全文获取类型
收费全文 | 25266篇 |
免费 | 1330篇 |
国内免费 | 37篇 |
专业分类
电工技术 | 167篇 |
综合类 | 26篇 |
化学工业 | 6017篇 |
金属工艺 | 500篇 |
机械仪表 | 463篇 |
建筑科学 | 850篇 |
矿业工程 | 49篇 |
能源动力 | 905篇 |
轻工业 | 4699篇 |
水利工程 | 214篇 |
石油天然气 | 137篇 |
武器工业 | 2篇 |
无线电 | 1171篇 |
一般工业技术 | 3648篇 |
冶金工业 | 4036篇 |
原子能技术 | 184篇 |
自动化技术 | 3565篇 |
出版年
2024年 | 36篇 |
2023年 | 181篇 |
2022年 | 489篇 |
2021年 | 806篇 |
2020年 | 500篇 |
2019年 | 607篇 |
2018年 | 713篇 |
2017年 | 737篇 |
2016年 | 816篇 |
2015年 | 702篇 |
2014年 | 944篇 |
2013年 | 1676篇 |
2012年 | 1395篇 |
2011年 | 1785篇 |
2010年 | 1323篇 |
2009年 | 1329篇 |
2008年 | 1204篇 |
2007年 | 1012篇 |
2006年 | 879篇 |
2005年 | 756篇 |
2004年 | 689篇 |
2003年 | 617篇 |
2002年 | 562篇 |
2001年 | 379篇 |
2000年 | 383篇 |
1999年 | 414篇 |
1998年 | 1432篇 |
1997年 | 922篇 |
1996年 | 676篇 |
1995年 | 373篇 |
1994年 | 330篇 |
1993年 | 325篇 |
1992年 | 126篇 |
1991年 | 120篇 |
1990年 | 88篇 |
1989年 | 113篇 |
1988年 | 91篇 |
1987年 | 85篇 |
1986年 | 67篇 |
1985年 | 107篇 |
1984年 | 70篇 |
1983年 | 54篇 |
1982年 | 55篇 |
1981年 | 58篇 |
1980年 | 63篇 |
1979年 | 36篇 |
1977年 | 97篇 |
1976年 | 188篇 |
1975年 | 33篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 921 毫秒
991.
R Manjarres-García GE Escorcia-Salas ID Mikhailov J Sierra-Ortega 《Nanoscale research letters》2012,7(1):489
ABSTRACT: The electronic states of a singly ionized on-axis double-donor complex (D2+) confined in two identical vertically coupled, axially symmetrical quantum dots in a threading magnetic field are calculated. The solutions of the Schrodinger equation are obtained by a variational separation of variables in the adiabatic limit. Numerical results are shown for bonding and antibonding lowest-lying artificial molecule states corresponding to different quantum dot morphologies, dimensions, separation between them, thicknesses of the wetting layers, and magnetic field strength. 相似文献
992.
993.
A. Madariaga I. Martínez de Alegría J.L. Martín P. Eguía S. Ceballos 《Renewable & Sustainable Energy Reviews》2012,16(5):3105-3116
This paper reviews offshore wind projects with a wide perspective. The current situation of the offshore wind market is presented, pointing out the countries leading the process in terms of installed capacity and in terms of technological leadership. Feasibility studies of alternative offshore wind farms (OWFs) are interesting not only in relation to the business but in relation to the techno-economical analyses that engineering researchers need to do. Details about the average energy yield assessment, the costs and the price for the purchased energy are commented on, as key elements of those feasibility studies. The higher cost of renewable energy sources of electricity (RESE) when compared with conventional sources, demands appropriate policy support. The European regulatory framework and the support schemes established by European Member States are presented, as well as the role that different transmission system operators (TSOs) are playing at the moment. Finally, most of the OWFs currently operating are presented, analysing the technical characteristics of their electric subsystems: the wind energy conversion systems (WECSs) transforming the kinetic energy of the wind into electricity, the collector system (CS) gathering the power output of all the turbines to a central collection point (CCP) and the transmission system (TS) taking that power to the onshore main grid. 相似文献
994.
