全文获取类型
收费全文 | 6440篇 |
免费 | 230篇 |
国内免费 | 24篇 |
专业分类
电工技术 | 93篇 |
综合类 | 14篇 |
化学工业 | 1151篇 |
金属工艺 | 274篇 |
机械仪表 | 143篇 |
建筑科学 | 286篇 |
矿业工程 | 5篇 |
能源动力 | 190篇 |
轻工业 | 460篇 |
水利工程 | 66篇 |
石油天然气 | 44篇 |
无线电 | 783篇 |
一般工业技术 | 984篇 |
冶金工业 | 1227篇 |
原子能技术 | 42篇 |
自动化技术 | 932篇 |
出版年
2023年 | 40篇 |
2022年 | 71篇 |
2021年 | 125篇 |
2020年 | 84篇 |
2019年 | 103篇 |
2018年 | 126篇 |
2017年 | 117篇 |
2016年 | 136篇 |
2015年 | 126篇 |
2014年 | 155篇 |
2013年 | 390篇 |
2012年 | 259篇 |
2011年 | 304篇 |
2010年 | 233篇 |
2009年 | 264篇 |
2008年 | 315篇 |
2007年 | 306篇 |
2006年 | 240篇 |
2005年 | 210篇 |
2004年 | 217篇 |
2003年 | 189篇 |
2002年 | 165篇 |
2001年 | 126篇 |
2000年 | 118篇 |
1999年 | 137篇 |
1998年 | 263篇 |
1997年 | 188篇 |
1996年 | 159篇 |
1995年 | 118篇 |
1994年 | 119篇 |
1993年 | 117篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 79篇 |
1989年 | 83篇 |
1988年 | 76篇 |
1987年 | 73篇 |
1986年 | 73篇 |
1985年 | 69篇 |
1984年 | 70篇 |
1983年 | 55篇 |
1982年 | 48篇 |
1981年 | 45篇 |
1980年 | 51篇 |
1979年 | 47篇 |
1978年 | 39篇 |
1977年 | 35篇 |
1976年 | 41篇 |
1975年 | 30篇 |
1974年 | 23篇 |
排序方式: 共有6694条查询结果,搜索用时 15 毫秒
71.
Dennis D. Pietronigro Myron L. Seligman W. Barrie G. Jones Harry B. Demopoulos 《Lipids》1976,11(11):808-813
Deoxyribonucleic acid (DNA) is associated with the cell membrane of prokaryotes and the inner nuclear membrane of eukaryotes.
The unsaturated fatty acids of phospholipids, which constitute the bilaminar structure of membranes, undergo autoxidation
in the presence of O2. Calf thymus DNA was incubated with methyl archidonate-enriched phosphatidyl choline liposomes in order to study the effect
of DNA upon the oxidation of phospholipids while present in their natural in vivo bilayer configuration. DNA retarded the
rate of lipid oxidation and the TBA test, but it did not alter the induction period. These results suggest that DNA is scavenging
free radicals produced within the phospholipid bilayer. 相似文献
72.
73.
This paper presents an investigation of the influence of plasma spray process conditions on the in-flight particle behavior
and their cumulative deposition to form a coating on the substrate. Three-dimensional computational fluid dynamics (CFD) analyses
were performed to model the in-flight particle behavior in the plasma-spray process and their deposition on the substrate.
The plasma spray was modeled as a jet issuing from the torch nozzle through the electrical heating of the arc gas. In the
model, particles were injected into the plasma jet where they acquired heat and momentum from the plasma, some got melted
and droplets were formed. By means of a droplet splatting model, the particle in-flight data generated by the CFD analyses
were further processed to build up an imaginary three-dimensional deposition profile on a flat stationary substrate. It is
found that the powder carrier gas flow rate influences the particle distribution on the substrate by imparting an injection
momentum to the particles that were directed radially into the plasma jet in a direction perpendicular to the plasma jet.
The larger sized particles will acquire higher injection momentum compared with the smaller sized particles. This causes particle
distribution at the substrate surface that is elliptical in shape with the major axis of ellipse parallel to the particle
injection port axis as illustrated in Fig. 1. Larger particles tend to congregate at the lower part of the ellipse, due to
their greater momentum. The distribution of particle size, temperature, velocity, and count distribution at the substrate
was analyzed. Further, based on the size and the computed particle temperature, velocity histories, and the impact sites on
the substrate, the data were processed to build up a deposition profile with the Pasandideh-Fard model. The shapes of deposition
profiles were found to be strongly driven by the segregation effect. 相似文献
74.
