全文获取类型
收费全文 | 11825篇 |
免费 | 909篇 |
国内免费 | 531篇 |
专业分类
电工技术 | 909篇 |
技术理论 | 2篇 |
综合类 | 923篇 |
化学工业 | 3405篇 |
金属工艺 | 271篇 |
机械仪表 | 314篇 |
建筑科学 | 546篇 |
矿业工程 | 297篇 |
能源动力 | 1788篇 |
轻工业 | 548篇 |
水利工程 | 166篇 |
石油天然气 | 341篇 |
武器工业 | 28篇 |
无线电 | 581篇 |
一般工业技术 | 934篇 |
冶金工业 | 522篇 |
原子能技术 | 348篇 |
自动化技术 | 1342篇 |
出版年
2024年 | 32篇 |
2023年 | 213篇 |
2022年 | 348篇 |
2021年 | 343篇 |
2020年 | 377篇 |
2019年 | 318篇 |
2018年 | 265篇 |
2017年 | 294篇 |
2016年 | 298篇 |
2015年 | 301篇 |
2014年 | 562篇 |
2013年 | 696篇 |
2012年 | 894篇 |
2011年 | 878篇 |
2010年 | 719篇 |
2009年 | 747篇 |
2008年 | 662篇 |
2007年 | 776篇 |
2006年 | 644篇 |
2005年 | 633篇 |
2004年 | 577篇 |
2003年 | 477篇 |
2002年 | 403篇 |
2001年 | 305篇 |
2000年 | 263篇 |
1999年 | 202篇 |
1998年 | 184篇 |
1997年 | 144篇 |
1996年 | 115篇 |
1995年 | 107篇 |
1994年 | 79篇 |
1993年 | 64篇 |
1992年 | 60篇 |
1991年 | 53篇 |
1990年 | 35篇 |
1989年 | 29篇 |
1988年 | 30篇 |
1987年 | 28篇 |
1986年 | 22篇 |
1985年 | 23篇 |
1984年 | 27篇 |
1983年 | 15篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1974年 | 2篇 |
1970年 | 1篇 |
1968年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
In this work we investigated the mechanism of the electrochemical intercalation reactions in rf sputtered nickel oxide thin films electrodes by two techniques: mechanical stress change measurements by means of an optical technique and mass changes using an electrochemical quartz microbalance (EQCM). The experiments were performed in alkaline electrolytes containing cations of the first column of the periodic table. Reversible mass and volume changes were observed. In order to explain these experimental results, an exchange reaction is proposed, in which the oxidation process is accompanied by the deinteractional of a relative large number of “light” cations, simultaneously with the intercalation of a smaller number of heaviest cations. 相似文献
12.
U(Ⅳ)-U(Ⅵ)同位素交换反应动力学研究 Ⅰ.Fe~(2+)对U(Ⅳ)-U(Ⅵ)同位素交换反应的催化作用 总被引:1,自引:0,他引:1
一、前言由于U(IV)-U(VI)同位素交换体系具有相当大的同位素效应和很好的稳定性,并且容易实现两相回流,这对于分离U同位素的工业应用都是十分有利的。但是,U(IV)-U(VI)同位素交换反应速度非常慢,常温下H~+浓度为1.0—4.0 mol/l时,速度常数为1.0×10~(-4)l~2/mol·s。因此要用U(IV)-U(VI)交换体系浓缩铀同位素,必须研究U(IV)-U(VI)交换反应动力学,找到加快交换反应的方法。 相似文献
13.
介绍了传统的全空间空调方式,指出全空间空调方式不能同时为所有人提供可接受的热感觉和室内空气品质,而置换通风和个体化控制的联合将是一种理想的空调方式,在更大程度上满足人们的不同需要。 相似文献
14.
Boeing has been working on the development and implementation of STEP AP 210 since its inception. Using a combination of internally funded activities, external government contracts and multi-company pilots, Boeing has developed prototype tools to utilize AP 210 and is poised to move these tools into production. This paper begins with a brief overview of STEP and AP 210. The status of available AP 210 vendor translators (data generators), along with viewers and analysis programs (data consumers) is covered. Discussion continues with present and planned usage of AP 210 in several companies with the primary emphasis on implementation at The Boeing Company. The document concludes with a summary of key points. 相似文献
15.
