全文获取类型
收费全文 | 21326篇 |
免费 | 472篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 328篇 |
综合类 | 16篇 |
化学工业 | 3817篇 |
金属工艺 | 333篇 |
机械仪表 | 423篇 |
建筑科学 | 801篇 |
矿业工程 | 126篇 |
能源动力 | 476篇 |
轻工业 | 1636篇 |
水利工程 | 166篇 |
石油天然气 | 184篇 |
武器工业 | 1篇 |
无线电 | 1609篇 |
一般工业技术 | 2958篇 |
冶金工业 | 6358篇 |
原子能技术 | 244篇 |
自动化技术 | 2343篇 |
出版年
2021年 | 212篇 |
2020年 | 173篇 |
2019年 | 196篇 |
2018年 | 227篇 |
2017年 | 233篇 |
2016年 | 274篇 |
2015年 | 212篇 |
2014年 | 302篇 |
2013年 | 982篇 |
2012年 | 601篇 |
2011年 | 836篇 |
2010年 | 586篇 |
2009年 | 634篇 |
2008年 | 781篇 |
2007年 | 765篇 |
2006年 | 731篇 |
2005年 | 636篇 |
2004年 | 539篇 |
2003年 | 514篇 |
2002年 | 507篇 |
2001年 | 383篇 |
2000年 | 386篇 |
1999年 | 446篇 |
1998年 | 950篇 |
1997年 | 685篇 |
1996年 | 607篇 |
1995年 | 470篇 |
1994年 | 456篇 |
1993年 | 549篇 |
1992年 | 393篇 |
1991年 | 325篇 |
1990年 | 337篇 |
1989年 | 368篇 |
1988年 | 309篇 |
1987年 | 327篇 |
1986年 | 333篇 |
1985年 | 366篇 |
1984年 | 309篇 |
1983年 | 288篇 |
1982年 | 254篇 |
1981年 | 251篇 |
1980年 | 226篇 |
1979年 | 254篇 |
1978年 | 256篇 |
1977年 | 245篇 |
1976年 | 318篇 |
1975年 | 226篇 |
1974年 | 185篇 |
1973年 | 183篇 |
1972年 | 122篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Intrinsic Volume Changes of Self-propagating Synthesis 总被引:1,自引:0,他引:1
The final product(s) of self-propagating synthesis are shown to be intrinsically denser than the starting reactants. This behavior results in intrinsic decreases in the sample volume that increase with both the heat of reaction and the adiabatic combustion temperature. Forming of liquid product(s) during reaction simply adds another intrinsic source of porosity, i.e. changes in volume on product solidification. Thus, obtaining fully dense bodies from self-propagating synthesis requires a mechanism for reducing porosity, e.g. hot-pressing. 相似文献
42.
William S. Vorus 《Journal of Engineering Mathematics》2004,48(3-4):253-277
The subject of this paper is analysis of high-speed planing-craft wave impact, with the inclusion of hull-surface compliance. The analysis methods were extended in an effort to develop compliant-surface technology for wave-impact shock reduction. The practical outcome of this work, along with experimental cylinder drop-test evaluations, have been reported previously. The overall technology developed is composed of compliant plates over a sub-length of the boat hull. The plates are hinged at the boat keel and supported by vented air bags at the chines. Thus, the required analysis has coupled hydrodynamic, gas-dynamic, and structural-dynamic parts. Only the hydrodynamic part of the complete model is covered here. On the basis of the cylindrical geometry of the drop-test cylinder, two-dimensional theory has been used exclusively. The time history of the distribution of plating deflection predicted from the full analysis is imposed in the free-falling cylinder analysis to demonstrate execution of the hydrodynamic part of the complete coupled theory. The reductions in impact acceleration reported here are therefore the same as determined from the complete analysis. 相似文献
43.
A unified theoretical approach is presented for the calculation of the performance of the single-phase capacitor-start permanent-magnet (PM) ac line-start motor. The earlier work of Chang and of Finch and Lawrenson on capacitor reluctance motors is extended. As far as possible, a common set of reference frame transformations for steady-state, transient, and asynchronous performance is also provided, permitting the use of all the theory developed for the analysis of the balanced polyphase PM motor. A new approximate technique is given for estimating the average asynchronous torque/speed curve from computed acceleration curves. 相似文献
44.
Amanda Alliband Daniel W. Lenz Laura E. Stevenson Travis Whitmer Rex Cash Dennis Burns Sarah Hall William T.K. Stevenson 《Progress in Organic Coatings》2008
A model has been proposed to explain the failure of the original BMS10-39 epoxy paint on upper vertical surfaces in B-52 fuel tanks. The model involves interaction of the paint with DIEGME, a fuel system ice inhibitor (FSII) in jet fuel, that is distilled from the liquid fuel. In this communication, distillation experiments used to support the model are refined to better match the mass transfer of vapor from fuel in a B-52 fuel tank at close to room temperature. The interaction of these lower temperature distillates with the paint affirms the earlier model. On the basis of these experiments it is proposed that paint failure may be controlled or eliminated by reducing the level of DIEGME in the fuel. Proposed changes in military jet fuel composition are detailed. 相似文献
45.
