全文获取类型
收费全文 | 682篇 |
免费 | 31篇 |
专业分类
电工技术 | 8篇 |
综合类 | 1篇 |
化学工业 | 178篇 |
金属工艺 | 11篇 |
机械仪表 | 8篇 |
建筑科学 | 33篇 |
能源动力 | 13篇 |
轻工业 | 123篇 |
水利工程 | 5篇 |
石油天然气 | 1篇 |
无线电 | 33篇 |
一般工业技术 | 97篇 |
冶金工业 | 115篇 |
原子能技术 | 1篇 |
自动化技术 | 86篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 32篇 |
2021年 | 42篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 23篇 |
2017年 | 15篇 |
2016年 | 24篇 |
2015年 | 17篇 |
2014年 | 18篇 |
2013年 | 40篇 |
2012年 | 42篇 |
2011年 | 59篇 |
2010年 | 42篇 |
2009年 | 28篇 |
2008年 | 47篇 |
2007年 | 36篇 |
2006年 | 36篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 5篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有713条查询结果,搜索用时 0 毫秒
91.
Object
Recent advances have allowed oscillating gradient (OG) diffusion MRI to infer the sizes of micron-scale axon diameters. Here the effects on the precision of the inferred diameters are studied when reducing the number of images collected to reduce imaging time for clinical feasibility.Materials and methods
Monte Carlo simulations of cosine OG sequences (50–1000 Hz) using a two-compartment model on a parallel cylinder (diameters 1–5 μm) geometry were conducted. Temporal diffusion spectroscopy was used to infer axon diameters. Three different gradient sets were simulated with different combinations of gradient strengths.Results
Five frequencies were adequate for d = 3–5 μm with single-sized cylinders and for effective mean axon diameters greater than 2 μm for cylinders with a distributions of diameters. There was some improvement in precision for d = 1–2 μm with 10 frequencies. It is better to repeat measurements at higher gradient strengths than to use a range of gradient strengths. The improvement tended to be greatest when using fewer frequencies and was especially noticeable at very high gradient strengths.Conclusion
Images can be collected with fewer gradient strengths and frequencies without sacrificing the precision of the measurements. This could be useful in reducing imaging time so that OG techniques can be used in clinical settings.92.
Duhamel M Wehr SD Yu L Rizvi H Seepersad D Dworatzek S Cox EE Edwards EA 《Water research》2002,36(17):4193-4202
An anaerobic mixed microbial culture was enriched from soil and groundwater taken from a site contaminated with trichloroethene (TCE). This enrichment culture was divided into four subcultures amended separately with either perchloroethene (PCE), TCE, cis-dichloroethene (cDCE) or vinyl chloride (VC). In each of the four subcultures, the chlorinated ethenes were rapidly, consistently, and completely converted to ethene at rates of 30-50 micromol/l of culture per day, or an average 160 micro-electron equivalents/l of culture per day. These cultures were capable of sustained and rapid dechlorination of VC, and could not dechlorinate 1,2-dichloroethane, differentiating them from Dehalococcoides ethenogenes, the only known isolate capable of complete dechlorination of PCE to ethene. Chloroform (CF) and 1,1,1-trichloroethane, frequent groundwater co-contaminants with TCE and PCE, inhibited chlorinated ethene dechlorination. Most strongly inhibited was the final conversion of VC to ethene, with complete inhibition occurring at an aqueous CF concentration of 2.5 microM. Differences in rates and community composition developed between the different subcultures, including the loss of the VC enrichment culture's ability to dechlorinate PCE. Denaturing gradient gel electrophoresis of amplified bacterial 16S rRNA gene fragments identified three different DNA sequences in the enrichment cultures, all phylogenetically related to D. ethenogenes. Based on the PCR-DGGE results and substrate utilization patterns, it is apparent that significant mechanistic differences exist between each step of dechlorination from TCE to ethene, especially for the last important dechlorination step from VC to ethene. 相似文献
93.
