全文获取类型
收费全文 | 12782篇 |
免费 | 445篇 |
国内免费 | 53篇 |
专业分类
电工技术 | 259篇 |
综合类 | 15篇 |
化学工业 | 2266篇 |
金属工艺 | 367篇 |
机械仪表 | 364篇 |
建筑科学 | 219篇 |
矿业工程 | 72篇 |
能源动力 | 706篇 |
轻工业 | 1174篇 |
水利工程 | 190篇 |
石油天然气 | 84篇 |
无线电 | 1618篇 |
一般工业技术 | 2787篇 |
冶金工业 | 1546篇 |
原子能技术 | 200篇 |
自动化技术 | 1413篇 |
出版年
2024年 | 31篇 |
2023年 | 176篇 |
2022年 | 483篇 |
2021年 | 505篇 |
2020年 | 413篇 |
2019年 | 410篇 |
2018年 | 553篇 |
2017年 | 516篇 |
2016年 | 483篇 |
2015年 | 280篇 |
2014年 | 447篇 |
2013年 | 891篇 |
2012年 | 519篇 |
2011年 | 680篇 |
2010年 | 541篇 |
2009年 | 531篇 |
2008年 | 478篇 |
2007年 | 392篇 |
2006年 | 332篇 |
2005年 | 264篇 |
2004年 | 246篇 |
2003年 | 221篇 |
2002年 | 180篇 |
2001年 | 143篇 |
2000年 | 147篇 |
1999年 | 157篇 |
1998年 | 357篇 |
1997年 | 232篇 |
1996年 | 252篇 |
1995年 | 219篇 |
1994年 | 182篇 |
1993年 | 172篇 |
1992年 | 145篇 |
1991年 | 151篇 |
1990年 | 114篇 |
1989年 | 111篇 |
1988年 | 130篇 |
1987年 | 109篇 |
1986年 | 90篇 |
1985年 | 117篇 |
1984年 | 96篇 |
1983年 | 108篇 |
1982年 | 99篇 |
1981年 | 88篇 |
1980年 | 78篇 |
1979年 | 54篇 |
1978年 | 46篇 |
1977年 | 57篇 |
1976年 | 76篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Other than temperature and voltage, load plays a key role in anodic bonding process. In this paper we present a new design of top electrode (cathode) for anodic bonding machine by which the bonding time has been reduced up to 30 % in case of bare silicon wafer at ?400 V and approximate 52 % in case of oxidized silicon wafer with Pyrex glass bonding at ?800 V. Experimentally it has been observed there was no bonding in oxidized silicon wafer with Pyrex glass up to ?600 V by using standard design while it has been successfully bonded at same voltage (?600 V) by using new design. 相似文献
192.
The group-contribution method for vapor pressures of hydrocarbons and organic compounds containing nitrogen or sulfur, based on the kinetic theory of fluids, is revised and extended to include new groups containing nitrogen or sulfur. Good representation is obtained for vapor pressure data in the region 1.30-270 kPa. The method may be used to estimate vapor pressures and enthalpies of vaporization for those organic fluids containing nitrogen or sulfur, where no experimental data are available. 相似文献
193.
The measurements of ac conductivity [σm(ω)], dielectric constant [?′(ω)] and loss [?″(ω)] have been performed on solution grown (thickness ∼85 μm) and uniaxially stretched (thickness ∼25, 45 and 80 μm) films of poly(vinylidene fluoride) (PVDF) in the frequency range 0.1 kHz-10 MHz and in the temperature range 77-400 K. The σm(ω) can be described by the relation σ(ω) = Aωs, where s is close to unity and decreases with increase in temperature. Three relaxations, observed in the present investigation, have been designated as the αc-, the αa- and the β-relaxations appearing from high temperature side to the low temperature side. The αc-relaxation could not be observed in the case of uniaxially stretched poly(vinylidene fluoride) films. The αc- and αa-relaxations are associated with the molecular motions in the crystalline regions and micro-Brownian motion in the amorphous regions of the main polymer chain, respectively, whereas the β-relaxation is attributed to the rotation of side group dipoles or to the local oscillations of the frozen main polymer chain. 相似文献
194.
