less efficient energy gain mechanisms, leading to a sharp transition in the carrier distribution function. The details of the bias and temperature dependence of injection are then interpreted as the combined effect of tunneling and carrier distribution. Furthermore, possible implications on MOSFET gate currents are briefly discussed 相似文献
8.
The ability of oral lactobacilli to coaggregate with streptococci and actinomycetes was investigated. Of the 7 species of lactobacilli studied, only two were capable of coaggregation and the coaggregation was restricted to streptococci. Lactobacillus salivarius strains (2/4) coaggregated with Streptococcus salivarius, Streptococcus gordonii, Streptococcus crista and tufted Streptococcus sanguis II strains. Lactobacillus fermentum (2/3) coaggregated with S. gordonii and S. sanguis. The coaggregation between L. salivarius and S. salivarius, S. gordonii or tufted S. sanguis II strains was mediated by a protein on the surface of the lactobacilli and was not inhibited by lactose. The coaggregation between L. fermentum and the streptococci was mediated by protein on the surface of the streptococci and was inhibited by lactose. 相似文献
9.
KW Sax SM Strakowski PE Keck SL McElroy SA West SP Stanton 《Canadian Metallurgical Quarterly》1998,44(8):784-786
BACKGROUND: This study examined patients with a first-episode of affective psychosis during acute and compensated states in order to determine whether changes in attentional functioning over time were accompanied by changes in the severity of psychotic or affective symptoms. METHODS: Attentional performance was measured in patients (n = 27) using the degraded-stimulus continuous Performance Test (CPT) and symptoms were assessed at the time of index hospitalization, and 2 months after discharge. A comparison group of normal volunteers (n = 31) also performed the CPT two months apart. RESULTS: Patients performed significantly worse than controls at the initial testing but not at follow-up. The improvement in attentional performance significantly correlated with decreased severity of manic symptoms. CONCLUSIONS: Results suggest attentional dysfunction is a state-dependent characteristic of mania, and may provide an additional measure of clinical improvement following treatment. 相似文献
10.
Sodium tolerance in yeast is disrupted by mutations in calcineurin, a Ca2+/calmodulin-dependent protein phosphatase, which is required for modulation of Na+ uptake and efflux mechanisms. Five Na+-tolerant mutants were isolated by selecting for suppressors of calcineurin mutations, and mapped to the PMA1 gene, encoding the plasma membrane H+-ATPase. One mutant, pma1-alpha4, which has the single amino acid change Glu367 --> Lys at a highly conserved site within the catalytic domain of the ATPase, was analyzed in detail to determine the mechanism of Na+ tolerance. After exposure to Na+ in the culture medium, 22Na influx in the pma1 mutant was reduced 2-fold relative to control, consistent with a similar decrease in ATPase activity. Efflux of 22Na from intact cells was relatively unchanged in the pma1 mutant. However, selective permeabilization of the plasma membrane revealed that mutant cells retained up to 80% of intracellular Na+ within a slowly exchanging pool. We show that NHX1, a novel gene homologous to the mammalian NHE family of Na+/H+ exchangers, is required for Na+ sequestration in yeast and contributes to the Na+-tolerant phenotype of pma1-alpha4. 相似文献