75.
Slavkovik Marija Dennis Louise A. Fisher Michael 《Distributed and Parallel Databases》2015,33(1):3-31
Distributed and Parallel Databases - Crowdsourcing, together with its related approaches, has become very popular in recent years. All crowdsourcing processes involve the participation of a digital... 相似文献
76.
“Simply, people can no longer remember passwords good enough to reliably defend against dictionary attacks, and are much more secure if they choose a password too complicated to remember and then write it down. We’re all good at securing small pieces of paper. I recommend that people write their passwords down on a small piece of paper, and keep it with their other valuable small pieces of paper: in their wallet.” 相似文献
77.
Abstract Previous research shows that although collaboration technology can improve the exchange of information during team decision making, one of the challenges is that this better discussion often does not lead to better decisions. In this paper, we investigate the impact of individual information processing on team decision making. We investigated the effects of two types of collaboration technology when participants were either the member of a team majority or a team minority. There was little impact due to the majority/minority, but the use of collaboration technology that required users to categorize the comments they received from others resulted in increased information processing, which in turn led to better decisions and more satisfied participants. 相似文献
78.
Underwater communication primarily utilizes propagation of acoustic waves in water. Its unique characteristics, including slow propagation speed and low data rates, pose many challenges to Media Access Control (MAC) protocol design. In most existing handshaking-based underwater MAC protocols, only an initiating sender can transmit data packets to its intended receiver after a channel reservation through a Request-to-Send (RTS)/Clear-to-Send (CTS) handshake. This conventional single-node transmission approach is particularly inefficient in underwater environments, as it does not account for long propagation delays. To improve channel utilization in high latency environments, we propose a novel approach that exploits the idle waiting time during a 2-way handshake to set up concurrent transmissions from multiple nodes. The sender can coordinate multiple first-hop neighbors (appenders) to use the current handshake opportunity to transmit (append) their data packets with partially overlapping transmission times. After the sender finishes transmitting its packets to its own receiver, it starts to receive incoming appended packets that arrive in a collision-free packet train. This not only reduces the amount of time spent on control signaling, but it also greatly improves packet exchange efficiency. Based on this idea, we propose an asynchronous, single-channel handshaking-based MAC protocol based on reverse opportunistic packet appending (ROPA). From extensive simulations (single- and multi-hop networks) and comparisons with several existing MAC protocols, including MACA-U, MACA-UPT, BiC-MAC, Slotted-FAMA, DACAP, unslotted Aloha, we show that ROPA significantly increases channel utilization and offers performance gains in throughput and delay while attaining a stable saturation throughput. 相似文献
79.
Flow cytometry has potential as a rapid assessment technique to evaluate phytoplankton biomass and species composition. It facilitates for multi-parameter analysis of individual cells on the basis of light scattering effects induced from cellular constituents, as well as auto-fluorescence. Fluorescence emission characteristics may be especially useful in classifying cyanobacteria as they contain phycoerythrin which emits light predominantly in the 550-600 nm waveband, chlorophyll-a (650-700 nm emission) and allophycocyanin (660 nm emission). The objective of our study was to assess the utility of flow cytometry for the rapid identification and sorting of freshwater algae and cyanobacteria species. Using a selection of laboratory-cultured freshwater algae and cyanobacteria species, this study demonstrated unique light scatter and fluorescent characteristics for each species examined, allowing for rapid species identification and sorting of mixed populations of laboratory cultures and samples from two lakes in the Rotorua region (New Zealand). Analysis of lake water samples collected over seven months demonstrated changes in abundance and community composition of phytoplankton in the two lakes and demonstrates that flow cytometry may be a useful technique for examining seasonal changes in phytoplankton composition. 相似文献
80.
Oi-Lam Ng Nathalie Sinclair 《Canadian Journal of Science, Mathematics, & Technology Education》2013,13(1):84-101
AbstractIn this article, we report on two lessons aimed at introducing junior high school students to the idea of shearing in a touchscreen dynamic geometry environment. By using shearing, we hoped to shift students’ attention away from a formula-driven, computational conception of area toward a more geometric one. We found that the students were able to solve several problems involving the comparison of polygons based on verbal and diagrammatic explanations. We describe the features of the touchscreen dynamic geometry technology that supported their learning, as well as the specific role that the teacher played in modeling students’ reasoning about area. 相似文献