Li-doped NiO was synthesized by molten salt method. LiNO3-LiOH flux was used as a source for Li doping. NiCl2 was added to the molten Li flux and then processed to make the Li-doped NiO material. Li:Ni ratios were maintained from 5:
1 to 30: 1 during the synthetic procedure and the chemical compositions after characterization were found from Li0.08Ni0.92O to Li0.16Ni0.84O. Li doping did not change the basic cubic structural characteristics of NiO as evidenced by XRD studies; however, the lattice
parameter decreased from 0.41769 nm in pure NiO to 0.41271 nm in Li0.16Ni0.84O. Hydrogen gas sensors were fabricated by using these materials as thick films on alumina substrates. The half surface of
each sensor was coated with the Pt catalyst. The sensor, when exposed to the hydrogen gas blended in air, heated up the catalytic
surface leaving the rest half surface (without catalyst) cold. The thermoelectric voltage thus built up along the hot and
cold surface of the Li-doped NiO made the basis for detecting hydrogen gas. The linearity of the voltage signal vs H2 concentration was checked up to 4% of H2 in air (as higher concentrations above 4.65% are explosive in air) using Li0.10Ni0.90O as the sensor material. The response time T90 and the recovery time RT90 were less than 25 sec. H2 concentration from 0.5% to 4% showed a good linearity against voltage. There was minimum interference of other gases and
hence H2 gas can easily be detected. 相似文献
195.
Investigations were carried out in a long term field experiment from 1976 to 1982, on a loamy sand soil to find out the fertilizer requirements of groundnut and wheat grown in fixed rotation. Application of 26 kgP/ha to wheat alone was found to be sufficient for both wheat and succeeding groundnut. Application of phosphorus to both wheat and groundnut did not result in extra beneficial effect over P application to wheat alone. However, application of 26 kg P/ha to groundnut alone was not sufficient for succeeding wheat. There was no response from K application (25 kg K/ha) in either of these two crops. Increasing the dose of N from 50–150 kg/ha to wheat significantly increased the grain yield of wheat but the pod yield of succeeding groundnut were markedly lowered. Response of wheat to 150 kg N/ha was more marked when P was also applied to wheat and response was less when P was applied to preceding groundnut alone. Zinc application at 6.25 kg/ha to wheat alone resulted in significant increase in grain yield of wheat and pod yield of succeeding groundnut. 相似文献
196.
Praying mantids are models for a wide variety of behavioral, physiological, and ecological studies, and sex pheromones have been assumed to be important components of their biology. However, no mantid pheromone has ever been identified. We collected volatiles emitted by females of the mantid, Sphodromantis lineola, via solid phase microextraction (SPME). Mass spectral analysis revealed the collected volatiles to be a mixture of pentadecanal and tetradecanal. We prepared a synthetic mixture of these compounds, and found that males were both attracted to this mixture and stimulated to exhibit typical precopulatory behavior. We then examined male antennae with scanning electron microscopy, and confirmed the presence of porous antennal sensilla typical of insect pheromone receptors, i.e., that male mantids are equipped with the appropriate morphological apparatus to receive volatile chemical signals. Pheromones, in conjunction with visual and tactile cues, are thus an important feature of the reproductive biology of this, and undoubtedly other species of mantids. In addition to adding a crucial aspect of behavioral biology to our knowledge of this group, identification and synthesis of mantid pheromones may be a first step in attracting and aggregating these generalist predators for use in pest control. 相似文献
197.
The last two decades have witnessed a phenomenal growth in the number of cellular wireless network users which in turn stressed the need to utilize the limited network bandwidth in an efficient manner. The network bandwidth is consumed not only by user traffic, but also by control traffic needed for ensuring the mobility of users. As we don’t have any control over the volume of user traffic, all attempts to efficiently use bandwidth are based on frequency reuse and minimizing the control traffic. The registration area planning (RAP) problem seeks a partition of the cells of the network into contiguous areas called registration areas so that the bandwidth consumed by control signals is minimized. RAP problem in an \(\mathcal {NP}\) -Hard problem. In this paper, we present a steady-state grouping genetic algorithm with local search to solve this problem. We have compared our approach with the state-of-the-art approaches reported in the literature. Computational results show the effectiveness of our approach. 相似文献
198.
