全文获取类型
收费全文 | 33126篇 |
免费 | 2556篇 |
国内免费 | 313篇 |
学科分类
工业技术 | 35995篇 |
出版年
2024年 | 79篇 |
2023年 | 338篇 |
2022年 | 438篇 |
2021年 | 998篇 |
2020年 | 840篇 |
2019年 | 849篇 |
2018年 | 1348篇 |
2017年 | 1334篇 |
2016年 | 1387篇 |
2015年 | 1132篇 |
2014年 | 1374篇 |
2013年 | 2662篇 |
2012年 | 2223篇 |
2011年 | 2091篇 |
2010年 | 1720篇 |
2009年 | 1533篇 |
2008年 | 1557篇 |
2007年 | 1475篇 |
2006年 | 1002篇 |
2005年 | 824篇 |
2004年 | 729篇 |
2003年 | 661篇 |
2002年 | 539篇 |
2001年 | 442篇 |
2000年 | 348篇 |
1999年 | 397篇 |
1998年 | 2333篇 |
1997年 | 1455篇 |
1996年 | 916篇 |
1995年 | 518篇 |
1994年 | 404篇 |
1993年 | 396篇 |
1992年 | 108篇 |
1991年 | 90篇 |
1990年 | 72篇 |
1989年 | 73篇 |
1988年 | 93篇 |
1987年 | 88篇 |
1986年 | 76篇 |
1985年 | 82篇 |
1984年 | 66篇 |
1983年 | 38篇 |
1982年 | 46篇 |
1981年 | 70篇 |
1980年 | 66篇 |
1978年 | 32篇 |
1977年 | 154篇 |
1976年 | 297篇 |
1975年 | 38篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
102.
103.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
104.
Joaquín Cortés Eliana Valencia Gonzalo Aguila Esteban Orellana Paulo Araya 《Catalysis Letters》2008,126(1-2):63-71
An experimental study is made of the time decay of activity of the CO–NO reaction on a Pd/Al2O3 looking at the effect on reaction order and apparent activation energy. The optimum kinetics parameters fitting the steady state data at moderate pressures are determined. The time decay curves are analyzed through various catalyst deactivation models. 相似文献
105.
In this paper, we analyze in some detail the manifold-mapping optimization technique introduced recently [Echeverría and Hemker in space mapping and defect correction. Comput Methods Appl Math 5(2): 107—136, 2005]. Manifold mapping aims at accelerating optimal design procedures that otherwise require many evaluations of time-expensive cost functions. We give a proof of convergence for the manifold-mapping iteration. By means of two simple optimization problems we illustrate the convergence results derived. Finally, the performances of several variants of the method are compared for some design problems from electromagnetics. 相似文献
106.
107.
Mariana Ušáková Jozef Lukáč Rastislav Dosoudil Vladimír Jančárik Anna Grusková Elemír Ušák Jozef Sláma Jan Šubrt 《Journal of Materials Science: Materials in Electronics》2007,18(12):1183-1189
The paper is devoted to the preparation of NiZn ferrite with small substitutions of copper by means of ceramic technology.
The influence of small Cu substitution on the microstructural and magnetic properties of NiZn ferrites have been analysed
by means of various experimental methods and interpreted from the point of view of preparation technology optimisation and
possible applications of such materials. A strong correlation between the substituent content and resulting properties has
been observed, thus allowing preparation of material with the properties tailored for any particular application. 相似文献
108.
J. L. Díez J. L. Navarro A. Sala 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2007,11(10):973-983
In this work, simple modifications on the cost index of particular local-model fuzzy clustering algorithms are proposed in
order to improve the readability of the resulting models. The final goal is simultaneously providing local linear models (reasonably
close to the plant’s Jacobian) and clustering in the input space so that desirable characteristics (regarding final model
accuracy, and convexity and smoothness of the cluster membership functions) are improved with respect to other proposals in
literature. Some examples illustrate the proposed approach. 相似文献
109.
J Alvarez-Sabín 《Canadian Metallurgical Quarterly》1997,25(142):919-923
Between 3.7% and 8.5% of all strokes occur before the age of 45 years old. In the population under 15 years of age, the annual incidence of strokes is 2.7 per 100,000 children, with ischaemic strokes making up 1.2 and haemorrhagic strokes 1.5 of this total. The main characteristic of ischaemic strokes in childhood is the wide variety of diagnoses involved. Some of these, such as congenital cardiopathy, are rare in adults, as are dissections and arterial dysplasias, arteritis, hereditary connective tissue disorders and disorders of metabolism. Similarly, the aetiology of haemorrhagic stroke is also very varied, with bursting of a vascular malformation or aneurysm being the commonest. Other aetiologies are disorders of haemostasis, arteritis, migraine, retarded post-traumatic phenomena and the use of drugs and sympathomimetic agents. The personal, family and social repercussions are considerable, since both ischaemic and haemorrhagic strokes have an appreciable mortality and morbidity. 相似文献
110.
Comparison evaluation of the methods of treatment was based on the analysis of the results of management of 347 patients with general purulent decompensated peritonitis with polyorganic insufficiency. The efficacy of closed drainage in 98 patients, continuous flow irrigation (dialysis) in 126, stage programmed irrigation and inspection of the abdominal cavity in 99, and open drainage in 24 patients was compared. The causes of peritonitis were: complications after acute surgical diseases (in 156 cases), in planned operations (59), and in obstetrical and gynecological diseases (132). Most of the patients were brought to the clinic from other hospitals because of unsuccessful treatment of peritonitis and absence of means for performing hemodialysis and management of polyorganic insufficiency. The incidence of the last-named reached 71.0 to 91.0% in the different groups of patients. In monotypic complex treatment, stage programmed irrigation was marked by a much lesser number of abscesses and other complications and a lower mortality (20.2%) as compared to flow irrigation (30.0%, closed drainage (27.5%), and open (laparostomy) treatment (37.5%). Despite the very serious contingent of patients, total mortality (27.0%) in the application of the indicated methods was quite low. 相似文献