全文获取类型
收费全文 | 5186篇 |
免费 | 193篇 |
国内免费 | 13篇 |
专业分类
电工技术 | 82篇 |
综合类 | 30篇 |
化学工业 | 1504篇 |
金属工艺 | 96篇 |
机械仪表 | 94篇 |
建筑科学 | 322篇 |
矿业工程 | 23篇 |
能源动力 | 99篇 |
轻工业 | 413篇 |
水利工程 | 34篇 |
石油天然气 | 2篇 |
无线电 | 317篇 |
一般工业技术 | 1087篇 |
冶金工业 | 474篇 |
原子能技术 | 40篇 |
自动化技术 | 775篇 |
出版年
2023年 | 38篇 |
2022年 | 49篇 |
2021年 | 85篇 |
2020年 | 74篇 |
2019年 | 68篇 |
2018年 | 83篇 |
2017年 | 98篇 |
2016年 | 142篇 |
2015年 | 102篇 |
2014年 | 163篇 |
2013年 | 248篇 |
2012年 | 221篇 |
2011年 | 321篇 |
2010年 | 245篇 |
2009年 | 254篇 |
2008年 | 248篇 |
2007年 | 238篇 |
2006年 | 236篇 |
2005年 | 202篇 |
2004年 | 174篇 |
2003年 | 137篇 |
2002年 | 111篇 |
2001年 | 86篇 |
2000年 | 90篇 |
1999年 | 100篇 |
1998年 | 113篇 |
1997年 | 83篇 |
1996年 | 92篇 |
1995年 | 71篇 |
1994年 | 73篇 |
1993年 | 77篇 |
1992年 | 77篇 |
1991年 | 57篇 |
1990年 | 60篇 |
1989年 | 57篇 |
1988年 | 60篇 |
1987年 | 54篇 |
1986年 | 46篇 |
1985年 | 45篇 |
1984年 | 54篇 |
1983年 | 39篇 |
1982年 | 49篇 |
1981年 | 47篇 |
1980年 | 31篇 |
1979年 | 29篇 |
1978年 | 35篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1975年 | 38篇 |
1973年 | 31篇 |
排序方式: 共有5392条查询结果,搜索用时 15 毫秒
991.
Aashrita Rajagopalan Miguel Lara Wolfgang Kroutil 《Advanced Synthesis \u0026amp; Catalysis》2013,355(17):3321-3335
The cleavage of alkenes to the corresponding carbonyl products is a widely employed method in organic synthesis, especially to introduce oxygen functionalities into molecules, remove protecting groups and tailor large molecules. Chemical methods available for alkene cleavage include, for instance, ozonolysis, several metal‐based variants (KMnO4, OsO4, RuO4, etc.), electrochemical alternatives, singlet oxygen, hypervalent iodine and organic molecules in combination with oxygen. Furthermore, several enzymatic methods for alkene cleavage have been described to establish safe, mild and selective oxidation methods. Various heme and non‐heme iron‐dependent enzymes catalyse the alkene cleavage at ambient temperature and atmospheric pressure in an aqueous buffer, showing good chemo‐ and regioselectivities in selected cases. Quite recently some Cu‐, Mn‐ and Ni‐dependent enzymes have been identified for this reaction. This review gives an overview of the different chemical and enzymatic methods available for the cleavage of alkenes.
992.
Elina Siirola Francesco G. Mutti Barbara Grischek Sebastian F. Hoefler Walter M. F. Fabian Gideon Grogan Wolfgang Kroutil 《Advanced Synthesis \u0026amp; Catalysis》2013,355(9):1703-1708
Prochiral bicyclic diketones were transformed to a single diastereomer of 3‐substituted cyclohexylamine derivatives via three consecutive biocatalytic steps. The two chiral centres were set up by a C C hydrolase (6‐oxocamphor hydrolase) in the first step and by an ω‐transaminase in the last step. The esterification of the intermediate keto acid was catalysed by a lipase in the second step if possible. For two substrates the C C hydrolytic step as well as the esterification could be run simultaneously in a one‐pot cascade in an organic solvent. In one example, the reaction mixture of the first two steps could be directly subjected to bio‐amination in an organic solvent without the need to change the reaction medium. Depending on the choice of the ω‐transaminase employed and the substrate the cis‐ as well as the trans‐diastereomers could be obtained in optically pure forms. 相似文献
993.
994.
