全文获取类型
收费全文 | 7813篇 |
免费 | 369篇 |
国内免费 | 15篇 |
专业分类
电工技术 | 159篇 |
综合类 | 21篇 |
化学工业 | 1525篇 |
金属工艺 | 218篇 |
机械仪表 | 402篇 |
建筑科学 | 172篇 |
矿业工程 | 5篇 |
能源动力 | 299篇 |
轻工业 | 605篇 |
水利工程 | 42篇 |
石油天然气 | 21篇 |
无线电 | 1457篇 |
一般工业技术 | 1360篇 |
冶金工业 | 720篇 |
原子能技术 | 89篇 |
自动化技术 | 1102篇 |
出版年
2023年 | 61篇 |
2022年 | 86篇 |
2021年 | 126篇 |
2020年 | 110篇 |
2019年 | 129篇 |
2018年 | 168篇 |
2017年 | 149篇 |
2016年 | 214篇 |
2015年 | 187篇 |
2014年 | 313篇 |
2013年 | 544篇 |
2012年 | 443篇 |
2011年 | 481篇 |
2010年 | 351篇 |
2009年 | 427篇 |
2008年 | 364篇 |
2007年 | 332篇 |
2006年 | 335篇 |
2005年 | 288篇 |
2004年 | 274篇 |
2003年 | 251篇 |
2002年 | 277篇 |
2001年 | 206篇 |
2000年 | 186篇 |
1999年 | 176篇 |
1998年 | 375篇 |
1997年 | 221篇 |
1996年 | 162篇 |
1995年 | 133篇 |
1994年 | 114篇 |
1993年 | 114篇 |
1992年 | 60篇 |
1991年 | 71篇 |
1990年 | 56篇 |
1989年 | 58篇 |
1988年 | 40篇 |
1987年 | 44篇 |
1986年 | 39篇 |
1985年 | 31篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有8197条查询结果,搜索用时 15 毫秒
21.
Our laboratory recently published several analytical equations that can be used to predict the melting rate of fully compacted solid polymers sliding on a heated metal surface, modeling the melting mechanism inside an extruder. These equations were obtained by seeking asymptotic solutions to the differential equations describing the melting mechanism, temperature, and shear-dependent viscosity of polymer melts. Following the same asymptotic approach, we successfully developed accompanying analytical equations for predicting the stress required to slide fully compacted solid polymers on a heated metal surface. The accuracy of these analytical stress equations was found to be reasonable, although not fully satisfactory, by comparing their predictions to the experimentally measured values. The accuracy of the stress calculation is directly related to the accuracy of the viscosity values at high shear rates. The consideration of the temperature and shear dependencies of melt viscosity is most important for accurate prediction of the stress, just as it is for the melting rate. The stress not only depends on the melt rheological properties of the polymer but also on the thermodynamic properties. 相似文献
22.
Seng F. Chung 《加拿大化工杂志》1972,50(5):657-662
A mathematical model of a through-circulation dryer is proposed. This model approximates the drying time of constantrate drying and fallingrate drying processes. Based on the proposed model, the optimal drying conditions of maximizing the drying production rate in a continuous through-circulation dryer are obtained. The drying production rate, in terms of the independent operating variables, is a nonlinear objective function, and is optimized under the nonlinear inequality constraint functions by a differential algorithm. 相似文献
23.
Chlorinated isotactic polypropylenes (CPP) having various chlorine contents were blended with poly(ethylene-co-vinyl acetate)s (EVA) having various vinyl acetate (VA) contents. The blends were made by casting films from dilute THF solutions and miscibility of the blends was identified by single glass transition temperature, which was confirmed by DSC and dynamic mechanical measurements. Based on the miscibility data from a large number of CPP/EVA combinations, a miscibility map was depicted where CO equivalent weight (CO-EQW) of EVA was plotted against chlorine equivalent weight (Cl-EQW) of CPP. Though an attractive interaction between CPP and EVA could be detected in all the miscible and immiscible blend pairs, miscibility of the CPP/EVA blends could solely be observed in a relatively narrow range of Cl-EQW ca. 65–100 and CO-EQW ca. 170–230. 相似文献
24.
O. K. Chung Y. Pomeranz K. F. Finney M. P. Shogren 《Journal of the American Oil Chemists' Society》1978,55(9):635-641
Petroleum ether (PE) extracted 1.00% total free lipids (0.70% nonpolar and 0.30% polar) and 2-propanol (PrOH) extracted 1.36%
total free and bound lipids (0.73% nonpolar and 0.63% polar) from wheat flour; the lipid fractions were characterized by thin
layer chromatography. PE- or PrOH-defatted flours were baked after reconstitution with total, nonpolar, or polar wheat flour
lipids; or with equivalent amounts of nonionic sucrose monopalmitate (SMP), ethoxylated monoglycerides (EMG) — each with a
hydrophile-lipophile balance (HLB) of 14.0 or anionic sodium stearoyl-2-lactylate (SSL) — with an HLB value of 9.0. Defatted
flours supplemented with surfactants alone or in combination with wheat flour lipids were used in bread with no-shortening
and with 3%-shortening. The importance of the polar flour lipids in breadmaking was verified. The lipids in wheat flour were
essential for maximizing the beneficial effects of shortening on breadmaking quality. Nonionic SMP or EMG completely replaced
both PE-extractable wheat flour free total lipids ( or their non-polar or polar fractions) and 3% shortening; nonionic surfactants
with high HLB were better than the anionic SSL for replacing free flour lipids. No surfactant completely replaced unfractionated
PrOH-extracted lipids (free + bound) and shortening or total polar flour lipids (free + bound). All surfactants, especially
anionic SSL, added with PrOH-extracted polar lipids improved the overall bread-making properties of the PrOH-defatted flour
both in the absence and in the presence of shortening.
