全文获取类型
收费全文 | 17515篇 |
免费 | 963篇 |
国内免费 | 28篇 |
专业分类
电工技术 | 196篇 |
综合类 | 58篇 |
化学工业 | 3830篇 |
金属工艺 | 351篇 |
机械仪表 | 365篇 |
建筑科学 | 763篇 |
矿业工程 | 46篇 |
能源动力 | 528篇 |
轻工业 | 1710篇 |
水利工程 | 130篇 |
石油天然气 | 52篇 |
无线电 | 1224篇 |
一般工业技术 | 3320篇 |
冶金工业 | 2468篇 |
原子能技术 | 128篇 |
自动化技术 | 3337篇 |
出版年
2023年 | 169篇 |
2022年 | 377篇 |
2021年 | 603篇 |
2020年 | 398篇 |
2019年 | 398篇 |
2018年 | 513篇 |
2017年 | 471篇 |
2016年 | 567篇 |
2015年 | 488篇 |
2014年 | 630篇 |
2013年 | 1111篇 |
2012年 | 1030篇 |
2011年 | 1235篇 |
2010年 | 870篇 |
2009年 | 810篇 |
2008年 | 855篇 |
2007年 | 840篇 |
2006年 | 642篇 |
2005年 | 577篇 |
2004年 | 429篇 |
2003年 | 417篇 |
2002年 | 384篇 |
2001年 | 245篇 |
2000年 | 222篇 |
1999年 | 245篇 |
1998年 | 299篇 |
1997年 | 246篇 |
1996年 | 225篇 |
1995年 | 226篇 |
1994年 | 193篇 |
1993年 | 183篇 |
1992年 | 150篇 |
1991年 | 91篇 |
1990年 | 148篇 |
1989年 | 134篇 |
1988年 | 102篇 |
1987年 | 119篇 |
1986年 | 133篇 |
1985年 | 139篇 |
1984年 | 123篇 |
1983年 | 89篇 |
1982年 | 108篇 |
1981年 | 112篇 |
1980年 | 94篇 |
1979年 | 91篇 |
1978年 | 89篇 |
1977年 | 106篇 |
1976年 | 89篇 |
1975年 | 61篇 |
1974年 | 77篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
David G. Calatayud Teresa Jardiel Mónica Rodríguez Marco Peiteado Daniel Fernández-Hevia Amador C. Caballero 《Ceramics International》2013,39(2):1195-1202
TiO2 nanoparticles with tailored morphology have been synthesized under exceptionally soft conditions. The strategy is based on the use of a non-aqueous alcoholic reaction medium in which water traces, coming either from the air (atmospheric water) or from an ethanol–water azeotropic mixture (ethanol 96%), are incorporated in order to accelerate hydrolysis of the Ti–precursor. Moreover, organic surfactants have been used as capping agents so as to tailor crystal growth in certain preferential directions. Combinations of oleic acid and oleylamine, which lead to the formation of another surfactant, dioleamide, are employed instead of fluorine-based compounds, thus increasing the sustainability of the process. As a result, TiO2 nanostructured hierarchical microspheres and individual nanoparticles with exposed high-energy facets can be obtained at atmospheric pressure and temperatures as low as 78 °C. 相似文献
992.
Chua Elizabeth F.; Schacter Daniel L.; Sperling Reisa A. 《Canadian Metallurgical Quarterly》2009,24(1):139
Although several studies have examined the neural basis for age-related changes in objective memory performance, less is known about how the process of memory monitoring changes with aging. The authors used functional magnetic resonance imaging to examine retrospective confidence in memory performance in aging. During low confidence, both younger and older adults showed behavioral evidence that they were guessing during recognition and that they were aware they were guessing when making confidence judgments. Similarly, both younger and older adults showed increased neural activity during low- compared to high-confidence responses in the lateral prefrontal cortex, anterior cingulate cortex, and left intraparietal sulcus. In contrast, older adults showed more high-confidence errors than younger adults. Younger adults showed greater activity for high compared to low confidence in medial temporal lobe structures, but older adults did not show this pattern. Taken together, these findings may suggest that impairments in the confidence–accuracy relationship for memory in older adults, which are often driven by high-confidence errors, may be primarily related to altered neural signals associated with greater activity for high-confidence responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
993.
Suniti Karunatillake Steven W. Squyres Olivier Gasnault John M. Keller Daniel M. Janes William V. Boynton Michael J. Finch 《Journal of scientific computing》2011,46(3):439-451
The Mars Odyssey Gamma Ray Spectrometer has yielded planetary data of global extent. Such remote-sensing missions usually
assign the value of a continuous-valued geospatial attribute to a uniform latitude-longitude grid of bins. Typical attributes
include elemental-mass fraction, areal fraction of a mineral type, areal fraction of rocks, thermal inertia, etc. The fineness
of the grid is chosen according to the spatial resolution of the orbiter and concomitant data processing. We describe methods
to maximize the information extracted from both bin and regional data. Rigorous use of statistical parameters and related
methods for inter- and intra- regional comparisons are also discussed. While we discuss results from the Mars Odyssey mission,
the techniques we describe are applicable whenever continuous-valued attributes of a planet’s surface are characterized with
bins and regions. Our goal is to distill the simplest statistical methods for regional comparisons that would be intuitively
accessible to planetary scientists. 相似文献
994.
