全文获取类型
收费全文 | 129994篇 |
免费 | 3413篇 |
国内免费 | 561篇 |
专业分类
电工技术 | 1450篇 |
综合类 | 2370篇 |
化学工业 | 21211篇 |
金属工艺 | 6549篇 |
机械仪表 | 5796篇 |
建筑科学 | 3197篇 |
矿业工程 | 585篇 |
能源动力 | 3173篇 |
轻工业 | 7270篇 |
水利工程 | 1516篇 |
石油天然气 | 428篇 |
武器工业 | 2篇 |
无线电 | 16753篇 |
一般工业技术 | 26592篇 |
冶金工业 | 6355篇 |
原子能技术 | 911篇 |
自动化技术 | 29810篇 |
出版年
2024年 | 50篇 |
2023年 | 570篇 |
2022年 | 870篇 |
2021年 | 1484篇 |
2020年 | 1071篇 |
2019年 | 1179篇 |
2018年 | 15446篇 |
2017年 | 14382篇 |
2016年 | 11360篇 |
2015年 | 1869篇 |
2014年 | 2306篇 |
2013年 | 3183篇 |
2012年 | 6237篇 |
2011年 | 12853篇 |
2010年 | 10694篇 |
2009年 | 8244篇 |
2008年 | 9265篇 |
2007年 | 9663篇 |
2006年 | 2136篇 |
2005年 | 2870篇 |
2004年 | 2643篇 |
2003年 | 2622篇 |
2002年 | 1830篇 |
2001年 | 1226篇 |
2000年 | 1169篇 |
1999年 | 982篇 |
1998年 | 1608篇 |
1997年 | 1018篇 |
1996年 | 846篇 |
1995年 | 565篇 |
1994年 | 472篇 |
1993年 | 414篇 |
1992年 | 302篇 |
1991年 | 296篇 |
1990年 | 258篇 |
1989年 | 241篇 |
1988年 | 212篇 |
1987年 | 168篇 |
1986年 | 119篇 |
1985年 | 115篇 |
1984年 | 92篇 |
1983年 | 63篇 |
1981年 | 39篇 |
1977年 | 38篇 |
1976年 | 61篇 |
1968年 | 47篇 |
1966年 | 45篇 |
1965年 | 46篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Kim DeFronzo Haselhoff 《Journal of Urban Affairs》2002,24(4):425-443
I argue that the motivation for the San Fernando Valley secession movement can be explained as a desire for local control based on democratic ideals, but I emphasize that the movement is also motivated in part by the tangible benefits that accompany such autonomy. After a brief look at possible economic and racial motivations behind the secession movement, I look for a political divide between the city and the Valley, based on literature that has found political divisions between urban and suburban areas. Evidence of a political divide is mixed, but does indicate that the Valley lacks representation in comparison to the rest of the city. Valley residents may also fear increasing minority political power, which could erode the dominance of Valley whites at the polls. There is also evidence that those who favor secession are most dissatisfied with representation and most concerned with getting their fair share of services from the city, indicating a strong desire for more local control. Images of a smaller, more democratic government, and a more engaged local civic community are prime motivations in the Valley’s quest for autonomy, though the possibility of reduced taxes, land use control, and increased political power do offer secessionists clear substantive benefits in addition to more democratic goals. 相似文献
12.
13.
J-M Choe 《欧洲信息系统杂志》2002,11(2):142-158
This study empirically examined the organisational learning effects of the nonfinancial performance information provided by management accounting information systems (MAISs) under advanced manufacturing technology (AMT). In this study, a target costing system and the frequent and quick reporting of information were considered the facilitators of learning. First, we examined the relationships between AMT level and the amount of nonfinancial performance information produced by MAISs. The empirical results showed that there are significant positive relationships between the level of AMT and nonfinancial performance information. With a systems approach, we also proved the impact of the relationships among AMT levels, nonfinancial performance information and learning facilitators on the organisational performance of a firm. The results of our research suggest that under a high level of AMT, for the provision of information to result in an increase of performance through organisational learning, a target costing system must be introduced and a large amount of information should be provided frequently and quickly. The results of this study also showed that although AMT level may be low, fairly well-arranged facilitators and a moderately large amount of information may be necessary for the improvement of performance. In conclusion, effective organisational learning depends on the provision of relevant information as well as efficient learning support mechanisms. 相似文献
14.
