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   766篇
  免费   26篇
  国内免费   3篇
电工技术   12篇
化学工业   241篇
金属工艺   22篇
机械仪表   13篇
建筑科学   14篇
能源动力   15篇
轻工业   98篇
水利工程   7篇
石油天然气   2篇
无线电   60篇
一般工业技术   106篇
冶金工业   142篇
原子能技术   12篇
自动化技术   51篇
  2024年   2篇
  2023年   6篇
  2022年   16篇
  2021年   20篇
  2020年   4篇
  2019年   11篇
  2018年   14篇
  2017年   10篇
  2016年   19篇
  2015年   14篇
  2014年   24篇
  2013年   31篇
  2012年   36篇
  2011年   45篇
  2010年   35篇
  2009年   29篇
  2008年   35篇
  2007年   30篇
  2006年   29篇
  2005年   25篇
  2004年   22篇
  2003年   18篇
  2002年   21篇
  2001年   11篇
  2000年   16篇
  1999年   14篇
  1998年   65篇
  1997年   44篇
  1996年   27篇
  1995年   19篇
  1994年   18篇
  1993年   11篇
  1992年   3篇
  1991年   7篇
  1990年   10篇
  1989年   5篇
  1988年   4篇
  1987年   2篇
  1986年   7篇
  1985年   4篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1981年   2篇
  1979年   3篇
  1978年   4篇
  1977年   2篇
  1976年   8篇
  1972年   2篇
  1969年   1篇
排序方式: 共有795条查询结果,搜索用时 0 毫秒
51.
Y. Nishiyama  Y. Tamai 《Carbon》1976,14(1):13-17
Formation of carbon on nickel sheet from benzene vapor carried by hydrogen was studied at a temperature range from 520 to 730°C. A maximum rate was observed at about 630°C, above which the deposition rate decreased rapidly. The carbon formed was hydrogenated in situ. Methane was the main gaseous product and a maximum rate was observed at about 670°C. Very high reactivity of deposited carbon toward hydrogenation was ascribed to the catalytic action of nickel particles dispersed in the carbon. The hydrogenation rates were divided into three zones and possible interpretations are discussed. A mechanism which is a reverse process to deposition was suggested. The decrease of the hydrogenation rate at higher temperatures was due to the equilibrium among carbon, hydrogen and methane, where carbon was more reactive than graphite.  相似文献   
52.
The reaction of poly(vinyl chloride) containing N-methyl dithiocarbamate (PMD) with metal ions in a heterogeneous system and the effect of γ-irradiation on the reactivity were studied. PMD powder suspended in aqueous solutions did not show any reactivity toward metal ions. However, the PMD powder suspended in a methyl alcohol solution formed a chelate with various metal ions. The effects of the reaction time, pH, and the initial concentration of the metal ion were examined. PMD irradiated in methyl alcohol with γ-irradiation doses up to 28 Mrad was compared with the original PMD. The reactivity of the irradiated PMD toward the metal ions did not show any apparent decrease.  相似文献   
53.
Poly(n-butyl acrylate) (PnBA) chemically crosslinked with tetraethylene glycol dimethacrylate (TEGDM) and physically crosslinked PnBAs produced by neutralization of poly(n-butyl acrylate-stat-acrylic acid) with NaOH or Ca(OH)2 were prepared as a polymer I network. Each polymer I was swollen with styrene and cured in situ into semi-IPN-TEGDM, semi-IPN-Na, or semi-IPN-Ca, respectively. Both physically crosslinked polymers maintained their shapes during the swelling procedure. Dynamic mechanical spectroscopy indicated that good mixing of the two polymers took place in the semi-IPN-Ca as well as in semi-IPN-TEGDM, but a distinct phase separation occurred in the semi-IPN-Na. These results were supported by their transparent or optical opaque appearances, respectively. Annealing at 180°C developed further phase separation in the semi-IPN-Na, but very little in the semi-IPN-Ca. Analyses by the incompatibility number (based on the modulus–temperature curve) and the calculation of individual phase compositions (from the glass transition temperature shifts) were used in estimating the extent of molecular mixing.  相似文献   
54.
This study investigates the adverse and persistent effects of ethinylestradiol (EE2) on mature gonads of transgenic olvas-GFPIST II-YI medaka (Oryzias latipes). The measurement of gonadal size calculating the GFP-fluorescent area was used as a technique that enabled monitoring gonads in living specimens by GFP fluorescence. First, mature medaka were exposed to EE2 (47.8-522 ng/L) for 4 weeks. The gonads showed a significant reduction of the GFP-fluorescent area and Gonadosomatic Index in males exposed to EE2 at >216 ng/L and females exposed at 522 ng/L. Histologically, males at all treatments exhibited testis-ova and additionally, high connective tissue prevalence at > or =216 ng/L. Next, mature male medaka were exposed to EE2 (43.7-473 ng/L) for 3 weeks and allowed to depurate for 6 weeks, to investigate persistent effects of EE2. Continuous gonad observation showed that GFP began to decline 3 weeks after initial exposure to > or =215 ng/L. After depuration, the gonad's fluorescent areas gradually recovered, with no statistical difference at the end of the depuration period; normal spermatogenesis was present in these individuals. Alterations in GFP fluorescence clearly indicate the condition of the gonad in transgenic medaka and this strain showed a facilitated screening fish model to detect the adverse effects on the gonad by estrogenic chemicals.  相似文献   
55.
