全文获取类型
收费全文 | 385篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 3篇 |
化学工业 | 116篇 |
金属工艺 | 5篇 |
机械仪表 | 16篇 |
建筑科学 | 8篇 |
能源动力 | 17篇 |
轻工业 | 40篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 28篇 |
一般工业技术 | 58篇 |
冶金工业 | 55篇 |
原子能技术 | 10篇 |
自动化技术 | 51篇 |
出版年
2023年 | 2篇 |
2022年 | 28篇 |
2021年 | 12篇 |
2020年 | 8篇 |
2019年 | 8篇 |
2018年 | 16篇 |
2017年 | 17篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 12篇 |
2013年 | 22篇 |
2012年 | 24篇 |
2011年 | 23篇 |
2010年 | 22篇 |
2009年 | 22篇 |
2008年 | 21篇 |
2007年 | 24篇 |
2006年 | 10篇 |
2005年 | 10篇 |
2004年 | 8篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 6篇 |
2000年 | 1篇 |
1999年 | 4篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1972年 | 2篇 |
1971年 | 2篇 |
1965年 | 1篇 |
1914年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有409条查询结果,搜索用时 414 毫秒
141.
Some critical aspects of the anisotropic absorption and emission properties of quasi one-dimensional structures are reviewed in the context of III-V compound semiconductor nanowires. The unique optical and electronic properties of III-V nanowires stem from the combination of dielectric effects due to their large aspect ratio, and their specific crystallographic structure which can differ significantly from the bulk case. The growth conditions leading to single-crystal nanowires with either zinc blende or wurtzite phase are first presented. Dipole selection rules for interband transitions in common III-V compounds are then summarized for the two different phases, and corroborated by ab initio Density Functional Theory calculations of the oscillator strength. The optical anisotropy is discussed considering both the effect of refractive index mismatch between the nanowire and its surroundings and the polarization of the emitting dipoles set by the nanowire crystallographic structure and orientation. Finite Difference Time Domain simulations are finally employed to illustrate the influence of the emitting dipole orientation and the nanowire diameter on the distribution of radiation in the far-field. The importance of the correlation between structural and optoelectronic properties is highlighted in view of potential applications in future nanowire photonics. 相似文献
142.
Fei Li Weiting Liu Xin Fu Gabriella Bonsignori Umberto Scarfogliero Cesare Stefanini Paolo Dario 《Mechatronics》2012,22(2):167-176
This paper presents a bio-inspired design of a jumping mini robot including the theoretical analysis on jumping dynamics based on a simplified biological model, the dynamically optimized saltatorial leg design, the overall design of the jumping robot prototype and, as a part of the bio-mimetic research, and the measuring and comparing of the jumping characteristics between the robot and animal. The artificial saltatorial leg is designed to imitate the characteristics of a real jumping insect, kinematically and dynamically, and proposed to reduce the contact force at tarsus–ground interface during jumping acceleration thus optimizes the jumping motion by minimizing the risk of both leg ruptures and tarsus slippage. Then by means of high speed camera experiment, the jumping characteristics of the theoretical jumping model, the jumping insect leafhopper and the robot are compared so as to show the dynamic similarity and optimization results among them. The final energy integrated jumping robot prototype is able to accomplish a movement of continuous jumping, of which a single jumping reaches 100 mm high and 200 mm long, about twice and four times of its body length respectively. 相似文献
143.
Nicola F. Della Vecchia Roberto Avolio Michela Alfè Maria E. Errico Alessandra Napolitano Marco d'Ischia 《Advanced functional materials》2013,23(10):1331-1340
Rational approaches to engineering polydopamine films with tailored properties for surface coating and functionalization are currently challenged by the lack of detailed information about the polymer structure and the mechanism of buildup. Using an integrated chemical and spectroscopic approach enables the demonstration of: a) a three‐component structure of polydopamine, comprising uncyclized (catecholamine) and cyclized (indole) units, as well as novel pyrrolecarboxylic acid moieties; b) remarkable variations in the relative proportions of the cyclized and uncyclized units with starting dopamine concentration; c) the occurrence of oligomer components up to the tetramer level; d) the covalent incorporation of Tris buffer; and e) the role of dopamine quinone as a crucial control point for directing the buildup pathways and tuning the properties. The importance of the uncyclized amine‐containing units in polydopamine adhesion is also highlighted. The proper selection of substrate concentration and buffer is thus proposed as a practical means of tailoring polydopamine functionality via control of competing pathways downstream of dopamine quinone. 相似文献
144.
Cesare ROSSI Thomas G. CHONDROS Kypros F. MILIDONIS Sergio SAVINO Flavio RUSSO 《Frontiers of Mechanical Engineering》2016,11(1):12-25
The development of transportation systems has significantly enhanced the welfare and modernization of society. Wooden vehicles pulled by animals have been used for land transportation since the early Bronze Age. Whole-body gharries with rigid wheels pulled by oxen appeared in Crete by 2000 BC or earlier. Horses originating from the East were depicted in early Cretan seal-rings of the same period. The two-wheeled horsedrawn chariot was one of the most important inventions in history. This vehicle provided humanity its first concept of personal transport and was the key technology of war for 2000 years. Chariots of Mycenaean and Archaic Greece with light and flexible four-spoked wheels acting as spring suspensions were depicted in vase paintings. The development of this vehicle incorporated the seeds of a primitive design activity and was important for engineering. The Trojan horse since 1194 BC and the helepolis since 700 BC were the first known machines on a wheeled base transported by horses or self-powered. Ancient engineers invented bearings lubricated with fat, and Romans introduced the ancestors of ball bearings for their wagons and carts. The historic evolution of wheeled transportation systems, along with early traction, suspension, and braking systems, is presented in this paper. Analytical and numerical methods are incorporated to analyze the most conceivable loading situations of typically reconstructed wheeled transportation systems in ancient times. Traction requirements both for horse-driven machines and the power for internal motors are also analyzed. This study can serve as a basis for further development of detailed reconstruction of transportation systems in antiquity. 相似文献
145.
