全文获取类型
收费全文 | 9757篇 |
免费 | 555篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 159篇 |
综合类 | 6篇 |
化学工业 | 1977篇 |
金属工艺 | 342篇 |
机械仪表 | 631篇 |
建筑科学 | 192篇 |
矿业工程 | 9篇 |
能源动力 | 391篇 |
轻工业 | 682篇 |
水利工程 | 34篇 |
石油天然气 | 12篇 |
无线电 | 1834篇 |
一般工业技术 | 1960篇 |
冶金工业 | 1078篇 |
原子能技术 | 162篇 |
自动化技术 | 872篇 |
出版年
2023年 | 112篇 |
2022年 | 157篇 |
2021年 | 278篇 |
2020年 | 216篇 |
2019年 | 184篇 |
2018年 | 250篇 |
2017年 | 279篇 |
2016年 | 322篇 |
2015年 | 231篇 |
2014年 | 345篇 |
2013年 | 600篇 |
2012年 | 570篇 |
2011年 | 699篇 |
2010年 | 500篇 |
2009年 | 527篇 |
2008年 | 505篇 |
2007年 | 409篇 |
2006年 | 347篇 |
2005年 | 344篇 |
2004年 | 297篇 |
2003年 | 257篇 |
2002年 | 274篇 |
2001年 | 234篇 |
2000年 | 221篇 |
1999年 | 238篇 |
1998年 | 444篇 |
1997年 | 264篇 |
1996年 | 196篇 |
1995年 | 132篇 |
1994年 | 138篇 |
1993年 | 114篇 |
1992年 | 63篇 |
1991年 | 76篇 |
1990年 | 52篇 |
1989年 | 48篇 |
1988年 | 37篇 |
1987年 | 49篇 |
1986年 | 30篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 25篇 |
1982年 | 16篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 20篇 |
1978年 | 11篇 |
1977年 | 16篇 |
1976年 | 38篇 |
1975年 | 13篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Hee Seok Song Jae Kyeong Kim Yeong Bin Cho Soung Hie Kim 《Artificial Intelligence Review》2004,21(2):161-184
Customer retention is an increasinglypressing issue in today's competitiveenvironment. This paper proposes a personalizeddefection detection and prevention procedurebased on the observation that potentialdefectors have a tendency to take a couple ofmonths or weeks to gradually change theirbehaviour (i.e., trim-out their usage volume)before their eventual withdrawal. For thispurpose, we suggest a SOM (Self-Organizing Map)based procedure to determine the possiblestates of customer behaviour from pastbehaviour data. Based on this staterepresentation, potential defectors aredetected by comparing their monitoredtrajectories of behaviour states with frequentand confident trajectories of past defectors.Also, the proposed procedure is extended toprevent the defection of potential defectors byrecommending the desirable behaviour state forthe next period so as to lower the likelihoodof defection. For the evaluation of theproposed procedure, a case study has beenconducted for a Korean online game site. Theresult demonstrates that the proposed procedureis effective for defection prevention andefficiently detects potential defectors withoutdeterioration of prediction accuracy whencompared to that of the MLP (Multi-LayerPerceptron) neural networks. 相似文献
132.
Although multiphoton fluorescence excitation microscopy has improved the depth at which useful fluorescence images can be collected in biological tissues, the reach of multiphoton fluorescence excitation microscopy is nonetheless limited by tissue scattering and spherical aberration. Scattering can be reduced in fixed samples by mounting in a medium whose refractive index closely matches that of the fixed material. Using optical 'clearing', the effects of refractive index heterogeneity on signal attenuation with depth are investigated. Quantitative measurements show that by mounting kidney tissue in a high refractive index medium, less than 50% of signal attenuates in 100 μm of depth. 相似文献
133.