Hemmrich K Salber J Meersch M Wiesemann U Gries T Pallua N Klee D 《Journal of materials science. Materials in medicine》2008,19(1):257-267
Biodegradable polyesters are established biomaterials in medicine due to their chemical characteristics and options for material
processing. A main problem, however, is the release of acid degradation products during biodegradation with severe local pH-drops
and inflammatory reactions. Polyesteramides, in contrast, show a less prominent pH-drop during degradation. In this study,
we developed a simple, reproducible synthesis of the poly(ester amide) (PEA) type C starting from ε-caprolactame, 1,4-butanediol,
and adipic acid in a one-batch two-step reaction and conducted the manufacturing of PEA-derived 3D textile scaffolds applicable
for tissue engineering purposes. The thermal and mechanical properties of PEA-type C were analysed and the structural conformity
of different batches was confirmed by NMR spectroscopy and size exclusion chromatography. The polymer was formed into nonwovens
by textile manufacturing. Cytotoxicity tests and X-ray photoelectron spectroscopy (XPS) were used to analyze the effect of
scaffold extraction before cell seeding. The manufactured carriers were seeded with human preadipocytes and examined for cellular
proliferation and differentiation. The production of PEA type C successfully occurred via simultaneous ring-opening polymerization
of ε-caprolactame and polycondensation with 1,4-butanediol and adipic acid at 250 °C under high-vacuum. Soxhlet extraction
allowed optimal cleaning of nonwoven scaffolds. Extracted PEA-derived matrices were capable of allowing good adherence, proliferation,
and differentiation of preadipocytes. These results are encouraging and guidance towards an optimally prepared nonwoven carrier
applicable for clinical use.
K. Hemmrich and J. Salber have contributed equally. 相似文献
94.
Fernandes Myra; Ross Michael; Wiegand Melanie; Schryer Emily 《Canadian Metallurgical Quarterly》2008,23(2):297
There is disagreement in the literature about whether a "positivity effect" in memory performance exists in older adults. To assess the generalizability of the effect, the authors examined memory for autobiographical, picture, and word information in a group of younger (17-29 years old) and older (60-84 years old) adults. For the autobiographical memory task, the authors asked participants to produce 4 positive, 4 negative, and 4 neutral recent autobiographical memories and to recall these a week later. For the picture and word tasks, participants studied photos or words of different valences (positive, negative, neutral) and later remembered them on a free-recall test. The authors found significant correlations in memory performance, across task material, for recall of both positive and neutral valence autobiographical events, pictures, and words. When the authors examined accurate memories, they failed to find consistent evidence, across the different types of material, of a positivity effect in either age group. However, the false memory findings offer more consistent support for a positivity effect in older adults. During recall of all 3 types of material, older participants recalled more false positive than false negative memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
95.
Ohan Jeneva L.; Cormier Nicole; Hepp Shellane L.; Visser Troy A. W.; Strain Melanie C. 《Canadian Metallurgical Quarterly》2008,23(3):436
This study surveyed elementary school teachers in Melbourne, Australia to investigate their knowledge about attention-deficit/hyperactivity disorder (ADHD) and its impact on their reported behavior toward and perceptions of children with ADHD. Consistent with previous international findings, teachers demonstrated good overall knowledge about ADHD, with strengths in knowledge of symptoms/diagnosis and weaknesses in knowledge of causes and treatments. To investigate how knowledge impacted reported behaviors and perceptions, teachers also read vignettes of children with ADHD symptoms and rated their reactions to these children. In general, teachers with high, and to some extent average, knowledge about ADHD reported more helpful behaviors (e.g., help-seeking for their students) and perceptions (e.g., perceive the benefit of behavioral and educational treatments). However, teachers with high and average knowledge also predicted that these children would be more disruptive in the classroom, and reported having less confidence in their ability to manage these children. Implications and need for future research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
The fast separation of a mixture of 29 compounds by using comprehensive two-dimensional gas chromatography is reported. Capillary column sets with shorter lengths and smaller inner diameter in both the first and second dimensions have been tested, for both fast chiral and achiral separations. Fast chiral separations, which included enantiomer separations of limonene, linalool, citronellol, and alpha-isomethylionone, were achieved within 23 min, which corresponds to approximately 2-fold faster than analyses under conditions previously considered as normal. Fast achiral separations, which do not have the restriction of requiring a minimum quality of chiral resolution, were obtained within 5 min, which is markedly faster than separations on the normal column set under conditions more commonly employed. The achiral fast GC x GC method used a 5 m x 0.1 mm i.d. first dimension column, interfaced to a 0.3 m x 0.05 mm i.d. second column, with temperature program rate of 35 degrees C.min-1; a modulation period of 1 s was employed. Peak widths at baseline on the first column were a little over 1 s, while modulated peak widths at half-height recorded with a flame ionization detector operating at 200 Hz were approximately 30 ms. The benefits and limitations of GC x GC for fast chiral and achiral separations are reported and discussed. 相似文献
97.
