全文获取类型
收费全文 | 965篇 |
免费 | 54篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 2篇 |
化学工业 | 239篇 |
金属工艺 | 13篇 |
机械仪表 | 20篇 |
建筑科学 | 12篇 |
矿业工程 | 1篇 |
能源动力 | 70篇 |
轻工业 | 31篇 |
水利工程 | 7篇 |
石油天然气 | 7篇 |
无线电 | 131篇 |
一般工业技术 | 226篇 |
冶金工业 | 73篇 |
原子能技术 | 3篇 |
自动化技术 | 193篇 |
出版年
2024年 | 4篇 |
2023年 | 23篇 |
2022年 | 36篇 |
2021年 | 43篇 |
2020年 | 38篇 |
2019年 | 35篇 |
2018年 | 41篇 |
2017年 | 30篇 |
2016年 | 40篇 |
2015年 | 35篇 |
2014年 | 61篇 |
2013年 | 105篇 |
2012年 | 47篇 |
2011年 | 60篇 |
2010年 | 46篇 |
2009年 | 50篇 |
2008年 | 54篇 |
2007年 | 32篇 |
2006年 | 18篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 18篇 |
2002年 | 17篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 23篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 5篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有1028条查询结果,搜索用时 578 毫秒
61.
Jing Yu Sathya Chary Saurabh Das John Tamelier Noshir S. Pesika Kimberly L. Turner Jacob N. Israelachvili 《Advanced functional materials》2011,21(16):3010-3018
Most geckos can rapidly attach and detach from almost any kind of surface. This ability is attributed to the hierarchical structure of their feet (involving toe pads, setal arrays, and spatulae), and how they are moved (articulated) to generate strong adhesion and friction forces on gripping that rapidly relax on releasing. Inspired by the gecko's bioadhesive system, various structured surfaces have been fabricated suitable for robotic applications. In this study, x–y–z asymmetric, micrometer‐sized rectangular flaps composed of polydimethylsiloxane (PDMS) were fabricated using massively parallel micro‐electromechanical systems (MEMS) techniques with the intention of creating directionally responsive, high‐to‐low frictional‐adhesion toe pads exhibiting properties similar to those found in geckos. Using a surface forces apparatus (SFA), the friction and adhesion forces of both vertical (symmetric) and angled/tilted (x–y–z asymmetric) microflaps under various loading, unloading and shearing conditIons were investigated. It was found that the anisotropic structure of tilted microflaps gives very different adhesion and tribological forces when articulated along different x–y–z directions: high friction and adhesion forces when articulated in the y–z plane along the tilt (+y) direction, which is also the direction of motion, and weak friction and adhesion forces when articulated against the tilt (–y) direction. These results demonstrate that asymmetric angled structures, as occur in geckos, are required to enable the gecko to optimize the requirements of high friction and adhesion on gripping, and low frictional‐adhesion on releasing. These properties are intimately coupled to a (also optimum) articulation mechanism. We discuss how both of these features can be simultaneously optimized in the design of robotic systems that can mimic the gecko adhesive system. 相似文献
62.
Solubilization of water and aqueous NaCl in mixed reverse micelles (RMs) comprising sodium bis(2‐ethylhexyl) sulfosuccinate (AOT), and polyoxyethylene (20) sorbitan trioleate or polyoxyethylene (20) sorbitan monooleate has been studied at different compositions (Xnonionic = 0–1.0) at a total surfactant concentration, ST = 0.10 × 103 mol m?3 in biocompatible oils of different chemical structures; viz., ethyl oleate (EO), isopropyl myristate (IPM) and isopropyl palmitate (IPP) at 303 K. The enhancement in water solubilization (i.e., synergism) has been evidenced by the addition of nonionic surfactant to dioctyl sulfosuccinate/oil(s)/water systems. Addition of NaCl in these systems at different Xnonionic enhances their solubilization capacities further until a maximum, ωNaCl,max is reached. ωNaCl,max and [NaCl]max (concentration at which maximization of NaCl solubilization occurs) depend on type of nonionic surfactant, its content (Xnonionic) and oil. A new solubilization efficiency parameter (SP*water or SP*NaCl) has been proposed to compare solubilization phenomena in these oils. The energetic parameters of the desolubilization process of water or aqueous NaCl in single and mixed RMs have been estimated. Energetically, the water dissolution process in oil has been found to be more exothermic as well as more organized in IPP. Overall, the dissolution of water and aqueous NaCl in mixed RMs is entropically driven process. Conductance behavior of these systems in the presence of NaCl has been investigated under different [NaCl] at 303 K. An attempt has been made to give an insight to the mechanism of solubilization phenomena, percolation in conductance and microstructures vis‐à‐vis role of biocompatible oils in these systems. 相似文献
63.
