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   1056篇
  免费   17篇
电工技术   53篇
化学工业   277篇
金属工艺   32篇
机械仪表   14篇
建筑科学   11篇
能源动力   25篇
轻工业   53篇
水利工程   3篇
石油天然气   1篇
无线电   138篇
一般工业技术   161篇
冶金工业   193篇
原子能技术   11篇
自动化技术   101篇
  2022年   18篇
  2021年   21篇
  2020年   4篇
  2019年   7篇
  2018年   12篇
  2017年   8篇
  2016年   17篇
  2015年   14篇
  2014年   15篇
  2013年   27篇
  2012年   45篇
  2011年   48篇
  2010年   50篇
  2009年   39篇
  2008年   37篇
  2007年   35篇
  2006年   30篇
  2005年   30篇
  2004年   25篇
  2003年   31篇
  2002年   17篇
  2001年   15篇
  2000年   10篇
  1999年   28篇
  1998年   81篇
  1997年   58篇
  1996年   37篇
  1995年   30篇
  1994年   31篇
  1993年   29篇
  1992年   12篇
  1991年   15篇
  1990年   12篇
  1989年   16篇
  1988年   9篇
  1987年   13篇
  1986年   13篇
  1985年   9篇
  1984年   18篇
  1983年   19篇
  1982年   7篇
  1981年   8篇
  1980年   7篇
  1979年   4篇
  1978年   7篇
  1977年   6篇
  1976年   11篇
  1975年   7篇
  1974年   8篇
  1973年   12篇
排序方式: 共有1073条查询结果,搜索用时 46 毫秒
991.
We have developed a broadcasting agent system, public opinion channel (POC) caster, which generates understandable conversational form from text-based documents. The POC caster circulates the opinions of community members by using conversational form in a broadcasting system on the Internet. We evaluated its transformation rules in two experiments. In experiment 1, we examined our transformation rules for conversational form in relation to sentence length. Twenty-four participants listened to two types of sentence (long sentences and short sentences) with conversational form or with single speech. In experiment 2, we investigated the relationship between conversational form and the user’s knowledge level. Forty-two participants (21 with a high knowledge level and 21 with a low knowledge level) were selected for a knowledge task and listened to two kinds of sentence (sentences about a well-known topic or sentences about an unfamiliar topic). Our results indicate that the conversational form aided comprehension, especially for long sentences and when users had little knowledge about the topic. We explore possible explanations and implications of these results with regard to human cognition and text comprehension.  相似文献   
992.
993.
Superconducting properties of layered ruthenocuprates, RuSr 2 RECu 2 O 8 and RuSr 2 (RE 1-x Ce x ) 2 Cu 2 O 10 (RE = Sm, Eu, Gd), are investigated. The differences between superconductivity of these two phases are considered to be due to, their structural differences ; The RE/Sr substitution is more feasible in RuSr 2 RECu 2 O 8 than in RuSr 2 (RE 1-x Ce x ) 2 Cu 2 O 10 , while the latter phase shows larger oxygen nonstoichiometry. The superconducting RuSr 2 Eu 2 Cu 2 O 8 (T c, onset = 25K, T c, zero = 7K) phase was successfully synthesized for the first time, and coexistence of superconductivity and ferromagnetism in these systems was reconfirmed by using single-phase samples.  相似文献   
994.
Catalytic activity of ZrO2 supported PdO catalysts for methane combustion has been investigated in comparison with Al2O3 supported PdO catalysts. It was found that the drop of catalytic activity owing to decomposition of PdO at a high temperature region (600–900°C) was suppressed by using ZrO2 support. Temperature-programmed reduction (TPR) measurements of the catalyst with hydrogen revealed that the PdO of PdO/Al2O3 catalyst was reduced at the temperature less than 100°C, whereas in PdO/ZrO2 catalyst the consumption of hydrogen was also observed at 200–300°C. This result indicates that the stable PdO species were present in the PdO/ZrO2 catalyst. In order to confirm the formation of the solid solution of PdO and ZrO2, X-ray diffraction (XRD) analyses of the mixtures of ZrO2 and PdO calcined at 700–900°C in air were carried out. The lattice volume of ZrO2 in the mixture was larger than that of ZrO2. Furthermore, the Pd thin film on ZrO2 substrate was prepared as a model catalyst and the depth profile of the elements in the Pd thin film was measured by Auger electron spectroscopy (AES). It was confirmed that Zr and O as well as Pd were present in the Pd thin film heated at 900°C in air. It was considered that the PdO on ZrO2 support might be stabilized by the formation of the solid solution of PdO and ZrO2.  相似文献   
995.
