全文获取类型
收费全文 | 2874篇 |
免费 | 119篇 |
国内免费 | 7篇 |
学科分类
工业技术 | 3000篇 |
出版年
2024年 | 5篇 |
2023年 | 17篇 |
2022年 | 25篇 |
2021年 | 47篇 |
2020年 | 60篇 |
2019年 | 48篇 |
2018年 | 72篇 |
2017年 | 81篇 |
2016年 | 83篇 |
2015年 | 69篇 |
2014年 | 86篇 |
2013年 | 205篇 |
2012年 | 129篇 |
2011年 | 165篇 |
2010年 | 156篇 |
2009年 | 156篇 |
2008年 | 168篇 |
2007年 | 165篇 |
2006年 | 125篇 |
2005年 | 88篇 |
2004年 | 92篇 |
2003年 | 102篇 |
2002年 | 74篇 |
2001年 | 36篇 |
2000年 | 51篇 |
1999年 | 48篇 |
1998年 | 165篇 |
1997年 | 92篇 |
1996年 | 64篇 |
1995年 | 44篇 |
1994年 | 39篇 |
1993年 | 39篇 |
1992年 | 23篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1986年 | 12篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 12篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1973年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有3000条查询结果,搜索用时 15 毫秒
991.
L. Aquino-Meneses R. Lozada-Morales P. del Angel-Vicente J. C. Percino-Picazo O. Zelaya-Angel M. Becerril J. Carmona-Rodriguez F. Rodriguez-Melgarejo S. Jiménez-Sandoval 《Journal of Materials Science》2014,49(5):2298-2302
Based on the melt-quenching method, V2O5 was doped with Nd3+ ions. Photoluminescent properties due to electronic transitions of Nd3+ were found. In spite of the used method in the fabrication of this material, which consisted in a thermal shock from 1073 to 100 K, all the characterization techniques indicated that V2O5 has a crystalline orthorhombic phase and is acting as a host matrix for the Nd3+ ions. For instance, in the X-ray diffraction patterns, only well-defined peaks associated to V2O5 were detected. By Raman spectroscopy, vibrational modes related to V2O5 were observed. An E g = 2.15 eV was determined from the optical absorption spectrum for this doped material. Scanning electron microscopy images recorded on a fresh fracture show that this material is formed by lamellar plates. The elemental semi quantitative analysis indicates that the doping level with Nd3+ was of the order of 2.0 ± 0.2 at.%. Dark conductivity measurements yielded values in the 10?6–10?12 (Ω cm)?1 range. Finally, by micro photoluminescence spectroscopy, the {4F5/2, 4F3/2} → 4I9/2 electronic transitions related to Nd3+ ions were observed. 相似文献
992.
Sharad Jaiswal Gianluca Iannaccone Christophe Diot Jim Kurose Don Towsley 《Networking, IEEE/ACM Transactions on》2007,15(1):54-66
We present a classification methodology and a measurement study for out-of-sequence packets in TCP connections going over the Sprint IP backbone. Out-of-sequence packets can result from many events including loss, looping, reordering, or duplication in the network. It is important to quantify and understand the causes of such out-of-sequence packets since it is an indicator of the performance of a TCP connection, and the quality of its end-end path. Our study is based on passively observed packets from a point inside a large backbone network-as opposed to actively sending and measuring end-end probe traffic at the sender or receiver. A new methodology is thus required to infer the causes of a connection's out-of-sequence packets using only measurements taken in the "middle" of the connection's end-end path. We describe techniques that classify observed out-of-sequence behavior based only on the previously and subsequently-observed packets within a connection and knowledge of how TCP behaves. We analyze numerous several-hour packet-level traces from a set of OC-12 and OC-48 links for tens of millions connections generated in nearly 7600 unique ASes. We show that using our techniques, it is possible to classify almost all out-of-sequence packets in our traces and that we can quantify the uncertainty in our classification. Our measurements show a relatively consistent rate of out-of-sequence packets of approximately 4%. We observe that a majority of out-of-sequence packets are retransmissions, with a smaller percentage resulting from in-network reordering 相似文献
993.
