全文获取类型
收费全文 | 35836篇 |
免费 | 1486篇 |
国内免费 | 118篇 |
专业分类
电工技术 | 414篇 |
综合类 | 234篇 |
化学工业 | 6108篇 |
金属工艺 | 739篇 |
机械仪表 | 810篇 |
建筑科学 | 1025篇 |
矿业工程 | 94篇 |
能源动力 | 1105篇 |
轻工业 | 4099篇 |
水利工程 | 243篇 |
石油天然气 | 157篇 |
武器工业 | 8篇 |
无线电 | 3000篇 |
一般工业技术 | 5087篇 |
冶金工业 | 9944篇 |
原子能技术 | 297篇 |
自动化技术 | 4076篇 |
出版年
2024年 | 55篇 |
2023年 | 191篇 |
2022年 | 541篇 |
2021年 | 864篇 |
2020年 | 625篇 |
2019年 | 718篇 |
2018年 | 830篇 |
2017年 | 897篇 |
2016年 | 914篇 |
2015年 | 705篇 |
2014年 | 1055篇 |
2013年 | 1677篇 |
2012年 | 1509篇 |
2011年 | 1912篇 |
2010年 | 1404篇 |
2009年 | 1466篇 |
2008年 | 1332篇 |
2007年 | 1114篇 |
2006年 | 915篇 |
2005年 | 957篇 |
2004年 | 1013篇 |
2003年 | 928篇 |
2002年 | 879篇 |
2001年 | 770篇 |
2000年 | 607篇 |
1999年 | 706篇 |
1998年 | 3107篇 |
1997年 | 1934篇 |
1996年 | 1395篇 |
1995年 | 855篇 |
1994年 | 672篇 |
1993年 | 780篇 |
1992年 | 266篇 |
1991年 | 356篇 |
1990年 | 311篇 |
1989年 | 294篇 |
1988年 | 260篇 |
1987年 | 237篇 |
1986年 | 213篇 |
1985年 | 244篇 |
1984年 | 133篇 |
1983年 | 99篇 |
1982年 | 138篇 |
1981年 | 139篇 |
1980年 | 149篇 |
1979年 | 95篇 |
1978年 | 84篇 |
1977年 | 228篇 |
1976年 | 467篇 |
1975年 | 94篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
221.
Lucila R. Geymonat de Destefani T. W. Allan Whitfield 《Color research and application》2008,33(1):55-60
A feature of the empirical literature in colour psychology is that little attention has been given to how people in real settings engage in colour selection. Surprisingly, with rare exceptions, we know almost nothing about this. Besides its theoretical significance within psychology, this question has practical implications for industries where colour choice is important. A study is reported into that most ubiquitous of activities, selecting a paint colour for the home. This used a retrospective method supported by qualitative data analysis (NVivo) in which participants described their process of colour selection. The results indicate a process that is far from uniform, but one that consists of two essential stages. The first involves arriving at what we refer to as an affective specification of the qualities sought. Once constructed, this leads to the second stage of matching colour attributes to that specification. Selecting a wall colour emerges as a surprisingly complex process, and one that corresponds more closely to a search than to a simple affective choice. A parallel is drawn with decision research, particularly the field of naturalistic decision‐making. From participants' reports, colour selection also emerges as a process that women appear to understand better than men. © 2007 Wiley Periodicals, Inc. Col Res Appl, 33, 55–60, 2008 相似文献
222.
