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   667篇
  免费   38篇
  国内免费   5篇
电工技术   15篇
综合类   4篇
化学工业   122篇
金属工艺   8篇
机械仪表   7篇
建筑科学   56篇
能源动力   8篇
轻工业   83篇
水利工程   4篇
无线电   61篇
一般工业技术   123篇
冶金工业   63篇
原子能技术   2篇
自动化技术   154篇
  2023年   3篇
  2022年   1篇
  2021年   28篇
  2020年   14篇
  2019年   13篇
  2018年   13篇
  2017年   10篇
  2016年   15篇
  2015年   22篇
  2014年   21篇
  2013年   42篇
  2012年   33篇
  2011年   40篇
  2010年   25篇
  2009年   32篇
  2008年   35篇
  2007年   30篇
  2006年   19篇
  2005年   35篇
  2004年   25篇
  2003年   14篇
  2002年   19篇
  2001年   16篇
  2000年   18篇
  1999年   11篇
  1998年   15篇
  1997年   21篇
  1996年   22篇
  1995年   9篇
  1994年   6篇
  1993年   6篇
  1992年   5篇
  1991年   5篇
  1990年   8篇
  1989年   13篇
  1988年   4篇
  1987年   11篇
  1986年   6篇
  1985年   7篇
  1984年   6篇
  1983年   6篇
  1982年   5篇
  1981年   7篇
  1980年   5篇
  1979年   4篇
  1978年   1篇
  1977年   2篇
  1976年   2篇
排序方式: 共有710条查询结果,搜索用时 78 毫秒
61.
The reactor pressure vessel (RPV) is the key component in the nuclear power plant, which is considered irreplaceable and can be the life-limiting feature of the operation of nuclear power plant if its mechanical properties degrade sufficiently. High temperature gas-cooled reactor (HTGR) has perfect inherent safety, which is intended to be one of the fourth generation advanced nuclear reactors. However, HTGR has different service temperature with pressurized water reactor (PWR), that the service temperature of HTGR is 250 degrees C and that of PWR is 290 degrees C. So the irradiation behaviour of RPV in HTGR is expected to be investigated. In this wok, 3 MeV Fe-ion irradiation was performed on Chinese A508-3 reactor pressure vessel steel which is employed by high-temperature gas-cooled reactors and pure Fe under room temperature (about 25 degrees C) and high temperature (250 degrees C). The ion doses were 0.1, 0.5 and 1.0 dpa for both room temperature irradiation and high temperature irradiation. SRIM modeling was performed before irradiation experiments to guide the experimental details. Positron annihilation Doppler broadening (PADB) spectroscopy experiments and nano-indentation tests (to study embrittlement behavior) were conducted for characterization. It is found that after both room temperature irradiation and high temperature irradiation, the densities of defects in the reactor pressure vessel steel and pure Fe increase, and the type of defects could be vacancy-type and solute cluster type from PADB results. The vacancy-type defect density under high temperature irradiation is lower than that under room temperature irradiation. That is because high temperature can recover the defects formed during irradiation. The hardness test results show that for both the reactor pressure vessel steel and pure Fe, the irradiation hardening increases with increasing dose. Compared to room temperature irradiation, high temperature irradiation can produce more solute clusters and fewer vacancy-type defects in the reactor pressure vessel steel. So the irradiation hardening of the reactor pressure vessel steel might be caused mainly by the formation of solute clusters.  相似文献   
62.

Background

Several studies demonstrated an association of homocysteine plasma levels and the plasma lipoprotein profile. This cross-sectional pilot study aimed at analyzing whether blood levels of the two important cofactors of homocysteine metabolism, folate and vitamin B12, coincide with the lipoprotein profile.

Methods

In a retrospective single center approach, we analyzed the laboratory database (2003-2006) of the University Hospital Bonn, Germany, including 1743 individuals, in whom vitamin B12, folate and at least one lipoprotein parameter had been determined by linear multilogistic regression.

Results

Higher folate serum levels were associated with lower serum levels of low density lipoprotein cholesterol (LDL-C; Beta = -0.164; p < 0.001), higher levels of high density lipoprotein cholesterol (HDL-C; Beta = 0.094; p = 0.021 for trend) and a lower LDL-C-C/HDL-C-ratio (Beta = -0.210; p < 0.001). Using ANOVA, we additionally compared the individuals of the highest with those of the lowest quartile of folate. Individuals of the highest folate quartile had higher levels of HDL-C (1.42 ± 0.44 mmol/l vs. 1.26 ± 0.47 mmol/l; p = 0.005), lower levels of LDL-C (3.21 ± 1.04 mmol/l vs. 3.67 ± 1.10 mmol/l; p = 0.001) and a lower LDL-C/HDL-C- ratio (2.47 ± 1.18 vs. 3.77 ± 5.29; p = 0.002). Vitamin B12 was not associated with the lipoprotein profile.

