全文获取类型
收费全文 | 13527篇 |
免费 | 1092篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 147篇 |
综合类 | 8篇 |
化学工业 | 3223篇 |
金属工艺 | 577篇 |
机械仪表 | 705篇 |
建筑科学 | 314篇 |
矿业工程 | 11篇 |
能源动力 | 484篇 |
轻工业 | 1267篇 |
水利工程 | 41篇 |
石油天然气 | 21篇 |
无线电 | 1951篇 |
一般工业技术 | 2762篇 |
冶金工业 | 1700篇 |
原子能技术 | 162篇 |
自动化技术 | 1269篇 |
出版年
2023年 | 112篇 |
2022年 | 189篇 |
2021年 | 335篇 |
2020年 | 250篇 |
2019年 | 350篇 |
2018年 | 373篇 |
2017年 | 423篇 |
2016年 | 486篇 |
2015年 | 413篇 |
2014年 | 607篇 |
2013年 | 907篇 |
2012年 | 804篇 |
2011年 | 990篇 |
2010年 | 718篇 |
2009年 | 699篇 |
2008年 | 693篇 |
2007年 | 528篇 |
2006年 | 437篇 |
2005年 | 395篇 |
2004年 | 392篇 |
2003年 | 371篇 |
2002年 | 326篇 |
2001年 | 254篇 |
2000年 | 235篇 |
1999年 | 266篇 |
1998年 | 531篇 |
1997年 | 386篇 |
1996年 | 234篇 |
1995年 | 183篇 |
1994年 | 182篇 |
1993年 | 180篇 |
1992年 | 121篇 |
1991年 | 103篇 |
1990年 | 107篇 |
1989年 | 103篇 |
1988年 | 68篇 |
1987年 | 61篇 |
1986年 | 58篇 |
1985年 | 91篇 |
1984年 | 78篇 |
1983年 | 52篇 |
1982年 | 46篇 |
1981年 | 45篇 |
1980年 | 45篇 |
1979年 | 44篇 |
1978年 | 37篇 |
1977年 | 54篇 |
1976年 | 80篇 |
1975年 | 41篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Poly(ethylene terephthalate) (PET)/silica composites were prepared by melt compounding, and their rheological properties and
isothermal crystallization were discussed. Introduction of silica particles (0.5–2 wt.%) increased the storage modulus (G′) and decreased loss tangent (tanδ). However, the effect of the particles on rheological properties became negligible at
a high frequency more than ca. 70 rad/s. In the Cole–Cole plot, the PET/silica composites showed little deviation from the
master curve regardless of the presence of silica particles. The particles increased the relaxation time of PET at particularly
low frequency. The isothermal crystallization kinetics of PET/silica was examined using a differential scanning calorimeter
(DSC). The half-time of crystallization was decreased with increasing the silica content. The incorporation of silica particles
decreased the equilibrium melting temperature by ca. 5.5 °C. In addition, the composites exhibited higher average value of
Avrami exponent (2.7–2.9) in comparison with that of pure PET (2.2). 相似文献
992.
Won Young Yun Young Man Song Ho-Gyun Kim 《Reliability Engineering & System Safety》2007,92(3):308-313
This paper deals with a multiple multi-level redundancy allocation problem (MMRAP) in which all available items for redundancy (system, module and component) can be simultaneously chosen. Due to a well-known principle that the redundancy at the component level (component redundancy) is more effective than the redundancy at the system level (system redundancy), the object of redundancy allocation has been limited to the component redundancy. In addition, multi-level redundancy allocation problems (MRAP) have been addressed, considering the redundancy at the subsystem level (modular redundancy). In this paper, the MMRAP is formulated and a GA algorithm is presented to solve the problem. Some numerical examples are illustrated. 相似文献
993.
Y. Tian C.‐Y. Chen Y.‐J. Cheng A. C. Young N. M. Tucker A. K.‐Y. Jen 《Advanced functional materials》2007,17(10):1691-1697
A series of new hydrophobic two‐photon absorbing (2PA) chromophores with varied electron‐donating groups in quasi‐linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two‐photon absorption cross‐sectional (δ, expressed in GM = 1 × 10–50 cm4 s photon–1 molecule–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)‐block‐polystyrene (PMAA‐b‐PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA‐b‐PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle‐containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water‐soluble 2PA materials, which have δ values of less than 100 GM. 相似文献
994.
Young‐Hwan Lee Baek Ho Jung Tapan K. Sarkar Mengtao Yuan Zhong Ji Seong‐Ook Park 《ETRI Journal》2007,29(1):8-17
In this paper, we present a time domain combined field integral equation formulation (TD‐CFIE) to analyze the transient electromagnetic response from dielectric objects. The solution method is based on the method of moments which involves separate spatial and temporal testing procedures. A set of the RWG functions is used for spatial expansion of the equivalent electric and magnetic current densities, and a combination of RWG and its orthogonal component is used for spatial testing. The time domain unknowns are approximated by a set of orthonormal basis functions derived from the Laguerre polynomials. These basis functions are also used for temporal testing. Use of this temporal expansion function characterizing the time variable makes it possible to handle the time derivative terms in the integral equation and decouples the space‐time continuum in an analytic fashion. Numerical results computed by the proposed formulation are compared with the solutions of the frequency domain combined field integral equation. 相似文献
995.