This paper presents a game theoretic solution for joint channel allocation and power control in cognitive radio networks analyzed under the physical interference model. The objective is to find a distributed solution that maximizes the network utility, defined with different criteria, with limited information. The problem is addressed through a non-cooperative game based on local information. Although the existence of a pure Nash Equilibrium cannot be assured for this game, simulation results show that it exists with high probability and with a performance similar to that of a potential game, where each player requires overall network information. The obtained results are compared with a centralized heuristic genetic algorithm to show the correctness of the proposals. From this point, utility functions for the local game are modified to restrict the transmitted power to drive the solution to a more cooperative approach. To overcome the convergence limitations of the local game, no-regret learning algorithms are used to perform the joint channel and power allocation. These algorithms provide stable mixed strategies in any scenario with even better global performance. This opens an interesting perspective to develop realistic protocols based on the modeled interactions and increases the adaptability to perform efficient opportunistic spectrum access. 相似文献
995.
Production of polyhydroxybutyrate (PHB) of high and ultra‐high molecular weight by Azotobacter vinelandii in batch and fed‐batch cultures
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
996.
Inés González‐Hidalgo Sancho Bañón José María Ros 《International Journal of Food Science & Technology》2012,47(4):674-681
The main by‐product from the table olive canning industry is the stone with some residual olive flesh. The purpose of this study was to evaluate the composition – phenolic compounds (hydroxytyrosol, tyrosol and oleuropein) and tocopherol – and the antioxidant activity in different fractions (flesh, stone and seed) from the table olive by‐product and the whole by‐product. The highest amounts of phenolic compounds (1710.0 ± 33.8 mg kg?1) as well as the highest antioxidant activity (8226.9 ± 9.9 hydroxytyrosol equivalents mg kg?1) were obtained in the seed. The highest amounts of hydroxytyrosol (854.8 ± 66.0 mg kg?1) and tyrosol (423.6 ± 56.9 mg kg?1) were found in the whole by‐product from the pepper stuffed olives, while the stone without seed had the maximum oleuropein content (750.2 ± 85.3 mg kg?1). α‐Tocopherol values were between 79.8 ± 20.8 mg kg?1 in the seed of the olive stone and 6.2 ± 1.2 mg kg?1 in the whole by‐product from the anchovy‐stuffed olives. In light of the results obtained, it would seem possible to use table olive by‐product as a source of natural antioxidants in foods, cosmetics or pharmaceutical products, thus contributing to diminishing the environmental impact of table olive by‐product and to its revalorisation. 相似文献
997.
Miguel A. Mazorra-Manzano Ramón Pacheco-Aguilar Juan C. Ramírez-Suárez Guillermina Garcia-Sanchez María E. Lugo-Sánchez 《Food and Bioprocess Technology》2012,5(1):130-137
A fish protein hydrolysate (FPH) from Pacific whiting (Merluccius productus) muscle was produced by autolysis of a minced homogenate (8% protein) at pH 7.0 and 60°C, where maximum endogenous proteolytic
activity was detected. FPH production was controlled by the pH stat method, yielding a 4.43% degree of hydrolysis after 1 h
of autolysis. Upon autolytic processing, 28.9 ± 0.7% of the total protein was found in the soluble fraction. FPH was 100%
soluble at pH 7.0 and 10.0 and was less soluble at pH 4 (82.5%, P ≤ 0.05). FPH showed better emulsifying properties than sodium caseinate (SCA) at pH 4.0 (P ≤ 0.05), but had a lower foaming capacity (P ≤ 0.05) than bovine albumin (BSA) at all evaluated pHs. FPH foaming capacity was not affected by pH, however, foam stability
was equal or better than that of BSA, especially at pH 4.0 (P ≤ 0.05). These results suggest the possibility of producing FPH with similar or better functional properties than those of
functional ingredients, such as SCA and BSA. Furthermore, the data presented support our hypothesis that the high proteolytic
activity in Pacific whiting could be used as an advantage in fish protein hydrolysate production or as a processing aid where
protein hydrolysis is required. 相似文献
998.