B. C. Pak B. S. Cho B. J. Baek C. S. Kim B. G. Min 《Journal of Mechanical Science and Technology》1993,7(3):223-230
Hydrodynamic comparison of two polymer valves with two mechanical valves is presented. The valves were perfused in a steady
flow system, and comparisons between the valves were made on the transvalvular pressure distribution and drop, opening area,
and leakage volume. Particular emphasis was placed on a slit-type bileaflet polymer valve which was newly designed and fabricated
in our research group. The results showed that the functional characteristics of a slit-type bileaflet polymer valve compared
favorably with that of mechanical valves. This valve may be a viable and inexpensive alternative, especially for short-term
use in TAH or VAD systems. 相似文献
134.
E. S. Lee J. K. Won Y. J. Chun M. W. Cho W. S. Cho J. H. Lee 《The International Journal of Advanced Manufacturing Technology》2007,31(11-12):1101-1108
The machinable ceramic Si3N4-BN is a material which is increasingly being employed for automobile bearings and machinable ceramics. This material is very hard and has high resistance against volatile temperature and wear. It's efficient quality and accurate surfaces have always been of high demand for many applications in the industrial field. Besides, this material is varied by the percentage of BN contained in it, and the characteristics of lapping also varies according to this percentage of BN. Hence, in-process electrolytic dressing for ultra-precision lapping was introduced and used to experiment with the differing BN percentages in machinable ceramic Si3 N4. Metal-bonded super-abrasive diamond lapping wheels have superior qualities such as high bond strength, high stability and high machinability. The major problems encountered are wheel loading and glazing, which impedes the effectiveness of the cast-iron bonded diamond lapping wheel and, therefore, dressing should be considered. In this respect, in-process electrolytic dressing (IED) is proposed as an effective method regarding continuous protruding abrasives on the surface of wheels, whereby loading and glazing phenomena can apparently disappear. In this paper, the machining characteristics of machinable ceramic Si3N4-BN have been studied by adapting the IED lapping process in terms of the percentage of h-BN material. 相似文献
135.
Soojeong Cho Tae Soup Shim Ju Hyeon Kim Dong‐Hyun Kim Shin‐Hyun Kim 《Advanced materials (Deerfield Beach, Fla.)》2017,29(22)
Black melanin inks are prepared to selectively exhibit colors under strong light, inspired by human hair. High absorbance of melanin suppresses multiple scattering, causing resonant Mie scattering predominant. Various colors can be developed as the resonant wavelength dictated by nanosphere diameter. Therefore, the melanin inks can be used to encrypt and selectively disclose multicolor patterns for anticounterfeiting applications. 相似文献
136.
Genipin is a protein cross-linking agent extracted from Gardenia (Gardenia jasminoides Ellis) fruits. This fruit has conventionally been used as a Chinese herbal medicine for the treatment of inflammation and jaundice and as an edible colorant in oriental countries. Uncoupling protein (UCP)-2 is a member of the family of uncoupling proteins, which are anion transporters positioned in the mitochondrial inner membrane. Genipin has been shown to have hepatoprotective activity, acting as an effective antioxidant and inhibitor of mitochondrial UCP2, and is also reported to exert significant anticancer effects. In this review, the author presents the latest progress of genipin as an anticancer agent and concisely describes its various mechanisms of action. In brief, genipin inhibits UCP2 to attenuate generation of reactive oxygen species (ROS), leading to ROS/c-Jun N-terminal kinase-dependent apoptosis of cancer cells. Genipin also increases the tissue inhibitors of matrix metalloproteases (MMP)-2, a kind of tumor promoter in a variety of cancers, as well as induces caspase-dependent apoptosis in in vitro and in vivo models. These findings suggest that genipin can serve as a promising novel antitumor agent that could be applicable for chemotherapy and/or chemoprevention for cancers. 相似文献
137.
138.
