全文获取类型
收费全文 | 11021篇 |
免费 | 1014篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 85篇 |
综合类 | 6篇 |
化学工业 | 2720篇 |
金属工艺 | 138篇 |
机械仪表 | 344篇 |
建筑科学 | 501篇 |
矿业工程 | 26篇 |
能源动力 | 239篇 |
轻工业 | 2237篇 |
水利工程 | 86篇 |
石油天然气 | 20篇 |
无线电 | 809篇 |
一般工业技术 | 2167篇 |
冶金工业 | 723篇 |
原子能技术 | 26篇 |
自动化技术 | 1921篇 |
出版年
2024年 | 39篇 |
2023年 | 161篇 |
2022年 | 137篇 |
2021年 | 371篇 |
2020年 | 319篇 |
2019年 | 311篇 |
2018年 | 443篇 |
2017年 | 455篇 |
2016年 | 560篇 |
2015年 | 477篇 |
2014年 | 614篇 |
2013年 | 1127篇 |
2012年 | 985篇 |
2011年 | 776篇 |
2010年 | 574篇 |
2009年 | 550篇 |
2008年 | 589篇 |
2007年 | 512篇 |
2006年 | 459篇 |
2005年 | 311篇 |
2004年 | 277篇 |
2003年 | 250篇 |
2002年 | 238篇 |
2001年 | 147篇 |
2000年 | 126篇 |
1999年 | 114篇 |
1998年 | 154篇 |
1997年 | 128篇 |
1996年 | 94篇 |
1995年 | 91篇 |
1994年 | 81篇 |
1993年 | 73篇 |
1992年 | 45篇 |
1991年 | 33篇 |
1990年 | 23篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 19篇 |
1986年 | 26篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 18篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Jacques Demongeot Nicolas Glade Andr��s Moreira Laurent Vial 《International journal of molecular sciences》2009,10(8):3420-3441
A number of small RNA sequences, located in different non-coding sequences and highly preserved across the tree of life, have been suggested to be molecular fossils, of ancient (and possibly primordial) origin. On the other hand, recent years have revealed the existence of ubiquitous roles for small RNA sequences in modern organisms, in functions ranging from cell regulation to antiviral activity. We propose that a single thread can be followed from the beginning of life in RNA structures selected only for stability reasons through the RNA relics and up to the current coevolution of RNA sequences; such an understanding would shed light both on the history and on the present development of the RNA machinery and interactions. After presenting the evidence (by comparing their sequences) that points toward a common thread, we discuss a scenario of genome coevolution (with emphasis on viral infectious processes) and finally propose a plan for the reevaluation of the stereochemical theory of the genetic code; we claim that it may still be relevant, and not only for understanding the origin of life, but also for a comprehensive picture of regulation in present-day cells. 相似文献
992.
Ana Júlia C. da Silva Fred A.R. Nogueira Odilon A.S. Araújo José Ginaldo da Silva Junior Marcelo Navarro Josealdo Tonholo Adriana S. Ribeiro 《Synthetic Metals》2009,159(21-22):2269-2272
12-Pyrrol-1′-yl dodecanoic acid was prepared and electrochemically polymerized on ITO electrodes by three different methods. The electrochemical and morphological properties of poly(12-pyrrol-1′-yl dodecanoic acid) films were investigated by cyclic voltammetry, galvanostatic charge–discharge curves and AFM, which characteristics varied as function of deposition method. Films deposited by potentiodynamic and galvanostatic methods showed capacitive properties and are promising for application in polymeric capacitors. 相似文献
993.
Rodrigo S. da Silveira Andréa M. de Oliveira Sibele B. C. Pergher Victor Teixeira da Silva Ione M. Baibich 《Catalysis Letters》2009,129(3-4):259-265
Palladium and/or molybdenum catalysts supported on mordenite were prepared and characterized by XRD, UV–vis, DRS, textural properties analysis, TPR, TPD and chemical analysis. The Mo-catalyst rapidly deactivated after the first minutes reaction. The Pd-catalysts were active in the NO decomposition reactions. The incorporation of Mo in the Pd-catalysts improved their catalytic properties. 相似文献
994.
995.
josé A. Iba?ez L. Victoria Rafael M. Barzanallana 《Journal of Automated Methods and Management in Chemistry》1989,11(3):129-133
An integrated computer system consisting of an expandable
ionanalyzer and a PC has been used to automate concentration
measurements with ion-selective electrodes (ISEs). The ionanalyzer
determines ionic concentrations using a reference electrode
coupled with an ISE. The measurements and calibrations are
carried out in a thermostated sample changer equipped with a flow
cell. The data obtained by the ionanalyzer are sent via a standard
RS 232-C interface to a microcomputer. In this paper, we describe
the automatic data acquisition system and the subsequent processing
of the measurements. One program (Transorion) automatically
collects the measurements carried out by the ionanalyzer, giving a
real-time graphic representation of the measurement on the
computer screen. A second program (Graforion) facilitates the
management of the data stored by the first program, and listing and
graphics of these can be obtained on the printer/plotter. The method
has been used to study continuous concentration changes in an
aqueous solution of potassium iodide. 相似文献
996.
