全文获取类型
收费全文 | 4983篇 |
免费 | 80篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 66篇 |
综合类 | 5篇 |
化学工业 | 971篇 |
金属工艺 | 76篇 |
机械仪表 | 103篇 |
建筑科学 | 211篇 |
矿业工程 | 27篇 |
能源动力 | 105篇 |
轻工业 | 358篇 |
水利工程 | 67篇 |
石油天然气 | 15篇 |
无线电 | 283篇 |
一般工业技术 | 613篇 |
冶金工业 | 1609篇 |
原子能技术 | 47篇 |
自动化技术 | 510篇 |
出版年
2021年 | 35篇 |
2018年 | 39篇 |
2016年 | 39篇 |
2015年 | 36篇 |
2014年 | 81篇 |
2013年 | 296篇 |
2012年 | 127篇 |
2011年 | 164篇 |
2010年 | 97篇 |
2009年 | 109篇 |
2008年 | 142篇 |
2007年 | 153篇 |
2006年 | 135篇 |
2005年 | 156篇 |
2004年 | 126篇 |
2003年 | 129篇 |
2002年 | 140篇 |
2001年 | 76篇 |
2000年 | 82篇 |
1999年 | 72篇 |
1998年 | 100篇 |
1997年 | 93篇 |
1996年 | 83篇 |
1995年 | 94篇 |
1994年 | 66篇 |
1993年 | 106篇 |
1992年 | 93篇 |
1991年 | 50篇 |
1990年 | 97篇 |
1989年 | 85篇 |
1988年 | 85篇 |
1987年 | 92篇 |
1986年 | 78篇 |
1985年 | 112篇 |
1984年 | 115篇 |
1983年 | 101篇 |
1982年 | 99篇 |
1981年 | 88篇 |
1980年 | 61篇 |
1979年 | 106篇 |
1978年 | 74篇 |
1977年 | 103篇 |
1976年 | 82篇 |
1975年 | 103篇 |
1974年 | 66篇 |
1973年 | 81篇 |
1972年 | 48篇 |
1971年 | 38篇 |
1970年 | 36篇 |
1969年 | 33篇 |
排序方式: 共有5066条查询结果,搜索用时 6 毫秒
51.
Randy V. Bradley Renée M. E. Pratt Terry Anthony Byrd Christina N. Outlay Donald E. Wynn Jr. 《Information Systems Journal》2012,22(2):97-127
Despite the possible benefits of implementing healthcare information technologies, successful implementation of effective healthcare information technology is constrained by cultural and regulatory concerns and technical obstacles encountered when establishing or upgrading an organisation's enterprise infrastructure. In this paper, we advance Ross' four‐stage model of enterprise architecture maturity as a valuable IT resource for helping healthcare organisations sustain a competitive advantage. We use partial least squares (PLS) structural equation modelling to analyse survey data from 164 US hospitals at different stages of EA maturity. Our results provide evidence that enterprise architecture maturity directly influences the effectiveness of hospitals' IT resources for achieving strategic goals. Further, enterprise architecture maturity indirectly influences the effectiveness of IT resources when IT alignment is incorporated as a mediating variable. We discuss the implications of our findings for research and practice and suggest opportunities for future research. 相似文献
52.
I. W. Donald B. L. Metcalfe D. J. Wood J. R. Copley 《Journal of Materials Science》1989,24(11):3892-3903
Lithium zinc silicate glasses are of interest for the preparation of moderately high thermal expansion glass-ceramics which are suitable for sealing to a number of nickel-based superalloys. The effect of composition, in particular the variation of nucleating species, on the crystallization behaviour of a number of these glasses has been examined using differential thermal analysis, X-ray diffraction, and electron microscopy. Various crystal phases have been identified, including cristobalite, quartz, tridymite and
0 Li2ZnSiO4. In addition, most of the glass-ceramics also contain an unidentified phase which may be related to the-series of lithium zinc silicates. Heat-treatment schedules have been derived on the basis of these results in order to produce a number of glass-ceramic materials. The resultant thermal expansion characteristics of the glass-ceramics have been monitored using dilatometry, and expansions in the range 12.3 to 17.1×10–6° C–1 (20 to 460° C), have been obtained, depending on the precise glass composition and heat-treatment schedule employed. In addition, the mechanical properties of a number of selected samples have been monitored, employing a biaxial flexure technique. 相似文献
53.
