全文获取类型
收费全文 | 34175篇 |
免费 | 1823篇 |
国内免费 | 131篇 |
学科分类
工业技术 | 36129篇 |
出版年
2023年 | 350篇 |
2022年 | 322篇 |
2021年 | 783篇 |
2020年 | 611篇 |
2019年 | 533篇 |
2018年 | 1078篇 |
2017年 | 978篇 |
2016年 | 1116篇 |
2015年 | 950篇 |
2014年 | 1128篇 |
2013年 | 2344篇 |
2012年 | 1605篇 |
2011年 | 1645篇 |
2010年 | 1389篇 |
2009年 | 1327篇 |
2008年 | 1397篇 |
2007年 | 1292篇 |
2006年 | 979篇 |
2005年 | 777篇 |
2004年 | 573篇 |
2003年 | 548篇 |
2002年 | 484篇 |
2001年 | 456篇 |
2000年 | 435篇 |
1999年 | 551篇 |
1998年 | 2534篇 |
1997年 | 1581篇 |
1996年 | 1054篇 |
1995年 | 643篇 |
1994年 | 538篇 |
1993年 | 496篇 |
1992年 | 208篇 |
1991年 | 198篇 |
1990年 | 182篇 |
1989年 | 183篇 |
1988年 | 172篇 |
1987年 | 176篇 |
1986年 | 153篇 |
1985年 | 245篇 |
1984年 | 218篇 |
1983年 | 179篇 |
1982年 | 149篇 |
1981年 | 213篇 |
1980年 | 193篇 |
1979年 | 147篇 |
1978年 | 122篇 |
1977年 | 255篇 |
1976年 | 527篇 |
1975年 | 102篇 |
1973年 | 133篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
71.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
72.
73.
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
74.
75.
Roland Gabriel Jürgen Kunz Lars Schwarze Peter Fettke Christian Scheer Franz Lehner Konrad Walser Thomas Deelmann 《WIRTSCHAFTSINFORMATIK》2006,48(3):218-222
Ohne Zusammenfassung 相似文献
76.
Kinetics of the reaction between bis(4-isocyanatocyclohexyl)methane, H-MDI, and n-butanol was studied in toluene at 100°C. Effects of various catalysts, such as Hg(CH3COO)2, Zn(CH3COO)2 · 2H2O, SnCl4 · 5H2O, and dibutyltindilaurate on the reaction rate and kinetics were also investigated. Reactions were followed by determining the unreacted isocyanate as a function of reaction time, using the standard dibutylamine back titration method. All catalysts seem to be very effective in increasing of the rate of the reaction compared to the uncatalyzed system. Depending on the initial stoichiometric ratio of (NCO) and (OH) and the concentration of the catalyst used, it seems possible to have preferential catalysis of the primary reaction between (NCO) and (OH) over the side reactions. 相似文献
77.
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
78.
Summary A group of new polyimides has been prepared by solution condensation of 2,6-bis[1-(p-dimethylaminophenylimino)ethyl] pyridine containing pendant NMe2 units and various dianhyrides in N-methylpyrrolidone (NMP). The tridentate (N-N′-N) pydim ligands were prepared by Schiff-base condensation of 2,6-diacetylpyridine and 4-dimethylaminoaniline in the presence of formic acid as catalyst. These polymers were investigated for their extraction capabilities for Zn(II), Mn(II), Cu(II), Cd (II) and Ni(II) and at different pH. Under different conditions enhanced selectivity was observed. Up to 98% quantitative recoveries were observed for all metals. 相似文献
79.
Christiane Stüber 《Ethik in der Medizin》2005,17(1):57-60
Ohne Zusammenfassung 相似文献
80.