Conclusion

In our study sample, high folate levels were associated with a favorable lipoprotein profile. A reconfirmation of these results in a different study population with a well defined status of health, diet and medication is warranted.  相似文献   
63.
<正>交异性钢桥面板改造的问题在于既有钢板与第二个钢板的粘结,以降低应力和增加正交异性钢板的使用寿命。通过试验和分析,对梁的弯曲性能进行参数研究。试验考虑不同厚度、温度和跨度的影响。从试验结果可见,应力降低与温度无关。最小化第二块钢板的厚度及最大化粘结层厚度,可降低重量,增加组合结构的刚度,这是最有效的解决方法。组合梁的弹性性能和屈服荷载取决于钢板的性能,温度的影响不显著。然而,粘结层的受剪最终导致梁的破坏,而粘结层的性能受温度的影响较大。  相似文献   
64.
This paper shows that a flame can be an intrinsically unstable acoustic element. The finding is clarified in the framework of an acoustic network model, where the flame is described by an acoustic scattering matrix. The instability of the flame acoustic coupling is shown to become dominating in the limit of no acoustic reflections. This is in contrast to classical standing-wave thermoacoustic modes, which originate from the positive feedback loop between system acoustics and the flame. These findings imply that the effectiveness of passive thermoacoustic damping devices is limited by the intrinsic stability properties of the flame.  相似文献   
65.
The multiprocessor SoC (MPSoC) revolution is fueled by the need to execute multiple advanced multimedia applications on a single embedded computing platform. At design-time, the applications that will run in parallel and their respective user requirements are unknown. Hence, a run-time manager (RTM) is needed to match all application needs with the available platform resources and services. Creating such a run-time manager requires two decisions. First, one needs to decide what functionality to implement. Second, one has to decide how to implement this functionality in order to meet boundary conditions like e.g. real-time performance. This paper is the first to detail a generic view on MPSoC run-time management functionality and its design space trade-offs. We substantiate the run-time components and the implementation trade-offs with academic state-of-the-art solutions and a brief overview of some industrial multiprocessor run-time management examples. We show a clear trend towards more hardware acceleration, a limited distribution of management functionality over the platform and increasing support for adaptive multimedia applications. In addition, we briefly detail upcoming run-time management research issues.  相似文献   
66.
Bacterial adhesion is problematic in many diverse applications. Coatings of hydrophilic polymer chains in a brush configuration reduce bacterial adhesion by orders of magnitude, but not to zero. Here, the mechanism by which polymer‐brush functionalized surfaces reduce bacterial adhesion from a flowing carrier fluid by relating bacterial adhesion with normally oriented adhesion and friction forces on polymer (PEG)‐brush coatings of different softness is studied. Softer brush coatings deform more than rigid ones, which yields extensive bond‐maturation and strong, normally oriented adhesion forces, accompanied by irreversible adhesion of bacteria. On rigid brushes, normally oriented adhesion forces remain small, allowing desorption and accordingly lower numbers of adhering bacteria result. Friction forces, generated by fluid flow and normally oriented adhesion forces, are required to oppose fluid shear forces and cause immobile adhesion. Summarizing, inclusion of friction forces and substratum softness provides a more complete mechanism of bacterial adhesion from flowing carrier fluids than available hitherto.  相似文献   
67.
As more and more organizations conduct business over the Internet, the need to securely identify users across the anonymity void of the Internet has never been more paramount. EEMA, the non-profit making trade organization for electronic business in Europe, has been at the forefront in the fight to create a legal framework for online identification, placing the issue high on the agenda at this year’s ISSE conference in October.  相似文献   
68.
In this paper, we compare by means of Monte Carlo simulations two approaches to take spatial autocorrelation into account: the classical spatial autoregressive model and the structural equations model with latent variables. The former accounts for spatial dependence and spillover effects in georeferenced data by means of a spatial weights matrix W. The latter represents spatial dependence and spillover effects by means of a latent variable in the structural (regression) model while the observed spatially lagged variables are related to the latent spatial dependence variable in the measurement model. The simulation results based on Anselin’s Columbus, Ohio, crime data set show that the misspecified latent variables approach slightly trails the correctly specified classical approach in terms of bias and root mean squared error of the coefficient estimators.  相似文献   
69.
This article discusses the consideration of factors involved in the selection of a system to provide process water, using ultrafiltration to treat surface water. The first part looks at on-site process water production from surface water for an Akzo Nobel Chemicals site in Amsterdam. The second part discusses UF membranes in such applications, and describes the development of the AquaFlex system.  相似文献   
70.
The influence of mechanical stress and chemical homogeneity on the permittivity of BaTi0.9Zr0.1O3 ceramics prepared from mixed-oxide and hydrothermal powders was studied. To reduce stress, liquid-phase sintering was applied in conjunction with a low heating rate to stimulate the formation of large grains. The influence of chemical homogeneity was studied by variations in sintering temperatures and times. For both types of ceramics, the dielectric constant at the Curie temperature was influenced by both factors, but to a different extent. In the mixed oxide ceramic, chemical homogeneity played a more prominent role, while internal stress appeared to exert a larger influence in the hydrothermal ceramics. The dielectric constant at the Curie temperature could be increased by 5%–10% by an annealing treatment at 200°C, followed by slow cooling.  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