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   1382篇
  免费   88篇
  国内免费   4篇
电工技术   12篇
化学工业   442篇
金属工艺   57篇
机械仪表   60篇
建筑科学   51篇
矿业工程   13篇
能源动力   46篇
轻工业   102篇
水利工程   5篇
石油天然气   9篇
无线电   87篇
一般工业技术   268篇
冶金工业   106篇
原子能技术   7篇
自动化技术   209篇
  2023年   11篇
  2022年   76篇
  2021年   137篇
  2020年   43篇
  2019年   45篇
  2018年   67篇
  2017年   50篇
  2016年   84篇
  2015年   64篇
  2014年   69篇
  2013年   108篇
  2012年   79篇
  2011年   99篇
  2010年   57篇
  2009年   53篇
  2008年   62篇
  2007年   40篇
  2006年   32篇
  2005年   35篇
  2004年   27篇
  2003年   25篇
  2002年   10篇
  2001年   11篇
  2000年   10篇
  1999年   10篇
  1998年   24篇
  1997年   24篇
  1996年   22篇
  1995年   13篇
  1994年   3篇
  1993年   8篇
  1992年   1篇
  1991年   7篇
  1990年   9篇
  1989年   7篇
  1988年   3篇
  1987年   2篇
  1986年   4篇
  1985年   4篇
  1984年   5篇
  1983年   4篇
  1981年   3篇
  1980年   5篇
  1978年   8篇
  1977年   6篇
  1976年   4篇
  1975年   1篇
  1973年   2篇
  1964年   1篇
排序方式: 共有1474条查询结果,搜索用时 31 毫秒
131.
132.
We have built and used a set of three cylindrical drift chambers with delay line readout. The azimuthal coordinate is obtained in the conventional way; the resolution obtained is about 300 microns. The axial coordinate is obtained fran signals induced on printed circuit delay lines with a resolution of ±5 mn FWHM. The chambers are 120 cm long and have diamters of 29.3 cm, 70.1 cm and 118.5.  相似文献   
133.
The temperature dependencies of the resistivity for the superconducting ruthenocuprates of nominal compositions RuSr2GdCu2O8, Ru0.98Sr2GdCu2O8 and Ru0.5Sr2GdCu2.5O8?δ were examined for the magnetic field dependent characteristics of the superconducting transitions. The effect of the insignificant diminishing of the Ru/Cu ratio in parent RuSr2GdCu2O8 was confirmed as relevant for the stabilisation of the superconducting phase. Noted differences in the compared characteristics are interpreted for possible inhomogeneous nucleation of the superconducting phase in the parent ruthenocuprate. The phase anisotropy in RuSr2GdCu2O8 and Ru0.98Sr2GdCu2O8, in presence of the compounds Ru magnetism, appears to be a cause of a significant softening of the H c2(T) phase line. An anomalous lowering of the magnetoresistivity was observed in the approx. 10 K range above the onset of the superconducting transition, which may suggest the presence of enhanced superconducting fluctuations in the samples. The positive magnetic field shift of the temperatures, which limit the magnetoresistivity and the specific heat signatures of the magnetic ordered state of the Ru sublattice, suggests probing the influence of the ferromagnetic Ru interactions in an effective metallic-like conduction channel present in the samples. Superconducting characteristics of the Ru0.5Sr2GdCu2.5O8?δ reveal a significant contribution of the Gd paramagnetic signal at low temperatures, interpreted for the presence of a significant anisotropy of the superconducting phase. It is concluded that the Ru–Cu substituted phases of ruthenocuprates may present an opportunity to investigate the effectively anisotropic superconducting phase despite its comparatively high T c in the compounds related to the 123-type cuprate superconductor.  相似文献   
134.
The aim of this study was to determine the influence of apple variety (Šampion, Idared and Gloster) on the polyphenol profile, volatile composition and sensory characteristics of apple wines. Apples were harvested from the orchard in Garlica Murowana (Poland) and the experiments were conducted on a laboratory scale. Statistically significant differences were detected in the chemical composition of the analyzed wines. The highest antioxidant activity was found in Šampion wines, which was associated with a relatively high concentration of chlorogenic acid and procyanidins. These samples also contained high amounts of acetaldehyde, ethyl acetate and methanol. Idared wines showed a similar polyphenol profile, but they had lower antioxidant capacity and were characterized by a high level of butanol and acetic acid. Gloster wines were distinguished from other samples by a lower concentration of polyphenols and higher concentration of fusel alcohols. During sensory evaluation, wines produced from Idared apples scored the highest value for overall quality.  相似文献   
135.
Expert ratings and confirmatory factor analyses were used to develop an alternative system for scoring the Child Behavior Checklist (CBCL; T. M. Achenbach, 1991) to measure specific dimensions corresponding to current conceptualizations of child symptomatology. Data were from a nonclinic and 2 independent clinic samples. Subscales measuring Anxiety, Attention Problems/Hyperactivity, Conduct Problems, Depression, Oppositional Defiant, Social Problems/Immaturity, and Somatization were created. Logistic regressions were conducted to evaluate the diagnostic efficiency and discrimination of the new and original approaches to scoring the CBCL. Some of the new subscales demonstrated better sensitivity, positive predictive power, and discriminant validity than the original CBCL subscales; however, subscales from both approaches demonstrated low sensitivity. Results support the use of the new subscales for specific research purposes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
136.
