全文获取类型
收费全文 | 30858篇 |
免费 | 3935篇 |
国内免费 | 1930篇 |
专业分类
电工技术 | 1579篇 |
技术理论 | 2篇 |
综合类 | 2567篇 |
化学工业 | 5622篇 |
金属工艺 | 2818篇 |
机械仪表 | 1955篇 |
建筑科学 | 2665篇 |
矿业工程 | 612篇 |
能源动力 | 716篇 |
轻工业 | 2514篇 |
水利工程 | 465篇 |
石油天然气 | 1007篇 |
武器工业 | 316篇 |
无线电 | 2246篇 |
一般工业技术 | 4421篇 |
冶金工业 | 1334篇 |
原子能技术 | 175篇 |
自动化技术 | 5709篇 |
出版年
2024年 | 108篇 |
2023年 | 395篇 |
2022年 | 602篇 |
2021年 | 824篇 |
2020年 | 988篇 |
2019年 | 1058篇 |
2018年 | 1010篇 |
2017年 | 1271篇 |
2016年 | 1323篇 |
2015年 | 1333篇 |
2014年 | 1856篇 |
2013年 | 1997篇 |
2012年 | 2138篇 |
2011年 | 2229篇 |
2010年 | 1740篇 |
2009年 | 1786篇 |
2008年 | 1605篇 |
2007年 | 2134篇 |
2006年 | 1815篇 |
2005年 | 1617篇 |
2004年 | 1357篇 |
2003年 | 1275篇 |
2002年 | 1228篇 |
2001年 | 1092篇 |
2000年 | 868篇 |
1999年 | 704篇 |
1998年 | 515篇 |
1997年 | 408篇 |
1996年 | 326篇 |
1995年 | 254篇 |
1994年 | 202篇 |
1993年 | 151篇 |
1992年 | 125篇 |
1991年 | 73篇 |
1990年 | 75篇 |
1989年 | 68篇 |
1988年 | 45篇 |
1987年 | 17篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 4篇 |
1975年 | 4篇 |
1972年 | 2篇 |
1964年 | 2篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Dr Joseph A. Cannataci 《AI & Society》1989,3(3):169-183
This paper examines some of the possible legal implications of the production, marketing and use of expert systems. The relevance of a legally useful definition of expert systems, comprising systems designed for use both by laymen and professionals, is related to the distinctions inherent in the legal doctrine underlying provision of goods and provision of services. The liability of the sellers and users of, and contributors to, expert systems are examined in terms of professional malpractice as well as product liability. A recurring theme indicates that legislators may be inclined to restrict possibilities of liability suits in order to avoid disincentives to the creation of expert systems. 相似文献
92.
《Petroleum Science and Technology》2007,25(7):915-923
Polymer modified bitumen (PMB) is used in various construction applications, especially in motorways. The aim of this study is to improve features of 60/70 penetration grade, modified bitumen used on highways. Increasing the sensitivity to temperature and oxidation resistance are very important points for the modified bitumen. This condition was provided by reacting the carboxylic acid groups in asphaltene with the reactive ethylene terpolymer to form ester. Reactive ethylene terpolymer (RETP) and ethylene terpolymer (ETP) manufactured by DuPont USA were used as additives in this study. Infrared Spectrophotometer (IR) graphics and optical pictures of the modified bitumen have been examined. It has been observed that the softening point has increased on the other hand, the penetration and ductility values have decreased according to the test results. 相似文献
93.
Herbert S. Bennett 《Journal of research of the National Institute of Standards and Technology》2007,112(4):209-221
In this paper, we present the theory for calculating Raman line shapes as functions of the Fermi energy and finite temperatures in zinc blende, n-type GaAs for donor densities between 1016 cm−3 and 1019 cm−3. Compared to other theories, this theory is unique in two respects: 1) the many-body effects are treated self-consistently and 2) the theory is valid at room temperature for arbitrary values of the ratio R = (Q2/α), where Q is the magnitude of the normalized wave vector and α is the normalized frequency used in the Raman measurements. These calculations solve the charge neutrality equation self-consistently for a two-band model of GaAs at 300 K that includes the effects of high carrier concentrations and dopant densities on the perturbed densities of states used to calculate the Fermi energy as a function of temperature. The results are then applied to obtain the carrier concentrations from Fermi energies in the context of line shapes in Raman spectra due to the coupling between longitudinal optical phonons and plasmons. Raman measurements have been proposed as a non-destructive method for wafer acceptance tests of carrier density in semiconductor epilayers. The interpretation of Raman spectra to determine the majority electron density in n-type semiconductors requires an interdisciplinary effort involving experiments, theory, and computer-based simulations and visualizations of the theoretical calculations. 相似文献
94.
