全文获取类型
收费全文 | 727篇 |
免费 | 35篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 197篇 |
金属工艺 | 14篇 |
机械仪表 | 8篇 |
建筑科学 | 27篇 |
矿业工程 | 2篇 |
能源动力 | 39篇 |
轻工业 | 107篇 |
水利工程 | 3篇 |
石油天然气 | 5篇 |
无线电 | 86篇 |
一般工业技术 | 107篇 |
冶金工业 | 57篇 |
原子能技术 | 4篇 |
自动化技术 | 100篇 |
出版年
2023年 | 10篇 |
2022年 | 26篇 |
2021年 | 29篇 |
2020年 | 24篇 |
2019年 | 23篇 |
2018年 | 26篇 |
2017年 | 21篇 |
2016年 | 24篇 |
2015年 | 14篇 |
2014年 | 23篇 |
2013年 | 55篇 |
2012年 | 34篇 |
2011年 | 41篇 |
2010年 | 34篇 |
2009年 | 49篇 |
2008年 | 46篇 |
2007年 | 30篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 10篇 |
2003年 | 18篇 |
2002年 | 20篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 14篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 5篇 |
1973年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有766条查询结果,搜索用时 31 毫秒
71.
H. Bahmanpour K. M. Youssef R. O. Scattergood C. C. Koch 《Journal of Materials Science》2011,46(19):6316-6322
Copper alloys with different amounts of zinc were synthesized via high energy ball milling at liquid nitrogen and room temperature.
Bulk samples were produced in situ by controlling the milling temperature. It is shown that temperature plays an important
role in formation of artifact-free consolidated samples via its effect on defect formation and annihilation during the milling
process. The mechanical behavior of Cu–Zn nanocrystalline alloys was examined using Vickers microhardness and tensile tests.
The nanostructure of the alloys was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The
hardness results of processed alloys vary as a function of the alloying elements. Considering typical low ductility of nanocrystalline
materials, the improved ductility with the high strength observed in these alloys suggests that they are artifact-free and
may have several deformation mechanisms, which may include dislocation activity and nano-twinning. 相似文献
72.
Hamdy M. Youssef 《热应力杂志》2013,36(12):1293-1309
A problem of thermoelastic interactions in an elastic infinite layer 0 ≤ x ≤ h with an elevated temperature field arising from ramp-type heating and loading has been constructed. The governing equations are written in a unified system from which the field equations for coupled thermoelasticity as well as for generalized thermoelasticity can be easily obtained as particular cases. Due attention has been paid to the finite rise times of temperature and stress. The problem has been solved analytically by using a state-space approach. Solutions from the derived analytical expressions have been computed for a specific situation. The solution for the half-space when (h → ∞) has been found also. Numerical results for the temperature distribution and thermal stress are represented graphically. A comparison was made among the results predicted by the theories. 相似文献
73.
The dynamic tensile strengths of E-glass composite/polyurea and polyurea/steel interfaces within the E-glass composite/polyurea/AL-6XN stainless steel joint were measured using a laser spallation technique. Values of 370?±?20?MPa were obtained for the polyurea/composite interface while a much higher value of 486?±?20?MPa was obtained for the steel/polyurea interface. Because of the transient nature of the stress pulse, the strain rate changes continuously as the interface stress builds up. A peak strain rate of 5?×?105?s?1 was estimated. The effect of moisture on the tensile strength of the E-glass/polyurea interface was also examined. The effect was found to be minimal, with the tensile strength stabilizing at 320?±?25?MPa after 30?days of exposure to a 90%RH, 50?°C environment. When comparing the strengths of corresponding interfaces in an epoxy-bonded joint from a previous study, it was concluded that polyurea results in a much stronger and durable joint. 相似文献
74.
