全文获取类型
收费全文 | 27322篇 |
免费 | 1190篇 |
国内免费 | 55篇 |
专业分类
电工技术 | 346篇 |
综合类 | 62篇 |
化学工业 | 5842篇 |
金属工艺 | 687篇 |
机械仪表 | 578篇 |
建筑科学 | 1542篇 |
矿业工程 | 128篇 |
能源动力 | 876篇 |
轻工业 | 2451篇 |
水利工程 | 257篇 |
石油天然气 | 110篇 |
武器工业 | 1篇 |
无线电 | 2076篇 |
一般工业技术 | 4762篇 |
冶金工业 | 3954篇 |
原子能技术 | 173篇 |
自动化技术 | 4722篇 |
出版年
2023年 | 191篇 |
2022年 | 319篇 |
2021年 | 650篇 |
2020年 | 415篇 |
2019年 | 458篇 |
2018年 | 630篇 |
2017年 | 604篇 |
2016年 | 712篇 |
2015年 | 562篇 |
2014年 | 841篇 |
2013年 | 1832篇 |
2012年 | 1287篇 |
2011年 | 1770篇 |
2010年 | 1212篇 |
2009年 | 1310篇 |
2008年 | 1370篇 |
2007年 | 1271篇 |
2006年 | 1094篇 |
2005年 | 1025篇 |
2004年 | 859篇 |
2003年 | 786篇 |
2002年 | 713篇 |
2001年 | 463篇 |
2000年 | 436篇 |
1999年 | 438篇 |
1998年 | 480篇 |
1997年 | 422篇 |
1996年 | 421篇 |
1995年 | 381篇 |
1994年 | 366篇 |
1993年 | 344篇 |
1992年 | 315篇 |
1991年 | 221篇 |
1990年 | 290篇 |
1989年 | 270篇 |
1988年 | 216篇 |
1987年 | 213篇 |
1986年 | 205篇 |
1985年 | 240篇 |
1984年 | 258篇 |
1983年 | 206篇 |
1982年 | 208篇 |
1981年 | 204篇 |
1980年 | 182篇 |
1979年 | 196篇 |
1978年 | 157篇 |
1977年 | 154篇 |
1976年 | 201篇 |
1975年 | 165篇 |
1973年 | 144篇 |
排序方式: 共有10000条查询结果,搜索用时 913 毫秒
21.
Hefei Zhao Xiaoqing Xie Paul Read Benjamin Loseke Stephen Gamet Wenkuan Li Changmou Xu 《International Journal of Food Science & Technology》2021,56(2):825-837
Enriching the micronutrients, selenium (Se) and lithium (Li), in grapes to improve their nutraceutical properties were implemented by foliar application of organic fertiliser rich in Se and Li onto five grape cultivars. The effects of this biofortification on vine vigour, fruit quality, overall micronutrients and phenolic compounds also were investigated. Agronomic biofortification was found greatly increased the Se and Li content in the whole grape by multiple times, meanwhile it did not significantly affect the vine vigour and fruit quality of grapes. However, the biofortification did impact the Ionome (including all the mineral nutrients and trace elements) and phenolic compounds in grapes and this varied among cultivars. This study demonstrated foliar spray of organic Se/Li fertiliser was a very effective strategy to biofortify these micronutrients in grape berries, particularly in the skin, and therefore might be a promising strategy to increase the consumption and awareness of these grapes. 相似文献
22.
Environmental concerns continue to pose the challenge to replace petroleum-based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy-based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum-based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone-based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m2·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy-based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum-based foam Baydur 683. 相似文献
23.
Dr. Iain J. W. McKean Prof. Paul A. Hoskisson Prof. Glenn A. Burley 《Chembiochem : a European journal of chemical biology》2020,21(20):2890-2897
This Concept article describes the latest developments in the emerging area of late-stage biocatalytic alkylation. Central to these developments is the ability to efficiently prepare S-adenosyl methionine (SAM) cofactor analogues and couple this with enzymatic alkyl transfer. Recent developments in the enzymatic synthesis of SAM cofactor analogues are summarized first, followed by their application as alkyl transfer agents catalyzed by methyltransferases (MTases). Second, innovative methods to regenerate SAM cofactors by enzymatic cascades is reported. Finally, future opportunities towards establishing a generalized platform for late-stage alkylation are described. 相似文献
24.