Polystyrene (PS)-polyether sulphone (PES) polymer blend thin films were prepared for examination in a scanning transmission electron microscope. The microstructures observed in 75 wt % PS-25 wt % PES films consisted of spherical inclusions, ranging from 0.2 to 1.2m in diameter. X-ray spectrometric analysis in the microscope revealed that the inclusions were PES-rich, while the matrix contained only PS. Attention in this paper is paid to the contrast in the annular dark-field detector (ADF) images from these thin films. This image contrast has a complicated dependence on both the angular range subtended by the dark-field detector and mass-thickness variations within the films. On microscopes with appropriate lens controls which permit the acceptance angle of the ADF detector to be varied, it becomes possible actually to reverse the contrast between the two phases. 相似文献
54.
The search for good lineal, or depth-first, spanning trees is an important aspect in the implementation of a wide assortment of graph algorithms. We consider the complexity of findingoptimal lineal spanning trees under various notions of optimality. In particular, we show that several natural problems, such as constructing a shortest or a tallest lineal tree, are NP-hard. We also address the issue of polynomial-time, near-optimization strategies for these difficult problems, showing that efficient absolute approximation algorithms cannot exist unlessP = NP. 相似文献
55.
D. T. Cambell and D. W. Fiske (1959) made the now-obvious statement that measures of the same variable made by different methods should agree (converge) and certainly should agree better than measures of different variables made by those several methods. Almost everyone accepted that statement, yet the multitrait–multimethod matrices published today show little or no improvement over the published examples cited in 1959. The article raised the conceptual problem of how a variable and its measurement should be linked and the methodological problem of clarifying the nature of methods and their effects. Given these unresolved problems, it is perhaps not surprising that the question of the appropriate statistical analysis of these matrices has also no consensual answer. Perhaps methods and traits or contents are so thoroughly intertwined that their interaction cannot be adequately analyzed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
56.
Davide Barbagallo Angela Caponnetto Cristina Barbagallo Rosalia Battaglia Federica Mirabella Duilia Brex Michele Stella Giuseppe Broggi Roberto Altieri Francesco Certo Rosario Caltabiano Giuseppe Maria Vincenzo Barbagallo Carmelina Daniela Anfuso Gabriella Lupo Marco Ragusa Cinzia Di Pietro Thomas Birkballe Hansen Michele Purrello 《International journal of molecular sciences》2021,22(4)
Circular RNAs (circRNAs) are a large class of RNAs with regulatory functions within cells. We recently showed that circSMARCA5 is a tumor suppressor in glioblastoma multiforme (GBM) and acts as a decoy for Serine and Arginine Rich Splicing Factor 1 (SRSF1) through six predicted binding sites (BSs). Here we characterized RNA motifs functionally involved in the interaction between circSMARCA5 and SRSF1. Three different circSMARCA5 molecules (Mut1, Mut2, Mut3), each mutated in two predicted SRSF1 BSs at once, were obtained through PCR-based replacement of wild-type (WT) BS sequences and cloned in three independent pcDNA3 vectors. Mut1 significantly decreased its capability to interact with SRSF1 as compared to WT, based on the RNA immunoprecipitation assay. In silico analysis through the “Find Individual Motif Occurrences” (FIMO) algorithm showed GAUGAA as an experimentally validated SRSF1 binding motif significantly overrepresented within both predicted SRSF1 BSs mutated in Mut1 (q-value = 0.0011). U87MG and CAS-1, transfected with Mut1, significantly increased their migration with respect to controls transfected with WT, as revealed by the cell exclusion zone assay. Immortalized human brain microvascular endothelial cells (IM-HBMEC) exposed to conditioned medium (CM) harvested from U87MG and CAS-1 transfected with Mut1 significantly sprouted more than those treated with CM harvested from U87MG and CAS-1 transfected with WT, as shown by the tube formation assay. qRT-PCR showed that the intracellular pro- to anti-angiogenic Vascular Endothelial Growth Factor A (VEGFA) mRNA isoform ratio and the amount of total VEGFA mRNA secreted in CM significantly increased in Mut1-transfected CAS-1 as compared to controls transfected with WT. Our data suggest that GAUGAA is the RNA motif responsible for the interaction between circSMARCA5 and SRSF1 as well as for the circSMARCA5-mediated control of GBM cell migration and angiogenic potential. 相似文献
57.
