全文获取类型
收费全文 | 556353篇 |
免费 | 2939篇 |
国内免费 | 1296篇 |
专业分类
电工技术 | 10189篇 |
综合类 | 543篇 |
化学工业 | 82190篇 |
金属工艺 | 23623篇 |
机械仪表 | 18113篇 |
建筑科学 | 11495篇 |
矿业工程 | 3809篇 |
能源动力 | 14919篇 |
轻工业 | 38725篇 |
水利工程 | 6579篇 |
石油天然气 | 13246篇 |
武器工业 | 36篇 |
无线电 | 64224篇 |
一般工业技术 | 114626篇 |
冶金工业 | 99884篇 |
原子能技术 | 13866篇 |
自动化技术 | 44521篇 |
出版年
2021年 | 5449篇 |
2020年 | 4414篇 |
2019年 | 5483篇 |
2018年 | 8747篇 |
2017年 | 8802篇 |
2016年 | 9542篇 |
2015年 | 5901篇 |
2014年 | 9703篇 |
2013年 | 26064篇 |
2012年 | 15183篇 |
2011年 | 20250篇 |
2010年 | 16073篇 |
2009年 | 18128篇 |
2008年 | 18688篇 |
2007年 | 18310篇 |
2006年 | 16235篇 |
2005年 | 14603篇 |
2004年 | 13774篇 |
2003年 | 13659篇 |
2002年 | 13027篇 |
2001年 | 12927篇 |
2000年 | 12085篇 |
1999年 | 12488篇 |
1998年 | 31671篇 |
1997年 | 21909篇 |
1996年 | 16854篇 |
1995年 | 12504篇 |
1994年 | 11037篇 |
1993年 | 11204篇 |
1992年 | 8213篇 |
1991年 | 7858篇 |
1990年 | 7708篇 |
1989年 | 7375篇 |
1988年 | 7140篇 |
1987年 | 6252篇 |
1986年 | 6157篇 |
1985年 | 6914篇 |
1984年 | 6397篇 |
1983年 | 5874篇 |
1982年 | 5334篇 |
1981年 | 5388篇 |
1980年 | 5138篇 |
1979年 | 5060篇 |
1978年 | 5082篇 |
1977年 | 5631篇 |
1976年 | 7044篇 |
1975年 | 4474篇 |
1974年 | 4231篇 |
1973年 | 4364篇 |
1972年 | 3733篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
S. Wolf 《Computer Physics Communications》2003,150(2):99-115
A revised and greatly improved version of the 3D continuum radiative transfer code MC3D is presented. It is based on the Monte Carlo method and solves the radiative transfer problem self-consistently. It is designed for the simulation of dust temperatures in arbitrary geometric configurations and the resulting observables: spectral energy distributions, wavelength-dependent images, and polarization maps. The main objective is the investigation of “dust-dominated” astrophysical systems such as young stellar objects surrounded by an optically thick circumstellar disk and an optically thin(ner) envelope, debris disks around more evolved stars, asymptotic giant branch stars, the dust component of the interstellar medium, and active galactic nuclei. 相似文献
992.
G. N. Apryshko 《Automatic Documentation and Mathematical Linguistics》2007,41(5):217-225
The structure of the biological module of the computer database in the ISIS/Base format of the Information System for Antitumor Agents of the GU Blokhin Cancer Research Center (CRC), RAMS, is given and the organizational and technological aspects of its loading, editing, retrieval, and use are described. 相似文献
993.
V. P. Deniskin A. M. Dmitriev V. I. Nalivaev I. I. Fedik P. M. Gavrilov N. A. Piskunova N. N. Khrennikov 《Atomic Energy》2007,103(3):675-680
The salient features of using a solid substance to cool the core of a nuclear reactor and the associated advantages and limitations
are examined. Conceptual proposals concerning the core design and the arrangement of the in-reactor space of a high-temperature
nuclear reactor with a solid coolant are presented. Evaluated data and some results for a model reactor are presented.
__________
Translated from Atomnaya énergiya, Vol. 103, No. 3, pp. 156–161, September, 2007. 相似文献
994.
A neuro-fuzzy approach to automatic diagnosis and location of stator inter-turn faults in CSI-fed PM brushless DC motors 总被引:2,自引:0,他引:2
Awadallah M.A. Morcos M.M. Gopalakrishnan S. Nehl T.W. 《Energy Conversion, IEEE Transaction on》2005,20(2):253-259
The paper presents a neuro-fuzzy-based perspective to the automation of diagnosis and location of stator-winding interturn short circuits in CSI-fed brushless dc motors. Performance of the drive under normal and short-circuit conditions are obtained through classical lumped-parameter network models. Waveforms of the electromagnetic torque and summation of phase voltages are monitored to develop two independent diagnostic algorithms. Diagnostic indices derived from the characteristic waveforms using discrete Fourier transform (DFT) lead to identifying the number of shorted turns. Fault location is achieved through a different set of indices extracted by the short-time Fourier transform (STFT). Adaptive neuro-fuzzy inference systems (ANFIS) are trained based on simulation results to automate the diagnostic process. ANFIS testing along with the good agreement between simulated and measured waveforms show the effectiveness of the proposed techniques. 相似文献
995.
