全文获取类型
收费全文 | 5229篇 |
免费 | 324篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 60篇 |
综合类 | 9篇 |
化学工业 | 1007篇 |
金属工艺 | 64篇 |
机械仪表 | 79篇 |
建筑科学 | 190篇 |
矿业工程 | 6篇 |
能源动力 | 173篇 |
轻工业 | 380篇 |
水利工程 | 67篇 |
石油天然气 | 35篇 |
无线电 | 459篇 |
一般工业技术 | 1291篇 |
冶金工业 | 710篇 |
原子能技术 | 27篇 |
自动化技术 | 1004篇 |
出版年
2024年 | 13篇 |
2023年 | 64篇 |
2022年 | 109篇 |
2021年 | 156篇 |
2020年 | 140篇 |
2019年 | 144篇 |
2018年 | 138篇 |
2017年 | 146篇 |
2016年 | 175篇 |
2015年 | 144篇 |
2014年 | 203篇 |
2013年 | 355篇 |
2012年 | 324篇 |
2011年 | 420篇 |
2010年 | 313篇 |
2009年 | 298篇 |
2008年 | 324篇 |
2007年 | 261篇 |
2006年 | 229篇 |
2005年 | 203篇 |
2004年 | 163篇 |
2003年 | 148篇 |
2002年 | 138篇 |
2001年 | 74篇 |
2000年 | 76篇 |
1999年 | 67篇 |
1998年 | 70篇 |
1997年 | 68篇 |
1996年 | 55篇 |
1995年 | 45篇 |
1994年 | 49篇 |
1993年 | 46篇 |
1992年 | 47篇 |
1991年 | 28篇 |
1990年 | 31篇 |
1989年 | 17篇 |
1988年 | 19篇 |
1987年 | 31篇 |
1986年 | 20篇 |
1985年 | 33篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 30篇 |
1979年 | 9篇 |
1977年 | 11篇 |
1976年 | 18篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 12篇 |
排序方式: 共有5561条查询结果,搜索用时 15 毫秒
61.
A sensing strategy for the reverse engineering of machined parts 总被引:1,自引:0,他引:1
The reverse engineering of machined parts requires sensing an existing part and producing a design (and perhaps a manufacturing process) for it. We have developed a reverse engineering system that has proven effective with a set of machined parts. This paper describes the system, presents some results, and discusses strategy for a new system.This work was supported by ARPA under ARO grant number DAAH04-93-G-0420, DARPA grant N00014-91-J-4123, NSF grant CDA 9024721, and a University of Utah Research Committee grant. All opinions, findings, conclusions or recommendations expressed in this document are those of the authors and do not necessarily reflect the views of the sponsoring agencies. 相似文献
62.
The Rules of Beeping: Exchanging Messages Via Intentional "Missed Calls" on Mobile Phones 总被引:1,自引:0,他引:1
Jonathan Donner 《Journal of Computer-Mediated Communication》2007,13(1):1-22
This article explores the practice of "beeping" or "missed calling" between mobile phone users, or calling a number and hanging up before the mobile's owner can pick up the call. Most beeps are requests to call back immediately, but they can also send a pre-negotiated instrumental message such as "pick me up now" or a relational sign, such as "I'm thinking of you." The practice itself is old, with roots in landline behaviors, but it has grown tremendously, particularly in the developing world. Based on interviews with small business owners and university students in Rwanda, the article identifies three kinds of beeps (callback, pre-negotiated instrumental, and relational) and the norms governing their use. It then assesses the significance of the practice using adaptive structuration theory. In concluding, the article contrasts beeping with SMS/text messaging, discusses its implications for increasing access to telecommunications services, and suggests paths for future research. 相似文献
63.
THE IMPORTANCE OF NEUTRAL EXAMPLES FOR LEARNING SENTIMENT 总被引:2,自引:0,他引:2
Most research on learning to identify sentiment ignores "neutral" examples, learning only from examples of significant (positive or negative) polarity. We show that it is crucial to use neutral examples in learning polarity for a variety of reasons. Learning from negative and positive examples alone will not permit accurate classification of neutral examples. Moreover, the use of neutral training examples in learning facilitates better distinction between positive and negative examples. 相似文献
64.
