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   782篇
  免费   76篇
电工技术   6篇
综合类   2篇
化学工业   297篇
金属工艺   9篇
机械仪表   5篇
建筑科学   50篇
矿业工程   4篇
能源动力   11篇
轻工业   147篇
水利工程   13篇
无线电   40篇
一般工业技术   89篇
冶金工业   125篇
原子能技术   2篇
自动化技术   58篇
  2024年   6篇
  2023年   17篇
  2022年   53篇
  2021年   60篇
  2020年   28篇
  2019年   29篇
  2018年   29篇
  2017年   19篇
  2016年   24篇
  2015年   33篇
  2014年   26篇
  2013年   55篇
  2012年   44篇
  2011年   49篇
  2010年   37篇
  2009年   34篇
  2008年   36篇
  2007年   29篇
  2006年   20篇
  2005年   32篇
  2004年   18篇
  2003年   16篇
  2002年   17篇
  2001年   9篇
  2000年   8篇
  1999年   9篇
  1998年   19篇
  1997年   12篇
  1996年   12篇
  1995年   7篇
  1994年   5篇
  1993年   7篇
  1992年   6篇
  1991年   4篇
  1990年   5篇
  1989年   6篇
  1988年   4篇
  1985年   3篇
  1983年   5篇
  1981年   2篇
  1978年   2篇
  1977年   3篇
  1976年   3篇
  1975年   2篇
  1974年   2篇
  1973年   2篇
  1968年   1篇
  1967年   1篇
  1964年   2篇
  1945年   1篇
排序方式: 共有858条查询结果,搜索用时 17 毫秒
71.
Examined the results of experiments where Ss were required to detect the misalignment of 2 abutting dot clusters on a monitor screen. Thresholds varied with the square root of dot density and did not appear to be affected by changing the sampling strategy used to generate the random dot clusters. Comparison of the Ss' performance with that expected of 3 information processing strategies suggested that Ss accomplished the task by locating the edges of the dot clusters rather than by extracting measures of global scope or of central position. The efficiency with which edge information was extracted was approximately 50% for low-density stimuli and declined exponentially with increasing dot density. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
72.
Forty-two volunteer clients with below-average dream recall and attitudes toward dreams participated in training sessions focusing on either improving dream recall and attitudes toward dreams, building dream interpretation skills, or educating about counseling. After training, individual dream interpretation sessions were conducted. No significant differences were found among the 3 conditions in regard to dream recall, attitudes toward dreams, or client- or therapist-reported session outcome, but effect sizes suggested that participants in the skills condition gained more from sessions than did participants in the dream recall–attitudes condition. Session outcome for all volunteer clients was equivalent to those in previous studies of volunteer clients with no training, suggesting that training was not necessary and that these participants were able to benefit from single-session dream interpretation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
73.
74.
A method is proposed for the preliminary estimation of the parameters of multivariate moving-average processes. Initially, m independent white-noise series are generated. Then the parameters are estimated through an iterative procedure. The algorithm is fast and simple since it does not require specialized software for time series but a least squares routine. The estimators are consistent and a simulation experiment shows good performance in finite samples. An applicati on to real data is also illustrated  相似文献   
75.
Volatile compounds were isolated from copoazú (Theobroma grandiflorum Schumann) fruit by liquid–liquid extraction at two different pH values of 3.3 (natural) and 7. The volatile extracts were analyzed by capillary GC–FID and GC–MS. Among the 56 compounds identified at two pH values, many of them were only present in the lower pH extract, confirming the presence of bound compounds in copoazú. Ethyl butanoate, ethyl hexanoate and linalool were the major constituents found in copoazú fruit.  相似文献   
76.