Alon M. Douek Mitra Amiri Khabooshan Jason Henry Sebastian-Alexander Stamatis Florian Kreuder Georg Ramm Minna-Liisa nk Donald Wlodkowic Jan Kaslin 《International journal of molecular sciences》2021,22(11)
Mucopolysaccharidosis IIIA (MPS IIIA, Sanfilippo syndrome type A), a paediatric neurological lysosomal storage disease, is caused by impaired function of the enzyme N-sulfoglucosamine sulfohydrolase (SGSH) resulting in impaired catabolism of heparan sulfate glycosaminoglycan (HS GAG) and its accumulation in tissues. MPS IIIA represents a significant proportion of childhood dementias. This condition generally leads to patient death in the teenage years, yet no effective therapy exists for MPS IIIA and a complete understanding of the mechanisms of MPS IIIA pathogenesis is lacking. Here, we employ targeted CRISPR/Cas9 mutagenesis to generate a model of MPS IIIA in the zebrafish, a model organism with strong genetic tractability and amenity for high-throughput screening. The sgshΔex5−6 zebrafish mutant exhibits a complete absence of Sgsh enzymatic activity, leading to progressive accumulation of HS degradation products with age. sgshΔex5−6 zebrafish faithfully recapitulate diverse CNS-specific features of MPS IIIA, including neuronal lysosomal overabundance, complex behavioural phenotypes, and profound, lifelong neuroinflammation. We further demonstrate that neuroinflammation in sgshΔex5−6 zebrafish is largely dependent on interleukin-1β and can be attenuated via the pharmacological inhibition of Caspase-1, which partially rescues behavioural abnormalities in sgshΔex5−6 mutant larvae in a context-dependent manner. We expect the sgshΔex5−6 zebrafish mutant to be a valuable resource in gaining a better understanding of MPS IIIA pathobiology towards the development of timely and effective therapeutic interventions. 相似文献
58.
A relatively simple instrumentation system is described which samples and records the body temperatures from up to twelve experimental animals over long periods of time. Body temperatures are sensed by temperature-sensitive FM transmitters implanted in the peritoneal cavities. The emitted signals are received by antennas, amplified, and sequentially gated into a frequency counter for counting; the resulting digital numbers are recorded in binarycoded decimal (BCD) format on punched paper tape. Samples can be spaced at intervals of from 1 to 60 minutes, and sampling can be continued over long periods of many months. This system eliminates the need for analog-to-digital conversion and allows rapid and direct transmission of the raw data to the digital computer for processing and analysis. 相似文献
59.
David A. Woodford Donald R. VanSteele Mohammed J. Hyder 《Journal of the American Ceramic Society》1991,74(12):3142-3144
The development of a tensile testing methodology for ceramics which enables a stress vs strain-rate response to be measured at high temperature is described. The test involves a carefully controled stress relaxation test at constant total strain using an experimental procedure and phenomenological analysis previously developed for metallic materials. It is demonstrated here with preliminary tests on alumina at 1050° and 1150°C. This offers, with further development, the possibility of establishing design stresses associated with low strain-rate behavior for structural applications. The results demonstrate that data covering four decades of strain rate may be generated in tests lasting a few hours. The inelastic strain consists of substantial anelastic recoverable strain in addition to a permanent creep strain. 相似文献
60.
Douglas A. Weirauch Jr. Donald P. Ziegler 《Journal of the American Ceramic Society》1996,79(4):920-926
Numerical analysis is used in this study to derive surface tension from the shape of a liquid silicate sessile drop. The speed afforded by the drop shape analysis package facilitates analysis of experimentally derived drop profiles. Drop symmetry, contact angles, and local shape variations can be readily determined, thereby permitting the detection of experimental errors. The experimental and analytical technique was first validated by determining the surface tension of high-purity gallium and aluminum under carefully controlled furnace atmospheres. Results for a calcium aluminosilicate melt are compared to pendant drop and maximum-bubble pressure measurements reported in the literature. The use of an internal scaling factor and the effect of substrate interactions are discussed. 相似文献