Raquel Alves dos Santos Teresinha Rosa Cabral Isabel Rosa Cabral Lusania Maria Greggi Antunes Cristiane Pontes Andrade Plínio Cerqueira dos Santos Cardoso Marcelo de Oliveira Bahia Claudia Pessoa José Luis Martins do Nascimento Rommel Rodríguez Burbano Catarina Satie Takahashi 《Biocell》2008,32(2):195-200
Physalis angulata L (Solanaceae) is a medicinal plant from North of Brazil, whose different extracts and infusions are commonly used in the popular medicine for the treatment of malaria, asthma, hepatitis, dermatitis and rheumatism. However, the genotoxic effects of P. angulata on human cells is not well known. The main purpose of the present study was to evaluate the in vitro genotoxic effects of aqueous extract of P. angulata using the comet assay and the micronucleus assay in human lymphocytes provided from 6 healthy donors. Treatments with P. angulata extracts were performed in vitro in order to access the extent of DNA damage. The comet assay has shown that treatments with P. angulata at 0.5, 1.0, 2.0, 3.0 and 6.0 microg/mL in culture medium were genotoxic. Lymphocytes treated with P. angulata at the concentrations of 3.0 and 6.0 microg/mL in culture medium showed a statistically significant increase in the frequency of micronucleus (p<0.05), however, the cytokinesis blocked proliferation index (CBPI) was not decreased after P. angulata treatment. In conclusion, the present work demonstrated the genotoxic effects of P. angulata extract on human lymphocytes in vitro. 相似文献
223.
Luciana Juncioni de Arauz Angela Faustino Jozala Gabriel Soares Pinheiro Priscila Gava Mazzola Adalberto Pessoa Júnior Thereza Christina Vessoni Penna 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):325-328
BACKGROUND: Nisin is a commercially available bacteriocin produced by Lactococcus lactis ATCC 11454 and used as a natural agent in the biopreservation of food. In the current investigation, milk whey, a byproduct from dairy industries was used as a fermentation substrate for the production of nisin. Lactococcus lactis ATCC 11454 was developed in a rotary shaker (30 °C/36 h/100 rpm) using two different media with milk whey (i) without filtration, pH 6.8, adjusted with NaOH 2 mol L?1 and without pH adjustment, both autoclaved at 121 °C for 30 min, and (ii) filtrated (1.20 µm and 0.22 µm membrane filter). These cultures were transferred five times using 5 mL aliquots of broth culture for every new volume of the respective media. RESULTS: The results showed that culture media composed of milk whey without filtration supplied L. lactis its adaptation needs better than filtrated milk whey. Nisin titers, in milk whey without filtration (pH adjusted), was 11120.13 mg L?1 in the second transfer, and up to 1628‐fold higher than the filtrated milk whey, 6.83 mg.L?1 obtained in the firstt transfer. CONCLUSIONS: Biological processing of milk byproducts (milk whey) can be considered a profitable alternative, generating high‐value bioproducts and contributing to decreasing river disposals by dairy industries. Copyright © 2008 Society of Chemical Industry 相似文献
224.
225.
Development of adolescent reading comprehension in language 1 and language 2: A longitudinal analysis of constituent components. 总被引:1,自引:0,他引:1
van Gelderen Amos; Schoonen Rob; Stoel Reinoud D.; de Glopper Kees; Hulstijn Jan 《Canadian Metallurgical Quarterly》2007,99(3):477
This study investigated the relationship between reading comprehension development of 389 adolescents in their dominant language (Language 1 [L1], Dutch) and a foreign language (Language 2 [L2], English). In each consecutive year from Grades 8 through 10, a number of measurements were taken. Students' reading comprehension, their linguistic knowledge (vocabulary and grammar knowledge) and processing efficiency (speed of word recognition and sentence comprehension) in both languages, and their metacognitive knowledge about reading were assessed. The relative strengths of the effects of these components of reading were analyzed to distinguish among 3 hypotheses about the relationship between L1 and L2 reading comprehension: the transfer hypothesis, the threshold hypothesis, and the processing efficiency hypothesis. The transfer hypothesis predicts a strong relationship between L1 and L2 reading comprehension and a strong effect of metacognitive knowledge on L2 reading comprehension, whereas the threshold and processing efficiency hypotheses predict a more important role of language-specific knowledge and processing skills. Results support the transfer hypothesis, although language-specific knowledge and fluency also contribute to L2 reading performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
226.
227.