Tapatee Kundu Roy Abhijit Ghosh Debasis Bhowmick Dirtha Sanyal Soumyajit Koley Alok Chakrabarti 《Ceramics International》2011,37(7):2679-2687
The ability of silica (SiO2) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO2 acts as a sintering inhibitor in the ZnO–SiO2 system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO2 to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO2 addition. It has been observed that SiO2 incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO2 doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO2 addition to ZnO. 相似文献
64.
Biodegradation of polyethylene via complete solubilization by the action of Pseudomonas fluorescens,biosurfactant produced by Bacillus licheniformis and anionic surfactant
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
65.
Arjun DeySamit Kumar Nandi Biswanath Kundu Chandrasekhar KumarPrasenjit Mukherjee Subhasis RoyAnoop Kumar Mukhopadhyay Mithlesh Kumar SinhaDebabrata Basu 《Ceramics International》2011,37(4):1377-1391
Here we report a comparative study of the healing kinetics of surgically created artificial defects in the tibia of New Zealand white rabbits. Comparison of the healing kinetics was made for uncoated conventional SS316L intramedullary pins, and the same pins with microplasma sprayed (MIPS) pure hydroxyapatite (HAp) and beta-tri calcium phosphate (β-TCP) coatings. After thorough material characterizations including XRD, FTIR, SEM, etc., MIPS coated pins were implanted to such animals. Serum biochemistry, radiology and fluorochrome labelling were used to evaluate the comparative healing kinetics of these implants in vivo. In comparison to those of the uncoated pins, the pins coated with both MIPS HAp and β-TCP showed significant increment of alkaline phosphatase up to 15th postoperative day, insignificant changes in serum phosphorus and calcium with uneventful healing of bone defect. There was development of Havarsian canals and well-defined peripherally placed osteoblasts along with evidence of angiogenesis and comparatively more new bone formation in the defect site. On a comparative scale, the performance of the β-TCP coated intramedullary pins was much better than that of the pure HAp coated pins than the uncoated intramedullary pins. 相似文献
66.
We have investigated laser action in a binary mixture of dyes, Rh-6G and DCM, resulting in tunable laser emission over an extended frequency region. The two dyes absorb the same pump radiation but fluoresce over frequency ranges that are shifted with respect to each other, thereby resulting in extended tunability. Following a time-dependent analysis of a rate-equation model that describe the operation of such a laser, theoretical estimates for optimum dye concentrations and the corresponding extension of the laser tuning range have been obtained. 相似文献
67.
N Kundu R Dorsey MJ Jackson P Guiterrez K Wilson S Fu K Ramanujam E Thomas AM Fulton 《Canadian Metallurgical Quarterly》1998,76(5):713-719
Transfection of cDNA for IL-10 into line 66.1 murine mammary tumor cells results in marked suppression of tumor growth and metastasis. Others have reported that nitric oxide has potent antitumor activity and IL-10 is known to regulate the inducible isoform of nitric oxide synthase (iNOS) expressed in macrophages. We identified nitric oxide production in mammary tumors as indicated by electron paramagnetic resonance detection of nitric oxide-hemoglobin (NO-Hb). IL-10 expression resulted in elevated levels of NO-Hb in mammary tumors. Immunohistochemical examination of mammary tumors for iNOS protein revealed few positively staining cells in parental or control neo-transfected tumors but strong iNOS staining in all IL-10 transfected tumors, consistent with the NO-Hb data. To determine if mammary epithelial tumor cells themselves, express nitric oxide synthase activity, cultured tumor cells were treated with pro-inflammatory cytokines and nitrite accumulation was assessed in the conditioned medium. All IL-10 producing cell lines accumulated uM concentrations of nitrite in response to short term (24 hr) cytokine stimulation. Cells not expressing IL-10 (parental and neo-transfectants) accumulated no nitrite under similar culture conditions. After longer stimulation (48 hr), parental and 66-neo cells accumulated lower amounts of nitrite. IL-10 gene transfer is associated with increased iNOS protein expression and enzymatic activity detected both in vitro and in vivo. Our findings suggest that the antimetastatic and antitumor activity of IL-10 is related to enhanced production of nitric oxide. 相似文献
68.