Yuan-Hui Yu 《中国电子科技》2007,5(3):215-217
The technical characters of mobile agent (MA) originated in the distributional artificial intelligence domain is introduced. A network management construction based on agent (NMCA) is then proposed. The NMCA structure features are elaborated in detail. A prototype design of NMCA is given by using the jKQML programming. The establishment of NMCA platform will be helpful to reduce the correspondence load of network management and improves the efficiency and the expansion ability of network management systems. 相似文献
95.
NiTi形状记忆合金激光气体氮化层表面特征 总被引:2,自引:0,他引:2
为改善NiTi合金的表面性能,利用2kW连续波Nd:YAG对NiTi合金进行激光气体氮化处理。采用SEM、TEM、XRD、XPS和纳米压痕研究了氮化层的显微组织及表面特征.结果表明:激光气体氮化可以在NiTi合金表面制备连续、无裂纹、厚度为2μm的TiN表面层,该表面层中基本不合有Ni元素且具有很高的硬度,其纳米压痕硬度为29.28GPa. 相似文献
96.
形状记忆聚氨酯的结构与性能研究 总被引:1,自引:0,他引:1
以 2 ,4 -甲苯二异氰酸酯 (2 ,4 -TDI)、不同分子量的聚己二酸丁二醇酯 (PBAG)和 1,4-丁二醇 (BDO)为原料合成了具有形状记忆功能的聚氨酯材料。通过DSC、弯曲实验和力学实验 ,研究了形状记忆聚氨酯的性能 ,发现软段高度结晶和硬段聚集形成硬段微区是其具有较好形状记忆性能的必要条件。 相似文献
97.
98.
O'Farrell Timothy J.; Fals-Stewart William; Murphy Marie; Murphy Christopher M. 《Canadian Metallurgical Quarterly》2003,71(1):92
This study examined partner violence in the year before and the year after individually based, outpatient alcoholism treatment for 301 married or cohabiting male alcoholic patients and used a demographically matched nonalcoholic comparison sample. In the year before treatment, 56% of the alcoholic patients had been violent toward their female partner, 4 times the rate of 14% in the comparison sample. In the year after treatment, violence decreased significantly to 25% of the alcoholic sample but remained higher than in the comparison group. Among remitted alcoholics after treatment, violence prevalence of 15% was nearly identical to the comparison sample and half the rate among relapsed patients (32%). Thus, partner violence decreased after alcoholism treatment, and clinically significant violence reductions occurred for patients whose alcoholism was remitted after treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
100.
测井曲线拐点在测井层序地层分析中的应用研究 总被引:4,自引:3,他引:1
在层序地层学研究中,层序界面的划分是基础和重要的环节,而利用测井资料分析可以进行层序界面划分和进行较长期基准面旋回识别。测井曲线的值是深度的函数,测井曲线的一阶导数表示了曲线变化的趋势和变化的快慢,在某一范围内,当一阶导数呈现符号转换时,相对应的深度点的测井值即为该范围内极大(极小)值;测井曲线的二阶导数则表示曲线的凹凸性,在某一范围内,当二阶导数呈现符号转换时,相对应的深度点代表了测井曲线的拐点,即反映曲线凹凸性变化的转折点,亦即地层的分界面。基于以上特点,提出利用测井曲线拐点进行层序界面划分的原理和方法,并结合岩心和录井资料,对白音查干凹陷达28井腾格尔组不同级次沉积旋回、地层垒积、旋回特征随沉积厚度变化特点和不同级次基准面旋回进行研究,最后得到该地层单井测井层序地层分析结果。 相似文献