全文获取类型
收费全文 | 9156篇 |
免费 | 635篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 137篇 |
综合类 | 24篇 |
化学工业 | 1885篇 |
金属工艺 | 245篇 |
机械仪表 | 215篇 |
建筑科学 | 527篇 |
矿业工程 | 39篇 |
能源动力 | 168篇 |
轻工业 | 1421篇 |
水利工程 | 42篇 |
石油天然气 | 16篇 |
无线电 | 694篇 |
一般工业技术 | 2651篇 |
冶金工业 | 226篇 |
原子能技术 | 89篇 |
自动化技术 | 1415篇 |
出版年
2023年 | 119篇 |
2022年 | 60篇 |
2021年 | 190篇 |
2020年 | 145篇 |
2019年 | 140篇 |
2018年 | 315篇 |
2017年 | 330篇 |
2016年 | 367篇 |
2015年 | 271篇 |
2014年 | 358篇 |
2013年 | 683篇 |
2012年 | 456篇 |
2011年 | 571篇 |
2010年 | 448篇 |
2009年 | 469篇 |
2008年 | 546篇 |
2007年 | 499篇 |
2006年 | 352篇 |
2005年 | 301篇 |
2004年 | 258篇 |
2003年 | 252篇 |
2002年 | 228篇 |
2001年 | 195篇 |
2000年 | 157篇 |
1999年 | 125篇 |
1998年 | 131篇 |
1997年 | 124篇 |
1996年 | 106篇 |
1995年 | 67篇 |
1994年 | 75篇 |
1993年 | 62篇 |
1992年 | 47篇 |
1991年 | 61篇 |
1990年 | 43篇 |
1989年 | 47篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1986年 | 57篇 |
1985年 | 109篇 |
1984年 | 74篇 |
1983年 | 60篇 |
1982年 | 53篇 |
1981年 | 44篇 |
1980年 | 53篇 |
1979年 | 41篇 |
1978年 | 45篇 |
1976年 | 28篇 |
1974年 | 30篇 |
1973年 | 31篇 |
1943年 | 26篇 |
排序方式: 共有9794条查询结果,搜索用时 31 毫秒
11.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
12.
Björn Täljsten 《International Journal of Fracture》1996,82(3):253-266
This paper presents the use of fracture mechanics for the plate bonding technique. Plates of steel or carbon-fibre reinforced
plastic are bonded with an epoxy adhesive to rectangular concrete prisms and loaded in shear up to failure, what is normally
known in fracture mechanics as mode II failure. In this special application a linear and a nonlinear approach are presented.
The nonlinear equation derived for a realistic shear-deformation curve can only be used for numerical calculations. However,
for simplified shear-deformation curves, the derived formula can be solved analytically. Results from tests, which are compared
with the theory, are also presented. 相似文献
13.
14.
CoNiFe-based amorphous films were magnetron-sputtered to investigate their structural and magnetic properties, including annealing-induced effects and interfacial influence from additional layers of Ta and Cu. The amorphous structure was confirmed by diffraction experiments. The magnetic measurements showed a well-defined uniaxial anisotropy in plane, arising possibly from atom oblique incidence effects competing with the stray field of the magnetron. The anisotropy could be influenced by using a Ta buffer layer, though the interfacial reaction gives rise to a dead layer. A coercive force H
c of 1–2 Oe and a magnetization of 680 emu/cm3 were measured at room temperature; properties which show promise for application in magnetotunneling junction devices. Thermal analyses showed a two-stage crystallization behavior, which started at 400°C and ended at about 600°C. The Curie temperature of the amorphous phase was estimated to be about 440°C. 相似文献
15.
Per Johan Råsmark Čestmír Koňák Petr Štěpánek Christer Elvingson 《Polymer Bulletin》2005,54(4-5):335-342
Summary Dynamic light scattering was used to investigate the dynamics of sodium poly(styrene sulfonate) and fully neutralized poly(acrylic acid) gels as a function of the degree of swelling and weight ratio of cross-linking agent. It was shown that the collective diffusion coefficient increases with increasing degree of swelling and that the diffusion coefficient shows stronger concentration dependence than predicted by scaling arguments. For gel samples measured at the swelling equilibrium, the diffusion coefficient increases with increasing gel concentration for both gel systems. 相似文献
16.
17.
18.
Henrik Pettersson Tadeusz Gruszecki Lars-Henrik Johansson Per Johander 《Solar Energy Materials & Solar Cells》2003,77(4):6595
A manufacturing technique for monolithic dye-sensitised solar cells is presented. Encapsulated modules designed for indoor low-power applications have been prepared using industrial methods and equipment. Under certain conditions (light intensity <5000 lx, temperature between –10°C and 50°C, and relative humidity of appr. 50%), the modules have performed well and shown excellent long-term stability. Moreover, modules withstand illumination in combination with storage at 100% relative humidity. However, a certain degradation of the module performance takes place at illuminations exceeding 5000 lx and temperatures exceeding 50°C. 相似文献
19.
Per Hovstad Liching Sung 《International Journal of Satellite Communications and Networking》2005,23(2):91-110
The 1977 Broadcasting‐Satellite Service (BSS) Plan for Region 1 & 3 had been widely acknowledged to be out‐of‐date by the late 1980s. Development of digital modulation in the early 1990s provided an opportunity to update the technical provisions of the Plan to make it more economically viable. After a decade of work and three World Radiocommunication Conferences (WRCs), the revision of Region 1 & 3 BSS Plan was finally completed in 2003. The new Plan increased channel assignments from 5 to 10 analog‐equivalent channels for each country in Region 1, and from 4 to 12 channels for each country in Region 3. Yet, despite the increase in capacity, the new Plan is surprisingly similar to the original one in terms of the technical parameters. It is still based on national coverage, and the channel plan, orbital location, orbital spacing, and polarization are also the same. As a result, the new Plan is no more economically viable to implement than the old. To create economically viable BSS systems would most likely require modifications to the assignment in the Plan. Yet, modification procedures were made more difficult to apply after replanning. Less future implementation of BSS networks than would otherwise have occurred can be expected, and an inefficient usage of these frequency bands will likely result. On the other hand, less implemented systems will mean more capacity set aside for future use. This is important for countries that currently do not have satellite operations. In the end, BSS replanning reflects the eternal conflict between efficient usage and guaranteed future access. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
20.
R. Hopfengärtner M. Lippert W. Dorsch H. Dietrich G. Kreiselmeyer G. Saemann-Ischenko 《Journal of Superconductivity and Novel Magnetism》1994,7(2):319-322
We report on measurements of the in-plane resistivityρ and Hall coefficientR H (B∥c) of various oxygen-deficient epitaxial films of YBa2Cu3O7?x in the normal state. The superconducting transition temperaturesT c of the samples vary from 14 to 90 K. Both the resistivity and the Hall coefficient exhibit a strong dependence on the oxygen content and the temperature. Asx increases,T c decreases continuously, whileρ andR H gradually increase in magnitude. Furthermore, also the characteristic linear dependences ofραT andR Hα T ?1 of the highly doped compounds changes to a nonlinear behavior for the samples withT c lower than 60 K. The unusual doping and temperature dependence ofR H will be compared to the predictions of our calculations, based on a two-dimensional tight-binding model using the relaxation-time approximation. The model considers also the next-nearest-neighbor hopping, which strongly influences the predicted Hall coefficient. Additionally, the cotangent of the Hall angle cot(Θ H ) is discussed in the framework of the two-dimensional Luttinger liquid theory. 相似文献