全文获取类型
收费全文 | 715篇 |
免费 | 20篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 7篇 |
综合类 | 1篇 |
化学工业 | 113篇 |
金属工艺 | 20篇 |
机械仪表 | 26篇 |
建筑科学 | 22篇 |
矿业工程 | 1篇 |
能源动力 | 23篇 |
轻工业 | 16篇 |
水利工程 | 2篇 |
石油天然气 | 4篇 |
无线电 | 147篇 |
一般工业技术 | 162篇 |
冶金工业 | 57篇 |
原子能技术 | 3篇 |
自动化技术 | 133篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 11篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 12篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 58篇 |
2012年 | 22篇 |
2011年 | 27篇 |
2010年 | 31篇 |
2009年 | 37篇 |
2008年 | 31篇 |
2007年 | 20篇 |
2006年 | 29篇 |
2005年 | 20篇 |
2004年 | 11篇 |
2003年 | 19篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 20篇 |
1999年 | 18篇 |
1998年 | 25篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 14篇 |
1993年 | 9篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 7篇 |
1989年 | 9篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1979年 | 6篇 |
1977年 | 6篇 |
1974年 | 3篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
排序方式: 共有737条查询结果,搜索用时 765 毫秒
1.
As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is
desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals.
We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate
the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation
(GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic
quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature.
We also obtain much closer agreement with experiment than earlier, more approximate calculations. 相似文献
2.
Two studies are presented. The first aimed to identify possible barriers to the uptake and use of commonly available telephony features and to determine whether greater knowledge of features/access codes and availability of user manuals could increase feature usage under certain conditions. Results showed that feature-usage patterns were not affected by any of the manipulations, but that they were determined by specific job demands. Using Constantine and Lockwood's (1999) conceptualization of user roles, a method to support feature bundling decisions for specific target markets was developed and tested in the second study. The method - Strategic User Needs Analysis (SUNA) - was shown to yield a useful balance between high- and low-level information about selected roles. SUNA provided sufficient information to distinguish between PDA feature usage patterns of two similar target user groups as well as to suggest additional features each of the two target groups would find useful. The development of SUNA and observational findings of actual PDA usage are reported. 相似文献
3.
Summary Novel PUs containing pyridinium moieties were synthesized by chain extending isocyanate endcapped prepolymers with N, N’-bis (2-hydroxyethyl) isonicotinamide. The pyridinium moieties in the PUs were chemically crosslinked using short-chain divalent quaternising agents. The polyurethane cationomers were characterized by spectral, thermal and mechanical analysis. Spectral results confirmed the quaternisation of tertiary nitrogen leading to crosslinking. Compared to conventional PUs, the crosslinked PU networks exhibited improved thermal stability. The damping value (i.e.) tan δ for cationomers were improved over a broad temperature range when compared to conventional PU. 相似文献
4.
5.
Dr Kalathur ‘Sim’ Narasimhan 《Metal Powder Report》2003,58(5):12-21
The 42-volt electrical system is to be introduced in automobiles to provide the extra power needed for various electromagnetic devices. This offers an opportunity for insulated iron powder to replace lamination steel in a variety of motors. Brushless motor design can probably benefit most from insulated iron powder compacts because of the design simplicity of powder metal parts and three-dimensional flux capability that is most beneficial in rotating devices says Sim Narasimhan… 相似文献
6.
A family of energy/economic/environmental (E3) models is presented as a mechanism for analysing national policy issues. The family consists of discrete models which are designed to be run in an integrated manner. The outputs of certain models provide the inputs to the next. This structure allows the analyst to readily incorporate an understanding of regional factors such as local energy prices, concerns over air quality, water availability, or attitudes towards construction of new energy facilities, into national assessments of energy policies. This paper reviews the analytic framework within which energy policy issues are currently addressed. The initial family of E3 models is described with the emphasis on the data linkages and feedback which are provided when these models are run sequentially. The ongoing MITRE research programme with the E3 family of models is presented and plans and opportunities for future work are outlined. 相似文献
7.
A series of experiments have been conducted using a recombinant baculovirus/insect cell expression system (Bm5/Bm5.NPV.CAT) to establish the optimum temperature for both cell growth and virus infection. Bm5 cell growth was found to be limited at temperatures below 22°C and ceased completely at temperatures above 34°C. In the range between 24 and 28°C, final cell densities always reached 96% of the highest achievable viable cell density. The shortest population doubling time was obtained at 28°C. Overall, a consistent increase in metabolism with increasing temperatures was observed. During the infection/viral replication phase, an increase in the temperature from 25 to 31°C resulted in a faster decrease in viable cell density and an earlier production of chloramphenicol acetyltransferase (CAT). Furthermore, protein yield at temperatures above 28°C was significantly reduced. Overall, the best temperature for the infection phase for the Bm5/Bm5.NPV expression system was found to be 25°C when the cells are cultured in serum free media. 相似文献
8.
SHARED: An information model for cooperative product development 总被引:6,自引:0,他引:6
One fundamental issue in developing collaborative engineering systems is the representation of product information which supports communication and coordination. This product information includes not only the geometric and physical properties of the product and its parts, but also information about functions, constraints and the design rationale. In this paper, we describe an information model, SHARED, which was developed for encoding product information in DICE, a distributed and integrated environment for computer-aided engineering. SHARED provides multiple levels of both functional and geometric abstractions, multiple views and techniques for maintaining consistency between the various abstractions and views. These elements are essential for a good representation model of product information. The use of the SHARED model is illustrated through an example, depicting the various representations of a product as it evolves through the design process. The SHARED model has been implemented over a distributed OODBMS as a toolkit/framework for developing environments which need to model, manipulate and communicate product information between distributed cooperating applications, while supporting coordination between them. 相似文献
9.
Model-Based Diagnosis of Hybrid Systems 总被引:3,自引:0,他引:3
Narasimhan S. Biswas G. 《IEEE transactions on systems, man, and cybernetics. Part A, Systems and humans : a publication of the IEEE Systems, Man, and Cybernetics Society》2007,37(3):348-361
Techniques for diagnosing faults in hybrid systems that combine digital (discrete) supervisory controllers with analog (continuous) plants need to be different from those used for discrete or continuous systems. This paper presents a methodology for online tracking and diagnosis of hybrid systems. We demonstrate the effectiveness of the approach with experiments conducted on the fuel-transfer system of fighter aircraft 相似文献
10.
JS Plummer KA Berryman C Cai WL Cody J DiMaio AM Doherty JJ Edmunds JX He DR Holland S Levesque DR Kent LS Narasimhan JR Rubin ST Rapundalo MA Siddiqui AJ Susser Y St-Denis PD Winocour 《Canadian Metallurgical Quarterly》1998,8(23):3409-3414
The synthesis and antithrombotic activity of a series of nonpeptide bicyclic thrombin inhibitors is described. We have explored the SAR with modifications to the P1 site. The introduction of arginine mimetics at the P1 site led to potent and selective thrombin inhibitors. 相似文献