全文获取类型
收费全文 | 6205篇 |
免费 | 547篇 |
国内免费 | 13篇 |
学科分类
工业技术 | 6765篇 |
出版年
2023年 | 78篇 |
2022年 | 58篇 |
2021年 | 197篇 |
2020年 | 149篇 |
2019年 | 203篇 |
2018年 | 187篇 |
2017年 | 222篇 |
2016年 | 262篇 |
2015年 | 205篇 |
2014年 | 308篇 |
2013年 | 406篇 |
2012年 | 459篇 |
2011年 | 525篇 |
2010年 | 343篇 |
2009年 | 382篇 |
2008年 | 338篇 |
2007年 | 263篇 |
2006年 | 220篇 |
2005年 | 198篇 |
2004年 | 194篇 |
2003年 | 190篇 |
2002年 | 181篇 |
2001年 | 130篇 |
2000年 | 139篇 |
1999年 | 119篇 |
1998年 | 151篇 |
1997年 | 112篇 |
1996年 | 85篇 |
1995年 | 53篇 |
1994年 | 51篇 |
1993年 | 56篇 |
1992年 | 40篇 |
1991年 | 42篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 22篇 |
1987年 | 11篇 |
1986年 | 14篇 |
1985年 | 29篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1977年 | 5篇 |
1976年 | 11篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有6765条查询结果,搜索用时 248 毫秒
991.
We present a systematic change of the magnetic domain structure with temperature in epitaxial ferromagnetic MnAs film on GaAs (001), observed in a wide temperature range of 15-45 degrees C by magnetic force microscopy. Interestingly, it is found that, as temperature increases, the domain structure within the ferromagnetic alpha-MnAs stripes shows a mixture of head-on and simple domains at 15 degrees C and then, takes a complete transition to simple ones above 15 degrees C. This change could be understood by change in the demagnetizing factor of the cross-section of the ferromagnetic stripes with temperature. 相似文献
992.
Wu Bin Ying Da Som Moon Min Woo Lee Na Yeong Ko Nho Hoon Kwak Bumjae Lee Jin Zhu Ruoyu Zhang 《应用聚合物科学杂志》2018,135(5)
To simultaneously improve the fracture toughness and heat resistance of a cured toughened epoxy resin along with a reduction in its viscosity during the mixing process, two novel polysulfone‐type polymers are synthesized via azide–alkyne polymerization for use as toughening agents. The epoxy resin toughened with these polymers by in situ azide–alkyne polymerization during the cure process, which shows excellent processibility and based on the significantly lower viscosity (61 and 62 cP) during epoxy mixing process than that of commonly commercial polyethersulfone (PES, 127,612 cP). The novel polysulfone‐type polymer toughened epoxy resin showed the advantage in excellent fracture toughness than the PES toughened epoxy. In addition, the glass transition temperature of the novel polysulfone‐type polymer toughened epoxy resin is similar to that of the neat one (~230 °C) and does not decrease, which implies excellent heat resistance of the toughened epoxy. These phenomena can be attributed to the formation of semi‐interpenetrating polymer networks comprising the epoxy network and the linear polysulfone‐type polymers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45790. 相似文献
993.
Chang?Woo?Lee Hyun?Kyoo?Kang Kee?Hyun?ShinEmail author 《Journal of Mechanical Science and Technology》2004,18(12):2174-2181
The metal processing system usually consists of various components such as motors, work rolls, backup rolls, idle rolls, sensors,
etc. Even a simple fault in a single component in the system may cause a serious damage on the final product. It is, therefore,
necessary to diagnose the faults of the components to detect and prevent a system failure. Especially, the defects in a work
roll are critical to the quality of strip. In this study, a new 3-D diagnosis method was developed for roll shape defects
in rolling processes. The new method was induced from analyzing the rolling mechanism by using a rolling force model, a tension
model, the Hitchcock’ s equation, and measurement of the strip thickness, etc. Computer simulation shows that the proposed
method is very useful in the diagnosis of the 3-D roll shape. 相似文献
994.