Min-Max MPC (MMMPC) controllers [P.J. Campo, M. Morari, Robust model predictive control, in: Proc. American Control Conference, June 10–12, 1987, pp. 1021–1026] suffer from a great computational burden which limits their applicability in the industry. Sometimes upper bounds of the worst possible case of a performance index have been used to reduce the computational burden. This paper proposes a computationally efficient MMMPC control strategy in which the worst case cost is approximated by an upper bound based on a diagonalization scheme. The upper bound can be computed with O(n3) operations and using only simple matrix operations. This implies that the algorithm can be coded easily even in non-mathematical oriented programming languages such as those found in industrial embedded control hardware. A simulation example is given in the paper. 相似文献
228.
This paper introduces a new single-phase high power factor rectifier, which features regulation by conventional PWM, soft commutation and instantaneous average line current control. Furthermore, thanks to the use of a single converter, instead of the conventional configuration composed of a four-diode front-end rectifier followed by a boost converter, a significant reduction in the conduction losses is achieved. A prototype rated at 1.6 kW, operating at 70 kHz, with an input AC voltage of 220 Vrms and an output voltage of 400 VDC has been implemented in the laboratory. An efficiency of 97.8 % at 1.6 kW has been measured. Analysis, design, and the control circuitry are also presented in the paper 相似文献
229.
We evaluated the effect of the image acquisition parameters on the accuracy of the principal axes and surface-fitting techniques for three-dimensional image registration. Using two types of phantom objects, MR brain image and a mathematically defined ellipsoid, we simulated pairs of scans with known acquisition parameters, including longitudinal coverage, magnitude of mis-registration, number of sections and section thickness. Both methods are sensitive to the systematic deformation of contours. The principal axes method is also sensitive to incomplete scan coverage and to the x-axis and y-axis misangulation. Both methods are insensitive to the number of sections, section thickness and the number of points per section. Surface fitting performed well without user supervision. There is no need for routine inclusion of the scaling factors as search parameters. The results confirm the feasibility of three-dimensional multimodality registration of brain scans with accuracy 1-2 mm, with surface fitting being the method of choice. 相似文献
230.
M Meyer B Keweloh K Güth JW Holmes B Pieske SE Lehnart H Just G Hasenfuss 《Canadian Metallurgical Quarterly》1998,30(8):1459-1470
Diastolic dysfunction at high heart rates may be associated with increased myocardial energy consumption. Frequency-dependent changes of isometric force and oxygen consumption (MVO2) were investigated in strip preparations from endstage failing human hearts exhibiting various degrees of diastolic dysfunction. MVO2 was determined by a new method which was validated. When stimulation rate was increased from 40 to 200 min-1 (n=7), developed force decreased from 16.5+/-4.3 to 7.9+/-2.9 mN/mm2 (P<0.01), diastolic force increased from 15.9+/-3.2 to 22.0+/-3.0 mN/mm2 (P<0.01), and total MVO2 increased from 2.6+/-0.6 to 4.7+/-0.9 ml/min/100 g (P<0.025). Resting MVO2 and resting force were 1.8+/-0.4 ml/min/100 g and 15.9+/-3.0 mN/mm2, respectively. After addition of 30 mm 2,3-butanedione monoxime (BDM) to inhibit crossbridges, resting MVO2 and resting force decreased by 46% (P<0.05) and 15% (P<0.01), respectively, indicating the presence of active force generation in unstimulated failing human myocardium. In each muscle preparation, there was a significant correlation between force-time integral (FTI) and total MVO2 (r=0.96+/-0.01). The strength of these correlations did not vary with the contribution of diastolic FTI to total FTI. The ratio of activity related MVO2 to developed FTI, an inverse index of the economy of contraction, increased depending on the rise of diastolic FTI at higher stimulation rates. In conclusion, in failing human myocardium, diastolic force development is occurring at the same energy expenditure as systolic force generation. Therefore, in muscle preparations with disturbed diastolic function economy of contraction decreases with higher stimulation rates, depending on the rise of diastolic force. 相似文献