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   8985篇
  免费   354篇
  国内免费   5篇
电工技术   88篇
综合类   12篇
化学工业   1768篇
金属工艺   135篇
机械仪表   164篇
建筑科学   536篇
矿业工程   18篇
能源动力   218篇
轻工业   682篇
水利工程   74篇
石油天然气   20篇
武器工业   1篇
无线电   512篇
一般工业技术   1683篇
冶金工业   1943篇
原子能技术   126篇
自动化技术   1364篇
  2023年   45篇
  2021年   143篇
  2020年   110篇
  2019年   135篇
  2018年   179篇
  2017年   171篇
  2016年   196篇
  2015年   160篇
  2014年   243篇
  2013年   612篇
  2012年   388篇
  2011年   527篇
  2010年   364篇
  2009年   408篇
  2008年   430篇
  2007年   454篇
  2006年   433篇
  2005年   361篇
  2004年   310篇
  2003年   294篇
  2002年   247篇
  2001年   171篇
  2000年   174篇
  1999年   179篇
  1998年   168篇
  1997年   147篇
  1996年   149篇
  1995年   163篇
  1994年   129篇
  1993年   128篇
  1992年   134篇
  1991年   75篇
  1990年   89篇
  1989年   108篇
  1988年   103篇
  1987年   102篇
  1986年   95篇
  1985年   103篇
  1984年   106篇
  1983年   98篇
  1982年   62篇
  1981年   77篇
  1980年   60篇
  1979年   57篇
  1978年   76篇
  1977年   53篇
  1976年   48篇
  1975年   47篇
  1974年   43篇
  1972年   41篇
排序方式: 共有9344条查询结果,搜索用时 656 毫秒
31.
32.
An adaptive product platform offers high customizability for generating feasible product variants for customer requirements. Customization takes place not only to product platform structure but also to its relevant parameters. Structural and parametric optimization processes are interwoven with each other to achieve the total optimality. This paper presents an evolutionary method dealing with interwoven structural and parametric optimization of adaptive platform product customization. The method combines genetic programming and genetic algorithm for handling structural and parametric optimization, respectively. Efficient genetic representation and operation schemes are carefully adapted. While designing these schemes, features specific to structural and parameter customization are considered for the simplification of platform product management. The experimental results show that the performance of the proposed algorithm outperforms that of the tandem evolutionary algorithm in which a genetic algorithm for parametric optimization is totally nested in a genetic programming for structural optimization.  相似文献   
33.
One hypothesis for the transcontinental and intra-Great Lakes basin transfer of round gobies (Neogobius melanostomus) has been that round gobies were pumped into the ballast water of ships. During June 2005 in Lake Erie, we obtained evidence of a vertical migration of round goby larvae, when we collected 167 round goby larvae in surface ichthyoplankton net tows at night and zero during day. These results complemented similar findings from the Muskegon River estuary of Lake Michigan during 2003 and 2004, documenting diel vertical migration for the first time in larval round gobies. We suggest vertical migration behavior may have allowed larval round gobies to be transported to and within the Great Lakes via ballast water and dispersed in the Great Lakes via advection of 6.5–8.5-mm long larvae at the surface. Based on our results, if ballast water was only taken on near the surface during daylight hours from May through September when larval round gobies were present, it would have mitigated the spread of round gobies throughout the Great Lakes.  相似文献   
34.
This study investigated the Stages of Change Readiness and Treatment Eagerness Scale (SOCRATES: W. R. Miller & J. S. Tonigan, 1996) in adolescents presenting for treatment of alcohol use disorder (AUD). The participants were 80 males and 43 females (mean age=16.8 years) who presented for AUD treatment (95.1% outpatient, 4.9% inpatient). Participants completed assessments at baseline and 1 year and provided information on alcohol use and related variables monthly between these 2 assessments. Principal-components and confirmatory factor analyses of the baseline SOCRATES identified 2 factors, Taking Steps and Recognition, which showed good internal consistency and concurrent and predictive evidence of validity. The results were interpreted as supporting the use of the SOCRATES with clinical samples of adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
35.
