全文获取类型
收费全文 | 33799篇 |
免费 | 2172篇 |
国内免费 | 31篇 |
专业分类
电工技术 | 242篇 |
综合类 | 18篇 |
化学工业 | 6826篇 |
金属工艺 | 645篇 |
机械仪表 | 722篇 |
建筑科学 | 944篇 |
矿业工程 | 75篇 |
能源动力 | 599篇 |
轻工业 | 5647篇 |
水利工程 | 318篇 |
石油天然气 | 121篇 |
武器工业 | 5篇 |
无线电 | 1283篇 |
一般工业技术 | 5830篇 |
冶金工业 | 8055篇 |
原子能技术 | 122篇 |
自动化技术 | 4550篇 |
出版年
2024年 | 66篇 |
2023年 | 307篇 |
2022年 | 350篇 |
2021年 | 823篇 |
2020年 | 703篇 |
2019年 | 802篇 |
2018年 | 1390篇 |
2017年 | 1346篇 |
2016年 | 1383篇 |
2015年 | 1070篇 |
2014年 | 1262篇 |
2013年 | 2654篇 |
2012年 | 1976篇 |
2011年 | 1798篇 |
2010年 | 1492篇 |
2009年 | 1331篇 |
2008年 | 1277篇 |
2007年 | 1199篇 |
2006年 | 803篇 |
2005年 | 692篇 |
2004年 | 646篇 |
2003年 | 585篇 |
2002年 | 574篇 |
2001年 | 421篇 |
2000年 | 392篇 |
1999年 | 441篇 |
1998年 | 2399篇 |
1997年 | 1631篇 |
1996年 | 1039篇 |
1995年 | 622篇 |
1994年 | 475篇 |
1993年 | 573篇 |
1992年 | 208篇 |
1991年 | 206篇 |
1990年 | 160篇 |
1989年 | 164篇 |
1988年 | 169篇 |
1987年 | 147篇 |
1986年 | 122篇 |
1985年 | 158篇 |
1984年 | 133篇 |
1983年 | 102篇 |
1982年 | 138篇 |
1981年 | 154篇 |
1980年 | 169篇 |
1979年 | 86篇 |
1978年 | 79篇 |
1977年 | 280篇 |
1976年 | 632篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
981.
David Sánchez Montserrat Batet David Isern Aida Valls 《Expert systems with applications》2012,39(9):7718-7728
Estimation of the semantic likeness between words is of great importance in many applications dealing with textual data such as natural language processing, knowledge acquisition and information retrieval. Semantic similarity measures exploit knowledge sources as the base to perform the estimations. In recent years, ontologies have grown in interest thanks to global initiatives such as the Semantic Web, offering an structured knowledge representation. Thanks to the possibilities that ontologies enable regarding semantic interpretation of terms many ontology-based similarity measures have been developed. According to the principle in which those measures base the similarity assessment and the way in which ontologies are exploited or complemented with other sources several families of measures can be identified. In this paper, we survey and classify most of the ontology-based approaches developed in order to evaluate their advantages and limitations and compare their expected performance both from theoretical and practical points of view. We also present a new ontology-based measure relying on the exploitation of taxonomical features. The evaluation and comparison of our approach’s results against those reported by related works under a common framework suggest that our measure provides a high accuracy without some of the limitations observed in other works. 相似文献
982.
983.
Ricardo Soto Hakan Kjellerstrand Orlando Durán Broderick Crawford Eric Monfroy Fernando Paredes 《Expert systems with applications》2012,39(13):11423-11427
Cell formation consists in organizing a plant as a set of cells, each of them containing machines that process similar types or families of parts. The idea is to minimize the part flow among cells in order to reduce costs and increase productivity. The literature presents different approaches devoted to solve this problem, which are mainly based on mathematical programming and on evolutionary computing. Mathematical programming can guarantee a global optimal solution, however at a higher computational cost than an evolutionary algorithm, which can assure a good enough optimum in a fixed amount of time. In this paper, we model and solve this problem by using state-of-the-art constraint programming (CP) techniques and Boolean satisfiability (SAT) technology. We present different experimental results that demonstrate the efficiency of the proposed optimization models. Indeed, CP and SAT implementations are able to reach the global optima in all tested instances and in competitive runtime. 相似文献
984.
Many techniques have been proposed for credit risk assessment, from statistical models to artificial intelligence methods. During the last few years, different approaches to classifier ensembles have successfully been applied to credit scoring problems, demonstrating to be generally more accurate than single prediction models. The present paper goes one step beyond by introducing composite ensembles that jointly use different strategies for diversity induction. Accordingly, the combination of data resampling algorithms (bagging and AdaBoost) and attribute subset selection methods (random subspace and rotation forest) for the construction of composite ensembles is explored with the aim of improving the prediction performance. The experimental results and statistical tests show that this new two-level classifier ensemble constitutes an appropriate solution for credit scoring problems, performing better than the traditional single ensembles and very significantly better than individual classifiers. 相似文献
985.
