全文获取类型
收费全文 | 44631篇 |
免费 | 3680篇 |
国内免费 | 1761篇 |
专业分类
电工技术 | 3381篇 |
综合类 | 3948篇 |
化学工业 | 2064篇 |
金属工艺 | 3492篇 |
机械仪表 | 6227篇 |
建筑科学 | 4041篇 |
矿业工程 | 1431篇 |
能源动力 | 1354篇 |
轻工业 | 1561篇 |
水利工程 | 905篇 |
石油天然气 | 2419篇 |
武器工业 | 652篇 |
无线电 | 2814篇 |
一般工业技术 | 8854篇 |
冶金工业 | 1253篇 |
原子能技术 | 286篇 |
自动化技术 | 5390篇 |
出版年
2024年 | 175篇 |
2023年 | 456篇 |
2022年 | 964篇 |
2021年 | 1024篇 |
2020年 | 1175篇 |
2019年 | 865篇 |
2018年 | 915篇 |
2017年 | 1290篇 |
2016年 | 1468篇 |
2015年 | 1711篇 |
2014年 | 2601篇 |
2013年 | 2310篇 |
2012年 | 3226篇 |
2011年 | 3397篇 |
2010年 | 2662篇 |
2009年 | 2645篇 |
2008年 | 2459篇 |
2007年 | 3064篇 |
2006年 | 2744篇 |
2005年 | 2333篇 |
2004年 | 1898篇 |
2003年 | 1789篇 |
2002年 | 1412篇 |
2001年 | 1336篇 |
2000年 | 1123篇 |
1999年 | 931篇 |
1998年 | 757篇 |
1997年 | 623篇 |
1996年 | 530篇 |
1995年 | 436篇 |
1994年 | 368篇 |
1993年 | 250篇 |
1992年 | 226篇 |
1991年 | 192篇 |
1990年 | 143篇 |
1989年 | 140篇 |
1988年 | 97篇 |
1987年 | 52篇 |
1986年 | 27篇 |
1985年 | 35篇 |
1984年 | 31篇 |
1983年 | 36篇 |
1982年 | 31篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1965年 | 19篇 |
1962年 | 7篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
High amplitude non-linear acoustic methods have shown potential for the identification of micro damage in brittle materials such as concrete. Commonly, these methods evaluate a non-linearity parameter from the relative change in frequency and attenuation with strain amplitude. Here, a novel attenuation model is introduced to describe the free reverberation from a standard impact resonance frequency test, together with an algorithm for estimating the unknown model coefficients. The non-linear variation can hereby by analyzed over a wider dynamic range as compared to conventional methods. The experimental measurement is simple and fully compatible with the standardized free-free linear impact frequency test. 相似文献
4.
A small handful of recent studies have addressed a phenomenon known as “phantom vibration syndrome”. This refers to when phone users perceive their device to vibrate, indicating that a call or text is incoming, when in fact the phone did not vibrate at all. Though these studies show that most users do not find phantom vibration hallucinations to be very bothersome, they also find that a large majority of users experience this phenomenon. This paper explores what the striking prevalence of phantom vibration syndrome means for our contemporary relationships with technology. I begin with a review of the theories purporting to explain these data, which largely rely on particular understandings of the brain. Next I develop an alternative theory of phantom vibration syndrome based on insights from the philosophical tradition of phenomenology. This account considers the ways users develop bodily and perceptual habits regarding how the phone is understood and used. By critically contrasting these different theories, we can refine our questions about what the high prevalence of phantom vibration syndrome implies about our contemporary technological situation. 相似文献
5.
In recent years, many tidal turbine projects have been developed using composites blades. Tidal turbine blades are subject to ocean forces and sea water aggressions, and the reliability of these components is crucial to the profitability of ocean energy recovery systems. The majority of tidal turbine developers have preferred carbon/epoxy blades, so there is a need to understand how prolonged immersion in the ocean affects these composites. In this study the long term behaviour of different carbon/epoxy composites has been studied using accelerated ageing tests. A significant reduction of composite strengths has been observed after saturation of water in the material. For longer immersions only small further changes in these properties occur. No significant changes have been observed for moduli nor for composite toughness. The effect of sea water ageing on damage thresholds and kinetics has been studied and modelled. After saturation, the damage threshold is modified while kinetics of damage development remain the same. 相似文献
6.
A method for simultaneous measurement of the thickness and density for Glass Fiber-Reinforced Polymer (GFRP) laminate plates with ultrasonic waves in C-Scan mode is presented in the form of maps. The method uses three different signals in immersion pulse-echo C-Scan mode. The maps obtained based on the density show the heterogeneity of the material at high resolution at the pixel level (1 × 1 mm2) and therefore they represent an efficient tool to assess and evaluate the damage of the composite structures after manufacturing and after an applied mechanical loading. 相似文献
7.
