全文获取类型
收费全文 | 390815篇 |
免费 | 5613篇 |
国内免费 | 2203篇 |
专业分类
电工技术 | 7463篇 |
技术理论 | 5篇 |
综合类 | 3449篇 |
化学工业 | 58124篇 |
金属工艺 | 20344篇 |
机械仪表 | 15574篇 |
建筑科学 | 9482篇 |
矿业工程 | 2810篇 |
能源动力 | 7175篇 |
轻工业 | 29437篇 |
水利工程 | 4736篇 |
石油天然气 | 7472篇 |
武器工业 | 243篇 |
无线电 | 41327篇 |
一般工业技术 | 78427篇 |
冶金工业 | 54017篇 |
原子能技术 | 6771篇 |
自动化技术 | 51775篇 |
出版年
2021年 | 2468篇 |
2019年 | 2104篇 |
2018年 | 22706篇 |
2017年 | 22232篇 |
2016年 | 15971篇 |
2015年 | 3759篇 |
2014年 | 4830篇 |
2013年 | 11553篇 |
2012年 | 12375篇 |
2011年 | 24814篇 |
2010年 | 21489篇 |
2009年 | 19025篇 |
2008年 | 20418篇 |
2007年 | 22976篇 |
2006年 | 8606篇 |
2005年 | 11523篇 |
2004年 | 9224篇 |
2003年 | 8560篇 |
2002年 | 7202篇 |
2001年 | 6459篇 |
2000年 | 6164篇 |
1999年 | 5944篇 |
1998年 | 12910篇 |
1997年 | 9575篇 |
1996年 | 7326篇 |
1995年 | 5549篇 |
1994年 | 5120篇 |
1993年 | 4987篇 |
1992年 | 3968篇 |
1991年 | 3802篇 |
1990年 | 3829篇 |
1989年 | 3772篇 |
1988年 | 3546篇 |
1987年 | 3022篇 |
1986年 | 3057篇 |
1985年 | 3411篇 |
1984年 | 3322篇 |
1983年 | 3075篇 |
1982年 | 2705篇 |
1981年 | 2908篇 |
1980年 | 2648篇 |
1979年 | 2849篇 |
1978年 | 2740篇 |
1977年 | 2846篇 |
1976年 | 3698篇 |
1975年 | 2460篇 |
1974年 | 2292篇 |
1973年 | 2324篇 |
1972年 | 1984篇 |
1971年 | 1788篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
David L. Hoover 《Computers and the Humanities》2003,37(2):151-178
This article examines the usefulness ofvocabulary richness for authorship attributionand tests the assumption that appropriatemeasures of vocabulary richness can capture anauthor's distinctive style or identity. Afterbriefly discussing perceived and actualvocabulary richness, I show that doubling andcombining texts affects some measures incomputationally predictable but conceptuallysurprising ways. I discuss some theoretical andempirical problems with some measures anddevelop simple methods to test how wellvocabulary richness distinguishes texts bydifferent authors. These methods show thatvocabulary richness is ineffective for largegroups of texts because of the extremevariability within and among them. I concludethat vocabulary richness is of marginal valuein stylistic and authorship studies because thebasic assumption that it constitutes awordprint for authors is false. 相似文献
993.
A. V. Solokhin S. L. Nazanskii V. S. Timofeev 《Theoretical Foundations of Chemical Engineering》2005,39(2):105-109
The evolution of the phase portrait for the dynamic system of open evaporation combined with a chemical reaction for a fixed liquid amount was studied as dependent on the rate constants of the reaction. A three-component azeotropic mixture whose vapor-liquid equilibrium diagram is characterized by two distillation regions was considered. The possibility of the open evaporation trajectory to transfer through the separatrix between the distillation regions was shown, as well as the possibility of implementing the principle of redistribution of the concentration fields due to chemical reactions occurring in reactive distillation columns.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 115–119.Original Russian Text Copyright © 2005 by Solokhin, Nazanskii, Timofeev. 相似文献
994.