Induced-emission cross section for neodymium doped optical fiber are measured from temporal and spectral studies of spontaneous fluorescence. Induced-emission cross section values are 1.5 to 2.5 10-20 cm2 according to fibers and fluorescence bands. From a semi-classical theory of absorption-emission process in the fiber we calculate the optical gain and justifie the use of the Füchtbauer-Ladenburg relation for fibers. 相似文献
997.
José A. Amador David Sotomayor-Ramírez Gustavo Martínez Lixian Chen Dave Bachoon 《Lakes & Reservoirs: Research and Management》2008,13(4):301-317
Using a combination of chemical and microbiological (culture-dependent and -independent) approaches, sources of human faecal contamination were identified in two water reservoirs in Puerto Rico – Guajataca and La Plata. Fluorescence from optical brighteners (OB) – commonly found in laundry detergents – was used as an indicator of contamination from septic systems and other household discharges. Traditional indicators of faecal contamination (e.g. Escherichia coli; faecal enterococci) were enumerated, and human faecal contamination was confirmed through detection of Bifidobacterium adolescentis utilizing polymerase chain reaction (PCR)-based analyses. For Guajataca Reservoir, four of 19 sampling sites (21%) were positive for the presence of B. adolescentis under baseflow conditions. The OB fluorescence data suggested that the most likely source for three of these sites was residential, whereas the source of contamination at the remaining site, although of human origin, was probably non-residential. B. adolescentis was present in 83% (19 of 23) of the sampling sites in La Plata. The La Plata sources were more difficult to identify because samples were taken under stormflow conditions, although the presence of OB fluorescence suggested a residential origin in a number of instances. OB fluorescence and traditional bacterial indicators of faecal contamination produced a number of false positive and negative findings for both reservoirs, pointing to the importance of understanding the limitations of these tools for tropical freshwater systems. The results of this study should be useful in developing a weight-of-evidence approach for the identification of potential sources and extent of human faecal contamination in similar tropical reservoirs, a necessary step in the development of management plans to reduce or eliminate these sources. 相似文献
998.
999.
Eduardo J. Peralías Adoración Rueda José L. Huertas 《Journal of Electronic Testing》2001,17(5):373-383
Two alternative BIST schemes are proposed for structural testing of pipelined Analog-to-Digital Converters (ADC). They are oriented to fault detection in the converter stages rather than to measure the whole ADC electrical performance parameters. The operational principle of both strategies relies on testing every ADC stage reconfigured as an A/D-D/A block and applying as input a simple DC stimuli set which is easily obtained, without strong precision requirements, by a resistive network. The main differences between both strategies relate to the way the output response is evaluated. In the BIST#1 scheme, analog and digital outputs are compared with reference levels generated with a reference D/A converter and a counter. In the BIST#2 strategy, only digital outputs are available and they are compared with fault-free values previously stored in an on-chip register. The new techniques are intended to be used in pipelined converters of an arbitrary number of conversion stages and with a digital self-correction mechanism. 相似文献
1000.
Remedios Yáñez Aloia Romaní Gil Garrote José Luis Alonso Juan Carlos Parajó 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2009,84(7):1070-1077
BACKGROUND: Acacia dealbata wood samples were subjected to hydrothermal processing in aqueous media, yielding a liquid phase (containing xylooligosaccharides) and a solid phase, enriched in cellulose, which was treated with alkaline solutions to obtain solids with improved susceptibility towards enzymatic hydrolysis. The effects of the most influential variables involved in the alkaline processing (sodium hydroxide concentration, temperature and reaction time) on solid yield, solid composition and kinetic parameters involved in the modelling of the enzymatic hydrolysis were assessed using the response surface methodology (RSM). RESULTS: Analysis of the RSM equations allowed selection of operational conditions (temperature = 130 °C, sodium hydroxide concentration = 4.5%, time of alkaline processing = 3 h), leading to selective removal of non‐cellulosic components and to a solid substrate highly susceptible to enzymatic hydrolysis. Operating at an enzyme loading of 20 FPU (filter paper units) g?1 autohydrolysed, extracted solids (denoted AES) with a liquor to solid ratio of 30 g liquor g?1 AES, solutions containing 29.7 g glucose L?1 (corresponding to a yield of 47.3 g glucose per 100 g solids from autohydrolysis) were obtained after 48 h. CONCLUSION: Samples of Acacia dealbata wood were processed by autohydrolysis, sodium hydroxide treatment and enzymatic hydrolysis, yielding xylooligomers and processed solids highly susceptible to the enzymatic hydrolysis. Copyright © 2009 Society of Chemical Industry 相似文献