全文获取类型
收费全文 | 97319篇 |
免费 | 8030篇 |
国内免费 | 5577篇 |
专业分类
电工技术 | 3839篇 |
技术理论 | 4篇 |
综合类 | 9728篇 |
化学工业 | 14590篇 |
金属工艺 | 7469篇 |
机械仪表 | 5719篇 |
建筑科学 | 18757篇 |
矿业工程 | 3518篇 |
能源动力 | 2769篇 |
轻工业 | 5143篇 |
水利工程 | 2366篇 |
石油天然气 | 4520篇 |
武器工业 | 891篇 |
无线电 | 6533篇 |
一般工业技术 | 11285篇 |
冶金工业 | 3814篇 |
原子能技术 | 658篇 |
自动化技术 | 9323篇 |
出版年
2024年 | 368篇 |
2023年 | 1437篇 |
2022年 | 2604篇 |
2021年 | 2926篇 |
2020年 | 2907篇 |
2019年 | 2379篇 |
2018年 | 2273篇 |
2017年 | 2861篇 |
2016年 | 2932篇 |
2015年 | 3187篇 |
2014年 | 5840篇 |
2013年 | 5056篇 |
2012年 | 6360篇 |
2011年 | 7394篇 |
2010年 | 5619篇 |
2009年 | 6147篇 |
2008年 | 5633篇 |
2007年 | 6525篇 |
2006年 | 5970篇 |
2005年 | 5193篇 |
2004年 | 4307篇 |
2003年 | 3912篇 |
2002年 | 3339篇 |
2001年 | 2732篇 |
2000年 | 2368篇 |
1999年 | 1997篇 |
1998年 | 1594篇 |
1997年 | 1361篇 |
1996年 | 1044篇 |
1995年 | 904篇 |
1994年 | 829篇 |
1993年 | 560篇 |
1992年 | 521篇 |
1991年 | 413篇 |
1990年 | 332篇 |
1989年 | 229篇 |
1988年 | 192篇 |
1987年 | 94篇 |
1986年 | 81篇 |
1985年 | 83篇 |
1984年 | 56篇 |
1983年 | 60篇 |
1982年 | 68篇 |
1981年 | 27篇 |
1980年 | 66篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1976年 | 10篇 |
1975年 | 11篇 |
1959年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Keizo Uematsu Masayori Miyashita Jin-Young Kim Zenji Kato Nozomu Uchida 《Journal of the American Ceramic Society》1991,74(9):2170-2174
Green bodies prepared by compaction of alumina granules were made transparent by an immersion liquid technique, and the internal structure was characterized with an optical microscope to study the effect of forming pressure on the internal structure. Clear images obtained by the technique provide more detailed information than other existing methods for structures ranging from one to tens of micrometers. Intergranular pores were present between unfractured granules. Their sizes and concentration tended to decrease with increasing forming pressure. However, pores were clearly present even in the green body prepared at 600 MPa. A rod- and needlelike feature was also found and was concluded to correspond to a high-density region. The significance of large pores and high-density regions on processing as well as the details of the technique is discussed. 相似文献
23.
John E. Lowther 《Journal of the American Ceramic Society》2002,85(1):55-58
Diamond and BN have common relatively soft precursor structures that are hexagonal. Electronic structure calculations have now revealed subtle energy differences between the two materials. Another hard material, stishovite, also has a relatively soft precursor phase, quartz, and here again electronic structure calculations have given insight into the nature of the phase transformation. On the other hand, with boron-related materials, the main focus is to connect basic icosahedra structures to produce a hard material. The structural aspects of these materials are examined and possible consequences for low- and high-coordination ultrahard nitrides considered. 相似文献
24.
The object of this paper is to demonstrate the usefulness of the transalkylation reaction for determining chemical structural features of products derived from coal. For example, the method is applied to derivatized coals, coals modified by thermolysis, and materials physically or chemically separated from coals. Data are presented for the pyridine soluble and insoluble parts of two coals, an O-methylated coal, a Birch reduced coal, a solvent refined coal, and a coke. Similarities and differences in chemical make-up of these materials are discussed. 相似文献
25.
As part of a study of the possible application of polymerisable Langmuir-Blodgett (LB) films as ultra-fine-line e-beam resists, an investigation of the variation of film structure of 22-tricosenoic acid with differing deposition conditions has been made. Unexpected effects with significant implications for deposition speed and resist sensitivity have been observed, and the new techniques for film characterisation developed during the investigation have resulted in a revised model of deposition explaining the observed independence of the disorder causing optical scattering and the macroscopic features observed by polarised microscopy. 相似文献
26.
高速短程纺技术能生产三维卷曲短纤维,该技术的关键之一是热流体喷射装置。本文介绍了热流体喷射装置的演变与特点及它的加工机理和某些已应用的实际装置。 相似文献
27.
28.
M. Portillo
J. H. Dohr
《Design Studies》1994,15(4):403-416Scholars in design face two central challenges in design methods inquiry: firstly, to integrate process and solution, and secondly, to examine developmental junctures leading to innovation. With these goals in mind, we maintain that design criteria deserve greater attention and illustrate this position with a study of noted designers' use of criteria. The primary finding was that five criteria functions were considered during the design process. The study also explored potential relationships between designer variables (i.e., professional expertise and personality type) and criteria use. 相似文献
29.
In a previous study a solvent mixture of heptane containing 40 mass % heptanol was selected as an alternative in the industrial extraction of caprolactam to replace benzene, toluene, or chlorinated hydrocarbons. This work reports the equilibrium distribution ratio of caprolactam and four model impurities of organic nature, namely, cyclohexanone, aniline, n‐methylcaprolactam, and cyclohexane‐carboxamide, comparing the mixed solvents with toluene as a reference. The resulting phase equilibria were interpreted using the equilibrium stage model. Based on these calculations it was found that, compared to toluene, the co‐extracted fraction of cyclohexanone and aniline was higher, that of n‐methylcaprolactam was comparable, and that of cyclohexane‐carboxamide was lower using the mixed solvent. Overall, the mixed solvent reduced the fraction of co‐extracted impurities by almost 10 %. 相似文献
30.
Reviews the book, The concept of structure in psychoanalysis by Theodore Shapiro (see record 1991-97355-000). The present volume is a hardcover edition of a previous supplement to the Journal of the American Psychoanalytic Association based on a series of panels presented at meetings of the American on the role of the concept of structure in current psychoanalytic theory and practice. The result can be taken as a more or less authoritative expression of current thinking about structure in orthodox analytic circles. As such, the volume is informative and in many regards thought provoking. But if readers are looking for a coherent, consistent, and consensually endorsed presentation of the idea of structure, or for a uniform conceptualization of the nature of psychic structure and its role in psychoanalytic praxis, they will have to look elsewhere. The volume is more remarkable for its diversity and often contradictory views on the nature of structure and the relevance of structure to clinical work in the analytic setting. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献