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   1496篇
  免费   86篇
  国内免费   5篇
电工技术   13篇
综合类   4篇
化学工业   319篇
金属工艺   15篇
机械仪表   33篇
建筑科学   73篇
矿业工程   1篇
能源动力   38篇
轻工业   317篇
水利工程   9篇
石油天然气   7篇
无线电   76篇
一般工业技术   223篇
冶金工业   268篇
原子能技术   11篇
自动化技术   180篇
  2024年   5篇
  2023年   20篇
  2022年   38篇
  2021年   59篇
  2020年   35篇
  2019年   37篇
  2018年   40篇
  2017年   55篇
  2016年   54篇
  2015年   42篇
  2014年   55篇
  2013年   93篇
  2012年   81篇
  2011年   126篇
  2010年   69篇
  2009年   69篇
  2008年   86篇
  2007年   73篇
  2006年   61篇
  2005年   56篇
  2004年   47篇
  2003年   30篇
  2002年   47篇
  2001年   32篇
  2000年   22篇
  1999年   20篇
  1998年   35篇
  1997年   43篇
  1996年   25篇
  1995年   14篇
  1994年   16篇
  1993年   9篇
  1992年   12篇
  1991年   8篇
  1990年   10篇
  1989年   9篇
  1988年   8篇
  1987年   4篇
  1985年   6篇
  1984年   3篇
  1983年   3篇
  1981年   4篇
  1980年   3篇
  1979年   2篇
  1978年   4篇
  1977年   3篇
  1976年   2篇
  1975年   2篇
  1974年   3篇
  1973年   2篇
排序方式: 共有1587条查询结果,搜索用时 15 毫秒
111.
From our measured differential cross section of Rayleigh scattering, the form factor for momentum transfers in the range was deduced. Data for U, Pb, Pt, W, Sn, Cd, Ag, Mo and Cu at energies from 60 to 662 keV and scattering angles ranging from 5° to 140° were used. In addition, for the region of momenta, experimental data from other authors at higher energies were analyzed. The experimental values obtained were compared with various form-factor theories and limits of validity are established. For the relativistic modified form factor G a good agreement always exists for θ ≤ 65°, independently of energy and atomic number.  相似文献   
112.
Olive trees (Olea europaea L. Cv. Cobrançosa) from the northeast of Portugal were sprayed with three different copper formulations [bordeaux mixture (copper sulphate + calcium hydroxide − 20% Cu), copper hydroxide (40% Cu) and copper oxychloride (50% Cu)] to control olive fungal diseases. The residues of copper in olive leaves, harvested at different times, were evaluated by atomic absorption spectrometry. At all the collection times, treated olive leaves had significantly higher copper contents, compared to the control. The different copper amounts in pesticide formulations lowered the leaves contents in total phenols and hence their antioxidant properties. Olive leaves sprayed with copper oxychloride possessed the highest copper levels and the lowest content in phenols, which influenced its antioxidant activity (higher EC50 values for reducing power, scavenging effect on DPPH radicals and inhibition of erythrocyte hemolysis). Leaves without copper residues proved to be a good natural source of antioxidants, giving values comparable to the reference compounds.  相似文献   
113.
This paper presents a new design automation tool, based on a modified genetic algorithm kernel, in order to improve efficiency on the analog IC design cycle. The proposed approach combines a robust optimization with corner analysis, machine learning techniques and distributed processing capability able to deal with multi-objective and constrained optimization problems. The resulting optimization tool and the improvement in design productivity is demonstrated for the design of CMOS operational amplifiers.  相似文献   
114.
We conducted three experiments to assess the hypothesis that mindlessness could be prevented with a simple linguistic variation. Subjects in the first two experiments were either introduced to new objects conditionally (e.g., this could be an X) or unconditionally (e.g., this is an X), and the objects used were either unfamiliar or familiar. In each study a different need was then generated for which the object in question was not explicitly suited but could fulfill. Only those subjects in the conditional-unfamiliar group gave the creative response and met the need. When subjects were asked explicitly to generate novel uses for the target items, they had no difficulty doing so. However, given the way we are traditionally taught, it simply does not occur to us to think creatively unless explicitly instructed to do so. In the third experiment we introduced an unfamiliar item in one of three ways. In addition to the groups used in the earlier experiments, we added a group that was led to believe that the object was identifiable (unconditional) but was currently unknown. We also added a second need to determine whether the original conditional group truly learned conditionally or if they were in search of an absolute understanding of the target object. Significantly more of the subjects in the conditional group gave the creative response to both needs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
115.
