全文获取类型
收费全文 | 36825篇 |
免费 | 1674篇 |
国内免费 | 1902篇 |
专业分类
电工技术 | 972篇 |
技术理论 | 1篇 |
综合类 | 1766篇 |
化学工业 | 2411篇 |
金属工艺 | 1318篇 |
机械仪表 | 3455篇 |
建筑科学 | 2315篇 |
矿业工程 | 697篇 |
能源动力 | 948篇 |
轻工业 | 855篇 |
水利工程 | 389篇 |
石油天然气 | 837篇 |
武器工业 | 327篇 |
无线电 | 3101篇 |
一般工业技术 | 1818篇 |
冶金工业 | 950篇 |
原子能技术 | 421篇 |
自动化技术 | 17820篇 |
出版年
2024年 | 65篇 |
2023年 | 311篇 |
2022年 | 454篇 |
2021年 | 665篇 |
2020年 | 619篇 |
2019年 | 517篇 |
2018年 | 583篇 |
2017年 | 758篇 |
2016年 | 942篇 |
2015年 | 1003篇 |
2014年 | 1873篇 |
2013年 | 1813篇 |
2012年 | 1940篇 |
2011年 | 2684篇 |
2010年 | 1828篇 |
2009年 | 1903篇 |
2008年 | 2073篇 |
2007年 | 2567篇 |
2006年 | 2498篇 |
2005年 | 2341篇 |
2004年 | 2076篇 |
2003年 | 2064篇 |
2002年 | 1575篇 |
2001年 | 1236篇 |
2000年 | 1001篇 |
1999年 | 919篇 |
1998年 | 772篇 |
1997年 | 596篇 |
1996年 | 519篇 |
1995年 | 474篇 |
1994年 | 331篇 |
1993年 | 249篇 |
1992年 | 193篇 |
1991年 | 131篇 |
1990年 | 114篇 |
1989年 | 128篇 |
1988年 | 92篇 |
1987年 | 54篇 |
1986年 | 57篇 |
1985年 | 64篇 |
1984年 | 54篇 |
1983年 | 42篇 |
1982年 | 38篇 |
1981年 | 38篇 |
1980年 | 25篇 |
1979年 | 22篇 |
1978年 | 20篇 |
1977年 | 15篇 |
1976年 | 38篇 |
1975年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
A new type of a single-axis azimuthal tracker is presented. The novel feature of this tracker is the ability to move the collector’s plane in two directions through a special support structure. This structure consists of a sliding mechanism on the central axis and a curved window on the cylindrical surface coaxial to the central axis. Consequently, the proposed novel heliotrope behaves similarly to a two-axis tracker. Two different windows designed on the cylindrical surface may be used to provide very high efficiencies throughout a year. Several performance measurements have been conducted on this novel tracker, a polar tracker and the reference two-axis tracker. Pyranometers, appropriately calibrated, were installed on all three systems to record the global incoming irradiance on the collector’s plane. It is shown that the new tracker system can be very efficient since its plane intercepts, at least, 98% of the insolation with respect to a two-axis tracker. The proposed system can be utilized in solar-related applications (photovoltaic or thermal). 相似文献
62.
说明了在异步串行通信(RS-232)的工作方式下,对所接收的数据进行接收、处理,丢弃乱码,并进行保存的可靠方法,并给出了相关的VC 语言程序. 相似文献
63.
