全文获取类型
收费全文 | 3257篇 |
免费 | 39篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 19篇 |
综合类 | 2篇 |
化学工业 | 208篇 |
金属工艺 | 11篇 |
机械仪表 | 27篇 |
建筑科学 | 55篇 |
矿业工程 | 5篇 |
能源动力 | 27篇 |
轻工业 | 71篇 |
水利工程 | 9篇 |
石油天然气 | 5篇 |
无线电 | 130篇 |
一般工业技术 | 171篇 |
冶金工业 | 2396篇 |
原子能技术 | 18篇 |
自动化技术 | 163篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 19篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 61篇 |
2012年 | 28篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 42篇 |
2008年 | 28篇 |
2007年 | 32篇 |
2006年 | 33篇 |
2005年 | 34篇 |
2004年 | 24篇 |
2003年 | 35篇 |
2002年 | 18篇 |
2001年 | 25篇 |
2000年 | 24篇 |
1999年 | 92篇 |
1998年 | 690篇 |
1997年 | 406篇 |
1996年 | 278篇 |
1995年 | 180篇 |
1994年 | 154篇 |
1993年 | 135篇 |
1992年 | 37篇 |
1991年 | 49篇 |
1990年 | 51篇 |
1989年 | 45篇 |
1988年 | 36篇 |
1987年 | 36篇 |
1986年 | 41篇 |
1985年 | 39篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 15篇 |
1980年 | 27篇 |
1979年 | 8篇 |
1978年 | 17篇 |
1977年 | 89篇 |
1976年 | 146篇 |
1975年 | 15篇 |
1973年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有3317条查询结果,搜索用时 15 毫秒
1.
Thin Film Thermoelectric Metal–Organic Framework with High Seebeck Coefficient and Low Thermal Conductivity
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
2.
3.
4.
Castro M. Foster R.S. Gunn K. Roberts E.B. 《Engineering Management, IEEE Transactions on》2003,50(3):297-306
The virtual agency concept is now used within the United States Government as an alliance approach to manage large research and development (R&D) processes across departments. This paper examines the history of the virtual agency concept and its important characteristics. The paper identifies the potential benefits and associated risks involved in managing R&D within a virtual agency. Three cases are examined where the virtual agency concept has been applied to R&D programs: the High Performance Computing and Communications initiative, the Next Generation Internet, and the Partnership for a New Generation of Vehicles. The case studies indicate that the R&D process is attempting to balance formal process controls with the agility to adapt rapidly to new research opportunities. Virtual agencies can be used to improve organizational efficiency, improve knowledge transfer, increase interoperability through standards, provide better alignment of agency missions with national policy, and introduce increased flexibility into the R&D process. At the same time, the virtual agency concept has major risks including inefficiencies due to organizational complexity, the danger of collective myopia, the problem of adopting standards too early, the difficulty of reaching objectives in a loose organizational structure, and the problem of properly balancing the tension between agency mission objectives and national policy agendas. 相似文献
5.
6.
Fetal alcohol syndrome in twins of alcoholic mothers: concordance of diagnosis and IQ 总被引:1,自引:0,他引:1
The effects of teratogens can be modified by genetic differences in fetal susceptibility and resistance. Twins of alcoholic mothers provide a unique opportunity to study this phenomenon with respect to alcohol teratogenesis. Sixteen pairs of twins, 5 MZ and 11 DZ, all heavily exposed to alcohol prenatally, were evaluated. They represented all available twins of alcohol-abusing mothers who were on the patient rolls of the authors. The rate of concordance for diagnosis was 5/5 for MZ and 7/11 for DZ twins. In two DZ pairs, one twin had fetal alcohol syndrome (FAS), while the other had fetal alcohol effects (FAE). In 2 other DZ pairs, one twin had no diagnosis while one had FAE. IQ scores were most similar within pairs of MZ twins and least similar within pairs of DZ twins discordant for diagnosis. Despite equivalent alcohol exposure within twin pairs, alcohol teratogenesis appears to be more uniformly expressed in MZ than in DZ twins. These data are interpreted as reflecting the modulating influence of genes in the expression of the teratogenic effects of alcohol. 相似文献
7.
Twenty-six patients with an intracardiac myxoma underwent surgical resection at our institution from 1977 through 1992. Left atrial myxoma was diagnosed in 22 patients, left ventricular in 1, right atrial in 2, and right ventricular in 1. Six patients were asymptomatic; preoperative symptoms included dyspnea, arrhythmias, embolic episodes, and syncope. The diagnosis was established with transthoracic echocardiography in all cases but one. Surgery was performed in all cases with the aid of cardiopulmonary bypass with moderate hypothermia and cold crystalloid cardioplegia. One patient with a left ventricular myxoma died in a comatose state during the immediate postoperative period. Long-term clinical and echocardiographic evaluation was performed in 19 patients; results were excellent (all the patients were in New York Heart Association functional class I or II), and no recurrences were documented. The clinical characteristics, diagnostic methods, and surgical approach are presented and discussed. 相似文献
8.
9.
Determination of the relative amounts of free and complexed manganese ions in aqueous solution by nuclear magnetic resonance. 总被引:1,自引:0,他引:1
The ratio of the transverse relaxation rate to the longitudinal relaxation rate of water protons (T1/T2) at 90 MHz can be used to determine the relative amounts of free Mn2+ ions (the hexaquo ion) and chelated manganese ions when both species are present in the same aqueous solution. This technique is demonstrated for simple aqueous solutions containing known concentrations of both the free Mn2+ ion and a manganese(III) porphyrin. The accuracy of the method is found to be +/- 7.3% for the solutions considered in this report. The determinations of the relative amounts of the free Mn2+ ion and the manganese(III) porphyrin by this T1/T2 method are shown to agree well with those determined by nuclear magnetic resonance dispersion profiles. The theoretical basis of this ratio method as well as the scope and limitations in its application to aqueous solutions containing both free Mn2+ ions and chelated manganese species other than manganese(III) porphyrins are also discussed. This work demonstrates a unique use of NMR as a means for the quantitative analysis of manganese in which the effects of the metal ion on the solvent, and not the metal itself, are observed. 相似文献
10.
The short contact time dissolution of vitrinite and inertinite concentrates of an Australian bituminous coal was studied under isothermal conditions with tetralin as solvent. The reactivity of the two maceral types and the yields and nature of the products were determined for a range of reaction temperatures (400, 420 and 440 °C) and reaction times (2–20 min). The dissolution of vitrinite proceeded at a significantly greater rate than for inertinite and was associated with greater selectivity to soluble non-gaseous products. At very short reaction times (2 min), the vitrinite underwent solubilizing reactions to yield products of higher molecular weight and greater oxygen functionality than was the case for inertinite, for which changes in the chemical nature of the products were negligible over the range of conditions studied. At longer reaction times (5 min), the composition of the vitrinite-derived products was similar to that of the inertinite-derived products. 相似文献