全文获取类型
收费全文 | 17456篇 |
免费 | 2058篇 |
国内免费 | 820篇 |
专业分类
电工技术 | 551篇 |
综合类 | 847篇 |
化学工业 | 7494篇 |
金属工艺 | 1167篇 |
机械仪表 | 301篇 |
建筑科学 | 576篇 |
矿业工程 | 247篇 |
能源动力 | 1368篇 |
轻工业 | 801篇 |
水利工程 | 158篇 |
石油天然气 | 785篇 |
武器工业 | 95篇 |
无线电 | 1016篇 |
一般工业技术 | 3891篇 |
冶金工业 | 648篇 |
原子能技术 | 189篇 |
自动化技术 | 200篇 |
出版年
2024年 | 67篇 |
2023年 | 540篇 |
2022年 | 589篇 |
2021年 | 747篇 |
2020年 | 794篇 |
2019年 | 775篇 |
2018年 | 721篇 |
2017年 | 832篇 |
2016年 | 702篇 |
2015年 | 708篇 |
2014年 | 979篇 |
2013年 | 1196篇 |
2012年 | 1240篇 |
2011年 | 1376篇 |
2010年 | 944篇 |
2009年 | 1052篇 |
2008年 | 844篇 |
2007年 | 1021篇 |
2006年 | 852篇 |
2005年 | 697篇 |
2004年 | 569篇 |
2003年 | 478篇 |
2002年 | 370篇 |
2001年 | 304篇 |
2000年 | 270篇 |
1999年 | 229篇 |
1998年 | 218篇 |
1997年 | 170篇 |
1996年 | 132篇 |
1995年 | 123篇 |
1994年 | 106篇 |
1993年 | 82篇 |
1992年 | 90篇 |
1991年 | 91篇 |
1990年 | 66篇 |
1989年 | 64篇 |
1988年 | 50篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 28篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 8篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
V. Anjos M.J.V. Bell E.F. da Silva Jr. R.W.A. Franco I.A. Esquef 《Microelectronics Journal》2005,36(11):977-980
In this paper we report the use of photothermal techniques such as Thermal lens (TL) spectrometry, Photoacoustic and heat capacity, ρcp, to determine the thermo-optical parameters, such as thermal conductivity (K), thermal diffusivity (D), specific heat (cp) and the optical path dependence with temperature (ds/dT), of an undoped polycrystalline 3C-SiC. To our knowledge, this is the first time that Thermal lens technique is used for wide band-gap systems. Results obtained for the polycrystalline sample with TL technique indicates that ds/dT is negative at room temperature. Moreover, the obtained values of thermal diffusivity and thermal conductivity are in good agreement with that found in the literature, indicating that the phototermal techniques can be used to obtain the referred parameters in circumstances where other techniques cannot be used, for example, in harsh environments. 相似文献
42.
The d.c. electrical conductivity of sodium vanadate, rubidium vanadate, cesium vanadate and their solid solutions sodium-rubidium
vanadate and sodium-cesium vanadate were studied by a two-probe method in the temperature range covering their transition
points. The electrical conductivity shows sharp change at the phase transition temperature of these materials. In NaVO3, RbVO3 and CsVO3, increase in d.c. conductivity is observed in the ferroelectric region while nonlinearities are observed above transition
temperatures. In solid solutions, the activation energy in the paraelectric state is higher than that in the ferroelectric
state and depends upon sodium concentration. 相似文献
43.
44.
P. M. Solozhenkin E. A. Deliyanni V. N. Bakoyannakis A. I. Zouboulis K. A. Matis 《Journal of Mining Science》2003,39(3):287-296
The original method is developed for producing the new inorganic sorption material of akaganeite bgr-FeO(OH). The material in question is characterized relative to arsenic contained in aqua. The possibility is established for removing arsenate ions from water by contemporary physicochemical methods. 相似文献
45.
Investigations of water inrushes from aquifers under coal seams 总被引:6,自引:0,他引:6
In many coal mines, limestone-confined aquifers underlie coal seams. During coal extraction from these mines, water inrushes occur frequently with disastrous consequences. This paper introduces the hydrogeological conditions of the coal mines and the potential water inrush disasters from aquifers under coal seams. It then presents the water inrush mechanism. The main factors which control water inrushes include strata pressure, mining size, geologic structures and the water pressure in the underlying aquifer. Analysis shows that reduction of confinement due to mining is the major cause of the water-conducting failure in the floor strata. The depth of the failure zone is strongly dependent on the mining width. This paper also presents field observation results of the water-conducting failure in the floor strata, and applies the finite element method coupled with stress-dependent permeability to analyze hydraulic conductivity enhancement due to coal extraction. Finally, theoretical and empirical methods to predict water inrushes are given, and technical measures for improving mine design and safety for coal extraction over aquifers are presented. These measures include fault and fracture grouting and mining method modification such as changing long-wall to short-wall mining. 相似文献
46.