San Miguel Montes Liza E.; Allen Daniel N.; Puente Antonio E.; Neblina Cris 《Canadian Metallurgical Quarterly》2010,22(2):465
The Wechsler Intelligence Scale for Children (WISC) is the most commonly used intelligence test for children. Five years ago, a Spanish version of the WISC–IV was published (WISC-IV Spanish; Wechsler, 2005), but a limited amount of published information is available regarding its utility when assessing clinical samples. The current study included 107 children who were Spanish speaking and of Puerto Rican descent that had been administered the WISC–IV Spanish. They were subdivided into a clinical sample of 35 children with diagnoses of various forms of brain dysfunction (primarily learning disability, attention-deficit/hyperactivity disorder, and epilepsy) and a comparison group made up of 72 normal children who were part of the WISC–IV Spanish version standardization sample. Comparisons between these groups and the standardization sample were performed for the WISC–IV Spanish index and subtest scores. Results indicated that the clinical sample performed worse than the comparison samples on the Working Memory and Processing Speed Indexes, although findings varied to some extent depending on whether the clinical group was compared with the normal comparison group or the standardization sample. These findings provide support for the criterion validity of the WISC–IV Spanish when it is used to assess a clinically referred sample with brain dysfunction. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
996.
997.
Guillaume Pichavant Daniel Beysens Denis Chatain Daniel Communal Clément Lorin Alain Mailfert 《Microgravity science and technology》2011,23(2):129-133
A ground based facility (OLGA), providing magnetic compensation of gravity in oxygen, has been developed. A 2-T superconducting
magnetic solenoid is used to create the required magnetic field. A novel electrical supply permits to quickly vary the magnetic
field, leading to rapid variation of the acceleration forces applied to oxygen. These variations can be made from overcompensation
of gravity (−0.5g) to zero gravity or from zero gravity to reduced gravity (0.4g) with a time constant of 340 ms. This time is typical of the cutoff or reignition of spacecraft engines. Preliminary results
on the transient flows induced by these acceleration variations in a reservoir filled with liquid and gaseous oxygen are presented. 相似文献
998.
Visualisation of taxonomies and sets has recently become an active area of research. Many application fields now require more than a strict classification of elements into a hierarchy tree. Euler diagrams, one of the most natural ways of depicting intersecting sets, may provide a solution to these problems.
In this paper, we present an approach for the automatic generation of Euler-like diagrams. This algorithm differs from previous approaches in that it has no undrawable instances of input, allowing it to be used in systems where the output is always required. We also improve the readability of Euler diagrams through the use of Bézier curves and transparent coloured textures. Our approach has been implemented using the Tulip platform. Both the source and executable program used to generate the results are freely available. 相似文献
In this paper, we present an approach for the automatic generation of Euler-like diagrams. This algorithm differs from previous approaches in that it has no undrawable instances of input, allowing it to be used in systems where the output is always required. We also improve the readability of Euler diagrams through the use of Bézier curves and transparent coloured textures. Our approach has been implemented using the Tulip platform. Both the source and executable program used to generate the results are freely available. 相似文献
999.
Qingqing Wang Victor Varela Guerrero Anirban Ghosh Seunguk Yeu Jonathan D. Lunn Daniel F. Shantz 《Journal of Catalysis》2010,269(1):15-25
The synthesis and catalytic testing of several dendron–ordered mesoporous silica hybrids are reported. These materials are active in both the nitroaldol (Henry) reaction and the transesterification of glyceryl tributyrate to afford methyl esters. In both reactions it is observed that dendrons terminated with primary amines are more catalytically active than samples containing dendrons terminated with secondary amines. On a mmol nitrogen per gram of silica basis, the first generation dendrons are the most active for both chemistries, and the SBA-15 samples display a higher activity than the MCM-41 samples. The pore-size effect observed is consistent with significant diffusion resistance in the MCM-41 samples. The activity trend observed in the SBA-15 materials is consistent with decreased cooperative effects between the amines and surface silanols as the dendrons become larger. Clear trends are observed indicating that higher generation dendrons are more selective to alcohol formation in the Henry reaction. The dendron catalysts are much more active and stable than simple amines attached to silica in the transesterification of triglycerides. Preliminary results shown indicate that these materials can also catalyze more demanding chemistries, an example of which is the Aldol condensation of 5-(hydroxymethyl)furfural and acetone. The results shown indicate that dendron–OMS hybrids can serve as effective solid base catalysts for a diverse range of chemistries. 相似文献
1000.
Evolutionary invasion analysis is a powerful technique for modelling in evolutionary biology. The general approach is to derive an expression for the growth rate of a mutant allele encoding some novel phenotype, and then to use this expression to predict long-term evolutionary outcomes. Mathematically, such ‘invasion fitness’ expressions are most often derived using standard linear stability analyses from dynamical systems theory. Interestingly, there is a mathematically equivalent approach to such stability analyses that is often employed in mathematical epidemiology, and that is based on so-called ‘next-generation’ matrices. Although this next-generation matrix approach has sometimes also been used in evolutionary invasion analyses, it is not yet common in this area despite the fact that it can sometimes greatly simplify calculations. The aim of this article is to bring the approach to a wider evolutionary audience in two ways. First, we review the next-generation matrix approach and provide a novel, and easily intuited, interpretation of how this approach relates to more standard techniques. Second, we illustrate next-generation methods in evolutionary invasion analysis through a series of informative examples. Although focusing primarily on evolutionary invasion analysis, we provide several insights that apply to biological modelling in general. 相似文献