全文获取类型
收费全文 | 92694篇 |
免费 | 1281篇 |
国内免费 | 423篇 |
专业分类
电工技术 | 869篇 |
综合类 | 2325篇 |
化学工业 | 13435篇 |
金属工艺 | 4997篇 |
机械仪表 | 3195篇 |
建筑科学 | 2496篇 |
矿业工程 | 589篇 |
能源动力 | 1310篇 |
轻工业 | 4381篇 |
水利工程 | 1375篇 |
石油天然气 | 379篇 |
武器工业 | 2篇 |
无线电 | 9868篇 |
一般工业技术 | 17951篇 |
冶金工业 | 4598篇 |
原子能技术 | 334篇 |
自动化技术 | 26294篇 |
出版年
2022年 | 115篇 |
2021年 | 188篇 |
2020年 | 148篇 |
2019年 | 140篇 |
2018年 | 14592篇 |
2017年 | 13509篇 |
2016年 | 10119篇 |
2015年 | 734篇 |
2014年 | 452篇 |
2013年 | 689篇 |
2012年 | 3523篇 |
2011年 | 9868篇 |
2010年 | 8577篇 |
2009年 | 5879篇 |
2008年 | 7163篇 |
2007年 | 8164篇 |
2006年 | 461篇 |
2005年 | 1515篇 |
2004年 | 1402篇 |
2003年 | 1417篇 |
2002年 | 798篇 |
2001年 | 216篇 |
2000年 | 304篇 |
1999年 | 191篇 |
1998年 | 239篇 |
1997年 | 184篇 |
1996年 | 211篇 |
1995年 | 157篇 |
1994年 | 157篇 |
1993年 | 167篇 |
1992年 | 130篇 |
1991年 | 129篇 |
1990年 | 135篇 |
1989年 | 106篇 |
1988年 | 95篇 |
1987年 | 129篇 |
1986年 | 98篇 |
1985年 | 133篇 |
1984年 | 129篇 |
1983年 | 134篇 |
1982年 | 104篇 |
1981年 | 93篇 |
1980年 | 79篇 |
1979年 | 77篇 |
1978年 | 96篇 |
1976年 | 76篇 |
1975年 | 79篇 |
1974年 | 83篇 |
1955年 | 97篇 |
1954年 | 78篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
123.
124.
In this paper, we argue that successful integration of knowledge across work domains in the short-term can mask the generation of long-term consequences. We explore a setting, the introduction of environmental considerations into semiconductor manufacturing, where the eventual adoption of common measurement artifacts and associated practices enabled knowledge integration, but failed to address significant underlying consequences. Drawing from observational, interview, and archival data we develop an understanding of the work practices of the Tech and EnviroTech groups as structured by the material world and broader collective conventions. We introduce the concept of knowledge regime to outline the differences in knowledge across these work domains. More specifically, we find that differences in the causal specificity and developmental time horizon of knowledge and the measurement artifacts that result contribute to the relative power of one knowledge regime over another. Understanding these sources of incompatibility provides insight into the design requirements of information systems as boundary objects for knowledge integration, but also specifies the potential limits to any design effort. 相似文献
125.
126.
127.
128.
Understanding consumer behaviour is of vital importance to consumer-oriented e-business models today. In this paper, we study the relationships between consumer perceptions of risk and trust and the attitude towards purchasing at a consumer-to-consumer electronic marketplace (EM). Typical for EM settings is that consumer behaviour is subject to perceptions of the selling party as well as of the institutional structures of the intermediary that is operating the EM. Building upon the well-established literature of trust, we consider the concepts of intermediary trust and seller trust. We extend this categorisation by introducing the concepts of intermediary risk and seller risk. We developed measurement instruments for intermediary risk and seller risk. All measurement scales have acceptable alphas and are unidimensional. An empirical study is conducted to explore the relationships between the risk and trust types and consumer purchase attitude. The results reveal significant, direct effects of seller trust and seller risk. Second-order effects of intermediary trust and intermediary risk are investigated and reported. The paper concludes with general observations and recommendations for research and practice. 相似文献
129.
NE Joseph C Fiocchi AD Levine 《Canadian Metallurgical Quarterly》1997,122(4):809-14; discussion 814-6
BACKGROUND: Crohn's disease (CD) and ulcerative colitis (UC) are chronic inflammatory diseases, and their pathogenesis is attributed, in part, to alterations of the mucosal immune system. This study was designed to define the possible contribution of epithelial cells to the activation of lamina propria T lymphocytes (LPTs) in CD and UC. METHODS: LPTs isolated from CD, UC, and control surgical specimens were cocultured with freshly isolated allogeneic or autologous epithelial cells or epithelial cell lines. Resulting T-cell proliferation was evaluated by tritiated thymidine incorporation on day 5. RESULTS: When intestinal epithelial cells were used to stimulate mucosal T-cell proliferation, CD and UC LPTs were less responsive than control LPTs (p < 0.05 and p < 0.03, respectively). This difference between inflamed and control T cells was consistently observed by using a variety of different intestinal epithelial cell types. CONCLUSIONS: CD and UC mucosal T cells are hyporesponsive to activation by intestinal epithelial cells when compared with control LPTs. Elucidating the mechanism underlying the differential activation of CD and UC LPTs may help to better understand the immunopathogenesis of these conditions. 相似文献
130.
J. S. Kim D. G. Seiler R. A. Lancaster M. B. Reine 《Journal of Electronic Materials》1996,25(8):1215-1220
Variable-magnetic-field Hall measurements (0 to 1.5 T) are performed on very-narrow-gap bulk-grown Hg1−xCdxTe single crystals (0.165 ≤ x ≤ 0.2) at various temperatures (10 to 300K). The electron densities and mobilities are obtained
within the one-carrier (electrons) approximation of the reduced-con-ductivity-tensor scheme. The present data together with
the selected data set reported by other workers exhibit a pronounced peak when the electron mobility is plotted against the
alloy composition x-value which has been predicted to be due to the effective-mass minimum at the bandgap-crossing (Eg ≈ 0). The observed position (x ≈ 0.165), height (≈4 x 102 m2Vs), and width (≈0.01 in x) of the mobility-peak can be explained by a simple simulation involving only ionized-impurity scattering.
A lower bound of the effective mass is introduced as a fitting parameter to be consistent with the finiteness of the observed
electron mobility and is found to be of the order of 10−4 of the mass of a free electron. 相似文献