Effects of seawater spray on leaf structure were investigated in Quercus acutissima by electron microscopy and X-ray microanalysis. Two-year-old seedlings of Q. acutissima were sprayed with seawater and kept in a greenhouse maintained at 25°C. The most recognizable symptoms of seawater-sprayed seedlings included leaf necrosis, crystal deposition, stomatal clogging, and chloroplast degeneration. Field emission scanning electron microscopy revealed that the leaf surface was covered with additional layers of remnants of seawater spray. Composed of sodium and chloride, cube-shaped crystals (halite) were prevalently found on trichomes and epidermis, and formed aggregates. Meanwhile, wedge-shaped crystals were deposited on epidermis and consisted of calcium and sulfur. As a result of stomatal clogging by crystal deposition on the abaxial surface, it was conceivable that plant respiration became severely hampered. Transmission electron microscopy showed degenerated cytoplasm of seawater-sprayed leaves. It was common to observe severe plasmolysis and disrupted chloroplasts with a reduced number of thylakoids in grana. These results indicate that foliar applications of seawater were sufficient to induce necrosis of Q. acutissima seedlings as an abiotic disturbance factor. 相似文献
995.
High‐Performance Triboelectric Nanogenerators Based on Electrospun Polyvinylidene Fluoride–Silver Nanowire Composite Nanofibers 下载免费PDF全文
Siuk Cheon Hyungseok Kang Han Kim Youngin Son Jun Young Lee Hyeon‐Jin Shin Sang‐Woo Kim Jeong Ho Cho 《Advanced functional materials》2018,28(2)
The preparation of ferroelectric polymer–metallic nanowire composite nanofiber triboelectric layers is described for use in high‐performance triboelectric nanogenerators (TENGs). The electrospun polyvinylidene fluoride (PVDF)–silver nanowire (AgNW) composite and nylon nanofibers are utilized in the TENGs as the top and bottom triboelectric layers, respectively. The electrospinning process facilitates uniaxial stretching of the polymer chains, which enhances the formation of the highly oriented crystalline β‐phase that forms the most polar crystalline phase of PVDF. The addition of AgNWs further promotes the β‐phase crystal formation by introducing electrostatic interactions between the surface charges of the nanowires and the dipoles of the PVDF chains. The extent of β‐phase formation and the resulting variations in the surface charge potential upon the addition of nanowires are systematically analyzed using X‐ray diffraction (XRD) and Kelvin probe force microscopy techniques. The ability of trapping the induced tribocharges increases upon the addition of nanowires to the PVDF matrix. The enhanced surface charge potential and the charge trapping capabilities of the PVDF–AgNW composite nanofibers significantly enhance the TENG output performances. Finally, the mechanical stability of the electrospun nanofibers is dramatically enhanced while maintaining the TENG performances by applying thermal welding near the melting temperature of PVDF. 相似文献
996.
Sanghoon Kim Seung Hyun Jaeyong Lee Kyu Seong Lee Woo Lee Jin Kon Kim 《Advanced functional materials》2018,28(23)
Two types (hard and soft) of the molds are widely used in nanoimprint lithography for a high throughput over a large area, and high‐resolution parallel patterning. Although hard molds have proven excellent resolutions and can be used at high temperatures, cracks often occur in the mold in addition to the requirement of high imprinting pressure. On the other hand, though soft molds can operate at lower pressures, they give poor pattern resolution. Here, a novel hybrid mold of anodized aluminum oxide (AAO) template attached to a flexible polydimethylsiloxane (PDMS) plate is introduced. Due to the flexible nature of PDMS, various polymer nanostructures are obtained on flat and curved substrates without crack formation on the AAO mold surface. Furthermore, the hybrid mold is successfully used for roll‐to‐roll imprinting for the fabrication of high density array of various shaped polymeric nanostructures over a large area. 相似文献
997.
