全文获取类型
收费全文 | 28362篇 |
免费 | 1006篇 |
国内免费 | 33篇 |
学科分类
工业技术 | 29401篇 |
出版年
2022年 | 278篇 |
2021年 | 444篇 |
2020年 | 355篇 |
2019年 | 454篇 |
2018年 | 506篇 |
2017年 | 501篇 |
2016年 | 599篇 |
2015年 | 476篇 |
2014年 | 758篇 |
2013年 | 1769篇 |
2012年 | 1195篇 |
2011年 | 1593篇 |
2010年 | 1189篇 |
2009年 | 1167篇 |
2008年 | 1336篇 |
2007年 | 1377篇 |
2006年 | 1125篇 |
2005年 | 1048篇 |
2004年 | 897篇 |
2003年 | 840篇 |
2002年 | 800篇 |
2001年 | 473篇 |
2000年 | 465篇 |
1999年 | 456篇 |
1998年 | 529篇 |
1997年 | 475篇 |
1996年 | 447篇 |
1995年 | 439篇 |
1994年 | 385篇 |
1993年 | 411篇 |
1992年 | 377篇 |
1991年 | 254篇 |
1990年 | 304篇 |
1989年 | 320篇 |
1988年 | 306篇 |
1987年 | 290篇 |
1986年 | 316篇 |
1985年 | 351篇 |
1984年 | 342篇 |
1983年 | 331篇 |
1982年 | 270篇 |
1981年 | 283篇 |
1980年 | 277篇 |
1979年 | 271篇 |
1978年 | 246篇 |
1977年 | 246篇 |
1976年 | 222篇 |
1975年 | 206篇 |
1974年 | 184篇 |
1973年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
EuLisp has an integrated object system with reflective capabilities. We discuss some example applications which use these facilities to experiment with some advanced and powerful concepts, namely, finalization, virtual shared memory and persistence. A secondary goal is to attempt to illustrate the additional possibilities of metaobject programming over non-metalevel techniques. 相似文献
72.
Discusses issues and interventions for working with adolescents who live in stepfamilies. A developmental perspective, using psychoeducation and brief strategic intervention approaches, is proposed for working with stepfamilies. Six major issues for adolescents in stepfamilies are discussed: developmental issues, sexuality issues, parent–child relationships, parenting in stepfamilies, nonresidential parent–child issues, and changes in visitation and custody. Case illustrations and suggested interventions are presented for each of these areas. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
73.
Ian G. Richardson Adrian R. Brough Rik Brydson Geoffrey W. Groves Christopher M. Dobson 《Journal of the American Ceramic Society》1993,76(9):2285-2288
Solid-state 27 Al and 29 Si magic angle spinning NMR spectroscopy has been combined with electron energy loss spectroscopy carried out in the transmission electron microscope to determine the location of Al substituting in a semicrystalline C-S-H gel present in a hydrated synthetic slag glass. The gel is found to contain mainly pentameric silicate chains in which the central silicon is substituted by aluminum. 相似文献
74.
Sabha Kesraoui-Ouki Christopher R. Cheeseman Roger Perry 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(2):121-126
This paper assesses the potential of natural zeolite utilization as a low-cost ion-exchange and sorbent material in pollution control and recovery of metals. The improvement of the purity of natural zeolites coupled with their chemical modification capabilities in order to provide specific properties may provide a cost-effective alternative for the treatment of heavy metal contaminated soil and water. The application of natural zeolites in industrial pollution control is becoming important and the level of technical effort is increasingly expanding. The extent of application is unlikely to be related solely to their low cost, but also to improved properties and performance characteristics, which will advance the practical implementation of natural zeolites' technology. 相似文献
75.
This paper reviews the characteristics of pulsating or cyclic flow of bulk solids during gravity discharge in bins and silos. The dynamic load phenomenon is often referred to as “silo quaking” and is influenced by various factors related to the type of flow pattern developed in the bin and the flow properties of the bulk material. Of particular relevance is the influence of ‘slip-stick’ during shear flow, and the velocity at critical sections in the silo during discharge. An overview of recent and current research on this subject is presented. 相似文献
76.
A conceptual critique of the EA:es comparison in the Comprehensive Rorschach System. 总被引:1,自引:0,他引:1
Despite its empirical and normative strengths, the underlying conceptual base of the Comprehensive Rorschach System at times lacks clarity and an overarching theory of personality that can help psychodiagnosticians make more clinically relevant inferences. After reviewing the functions provided by an integral theory of personality, the author focuses on the Experience Actual:Experienced Stimulation (EA:es) index as a way of demonstrating how mechanistic jargon and lack of a guiding theory and conceptual clarity can lead to misleading and contradictory inferences. Case examples are provided, and some of the empirical foundations of the EA:es index are reviewed. The author concludes by offering recommendations on ways in which the Comprehensive System can become more sensitive in its appearance to capturing the complexities of personality functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
77.
