全文获取类型
收费全文 | 302598篇 |
免费 | 28011篇 |
国内免费 | 17502篇 |
专业分类
电工技术 | 17094篇 |
技术理论 | 4篇 |
综合类 | 19790篇 |
化学工业 | 77341篇 |
金属工艺 | 23706篇 |
机械仪表 | 14432篇 |
建筑科学 | 16315篇 |
矿业工程 | 6476篇 |
能源动力 | 10672篇 |
轻工业 | 25183篇 |
水利工程 | 3457篇 |
石油天然气 | 11693篇 |
武器工业 | 2317篇 |
无线电 | 28889篇 |
一般工业技术 | 39882篇 |
冶金工业 | 12742篇 |
原子能技术 | 3200篇 |
自动化技术 | 34918篇 |
出版年
2024年 | 1148篇 |
2023年 | 4911篇 |
2022年 | 10110篇 |
2021年 | 11513篇 |
2020年 | 9006篇 |
2019年 | 8568篇 |
2018年 | 8059篇 |
2017年 | 10331篇 |
2016年 | 11710篇 |
2015年 | 12260篇 |
2014年 | 16228篇 |
2013年 | 17947篇 |
2012年 | 18643篇 |
2011年 | 21224篇 |
2010年 | 16994篇 |
2009年 | 18797篇 |
2008年 | 16967篇 |
2007年 | 20464篇 |
2006年 | 19516篇 |
2005年 | 15892篇 |
2004年 | 13019篇 |
2003年 | 11788篇 |
2002年 | 9630篇 |
2001年 | 7655篇 |
2000年 | 6779篇 |
1999年 | 5260篇 |
1998年 | 4011篇 |
1997年 | 3238篇 |
1996年 | 2895篇 |
1995年 | 2642篇 |
1994年 | 2344篇 |
1993年 | 1879篇 |
1992年 | 1411篇 |
1991年 | 1045篇 |
1990年 | 809篇 |
1989年 | 673篇 |
1988年 | 435篇 |
1987年 | 317篇 |
1986年 | 293篇 |
1985年 | 250篇 |
1984年 | 223篇 |
1983年 | 142篇 |
1982年 | 151篇 |
1981年 | 138篇 |
1980年 | 130篇 |
1979年 | 79篇 |
1978年 | 42篇 |
1977年 | 46篇 |
1976年 | 46篇 |
1962年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Colour Centres and Energy Transfer in BaF2-xClx:Eu2+ Phosphors 总被引:1,自引:1,他引:0
The optical absorption spectra of BaF2-xClx:Eu2 after ultraviolet (UV) light excitation were investigated.The differences between the absorption spectra after and before excitation (DAS) were observed.The DAS increase at both the high and the low energy side of F band in BaF2-xClx:Eu2 after 245 nm UV light excitation.The bleach effect of UV light and the absorption of electrons in the valence band may account for the former and the formation of Fa centres (association of F(Cl-) centres), whose absorption band matches the HeNe laser better, may explain the latter.In the write-in process, the transfer of electrons is via tunneling.In the readout process, the transfer of electrons captured in F(F-) and Fa centres is more likely via tunneling, and that of F(Cl-) centres is more likely via conduction band. 相似文献
102.
在薄板坯连铸连轧流程上,经过对Ti微合金化技术研究,有效解决了Ti微合金化强度性能波动大的问题,开发出屈服强度450~700MPa高强钢。对试制钢组织性能和工业应用分析研究,表明该产品通板性能良好,通板强度差30MPa左右;成形性能良好,d=0时冷弯测试全部合格;同时还具有良好焊接性能,焊接后,强度波动较小,均在母材部位断开;试制钢显微组织为珠光体和铁素体,晶粒均匀细小,平均尺寸为4~8/μm;实物质量满足集装箱和汽车制造行业要求,具有广阔市场前景。 相似文献
103.
The dynamic response of highway bridges subjected to moving truckloads has been observed to be dependent on (1) dynamic characteristics of the bridge; (2) truck configuration, speed, and lane position on the bridge; and (3) road surface roughness profile of the bridge and its approach. Historically, truckloads were measured to determine the load spectra for girder bridges. However, truckload measurements are either made for a short period of time [for example, weigh-in-motion (WIM) data] or are statistically biased (for example, weigh stations) and cost prohibitive. The objective of this paper is to present results of a 3D computer-based model for the simulation of multiple trucks on girder bridges. The model is based on the grillage approach and is applied to four steel girder bridges tested under normal truck traffic. Actual truckload data collected using a discrete bridge WIM system are used in the model. The data include axle loads, truck gross weight, axle configuration, and statistical data on multiple presence (side by side or following). The results are presented as a function of the static and dynamic stresses in each girder and compared with code provisions for dynamic load factor. The study provides an alternate method for the development of live-load models for bridge design and evaluation. 相似文献
104.
