全文获取类型
收费全文 | 16854篇 |
免费 | 1173篇 |
国内免费 | 22篇 |
专业分类
电工技术 | 134篇 |
综合类 | 10篇 |
化学工业 | 6086篇 |
金属工艺 | 238篇 |
机械仪表 | 407篇 |
建筑科学 | 553篇 |
矿业工程 | 26篇 |
能源动力 | 445篇 |
轻工业 | 3972篇 |
水利工程 | 159篇 |
石油天然气 | 93篇 |
无线电 | 705篇 |
一般工业技术 | 2396篇 |
冶金工业 | 988篇 |
原子能技术 | 66篇 |
自动化技术 | 1771篇 |
出版年
2024年 | 60篇 |
2023年 | 217篇 |
2022年 | 1032篇 |
2021年 | 1234篇 |
2020年 | 558篇 |
2019年 | 610篇 |
2018年 | 673篇 |
2017年 | 691篇 |
2016年 | 707篇 |
2015年 | 571篇 |
2014年 | 736篇 |
2013年 | 1148篇 |
2012年 | 1087篇 |
2011年 | 1208篇 |
2010年 | 899篇 |
2009年 | 884篇 |
2008年 | 785篇 |
2007年 | 733篇 |
2006年 | 569篇 |
2005年 | 439篇 |
2004年 | 362篇 |
2003年 | 333篇 |
2002年 | 305篇 |
2001年 | 204篇 |
2000年 | 159篇 |
1999年 | 181篇 |
1998年 | 257篇 |
1997年 | 199篇 |
1996年 | 176篇 |
1995年 | 118篇 |
1994年 | 107篇 |
1993年 | 93篇 |
1992年 | 90篇 |
1991年 | 61篇 |
1990年 | 53篇 |
1989年 | 59篇 |
1988年 | 43篇 |
1987年 | 42篇 |
1986年 | 56篇 |
1985年 | 44篇 |
1984年 | 39篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 22篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 18篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
We examined whether personality judgments were present in texts of the diverse religious and philosophical traditions that emerged during the Great Transformation, an era spanning roughly 1000 BCE to 200 BCE. Some psychologists have suggested that the tendency of humans to judge personality has evolved; if some ancient societies failed to record personality judgments, it would be evidence against such an evolutionary position. In addition, learning about the prevalence and specifics of ancient personality judgments can help psychologists better understand the prehistory of personality psychology. Eight cultural traditions were studied: two each from China (Confucianism, Taoism), Greece (Classical and Hellenistic philosophy), India (Buddhism, Hinduism), and the Middle East (Judaism, Zoroastrianism). We found evidence that personality judgments were an important aspect of all of these traditions. Not only did people judge one another, but they also offered instructions on how to judge others. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
102.
103.
M. J. P. Biggs M. C. Milone L. C. Santos A. Gondarenko S. J. Wind 《Journal of the Royal Society Interface》2011,8(63):1462-1471
T-cell activation via antigen presentation is associated with the formation of a macromolecular membrane assembly termed the immunological synapse (IS). The genesis of the IS and the onset of juxtacrine signalling is characterized by the formation of cell membrane microclusters and the organization of such into segregated microdomains. A central zone rich in T-cell receptor (TCR)–major histocompatibility complex microclusters termed the central supramolecular activation cluster (cSMAC) forms the bullseye of this structure, while the cellular interface surrounding the cSMAC is characterized by regions enriched in adhesion and co-stimulatory molecules. In vitro, the study of dynamic TCR microcluster coalescence and IS genesis in T-cell populations is hampered by cell migration within the culture system and resolution constraints resulting from lateral cell–cell contact. Here, we detail a novel system describing the fabrication of micropit arrays designed to sequester single T-cell–antigen presenting cell (APC) conjugates and promote IS formation in the horizontal imaging plane for high-resolution studies of microcluster dynamics. We subsequently use this system to describe the formation of the cSMAC in T-cell populations and to investigate the morphology of the interfacial APC membrane. 相似文献
104.
Ross D. King Maria Liakata Chuan Lu Stephen G. Oliver Larisa N. Soldatova 《Journal of the Royal Society Interface》2011,8(63):1440-1448
The reuse of scientific knowledge obtained from one investigation in another investigation is basic to the advance of science. Scientific investigations should therefore be recorded in ways that promote the reuse of the knowledge they generate. The use of logical formalisms to describe scientific knowledge has potential advantages in facilitating such reuse. Here, we propose a formal framework for using logical formalisms to promote reuse. We demonstrate the utility of this framework by using it in a worked example from biology: demonstrating cycles of investigation formalization [F] and reuse [R] to generate new knowledge. We first used logic to formally describe a Robot scientist investigation into yeast (Saccharomyces cerevisiae) functional genomics [f1]. With Robot scientists, unlike human scientists, the production of comprehensive metadata about their investigations is a natural by-product of the way they work. We then demonstrated how this formalism enabled the reuse of the research in investigating yeast phenotypes [r1 = R(f1)]. This investigation found that the removal of non-essential enzymes generally resulted in enhanced growth. The phenotype investigation was then formally described using the same logical formalism as the functional genomics investigation [f2 = F(r1)]. We then demonstrated how this formalism enabled the reuse of the phenotype investigation to investigate yeast systems-biology modelling [r2 = R(f2)]. This investigation found that yeast flux-balance analysis models fail to predict the observed changes in growth. Finally, the systems biology investigation was formalized for reuse in future investigations [f3 = F(r2)]. These cycles of reuse are a model for the general reuse of scientific knowledge. 相似文献
105.