25.
Paul Ocheje Ameh Nnabuk Okon Eddy 《Protection of Metals and Physical Chemistry of Surfaces》2018,54(6):1169-1181
Protection of Metals and Physical Chemistry of Surfaces - In this work, phthalic acid is investigated for its corrosion inhibition properties (for aluminum in solutions of HCl and H2SO4) through... 相似文献
26.
27.
Daniel Biedermann Jan Schneider Hendrik Drachsler 《Journal of Computer Assisted Learning》2021,37(5):1217-1231
Digital distractions can interfere with goal attainment and lead to undesirable habits that are hard to get red rid of. Various digital self-control interventions promise support to alleviate the negative impact of digital distractions. These interventions use different approaches, such as the blocking of apps and websites, goal setting, or visualizations of device usage statistics. While many apps and browser extensions make use of these features, little is known about their effectiveness. This systematic review synthesizes the current research to provide insights into the effectiveness of the different kinds of interventions. From a search of the ‘ACM’, ‘Springer Link’, ‘Web of Science’, ’IEEE Xplore’ and ‘Pubmed’ databases, we identified 28 digital self-control interventions. We categorized these interventions according to their features and their outcomes. The interventions showed varying degrees of effectiveness, and especially interventions that relied purely on increasing the participants' awareness were barely effective. For those interventions that sanctioned the use of distractions, the current literature indicates that the sanctions have to be sufficiently difficult to overcome, as they will otherwise be quickly dismissed. The overall confidence in the results is low, with small sample sizes, short study duration, and unclear study contexts. From these insights, we highlight research gaps and close with suggestions for future research. 相似文献
28.
Greg A. Breed Paul M. Severns Andrew M. Edwards 《Journal of the Royal Society Interface》2015,12(103)
Lévy flights have gained prominence for analysis of animal movement. In a Lévy flight, step-lengths are drawn from a heavy-tailed distribution such as a power law (PL), and a large number of empirical demonstrations have been published. Others, however, have suggested that animal movement is ill fit by PL distributions or contend a state-switching process better explains apparent Lévy flight movement patterns. We used a mix of direct behavioural observations and GPS tracking to understand step-length patterns in females of two related butterflies. We initially found movement in one species (Euphydryas editha taylori) was best fit by a bounded PL, evidence of a Lévy flight, while the other (Euphydryas phaeton) was best fit by an exponential distribution. Subsequent analyses introduced additional candidate models and used behavioural observations to sort steps based on intraspecific interactions (interactions were rare in E. phaeton but common in E. e. taylori). These analyses showed a mixed-exponential is favoured over the bounded PL for E. e. taylori and that when step-lengths were sorted into states based on the influence of harassing conspecific males, both states were best fit by simple exponential distributions. The direct behavioural observations allowed us to infer the underlying behavioural mechanism is a state-switching process driven by intraspecific interactions rather than a Lévy flight. 相似文献
29.
30.
Christian Veauthier Gunnar Gaede Helena Radbruch Klaus-Dieter Wernecke Friedemann Paul 《International journal of molecular sciences》2015,16(7):16514-16528
Quality of Life (QoL) is decreased in multiple sclerosis (MS), but studies about the impact of sleep disorders (SD) on health-related quality of Life (HRQoL) are lacking. From our original cohort, a cross-sectional polysomnographic (PSG) study in consecutive MS patients, we retrospectively analysed the previously unpublished data of the Nottingham Health Profile (NHP). Those MS patients suffering from sleep disorders (n = 49) showed significantly lower HRQoL compared to MS patients without sleep disorders (n = 17). Subsequently, we classified the patients into four subgroups: insomnia (n = 17), restless-legs syndrome, periodic limb movement disorder and SD due to leg pain (n = 24), obstructive sleep apnea (n = 8) and patients without sleep disorder (n = 17). OSA and insomnia patients showed significantly higher NHP values and decreased HRQoL not only for the sleep subscale but also for the “energy” and “emotional” area of the NHP. In addition, OSA patients also showed increased NHP values in the “physical abilities” area. Interestingly, we did not find a correlation between the objective PSG parameters and the subjective sleep items of the NHP. However, this study demonstrates that sleep disorders can reduce HRQoL in MS patients and should be considered as an important confounder in all studies investigating HRQoL in MS. 相似文献