SA Mousa M Forsythe J Bozarth A Youssef J Wityak R Olson T Sielecki 《Canadian Metallurgical Quarterly》1998,32(5):736-744
XV454 demonstrated high potency (IC50 = 14-25 nM) in inhibiting human platelet aggregation induced by adenosine diphosphate (ADP, 10 microM), thrombin receptor agonist peptide (TRAP) (10 microM), or collagen (20 microg/ml). XV454 exhibited a high degree of selectivity for platelet alpha(IIb)beta3 in comparison with c7E3, which is a nonspecific antagonist for both alpha(IIb)beta3 and alpha(v)beta3. Both XV454 and c7E3 bind with high affinity to either activated (A) or unactivated (U) human, baboon, or canine platelets. XV454 binds with a relatively higher affinity [Kd = 0.5 nM (A), 0.6 nM (U)] as compared with c7E3 [Kd = 9.1 nM (A), 9.2 (U) nM]. XV454 demonstrated a tight association with human, baboon, and, to a lesser extent, with canine platelets (t(1/2) of dissociation = 110 +/- 6, 80 +/- 10, and 23 +/- 2 min, respectively). Both c7E3 and XV454 associate tightly with a slower dissociation rate with unactivated human platelets: t(1/2) of 42 and 116 min, respectively. In non-human primates, oral (0.1 mg/kg, p.o.) and intravenous (0.05 mg/kg, i.v. bolus administration of XV454 methyl ester pro-drug resulted a long-lasting maximal antiplatelet efficacy for < or = 72 h with significant but reversible prolongation of bleeding time and without effects on platelet count, clinical chemistry, or hemodynamic profile. In conclusion, XV454 represents a potent antiplatelet agent in inhibiting platelet aggregation along with a high affinity and relatively slow dissociation rate from human platelet GPIIb/IIIa receptors that allow a long-lasting antiplatelet efficacy after single i.v. or oral administration. 相似文献
75.
76.
Based on the theory of variable structure systems (VSS), control system design for the trajectory control of robotic systems is presented. It is assumed that the parameters of the system are uncertain and unknown frictional torques are acting at the various joints of the arm. For simplicity, the control of a three-link PUMA arm is considered. For trajectory following, two control laws, CH and Cθ, based on the choice of coordinates of the end effector or joint angles as the controlled outputs, respectively, are derived. It is seen that whereas control Cθ has no singularity, certain singular surfaces arise where feedback elements of CH become infinity. These singular surfaces describe the boundary of the reachable region (workspace). Digital simulation results are presented to show that accurate trajectory following can be accomplished using the control CH or Cθ for large maneuvers of the arm in spite of the uncertainty in the system. 相似文献
77.
Analysis and design consideration of mean temperature differential Stirling engine for solar application 总被引:1,自引:0,他引:1
This article presents a technical innovation, study of solar power system based on the Stirling dish (SD) technology and design considerations to be taken in designing of a mean temperature differential Stirling engine for solar application. The target power source will be solar dish/Stirling with average concentration ratio, which will supply a constant source temperature of 320 °C. Hence, the system design is based on a temperature difference of 300 °C, assuming that the sink is kept at 20 °C. During the preliminary design stage, the critical parameters of the engine design are determined according to the dynamic model with losses energy and pressure drop in heat exchangers was used during the design optimisation stage in order to establish a complete analytical model for the engine. The heat exchangers are designed to be of high effectiveness and low pressure-drop. Upon optimisation, for given value of difference temperature, operating frequency and dead volume there is a definite optimal value of swept volume at which the power is a maximum. The optimal swept volume of 75 cm3 for operating frequency 75 Hz with the power is 250 W and the dead volume is of 370 cm3. 相似文献
78.