数据包络分析模型及其应用研究 总被引:1,自引:1,他引:0
郑明贵 《南方冶金学院学报》2004,25(4):62-66
通过对传统的C^2R模型进行研究并加以改进,建立了C2RHZ模型,利用有色金属矿采选业1993-2001年科技创新的相关数据进行了计算分析。说明了C^2RHZ模型的应用价值. 相似文献
105.
106.
In this paper, the test results of liquid injection impact on the performance of new alternative refrigerant mixtures such as: R-410A, R-507, R-407C and R-404A are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various liquid injection ratios. Performance tests were conducted according to the ARI/ASHRAE standards. The performance data demonstrated that as liquid injection ratio increases, compressor head pressure and discharge temperature decrease. This has a positive effect in protecting the compressor. The effect of liquid injection on mixture behaviour varies from one mixture to another depending upon the mixture's composition. Furthermore, liquid injection appears to have a significant influence on R-410A behaviour compared to the other mixtures in question. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
107.
O. Khamman 《Materials Letters》2007,61(3):639-643
The solid-state mixed oxide method via a rapid vibro-milling technique is explored in the preparation of single-phase nickel niobate (NiNb2O6) powders. The formation of the NiNb2O6 phase in the calcined powders has been investigated as a function of calcination conditions by TG-DTA and XRD techniques. Morphology, particle size and chemical composition have been determined via a combination of SEM and EDX techniques. It has been found that the minor phases of unreacted NiO and Nb2O5 precursors and the Ni4Nb2O9 phase tend to form together with the columbite NiNb2O6 phase, depending on calcination conditions. More importantly, it is seen that optimization of calcination conditions can lead to a single-phase NiNb2O6 in an orthorhombic phase. 相似文献
108.
2-环戊基环戊酮香料的制备与应用 总被引:2,自引:0,他引:2
以尼龙酸副产物2-亚环戊基环戊酮为原料,液体镍为催化剂,催化加氢制得了2-环戊基环戊酮。经元素分析、GCMS、IR、^1HNMR、^13C NMR检测,认为结构正确,色谱纯度大于99.9%。大鼠口服LD50雄性5381.5mg/kg,雌性5087.5mg/kg。具有留兰香样的香气,可用作食用和日用香料。 相似文献
109.
The results of a comprehensive experimental program, aimed at providing a fundamental understanding of the behavior of shear-critical exterior reinforced concrete (RC) joints strengthened with fiber reinforced polymers (FRP) under simulated seismic load, are presented in this study. The role of various parameters on the effectiveness of FRP is examined through 2/3-scale testing of 18 exterior RC joints. Conclusions are drawn on the basis of certain load versus imposed displacement response characteristics, comprising the strength (maximum lateral load), the stiffness, and the cumulative energy dissipation capacity. The results demonstrate the important role of mechanical anchorages in limiting premature debonding, and they provide important information on the role of various parameters, including: area fraction of FRP; distribution of FRP between the beam and the column; column axial load; internal joint (steel) reinforcement; initial damage; carbon versus glass fibers; sheets versus strips; and effect of transverse beams. 相似文献
110.
Shuichi Yamamoto Teruaki Morihiro Koichi Ariyoshi Turkan Aktas 《Drying Technology》2005,23(6):1319-1330
As the surface properties of the drying materials are very important not only for the drying rate but also for the quality change during drying, the effects of surface concentration on the drying behavior of liquid foods (sugar solutions) were investigated by isothermal drying experiments and by numerical calculation experiments. The isothermal drying experiments with gelled sugar solution systems (sucrose and maltodextrin) were carried out at various relative humidity (RH) values (RH = 0 to 84%). Separate experiments were carried out for determination of the desorption isotherms.
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献
The isothermal drying curves of sugar solutions at RH = 0 to 51% were very similar. Numerical simulations also showed that the drying curves of these sugars at the surface concentration = 0 and 0.1 are almost the same, although the concentration distributions are different.
When a small amount of gelatin was added to sugar solutions, the drying rate decreased remarkably as the gelatin might form a thin film (skin) near the surface, and consequently the retention of ethanol increased. 相似文献