This research used a weight-of-evidence approach to evaluate sources of contaminants in a drinking water watershed that serves as part of the City of Boston's water supply. The approach incorporated land use analysis using GIS, sanitary surveys, traditional water quality monitoring and microbial source tracking (MST) tools. Case-study tributaries were selected based on elevated faecal coliform counts. Land use analysis and sanitary surveys were used to identify suspected microbial sources, including residential septic systems, agricultural animal operations, commercial/industrial operations and wildlife activity. Sampling sites were selected to hydrologically isolate potential contamination sources. Samples were collected seasonally over 1 year and analysed for traditional and MST parameters. Results demonstrated that both septic systems and a horse stable were contributing microbial loads in the first tributary. In the second tributary, septic systems from the townhouses were contributing microbial loads while a plant nursery was contributing organic matter. This evidence was used to evaluate best management practices to mitigate the contamination. 相似文献
996.
The fate of bromine species from human activity is affected by the bromination reaction in water treatment processes. In this study, kinetic information of the reaction between hypobromous acid (HOBr) and seven different natural organic matters (NOM) was collected by sequential stopped-flow techniques. Multiple reaction phases were found in the reaction between HOBr and NOM. The number of reaction sites for the faster reaction phase ranged from 0.26 to 0.92 micromole (mg DOC)(-1), and was correlated to both SUVA and specific phenolic content at pH 7.0. The apparent second-order rate constants for the faster reaction phase at pH 7.0 ranged from 5.4 x 10(5) to 1.4 x 10(6) M(-1) x s(-1), indicating that vanillin-like structures are involved in this reaction phase. 相似文献
997.
María Esther Diupotex-Chong Néstor J Cazzaniga Alejandra Hernández-Santoyo José Miguel Betancourt-Rule 《Biocell》2004,28(3):279-285
Mitotic chromosomes of the freshwater snail Pomacea patula catemacensis (Baker 1922) were analyzed on gill tissue of specimens from the type locality (Lake Catemaco, Mexico). The diploid number of chromosomes is 2n = 26, including nine metacentric and four submetacentric pairs; therefore, the fundamental number is FN = 52, No sex chromosomes could be identified. The same chromosome number and morphology were already reported for P. flagellata, i.e., the other species of the genus living in Mexico. The basic haploid number for family Ampullariidae was reported to be n = 14 in the literature; so, its reduction to n = 13 is probably an apomorphy of the Mexican Pomacea snails. Lanistes bolteni, from Egypt, also shows n = 13, but its karyotype is much more asymmetrical, and seems to have evolved independently from P. flagellata and P. patula catemacensis. The nominotypical subspecies, P. patula patula (Reeve 1856), is a poorly known taxon, whose original locality is unknown. A taxonomical account is presented here, and a Mexican origin postulated as the most parsimonious hypothesis. 相似文献
998.
Drives to increase the volume of customers who use self-service channels are a common strategic goal. The promise of significant cost reduction is a tempting carrot. Couple this with the vision of customers benefiting from quick, effective and usable contact channels, avoiding human error (except perhaps their own!) or potential frustration at being passed around to an ‘appropriate’ contact centre advisor is a very worthy vision … but is it as simple as this? In this discussion paper the authors speculate that self-service, while potentially being a revenue-saving opportunity, could also erode customer satisfaction and loyalty. Self-service doubtless appeals to some customers, but is it what all customers want? Do organisations understand enough about customer experience to enable them to build successful self-service channels, i.e. those that are useful, usable and used by customers? Do businesses really want to lose the opportunity to actually talk to customers and gain insight and knowledge about them? What impact will increased levels of self-service have on more traditional channels, such as customer contact centres? This paper also discusses evidence that self-service can actually serve to increase communication between organisations and customers across multiple channels. For many organisations, the Internet has actually resulted in more calls to the contact centre, not less. The seductive promise of self-service to cut costs through reducing call volumes may be an empty one. 相似文献
999.
1000.
Delorme A. Makeig S. 《IEEE transactions on neural systems and rehabilitation engineering》2003,11(2):133-137
We analyzed 15 sessions of 64-channel electroencephalographic (EEG) data recorded from a highly trained subject during sessions in which he attempted to regulate power at 12 Hz over his left- and right-central scalp to control the altitude of a cursor moving toward target boxes placed at the top-, middle-, or bottom-right of a computer screen. We used infomax independent component analysis (ICA) to decompose 64-channel EEG data from trials in which the subject successfully up- or down-regulated the measured EEG signals. Applying time-frequency analysis to the time courses of activity of several of the resulting 64 independent EEG components revealed that successful regulation of the measured activity was accompanied by extensive, asymmetrical changes in power and coherence, at both nearby and distant frequencies, in several parts of cortex. A more complete understanding of these phenomena could help to explain the nature and locus of learned regulation of EEG rhythms and might also suggest ways to further optimize the performance of brain-computer interfaces. 相似文献