The Euler equations associated with diffeomorphism groups have received much recent study because of their links with fluid dynamics, computer vision, and mechanics. In this article, we consider the dynamics of N point particles or “blobs” moving under the action of the Euler equations associated with the group of diffeomorphisms of the plane in a variety of different metrics. This dynamical system is already in widespread use in the field of image registration, where the point particles correspond to image landmarks, but its dynamical behavior has not previously been studied. The 2-body problem is always integrable, and we analyze its phase portrait under different metrics. In particular, we show that 2-body capturing orbits (in which the distances between the particles tend to 0 as t  → ∞) can occur when the kernel is sufficiently smooth and the relative initial velocity of the particles is sufficiently large. We compute the dynamics of these “dipoles” with respect to other test particles, and supplement the calculations with simulations for larger N that illustrate the different regimes.  相似文献   
36.
It has been reported that it is harder to switch to a strong, well-practiced task from a weaker, less-practiced task than vice versa. Three experiments replicated this surprising asymmetry and investigated how it is affected by a reduction in interference between tasks. Experiment 1 progressively delayed the onset of the stimulus attribute associated with the stronger task. Experiments 2 and 3 separated the response sets of the tasks. Both manipulations reduced, without eliminating, interference of the stronger with the weaker task but reversed the asymmetry of switch costs, resulting in a larger cost of switching to the weaker task. The results are interpreted in terms of a model of the interactions between control input, task strength, and task priming. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
37.
This article examines the psychological impact of participating in sigmoidoscopy screening for colorectal cancer prevention. The 1st study examined psychological well-being at 3 months, in relation to screening outcome, in 4,153 individuals. The 2nd study used longitudinal data to examine changes in psychological functioning from before to after screening in relation both to screening outcome and baseline indicators of vulnerability. There were few psychological differences between those who had received negative results or had polyps detected. These findings were confirmed in the longitudinal study, which also found no evidence for vulnerability to adverse effects among those who were initially most anxious or who perceived their risk of cancer to be higher. The longitudinal data suggested that screening might produce transient positive effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
38.
39.
Over the last century, IQ scores have been steadily rising, a phenomenon dubbed the Flynn effect. Because of the Flynn effect, IQ tests are periodically renormed, making them harder. Given that eligibility for mental retardation (MR) services relies heavily on IQ scores, renormed tests could have a significant impact on MR placements. In longitudinal IQ records from 9 sites around the country, students in the borderline and mild MR range lost an average of 5.6 points when retested on a renormed test and were more likely to be classified MR compared with peers retested on the same test. The magnitude of the effect is large and affects national policies on education, social security, the death penalty, and the military. This paper reports the perceptions of professionals as they relate to IQ score fluctuations in normal, borderline, and/or MR populations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
40.
The corrosion behavior of NiCrMo Alloy 625 (UNS N06625) has been characterized in a 10,000 h test conducted in hydrogenated water at 260 °C. The corrosion kinetics were observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 0.074 mg dm−2 h−1/2. Characterizations of the corrosion oxide layer via grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy in combination with argon ion milling and target factor analysis, revealed the presence of two spinel oxide phases and significant amounts of recrystallized nickel. Based on the distribution of three oxidized alloying constituents (Ni, Cr, Fe) with respect to depth and oxidation state, it was concluded that: (a) corrosion occurs in a non-selective manner, but significant amounts of nickel(II) ions are released to the water, and (b) the spinel oxides exist as a chromite-rich inner layer (Ni0.7Fe0.3)(Cr0.8Fe0.2)2O4 underneath a coarser, ferrite-rich outer layer (Ni0.9Fe0.1)(Cr0.1Fe0.9)2O4. The trivalent cation distribution in each of these phases appears to represent a solvus in the immiscible NiCr2O4-NiFe2O4 binary.  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