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   5308篇
  免费   422篇
  国内免费   3篇
电工技术   33篇
综合类   3篇
化学工业   1029篇
金属工艺   55篇
机械仪表   74篇
建筑科学   156篇
矿业工程   9篇
能源动力   94篇
轻工业   1263篇
水利工程   72篇
石油天然气   28篇
无线电   204篇
一般工业技术   758篇
冶金工业   1233篇
原子能技术   10篇
自动化技术   712篇
  2024年   9篇
  2023年   52篇
  2022年   61篇
  2021年   143篇
  2020年   116篇
  2019年   127篇
  2018年   214篇
  2017年   203篇
  2016年   192篇
  2015年   168篇
  2014年   215篇
  2013年   410篇
  2012年   352篇
  2011年   334篇
  2010年   250篇
  2009年   231篇
  2008年   246篇
  2007年   237篇
  2006年   164篇
  2005年   126篇
  2004年   110篇
  2003年   103篇
  2002年   97篇
  2001年   81篇
  2000年   53篇
  1999年   68篇
  1998年   498篇
  1997年   271篇
  1996年   179篇
  1995年   92篇
  1994年   72篇
  1993年   72篇
  1992年   21篇
  1991年   15篇
  1990年   11篇
  1989年   13篇
  1988年   14篇
  1987年   17篇
  1986年   12篇
  1985年   13篇
  1984年   7篇
  1983年   5篇
  1982年   2篇
  1981年   10篇
  1980年   8篇
  1978年   8篇
  1977年   8篇
  1976年   18篇
  1973年   2篇
  1960年   1篇
排序方式: 共有5733条查询结果,搜索用时 15 毫秒
991.
Evolutionary processes in biological tissue, such as adaptation or remodeling, represent an enterprising area of research. In this paper, we present a multiscale model for the remodeling of fibered structures, such as bundles of collagen fibrils. With this aim, we introduce a von Mises statistical distribution function to account for the directional dispersion of the fibrils, and we remodel the underlying fibrils by changing their orientation. To numerically compute this process, we make use of the microsphere approach, which provides a useful multiscale tool for homogenizing the microstructure behavior, related to the fibrils of the bundle, in the macroscale of the problem. The results show how the fibrils respond to the stimulus by reorientation of their structure. This process leads to a stiffer material eventually reaching a stationary state. These results are in agreement with those reported in the literature, and they characterize the adaptation of biological tissue to external stimuli.  相似文献   
992.
EMPIRE10 (Evaluation of Methods for Pulmonary Image REgistration 2010) is a public platform for fair and meaningful comparison of registration algorithms which are applied to a database of intrapatient thoracic CT image pairs. Evaluation of nonrigid registration techniques is a nontrivial task. This is compounded by the fact that researchers typically test only on their own data, which varies widely. For this reason, reliable assessment and comparison of different registration algorithms has been virtually impossible in the past. In this work we present the results of the launch phase of EMPIRE10, which comprised the comprehensive evaluation and comparison of 20 individual algorithms from leading academic and industrial research groups. All algorithms are applied to the same set of 30 thoracic CT pairs. Algorithm settings and parameters are chosen by researchers expert in the configuration of their own method and the evaluation is independent, using the same criteria for all participants. All results are published on the EMPIRE10 website (http://empire10.isi.uu.nl). The challenge remains ongoing and open to new participants. Full results from 24 algorithms have been published at the time of writing. This paper details the organization of the challenge, the data and evaluation methods and the outcome of the initial launch with 20 algorithms. The gain in knowledge and future work are discussed.  相似文献   
993.
The inactivation of pectinesterase (PE) in a commercial enzyme formulation (CEF) under pulsed electric fields (PEF) was studied. Samples of an aqueous solution of the CEF were exposed to exponential waveform pulses for up to 16 ms at electric field intensities ranging from 5 to 24 kV cm–1. Pulses were delivered in monopolar mode. The observed inactivation of the enzyme was described by several kinetics and regarding the input of electrical energy density (Q) models using Bayesian non-linear regression. Posterior distributions of the characteristic parameters for each kinetic model (based on the Hülsheger or the Weibull equation) and each Q model (based on exponential decay or the Weibull equation) were obtained. Kinetics models based on the Weibull equation showed better goodness and accuracy than the other models.  相似文献   
994.