从2004年下半年起,AMD和Intel这两大主流处理器供应商开始向多核处理器进军.两家公司尽可能在芯片上集成更多的处理核,同时简化设计减少系统功耗并提高整体性能.多核处理器的实质是在同一芯片中集成很多同样的处理核.这一方法降低了设计的复杂性,减小了处理节点,并成为多核处理器发展的一种趋势-这种趋势显然对于服务器应用来说更合适,因为服务器通常为多用户提供固定且有限的功能. 相似文献
994.
David J. Jude Richard Rediske Jim O'Keefe Stephen Hensler John P. Giesy 《Journal of Great Lakes research》2010
Concentrations of polychlorinated biphenyls (PCBs) were measured in composited samples of walleyes Sander vitreus and their prey during 2005–2007 from Saginaw Bay, Lake Huron. There was a linear relationship between fish length and PCB concentrations in walleyes between 356 and 608 mm, but fish 680 mm had lesser concentrations than 608-mm fish. When fish 222–550 mm from 1990 were compared with those from 2007, there was a decrease of 1315 ng PCBs/g wet wt (ww). Concentrations of PCBs in gizzard shad Dorosoma cepedianum (190 ng PCBs/g ww) were three-fold less than fish collected in 1990 (516 ng PCBs/g ww). Round gobies Neogobius melanostomus collected from the Saginaw River had the greatest concentrations of PCBs (range: 200–350 ng PCBs/g ww) compared with other prey fishes (45–190 ng PCBs/g ww). Concentrations of PCBs in Saginaw River round gobies were three-fold greater than those from Saginaw Bay. Zooplankton from 1990 and 2008 contained 8.0 and 32 ng PCBs/g ww, respectively, while zebra mussels Dreissena polymorpha from 2008 contained 351 ng PCBs/g ww. Principal components analysis showed that PCB congeners differed between the largest walleyes and other fish. There are several possible explanations for lesser concentrations of PCBs observed in 2007. These include effects of dredging, changes in the food web related to round gobies, loss of alewife Alosa pseudoharengus, which was a major walleye prey item in 1990, and replacement by yellow perch Perca flavescens, or decreases in release of PCBs from sediments due to weathering, burial, or diffusion. 相似文献
995.
Alfonso Clemente Francisco Javier Moreno Maria del Carmen Marín‐Manzano Elisabeth Jiménez Claire Domoney 《Molecular nutrition & food research》2010,54(3):396-405
Bowman–Birk inhibitors (BBI) from soybean and related proteins are naturally occurring protease inhibitors with potential health‐promoting properties within the gastrointestinal tract. In this work, we have investigated the effects of soybean BBI proteins on HT29 colon adenocarcinoma cells, compared with non‐malignant colonic fibroblast CCD‐18Co cells. Two major soybean isoinhibitors, IBB1 and IBBD2, showing considerable amino acid sequence divergence within their inhibitory domains, were purified in order to examine their functional properties, including their individual effects on the proliferation of HT29 colon cancer cells. IBB1 inhibited both trypsin and chymotrypsin whereas IBBD2 inhibited trypsin only. Despite showing significant differences in their enzyme inhibitory properties, the median inhibitory concentration values determined for IBB1 and IBBD2 on HT29 cell growth were not significantly different (39.9±2.3 and 48.3±3.5 μM, respectively). The cell cycle distribution pattern of HT29 colon cancer cells was affected by BBI treatment in a dose‐dependent manner, with cells becoming blocked in the G0–G1 phase. Chemically inactive soybean BBI had a weak but non‐significant effect on the proliferation of HT29 cells. The anti‐proliferative properties of BBI isoinhibitors from soybean reveal that both trypsin‐ and chymotrypsin‐like proteases involved in carcinogenesis should be considered as potential targets of BBI‐like proteins. 相似文献
996.