A bulk p-type thermoelectric compound with nominal composition Bi0.5Sb1.5 Te3 has been exfoliated using dimethyl sulfoxide as a solvent. Samples have been prepared from the exfoliated platelets by pressing followed by sintering or hot pressing. The exfoliated nanoplatelets have been characterized for size distribution and composition using scanning electron microscopy and energy-dispersive spectrometry. The smallest size platelet was 40 nm, and the maximum in the size distribution was near 80 nm. The exfoliated platelets and sintered sample showed significant deficiency in Sb and Te. The nonstoichiometry in the composition of the exfoliated platelets indicates that the mechanism of exfoliation may not be between quintuplets only, with other layers also being active. The composition of the hot-pressed sample remained closer to that of the bulk. Results of x-ray diffraction indicated the presence of Bi2Te3 and Bi0.5Sb1.5Te3 phases and pure Te and Sb. Residual porosity was observed in the hot-pressed and sintered samples. The thermal conductivity of the samples was measured by transient thermoreflectance. The results showed that the thermal conductivity of the hot-pressed sample was reduced by a factor of two compared with that of the bulk as a result of the presence of a high density of interfaces and residual porosity. The thermal conductivity of the sintered sample showed an increase above that of the bulk sample, which is explained by the change in composition due to loss of Sb and Te. 相似文献
79.
Lakhdar A Falleh H Ouni Y Oueslati S Debez A Ksouri R Abdelly C 《Journal of hazardous materials》2011,191(1-3):373-379
Organic wastes were successfully used as soil amendment to improve agrosystems productivity. Yet, the effectiveness of this practice to enhance plant antioxidant capacities has received little attention. Here, we assess the effect of municipal solid waste (MSW) compost (at 40 t ha(-1)) on growth, polyphenol contents and antioxidant activities of Mesembryanthemum edule. MSW compost application significantly increased the soil contents of carbon, nitrogen, calcium, phosphorus and potassium. This was associated with higher nutrient (N, P, and K) uptake, which likely led to the significant improvement of the plant biomass and relative growth rate (RGR) (+93% on average) as compared to the control. In the same way, the fertilizing effect of the added organic matter significantly enhanced the antioxidant potential M. edule, assessed by radical scavenging activity, iron reducing power and β-carotene bleaching capacity. This was associated with significantly higher antioxidant contents, mainly total phenols and flavonoids. Heavy metal (Pb, Cd, Cu, and Zn) concentrations were slightly increased upon compost application, but remained lower than phytotoxic values. Overall, our results point out that short-term MSW compost application at 40 t ha(-1) is efficient in enhancing the productivity together with the antioxidant potentiality of M. edule without any adverse environmental impact. 相似文献
80.
PP Youssef TJ Smeets B Bresnihan G Cunnane O Fitzgerald F Breedveld PP Tak 《Canadian Metallurgical Quarterly》1998,37(9):1003-1007
BACKGROUND: A significant proportion of burn patients with inhalation injuries incur difficulties with airway protection, dysphagia, and aspiration. In assessing the need for intubation in burn patients, the efficacy of fiberoptic laryngoscopy was compared with clinical findings and the findings of diagnostic tests, such as arterial blood gas analysis, measurement of carboxyhemoglobin levels, pulmonary function tests, and radiography of the lateral aspect of the neck. OBJECTIVE: To determine if these patients were at risk for aspiration or dysphagia, barium-enhanced fluoroscopic swallowing studies were performed. DESIGN: Prospective study. SETTINGS: Burn intensive care unit in an academic tertiary referral center. MAIN OUTCOME MEASURES: Need for endotracheal intubation and potential for aspiration. RESULTS: Six (55%) of 11 patients had clinical findings and symptoms that indicated, under traditional criteria, endotracheal intubation for airway protection. Visualization of the upper airway with fiberoptic laryngoscopy obviated the need for endotracheal intubation in all 11 patients. These patients also failed to evidence an increased risk of aspiration or other swallowing dysfunction. CONCLUSIONS: In comparison with other diagnostic criteria, fiberoptic laryngoscopy allows differentiation of those patients with inhalation injuries who, while at risk for upper airway obstruction, do not require intubation. These patients may be safely observed in a monitored setting with serial fiberoptic examinations, thus avoiding the possible complications associated with intubation of an airway with a compromised mucosalized surface. In these patients, swallowing abnormalities do not manifest. 相似文献