106.
Maria Clariana Isabel D��az Carmen S��rraga Jose A. Garc��a-Regueiro 《Food Analytical Methods》2011,4(4):465-474
The analysis of eight cholesterol oxidation products: 7α–hydroxycholesterol, 7β–hydroxycholesterol, α–epoxycholesterol, β–epoxycholesterol, 20α–hydroxycholesterol, cholestanetriol, 25–hydroxycholesterol, and 7–ketocholesterol in dry–cured shoulder was carried out. The extraction of lipids was performed by using the Bligh and Dyer method (1959). Interferences were removed by solid-phase extraction (SPE) in two steps with silica and aminipropylsilica SPE columns. The separation of the eight cholesterol oxidation products was done by gas chromatography, and the detection was performed by flame ionization detection (FID) and mass spectrometry (MS). The results obtained from the use of both systems of detection were compared. The results showed that gas chromatography-mass spectrometry (GC–MS) was the most suitable technique to obtain reliable quantitative data, and significant differences (p < 0.05) between FID and MS determining 7α–hydroxycholesterol, 20α–hydroxycholesterol, and 25–hydroxycholesterol were observed. For the determination of cholesterol oxidation products, it was necessary to apply gas chromatography-tandem mass spectrometry to increase the sensitivity and to avoid interference from other compounds. 相似文献
107.
Formalising the Fisherman's Folly puzzle 总被引:2,自引:0,他引:2
This paper investigates the challenging problem of encoding the common sense knowledge involved in the manipulation of spatial objects from a reasoning about actions and change perspective. In particular, we propose a formal solution to a puzzle composed of non-trivial objects (such as holes and strings) assuming a version of the Situation Calculus written over first-order Equilibrium Logic, whose models generalise the stable model semantics. 相似文献
108.
Jaime Bonachea Martín A. Hurtado Mario da Silva José L. Cavallotto Osni J. Pejon Maria Angélica de O. Bezerra Victoria Rivas Gema Fernández 《The Science of the total environment》2010,408(13):2674-2695
An analysis of geomorphic system's response to change in human and natural drivers in some areas within the Río de la Plata basin is presented. The aim is to determine whether an acceleration of geomorphic processes has taken place in recent years and, if so, to what extent it is due to natural (climate) or human (land-use) drivers. Study areas of different size, socio-economic and geomorphic conditions have been selected: the Río de la Plata estuary and three sub-basins within its watershed. Sediment cores were extracted and dated (210Pb) to determine sedimentation rates since the end of the 19th century. Rates were compared with time series on rainfall as well as human drivers such as population, GDP, livestock load, crop area, energy consumption or cement consumption, all of them related to human capacity to disturb land surface. Data on river discharge were also gathered. Results obtained indicate that sedimentation rates during the last century have remained essentially constant in a remote Andean basin, whereas they show important increases in the other two, particularly one located by the São Paulo metropolitan area. Rates in the estuary are somewhere in between. It appears that there is an intensification of denudation/sedimentation processes within the basin.Rainfall remained stable or varied very slightly during the period analysed and does not seem to explain increases of sedimentation rates observed. Human drivers, particularly those more directly related to capacity to disturb land surface (GDP, energy or cement consumption) show variations that suggest human forcing is a more likely explanation for the observed change in geomorphic processes. It appears that a marked increase in denudation, of a “technological” nature, is taking place in this basin and leading to an acceleration of sediment supply. This is coherent with similar increases observed in other regions. 相似文献
109.
Daniele Passeri Ugo Sassi Andrea Bettucci Emanuela Tamburri Francesco Toschi Silvia Orlanducci Maria Letizia Terranova Marco Rossi 《Advanced functional materials》2012,22(14):2956-2963
The thermoacoustic effect of isolated single‐wall carbon nanotubes aligned between electrodes is experimentally observed for the first time by imaging the emitted acoustic wave using an atomic force microscopy‐based technique specifically developed for the task. The capability of such a technique for single‐point thermoacoustic measurements is first verified on carbon nanotubes layers with two electrodes for injecting alternate electric current. The technique is then demonstrated to allow the acquisition, simultaneously with the topography, of images reflecting the pressure of the acoustic wave at fixed distance from the sample. Such a capability is used to collect images reflecting the amplitude of acoustic waves generated by isolated nanotubes and nanotube bundles by the thermoacoustic effect. 相似文献
110.