M. Jergel T. Melíšek H Allárová D. I. Belyj V. P. Kutepov A. J. Izrailev D. Synak J. Neuschl J. Ivan 《Journal of Materials Science》1982,17(6):1579-1584
The influence of the presence of oxygen in the Nb-Zr substrate upon some physical and mechanical properties of the Nb-ZrO2 substrate and/or Nb3Sn tape superconductor prepared from such a substrate has been studied. The results have shown that the Nb3Sn grains are much finer in the case of Nb-ZrO2, than those obtained on Nb-Zr substrate. As a result, both the electrical and mechanical properties have been substantially improved. The critical current at a field of 5 T increased by between 100 and 200 %, the alternating current losses decreased by about one order of magnitude, the tensile strength increased by about a factor of three and the microhardness value also increased by about a factor of three for oxygen contents in the range 0.03 to 0.70 wt%. The specific resistance of this substrate increased at the same time from 17 to 22 cm and the relative elongation decreased from 5 to 3 %. 相似文献
986.
The sorption and deposition of technetium species formed from TcO
4
–
at gold and platinized surfaces was followed by a coupledin situ radiometric and electrochemical technique. It was found: (i) that a layer of TcO2 species is formed preceding the massive deposition of technetium species, and (ii) that the deposition process is not connected with hydrogen evolution or reaction with adsorbed hydrogen as has been assumed in the literature. An important new finding, the electrocatalytic reduction of ClO4 ions at surfaces covered by technetium species, was demonstrated on the basis of a comparative study of the phenomena observed in H2SO4 and HClO4 supporting electrolytes.This paper is dedicated to Professor Brian E. Conway on the occasion of his 65th birthday, and in recognition of his outstanding contribution to electrochemisty. 相似文献
987.
A Santavá J Hyánek A Mrskos R Pospísil M Macek Z Kaspárková A Zwinger M Slouková J Santavy 《Canadian Metallurgical Quarterly》1976,31(10):559-562
Trasditional Chinese medicine is based on inductive-synthetic reasoning with regard to all life processes, in contrast to the causal-analytic orientation in our Western medicine. This philosophical approach is based on a system of comparisons (equivalents), referred to as Yin and Yang. Vital functions are seen as "energizing" processes, whereby the acupuncture points and the system of meridians are seen as a means of regulation for this "energy". A disturbed balance in this energy results in illness. The therapy according to the acupuncture method is to acheive a balance in the disturbed flow of energy by means of acupuncture points. By utilizing biophysical methods of measurement, it is possible to prove that a change in this energy takes place. The complex active principle which results in the effectiveness of acupuncture includes neurophysiological, biochemical and biophysical functional processes. 相似文献
988.
We have found experimentally that rf SQUID's working in a nonhysteretic mode with small critical currents give exactly at resonance and at very low rf bias a triangular pattern with a period equal to half of one elementary quantum of magnetic flux. We discuss a possible explanation of this peculiar result. 相似文献
989.
The student population at Edinburgh University was surveyed in 1974 to collect data on women's menstrual cycles and to examine sources of individual differences in reporting symptoms associated with the cycle. 2542 non-oral contraceptive (OC) users and 756 OC users provided data. Both sets of respondents were questioned about the occurrence, both premenstrually and during menstruation, of 9 symptoms. The "physical" symptoms (stomachache, backache, nausea, fainting) were more often reported during menstruation, whereas the so-called "emotional" symptoms (lethargy, irritability, depression, tension, headache) had a greater prevalence premenstrually. When the 9 menstrual symptoms were broken down by students' fields of concentration, arts students were found to report more "emotional" symptoms than those in the sciences and professions (medicine and law). Further analysis showed that only and 1st born children were slightly less likely to report symptoms than those whose nearest sibling is 7 or more years older or younger or later born children. A similar trend was found for the reporting of illness in an earlier analysis of data from this sample. When cycle length and reqularity were analyzed together, women with long and regular cycles were found to have the lowest proportion reporting symptoms during menstruating with the exception of tension, nausea, and fainting, and women with short and irregular cycles had a correspondingly high incidence of all symptoms. In addition, women with more regular cycles were more likely to report infrequent recall of dreams than those with irregular cycles. Overall, the women who are most likely to report menstrual symptoms, especially those of an "emotional" character, are more likely to report other illnesses with emotional connotations, recall their dreams more frequently, show a preference for the arts, and tend to have been brought up with older siblings. This cluster of personality attributes defines an "expressive" personaltiy in contrast to the more "controlled" style of women at the other extreme. 相似文献
990.
H Villalobos ES Canales A Zárate J Soria C MacGregor 《Canadian Metallurgical Quarterly》1976,83(2):236-242
Serum levels of prolactin (PRL), FSH, LH and oestradiol-17 beta were determined by radioimmunoassay in 57 lactating women and in 20 women in whom lactation was inhibited by ergocryptine (CS-154). Women who breast fed their infants exhibited high PRL levels which abruptly declined within 48 h post-partum, and remained low for the duration of the study. Serum FSH was undetectable during the first week post-partum in lactating as well as in CB-154 treated women. Thereafter, lactating women showed increasing FSH levels which reached a maximum by the third week post-partum. These FSH values were higher in lactating women than in the CBS-154 treated group. In contrast, LH levels were higher in those women receiving CB-154. Serum oestradiol-17 beta remained in low levels throughout the study, and no difference was observed between the two groups of subjects. From these results it seems that: 1) inhibition of PRL secretion leads to a faster recovery of gonadotrophin secretion toward the "menstrual type", and 2) PRL suppression produces no effect on the ovarian oestrogen production. 相似文献