Polymerase chain reaction amplification of a conserved region of the -actin gene has been used for the specific identification of goose (Anser anser) and mule duck (Anas platyrhynchos×Cairina moschata) foie gras. Universal primers were used for the amplification of a DNA fragment containing three introns and four exons of the -actin gene in goose and mule duck. Sequence analysis of the amplified fragments was necessary for the design of forward species-specific primers in the goose and mule duck -actin genes. The use of species-specific forward primers, together with a reverse universal primer, produced amplicons of different length, allowing clear identification of goose and mule duck foie gras samples. Analysis of experimental mixtures demonstrated that 1% of duck can be easily detected in goose foie gras using the PCR method developed here. This genetic marker can be very useful for the accurate identification of these two species in foie gras products.  相似文献   
995.
The aim of this research was to study and model the kinetics of the hot-air drying of Aloe vera (Aloe barbadensis Miller) and to evaluate the influence of temperature on the kinetic parameters for the proposed models. A convective dryer was used at 50, 60, 70, 80 and 90 °C with an air flow of 2.0±0.2 m/s. The sorption isotherm of the fresh product was mathematically described by the Guggenheim, Anderson and de Boer (GAB) model, giving as a result monolayer moisture of 0.20 g water/g d.b. The mathematical models evaluated in the kinetic research included five empirical equations (Newton, Henderson-Pabis, Page, modified Page and Fick's diffusional model). The fit quality of the proposed models was evaluated by using the linear regression coefficient (r2), sum square error (SSE), root mean square error (RMSE) and Chi-square statistic (χ2). The diffusivity coefficient increased with the temperature from 5.30 to 17.73×10−10 m2/s, for a range of temperatures between 50 and 90 °C, with an estimated activation energy of 30.37 kJ/mol. When comparing the experimental moisture values with those estimated by the proposed models, the modified Page model provided the best to fit of the data, showing that this equation correctly simulates the Aloe vera drying process and represents an excellent tool for estimating its drying time.  相似文献   
996.
Penicillium polonicum, a common mold on dry-cured meat products, is able to produce verrucosidin, a potent neurotoxin. The ability of P. polonicum isolated from dry-cured ham to grow and produce verrucosidin from 4 to 40 degrees C at water activities (a(w)) of 0.99, 0.97, and 0.95 on malt extract agar (MEA) and a medium made up with meat extract, peptone, and agar (MPA) was evaluated. Verrucosidin was quantified by high-pressure liquid chromatography and mass spectrometry. P. polonicum was able to grow on MEA and MPA at all the a(w) values tested from 4 to 37 degrees C but not at 40 degrees C. The optimal environmental conditions for growth were 20 degrees C, 0.99 a(w) on MEA and 20 to 25 degrees C, 0.97 a(w) on MPA, but the highest amount of verrucosidin was obtained at 25 degrees C, 0.99 a(w) in both media. No direct correlation between extension of mold growth and verrucosidin production was found. Temperature appears to be the most important factor ruling mycelial growth, whereas verrucosidin accumulation is mostly influenced by a(w). However, analysis of variance of the data showed that there was a complex interaction among all the environmental factors (medium, temperature, and a(w)) that significantly (P < 0.0001) affected growth and verrucosidin production. The reduction of a(w) to intermediates values of 0.95 has a stronger effect on growth on MEA than on MPA. Given that the meat-based medium proved to be an appropriate substrate for the biosynthesis of verrucosidin by P. polonicum, the ability of this mold to produce the toxin on meat products should be established.  相似文献   
997.
Antimicrobial action of synthetic peptides towards wine spoilage yeasts   总被引:1,自引:0,他引:1  
The antimicrobial action of selected short synthetic peptides against wine spoilage yeasts such as Cryptococcus albidus, Dekkera bruxellensis, Pichia membranifaciens, Saccharomyces cerevisiae, Zygosaccharomyces bailii and Zygosaccharomyces bisporus has been examined. Peptides analyzed include nine sequence-related antifungal hexapeptides (PAFs) previously developed by a combinatorial approach, and two representative lactoferricin B (LfcinB)-derived peptides. Different peptides had distinct activity profiles. In vitro assays identified the peptides PAF26, PAF36, and LfcinB(17-31), as having growth inhibitory properties towards several of the yeasts at low micromolar concentrations. Z. bailii and Z. bisporus were the most sensitive yeasts. In addition to their fungistatic activity, the three peptides showed fungicidal properties towards Z. bailii, Z. bisporus, and S. cerevisiae in laboratory growth medium. Remarkably, only LfcinB(17-31) against Z. bisporus had inhibitory and fungicidal properties in wine at the concentrations assayed, showing that the antimicrobial action of each peptide is dependent on both the food matrix and the target micro-organism. Lack of fungicidal activity of peptides against Z. bailii in wine is related to the presence of salt ions other than divalent cations. On the contrary, fungicidal activity of LfcinB(17-31) towards Z. bisporus was not significantly affected by wine salts. Our data identify a bioactive peptide from natural origin with potential use against the food spoilage yeast Z. bisporus, and indicate that the application of antimicrobial peptides in wine preservation deserves further investigation.  相似文献   
998.