A number of copolymers were synthesised by condensing the 2,4-dinitrophenylhydrazone of resacetophenone with substituted benzoic acids/ phenols and formaldehyde in the presence of sodium hydroxide or hydrochloric acid. The decomposition temperature, solubility and viscosity of the polymers have been determined. The ion-exchange properties have been studied by using a batch equilibrium method. The distribution of a number of metal ions between an aqueous solution and the resin have been measured. A wide range of pH and variable ionic strengths have been investigated. 相似文献
16.
Katherine A. B. Logan Michael J. S. Floate 《Journal of the science of food and agriculture》1985,36(11):1084-1092
For 30 acid upland and hill soils, with initial pH from 3.5 to 5.8, and loss on ignition from 14% to 94%, cation exchange capacity varied with pH according to the relationship CEC = m pH+C, where m and C are characteristic of each soil. The slope m depended on loss on ignition (LOI), and is given by: m=Δ CEC/Δ=0.22 LOI+1.92. Because of these relationships, CEC measured at the natural pH of the soil (in 0.025 M MgSO4 solution) is more relevant to field conditions than a conventional measurement at pH7. An improved method for estimating lime requirement (LR) of these soils was developed, based on the relationship found between LR and the difference in CEC (ΔCEC) between that at the natural pH of the soil and that at the target pH of 5.5: LR=1.12 ΔCEC+1.48. Lime requirement can therefore also be estimated from loss on ignition using the earlier relationships, and is given by: LR=(0.25 LOI+2.15) Δ+1.48, where Δ is the difference between the natural pH (in 0.025 M MgSO4) and the target pH. Predictions based on this agreed well with results for a further 10 soils. 相似文献
17.
18.
近几年,我国外汇储备逐年增加,而美元汇率偏弱,使我国承担很大的外汇风险。为了规避外汇风险,应增加黄金储备。文中提出了我国增加黄金储备总量的理由以及增加黄金储备的途径。这些建议具有可操作性,可以提供给有关部门参考。 相似文献
19.
Takaaki Wajima Tomoe Shimizu Yasuyuki Ikegami 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):921-927
BACKGROUND: This study aimed to investigate the synthesis of zeolites from paper sludge ash (PSA) with added diatomite to remove both NH4+ and PO43? for water purification. The PSA had low Si and significant Ca contents. Four types of diatomite: white (T‐W) and brown (T‐B) from deposits of marine origin in Takanosu, and white (S‐W) and gray (S‐G) from lacustrine deposits in Shonai, were added to NaOH solution to increase the Si content and thereby synthesize zeolites with high cation exchange capacity (CEC). RESULTS: The order of the amounts of Si extracted from the diatomite to the alkali solution was S‐W > T‐W = T‐B > S‐G, which correlates with the amorphous SiO2 content of diatomite. The original ash without addition of diatomite yielded hydroxysodalite with CEC of about 1.0 mmol g?1. For all samples, the addition of diatomite to the solution yielded zeolite‐P with a higher CEC, but the addition of excess Si inhibited the synthesis of zeolite‐P, and the CEC of the product was low. A product with high CEC including zeolite‐P was obtained in a solution with around 500 mmol L?1 of Si concentration, and had the ability to remove both NH4+ and PO43?. CONCLUSION: Diatomite has the potential for used as an additive for the synthesis of high CEC zeolite from PSA. The product with zeolite‐P exhibited relatively high CEC, capacity for NH4+ uptake, and the ability to remove PO43? by precipitation, which is preferable for water purification applications. Copyright © 2008 Society of Chemical Industry 相似文献
20.
David P. Cormode Jason J. Davis Paul D. Beer 《Journal of Inorganic and Organometallic Polymers and Materials》2008,18(1):32-40
Disulfide and dithiocarbamate functionalized porphyrins have been synthesized and used as protecting ligands for gold nanoparticle
formation either via ligand substitution reactions or by direct synthesis. These nanoparticles have been shown to recognize
anions via changes in the absorbance spectrum of the surface adsorbed porphyrin moieties. Association constants, derived from
quantitative titrations, indicate a remarkable surface enhancement effect where the surface bound porphyrins bind anions much
more strongly than the free receptor in solution. 相似文献