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   249篇
  免费   13篇
电工技术   1篇
化学工业   51篇
金属工艺   15篇
机械仪表   2篇
建筑科学   5篇
矿业工程   1篇
能源动力   1篇
轻工业   33篇
水利工程   2篇
石油天然气   2篇
无线电   26篇
一般工业技术   33篇
冶金工业   61篇
原子能技术   2篇
自动化技术   27篇
  2023年   2篇
  2022年   7篇
  2021年   6篇
  2019年   9篇
  2018年   4篇
  2017年   4篇
  2016年   8篇
  2015年   3篇
  2014年   6篇
  2013年   16篇
  2012年   14篇
  2011年   15篇
  2010年   9篇
  2009年   15篇
  2008年   14篇
  2007年   6篇
  2006年   4篇
  2005年   3篇
  2004年   6篇
  2003年   4篇
  2002年   4篇
  2001年   7篇
  2000年   2篇
  1999年   2篇
  1998年   16篇
  1997年   10篇
  1996年   8篇
  1995年   10篇
  1994年   3篇
  1993年   4篇
  1992年   2篇
  1991年   5篇
  1989年   2篇
  1988年   4篇
  1986年   2篇
  1985年   3篇
  1984年   3篇
  1983年   1篇
  1980年   1篇
  1976年   3篇
  1974年   1篇
  1972年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
  1965年   1篇
  1964年   1篇
  1963年   3篇
  1961年   1篇
  1954年   1篇
排序方式: 共有262条查询结果,搜索用时 15 毫秒
1.
2.
Financial theory creates a puzzle. Some authors argue that high-risk entrepreneurs choose debt contracts instead of equity contracts since risky but high returns are of relatively more value for a loan-financed firm. Conversely, authors who focus explicitly on start-up finance predict that entrepreneurs are the more likely to seek equity-like venture capital contracts, the more risky their projects are. Our paper is an initial step towards resolving this puzzle empirically. We present microeconometric evidence on the determinants of debt and equity financing in young and innovative SMEs. We pay special attention to the role of risk for the choice of the method of financing. Since risk is not directly observable we use different indicators for financial and project risk. It turns out that our data generally confirms the hypothesis that the probability that a young high-tech firm receives equity financing is an increasing function of the financial risk. With regard to the intrinsic project risk, our results are less conclusive, as some of our indicators of a risky project are found to have a negative effect on the likelihood to be financed by private equity.  相似文献   
3.
OBJECTIVES: The age-dependence of the development of ventricular arrhythmias was studied in German shepherd dogs with inherited ventricular arrhythmias and sudden death. BACKGROUND: A colony of German shepherd dogs has been established that exhibit inherited ventricular arrhythmias and sudden death. The incidence of arrhythmias increases with age. Because ventricular tachycardia is associated with bradycardia, it was hypothesized that the increased incidence of arrhythmias was related to age-dependent slowing of heart rate. METHODS: Arrhythmia counts and RR intervals were measured from serial ambulatory ECG recordings obtained in 71 dogs (1-48 weeks). In addition, 19 dogs were challenged with phenylephrine (10 micrograms/kg i.v.) at 15, 28, and 45 weeks of age, 10 dogs were challenged with epinephrine (1 microgram/kg i.v.) at 3, 5, 7, 9, 11, 18, and 28 weeks of age, and 10 dogs were challenged at 28 weeks with epinephrine (2.5 micrograms/kg i.v.), before and after propranolol (0.5 mg/kg i.v.). RESULTS: The incidence and severity of ventricular arrhythmias increased between 7 and 28 weeks of age and decreased between 28 and 44 weeks of age. The age-dependent increase in the incidence of ventricular tachycardia was associated with age-dependent reductions in sinus rate. Baroreflex-mediated slowing of the heart rate unmasked arrhythmias in young animals that did not spontaneously display arrthythmias and exacerbated existing arrhythmias in older animals. However, the magnitude of baroreflex-induced bradycardia was similar from 7-18 weeks of age, yet the incidence of arrhythmias increased progressively. Moreover, the waning of ventricular arrhythmias in older animals was not associated with more rapid sinus rates. CONCLUSION: The risk for sudden death in dogs with inherited ventricular arrhythmias increases with age in part because of age-dependent slowing of heart rate and in part because of other heart-rate-independent factors. The correspondence between the development of ventricular tachycardia and sinus pauses is consistent with the hypothesis that ventricular arrhythmias are initiated by early afterdepolarization-induced triggered activity.  相似文献   
4.
JOM - When considering the fracture resistance of high strength casing that may be used for deep gas well interests onshore or offshore, it is important that the casing meet minimum performance...  相似文献   
5.
