首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   289篇
  免费   3篇
电工技术   5篇
化学工业   63篇
金属工艺   6篇
机械仪表   5篇
建筑科学   8篇
矿业工程   1篇
能源动力   6篇
轻工业   18篇
石油天然气   2篇
无线电   22篇
一般工业技术   41篇
冶金工业   75篇
原子能技术   3篇
自动化技术   37篇
  2023年   1篇
  2022年   4篇
  2021年   5篇
  2020年   5篇
  2019年   2篇
  2018年   8篇
  2017年   3篇
  2016年   3篇
  2015年   3篇
  2014年   9篇
  2013年   8篇
  2012年   6篇
  2011年   8篇
  2010年   6篇
  2009年   8篇
  2008年   14篇
  2007年   11篇
  2006年   12篇
  2005年   11篇
  2004年   10篇
  2003年   4篇
  2002年   10篇
  2001年   3篇
  2000年   5篇
  1999年   5篇
  1998年   29篇
  1997年   13篇
  1996年   9篇
  1995年   11篇
  1994年   5篇
  1993年   8篇
  1992年   3篇
  1991年   4篇
  1990年   5篇
  1989年   4篇
  1988年   4篇
  1987年   2篇
  1985年   1篇
  1984年   3篇
  1983年   2篇
  1981年   3篇
  1980年   2篇
  1979年   3篇
  1977年   1篇
  1976年   5篇
  1975年   4篇
  1974年   2篇
  1973年   1篇
  1972年   3篇
  1966年   1篇
排序方式: 共有292条查询结果,搜索用时 0 毫秒
11.
12.
The combined use of global positioning system (GPS) technology and motion sensors within the discipline of movement ecology has increased over recent years. This is particularly the case for instrumented wildlife, with many studies now opting to record parameters at high (infra-second) sampling frequencies. However, the detail with which GPS loggers can elucidate fine-scale movement depends on the precision and accuracy of fixes, with accuracy being affected by signal reception. We hypothesized that animal behaviour was the main factor affecting fix inaccuracy, with inherent GPS positional noise (jitter) being most apparent during GPS fixes for non-moving locations, thereby producing disproportionate error during rest periods. A movement-verified filtering (MVF) protocol was constructed to compare GPS-derived speed data with dynamic body acceleration, to provide a computationally quick method for identifying genuine travelling movement. This method was tested on 11 free-ranging lions (Panthera leo) fitted with collar-mounted GPS units and tri-axial motion sensors recording at 1 and 40 Hz, respectively. The findings support the hypothesis and show that distance moved estimates were, on average, overestimated by greater than 80% prior to GPS screening. We present the conceptual and mathematical protocols for screening fix inaccuracy within high-resolution GPS datasets and demonstrate the importance that MVF has for avoiding inaccurate and biased estimates of movement.  相似文献   
13.
The antifungal activity of several components of essential oils were evaluated using a paper-disk method. The substances investigated are structurally related to eugenol. Equimolar amounts were tested on more than ten fungal strains known to contaminate food. Iso-eugenol, cinnamaldehyde, carvacrol, eugenol and thymol revealed the strongest antifungal activity. The most resistant strain appeared to be Penicillium verrucosum var. cyclopium, and the most sensitive was P. viridicatum. Some of the structural effects were considered, including a free hydroxyl group in connection with an alkyl substituent which seemed to represent an especially active configuration of phenolic compounds and which rendered antimicrobial activity.  相似文献   
14.
Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 + TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions with energies ranging from 0.5 to 10 MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5 nm individual layer thickness.  相似文献   
15.
The present electromyographic study is a first step toward shedding light on the involvement of affective processes in congruent and incongruent facial reactions to facial expressions. Further, empathy was investigated as a potential mediator underlying the modulation of facial reactions to emotional faces in a competitive, a cooperative, and a neutral setting. Results revealed less congruent reactions to happy expressions and even incongruent reactions to sad and angry expressions in the competition condition, whereas virtually no differences between the neutral and the cooperation condition occurred. Effects on congruent reactions were found to be mediated by cognitive empathy, indicating that the state of empathy plays an important role in the situational modulation of congruent reactions. Further, incongruent reactions to sad and angry faces in a competition setting were mediated by the emotional reaction of joy, supporting the assumption that incongruent facial reactions are mainly based on affective processes. Additionally, strategic processes (specifically, the goal to create and maintain a smooth, harmonious interaction) were found to influence facial reactions while being in a cooperative mindset. Now, further studies are needed to test for the generalizability of these effects. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
16.
This paper describes a set of simple methods for comparative light and electron microscopy studies on tissue cultured tumour cells derived from both noninvasive and invasive carcinogen-induced rat urinary bladder carcinomas. Cells are grown on Thermanox plastic coverslips and fixed in situ. Each plastic coverslip is then divided with scissors into four parts: the first is processed for light microscopy, the second for thin-section electron microscopy, the third for freeze-fracture electron microscopy, and the fourth for scanning electron microscopy. In some experiments, portions of the culture which have first been examined by light microscopy are subsequently prepared for electron microscopy. In this way, the culture conditions are kept constant and comparison of structural features (i.e. intercellular junctions) by several preparative techniques is possible. Noninvasive and invasive rat bladder tumour cells, characterized by numerous pleomorphic microvilli, have normal zonulae occludentes at the apices of lateral surfaces of tumour cells in all cultures. In some areas of invasive tumour cells, occludens junctions are focally attenuated, consisting of only one or two strands, and occasionally the strands are discontinuous. Gap junctions, type PF-1, as well as numerous demosomes are present in all cell lines. Thus, intercellular junctions in noninvasive and invasive rate bladder epithelial cell lines bear a striking resemblance to those previously described in the comparable solid primary tumours. These culture systems may be useful for studying factors which influence the formation of intercellular junctions during malignant transformation.  相似文献   
17.
