全文获取类型
收费全文 | 26464篇 |
免费 | 1490篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 389篇 |
综合类 | 64篇 |
化学工业 | 5297篇 |
金属工艺 | 717篇 |
机械仪表 | 591篇 |
建筑科学 | 1135篇 |
矿业工程 | 138篇 |
能源动力 | 424篇 |
轻工业 | 4110篇 |
水利工程 | 154篇 |
石油天然气 | 27篇 |
无线电 | 1369篇 |
一般工业技术 | 5938篇 |
冶金工业 | 3824篇 |
原子能技术 | 266篇 |
自动化技术 | 3532篇 |
出版年
2023年 | 274篇 |
2022年 | 233篇 |
2021年 | 489篇 |
2020年 | 433篇 |
2019年 | 411篇 |
2018年 | 750篇 |
2017年 | 762篇 |
2016年 | 838篇 |
2015年 | 726篇 |
2014年 | 883篇 |
2013年 | 1684篇 |
2012年 | 1079篇 |
2011年 | 1328篇 |
2010年 | 1128篇 |
2009年 | 1009篇 |
2008年 | 1154篇 |
2007年 | 1095篇 |
2006年 | 812篇 |
2005年 | 630篇 |
2004年 | 553篇 |
2003年 | 565篇 |
2002年 | 586篇 |
2001年 | 486篇 |
2000年 | 432篇 |
1999年 | 427篇 |
1998年 | 1319篇 |
1997年 | 836篇 |
1996年 | 647篇 |
1995年 | 436篇 |
1994年 | 370篇 |
1993年 | 368篇 |
1992年 | 189篇 |
1991年 | 184篇 |
1990年 | 151篇 |
1989年 | 151篇 |
1988年 | 159篇 |
1987年 | 135篇 |
1986年 | 133篇 |
1985年 | 229篇 |
1984年 | 192篇 |
1983年 | 140篇 |
1982年 | 139篇 |
1981年 | 181篇 |
1980年 | 165篇 |
1979年 | 121篇 |
1978年 | 125篇 |
1977年 | 159篇 |
1976年 | 238篇 |
1975年 | 117篇 |
1973年 | 98篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today. 相似文献
53.
54.
55.
Dr. G. Pönisch 《Computing》1987,39(1):1-17
A direct method is described for computing a hysteresis point (double turning point) corresponding to a cusp point of a system ofn nonlinear equations inn variables depending on two parameters. By addition of two equations a minimally extended system ofn+2 nonlinear equations is constructed for which the hysteresis point is an isolated solution. An efficient implementation of Newton's method is presented not requiring evaluations of second derivatives of the original problem. Two numerical examples show the efficiency of theQ-quadratically convergent method. 相似文献
56.
A one-dimensional mesoscopic ring with one input and two output leads acts as a spintronic beam splitter. The spatial degree of freedom, i.e., the presence of two different possible output channels, gets intertwined with the spin direction as a consequence of quantum interference and spin-orbit interaction. We investigate this kind of spatial-spin correlation, and show that the output density operator contains no quantum entanglement in the important special case when the device polarizes a perfectly random input spin state. However, the correlations are in general not purely classical, we also present specific input states with maximal spatial-spin entanglement after the ring. 相似文献
57.
Dipl.-Biol. Michael Gommel Claudia Raichle Patrick Müller Frieder Keller 《Ethik in der Medizin》2005,17(1):21-27
Definition of the problem: Ethical reasoning cannot be enforced. Voluntary understanding is a basic condition for the development of ethical competencies and attitudes. The aim of this survey was to investigate whether the presence of those students who attended our seminars compulsorily would have a negative effect upon the quality of the course. Methods and results: The participants of our small-group seminars in medical ethics were asked to complete a questionnaire on teaching aims, seminar atmosphere, moderation and importance of subjects. One hundred and ninety-two voluntary participants (2001/2) and 293 compulsory participants (2002/3) completed the questionnaire and were statistically compared. There was no significant difference between voluntary and compulsory participants in any of the important items. However, there were considerable differences in some items between male and female participants. Conclusion: We were surprised that there was no difference between the two groups. This leads us to hope that our concept of case-based small-group seminars will prove capable of realising our teaching aims for all students. The difference between male and female participants may have important didactic consequences and will be the subject of further studies. 相似文献
58.
Ohne Zusammenfassung
VDI 相似文献
59.
60.
O Baeder-Bederski M Dürr M Borneff-Lipp P Kuschk R Netter G Daeschlein P Mosig R A Müller 《Water science and technology》2005,51(9):205-212
Different types of constructed wetlands in a pilot-plant system were fed with identical municipal waste water to compare the sanitisation process in two-stage systems. With combinations of a vertical and a horizontal flow filter an E. coli reduction of 5 log10 with an E. coli influent concentration of 10(7) MPN/100 ml was achieved. Using different filter materials in each stage the total performance of the two-stage system was independent from the sequence of these materials. However, using coarser filter material in the first stage makes the filter less prone to clogging and is thus the preferential option with regard to operational reliability. 相似文献