Barch Deanna M.; Cohen Jonathan D.; Servan-Schreiber David; Steingard Sandra; Steinhauer Stuart S.; van Kammen Daniel P. 《Canadian Metallurgical Quarterly》1996,105(4):592
Semantic priming in word pronunciation was examined at 5 stimulus onset asynchronies (SOAs) in 75 medicated and 25 unmedicated people with schizophrenia (SCZ) and in 10 depressed and 28 normal controls. At SOAs 相似文献
65.
Flow experience, the degree to which a person feels involved in a particular activity, is an important influence on human–computer interaction. Building on Guo and Poole’s (2009) model of flow experience in Web navigation, and van Schaik and Ling's (in press) cognitive-experiential approach to modelling interaction experience, this research demonstrates the crucial role of the preconditions of flow experience in human–computer interaction. In an experiment, the preconditions of flow experience – but not flow experience proper – mediated the effects of artefact complexity, task complexity and intrinsic motivation (as a situation-specific trait) on both flow and task outcome. However, preconditions did not predict overall artefact evaluation. Within a staged model of flow experience, the broader implications of this work for human–computer interaction are explored. 相似文献
66.
Pollock B Burton M Kelly JW Gilbert S Winer E 《IEEE transactions on visualization and computer graphics》2012,18(4):581-588
Stereoscopic depth cues improve depth perception and increase immersion within virtual environments (VEs). However, improper display of these cues can distort perceived distances and directions. Consider a multi-user VE, where all users view identical stereoscopic images regardless of physical location. In this scenario, cues are typically customized for one "leader" equipped with a head-tracking device. This user stands at the center of projection (CoP) and all other users ("followers") view the scene from other locations and receive improper depth cues. This paper examines perceived depth distortion when viewing stereoscopic VEs from follower perspectives and the impact of these distortions on collaborative spatial judgments. Pairs of participants made collaborative depth judgments of virtual shapes viewed from the CoP or after displacement forward or backward. Forward and backward displacement caused perceived depth compression and expansion, respectively, with greater compression than expansion. Furthermore, distortion was less than predicted by a ray-intersection model of stereo geometry. Collaboration times were significantly longer when participants stood at different locations compared to the same location, and increased with greater perceived depth discrepancy between the two viewing locations. These findings advance our understanding of spatial distortions in multi-user VEs, and suggest a strategy for reducing distortion. 相似文献
67.
A Gaussian sum filter (GSF) with component extended Kalman filters (EKF) is proposed as an approach to localizing an autonomous vehicle in an urban environment with limited GPS availability. The GSF uses vehicle‐relative vision‐based measurements of known map features coupled with inertial navigation solutions to accomplish localization in the absence of GPS. The vision‐based measurements have multimodal measurement likelihood functions that are well represented as weighted sums of Gaussian densities. The GSF is used because of its ability to represent the posterior distribution of the vehicle pose with better efficiency (fewer terms, less computational complexity) than a corresponding bootstrap particle filter with various numbers of particles because of the interaction with measurement hypothesis tests. The expectation‐maximization algorithm is used off line to determine the representational efficiency of the particle filter in terms of an effective number of Gaussian densities. In comparison, the GSF, which uses an iterative condensation procedure after each iteration of the filter to maintain real‐time capabilities, is shown through a series of in‐depth empirical studies to more accurately maintain a representation of the posterior distribution than the particle filter using 37 min of recorded data from Cornell University's autonomous vehicle driven in an urban environment, including a 32 min GPS blackout. © 2012 Wiley Periodicals, Inc. 相似文献
68.