4‐Anilinoquinolines were identified as potent and narrow‐spectrum inhibitors of the cyclin G associated kinase (GAK), an important regulator of viral and bacterial entry into host cells. Optimization of the 4‐anilino group and the 6,7‐quinoline substituents produced GAK inhibitors with nanomolar activity, over 50 000‐fold selectivity relative to other members of the numb‐associated kinase (NAK) subfamily, and a compound (6,7‐dimethoxy‐N‐(3,4,5‐trimethoxyphenyl)quinolin‐4‐amine; 49 ) with a narrow‐spectrum kinome profile. These compounds may be useful tools to explore the therapeutic potential of GAK in prevention of a broad range of infectious and systemic diseases.  相似文献   
18.
The purpose of this work is to demonstrate how α-methylstyrene (AMS) can replace styrene in preparing styrene–butadiene (SB) type latexes and to compare the properties of the paper coating of the prepared α-methylstyrene–butadiene emulsion with the commercial styrene–butadiene latex reference sample. A lot of work is nowadays being conducted on different biorefinery concepts replacing fossil oil with biomass based raw materials due to the expected rise of the fossil oil cost. Aromatics can in principle be produced from renewable raw materials, such as lignin, sugars and terpenes for example. The potential methods include thermochemical conversions, catalytic fast pyrolysis, metabolic engineering, catalytic aromatisation and dehydrogenation among others. Terpenes, such as α-limonene and pinene, are possible sources of aromatics, and they can indeed be catalytically converted to p-cymene. Industrial hydrodealkylation and disproportionation processes developed by major petrochemical companies can further convert p-cymene to BTX aromatics or simultaneously dehydrogenate the alkyl chain of p-cymene to styrenic monomers such as α-methylstyrene. Based on the measured paper properties for uncalendered and calendered coated samples, AMS proved to be adequate to replace the oil based styrene in commercial reference SB latexes. Even though the emulsion polymerisation for the α-methylstyrene–butadiene latex was not optimised, almost all tested properties were at least equally good as in the commercial reference sample. α-Methylstyrene containing coating colours had slightly higher viscosity than the other coating colours. Coating colours containing α-methylstyrene seems to have an improved water retention compared to the commercial reference styrene–butadiene latex coating colour and the laboratory prepared styrene–butadiene coating colour. The paper coated with the commercial reference latex containing coating colour was less porous than the other coated papers. Despite of that, both dry and wet surface strength were at least equally good as in the case of the commercial reference latex. The results are promising when thinking of the future development of the bio-based latexes.  相似文献   
19.
Rosemary (Rosmarinus officinalis) is mainly known for its cooking qualities, but it possesses an essential oil with pharmacological properties. Moreover, this plant was the start of forest fires in Provence, France. The presence of biopolymers can contribute to electrical energy production by biomass combustion. The aim of this work was to study a stalk of rosemary during its biological cycle (November 1998 to June 1999). The chemical analysis (water, mineral ashes, cellulose, lignin, holocellulose, and extractives) showed few variations during this period. Leaves and branches differentiated themselves according to their chemical composition. Analyzed by chromatography gas–liquid chromatography/mass spectroscopy (GC‐MS) and gas–liquid chromatography/flam ionization detector (GC‐FID), the essential oil of this rosemary had a high level of camphor (30–45%), which could be used in new therapeutics (cardiac and respiratory analeptic). Finally, the simultaneous thermal analysis (DTA‐TG) was run on the fresh plants and the dried powdered samples. Several kinetic constants of the biopolymers had been computed: activation energies of cellulose and holocellulose. During heating, the rosemary's lignin decomposed more than others plants, thereby increasing the fire risks. The chemical, chromatographic, and thermal analysis run on the rosemary could be applied on other species in the Mediterranean basin. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 747–756, 2002  相似文献   
20.
The assignment of nonexchanging protons of a small microcrystalline protein, the alpha-spectrin SH3 domain (7.2 kDa, 62 residues), was achieved by means of three-dimensional (3D) heteronuclear (1H-13C-13C) magic-angle spinning (MAS) NMR dipolar correlation spectroscopy. With the favorable combination of a high B(0)-field, a moderately high spinning frequency, and frequency-switched Lee-Goldburg irradiation applied during 1H evolution, a proton linewidth < or =0.5 ppm at 17.6 Tesla was achieved for the particular protein preparation used. A comparison of the solid-state 1H chemical shifts with the shifts found in solution shows a remarkable similarity, which reflects the identical protein structures in solution and in the solid. Significant differences between the MAS solid- and liquid-state 1H chemical shifts are only observed for residues that are located at the surface of the protein and that exhibit contacts between different SH3 molecules. In two cases, aromatic residues of neighboring SH3 molecules induce pronounced upfield ring-current shifts for protons in the contact area.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号