Roger Norman Rothon Christopher Mark Liauw Graham Clayton Lees Wayne Christopher Edward Schofield 《The Journal of Adhesion》2002,78(7):603-628
The interaction of ammonium stearate (AS) and γ-aminopropyltriethoxysilane (APS) treatments with a magnesium hydroxide flame retardant filler and their effects on its use in an ethylene vinyl acetate copolymer compound have been investigated. The work has shown clear evidence of changes in the structure of the surface layers formed on the filler as the amount of additive is increased and the levels at which these occur can be correlated with theoretical monolayer quantities. Infrared (IR) spectroscopy data suggest that the stearate coating changes from a half salt to a full salt as the coating level is increased and that the APS coating on the filler initially has a significant bicarbonate content, presumably due to reaction with atmospheric carbon dioxide. The effect of coating level on the melt flow rate, insoluble matrix content, crystallisation behaviour, tensile properties, limiting oxygen index, and ageing of the filled compound has been studied. Distinct trends have been observed, many of which can be correlated with the structure of the filler surface layers. Of particular importance is the observation that, unlike APS, excess stearate appears to promote detrimental ageing effects. 相似文献
78.
Examined the effect of lesions of the caudate nucleus or fimbria-fornix on the acquisition of 2 water maze tasks. In both tasks, 2 rubber balls with different visual patterns were used as cues. The correct cue was attached to a submerged rectangular platform and could be mounted by an animal to escape the water. The incorrect cue was attached to a thin round pedestal and could not be mounted. In a spatial version of the task, the correct cue was located in the same quadrant of the maze on all trials, whereas the visual pattern on the cue was varied from trial to trial. Lesions of the fornix, but not the caudate nucleus, impaired acquisition of this spatial task in relation to control animals. In a simultaneous visual discrimination version of the task, the correct cue on all trials was one with a specific visual pattern, and the spatial location of the correct cue was varied from trial to trial. Lesions of the caudate nucleus, but not the fornix, impaired acquisition of this visual discrimination task in relation to control animals. The double dissociation observed supports the hypothesis that the hippocampus and caudate nucleus are parts of systems that differ in the type of memory they mediate. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
79.
Youngjohn James R.; Larrabee Glenn J.; Crook Thomas H. 《Canadian Metallurgical Quarterly》1992,4(1):54
The authors attempt to provide a better understanding of the differences between the normal memory decline characteristic of age-associated memory impairment (AAMI) and the pathological decline typical of mild Alzheimer's disease (AD). Batteries of traditional memory tests and computer-simulated everyday-memory tests discriminated between the 2 groups, which were matched on age, gender, and education, with reasonable degrees of accuracy (87.5% and 88.4%, respectively). False positives were the most frequent classification errors when using either battery. These results indicate that it is possible to use ecologically valid memory assessment paradigms without sacrificing discriminant validity. The clinical significance of discriminating mild AD from AAMI is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
80.
Analysis of characteristic odors from human male axillae 总被引:7,自引:0,他引:7
Xiao -nong Zeng James J. Leyden Henry J. Lawley Kiyohito Sawano Isao Nohara George Preti 《Journal of chemical ecology》1991,17(7):1469-1492
A number of studies concerning the analysis of axillary odors have assumed that the characteristic odor produced in the axillae is due to volatile steroids and isovaleric acid. Organoleptic evaluation of Chromatographic eluants from axillary extracts was employed to isolate the region in the chromatogram where the characteristic odor eluted. The odor of the dissolved eluant was eliminated when it was treated with base, suggesting that acids make up the characteristic axillary odor. Subsequent extraction of the pH-adjusted axillary extract in conjunction with organoleptic evaluation of the Chromatographic eluant, preparative gas chromatography, and analysis by GC-MS as well as GC-FTIR showed the presence of a number of C6 to C11 straight-chain, branched, and unsaturated acids as important contributors to the axillary odor. The major odor component is (E)-3-methyl-2-hexenoic acid. Three homologous series of minor components are also important odor contributors; these consist of the terminally unsaturated acids, the 2-methyl-C6 to -C10 acids and the 4-ethyl-C5 to -C11 acids. These types of acids have not been reported previously as components of the human axillary secretions and have not been proposed previously as part of the principal odor components in this area. 相似文献