Sepsis is characterized by a dysregulated immune response to infections that causes life-threatening organ dysfunction and even death. When infections occur, bacterial cell wall components (endotoxin or lipopolysaccharide), known as pathogen-associated molecular patterns, bind to pattern recognition receptors, such as toll-like receptors, to initiate an inflammatory response for pathogen elimination. However, strong activation of the immune system leads to cellular dysfunction and ultimately organ failure. Damage-associated molecular patterns (DAMPs), which are released by injured host cells, are well-recognized triggers that result in the elevation of inflammatory cytokine levels. A cytokine storm is thus amplified and sustained in this vicious cycle. Interestingly, during sepsis, neutrophils transition from powerful antimicrobial protectors into dangerous mediators of tissue injury and organ dysfunction. Thus, the concept of blood purification has evolved to include inflammatory cells and mediators. In this review, we summarize recent advances in knowledge regarding the role of lipopolysaccharides, cytokines, DAMPs, and neutrophils in the pathogenesis of sepsis. Additionally, we discuss the potential of blood purification, especially the adsorption technology, for removing immune cells and molecular mediators, thereby serving as a therapeutic strategy against sepsis. Finally, we describe the concept of our immune-modulating blood purification system.  相似文献   
996.
Experiments were carried out to verify if the low friction range of SiC in water lubrication can be expanded by micro-pores on the contact surface. Pores were formed by laser, with a diameter of 150 μm and a depth of about 8–10 μm and were distributed in a square array on the contact surface. Seven kinds of textured specimens with different intervals between the pores were tested and compared with the untextured specimen. The effect of the pore area ratio on friction coefficient and the critical load for the transition from hydrodynamic lubrication to mixed lubrication was reported and discussed.  相似文献   
997.
Grating coupling between vertically integrated waveguides via supermode was discussed and demonstrated. Two thin-film waveguides with grating couplers were stacked on a substrate. A guided wave in one waveguide is converted by a grating coupler to a supermode propagating contradirectionally, and then converted by another grating coupler to a guided wave in the other waveguide. The coupling shows high wavelength selectivity, and the wavelength-division add/drop multiplexing function can be combined. A demonstrator was designed and fabricated. Theoretically predicted coupling efficiency was almost 100% with wavelength selectivity of 2 nm, while the experimentally obtained value was 40% in the efficiency and 1 nm in the selectivity  相似文献   
998.
The effects of processing and cooking on the levels of pesticide residues in wheat samples were investigated for 13 pesticides in pre-harvest (Pre, 9 pesticides) and post-harvest (Post, 6 pesticides) samples. In the milling process, the transfer ratios (%, total pesticide residue amount in product/that in wheat grain) of wheat bran were greater than 70% and 80% for pre-harvest and post-harvest samples, respectively. The transfer ratios of flour ranged from 1.7% to 23% (Pre) and 4.0% to 11% (Post). There was no significant difference in transfer ratio among the pesticides investigated. The processing factors (Pf, the concentration (mg/kg) of pesticide in product/that in the wheat grain) of flour ranged from 0.030 to 0.40 (Pre) and 0.069 to 0.18 (Post). The values in pre-harvest samples were higher than those in post-harvest samples. Investigation of changes of pesticide residues during processing and/or cooking is useful not only to establish MRLs, but also to recognize actual levels of pesticide residues in food.  相似文献   
999.
The effects of processing and cooking on the levels of pesticide residues in rice samples were investigated for 11 pesticides in pre-harvest (9 pesticides) and post-harvest (4 pesticides) samples. In the polishing process, the transfer ratio (%, total pesticide residue amount in product/that in brown rice) of rice bran ranged from 40% to 106%, and the transfer ratio of polished rice ranged from 9% to 65% in pre-harvest samples. These values varied from pesticide to pesticide. The processing factor (the concentration (mg/kg) of pesticide in product/that in the brown rice) of polished rice ranged from 0.11 to 0.73. The loss of pesticides during processing and/or cooking did not correlate to any single physical or chemical property. Investigation of changes of pesticide residues during processing and/or cooking is useful not only to establish MRLs, but also to recognize actual levels of pesticide residues in food.  相似文献   
1000.
Embryonic stem (ES) cells are a type of pluripotent stem cell line isolated from the inner cell mass of blastocysts and characterized by an almost unlimited self-renewal capacity and differentiation potential in vitro into multiple cell lineages. Therefore the use of ES cells has recently received much attention as a novel cell source for various hybrid artificial organs. To use ES cells, it is necessary to be able to produce functional matured cells from ES cells in large quantities. In this study, we applied polyurethane foam (PUF)/spheroid culture, which enables spontaneous spheroid formation and mass cultivation of cultured cells, to mouse ES cells for hepatic differentiation. Mouse ES cells spontaneously formed spherical multicellular aggregates (spheroids) in the pores of the PUF within 1 d. To induce hepatic differentiation, specific growth factors were added to the culture medium. Mouse ES cells proliferated by day 20, and high cell density (about 1.0 x 10(8) cells/cm(3)-PUF) was achieved. Differentiating ES cells expressed endodermal-specific genes, such as alpha-fetoprotein, albumin and tryptophan 2,3-dioxygenase. The activity of ammonia removal of mouse ES cells per unit volume of the module was detected by day 21 and increased with culture time. Maximum expression levels were comparable to those of primary mouse hepatocytes. Mouse ES cells could express liver-specific functions at high level because of the high cell density culture and hepatic differentiation. These results suggest that the PUF/spheroid culture method could be useful to develop mass differentiation cultures.  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