Resveratrol is a phenolic compound of the stilbene family present in wines and various parts of the grape, including the skin. In this study, the antioxidant and prooxidant activities of resveratrol were compared with other antioxidants (butylated hydroxytoluene [BHT], butylated hydroxyacetone [BHA], phenol, propyl gallate [PG], sodium tripolyphosphate [TPP], alpha-tocopherol, and vanillin) widely used in foods. The ability of these compounds to inhibit lipid peroxidation was as follows: BHA > resveratrol > PG > tripolyphosphate > vanillin > phenol > BHT > alpha-tocopherol, the first three inhibiting the peroxidation in a concentration-dependent manner. The order of OH* scavenger activity of the tested compounds was BHA > TPP > BHT. Resveratrol and vanillin produced between 10 to 7% and 16 to 10% inhibition of the deoxyribose attack, respectively, but they do not scavenge OH*. Neither the resveratrol analyzed nor PG or the rest of compounds reacted with H202 and must be considered inefficient in catalyzing any subsequent oxidation. The ability to scavenge HOCI was, in decreasing order, PG > resveratrol > alpha-tocopherol > phenol. The other compounds did not scavenge HOCl.  相似文献   
999.
Oligosaccharide profiles in yeasted and unyeasted wheat sourdoughs inoculated withLactobacillus plantarum have been investigated. A surface response design (central composite design structure) has been used to study the effect of flour extraction rate (0.54, 1.11 and 1.68% ash content), dough yield (160, 200, and 240) and fermentation temperature (25, 30 and 35°C). Unfermented and 20 h fermented doughs were evaluated. Multivariate data analysis was used to analyse the data. Unfermented doughs contained variable amounts of glucose, fructose and maltose, but oligosaccharides with a degree of polymerization (DP) over 3 were not detected. The greatest levels of monosaccharides corresponded to yeasted sourdoughs from brown flours prepared at 30 and 35°C. Factor analysis of fermented sourdoughs showed three factors explaining 83% variability of the data. The first factor (43% variance explained) was directly related to oligosaccharides with a DP above 5, and inversely related to maltose content. Factor two (27%) was related to DP 3 and DP 4, and the third factor (16%) to glucose and fructose levels. The greatest quantities of maltose corresponded to white unyeasted sourdoughs, and the highest amounts of monosaccharides corresponded to brown unyeasted samples. On the other hand, yeasted sourdoughs contained higher amounts of oligosaccharides with DP 3 to DP 5. Samples of white flour, low consistency, yeasted and fermented at ≧30°C showed the biggest content of DP 6 and DP 7.  相似文献   
1000.
Density values are essential for the characterization of wood elements in existing structures. A new method for the in-situ density estimation of timber pieces is proposed based on weighting the residue generated by conventional drilling. This research includes the design and development of a residue collector device coupled to a conventional drill and testing on four Spanish coniferous species: Laricio pine, Scots pine, Radiata pine and Maritime pine (Pinus nigra Arn., Pinus sylvestris L., Pinus radiata D. Don. and Pinus pinaster Ait., respectively). For each species, 44 specimens (except Scots pine, with 42) 60?×?90 mm cross-section and 150 mm length (half radial and half tangential orientation) were tested. Specimen density was obtained by mass/volume ratio. Three 8 mm diameter 46.5 mm deep holes were drilled in each specimen using a brad point bit. The drilling residue was weighed and density was calculated as a ratio to bore volume. Although only slightly smaller, residue density statistically differs from average specimen density. But the specimen density can be inferred by the correlation, statistically significant, with residuals drilling density (R2?=?80.7%) and even better with residual drilling mass (R2?=?84.4%).  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