全文获取类型
收费全文 | 2368篇 |
免费 | 9篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 41篇 |
金属工艺 | 3篇 |
机械仪表 | 5篇 |
建筑科学 | 3篇 |
能源动力 | 2篇 |
轻工业 | 13篇 |
水利工程 | 1篇 |
石油天然气 | 1篇 |
无线电 | 38篇 |
一般工业技术 | 46篇 |
冶金工业 | 2191篇 |
原子能技术 | 1篇 |
自动化技术 | 28篇 |
出版年
2022年 | 4篇 |
2020年 | 2篇 |
2019年 | 7篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2015年 | 5篇 |
2014年 | 4篇 |
2013年 | 20篇 |
2012年 | 4篇 |
2011年 | 5篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 9篇 |
2005年 | 3篇 |
2004年 | 10篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 76篇 |
1998年 | 641篇 |
1997年 | 368篇 |
1996年 | 271篇 |
1995年 | 165篇 |
1994年 | 123篇 |
1993年 | 129篇 |
1992年 | 21篇 |
1991年 | 34篇 |
1990年 | 28篇 |
1989年 | 40篇 |
1988年 | 44篇 |
1987年 | 39篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1980年 | 15篇 |
1978年 | 4篇 |
1977年 | 43篇 |
1976年 | 91篇 |
1975年 | 4篇 |
1973年 | 2篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1955年 | 1篇 |
1943年 | 1篇 |
排序方式: 共有2377条查询结果,搜索用时 0 毫秒
91.
Kenneth H. Moyer Michael J. McDermott Mark J. Topolski David F. Kearney 《Powder Technology》1981,30(1):51-71
The purpose of this work was to compare the properties of high purity atomized iron powder compacts with conventional high purity irons and to show the effects of porosity on magnetic properties. It was found that if powders were hot repressed so that no porosity was present, the magnetic properties were as good as or better than conventional high purity irons, depending on the sintering conditions employed. Intrinsic properties were similar because the amount of iron available to magnetize was equivalent. Structure-sensitive properties depended on the grain size. If the compacts were sintered above the delta transition temperature, these properties were equivalent to the purest of the conventional high purity irons. As the compacts became less dense and more porosity was present, induction and remanent magnetization decreased linearly with density; resistivity increased. In the case of structure-sensitive properties, porosity restricted grain growth. Small, closely spaced pores caused the greatest degradation of properties. Equations were derived through regression analyses and were found to explain more than 90% of the data. The intrinsic properties: induction, remanent magnetization, and resistivity were all linear functions of the density. The maximum permeability and the coercive force were power functions of the mean grain size intercept. These equations provide a basis for design of magnetic components using P/M compacts. If the properties that are desired are known, the density or the grain size required may be calculated. From this, the powder and the processing conditions required can be established to provide the desired properties. 相似文献
92.
93.
94.
The nature of the weak lipophilic acid used in synergistic combination with a model crown ether cation host was shown to have a strong effect on the strength and selectivity of sodium hydroxide separation from alkaline aqueous salt solutions. Sodium ion-pair extraction employing only cis-syn-cis-dicyclohexano-18-crown-6 (1) in nitrobenzene (NB) was correlated with the standard Gibbs energy (deltaG(p)o) of anion partitioning into NB and was notably weak and nonselective for the hydroxide ion, in accord with Hofmeister bias. The Hofmeister order can be selectively overcome for NaOH by utilization of acid-base chemistry coupled with complexation of sodium ion in the NB phase. Upon addition of a lipophilic organic acid into the solution of 1 in NB, sodium extraction was selectively enhanced due to the initiation of an exchange reaction between the aqueous sodium ion and the ionizable proton of the organic acid. A series of weak lipophilic hydroxy acids (HA) including fluorinated alcohols and phenols was tested. The resulting synergistic pseudo-hydroxide extraction correlates with the pKa of the employed HA; the most acidic cation exchangers provide the greatest synergism. The synergistic factor obtained using a fluorinated benzyl alcohol 7 was as high as 256. Ion-pair extraction of neutral sodium salts was not changed or only mildly enhanced by addition of HA into the NB solution of 1. This enhancement was explained by hydrogen bonding of HA with the anion as related to the hardness of the anion and the acidity of HA. In comparison with the synergism observed for NaOH, this enhancement was weak and unable to overcome the Hofmeister effect. Examination of extraction selectivity revealed that the combination of 1 and 7 preferentially extracted NaOH over all other sodium salts, including the normally preferred nitrate and perchlorate salts. Quantitative recovery of NaOH from the NB phase was demonstrated via hydrolysis of the organic acid upon a single contact of the loaded solvent with water. 相似文献
95.
A new high-pressure matrix-assisted laser desorption/ionization (HP-MALDI) source for FTMS has recently been described (O'Connor et al. J. Am. Soc. Mass Spectrom., in press). Improvements to the source design, including the incorporation of a new high-pressure gas channel plate, resulted in ions devoid of metastable fragmentation and also in increased sensitivity compared to the HP-MALDI prototype source design. The focus of this contribution is the evaluation of the current HP-MALDI FTMS configuration. The use of nonconductive sample surfaces, such as Parafilm and Teflon, was explored, and spectra from 30 amol of peptide applied to these surfaces were routinely obtained. In addition, the current limit of detection for this configuration is demonstrated to be 300 zmol for the phosphopeptide RRREEE(pS)EEEAA using multishot accumulation of the ions from 15 laser shots in the hexapole and 1 scan. In addition, the performance of the new HP-MALDI FTMS configuration and its potential application for high-throughput proteomics analyses are discussed. 相似文献
96.
Gerling GJ Rigsbee S Childress RM Martin ML 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》2009,39(2):388-403
97.
98.
99.
100.
Hepatitis C, which is caused by the hepatitis C virus (HCV), is a major public health problem in the United States. HCV is most efficiently transmitted through large or repeated percutaneous exposures to blood. Most patients with acute HCV infection develop persistent infection, and 70 percent of patients develop chronic hepatitis. HCV-associated chronic liver disease results in 8,000 to 10,000 deaths per year, and the annual costs of acute and chronic hepatitis C exceed $600 million. An estimated 3.9 million Americans are currently infected with HCV, but most of these persons are asymptomatic and do not know they are infected. To identify them, primary health care professionals should obtain a history of high-risk practices associated with the transmission of HCV and other bloodborne pathogens from all patients. Routine testing is currently recommended only in patients who are most likely to be infected with HCV. 相似文献