This paper addresses the nonlinear stress-strain response in glass fibre non-crimp fabric reinforced vinylester composite laminates subjected to in-plane tensile loading. The nonlinearity is shown to be a combination of brittle and plastic failure. It is argued that the shift from plastic to brittle behaviour in the vinylester is caused by the state of stress triaxiality caused by the interaction between fibre and vinylester. A model combining damage and plasticity is calibrated and evaluated using data from extensive experimental testing. The onset of damage is predicted using the Puck failure criterion, and the evolution of damage is calibrated from the observed softening in plies loaded in transverse tension. Shear loading beyond linear elastic response is observed to result in irreversible strains. A yield criterion is implemented for shear deformation. A strain hardening law is fitted to the stress-strain response observed in shear loaded plies. Experimental results from a selection of laminates with different layups are used to verify the numerical models. A complete set of model parameters for predicting elastic behaviour, strength and post failure softening is presented for glass fibre non-crimped fabric reinforced vinylester. The predicted behaviour from using these model parameters are shown to be in good agreement with experimental results. 相似文献
8.
In this study, the crystal structure, thermal, oxygen transport, electrical conductivity and electrochemical properties of the perovskite NdBa0.5Sr0.5Co2O5+δ (NBSC55) are investigated. In the temperature range of 250 °C–350 °C, the weight loss upon heating was due to a partial loss of lattice oxygen and along with a reduction of Co4+ to Co3+. The tend of weight-loss slows down as temperature increased above 350 °C indicating a reduction of Co3+ to Co2+ during this stage. The oxygen migration is dominated by surface exchange process at high temperature range (650-800 °C); however, the bulk diffusion process prevails at low temperature range (500–600 °C). For long-term testing, the polarization resistance of NBSC55 increases gradually form 3.13 Ω cm2 for 2 h to 3.34 Ω cm2 for 96 h at 600 °C and an increasing-rate for polarization resistance is around 0.22% h?1. The power density of the single cell with NBSC55 cathode reached 341 mW cm?2 at 800 °C. 相似文献
9.
Simone Grassi Oscar Campuzano Mnica Coll Francesca Cazzato Georgia Sarquella-Brugada Riccardo Rossi Vincenzo Arena Josep Brugada Ramon Brugada Antonio Oliva 《International journal of molecular sciences》2021,22(8)
Inherited cardiomyopathies are frequent causes of sudden cardiac death (SCD), especially in young patients. Despite at the autopsy they usually have distinctive microscopic and/or macroscopic diagnostic features, their phenotypes may be mild or ambiguous, possibly leading to misdiagnoses or missed diagnoses. In this review, the main differential diagnoses of hypertrophic cardiomyopathy (e.g., athlete’s heart, idiopathic left ventricular hypertrophy), arrhythmogenic cardiomyopathy (e.g., adipositas cordis, myocarditis) and dilated cardiomyopathy (e.g., acquired forms of dilated cardiomyopathy, left ventricular noncompaction) are discussed. Moreover, the diagnostic issues in SCD victims affected by phenotype-negative hypertrophic cardiomyopathy and the relationship between myocardial bridging and hypertrophic cardiomyopathy are analyzed. Finally, the applications/limits of virtopsy and post-mortem genetic testing in this field are discussed, with particular attention to the issues related to the assessment of the significance of the genetic variants. 相似文献
10.
Structural bonding and bonded repairs of composite materials become more and more important. Understanding the strain within the bondline leads to suitable bonding design. For new design approaches the strain distribution within the bondline has to be analyzed. Thus, often finite element analysis (FE) are used. However, a huge challenge is the availability of reliable material properties for the adhesives and their validation. Previous work has shown that it is possible to measure the small displacements resulting within thin epoxy film adhesives using high resolution digital image correlation (DIC). In this work a 2D DIC setup with a high resolution consumer camera is used to visualize the strain distribution within the bondline over the length of the joint as well as over the adhesive thickness. Therefore, single lap joints with thick aluminum adherends according to ASTM D 5656 are manufactured and tested. Local 2D DIC strain measurements are performed and analyzed. Two different camera setups are used and compared. The evaluation provides reliable material data and enables a look insight the bondline. The results of the full field strain data measured with DIC are compared with numerical simulations. Thus, material models as well as chosen parameters for the adhesive are validated. Compared to extensometers, giving only point-wise information for fixed measuring points, the DIC allows a virtual point-wise inspection along the complete bondline. Furthermore, it allows measuring close to the bondline to reduce the influence of adherend deformation. 相似文献