Kirsch P Assouar MB Elmazria O Hakiki ME Mortet V Alnot P 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(7):1486-1491
In this work, we report on the fabrication results of surface acoustic wave (SAW) devices operating at frequencies up to 8 GHz. In previous work, we have shown that high acoustic velocities (9 to 12 km/s) are obtained from the layered AIN/diamond structure. The interdigital transducers (IDTs) made of aluminium with resolutions up to 250 nm were successfully patterned on AIN/diamond-layered structures with an adapted technological process. The uniformity and periodicity of IDTs were confirmed by field emission scanning electron microscopy and atomic force microscopy analyses. A highly oriented (002) piezoelectric aluminum nitride thin film was deposited on the nucleation side of the CVD diamond by magnetron sputtering technique. The X-ray diffraction effectuated on the AIN/diamond-layered structure exhibits high intensity peaks related to the (002) AIN and (111) diamond orientations. According to the calculated dispersion curves of velocity and the electromechanical coupling coefficient (K2), the AIN layer thickness was chosen in order to combine high velocity and high K2. Experimental data extracted from the fabricated SAW devices match with theoretical values quite well. 相似文献
98.
Bueno JM Hunter JJ Cookson CJ Kisilak ML Campbell MC 《Journal of the Optical Society of America. A, Optics, image science, and vision》2007,24(5):1337-1348
We present a polarimetric technique to improve fundus images that notably simplifies and extends a previous procedure [Opt. Lett.27, 830 (2002)]. A generator of varying polarization states was incorporated into the illumination path of a confocal scanning laser ophthalmoscope. A series of four images, corresponding to independent incoming polarization states, were recorded. From these images, the spatially resolved elements of the top row of the Mueller matrix were computed. From these elements, images with the highest and lowest quality (according to different image quality metrics) were constructed, some of which provided improved visualization of fundus structures of clinical importance (vessels and optic nerve head). The metric values were better for these constructed images than for the initially recorded images and better than averaged images. Entropy is the metric that is most sensitive to differences in the image quality. Improved visualization of features could aid in the detection, localization, and tracking of ocular disease and may be applicable in other biomedical imaging. 相似文献
99.
Nanoporous hard carbon membranes for medical applications 总被引:1,自引:0,他引:1
Narayan RJ Jin C Menegazzo N Mizaikoff B Gerhardt RA Andara M Agarwal A Shih CC Shih CM Lin SJ Su YY 《Journal of nanoscience and nanotechnology》2007,7(4-5):1486-1493
Current blood glucose sensors have proven to be inadequate for long term in vivo applications; membrane biofouling and inflammation play significant roles in sensor instability. An ideal biosensor membrane material must prevent protein adsorption and promote integration of the sensor with the surrounding tissue. Furthermore, biosensor membranes must be sufficiently thin and porous in order to allow the sensor to rapidly respond to fluctuations in analyte concentration. In this study, the use of diamondlike carbon-coated anodized aluminum oxide as a potential biosensor membrane is discussed. Diamondlike carbon films and diamondlike carbon-coated anodized aluminum oxide nanoporous membranes were examined using scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and platelet rich plasma testing. The diamondlike carbon-coated anodized aluminum oxide membranes remained free from protein adsorption during in vitro platelet rich plasma testing. We anticipate that this novel membrane could find use in immunoisolation devices, pacemakers, kidney dialysis membranes, microdialysis systems, and other devices facing biocompatibility issues that limit in vivo function. 相似文献
100.
The living radical polymerization of styrene, some styrene-analogous vinyl monomers as well as methyl methacrylate (MMA) and butyl methacrylate (BuMA) was investigated with a differential scanning calorimeter. The ability to polymerize was estimated by dynamic measurements, showing that p-methylstyrene, p-chlorostyrene, 3,4-dimethoxystyrene and 4-vinylpyridine polymerize in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) while MMA and BuMA do not. Isothermal measurements revealed an activation energy of EA = 81 kJ mol–1 for thermal bulk polymerization of styrene and values of EA = 78–94 kJ mol–1 were measured with different iniferter systems. These polymerizations have induction times which depend on the reaction temperature and the initial concentration of the iniferter systems. An influence of the kind of nitroxyl radical on the induction times was not observed. 相似文献