In the national research project “Multifunctional Battery Storage System (MBS)” open questions were answered concerning the technical feasibility and profitability of a grid-connected battery storage system using a vanadium-redox-flow battery in combination with the renewable power generation plants PV and small wind power (Sterrer et al., Multifunktionales Batteriespeichersystem—MBS-Endbericht. Industrielle Forschung im Rahmen der österreichischen Programmlinie Neue Energie 2020, 3. Ausschreibung, noch nicht veröffentlicht, 2013). The technical implementation and the demonstration operation of the pilot plant over a period of two years showed that the battery storage system is suitable for intelligent marketing of renewable energy as well as the provision of system services for grid stabilisation. However, the investigation of different operating strategies of the pilot battery-storage system, a large scale storage system and pooled PV/battery storage systems as virtual power plant for the participation at the energy trading market and energy reserve market showed that all operation strategies being considered in this study may not be profitable in foreseeable future. However, if the costs of the battery storage system can be reduced to about 250 €/kWh until the year 2030, the application of the vanadium-redox-flow battery in particular in large-scale storage plants (e.g. 10 MW, 100 MWh) for the participation at the energy reserve market seems realistic. 相似文献
995.
996.
This work is a review of research results, which have been determined in recent years in order to reveal the effects of the chemical compositions on the high temperature properties of structural steels. Special emphasis has been laid on the solidification structure, phase reactions and precipitates. For this comparison exemplary different structural steel grades have been chosen. The effect of the chemical composition on the solidification structure is shown by increasing Ni mass contents up to 10 %, the influence on the phase transformation is illustrated on the basis of a steel with a Mn mass content of 1.6 % and varying carbon contents. The influence of precipitates has been investigated both on the basis of the Mn/S‐ratio and by microalloyed structural steels with different Nb, V and Ti additions. For all these steel grades the laboratory testing conditions were the same. The high temperature properties of steels can be investigated by high temperature tensile tests; the range of good ductility is determined by the measurement of the reduction of area, e.g. RoA > 50 % or >70 %. The upper limit of the ductility range is the temperature of zero ductility, TZD%. The lower limit of the good ductility range is marked by the transition to the ductility minimum II. The experiments for a series of different structural steels show that the hot ductility properties are affected by the metallurgical phenomena mentioned before. 相似文献
997.
998.
The mechanical properties of eight different steels, representing the wide range of steels for automotive application, are determined by accomplishing high speed tensile tests using flat sheet specimens. The steels chosen for investigations are deep drawing grade DC04, high strength steel ZStE340, three dual phase steels with strengths of 600, 800 and 1000 MPa, a TRIP steel and two austenitic stainless steels 1.4301 and 1.4318. Tests are carried out at five different strain rates within the range of 5‐10?3 and 200 s?1, all at room temperature. The results show different strain rate sensitivities according to the different grades of steel. The TRIP steel and both stainless steels show a great potential for energy consumption, when tested at high strain rates. 相似文献
999.
In this study, the authors applied methods and theories from research of stimulus–response compatibility (SRC) to action imitation. In 6 experiments, they adopted the logic of the Simon paradigm (B. Hommel & W. Prinz, 1996) to explore interference between task-relevant symbolic stimulus features (color) and task-irrelevant iconic stimulus features (2 hand gestures and 2 postures). The same 2 hand gestures served as responses. Pronounced correspondence effects for both gestures and postures showed up throughout. In line with theories of SRC, the authors account for these correspondence effects in terms of overlap arising between stimulus and response features in a common representational domain. As a specific extension of this approach, they propose 2 functionally independent mechanisms: One operates movement-based when dynamic information is provided, and the other operates state-based with static postures as stimuli. Implications for theories of both SRC and action imitation are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
1000.
Frequently, affine recurrence equations can be scheduled more efficiently by quadratic scheduling functions than by linear scheduling functions. In this paper, the problem of finding optimal quadratic schedules for affine recurrence equations is formulated as a convex nonsmooth programming problem. In particular, sufficient constraints for causality are used generalizing Lamport's condition. In this way, the presented problem formulation becomes independent of the problem size. The research tool AQUAD is described implementing this problem formulation. Several nontrivial examples demonstrate that AQUAD can be effectively used to calculate quadratic schedules for affine recurrence equations. Finally, it is shown how array processors can be synthesized from affine recurrence equations which are scheduled by quadratic functions with a singular Hessian matrix. 相似文献