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   1005篇
  免费   59篇
  国内免费   9篇
电工技术   59篇
综合类   5篇
化学工业   318篇
金属工艺   32篇
机械仪表   29篇
建筑科学   19篇
矿业工程   9篇
能源动力   63篇
轻工业   93篇
水利工程   5篇
石油天然气   7篇
武器工业   4篇
无线电   64篇
一般工业技术   194篇
冶金工业   55篇
原子能技术   35篇
自动化技术   82篇
  2024年   4篇
  2023年   12篇
  2022年   32篇
  2021年   49篇
  2020年   27篇
  2019年   29篇
  2018年   30篇
  2017年   34篇
  2016年   43篇
  2015年   25篇
  2014年   54篇
  2013年   81篇
  2012年   77篇
  2011年   68篇
  2010年   52篇
  2009年   55篇
  2008年   58篇
  2007年   40篇
  2006年   37篇
  2005年   30篇
  2004年   25篇
  2003年   30篇
  2002年   21篇
  2001年   13篇
  2000年   13篇
  1999年   6篇
  1998年   10篇
  1997年   11篇
  1996年   19篇
  1995年   7篇
  1994年   4篇
  1993年   6篇
  1992年   8篇
  1991年   7篇
  1990年   6篇
  1989年   4篇
  1987年   7篇
  1985年   6篇
  1984年   3篇
  1983年   2篇
  1982年   4篇
  1981年   6篇
  1980年   1篇
  1979年   3篇
  1977年   4篇
  1976年   3篇
  1973年   2篇
  1971年   2篇
  1970年   1篇
  1966年   1篇
排序方式: 共有1073条查询结果,搜索用时 93 毫秒
61.
本文介绍了液化石油气残液的组成。借助计算机模拟闪蒸操作,从理论的角度出发分析处理利用残液的可行性。通过这种既简单又经济的方法可将液化石油气残液加工成石油醚和汽油。  相似文献   
62.
We developed new heat-resisting transparent conductive oxide (TCO) films with resistivity of 1.4×10−4 Ω cm, an optical transmittance of above 80% (at 550 nm) and heat-resisting temperature at above 600 °C. The TCO films consists of fluorine-doped tin oxide films coated on indium–tin oxide films. They were prepared by a spray pyrolysis deposition method on glass substrates. The 100×100 mm2 dye-sensitized solar cells (DSCs) were prepared with the TCO films. An energy conversion efficiency of the DSC was improved drastically in comparison to the case with conventional TCO films.  相似文献   
63.
Oligoribonucleotides containing four G clusters, (UGnU)4 (n = 3-5), were synthesized and characterized by electrophoretic analysis and resistance to nucleases. Electrophoretic analyses indicate that the oligomers except for (UG3U)4 can form antiparallel-stranded monomeric quadruplexes in the presence of potassium cation. The oligomers used in this study are protected from endonuclease P1 and venom phosphodiesterase degradation. In addition, the oligomers indicate resistance to nucleases in human serum and E. coli S-100 fraction.  相似文献   
64.
Nishimukai M  Wakisaka T  Hara H 《Lipids》2003,38(12):1227-1235
Plasmalogens, a subclass of phospholipids, are widely distributed in human and animals, and are taken into the body as food. However, no data exist on the intestinal absorption or fate of ingested plasmalogen. Here, we determined whether dietary plasmalogen is absorbed and whether blood and tissue concentrations increased in normal male Wistar rats by using four separate experiments. Phospholipids containing more than 20 wt% of plasmalogen extracted from the bovine brain were incorporated into test diets (10–15 wt%). In experiment 1, we estimated the absorption rate by measuring the plasmalogen vinyl ether bonds remaining in the alimentary tract of rats after the ingestion of 2 g of test diet containing 91 μmol plasmalogen. The absorption rate of plasmalogen was nearly 80 mol% after 4 h, comparable to the total phospholipid content in the test diet. In experiment 2, we observed no degradation of the plasmalogen vinyl ether bonds under in vitro conditions simulating those of the stomach and small intestinal lumen. In experiment 3 we confirmed a comparable absorption (36 mol%) by using a closed loop of the upper small intestine in anesthetized rats 90 min after injecting a 10 wt% brain phospholipid emulsion. Feeding a test diet containing 10 wt% brain phospholipids for 7 d increased plasmalogen concentration threefold in blood plasma and by 25% in the liver; however, no increases were seen in blood cells, skeletal muscle, brain, lungs, kidneys, or adipose tissue (experiment 4). We concluded that dietary plasmalogen is absorbed from the intestine and contributes to a large increase in plasmalogen levels in blood plasma.  相似文献   
65.
Effects of steroid hormones on vascular functions   总被引:6,自引:0,他引:6  
The purpose of this review is to present reported findings of effects of steroids on vascular function and to discuss the biological significance in vascular physiology and pathology. Steroid hormones play various roles in vascular functions through the specific receptor localized in the endothelium and underlying vascular smooth muscle cells (VSMCs). Estrogen replacement therapy in postmenopausal women is in general associated with a reduction in mortality from cardiovascular disease and the beneficial effects of estrogens are caused by modulation of lipid metabolism, expression of leukocyte adhesion molecules, and migration of VSMCs in the vascular wall. Estrogens also play a role as vasodilators through an increment in nitric oxide (NO) production in endothelium or modulation of calcium homeostasis in VSMCs. Some progestin molecules partially oppose the effects of estrogens on vascular functions, but striking differences exist among the types of molecules. Testosterone shows a vasorelaxant response, but detailed actions of androgens on vascular functions remain unknown. Glucocorticoids act on vasoconstriction through reduced prostacyclin production, increased alpha-adrenoceptor numbers, and inhibition of NO synthase, while mineralocorticoids induce hypertrophy and hyperplasia of VSMCs and perivascular fibrosis and cause peripheral vascular resistance, in addition to changes in vascular electrocyte permeability. Some rapid actions of steroids are mediated by "nongenomic" responses in vascular tissues. Recent studies have also demonstrated that steroid-producing or -metabolizing enzymes are expressed in the vascular wall, suggesting the local regulation of steroids in the vascular system. Thus, steroid hormones greatly influence vascular functions and an understanding of the mechanisms may provide new means to prevent vascular diseases.  相似文献   
66.