Presented at the AOCS Meeting, New York, May 1977 相似文献
25.
A personalized service in the ubiquitous environment is to provide services or items, which reflect personal tastes, attitudes, and contexts. It is impossible to reflect the context information generated in u-healthcare environments due to the existing recommendation system performing the recommendation using the information directly input by users and application usage record only. This study develops a context-aware model using the context information provided by the context information model. The study applies it to the extraction of the missing value in a collaborative filtering process. The context-aware model reflects the information that selects items by users according to the appropriate context using the C-HMM and provides it to users. The solution of the missing value in the preference significantly affects the recommendation accuracy in a preference based item supply method. Thus, this study developed a new collaborative filtering for ubiquitous environments by reflecting the missing preference value and reflecting it to the collaborative filtering using the context-aware model. Also, the validity of this method will be evaluated by applying it to menu services in u-healthcare services. 相似文献
26.
This paper proposes a technique for the detection of head nod and shake gestures based on eye tracking and head motion decision. The eye tracking step is divided into face detection and eye location. Here, we apply a motion segmentation algorithm that examines differences in moving people’s faces. This system utilizes a Hidden Markov Model-based head detection module that carries out complete detection in the input images, followed by the eye tracking module that refines the search based on a candidate list provided by the preprocessing module. The novelty of this paper is derived from differences in real-time input images, preprocessing to remove noises (morphological operators and so on), detecting edge lines and restoration, finding the face area, and cutting the head candidate. Moreover, we adopt a K-means algorithm for finding the head region. Real-time eye tracking extracts the location of eyes from the detected face region and is performed at close to a pair of eyes. After eye tracking, the coordinates of the detected eyes are transformed into a normalized vector of x-coordinate and y-coordinate. Head nod and shake detector uses three hidden Markov models (HMMs). HMM representation of the head detection can estimate the underlying HMM states from a sequence of face images. Head nod and shake can be detected by three HMMs that are adapted by a directional vector. The directional vector represents the direction of the head movement. The vector is HMMs for determining neutral as well as head nod and shake. These techniques are implemented on images, and notable success is notified. 相似文献
27.
A supercritical fluid extraction method has been applied to test the feasibility of tocopherol concentration from soybean
sludge with carbon dioxide at temperatures and pressures ranging from 35 to 70°C and 200 to 400 bar, respectively. The supercritical
solubility of the esterified soybean sludge was over 4–6 times greater than that of the original soybean sludge. By a simple
batch-type one-stage method the tocopherols in the esterified soybean sludge could be concentrated up to 40 wt%. The overall
results of the present study show that soybean sludge initially containing about 13–14 wt% tocopherols may require a countercurrent
multistage column to be highly and effectively concentrated. 相似文献
28.
Tensile properties of polyethertherketone (PEEK) have been studied at 125, 25, and ?100°C for thin films prepared with different thermal histories. Initial morphology was controlled by rate of cooling from the melt. Amorphous films resulted from quenching the melt, while semicrystalline films were obtained by cooling the melt at different rates, or by crystallization of the rubbery amorphous state. The films were characterized using density, X-ray scattering, differential scanning calorimetry, and infrared spectroscopy. Scanning electron microscopy was used to examine fracture surfaces. Degree of crystallinity and rate of cooling from the melt affected the tensile properties at all test temperatures. For films with nearly the same degree of crystallinity, those which were more slowly cooled from the melt fractured at the lowest strain. The amorphous films were most tough, drawing to 233% at ?100°C and to over 500% at 125°C. Films crystallized from the rubbery amorphous state had stress–strain behavior intermediate between that of the amorphous and melt-crystallized films at all test temperatures. Density measurements on the drawn material indicate that void formation occurs simultaneously with the formation of fibrillar crystals. Necking resulted in density increases for amorphous films, and density decreases for the semicrystalline films. 相似文献
29.
Chan-Ik?Park Han-Cheol?ChoeEmail author Chae-Heon?Chung 《Metals and Materials International》2004,10(6):549-553
Regardless of the type of performed restoration, in most cases, a screw connection is employed between the abutment and implant.
For this reason, implant screw loosening has remained a problem in restorative practices. The purpose of this study was to
compare the surface of coated/plated screws with titanium and gold alloy screws and to evaluate the physical properties of
coated/plated material after scratch tests via FE-SEM (field emission scanning electron microscopy) investigation. GoldTite,
titanium screws provided by 3i (Implant Innovation, USA) and TorqTite, titanium screws by Steri-Oss (Nobel Biocare, USA) and
gold screws and titanium screws by AVANA (Osstem Implant, Korea) were selected for this study. The surface, crest, and root
of the abutment screws were observed by FE-SEM. A micro-diamond needle was also prepared for the scratch test. Each abutment
screw was fixed, and a scratch on the surface of the head region was made at constant load and thereafter the fine trace was
observed with FE-SEM. The surface of GoldTite was smoother than that of other screws and it also had abundant ductility and
malleability compared with titanium and gold screws. The scratch tests also revealed that teflon particles were exfoliated
easily in the screw coated with teflon. The titanium screw had rough surface and low ductility. The clinical use of gold-plated
screws is recommended as a means of preventing screw loosening. 相似文献
30.