全文获取类型
收费全文 | 51278篇 |
免费 | 1358篇 |
国内免费 | 257篇 |
专业分类
电工技术 | 715篇 |
综合类 | 719篇 |
化学工业 | 6069篇 |
金属工艺 | 790篇 |
机械仪表 | 1145篇 |
建筑科学 | 1171篇 |
矿业工程 | 402篇 |
能源动力 | 675篇 |
轻工业 | 2482篇 |
水利工程 | 629篇 |
石油天然气 | 92篇 |
武器工业 | 6篇 |
无线电 | 3579篇 |
一般工业技术 | 4921篇 |
冶金工业 | 22590篇 |
原子能技术 | 271篇 |
自动化技术 | 6637篇 |
出版年
2023年 | 276篇 |
2022年 | 217篇 |
2021年 | 277篇 |
2020年 | 155篇 |
2019年 | 176篇 |
2018年 | 636篇 |
2017年 | 859篇 |
2016年 | 1230篇 |
2015年 | 969篇 |
2014年 | 702篇 |
2013年 | 936篇 |
2012年 | 2569篇 |
2011年 | 2906篇 |
2010年 | 1044篇 |
2009年 | 1192篇 |
2008年 | 1045篇 |
2007年 | 1031篇 |
2006年 | 928篇 |
2005年 | 3647篇 |
2004年 | 2846篇 |
2003年 | 2336篇 |
2002年 | 1093篇 |
2001年 | 959篇 |
2000年 | 485篇 |
1999年 | 809篇 |
1998年 | 6605篇 |
1997年 | 4112篇 |
1996年 | 2713篇 |
1995年 | 1587篇 |
1994年 | 1187篇 |
1993年 | 1242篇 |
1992年 | 324篇 |
1991年 | 379篇 |
1990年 | 371篇 |
1989年 | 323篇 |
1988年 | 343篇 |
1987年 | 273篇 |
1986年 | 256篇 |
1985年 | 198篇 |
1984年 | 100篇 |
1983年 | 100篇 |
1982年 | 137篇 |
1981年 | 215篇 |
1980年 | 212篇 |
1979年 | 80篇 |
1978年 | 123篇 |
1977年 | 648篇 |
1976年 | 1362篇 |
1975年 | 110篇 |
1971年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Mg-Al hydrotalcites intercalated with five different interlayer anions—CO32−, SO42−, Cl−, HPO42− or terephthalate—were synthesized by either the coprecipitation or ion-exchange method. The structure of the as-synthesized samples and the presence of intended anions in the interlayer gallery of hydrotalcites were determined by X-ray diffraction and FTIR spectroscopy. On calcination at 600 °C the materials were transformed into mixed metal oxides. The kind of the counterbalancing anions present in the parent hydrotalcite influences strongly textural parameters of the obtained Mg-Al oxides. Both temperature-programmed desorption of NH3 and CO2, and test reaction of 2-methyl-3-butyn-2-ol (MBOH) conversion were used to determine the acidity and basicity of the samples. The hydrotalcite derived mixed Mg-Al oxides showed the presence of Brønsted and Lewis acid and base sites. However, the strong basic character of the solids caused that acetone and acetylene were observed as the major products of MBOH conversion. 相似文献
102.
E St?lberg S St?lberg M Melander K Arimura 《Computer methods and programs in biomedicine》1991,34(2-3):219-227
Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation. 相似文献
103.
Cristina Ca?ero Nikolaos Thomos George A Triantafyllidis George C Litos Michael Gerassimos Strintzis 《IEEE transactions on information technology in biomedicine》2005,9(1):44-49
Ultrasound imaging allows the evaluation of the degree of emergency of a patient. However, in some instances, a well-trained sonographer is unavailable to perform such echography. To cope with this issue, the Mobile Tele-Echography Using an Ultralight Robot (OTELO) project aims to develop a fully integrated end-to-end mobile tele-echography system using an ultralight remote-controlled robot for population groups that are not served locally by medical experts. This paper focuses on the user interface of the OTELO system, consisting of the following parts: an ultrasound video transmission system providing real-time images of the scanned area, an audio/video conference to communicate with the paramedical assistant and with the patient, and a virtual-reality environment, providing visual and haptic feedback to the expert, while capturing the expert's hand movements. These movements are reproduced by the robot at the patient site while holding the ultrasound probe against the patient skin. In addition, the user interface includes an image processing facility for enhancing the received images and the possibility to include them into a database. 相似文献
104.