María‐Jesús Oliveras‐López Marzia Innocenti Francisco Martín Bermudo Herminia López‐García de la Serrana Nadia Mulinacci 《European Journal of Lipid Science and Technology》2012,114(9):999-1006
In this approach we studied the glycaemia levels in 20 healthy young volunteers (26 ± 2 years), before and after a 30‐day intake of 50 mL of extra virgin olive oil (EVOO). We selected an oil rich in phenolic compounds (523 mg/L) with a high content of secoiridoidic derivatives (over 94.5%). The findings from our study reveal a significant decrease of glycaemia from 89.6 ± 6.8 to 82.7 ± 10.3 mg/dL (p<0.05), related to a long term daily intake of the study EVOO, as the only added fat. A significant increment of the HDL cholesterol, from 68.7 ± 11.5 to 75.2 ± 4.9 mg/dL, was also highlighted. Total cholesterol, LDL, VLDL, triglycerides, and blood pressure did not show significant variation after the 30‐day consumption of this EVOO. So far, few articles have described the influence of EVOO consumption, on plasma glucose levels in humans. This effect is observed in a group of healthy young humans. Moreover, we confirm that the level of free hydroxytyrosol (OH‐Tyr) in plasma increased up to fourfold (p<0.05) after the 30‐day intake of this EVOO. In addition, the excretion in urine of the main metabolite of OH‐Tyr, homovanillic acid (HVA), significantly increased. 相似文献
999.
Enrique Costa-Montenegro Ana Belén Barragáns-Martínez Marta Rey-López 《Expert systems with applications》2012,39(10):9367-9375
Users face the information overload problem when downloading applications in markets. This is mainly due to (i) the increasing unmanageable number of applications and (ii) the lack of an accurate and fine-grained categorization of the applications in the markets. To address this issue, we present an integrated solution which recommends to the users applications by considering a big amount of information: that is, according to their previously consumed applications, use pattern, tags used to annotate resources and history of ratings. We focus this paper on the service for monitoring users’ interaction. 相似文献
1000.
In vitro digestibility of phenolic compounds from edible fruits: could it be explained by chemometrics?
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Francisco J. Olivas‐Aguirre Marcela Gaytán‐Martínez Sandra O. Mendoza‐Díaz Gustavo A. González‐Aguilar Joaquín Rodrigo‐García Nina del Rocío Martínez‐Ruiz Abraham Wall‐Medrano 《International Journal of Food Science & Technology》2017,52(9):2040-2048
The health benefits of phenolic compounds depend on the ingested amount, molecular diversity and gastrointestinal digestibility. The phenolic profile of eight fruits (blackberry, blueberry, strawberry, raspberry, mulberry, pomegranate, green and red globe grapes) was chemometrically associated with their in vitro digestibility (oral, gastric, intestinal). Extractable phenols, flavonoids and anthocyanins strongly correlated with each other (r ≥ 0.84), proanthocyanidins with anthocyanins (r = 0.62) and hydrolysable phenols with both extractable phenols (r = 0.45) and proanthocyanidins (r = ?0.54). Two principal components explained 93% of the variance [61% (free‐phenols), 32% (bounded‐phenols)], and four clusters were confirmed by hierarchical analysis, based in their phenolic richness (CLT 1‐4: low to high) and molecular diversity. In vitro digestibility of extractable phenols and flavonoids was blackberry (CLT‐4)> raspberry (CLT‐2)> red grape (CLT‐1) related to their phenolic richness (r ≥ 0.96; P < 0.001), but anthocyanins’ digestibility was pH‐dependent. Chemometrics is useful to predict the in vitro digestibility of phenolic compounds in the assayed fruits. 相似文献