15.
Gyeong-Ho Kim 《Computer Methods in Applied Mechanics and Engineering》2008,198(2):234-244
A continuum-based modeling of coupled electrostatics-structure interactions is presented for the frequency computations of MEMS devices. The present general formulation of electrostatics accounting for free space is validated first by specializing it to one-dimensional uniform motion of conducting surfaces and comparing the resulting electrostatics to conventional lumped models. The general coupled electrostatics-structure interactions are then applied for the prediction of resonant frequencies of MEMS devices due to bias-voltage changes and temperature variations. Comparisons of predicted resonant frequencies obtained by the present coupled electrostatics-structure interaction models with experimental results available in the literature demonstrate that the proposed continuum-based interaction modeling yields high-confidence predictions of resonant frequencies of MEMS devices. 相似文献
16.
Jon T. Carter Paul E. Krajewski Ravi Verma 《JOM Journal of the Minerals, Metals and Materials Society》2008,60(11):77-81
The hot blow forming of magnesium sheet offers significant opportunity for forming complex, lightweight parts for automotive
applications. This paper characterizes the elevated-temperature formability of AZ31 magnesium sheet materials and the effect
of processing conditions on the performance of these materials. In addition, magnesium sheet application development at General
Motors Corporation is reviewed. 相似文献
17.
本文详细探讨了使用无线网络分析器调试ZigBee协议系统的基本方法,从而便于更好地确保网络的可靠性. 相似文献
18.
Toshihiko Hoshide Junpei Fujita 《Journal of Materials Engineering and Performance》2008,17(5):627-632
Strength of ground ceramics may be affected by residual stress as well as surface flaws induced by grinding. Strength prediction
for ground ceramics is convenient for mechanical design of ceramic components. In this article, a numerical procedure based
on fracture mechanics was proposed to estimate strength distribution of ground ceramics by considering grinding-induced residual
stress. Bending strength and residual stress of ground ceramics were measured for three grinding-conditions. By comparison
of simulated results with experimental ones, it was revealed that strength characteristics in experiments were well simulated
by using the proposed procedure. 相似文献
19.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC 总被引:1,自引:0,他引:1
Min Gyu Kim Gil-Cho Ahn Hanumolu P.K. Sang-Hyeon Lee Sang-Ho Kim Seung-Bin You Jae-Whui Kim Temes G.C. Un-Ku Moon 《Solid-State Circuits, IEEE Journal of》2008,43(5):1195-1206
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation. 相似文献
20.
Nanocomposites based on poly(butylene terephthalate) (PBT) and an organoclay (Cloisite 30B) were prepared by melt blending using a twin‐screw extruder. Two kinds of PBTs, ie PBT‐A and PBT‐B, with different inherent viscosities (ηinh), were used for this study (ηinh of PBT‐A and PBT‐B were 0.74 and 1.48, respectively). Dispersion of the clay layers in the PBT nanocomposites was characterized by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Tensile and dynamic mechanical properties and non‐isothermal crystallization temperatures of the nanocomposites were also examined. Nanocomposites based on the higher‐viscosity PBT (PBT‐B) showed a higher degree of exfoliation of the clay and a higher reinforcing effect when compared to the composites based on the lower‐viscosity PBT (PBT‐A). The clay nanolayers dispersed in PBT matrices lead to increases in the non‐isothermal crystallization temperatures of the PBTs, with such increases being more significant for the PBT‐B nanocomposites than for the PBT‐A nanoocomposites. Copyright © 2004 Society of Chemical Industry 相似文献