Formation process of core‐shell microparticles by solute migration during drying of homogenous composite droplets 下载免费PDF全文
Nan Fu Winston Duo Wu Zhangxiong Wu Fei Tzhung Moo Meng Wai Woo Cordelia Selomulya Xiao Dong Chen 《American Institute of Chemical Engineers》2017,63(8):3297-3310
Particle formation process during spray drying profoundly impacts particle morphology and microstructure. This study experimentally investigated the formation of core‐shell‐structured microparticles by one‐step drying of composite droplets made of Eudragit® RS (a polycationic acrylic polymer in nanoparticle form) and silica sol. The formation of an incipient surface shell was monitored using single droplet drying technique, and the freshly formed shell was recovered for subsequent analyses. Adding silica to RS precursor increased the shell formation time and altered the properties of the incipient shell from water‐dispersible to nondispersible. The incipient shell formed from RS/silica droplets with mass ratios of 1.5%:1.5% and 0.5%:2.5% showed ingredient segregation with a preferential accumulation of RS, similar to the shell region of dried microparticles. After shell formation, excess silica sol in the liquid phase could flow inward, producing a dense core. This mobility‐governed solute migration would be useful for constructing core‐shell microparticles using other precursor systems. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3297–3310, 2017 相似文献
998.
The synthesis of a novel interpenetrating chitosan network post‐modified with spiropyran (SP) derivatives has been used to develop photochromic hydrogels. We have synthesized succinyl chitosan polymers containing a considerable number of both amines and carboxylic groups. Their intra/inter molecular amide coupling reactions and postmodification with SP derivatives resulted in the photochromic hydrogels functionalized with chitosan‐based interpenetrating polymer network structures. In this hydrogel system, SPs undergo reversible photoresponsive structural switching between a ring‐closed colorless SP form and a ring‐opened purple merocyanine form under specific light‐irradiation conditions. Notably, the photo‐mediated wettabilities and color intensities of the hydrogels increase by the increment in the molecular weight of SP‐functionalized chitosans. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45120. 相似文献
999.
Hyun-Woo Oh Chan-Seok Yun Jun Hyoung Jeon Ji-Ae Kim Doo-Sang Park Hyung Won Ryu Sei-Ryang Oh Hyuk-Hwan Song Yunhee Shin Chan Sik Jung Sang Woon Shin 《Journal of chemical ecology》2017,43(7):703-711
Diterpene resin acids (DRAs) are important components of oleoresin and greatly contribute to the defense strategies of conifers against herbivorous insects. In the present study, we determined that DRAs function as insect juvenile hormone (JH) antagonists that interfere with the juvenile hormone-mediated binding of the JH receptor Methoprene-tolerant (Met) and steroid receptor coactivator (SRC). Using a yeast two-hybrid system transformed with Met and SRC from the Indian meal moth Plodia interpunctella, we tested the interfering activity of 3704 plant extracts against JH III-mediated Met-SRC binding. Plant extracts from conifers, especially members of the Pinaceae, exhibited strong interfering activity, and four active interfering DRAs (7α-dehydroabietic acid, 7-oxodehydroabietic acid, dehydroabietic acid, and sandaracopimaric acid) were isolated from roots of the Japanese pine Pinus densiflora. The four isolated DRAs, along with abietic acid, disrupted the juvenile hormone-mediated binding of P. interpunctella Met and SRC, although only 7-oxodehydroabietic acid disrupted larval development. These results demonstrate that DRAs may play a defensive role against herbivorous insects via insect endocrine-disrupting activity. 相似文献
1000.
Jin Woo Kook In Seop Gwak You Ra Gwak Myung Won Seo See Hoon Lee 《Korean Journal of Chemical Engineering》2017,34(12):3092-3101
Characteristics of Char-CO2 gasification were compared in the temperature range of 1,100–1,400 °C using a thermogravimetric analyzer (TGA) for petroleum coke, coal chars and mixed fuels (Petroleum coke/coal ratios: 0, 0.25, 0.5, 0.75, 1). The results showed that reaction time decreased with increasing gasification temperature, BET surface area and alkali index of coal. Mixed fuels composed of petroleum coke/coal exhibited reduced activation energies. Modified volumetric reaction model and shrinking core model might be suitably matched with experimental data depending on coal type and petroleum coke/coal ratio. Rate equations were suggested by selecting gas-solid reaction rate models for each sample that could simulate CO2 gasification behavior. 相似文献