The essential oils, isolated by hydrodistillation and distillation-extraction, from the aerial parts of different populations of Pterospartum tridentatum collected during the flowering phase, at different locations in Portugal, were analysed by GC and GC–MS. All the P. tridentatum populations studied afforded a yellowish oil in a yield <0.05% (v/w). cis-Theaspirane (2–14%), trans-theaspirane (2–17%) and octen-3-ol (2–37%) were, in variable amounts, the dominant components of the oils. Cluster analysis of the essential oil compositions from the nine populations studied, confirmed a major chemical variability.  相似文献   
77.
Confirmatory factor analysis was used to evaluate 2 multidimensional measures of perfectionism (R. 0 Frost, P. Marten, C. Lahart, & R. Rosenblate, 1990; P. L. Hewitt & G. L. Flett, 1991). On a first-order level, support was found for Hewitt and Flett's (1991) original 3-factor conceptualization of perfectionism, although only for an empirically derived 15-item subset. Support was also obtained for 5 of the 6 dimensions proposed by R. O. Frost et al. (1990), but the model only displayed good fit when a refined scale containing 22 of the original 35 items was used. A second-order analysis found evidence for 2 higher-order factors of adaptive and maladaptive perfectionism. Perfectionism dimensions correlated in expected directions with personality domains, symptom distress, and academic achievement. The brief measures of perfectionism also retained the construct-related validity displayed by the full-item versions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
BACKGROUND: The possibility to use β‐cyclodextrin as biodegradable tensioactive and an electromagnetic field in order to improve the kinetic parameters of radical emulsion polymerization is of interest. Thus, the influence of different surfactants—sodium lauryl sulfate (SLS) and β‐cyclodextrin (CD)—on the pathway of emulsion polymerization of methyl methacrylate (MMA) and emulsion copolymerization of MMA with 2,3‐epoxypropyl methacrylate (GMA) performed with or without the presence of a continuous electromagnetic field (MF) was studied. RESULTS: The presence of the MF leads to a considerable increase of the conversion during the first part of the reaction if the classic surfactant (SLS) is used. The reactions performed without MF and with CD exhibit a decrease of the conversion and of the polymerization rate as compared with the variants using SLS. The swelling rate and the maximum degree of swelling vary with the surfactant nature and with the reaction conditions and MF presence. Data from thermogravimetry and differential scanning calorimetry evidence the dependences between the polymer characteristics and the preparation conditions. CONCLUSION: This research underlines the coupling possibilities of the influence of a MF—growth of the reaction rate and conversion explained through radical pairs mechanism—with a combination of the ‘cage’ effect and ‘conformational control’ afforded by CD. The presence of MF and CD during the syntheses leads to an increase of Tg and an increase of PMMA and P(MMA‐co‐GMA) thermal stability. Copyright © 2007 Society of Chemical Industry  相似文献   
79.
The microstructure of a duplex stainless steel slab 1.4362 produced by continuous casting has been investigated by optical microscopy, scanning electron microscopy, EBSD and EDS. The slab showed different macrostructures through the thickness. The macrostructure can be divided into 3 types: fine equiaxed, columnar and coarse equiaxed grains. In all three regions, the volume fraction of each phase austenite and delta‐ferrite is close to 50% and the hardness is very similar for both. The austenite has Kurdjumov‐Sachs or Nishiyama‐Wassermann relationship with the delta‐ferrite. The slab does not show a strong segregation profile through the thickness. The delta‐ferrite is enriched in Cr and Mo, while austenite is enriched in Ni and Mn.  相似文献   
80.
An anionic surface‐active agent derived from wool proteins was developed as an alternative to the anionic surfactants extensively used in shampoo formulations. The physicochemical properties of this new surface‐active agent prepared form wool proteins and its application for human hair treatments were studied. This new product could be considered a new mild anionic surface‐active agent, as evidenced by the results found by the evaluation of its physicochemical properties. The new wool anionic surface‐active agent was shown to be very substantive to hair, coating the fiber surface, giving rise to a significant improvement in the mechanical properties of the hair fibers, and providing a certain damage‐prevention effect on the hair. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  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