Saurabh Garg Surjya K. Pal Debabrata Chakraborty 《Neural computing & applications》2007,16(4-5):407-417
This study compares the performance of backpropagation neural network (BPNN) and radial basis function network (RBFN) in predicting
the flank wear of high speed steel drill bits for drilling holes on mild steel and copper work pieces. The validation of the
methodology is carried out following a series of experiments performed over a wide range of cutting conditions in which the
effect of various process parameters, such as drill diameter, feed-rate, spindle speed, etc. on drill wear has been considered.
Subsequently, the data, divided suitably into training and testing samples, have been used to effectively train both the backpropagation
and radial basis function neural networks, and the individual performance of the two networks is then analyzed. It is observed
that the performance of the RBFN fails to match that of the BPNN when the network complexity and the amount of data available
are the constraining factors. However, when a simpler training procedure and reduced computational times are required, then
RBFN is the preferred choice. 相似文献
69.
The solid-state diffusion bonding was carried out between commercially pure titanium and Type 304 stainless steel using nickel
as an interlayer in the temperature range of 800–900 °C for 9 ks under 3 MPa load in vacuum. The transition joints thus formed
were characterized in the optical and scanning electron microscopes. The inter-diffusion of the chemical species across the
diffusion interfaces were evaluated by electron probe microanalysis. TiNi3, TiNi and Ti2Ni are formed at the nickel–titanium (Ni–Ti) interface; however, the stainless steel–nickel (SS–Ni) diffusion interface is
free from intermetallic compounds up to 850 °C temperature. At 900 °C, the Ni–Ti interface exhibits the presence of α-β Ti
discrete islands in the matrix of Ti2Ni and λ + χ + α-Fe, λ + FeTi and λ + FeTi + β-Ti phase mixtures occur at the SS–Ni interface. The occurrence of different
intermetallics are confirmed by the x-ray diffraction technique. The maximum tensile strength of ∼276 MPa and shear strength
of ∼209 MPa along with 7.3% elongation were obtained for the diffusion couple processed at 850 °C. At the 900 °C joining temperature,
the formation of Fe–Ti base intermetallics reduces the bond strength. Evaluation of the fracture surfaces using scanning electron
microscopy and energy dispersive spectroscopy demonstrates that failure takes place through Ni–Ti interface up to 850 °C and
through the SS–Ni interface of the joint when processed at 900 °C. 相似文献
70.
Fedor V. Fomin Fabrizio Grandoni Dieter Kratsch Daniel Lokshtanov Saket Saurabh 《Algorithmica》2013,65(3):584-604
Given an n-node edge-weighted graph and a subset of k terminal nodes, the NP-hard (weighted) Steiner tree problem is to compute a minimum-weight tree which spans the terminals. All the known algorithms for this problem which improve on trivial O(1.62 n )-time enumeration are based on dynamic programming, and require exponential space. Motivated by the fact that exponential-space algorithms are typically impractical, in this paper we address the problem of designing faster polynomial-space algorithms. Our first contribution is a simple O((27/4) k n O(logk))-time polynomial-space algorithm for the problem. This algorithm is based on a variant of the classical tree-separator theorem: every Steiner tree has a node whose removal partitions the tree in two forests, containing at most 2k/3 terminals each. Exploiting separators of logarithmic size which evenly partition the terminals, we are able to reduce the running time to $O(4^{k}n^{O(\log^{2} k)})$ . This improves on trivial enumeration for roughly k<n/3, which covers most of the cases of practical interest. Combining the latter algorithm (for small k) with trivial enumeration (for large k) we obtain a O(1.59 n )-time polynomial-space algorithm for the weighted Steiner tree problem. As a second contribution of this paper, we present a O(1.55 n )-time polynomial-space algorithm for the cardinality version of the problem, where all edge weights are one. This result is based on a improved branching strategy. The refined branching is based on a charging mechanism which shows that, for large values of k, convenient local configurations of terminals and non-terminals exist. The analysis of the algorithm relies on the Measure & Conquer approach: the non-standard measure used here is a linear combination of the number of nodes and number of non-terminals. Using a recent result in Nederlof (International colloquium on automata, languages and programming (ICALP), pp. 713–725, 2009), the running time can be reduced to O(1.36 n ). The previous best algorithm for the cardinality case runs in O(1.42 n ) time and exponential space. 相似文献