To establish cheese as a dairy product with health benefits, we examined the multifunctional role of cheeses. In this report, we clarify whether different types of commercial cheeses may possess antiproliferative activity using HL-60 human promyelocytic leukemia cell lines as a cancer model. Among 12 cheese extracts tested, 6 (Montagnard, Pont-l’Eveque, Brie, Camembert, Danablue, and Blue) revealed strong growth inhibition activity and induction of DNA fragmentation in HL-60 cells. Based on the quantification of nitrogen contents in different cheese samples, a positive correlation between the ripeness of various cheeses and their antiproliferative activity tested in HL-60 cells was displayed. Four varieties of Blue cheese ripened for 0, 1, 2, or 3 mo demonstrated that the Blue cheese ripened for a long term was capable of causing the strong suppression of the cell growth and the induction of apoptotic DNA damage as well as nucleic morphological change in HL-60 cells. Collectively, these results obtained suggest a potential role of highly ripened cheeses in the prevention of leukemic cell proliferation.  相似文献   
56.
In a study of polyacrylamide in solutions we have required the rapid characterization on chromatographies. The application to the aqueous solution of the GPC using controlled-porosity glass has been examined from both the viewpoint of the effect of salt addition and the GPC mechanism. An adequate addition to neutral salt, 0.005M KCI to the eluent, gave rise to the elution behaviors being in accord with the hydrodynamic volume concept of the GPC separation.  相似文献   
57.
It has been reported that radon inhalation activates antioxidative functions in liver and has an antioxidative effect against hepatopathy similar to that of the antioxidative effects of ascorbic acid (VC) or α-tocopherol (VE). In this study, we examined the combined effects of radon inhalation and antioxidant vitamin administration on acute alcohol-induced hepatopathy in mice. ICR mice were subjected to intraperitoneal (i.p.) administration of alcohol after pretreating with air only (sham) or radon at a concentration of approximately 2000 Bq/m3 for 24 hours and i.p. administration of VC (300 mg/kg body weight) or VE (300 mg/kg body weight). In mice injected with alcohol, the combined radon and antioxidant vitamins treatment significantly decreased the activities of glutamic oxaloacetic transaminase in serum compared to not only the alcohol-administered group (sham group), but also the radon inhalation with alcohol administration group or the vitamin and alcohol administration group. In addition, radon inhalation significantly increased the antioxidant level, in such as the catalase activity and the total glutathione content in liver compared to the sham group. These results suggested that the combined radon and antioxidant vitamin treatment could effectively inhibit alcohol-induced hepatopathy in mice without any antagonizing action.  相似文献   
58.
Episodes of acute exacerbation are the major clinical feature of asthma and therefore represent an important focus for developing novel therapies for this disease. There are many reports that the n-3 fatty acids found in fish oil exert anti-inflammatory effects, but there are few studies of the action of fish oil on airway smooth muscle (ASM) function. In the present investigation, we evaluated the effect of fish oil supplementation on smooth muscle force of contraction in ovalbumin-induced asthmatic Wistar rats, and its consequences on static lung compliance, mucus production, leukocyte chemotaxis and production of proinflammatory cytokines. Fish oil supplementation suppressed the infiltration of inflammatory cells into the lung in asthmatic animals (2.04 ± 0.19 × 106 cells vs. 3.33 ± 0.43 × 106 cells in the control asthmatic group; P < 0.05). Static lung compliance increased with fish oil supplementation in asthmatic rats (0.640 ± 0.053 mL/cm H2O vs. 0.399 ± 0.043 mL/cm H2O; P < 0.05). However, fish oil did not prevent asthma-associated lung eosinophilia and did not affect the concentrations of tumor necrosis factor-α and interleukin-1β in lung tissue or the proportion of the airways obliterated with mucus. Fish oil had no effect on the force of contraction in asthmatic rats in response to acetylcholine (3.026 ± 0.274 mN vs. 2.813 ± 0.364 mN in the control asthmatic group). In conclusion, although fish oil exerts some benefits in this model of asthma, its effectiveness appears to be limited by an inefficient action on airway smooth muscle function.  相似文献   
59.
60.
1.3- and 1.55-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs) on InP have been realized. High-reflectivity AlGaInAs-InP lattice matched distributed Bragg reflectors (DBRs) were grown on InP substrates. 1.7 (for 1.3 /spl mu/m) and 2.0 (for 1.55 /spl mu/m) mW single mode power at 25/spl deg/C, 0.6 mW single mode power at 85/spl deg/C and lasing operation at >100/spl deg/C have been achieved. 10 Gbit/s error free transmissions through 10 km standard single mode fiber for 1.3-/spl mu/m VCSELs, and through 15 km nonzero dispersion shift fiber for 1.55-/spl mu/m VCSELs, have been demonstrated. With the addition of an SOA, 100 km error free transmission at 10 Gbit/s also has been demonstrated through a negative dispersion fiber. No degradation has been observed after over 2500-h aging test.  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