Axial-field electrical machines offer an alternative to the conventional machines. In the axial-field machine, the airgap flux is axial in direction and the active current carrying conductors are radially positioned. This paper presents the design characteristics, special features, manufacturing aspects and potential applications for axial-field electrical machines. The experimental results from several prototypes, including d.c. machines, synchronous machines and single-phase machines are given. The special features of the axial-field machine, such as its planar and adjustable airgap, flat shape, ease of diversification, etc., enable axial-field machines to have distinct advantages over conventional machines in certain applications, especially in special-purpose applications. 相似文献
105.
Zhang Z.G. Chan S.C. Tsui K.M. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(6):576-580
This paper proposes a new Kalman-filter-based recursive frequency estimator for discrete-time multicomponent sinusoidal signals whose frequencies may be time-varying. The frequency estimator is based on the linear prediction approach and it employs the Kalman filter to track the linear prediction coefficients (LPCs) recursively. Frequencies of the sinusoids can then be computed using the estimated LPCs. Due to the coloredness of the linear prediction error, an iterative algorithm is employed to estimate the covariance matrix of the prediction error and the LPCs alternately in the Kalman filter in order to improve the tracking performance. Simulation results show that the proposed Kalman-filter-based iterative frequency estimator can achieve better tracking results than the conventional recursive least-squares-based estimators. 相似文献
106.
Min Chan Kim Dong Won Lee Chang Kyun Choi 《Korean Journal of Chemical Engineering》2008,25(6):1239-1244
When a horizontal homogeneous solid is melted from below, convection can be induced in a thermally unstable melt layer. In
this study the onset of buoyancy-driven convection during time-dependent melting is investigated by using similarly transformed
disturbance equations. The critical Rayleigh numbers based on the melt-layer thickness are found numerically for various conditions.
For small superheats, the present predictions approach the well known results of classical Rayleigh-Bénard problems, that
is, critical Rayleigh numbers are located between 1,296 and 1,708, regardless of the Prandtl number. However, for high superheats
the critical Rayleigh number increases with an increase in phase change rate but with decrease in Prandtl number. 相似文献
107.
Pulkki-R?back Laura; Elovainio Marko; Kivim?ki Mika; Raitakari Olli T.; Keltikangas-J?rvinen Liisa 《Canadian Metallurgical Quarterly》2005,24(3):307
This study examined associations of temperament at ages 6 to 12 with body-mass index (BMI) and waist circumference (WC) at ages 24 to 30 years. The participants were 619 men and women derived from the population-based Cardiovascular Risk in Young Finns Study. Temperament was operationalized as (negative) emotionality, sociability, and activity. High emotionality predicted increased BMI, independently of WC, and independently of childhood and adulthood risk factors for adult obesity. None of the temperament dimensions had any associations with WC after controlling for BMI. The findings suggest that temperamental difficulty in childhood may be a useful risk indicator for general body mass in adulthood, and the mechanisms relating temperament with body mass should be further explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
108.
Motivated by a study of similar problems stated for factors of words, we study forbidden subwords of a language or a word. A procedure for obtaining the set of all words avoiding a given set of subwords is presented. On the other hand, an algorithm for computing the set of minimal forbidden subwords for a word is given. The case of a two-letter alphabet appears to be particularly interesting and it is considered separately. 相似文献
109.
110.
Cyclic oxidation response of multiphase niobium-based alloys 总被引:4,自引:0,他引:4
Kwai S. Chan 《Metallurgical and Materials Transactions A》2004,35(2):589-597
Cyclic oxidation tests were performed on multiphase Nb-based alloys containing silicide, Laves, and Nb solid solution phases.
In particular, the oxidation resistance of six alloys with various compositions (Nb, Ti, Hf, Cr, Ge, and Si) and microstructures
was characterized by thermal cycling from ambient temperature to a peak temperature that ranges from 900 °C to 1400 °C. Weight
change data were obtained and the corresponding spalled oxides were collected and identified by X-ray diffraction. The results
indicated that Nb-based alloys formed a mixture of CrNbO4, Nb2O5, and Nb2O5 · TiO2, with possibly small amounts of SiO2 or GeO2. The oxidation resistance was improved when CrNbO4 formed instead of Nb2O5 and Nb2O5 · TiO2. These results were used to assess the influence of microstructure and composition on the oxidation resistance of multiphase
Nb-based alloys. 相似文献