K. D. Irwin H. M. Cho W. B. Doriese J. W. Fowler G. C. Hilton M. D. Niemack C. D. Reintsema D. R. Schmidt J. N. Ullom L. R. Vale 《Journal of Low Temperature Physics》2012,167(5-6):588-594
Multiplexers based on the modulation of superconducting quantum interference devices are now regularly used in multi-kilopixel arrays of superconducting detectors for astrophysics, cosmology, and materials analysis. Over the next decade, much larger arrays will be needed. These larger arrays require new modulation techniques and compact multiplexer elements that fit within each pixel. We present a new in-focal-plane code-division multiplexer that provides multiplexing elements with the required scalability. This code-division multiplexer uses compact lithographic modulation elements that simultaneously multiplex both signal outputs and superconducting transition-edge sensor (TES) detector bias voltages. It eliminates the shunt resistor used to voltage bias TES detectors, greatly reduces power dissipation, allows different dc bias voltages for each TES, and makes all elements sufficiently compact to fit inside the detector pixel area. These in-focal plane code-division multiplexers can be combined with multi-GHz readout based on superconducting microresonators to scale to even larger arrays. 相似文献
139.
Hannah R. Hall Cressida Mahung Julia L. M. Dunn Laurel M. Kartchner Roland F. Seim Bruce A. Cairns Shannon M. Wallet Robert Maile 《International journal of molecular sciences》2022,23(15)
Severe burn injury leads to a cascade of local and systemic immune responses that trigger an extreme state of immune dysfunction, leaving the patient highly susceptible to acute and chronic infection. When combined with inhalation injury, burn patients have higher mortality and a greater chance of developing secondary respiratory complications including infection. No animal model of combined burn and inhalation injury (B+I) exists that accurately mirrors the human clinical picture, nor are there any effective immunotherapies or predictive models of the risk of immune dysfunction. Our earlier work showed that the mechanistic/mammalian target of rapamycin (mTOR) pathway is activated early after burn injury, and its chemical blockade at injury reduced subsequent chronic bacterial susceptibility. It is unclear if mTOR plays a role in the exacerbated immune dysfunction seen after B+I injury. We aimed to: (1) characterize a novel murine model of B+I injury, and (2) investigate the role of mTOR in the immune response after B+I injury. Pulmonary and systemic immune responses to B+I were characterized in the absence or presence of mTOR inhibition at the time of injury. Data describe a murine model of B+I with inhalation-specific immune phenotypes and implicate mTOR in the acute immune dysfunction observed. 相似文献
140.
Chao-Wei Chuang Kuo-Pin Chang Hsin-Yen Cho Tzu-Hsien Chuang Meng-Cheng Yu Chao-Liang Wu Sheng-Nan Wu 《International journal of molecular sciences》2022,23(13)
Lutein (β,ε-carotene-3,3′-diol), a xanthophyll carotenoid, is found in high concentrations in the macula of the human retina. It has been recognized to exert potential effectiveness in antioxidative and anti-inflammatory properties. However, whether and how its modifications on varying types of plasmalemmal ionic currents occur in electrically excitable cells remain incompletely answered. The current hypothesis is that lutein produces any direct adjustments on ionic currents (e.g., hyperpolarization-activated cation current, Ih [or funny current, If]). In the present study, GH3-cell exposure to lutein resulted in a time-, state- and concentration-dependent reduction in Ih amplitude with an IC50 value of 4.1 μM. There was a hyperpolarizing shift along the voltage axis in the steady-state activation curve of Ih in the presence of this compound, despite being void of changes in the gating charge of the curve. Under continued exposure to lutein (3 μM), further addition of oxaliplatin (10 μM) or ivabradine (3 μM) could be effective at either reversing or further decreasing lutein-induced suppression of hyperpolarization-evoked Ih, respectively. The voltage-dependent anti-clockwise hysteresis of Ih responding to long-lasting inverted isosceles-triangular ramp concentration-dependently became diminished by adding this compound. However, the addition of 10 μM lutein caused a mild but significant suppression in the amplitude of erg-mediated or A-type K+ currents. Under current-clamp potential recordings, the sag potential evoked by long-lasting hyperpolarizing current stimulus was reduced under cell exposure to lutein. Altogether, findings from the current observations enabled us to reflect that during cell exposure to lutein used at pharmacologically achievable concentrations, lutein-perturbed inhibition of Ih would be an ionic mechanism underlying its changes in membrane excitability. 相似文献