Scale-up and control of droplet production in coupled microfluidic flow-focusing geometries 总被引:1,自引:1,他引:0
A single microfluidic chip consisting of six microfluidic flow-focusing devices operating in parallel was developed to investigate the feasibility of scaling microfluidic droplet generation up to production rates of hundreds of milliliters per hour. The design utilizes a single inlet channel for both the dispersed aqueous phase and the continuous oil phase from which the fluids were distributed to all six flow-focusing devices. The exit tubing for each of the six flow-focusing devices is separate and individually plumbed to each device. Within each flow-focusing device, the droplet size was monodisperse, but some droplet size variations were observed across devices. We show that by modifying the flow resistance in the outlet channel of an individual flow-focusing device it is possible to control both the droplet size and frequency of droplet production. This can be achieved through the use of valves or, as is done in this study, by changing the length of the exit tubing plumbed to the outlet of the each device. Longer exit tubing and larger flow resistance is found to lead to larger droplets and higher production frequencies. The devices can thus be individually tuned to create a monodisperse emulsion or an emulsion with a specific drop size distribution. 相似文献
69.
Inga Baasch Christensen Lei Cheng Jonathan R. Brewer Udo Bartsch Robert A. Fenton Helle H. Damkier Jeppe Praetorius 《International journal of molecular sciences》2021,22(4)
(1) Background: The unusual accumulation of Na,K-ATPase complexes in the brush border membrane of choroid plexus epithelial cells have intrigued researchers for decades. However, the full range of the expressed Na,K-ATPase subunits and their relation to the microvillus cytoskeleton remains unknown. (2) Methods: RT-PCR analysis, co-immunoprecipitation, native PAGE, mass spectrometry, and differential centrifugation were combined with high-resolution immunofluorescence histochemistry, proximity ligase assays, and stimulated emission depletion (STED) microscopy on mouse choroid plexus cells or tissues in order to resolve these issues. (3) Results: The choroid plexus epithelium expresses Na,K-ATPase subunits α1, α2, β1, β2, β3, and phospholemman. The α1, α2, β1, and β2, subunits are all localized to the brush border membrane, where they appear to form a complex. The ATPase complexes may stabilize in the brush border membrane via anchoring to microvillar actin indirectly through ankyrin-3 or directly via other co-precipitated proteins. Aquaporin 1 (AQP1) may form part of the proposed multi-protein complexes in contrast to another membrane protein, the Na-K-2Cl cotransporter 1 (NKCC1). NKCC1 expression seems necessary for full brush border membrane accumulation of the Na,K-ATPase in the choroid plexus. (4) Conclusion: A multitude of Na,K-ATPase subunits form molecular complexes in the choroid plexus brush border, which may bind to the cytoskeleton by various alternative actin binding proteins. 相似文献
70.
Peter K. Windsor Stephen P. Plassmeyer Dominic S. Mattock Jonathan C. Bradfield Erika Y. Choi Bill R. Miller III Byung Hee Han 《International journal of molecular sciences》2021,22(6)
Deposition of amyloid β (Aβ) fibrils in the brain is a key pathologic hallmark of Alzheimer’s disease. A class of polyphenolic biflavonoids is known to have anti-amyloidogenic effects by inhibiting aggregation of Aβ and promoting disaggregation of Aβ fibrils. In the present study, we further sought to investigate the structural basis of the Aβ disaggregating activity of biflavonoids and their interactions at the atomic level. A thioflavin T (ThT) fluorescence assay revealed that amentoflavone-type biflavonoids promote disaggregation of Aβ fibrils with varying potency due to specific structural differences. The computational analysis herein provides the first atomistic details for the mechanism of Aβ disaggregation by biflavonoids. Molecular docking analysis showed that biflavonoids preferentially bind to the aromatic-rich, partially ordered N-termini of Aβ fibril via the π–π interactions. Moreover, docking scores correlate well with the ThT EC50 values. Molecular dynamic simulations revealed that biflavonoids decrease the content of β-sheet in Aβ fibril in a structure-dependent manner. Hydrogen bond analysis further supported that the substitution of hydroxyl groups capable of hydrogen bond formation at two positions on the biflavonoid scaffold leads to significantly disaggregation of Aβ fibrils. Taken together, our data indicate that biflavonoids promote disaggregation of Aβ fibrils due to their ability to disrupt the fibril structure, suggesting biflavonoids as a lead class of compounds to develop a therapeutic agent for Alzheimer’s disease. 相似文献