Measurements of the detachment force of an air bubble from the surface of various coal ranks were carried out in water. These values were compared with those calculated from the contact angle values measured in coal - air bubble - water system and from the values (from literature) of the dispersion and the nondispersion components of the surface free energy of the studied coals. On the basis of the obtained results we found that there is a good agreement among the measured and calculated values of the detachment force for given coal rank. The coals studied may be divided into three groups according to their ability to form the stable attachment with air bubble. The arithmetic weighted mean of the detachment forces were correlated with the natural flotability of coals and the linear relationship as obtained.  相似文献   
137.
This work shows the effect on the soldering process of the addition of Ag and Cu to Sn–Zn alloys. Soldering of Al/Cu and Al/Al joints was performed for a time of 3?min, at a temperature of 250°C, with the use of flux. Aging was carried out at 170°C for Al/Cu and Al/Al joints for 1 and 10 days. During the aging process, intermetallic layers grew at the interface of the Al/Cu joint at the Cu substrate. Intermetallic layers were not observed during wetting of Al/Al joints. On the contrary, dissolution of the Al substrate and migration of Al-rich particles into the bulk of the solder were observed. The experiment was designed to demonstrate the effect of Ag and Cu addition on the dissolution of Al substrate during the soldering and aging processes. In the solder alloys, small precipitates of AgZn3 and Cu5Zn8 were observed.  相似文献   
138.
The dependence of the depth of cure (DOC) and degree of conversion (DC) on the depth of experimental and commercial materials were determined according to ISO 4049 procedure and with the use of Raman spectroscopy, respectively. Moreover, an attempt was made to find the correlation between the DOC and DC and the depth of the material. The hypothesis was that curing time recommended by the manufacturers is appropriate for curing both commercial and experimental materials to achieve comparable values of the examined properties. The impact of the filler characteristic was clearly observed. The longer curing time provides a deeper curing (DOC values) and higher reaction rate (DC); however, the dependence between the DC values and DOC values was not visible. Instead, a logarithmic trend in the relation of the DOC and curing time was clearly observed. The results of this study suggest that the experimental materials give some hope for potential clinical applications and should be further investigated. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42812.  相似文献   
139.
The deep-sequencing of small RNAs has revealed that different numbers and proportions of miRNA variants called isomiRs are formed from single miRNA genes and that this effect is attributable mainly to imprecise cleavage by Drosha and Dicer. Factors that influence the degree of cleavage precision of Drosha and Dicer are under investigation, and their identification may improve our understanding of the mechanisms by which cells modulate the regulatory potential of miRNAs. In this study, we focused on the sequences and structural determinants of Drosha and Dicer cleavage sites, which may explain the generation of homogeneous miRNAs (in which a single isomiR strongly predominates) as well as the generation of heterogeneous miRNAs. Using deep-sequencing data for small RNAs, we demonstrate that the generation of homogeneous miRNAs requires more sequence constraints at the cleavage sites than the formation of heterogeneous miRNAs. Additionally, our results indicate that specific Drosha cleavage sites have more sequence determinants in miRNA precursors than specific cleavage sites for Dicer and that secondary structural motifs in the miRNA precursors influence the precision of Dicer cleavage. Together, we present the sequence and structural features of Drosha and Dicer cleavage sites that influence the heterogeneity of the released miRNAs.  相似文献   
140.
A comprehensive investigation to determine the initiation power of detonators containing as a base charge the novel explosives: dihydroxylammonium 5,5′‐bis(tetrazolate‐1N‐oxide) – TKX‐50, dihydroxylammonium 5,5′‐bis(3‐nitro‐1,2,4‐triazolate‐1N‐oxide) – MAD‐X1, pentaerythritol tetranitrocarbamate – PETNC and 3,3′‐diamino‐4,4′‐azoxyfurazan – DAAF in comparison with RDX, HMX and PETN was undertaken. In order to estimate the initiation power of the detonators, the underwater initiating capability test was used. The total energy as a sum of the primary shock wave energy and the bubble gas energy was determined for each of these explosives, by measuring the overpressure of the shock waves generated in water. Moreover, the complete synthesis for novel explosives is presented. The thermal behavior of the explosives was investigated using DSC (differential scanning calorimetry). The gas phase absolute molar enthalpies at 298 K and 105 Pa were calculated theoretically using the modified complete basis set method (CBS‐4M; M referring to the use of minimal population localization) with the Gaussian 09 software. Gas phase standard molar enthalpies of formation (ΔHf°(g)) at 298 K were computed using the atomization energy method. Standard molar enthalpies of formation (▵H(s)°) were calculated using ΔHf°(g) and the standard molar enthalpies of sublimation by applying Trouton’s rule. The Chapman‐Jouguet (CJ) characteristics based on calculated ▵H(s)° values were computed using the EXPLO5 V6.01 thermochemical computer code. For the calculations the theoretical maximum densities and densities obtained during the experiments presented in this work were used.  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