Determination of Pentane as an Indicator of Oil Rancidity Pentane, determined by a headspace gas chromatographic method, is an excellent indicator of oil rancidity. The methodology applied is very simple and could be performed in an oil laboratory without purchasing additional equipment. The amount of pentane correlated well with the iodometrically determined peroxide value (R2-value of 0.976). Heating the oil sample in air followed by an estimation of pentane is an alternative means to assess oil stability against oxidative deterioration.  相似文献   
6.
Properties of a single-chain antibody containing different linker peptides   总被引:1,自引:0,他引:1  
Single-chain antibodies were constructed using six differentlinker peptides to join the VH and VL domains of an anti-2-phenyloxazolone(Ox) antibody. Four of the linker peptides originated from theinterdomain linker region of the fungal cellulase CBHI and consistedof 28, 11, six and two amino acid residues. The two other linkerpeptides used were the (GGGGS)3 linker with 15 amino acid residuesand a modified IgG2b hinge peptide with 22 residues. Proteolyticstability and Ox binding properties of the six different scFvderivatives produced in Escherichia coli were investigated andcompared with those of the corresponding Fv fragment containingno joining peptide between the V domains. The hapten bindingproperties of different antibody fragments were studied by ELISAand BIAcoreTM. The interdomain linker peptide improved the haptenbinding properties of the antibody fragment when compared withFv fragment, but slightly increased its susceptibility to proteases.Single-chain antibodies with short CBHI linkers of 11, six andtwo residues had a tendency to form multimers which led to ahigher apparent affinity. The fragments with linkers longerthan 11 residues remained monomeric.  相似文献   
7.
Kinetic and thermodynamic analyses of catalytic hydrodechlorinations in supercritical carbon dioxide (SC-CO2) were performed using 5% Pd supported on γ-Al2O3. The selected standard compounds used for the study represented chlorinated wood resins commonly found in pitch deposits; 1-chlorooctadecane (C18-Cl), 9,10-dichlorostearic acid (Stearic-Cl2), and 12,14-dichlorodehydroabietic acid (DHA-Cl2). The reaction utilized isopropanol as a hydrogen donor. Pressure, temperature, and the concentrations of isopropanol and palladium were varied to study the effect of each parameter and to optimize the dechlorination yield. The reaction in SC-CO2 was compared to the one in liquid solvents at atmospheric pressure. By applying a Langmuir–Hinshelwood kinetic model, the rate-determining step of the reaction was deduced to be adsorption of the chlorinated molecules on the palladium surface. The apparent activation energies of the reactions for C18-Cl, Stearic-Cl2, DHA-Cl2 were 43±5, 40±7, and 135±7 kJ mol−1, respectively, in SC-CO2. The relatively high activation energy for DHA-Cl2 was apparently due to structural differences from the other two compounds. The apparent activation energy of dechlorination of C18-Cl in liquid isopropanol at atmospheric pressure was determined to be 35±3 kJ mol−1, leading to the conclusion that the rate-determining step is the same for this compound in both fluid systems. The enthalpies of desorption of stearic acid and dehydroabietic acid were determined to be 18±2 and 12±2 kJ mol−1, respectively. These values being less than half of the apparent activation energies of dechlorination of their corresponding chlorinated compounds indicates that desorption of the dechlorinated products is not the rate-determining step of the reaction. This was consistent with the conclusion that the rate-determining step is adsorption, on the understanding that the reaction mechanism is same in both fluid systems.  相似文献   
8.
Superhydrophobic coatings are widely applicable, e.g., as self-cleaning surfaces or water–oil separation membranes, yet their wider usage is impeded due to costs of fabrication, size, or substrate limitation. Spray-coating is a versatile coating procedures and might offer a good solution for the fabrication of these superhydrophobic coatings, due to the fact that coatings can be fabricated on various materials in a simple, fast, and inexpensive manner. Most procedures rely on hybrid coatings of hydrophobized nanoparticles and a polymeric matrix, which have several drawbacks including the easy loss of nanoparticles and difficult waste handling. Here, the fabrication of the superhydrophobic material, called Fluoropor, for the first time, by spray-coating on various substrates including metals, tissues, concrete, and glass is presented. It is fabricated by spray-coating a mixture of a highly fluorinated monomer blended with porogens followed by photopolymerization. The superhydrophobicity of the material relies on the porous structure on the micro-/nanoscale across the bulk material and does not require any nanoparticles. Excellent self-cleaning ability of these coatings, resistance against thermal and abrasive impact, and their application as oil–water separation membranes are shown. This versatile applicability is highly promising for real-world application as self-cleaning coatings or oil–water separating membranes.  相似文献   
9.
10.
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