全文获取类型
收费全文 | 950篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 6篇 |
综合类 | 1篇 |
化学工业 | 206篇 |
金属工艺 | 52篇 |
机械仪表 | 31篇 |
建筑科学 | 8篇 |
矿业工程 | 1篇 |
能源动力 | 31篇 |
轻工业 | 48篇 |
水利工程 | 7篇 |
石油天然气 | 3篇 |
无线电 | 77篇 |
一般工业技术 | 267篇 |
冶金工业 | 83篇 |
原子能技术 | 15篇 |
自动化技术 | 133篇 |
出版年
2023年 | 6篇 |
2022年 | 13篇 |
2021年 | 26篇 |
2020年 | 12篇 |
2019年 | 18篇 |
2018年 | 18篇 |
2017年 | 20篇 |
2016年 | 17篇 |
2015年 | 15篇 |
2014年 | 23篇 |
2013年 | 69篇 |
2012年 | 44篇 |
2011年 | 71篇 |
2010年 | 59篇 |
2009年 | 51篇 |
2008年 | 51篇 |
2007年 | 49篇 |
2006年 | 29篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 17篇 |
2000年 | 28篇 |
1999年 | 24篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 17篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1971年 | 2篇 |
排序方式: 共有969条查询结果,搜索用时 15 毫秒
81.
This article, presents discrete sliding mode control algorithm using multirate output feedback for control of stepper motor. The algorithm developed by the authors uses past output samples and past control inputs. When all the states of the system are neither physical variable nor available for measurement, multirate output feedback can be used. The stepper motor is known to be a differentially flat system. The dynamics of the stepper motor are highly nonlinear, hence feedback linearization based on endogenous feedback has been used. The linear model is obtained and multirate output feedback-based discrete sliding mode control has been designed. The discrete sliding mode control with multirate output feedback has been applied for regulator as well as tracking case for the motor. The proposed algorithm uses only two outputs. It is essentially shown that first output needs to be sampled only once and second output must be sampled at least thrice in every τ sampling interval in order to achieve acceptable performance. The system parameter variation has been considered and the results obtained are found to be satisfactory. Thus, it has been shown that discrete sliding mode control algorithm using multirate output feed back can be extended to a class of nonlinear MIMO system. 相似文献
82.
A stability-based distributed routing mechanism to support unicast and multicast routing in ad hoc wireless network 总被引:6,自引:0,他引:6
An ad hoc network can be envisioned as a collection of mobile routers, each equipped with a wireless transceiver, which are free to move about arbitrarily. In ad hoc wireless networks, even if two nodes are outside the wireless transmission range of each other, they may still be able to communicate in multiple hops using other intermediate nodes. However, the dynamics of these networks, as a consequence of mobility and disconnection of mobile hosts, pose a number of problems in designing routing schemes for effective communication between any pair of source and destination. In this paper, a stability-based unicast routing mechanism, that considers both link affinity and path stability in order to find out a stable route from source to destination, is proposed. It is then extended to support multicast routing as well where only local state information (at source) is utilized for constructing a multicast tree. The performance of the proposed scheme is evaluated on a simulated environment to show that the stability-based scheme provides a unified framework for both unicast and multicast routing and reduces the probability of route error drastically in both the cases. 相似文献
83.
SAFE: An Efficient Feature Extraction Technique 总被引:1,自引:0,他引:1
Ujjwal Maulik Sanghamitra Bandyopadhyay John C. Trinder 《Knowledge and Information Systems》2001,3(3):374-387
This paper proposes an efficient window-based semi-automatic feature extraction technique which uses simulated annealing
for minimizing the energy of an active contour within a specified image region. The energy is computed based on a chamfer
image, in which pixel values are a function of distance to image edges. A user places a number of control points close to
the feature of interest. B-spline fitted to these points provides an initial approximation of the contour. A window containing
both the initial contour and the feature of interest is considered. The contour with minimum energy inside the window provides
the final delineation. Comparison of the performance of the proposed algorithm with traditional snake, a popular feature extraction technique based on energy minimization, demonstrates the superiority of the SAFE technique.
Received 18 August 1999 / Revised 25 October 2000 / Accepted in revised form 8 December 2000 相似文献
84.
The flame spraying process, which is a common industrial thermal spraying application, has been analyzed by means of three-dimensional
computational fluid dynamics (CFD) simulations. The process used at the Volvo Aero Corporation for the coating of fan and
compressor housings has been modeled. The process uses the Metco 6P torch (Metco, Westbury, NY), which ejects a mixture of
acetylene and oxygen at high speed through a ring of 16 orifices to form the flame. A stream of argon gas flowing through
an orifice in the center of the ring carries a powder of nickel-covered bentonite through the flame to the spray substrate.