A model is developed for the analysis of factors influencing organizational and technological changes associated with CAD and CAD/CAM (computer-aided design/computer-aided manufacture). Different pressures for adoption and the sociopolitical environment of the organization and related to managerial strategies and their impact on skills, tasks, training, and changes in work organization. Opportunities are illustrated through the experiences of seven British engineering companies implementing the technologies. Six of the companies are in manufacturing and one is an engineering services organization. Four of the companies are of small to medium size (under 500 employees) and the other three are large, multisite organizations. Key elements of the technological change are identified, and the position of the seven companies in relation to these elements is summarized and discussed 相似文献
995.
Z. P. Shul'man B. M. Khusid I. L. Ryklina É. A. Zal'tsgendler O. R. Dornyak É. V. Ivashkevich Z. A. Shabunina 《Journal of Engineering Physics and Thermophysics》1987,53(5):1285-1291
Dynamic processes are studied in media with softly and hardly internal destroyable configurations. A method is examined for the measurement of properties of media with spatial separation of the chemical transformation stages and thermal hydrodynamic measurements.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 781–789, November, 1987. 相似文献
996.
N. V. Vostokov Yu. N. Drozdov Z. F. Krasil’nik O. A. Kuznetsov A. V. Novikov V. A. Perevoshchikov M. V. Shaleev 《Russian Microelectronics》2005,34(4):203-209
The results are presented of the fabrication of strain-relaxed graded Si1 − x
Gex/Si(001) buffer layers with a maximum Ge fraction of about 0.25 that have a low density of threading dislocations (<106 cm−2) and low surface roughness. The buffer layers are grown by atmospheric-pressure hydride CVD. It is found that chemical mechanical polishing can reduce their surface roughness to a level comparable with that of the original Si(001) substrates. It is shown that the polished buffer layers can serve as substrates for MBE-grown SiGe/Si heterostructures.__________Translated from Mikroelektronika, Vol. 34, No. 4, 2005, pp. 243–250.Original Russian Text Copyright © 2005 by Vostokov, Drozdov, Krasil’nik, Kuznetsov, Novikov, Perevoshchikov, Shaleev. 相似文献
997.
V. S. Dronov L. R. Botvina V. M. Blinov M. R. Tyutin I. A. Afanas’ev 《Russian Metallurgy (Metally)》2006,(5):458-466
The kinetics of development of fatigue microcracks in a high-strength 08Kh14AN4MD steel is studied when a cantilever specimen with several notches is subjected to rotational bending tests. The specific feature of the tests consists in the fact that, when the specimen is loaded at a constant load, different stress amplitudes are realized in different notches. As a result, after the sample has failed across the section with the maximum stress, a longitudinal polished section of the specimen contains fatigue cracks having nucleated in the mouths of the other notches at lower stress amplitudes. A relation between inflection points in the fatigue curve and the conditions of local and developed yield in a notch has been established. Fatigue fracture mechanisms at a superhigh number of loading cycles are studied, and their relation to the structure near a crack is found. A rapid method for estimating the fatigue limit at a superhigh number of loading cycles is proposed. 相似文献
998.
M. M. Stadnyk 《Materials Science》2007,43(6):764-768
We deduce the theoretical formula taking into account the influence of biaxial loading of a plate weakened by a crack on the
stress intensity factor K
I. This enables us to compute the characteristic of crack resistance K
c according to the known boundary forces.
__________
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 6, pp. 14–16, November–December, 2007. 相似文献
999.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
1000.
In many legal proceedings, fact finders scrutinize the demeanor of a defendant or witness, particularly his or her nonverbal behavior, for indicators of deception. This meta-analysis investigated directly observable nonverbal correlates of deception as a function of different moderator variables. Although lay people and professionals alike assume that many nonverbal behaviors are displayed more frequently while lying, of 11 different behaviors observable in the head and body area, only 3 were reliably associated with deception. Nodding, foot and leg movements, and hand movements were negatively related to deception in the overall analyses weighted by sample size. Most people assume that nonverbal behaviors increase while lying; however, these behaviors decreased, whereas others showed no change. There was no evidence that people avoid eye contact while lying, although around the world, gaze aversion is deemed the most important signal of deception. Most effect sizes were found to be heterogeneous. Analyses of moderator variables revealed that many of the observed relationships varied as a function of content, motivation, preparation, sanctioning of the lie, experimental design, and operationalization. Existing theories cannot readily account for the heterogeneity in findings. Thus, practitioners are cautioned against using these indicators in assessing the truthfulness of oral reports. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献