Connecting people across the “digital divide” is as much a social effort as a technological one. We are developing a community-centred
approach to learn how interaction techniques can compensate for poor communication across the digital divide. We have incorporated
the lessons learned regarding social intelligence design in an abstraction and in a device called the SoftBridge. The SoftBridge
allows communication to flow from endpoints through adapters, getting converted if necessary, and out to destination endpoints.
Field trials are underway with two communities in South Africa: disadvantaged Deaf users and an isolated rural community.
Initial lessons learned show that we have to design user interfaces that allow users to understand and cope with delay. We
also learned that social concerns are often more important than the technical issues in designing such systems. 相似文献
46.
In classical model reference adaptive control, the goal is to design a controller to make the closed-loop system act like a prespecified reference model in the face of significant plant uncertainty. Typically, the controller consists of an identifier (or tuner) which is used to adjust the parameters of a linear time-invariant (LTI) compensator, and under suitable assumptions on the plant model uncertainty it is proven that asymptotic matching is achieved. However, the controller is typically highly nonlinear, and the closed loop system can exhibit undesirable behavior, such as large transients or a large control signal, especially if the initial parameter estimates are poor. Furthermore, its ability to tolerate time-varying parameters is typically limited. Here, we propose an alternative approach. Rather than estimating the plant or compensator parameters, instead we estimate what the control signal would be if the plant parameters and plant state were known and the "ideal LTI compensator" were applied. We end up with a linear periodic controller. Our assumptions are reasonably natural extensions of the classical ones to the time-varying setting; we allow rapid parameter variations, although we add a compactness requirement. We prove that we can obtain arbitrarily good tracking, explore the benefits and limitations of the approach, and provide a simulation study. 相似文献
47.
Yanqing Ji Hao Ying John Yen Shizhuo Zhu Daniel C. Barth‐Jones Richard E. Miller R. Michael Massanari 《国际智能系统杂志》2007,22(8):827-845
Discovering unknown adverse drug reactions (ADRs) in postmarketing surveillance as early as possible is highly desirable. Nevertheless, current postmarketing surveillance methods largely rely on spontaneous reports that suffer from serious underreporting, latency, and inconsistent reporting. Thus these methods are not ideal for rapidly identifying rare ADRs. The multiagent systems paradigm is an emerging and effective approach to tackling distributed problems, especially when data sources and knowledge are geographically located in different places and coordination and collaboration are necessary for decision making. In this article, we propose an active, multiagent framework for early detection of ADRs by utilizing electronic patient data distributed across many different sources and locations. In this framework, intelligent agents assist a team of experts based on the well‐known human decision‐making model called Recognition‐Primed Decision (RPD). We generalize the RPD model to a fuzzy RPD model and utilize fuzzy logic technology to not only represent, interpret, and compute imprecise and subjective cues that are commonly encountered in the ADR problem but also to retrieve prior experiences by evaluating the extent of matching between the current situation and a past experience. We describe our preliminary multiagent system design and illustrate its potential benefits for assisting expert teams in early detection of previously unknown ADRs. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 827–845, 2007. 相似文献
48.
Krenz William Robin Michael Barez Shirin Stark Lawrence 《IEEE transactions on bio-medical engineering》1985,(10):817-825
A model of the pathways controlling the size of the human pupil is presented. Computer simulation of this model demonstrates the role played by each of the elements in the pupil pathways. Simulations of the effects of drugs and a few common abnormalities in the system also help to illustrate the workings of the internal processes. Computer models of this type can be used as teaching aids or as tools for testing of hypotheses regarding the system. 相似文献
49.
Cellulose can be totally liquefied by heating to 350 °C in the presence of an aqueous phenolic solvent containing a catalyst. The main products are light aromatic hydrocarbons, benzofurans, heavier aromatic hydrocarbons such as substituted indanes and tetralin, and xanthenes. The variation of product distribution with catalyst was examined and it was found that in aqueous phenol, xanthene formation was enhanced by acidity. By substituting guaiacol for phenol, it was determined that most benzofuran formation involved the phenol solvent molecules, although a small proportion did not. This benzofuran may have arises from phenol generated from cellulose, the incorporation of phenol in the products being enhanced through a cage effect. 相似文献
50.
The technique of analytical pyrolysis has been used to characterize 40 similar mid-rank western Kentucky coals of widely differing ASTM Gieseler plasticity. Certain pyrolysis/g.c. variables were shown to correlate well with both ASTM Gieseler and isothermal plasticity. Highly plastic coals were shown to exhibit certain characteristic peaks in the 450 °C pyrogram which were absent in the pyrogram of the non-plastic coals. Two coals, representing the two extremes in plasticity, were selected for further study. After extraction with solvents such as DMF the characteristic peaks were absent in the 450 °C pyrogram of the extraction residue of the highly plastic coal. These peaks were also shown to decrease with increasing severity of air oxidation of the plastic coal. This technique appears to be a useful tool for the analysis of mid-rank plastic coals and supports the view that the substances contained in the bitumen fraction of these coals are involved in the development of the plastic state. 相似文献