A system level implementation of a large area hybrid detector is presented. The detector used in this system consists of an array of hydrogenated amorphous silicon photodiodes directly connected to a CMOS readout chip, which is vertically integrated over the sensor array using flip-chip bonding. In particular, the proposed solution relies on a stack of interconnection layers, deposited on top of the photodiode array, to route each individual pixel output to a separate pre-amplifier channel. This avoids the need for a geometrical matching between the sensor array and the chip contact pads. As a consequence, conventional non-pixelated readout chip can be used and easy-scalable large area detectors can be produced. The CMOS chip is connected to an electronic board, providing the interfaces needed to read the signals as well as providing voltage references and power to the chip. The signals are collected and pre-processed by an FPGA chip, providing a very compact and flexible setup. 相似文献
146.
Cenni E Perut F Ciapetti G Savarino L Dallari D Cenacchi A Stagni C Giunti A Fornasari PM Baldini N 《Journal of materials science. Materials in medicine》2009,20(1):45-50
Freeze-dried bone allograft (FDBA) might be more effective in combination with platelet rich plasma (PRP) and bone marrow
stromal cells (BMSC) in accelerating bone healing. The isolation of BMSC through density gradient (pBMSC) is not extensively
applicable in clinical practice, because it increases the risk of infection. Alternatively, BMSC can be concentrated by simple
centrifugation (wBMSC) directly in the operating room. However, we do not know if wBMSC act in the same way as pBMSC. BMSC
from 10 donors were tested whether, in the presence of a combination of FDBA and autologous PRP, the osteogenic differentiation
of the cells concentrated by simple centrifugation (wBMSC + FDBA + PRP) was similar to that of pBMSC. Cell-associated alkaline
phosphatase, osterix and fibroblast growth factor-2 were higher in wBMSC + FDBA + PRP. In conclusion, the combination of FDBA
and PRP had a favouring effect on the differentiation towards osteoblasts and allowed BMSC concentrated by simple centrifugation
to differentiate as fast as BMSC purified by density gradient. 相似文献
147.
Chiesa G Rigamonti E Lovati MR Disconzi E Soldati S Sacco MG Catò EM Patton V Scanziani E Vezzoni P Arnoldi A Locati D Sirtori CR 《Molecular nutrition & food research》2008,52(10):1121-1129
Dietary exposure to soy has been associated with reduced breast cancer incidence. Soy isoflavones and protein components, such as protease inhibitors and the lunasin peptide, have been indicated as potential agents reducing carcinogenesis. In this study, the effect of soy-based diets was evaluated in a transgenic mouse model of breast carcinoma, overexpressing the neu oncogene. Neu female mice were fed for 20 wk a soy- and isoflavone-free diet (IFD), 4RF21 laboratory mouse diet, soy-based, thus isoflavone-rich (STD), or AIN-76-based semisynthetic diets with a soy protein isolate (SPI) or an isoflavone-poor soy protein concentrate (IPSP) as protein source. Mice were then sacrificed and tumors removed. Mammary tumor weights were not different in SPI versus IFD and STD fed mice. In contrast, mice fed IPSP showed reduced tumor progression versus IFD and STD groups (p < 0.05). Moreover, IPSP fed mice showed lower bromo-2'-deoxyuridine (BrdU) incorporation into breast tumor cells compared to STD and SPI fed animals (p < 0.02). Lung metastases were detected in 80% of IFD fed mice, in 70% of mice fed STD and SPI, and only in 50% of the IPSP fed animals. These results indicate that a diet containing an isoflavone-poor soy protein concentrate may inhibit breast tumor progression and metastasis development. 相似文献
148.
Aspects of Vietnamese Sutchi Catfish (Pangasius Hypophthalmus) Frozen Fillet Quality: Microbiological Profile and Chemical Residues.
下载免费PDF全文
![点击此处可从《Journal of Food Safety》网站下载免费的PDF全文](/ch/ext_images/free.gif)
149.
Nicola Detta Cesare Errico Dinuccio Dinucci Dario Puppi David A. Clarke Gwendolen C. Reilly Federica Chiellini 《Journal of materials science. Materials in medicine》2010,21(5):1761-1769
Novel polymeric micro-nanostructure meshes as blood vessels substitute have been developed and investigated as a potential solution to the lack of functional synthetic small diameter vascular prosthesis. A commercial elastomeric polyurethane (Tecoflex® EG-80A) and a natural biopolymer (gelatin) were successfully co-electrospun from different spinnerets on a rotating mandrel to obtain composite meshes benefiting from the mechanical characteristics of the polyurethane and the natural biopolymer cytocompatibility. Morphological analysis showed a uniform integration of micrometric (Tecoflex®) and nanometric (gelatin) fibers. Exposure of the composite meshes to vapors of aqueous glutaraldehyde solution was carried out, to stabilize the gelatin fibers in an aqueous environment. Uniaxial tensile testing in wet conditions demonstrated that the analyzed Tecoflex®–Gelatin specimens possessed higher extensibility and lower elastic modulus than conventional synthetic grafts, providing a closer matching to native vessels. Biological evaluation highlighted that, as compared with meshes spun from Tecoflex® alone, the electrospun composite constructs enhanced endothelial cells adhesion and proliferation, both in terms of cell number and morphology. Results suggest that composite Tecoflex®–Gelatin meshes could be promising alternatives to conventional vascular grafts, deserving of further studies on both their mechanical behaviour and smooth muscle cell compatibility. 相似文献
150.