常压渣油热反应过程中胶体的稳定性 总被引:10,自引:0,他引:10
利用质量分数电导率方法研究了中东和克拉玛依常压渣油在热反应过程中胶体的稳定性。结果表明,随着反应时间的增长,在热反应生焦诱导期内,渣油的胶体稳定性迅速下降;开始生焦后,胶体稳定性缓慢下降。从中东常压渣油的SARA四组分的数均相对分子质量、碳氢元素组成、平均芳碳率等方面探讨了中东常压渣油在热反应过程中胶体稳定性下降的原因。结果表明,在热反应中,由于裂解和缩聚反应的共同作用,使渣油的沥青质和饱和分含量上升,芳香分含量下降,胶质含量变化不大;随着热反应的进行,四组分的数均相对分子质量均呈下降趋势,导致了渣油胶体稳定性的下降并发生生焦反应。 相似文献
47.
ZnS, ZnSe, and CdTe polycrystals are experimentally investigated. Mechanisms are treated which restrict the thermal conductivity in samples prepared by recrystallization pressing and by deposition from the vapor phase and subjected to additional strain. Anomalies are observed on the temperature dependences of the thermal resistance of investigated samples, which are due to the special features of their phonon spectra and to the variation of the contribution made by longitudinal and transverse phonon branches to the heat transfer in the Debye temperature region and higher. 相似文献
48.
《Particulate Science and Technology》2007,25(1):77-89
The removal of particulate contamination is a critical issue for many manufacturing processes. It is particularly critical to the electronics industry in which small pieces of microscopic debris remaining after chemical mechanical planarization (cmp) using submicron polishing particles can cause device failure. One way to enhance particle removal following the cmp process is to utilize surfactants. Recent research has shown ways to model the effect of surfactants on enhanced particle removal. However, previous research has not demonstrated the effect of ionic strength on enhanced particle removal associated with surfactant use. Past research has also not shown the combined effects of ionic strength and surfactant concentration on enhanced particle removal using surfactants. This article summarizes the parameters affecting particle removal, and it provides data and analysis on the effect of ionic strength as well as the combined effects of ionic strength and surfactant concentration on particle removal following cmp processing. 相似文献
49.
An analytical solution is presented to the problem of steady groundwater flow seeping into a pumped cylindrical hole partially penetrating a homogeneous and anisotropic confined aquifer overlying a gravel substratum. Solutions are obtained for two general cases of the problem: (1) when the level of the pumped hole is below the confining layer; (2) when it is above it. The validity of the proposed theory is tested by comparing analytical predictions obtained for a few flow situations with corresponding results obtained by numerical means. The theory presented here can be utilized to convert the rate of rise of water in a pumped auger hole into directional conductivities of soil, in areas where water is found to be in a confined state overlying a gravel substratum. The study shows that the conductivity values calculated by neglecting the confining pressure of an artesian aquifer with a gravel base [i.e., by applying the existing (Boast and Kirkham in 1971), auger hole seepage theory for a phreatic aquifer with a gravel base to confined situations] may result in serious error; hence, the artesian head of an aquifer must be accounted for while computing the conductivity values. Further, it is observed that the area contributing flow to a pumped auger hole/well with a gravel base is mostly restricted to a short radial distance from the center of the hole, particularly for situations where the gravel substratum is located close to the bottom of the hole. This is in contrast to auger hole flow situations overlying an impervious substratum, where the domain contributing flow is mostly spread out to a considerable distance from the center of the hole. 相似文献
50.
E. M. Abdel-Bary H. H. Hassan A. M. El-Lawindy M. K. Abu-Assy F. K. El-Tantawy 《Polymer International》1993,30(3):371-374
Butyl rubber mixtures loaded with 70 phr general purpose furnace black (GPF) and tetramethyl thiuram disulphide (TMTD)/S as vulcanizing system were prepared. The kinetics of their electrical conductivity development during the vulcanization process were followed by using an especially devised system. It was found that the increase in the electrical conductivity during vulcanization obeys an exponential growth function with time constant τ, which markedly decreases with increasing vulcanization temperature as well as with the efficiency of the vulcanizing system. After completion of the vulcanization process, about 80 min, the samples obtained possess reasonable stability and reproducibility of electrical conductivity. 相似文献