T.S. Nguyen A.P.S. Selvadurai G. Armand 《International Journal of Rock Mechanics and Mining Sciences》2005,42(5-6):639
Buffer materials being considered as engineered barriers in nuclear fuel waste (NFW) disposal systems possess a pronounced nonlinear behaviour in the unsaturated state. In order to simulate such non-linear responses,the authors adopted an incrementally nonlinear poro-elastic approach where the coefficients of the governing equations are assumed to be functions of suction and the void ratio. These functions are in turn developed from a state-surface equation obtained from suction-controlled oedometric tests. In this paper we show the derivation of the governing equations of the poro-elastic model. A finite element computer code, FRACON, was developed by the authors to numerically solve the above equations. We first use the code to simulate laboratory tests to characterize the swelling properties of a typical bentonite. That same bentonite was used in the FEBEX in-situ heater experiment, conducted at the Grimsel site, Switzerland. The FRACON code was also used to perform blind predictions of the FEBEX heater experiment. It is shown that the model correctly predicts drying of the bentonite near the heaters and re-saturation near the rock interface. The evolution of temperature and the heater thermal output were also reasonably well predicted by the model. The trends in the total stresses developed in the bentonite were correctly predicted; the absolute values however were underestimated probably due to the omission of pore pressure build-up in the rock mass. 相似文献
64.
Psychologists' appropriation of language and ideas from Thomas Kuhn's (1962, 1970b) The Structure of Scientific Revolutions reveals deep and contradictory concerns about truth, science, and the progress of the field. The author argues that psychologists, uncomfortably straddling natural and social science traditions, reference Structure for 2 reasons largely overlooked: first, because it presents an intermediate, naturalistic position in the war between relativist and rationalist views of scientific truth, and second, because it presents a psychologized model of scientific change. The author suggests that the history of this mutual influence--psychologists being influenced by Kuhn and vice versa--may usefuly inform current practices of psychological science. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
65.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
66.
Dealing with discrepancies in data is still a big challenge in data integration systems. The problem occurs both during eliminating duplicates from semantic overlapping sources as well as during combining complementary data from different sources. Though using SQL operations like grouping and join seems to be a viable way, they fail if the attribute values of the potential duplicates or related tuples are not equal but only similar by certain criteria. As a solution to this problem, we present in this paper similarity-based variants of grouping and join operators. The extended grouping operator produces groups of similar tuples, the extended join combines tuples satisfying a given similarity condition. We describe the semantics of this operator, discuss efficient implementations for the edit distance similarity and present evaluation results. Finally, we give examples of application from the context of a data reconciliation project for looted art. 相似文献
67.
68.
69.
The dynamic flexibility (DF) and improved dynamic flexibility (IDF) methods can be applied to extract constrained structural modes from free-free modal test data. The residual flexibility method is also good for boundaries of constrained structure with rigid supports. Under elastic support boundary conditions both the DF and residual flexibility methods cannot produce accurate results. This paper expands the previously published IDF method to become a more general approach for structural design engineers. A new method called the general dynamic flexibility (GDF) method has been developed in this paper to extract constrained structural modes from free test data. The GDF method can always be applied as follows: (1) when the boundary support stiffness is very stiff, the GDF method can accurately obtain results from rigid support as by Liu et al. in 2001 and Zhang and Wei in 2003; (2) when the support stiffness is soft, the present method can produce results similar to those free-free modal parameters measured by hanging structures using rubber band; (3) when the support stiffness is zero, the method can reproduce true free-free modal parameters; and (4) when the support stiffness has any finite values, the GDF method can also achieve satisfactory results for engineering use. The algorithm included in the GDF method converges rapidly and is numerically stable in the analysis. This feature is very practical for many engineering applications for using the GDF method. 相似文献
70.
Awareness of the construction environment can be improved by automatic three-dimensional (3D) sensing and modeling of job sites in real time. Commercially available 3D modeling approaches based on range scanning techniques are capable of modeling static objects only, and thus cannot model dynamic objects in real time in an environment comprised of moving humans, equipment, and materials. Emerging prototype video range cameras offer an alternative by facilitating affordable, wide field of view, dynamic object tracking at frame rates better than 1?Hz (real time). This paper describes a methodology to model, detect, and track the position of static and moving objects in real time, based on data obtained from video range cameras. Experiments with this technology have produced results that indicate that video rate 3D data acquisition and analysis of construction environments can support effective modeling, detection, and tracking of project resources. This approach to job site awareness has inherent value and broad application. In combination with effective management practices and other sensing techniques, this technology has the potential to significantly improve safety on construction job sites. 相似文献