The room temperature modulus of rupture (MOR) and the plane strain fracture toughness (K IC) of two Co-Mo-Cr-Si wear resistant alloys in various microstructure conditions have been determined. The modulus of rupture varied from 304 to 927 MN m–2 and as such was more structure sensitive thanK IC, which was in the range 15 to 26 MN m–3/2 for all conditions of the alloys. The best combination of room-temperature properties was associated with an f c c solid solution whereas h c p solid solution with a Widmanstätten precipitate produced the poorest properties. The industrial significance of these results are discussed.  相似文献   
116.
Principal component transform — Outer product analysis in the PCA context   总被引:1,自引:0,他引:1  
Outer product analysis is a method that permits the combination of two spectral domains with the aim of emphasizing co-evolutions of spectral regions. This data fusion technique consists in the product of all combinations of the variables that define each spectral domain. The main issue concerning the application of this technique is the very wide data matrix obtained which can be very hard to handle with multivariate techniques such as PCA or PLS, due to computer resources constraints. The present work presents an alternative way to perform outer product analysis in the PCA context without incurring into high demands on computational resources. This works shows that by decomposing each spectral domain with PCA and performing the outer product on the recovered scores, one can obtain the same results as if one calculated the outer product in the original variable space, but using much less computational resources. The results show that this approach will make possible to apply outer product analysis to very wide domains.  相似文献   
117.
The proposition that the difference in memory span between Welsh digits and English digits is accounted for by the longer articulatory duration of Welsh digits is critically reexamined. Two methods of measuring digit duration are contrasted. One is derived from digits spoken in isolation, the other is based on digits spoken in list format. Duration of Welsh digits was greater only when spoken in lists; with isolated production Welsh digits were significantly shorter than English digits. Also, span was shorter for Welsh digits. The results are interpreted in the light of the different articulatory demands made at the junctures between words in the English and Welsh lists. A supplementary experiment, using English words, illustrated that articulatory complexity at item boundaries increased serial recall error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
118.
Data from the National Institute of Child Health and Human Development Study of Early Child Care were analyzed to explore effects of marital separation on children in the first 3 years of life. The sample included 73 never-married mothers and 97 separated mothers; a comparison group of 170 was conditionally randomly selected from the 2-parent families. Children in 2-parent families performed better than children in 1-parent families on assessments of cognitive and social abilities, problem behavior, attachment security, and behavior with mother. However, controlling for mothers' education and family income reduced these differences, and associations with separated-intact marital status were nonsignificant (the effect size was .01). Thus, children's psychological development was not affected by parental separation per se; it was related to mothers' income, education, ethnicity, childrearing beliefs, depressive symptoms, and behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
119.
Seven experiments assessed the hypothesis derived from terror management theory that reminding people of their mortality would increase accessibility of constructs central to their worldview. Experiment 1 found that mortality primes, relative to control primes, increased accessibility of nationalistic constructs for men but not for women. Experiment 2 replicated this finding and also found that mortality salience increased romantic accessibility for women but not for men. Four subsequent experiments supported the role of unconscious death-related ideation in producing these effects. A final experiment demonstrated that situational primes can increase the accessibility of nationalistic constructs for women after mortality salience. The roles of situational cues and individual differences in the effects of exposure to death-related stimuli on worldview-relevant construct accessibility are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
120.
The psychological functioning and behavior of 46 sexually abused girls (ages 6–14) was compared with that of 46 nonabused girls who were matched on age, race, family income, and family constellation. Sexually abused children demonstrated heightened sexual preoccupation and behavior problems, lower cognitive abilities and school achievement, and more stressful past histories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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