In this letter, we study the impact of single event upsets (SEUs) in space or defense electronic systems which use memory devices such as EEPROM, and SRAM. We built a microcontroller test board to measure the effects of protons on electronic devices at various radiation levels. We tested radiation hardening at beam current, and energy levels, measured the phenomenon of SEUs, and addressed possible reasons for SEUs. 相似文献
996.
A 9‐bit 80‐MS/s CMOS pipelined folding analog‐to‐digital converter employing offset‐canceled preamplifiers and a subranging scheme is proposed to extend the resolution of a folding architecture. A fully differential dc‐decoupled structure achieves high linearity in circuit design. The measured differential nonlinearity and integral nonlinearity of the prototype are ×0.6 LSB and ×1.6 LSB, respectively. 相似文献
997.
Interference effects of ultra‐wideband devices using the frequency band from 3.1 to 10.6 GHz on wireless broadband are evaluated. The ultra‐wideband emission power spectral density that would be necessary to protect a wireless broadband station is considered. Also, an analytic scheme based on a system level simulation of a WiBro system is proposed. 相似文献
998.
Ju-Yeon Lee Jin-Hyang Kim Won-Taek Jung Young Kum Park 《Journal of Materials Science》2007,42(11):3936-3943
2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type
polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of
the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition
temperatures (T
g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG)
coefficients (d
33) of poled polymer films at 106.4 mm−1 fundamental wavelength were around 9.07 × 10−19 C (2.72 × 10−9 esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T
g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable
for nonlinear optical device applications. 相似文献
999.
The Orientations of Large Aspect‐Ratio Coiled‐Coil Proteins Attached to Gold Nanostructures
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jae‐Byum Chang Yong Ho Kim Evan Thompson Young Hyun No Nam Hyeong Kim Jose Arrieta Vitor R. Manfrinato Amy E. Keating Karl K. Berggren 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(11):1498-1505
Methods for patterning biomolecules on a substrate at the single molecule level have been studied as a route to sensors with single‐molecular sensitivity or as a way to probe biological phenomena at the single‐molecule level. However, the arrangement and orientation of single biomolecules on substrates has been less investigated. Here, the arrangement and orientation of two rod‐like coiled‐coil proteins, cortexillin and tropomyosin, around patterned gold nanostructures is examined. The high aspect ratio of the coiled coils makes it possible to study their orientations and to pursue a strategy of protein orientation via two‐point attachment. The proteins are anchored to the surfaces using thiol groups, and the number of cysteine residues in tropomyosin is varied to test how this variation affects the structure and arrangement of the surface‐attached proteins. Molecular dynamics studies are used to interpret the observed positional distributions. Based on initial studies of protein attachment to gold post structures, two 31‐nm‐long tropomyosin molecules are aligned between the two sidewalls of a trench with a width of 68 nm. Because the approach presented in this study uses one of twenty natural amino acids, this method provides a convenient way to pattern biomolecules on substrates using standard chemistry. 相似文献
1000.
A Nonconventional Approach to Patterned Nanoarrays of DNA Strands for Template‐Assisted Assembly of Polyfluorene Nanowires
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dong Geun Bae Ji‐Eun Jeong Seok Hee Kang Myunghwan Byun Dong‐Wook Han Zhiqun Lin Han Young Woo Suck Won Hong 《Small (Weinheim an der Bergstrasse, Germany)》2016,12(31):4254-4263
DNA molecules have been widely recognized as promising building blocks for constructing functional nanostructures with two main features, that is, self‐assembly and rich chemical functionality. The intrinsic feature size of DNA makes it attractive for creating versatile nanostructures. Moreover, the ease of access to tune the surface of DNA by chemical functionalization offers numerous opportunities for many applications. Herein, a simple yet robust strategy is developed to yield the self‐assembly of DNA by exploiting controlled evaporative assembly of DNA solution in a unique confined geometry. Intriguingly, depending on the concentration of DNA solution, highly aligned nanostructured fibrillar‐like arrays and well‐positioned concentric ring‐like superstructures composed of DNAs are formed. Subsequently, the ring‐like negatively charged DNA superstructures are employed as template to produce conductive organic nanowires on a silicon substrate by complexing with a positively charged conjugated polyelectrolyte poly[9,9‐bis(6′‐N,N,N‐trimethylammoniumhexyl)fluorene dibromide] (PF2) through the strong electrostatic interaction. Finally, a monolithic integration of aligned arrays of DNA‐templated PF2 nanowires to yield two DNA/PF2‐based devices is demonstrated. It is envisioned that this strategy can be readily extended to pattern other biomolecules and may render a broad range of potential applications from the nucleotide sequence and hybridization as recognition events to transducing elements in chemical sensors. 相似文献