全文获取类型
收费全文 | 456064篇 |
免费 | 43324篇 |
国内免费 | 18304篇 |
专业分类
电工技术 | 25036篇 |
技术理论 | 48篇 |
综合类 | 29220篇 |
化学工业 | 84737篇 |
金属工艺 | 24961篇 |
机械仪表 | 27082篇 |
建筑科学 | 33466篇 |
矿业工程 | 13522篇 |
能源动力 | 12004篇 |
轻工业 | 34460篇 |
水利工程 | 8486篇 |
石油天然气 | 27119篇 |
武器工业 | 3362篇 |
无线电 | 50534篇 |
一般工业技术 | 58265篇 |
冶金工业 | 23275篇 |
原子能技术 | 5182篇 |
自动化技术 | 56933篇 |
出版年
2024年 | 1676篇 |
2023年 | 6308篇 |
2022年 | 11437篇 |
2021年 | 16195篇 |
2020年 | 13245篇 |
2019年 | 12473篇 |
2018年 | 14109篇 |
2017年 | 15781篇 |
2016年 | 15165篇 |
2015年 | 19588篇 |
2014年 | 23719篇 |
2013年 | 28801篇 |
2012年 | 28915篇 |
2011年 | 31357篇 |
2010年 | 28178篇 |
2009年 | 26768篇 |
2008年 | 25771篇 |
2007年 | 24534篇 |
2006年 | 24399篇 |
2005年 | 21375篇 |
2004年 | 15135篇 |
2003年 | 13742篇 |
2002年 | 13172篇 |
2001年 | 11695篇 |
2000年 | 11101篇 |
1999年 | 10987篇 |
1998年 | 8023篇 |
1997年 | 6862篇 |
1996年 | 6471篇 |
1995年 | 5380篇 |
1994年 | 4351篇 |
1993年 | 3040篇 |
1992年 | 2446篇 |
1991年 | 1911篇 |
1990年 | 1567篇 |
1989年 | 1321篇 |
1988年 | 1145篇 |
1987年 | 793篇 |
1986年 | 717篇 |
1985年 | 540篇 |
1984年 | 507篇 |
1983年 | 447篇 |
1982年 | 396篇 |
1980年 | 357篇 |
1978年 | 376篇 |
1977年 | 364篇 |
1976年 | 378篇 |
1974年 | 403篇 |
1973年 | 383篇 |
1972年 | 365篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
3.
Xue‐Yong Liu Xiao‐Bin Ding Zhao‐Hui Zheng Yu‐Xing Peng Albert S
C Chan C
W Yip Xin‐Ping Long 《Polymer International》2003,52(2):235-240
Amphiphilic magnetic microspheres ranging in diameter from 5 to 100 µm were prepared by dispersion copolymerization of styrene and poly(ethylene oxide) vinylbenzyl (PEO‐VB) macromonomer (MPEO) in the presence of Fe3O4 magnetic fluid. The effects of various polymerization parameters on the average particle size were systematically investigated. The average particle size was found to increase with increasing styrene concentration and initiator concentration. It also increased with decreasing stabilizer concentration and molecular weight of MPEO. The content of the hydroxyl groups localized in the microspheres ranged from 0.01 to 0.2 mmol g?1. © 2003 Society of Chemical Industry 相似文献
4.
World oil production and reserve additions heavily depend on giant oilfields. Currently, there are more than 4,000 producing oilfields in the world, producing around 68 million barrels of oil per day. Most oilfields in the world are minor ones, with oil production below 20,000 barrels per day; only 3% (about 120) oilfields in the world produce over 100,000 barrels per day with overall daily production exceeding 32 million barrels, which accounts for 47% of the total world oil supply . The scales of the oilfields heavily influence economic indices like investment, production and life spans of the oilfields. Therefore, giant oilfields have always been the dream of oil finders and targets of geologists' researches . 相似文献
5.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
6.
In advancement of Pyrosil®‐technology a new kind of precursor delivery was developed, build and tested on real substrates. A Lab‐demonstrator was build to demonstrate the resources of the technology. 相似文献
7.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
8.
Nucleation and growth mechanisms and kinetics of crystals of an amino acid salt were investigated in a methanol‐water system by measuring and evaluating the induction time as a function of the supersaturation ratio and temperature in batch salting out crystallization experiments. Discrimination between the possible crystallization mechanisms, and estimation of the kinetic parameters were carried out using nonlinear parameter identification. The results concerning the growth mechanism obtained were checked additionally by measuring the induction time as a function of number density of seed crystals. 相似文献
9.
Conducting poly(aniline‐co‐o‐anisidine) (PAS) films with different ratios of aniline units in the polymer chain were prepared by oxidative polymerization of different molar ratios of aniline and o‐anisidine in 1 M HCl using cyclic voltammetry. Due to the much higher reactivity of o‐anisidine, the structure and properties of PASs were found to be dominated by the o‐anisidine units. The polymerization of poly‐o‐anisidine and PASs followed zero‐order kinetics with respect to formation of the polymer (film thickness) and the autocatalytic polymerization of aniline was completely inhibited. In contrast to polyaniline, a decrease in the polymerization temperature was found to increase the amount of copolymer formed and its redox charge. The presence of aniline units in PASs led to a pronounced increase in the molecular weight and conductivity, and a decrease in the solubility in organic solvents. Repetitive charging/discharging cycles showed that PASs resist degradation more than polyaniline. Copyright © 2003 Society of Chemical Industry 相似文献
10.
Data mining extracts implicit, previously unknown, and potentially useful information from databases. Many approaches have been proposed to extract information, and one of the most important ones is finding association rules. Although a large amount of research has been devoted to this subject, none of it finds association rules from directed acyclic graph (DAG) data. Without such a mining method, the hidden knowledge, if any, cannot be discovered from the databases storing DAG data such as family genealogy profiles, product structures, XML documents, task precedence relations, and course structures. In this article, we define a new kind of association rule in DAG databases called the predecessor–successor rule, where a node x is a predecessor of another node y if we can find a path in DAG where x appears before y. The predecessor–successor rules enable us to observe how the characteristics of the predecessors influence the successors. An approach containing four stages is proposed to discover the predecessor–successor rules. © 2006 Wiley Periodicals, Inc. Int J Int Syst 21: 621–637, 2006. 相似文献