F. Fernández-Martín Paloma Fernández José Carballo Francisco Jiménez-Colmenero 《European Food Research and Technology》2000,211(6):387-392
Hydrostatic high-pressure/temperature treatments were conducted at low (10 °C) and high temperatures (60, 70, and 80°C) on
different types of meat batters. Pressure-induced effects on proteins were intensified by sodium chloride molarity at low
and high temperatures. Treatments at 10°C under pressurisation yielded net thermal destabilisation effects on meat proteins
pertaining either to muscle or batter systems. Heating at usual cooking temperature of 70°C under pressure yielded net stabilising
effects on meat batter proteins. Overheating at 80°C was needed for entire protein denaturation. Pork and chicken meats were
very similar in behaviour but chicken batters exhibited relatively higher thermal- and pressure-induced protein denaturation.
Both kinds of physical destabilisation/stabilisation of proteins by pressure-induced effects increased with pressure level.
Received: 30 December 1999 / Revised version: 14 February 2000 相似文献
997.
M. Antonia Martínez-Anaya Teresa Jiménez 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1998,206(2):134-142
The textural properties of wheat doughs made with different commercial amylases, xylanases/pentosanases, lipases and glucose-oxidase,
singly and in mixed combinations, were investigated. Parameters from the texture profile analysis (TPA) and measurement of
stickiness (Chen and Hoseney test) were determined after mixing the dough and after it had rested for 3.5 h. Resting of doughs
led to softer and less cohesive doughs, with higher adhesive properties. Enzymes acted quickly and induced significant changes
in the textural properties of doughs immediately after mixing. The influence of enzymes continued during resting. Xylanases/pentosanases
substantially reduced dough consistency and increased stickiness, while addition of glucose-oxidase and specific lipases overcame
these effects. Strong correlations could be established between different TPA parameters and stickiness and bread quality
characteristics (i.e. volume, density and texture). Bread quality could be described by a single or multiple linear combination
of textural variables.
Received: 21 May 1997 / Revised version: 10 July 1997 相似文献
998.
R. Carbajal. Valdez J. L. Jiménez. Pérez A. Cruz-Orea E. San. Martín-Martínez 《International Journal of Thermophysics》2006,27(6):1890-1897
Time resolved thermal lens (TL) spectrometry is applied to the study of the thermal diffusivity of edible oils such as olive, and refined and thermally treated avocado oils. A two laser mismatched-mode experimental configuration was used, with a He–Ne laser as a probe beam and an Ar+ laser as the excitation one. The characteristic time constant of the transient thermal lens was obtained by fitting the experimental data to the theoretical expression for a transient thermal lens. The results showed that virgin olive oil has a higher thermal diffusivity than for refined and thermally treated avocado oils. This measured thermal property may contribute to a better understanding of the quality of edible oils, which is very important in the food industry. The thermal diffusivity results for virgin olive oil, obtained from this technique, agree with those reported in the literature.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5-8, 2005, Bratislava, Slovak Republic. 相似文献
999.
Morphodynamic signatures derived from daily surface elevation dynamics can explain the morphodynamic development of tidal flats 下载免费PDF全文
Tim J. Grandjean Jaco C. de Smit Jim van Belzen Gregory S. Fivash Jeroen van Dalen Tom Ysebaert Tjeerd J. Bouma 《水科学与水工程》2023,16(1):14-25
Understanding the sensitivity of tidal flats to environmental changes is challenging. Currently, most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats. In this study, we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development. Surface elevation dynamic (SED) indices focus on the magnitude and period of surface elevation changes, while morphodynamic signature (MDS) indices relate sediment dynamics to environmental drivers. The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat. Using these analyses, we were able to (1) detect a reduction in the daily SED and (2) determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents. Overall, the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats, ecosystem functioning, and sensitivity to physical drivers (wind and tides). Finally, we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats. 相似文献
1000.
本文探讨了人们通常面对的嵌入设计挑战.并以实用的方式探讨如何运用PSoC芯片这种系统级的可编程能力克服这些挑战. 相似文献