The torch is cooled by a flow of air through an outer ring of 9 orifices. The simulation emulated reality closely by including
the individual inlets for fuel, cooling air, and injected particles. The gas combustion was simulated as a turbulent, multicomponent
chemically reacting flow. The standard, two-equation k-ε turbulence model was used. The chemical reaction rates appeared as
source terms in the species transport equations. They were computed from the contributions of the Arrhenius rate expressions
and the Magnussen and Hjertager eddy dissipation model. The first simulations included several intermediate chemical substances
whose predicted concentration agreed favorably with measurements. Later, more simplified simulations incorporated only the
global chemical reaction involving the initial and the final products, with corrections to the thermal properties being made
to account for the missing intermediaries. The gas velocity and temperature fields predicted by the later simulations compared
satisfactorily to those predicted by the earlier, more elaborate, ones. Therefore, the final simulations, which incorporated
injected particles, were conducted employing the simplified model with only the global reaction. An in-house finite difference
code was developed to calculate particle properties. Allowance was made for elliptical shapes, phase changes, and internal
heat transfer with regard to the composite material. The particle velocities and temperatures predicted by the final simulations
compared fairly well with experimental results obtained with the optical DPV2000 system. 相似文献
85.
Weichang Xue Amit Bandyopadhyay Susmita Bose Chuanxian Ding K.M.C. Cheung 《Surface & coatings technology》2007,201(8):4685-4693
The use of strontium-containing hydroxyapatite (Sr-HA) as a biomaterial has been reported recently. In vitro and in vivo studies have shown that Sr-HA promotes osteoblast response and stimulates new bone formation. In order to extend its usage to major load-bearing applications, such as artificial hip replacement, it has been proposed that the material could be used in the form of a coating on implant surfaces. This paper reports a preliminary study of biocompatibility of plasma sprayed Sr-HA coatings on a metallic substrate. Coatings of Sr-HA containing 10 mol% Sr2+ was produced on titanium alloy substrates. The coating exhibited good bonding with the substrate. The bioactivity of Sr-HA coating was evaluated in vitro by immersion in simulated body fluid (SBF). After immersion in SBF, Sr-HA coating exhibited great ability to induce apatite precipitation on its surface. The possible effects of cell-materials interactions of Sr-HA coating were examined by culturing osteoprecursor cells (OPC1) on coating surfaces. The effect of Sr-HA was also compared to a hydroxyapatite (HA) coating, which is widely used in orthopedics and dentistry. The results indicated that Sr-HA coating had good biocompatibility with human osteoblasts. OPC1 cells survived and proliferated well on the surface of coating. Sr-HA coating promoted OPC1 cells attachment, and more local contacts were produced on the surface. The presence of Sr stimulated OPC1 cell differentiation and ALP expression. No deleterious effect on ECM formation and mineralization was found with Sr-HA coating. The results indicated that Sr-HA coating had good mechanical properties and bioactivity in vitro. 相似文献
86.
Jayita Bandyopadhyay Caroline Mekoa Dimakatso Makwakwa Sifiso Skosana Suprakas Sinha Ray 《Polymer Engineering and Science》2021,61(4):1195-1208
The development of a reactively processed polypropylene nanocomposite (PPNC) with consequential improvements in the heat deflection temperature (HDT), Vicat softening temperature (VST), and crystallization peak temperature (Tc) is reported herein. Neat PP without nanoclay was also reactively processed to elucidate the effects of fillers on the improvement in physical properties. The results show a considerable improvement in the HDT of PPNC (77.9 °C) compared to those of neat PP (62.6 °C) and reactively processed branched PP (BPP; 69.2 °C). Moreover, the Tc of PP in PPNC improved by ~14% compared to that of neat PP. Various models of nonisothermal crystallization kinetics were employed to elucidate the nucleation and crystal growth mechanisms, and to correlate them with the observed HDT improvement in PPNC. Thermal transitions investigated by modulated differential scanning calorimetry explained the changes observed in the VSTs of all the samples. To the best of our knowledge, this is the first report on a significant improvement in HDT along with a marked increase in Tc. Such simultaneous improvements in HDT, VST, and Tc are highly desirable for applications involving the use of PP-based materials in rigid packaging. 相似文献
87.