The present work involves single-phase computational fluid dynamics (CFD) simulations of continuous flow pump-mixer employing top-shrouded Rushton turbines with trapezoidal blades. Baffle—impeller interaction has been modeled using sliding mesh and multiple reference frame approaches. Standard k-ε model has been used for turbulence modeling. Several CFD runs representing different combinations of geometric and process parameters have been carried out. Results of CFD simulations have been used to find out two macroscopic performance parameters of pump-mixer—power consumption and head generated by the impeller. The simulation results have been compared with the experimental data obtained on a pilot-scale setup. Good agreement between CFD predictions and experimental results is observed. In most cases, sliding mesh approach is found to perform better than multiple reference frame approach. Details from CFD simulations have been used to have an insight into the pumping action of the impeller. 相似文献
199.
Cerebronic acid (2-hydroxytetracosanoic acid), an α-hydroxy very long-chain fatty acid (VLCFA) and a component of cerebrosides
and sulfatides, is unique to nervous tissues. Studies were carried out to identify the pathway and the subcellular site involved
in the oxidation of cerebronic acid. The results from these studies revealed that cerebronic acid was catabolized by α-oxidation
to CO2 and tricosanoic acid (23:0). Studies with subcellular fractions indicated that cerebronic acid was α-oxidized in fractions
having particulate bound catalase and enzyme systems for the β-oxidation of VLCFA (e.g., lignoceric acid), suggesting peroxisomes
as the subcellular organelle responsible for α-oxidation of cerebronic acid. Etomoxir, an inhibitor of mitochondrial fatty
acid oxidation, had no effect on cerebronic acid α-oxidation. Further, cerebronic acid oxidation was found to be dependent
on the presence of NAD+ but not FAD, NADPH, ATP, Mg2+, or CoASH. Intraorganellar localization studies indicated that the enzyme system for the α-oxidation of cerebronic acid was
associated with the peroxisomal limiting membranes. Studies on cultured fibroblasts from normal subjects and patients with
peroxisomal disorders indicated an impairment of α-oxidation of cerebronic acid in cell lines that lack peroxisomes [e.g.,
Zellweger syndrome (ZS)]. On the other hand, α-oxidation of cerebronic acid was found to be normal in cell lines from X-linked
adrenoleukodystrophy, adult Refsum disease, and rhizomelic chondrodysplasia punctata. Our results clearly demonstrate that
α-oxidation of α-hydroxy VLCFA (cerebronic acid) is a peroxisomal function and that this oxidation is impaired in ZS. Furthermore,
this α-oxidation enzyme system is distinct from the one for the α-oxidation of β-carbon branched-chain fatty acids (e.g.,
phytanic acid). 相似文献
200.
Shamsher Singh Kanwar Rajeev Kumar Kaushal Amit Aggarwal Sandeep Chauhan Swapandeep Singh Chimni Ghansham Singh Chauhan 《应用聚合物科学杂志》2007,105(3):1437-1443
A purified alkaline thermotolerant bacterial lipase of Bacillus coagulans MTCC‐6375 was efficiently immobilized onto poly(N‐AEAAm‐co‐AAc‐cl‐MBAm)‐hydrogel at pH 8.5 and at temperature 55°C in 16 h. The hydrogel‐bound matrix possessed 1.04 U/g (matrix) lipase activity with a specific activity of 1.8 U/mg of protein. The immobilized lipase resulted in formation of 52.5 mM of ethyl propionate (52% conversion) at 55°C in 9 h in n‐nonane. Ethanol and propionic acid when used in a ratio of 300 : 100 mM, respectively, in n‐nonane along with 10 mg of hydrogel‐bound lipase resulted in optimal synthesis of ethyl propionate (82.5 mM). Addition of molecular sieves (3 Å, 0.7 g/reaction volume) further enhanced the conversion rate to 82.4% resulting in 83.5 mM of ethyl propionate. Incubation temperature below or above 55°C had a marked effect on the synthesis of ethyl propionate. However, esterification performed in n‐heptane at 65°C resulted in 87.5 mM of ethyl propionate with a conversation rate of 89.3%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献