中国液态锂铅包层材料研究进展   总被引:2,自引:0,他引:2  
液态锂铅包层是国际上普遍关注和最有发展潜力的聚变堆包层概念设计之一,而包层材料是液态锂铅包层的核心问题之一.目前,液态锂铅包层普遍选用低活化铁素体/马氏体钢(RAFM钢)作为结构材料,液态锂铅作为中子倍增剂及氚增殖剂.另外,部分设计采用了耐高温、电绝缘流道插件作为功能材料,以降低磁流体动力学效应及提高冷却剂出口温度(高于700℃).为适应液态包层的发展需求,中国科学院等离子体物理研究所FDS团队联合国内外相关研究单位,进行了具有中国自主知识产权的中国低活化马氏体钢(CLAM钢)及液态锂铅包层功能材料研发,并开展了锂铅热对流及强迫对流回路的设计、研制及腐蚀实验研究,以研究液态金属锂铅的流动特性及其与结构和功能材料的相容性.同时建立了聚变堆材料数据库平台,为促进中国聚变堆液态包层及材料技术的研究和发展提供数据支持.  相似文献   
67.
Titanium dioxide (TiO2) powder-containing sheet composites, called TiO2 sheet, were prepared by a papermaking technique, and their photocatalytic efficiency was investigated. The TiO2 powders were homogeneously scattered over the fiber-mix networks tailored within the catalyst sheet. Under UV irradiation, the TiO2 paper could decompose p-hydroxyacetophenone (p-HAP), although the degradation efficiency by the TiO2 sheet was lower than that by the TiO2 powder. Scanning electron microscopy revealed that coverage of the TiO2 particles inside the sheet by alumina binder which was used to improve the sheet strength caused the deterioration of the photocatalytic performance. Internal addition of alumina binder made the TiO2 sheet porous and such a TiO2 sheet exhibited high photocatalytic performance equivalent to that of TiO2 powder. The porous structure of TiO2 sheet might contribute to effective transport of p-HAP to the surface of TiO2 particles inside the sheet, resulting in high degradation performance. In addition, TiO2 sheet prepared using TiO2 sol showed higher photocatalytic efficiency than TiO2 powder and it was indicated that the porous sheet structure might provide suitable conditions for TiO2 catalysis for photodecomposition.  相似文献   
68.
This study estimates pretreatment-posttreatment effect size benchmarks for the treatment of major depression in adults that may be useful in evaluating psychotherapy effectiveness in clinical practice. Treatment efficacy benchmarks for major depression were derived for 3 different types of outcome measures: the Hamilton Rating Scale for Depression (M. A. Hamilton, 1960, 1967), the Beck Depression Inventory (A. T. Beck, 1978; A. T. Beck & R. A. Steer, 1987), and an aggregation of low reactivity-low specificity measures. These benchmarks were further refined for 3 conditions: treatment completers, intent-to-treat samples, and natural history (wait-list) conditions. The study confirmed significant effects of outcome measure reactivity and specificity on the pretreatment-posttreatment effect sizes. The authors provide practical guidance in using these benchmarks to assess treatment effectiveness in clinical settings. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
69.
In previous studies, various stabilizing control methods for humanoids during the stance phase while hopping and running were proposed. Although these methods contribute to stability while hopping and running, it is possibility that the control during the flight phase could also affect the stability. In this study, we investigated whether the control during the flight phase can affect the stability of a humanoid while running. To achieve stable hopping, we developed a control system that accounts for the angular momentum of the whole body during the flight phase. In this system, the angular momentum generated by the motion of the lower body in each time interval is calculated during the flight phase, and the trunk joints are controlled to generate the angular momentum necessary to compensate for the deviation of the waist posture, which is used as the reference point for the motion coordinate system of the robot. Once the proposed control system was developed and simulated, we found that the hopping duration in the unconstrained state was extended.  相似文献   
70.
Research on noise robust speech recognition has mainly focused on dealing with relatively stationary noise that may differ from the noise conditions in most living environments. In this paper, we introduce a recognition system that can recognize speech in the presence of multiple rapidly time-varying noise sources as found in a typical family living room. To deal with such severe noise conditions, our recognition system exploits all available information about speech and noise; that is spatial (directional), spectral and temporal information. This is realized with a model-based speech enhancement pre-processor, which consists of two complementary elements, a multi-channel speech–noise separation method that exploits spatial and spectral information, followed by a single channel enhancement algorithm that uses the long-term temporal characteristics of speech obtained from clean speech examples. Moreover, to compensate for any mismatch that may remain between the enhanced speech and the acoustic model, our system employs an adaptation technique that combines conventional maximum likelihood linear regression with the dynamic adaptive compensation of the variance of the Gaussians of the acoustic model. Our proposed system approaches human performance levels by greatly improving the audible quality of speech and substantially improving the keyword recognition accuracy.  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