Eugenia Awuah Boadi Samuel Shin Samuel Yeroushalmi Bok-Eum Choi Peijun Li Bidhan C. Bandyopadhyay 《International journal of molecular sciences》2021,22(6)
Proximal tubular (PT) acidosis, which alkalinizes the urinary filtrate, together with Ca2+ supersaturation in PT can induce luminal calcium phosphate (CaP) crystal formation. While such CaP crystals are known to act as a nidus for CaP/calcium oxalate (CaOx) mixed stone formation, the regulation of PT luminal Ca2+ concentration ([Ca2+]) under elevated pH and/or high [Ca2+] conditions are unknown. Since we found that transient receptor potential canonical 3 (TRPC3) knockout (KO; -/-) mice could produce mild hypercalciuria with CaP urine crystals, we alkalinized the tubular pH in TRPC3-/- mice by oral acetazolamide (0.08%) to develop mixed urinary crystals akin to clinical signs of calcium nephrolithiasis (CaNL). Our ratiometric (λ340/380) intracellular [Ca2+] measurements reveal that such alkalization not only upsurges Ca2+ influx into PT cells, but the mode of Ca2+ entry switches from receptor-operated to store-operated pathway. Electrophysiological experiments show enhanced bicarbonate related current activity in treated PT cells which may determine the stone-forming phenotypes (CaP or CaP/CaOx). Moreover, such alkalization promotes reactive oxygen species generation, and upregulation of calcification, inflammation, fibrosis, and apoptosis in PT cells, which were exacerbated in absence of TRPC3. Altogether, the pH-induced alteration of the Ca2+ signaling signature in PT cells from TRPC3 ablated mice exacerbated the pathophysiology of mixed urinary stone formation, which may aid in uncovering the downstream mechanism of CaNL. 相似文献
88.
Polypropylene (PP) was melt‐blended in a single‐screw extruder with a thermotropic Vectra B‐950 liquid crystalline polymer (LCP) in different proportions. The mechanical properties of such blends were compared in respect of their Young's moduli, ultimate tensile strength (UTS), percent elongation at break, and toughness to those of pure PP. The thermal properties of these blends were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology was studied by using a polarizing light microscope (PLM) and a scanning electron microscope (SEM) while the rheological aspects of the blends and the pure PP were studied by a Haake Rheowin equipment. Mechanical analysis (tensile properties) of the blends showed pronounced improvement in the moduli and the UTS of the PP matrix in the presence of 2–10% of LCP incorporation. TGA of all the blends showed an increase in the thermal stability for all the blends with respect to the matrix polymer PP, even at a temperature of 410°C, while PP itself undergoes drastic degradation at this temperature. DSC studies indicated an increase in the softening range of the blends over that of PP. Morphological studies showed limited mixing and elongated fibril formation by the dispersed LCP phase within the base matrix (PP) at the lower ranges of LCP incorporation while exhibiting a tendency to undergo gross phase separation at higher concentrations of LCP, which forms mostly agglomerated fibrils and large droplets. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 767–774, 2003 相似文献
89.
In the present work, thermoplastic elastomer (TPE)–clay nanocomposites (TPN) based on different rubber–plastic blends from ethylene–octene copolymer [Engage]–Polypropylene and brominated poly(isobutylene‐co‐paramethyl styrene)–nylon 6 were prepared by melt blending. Hexadecyltrimethylammonium bromide and octadecyl amine‐modified sodium montmorillonite were used as organoclays. The nanocomposites were prepared by adding the nanoclay separately into the rubber and plastic phases. The TPNs were characterized with the help of transmission electron microscopy (TEM) and X‐ray diffraction. The X‐ray diffraction peaks observed in the range of 3–10° for the modified clays disappeared in the thermoplastic elastomeric nanocomposites. TEM photographs showed exfoliation and intercalation of the clays in the range of 20–30 nm in the particular phase where the clay was added. Excellent improvement in mechanical properties like tensile strength, elongation at break, and modulus was observed on incorporation of the nanoclays in the rubber phase of TPN. When the nanoclay was added to the plastic phase, the mechanical reinforcement is comparatively poorer due to partial destruction of the crystallinity. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1645–1656, 2006 相似文献
90.
Sulfuration of natural rubber (NR) by the binary accelerator 2-mercaptobenzothiazole (MBT) and diphenylguanidine (DPG) both in presence and in absence of ZnO and stearic acid with or without dicumylperoxide (DCP) was studied in detail. It was observed that the rate of decomposition of DCP in presence of both MBT and DPG is quite similar to that with MBT alone. The reduction of crosslinking depends also on MBT only. Through DPG has no influence on the decomposition rate, it reacts with MBT during the vulcanization process and suppresses the retardation caused by MBT on the DCP vulcanization. In accordance with the initial additiveness of crosslinking in systems containing DCP, the free sulfur decrease, and the rapidity of crosslink formation the vulcanization process of MBT-DPG-S-NR systems was interpreted in terms of a polar mechanism induced by the complex MSH2NR′R″. In mixtures containing DCP together with sulfur, MBT, DPG, ZnO, and stearic acid, the initial stage of crosslinking is additive as indicated by a mixed reaction as well as by a methyl iodide treatment of the vulcanizates. Comparison with single accelerators shows a pronounced synergistic effect. This is because of the enhanced activity of the MBT-ZnO-stearic acid complex due to DPG which also induces polar sulfuration of NR by forming the active complex MSH2NR′R″. In presence of ZnO and stearic acid, DCP cannot increase the net crosslink density but suppresses the reversion so much pronounced in its absence. 相似文献