首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   57260篇
  免费   3851篇
  国内免费   600篇
电工技术   1314篇
综合类   668篇
化学工业   11724篇
金属工艺   2549篇
机械仪表   3797篇
建筑科学   1743篇
矿业工程   222篇
能源动力   2408篇
轻工业   4555篇
水利工程   424篇
石油天然气   331篇
武器工业   122篇
无线电   8949篇
一般工业技术   11589篇
冶金工业   4229篇
原子能技术   744篇
自动化技术   6343篇
  2024年   132篇
  2023年   823篇
  2022年   1333篇
  2021年   2077篇
  2020年   1527篇
  2019年   1502篇
  2018年   1740篇
  2017年   1745篇
  2016年   2103篇
  2015年   1724篇
  2014年   2628篇
  2013年   3541篇
  2012年   3847篇
  2011年   4474篇
  2010年   3304篇
  2009年   3363篇
  2008年   3270篇
  2007年   2582篇
  2006年   2330篇
  2005年   1983篇
  2004年   1763篇
  2003年   1658篇
  2002年   1474篇
  2001年   1241篇
  2000年   1107篇
  1999年   1018篇
  1998年   1624篇
  1997年   1074篇
  1996年   866篇
  1995年   610篇
  1994年   503篇
  1993年   423篇
  1992年   313篇
  1991年   290篇
  1990年   274篇
  1989年   246篇
  1988年   210篇
  1987年   172篇
  1986年   122篇
  1985年   118篇
  1984年   99篇
  1983年   68篇
  1982年   41篇
  1981年   40篇
  1980年   44篇
  1979年   34篇
  1978年   31篇
  1977年   38篇
  1976年   64篇
  1973年   21篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
This study investigates the impact of lighting colors on subjective judgments of fabric: in particular, whether the influence of lighting varies depending on fabric types and color combinations. We conducted two visual assessments. In Study 1 (N = 44), eight illuminants and six types of fabric were presented as cloth stimuli. Derived from the literature review, four sets of adjectives (humble-luxurious, cool-warm, old-new, and not preferred-preferred) were used as metrics. In Study 2 (N = 41), five sets of fabric color combination swatches were assessed under lighting conditions that were identical to those of Study 1. Three bipolar scales (ordinary-characterful, classic-modern, and soft-rigid), were employed from factor analysis along with three unipolar scales (luxurious, preferred, harmonious with lighting). The results showed that hue characteristics of lighting and cloth types influenced participants' perceptions of the fabric. Overall, white lighting with 4000 K was the most preferred and luxurious lighting across various types of clothes, while a pinkish white with 4700 K (duv = −0.0127) was the best matched in every color combination. In addition, there were interaction effects between lighting colors, clothes types, and fabric color combinations with regard to each of the perceptual qualities. This study provides empirical evidence for optimally match lighting colors with fabric in the presentation of fabric goods.  相似文献   
22.
A series of anionic conjugated polyelectrolytes (CPEs) is synthesized based on poly(fluorene-co-phenylene) by varying the side-chain ionic density from two to six per repeat units (MPS2-TMA, MPS4-TMA, and MPS6-TMA). The effect of MPS2, 4, 6-TMA as interlayers on top of a hole-extraction layer of poly(bis(4-phenyl)-2,4,6-trimethylphenylamine (PTAA) is investigated in inverted perovskite solar cells (PeSCs). Owing to the improved wettability of perovskites on hydrophobic PTAA with the CPEs, the PeSCs with CPE interlayers demonstrate a significantly enhanced device performance, with negligible device-to-device dependence relative to the reference PeSC without CPEs. By increasing the ionic density in the MPS-TMA interlayers, the wetting, interfacial defect passivation, and crystal growth of the perovskites are significantly improved without increasing the series resistance of the PeSCs. In particular, the open-circuit voltage increases from 1.06 V for the PeSC with MPS2-TMA to 1.11 V for the PeSC with MPS6-TMA. The trap densities of the PeSCs with MPS2,4,6-TMA are further analyzed using frequency-dependent capacitance measurements. Finally, a large-area (1 cm2) PeSC is successfully fabricated with MPS6-TMA, showing a power conversion efficiency of 18.38% with negligible hysteresis and a stable power output under light soaking for 60 s.  相似文献   
23.
24.
We investigated some properties of the hydride Mg2FeH6 substituted with yttrium by a first principles calculation. Some experimental results showed that 4d transition metal, yttrium serves as a good catalyst for magnesium based hydrogen storage alloys, but there are a few theoretical studies about magnesium based hydrides substituted with it. Mg2FeH6 is regarded as a cheaper material than pure MgH2, while it is crystalized into Fm3m structure (space group 225). Although it has high hydrogen storage capacity, many investigations have not been devoted to it due to its extremely high thermodynamic stability. The yttrium substituted Mg2FeH6 exhibits very low energy of formation, and its desorption temperature, 75 °C is very suitable for practical hydrogen storage applications. Our results showed that Mg2FeH6 is destabilized effectively by yttrium substitution and introducing vacancy defects has additive effect to the improvement of dehydrogenation performance.  相似文献   
25.
Tryptophan halogenases are found in diverse organisms and catalyze regiospecific halogenation. They play an important role in the biosynthesis of halogenated indole alkaloids, which are biologically active and of therapeutic importance. Here, a tryptophan 6-halogenase (SatH) from Streptomyces albus was characterized by using a whole-cell reaction system in Escherichia coli. SatH showed substrate specificity for chloride and bromide ions, leading to regiospecific halogenation at the C6-position of l -tryptophan. In addition, SatH exhibited higher performance in bromination than that of previously reported tryptophan halogenases in the whole-cell reaction system. Through structure-based protein mutagenesis, it has been revealed that two consecutive residues, A78/V79 in SatH and G77/I78 in PyrH, are key determinants in the regioselectivity difference between tryptophan 6- and 5-halogenases. Substituting the AV with GI residues switched the regioselectivity of SatH by moving the orientation of tryptophan. These data contribute to an understanding of the key residues that determine the regioselectivity of tryptophan halogenases.  相似文献   
26.
27.
Journal of Mechanical Science and Technology - This study delivers equations useful for low-height pleated fibrous filter design: two pressure drop equations and one set of optimum design equations...  相似文献   
28.
29.
Over the past decades, the number of patients with dry eye disease (DED) has increased dramatically. The incidence of DED is higher in Asia than in Europe and North America, suggesting the involvement of cultural or racial factors in DED etiology. Although many definitions of DED have been used, discrepancies exist between the various definitions of dry eye disease (DED) used across the globe. This article presents a clinical consensus on the definition of DED, as formulated in four meetings with global DED experts. The proposed new definition is as follows: “Dry eye is a multifactorial disease characterized by a persistently unstable and/or deficient tear film (TF) causing discomfort and/or visual impairment, accompanied by variable degrees of ocular surface epitheliopathy, inflammation and neurosensory abnormalities.” The key criteria for the diagnosis of DED are unstable TF, inflammation, ocular discomfort and visual impairment. This definition also recommends the assessment of ocular surface epitheliopathy and neurosensory abnormalities in each patient with suspected DED. It is easily applicable in clinical practice and should help practitioners diagnose DED consistently. This consensus definition of DED should also help to guide research and clinical trials that, to date, have been hampered by the lack of an established surrogate endpoint.  相似文献   
30.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号