全文获取类型
收费全文 | 670篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 121篇 |
金属工艺 | 28篇 |
机械仪表 | 5篇 |
建筑科学 | 15篇 |
矿业工程 | 2篇 |
能源动力 | 8篇 |
轻工业 | 75篇 |
水利工程 | 2篇 |
无线电 | 69篇 |
一般工业技术 | 102篇 |
冶金工业 | 174篇 |
原子能技术 | 7篇 |
自动化技术 | 69篇 |
出版年
2022年 | 7篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 9篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 12篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 21篇 |
2012年 | 19篇 |
2011年 | 23篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 21篇 |
2006年 | 23篇 |
2005年 | 17篇 |
2004年 | 16篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 14篇 |
2000年 | 19篇 |
1999年 | 9篇 |
1998年 | 55篇 |
1997年 | 29篇 |
1996年 | 29篇 |
1995年 | 28篇 |
1994年 | 14篇 |
1993年 | 19篇 |
1992年 | 12篇 |
1991年 | 16篇 |
1990年 | 7篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 9篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1972年 | 5篇 |
1971年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有681条查询结果,搜索用时 15 毫秒
61.
Schuster M. Klein N. Ruther P. Trautmann A. Paul O. Kuzel P. Kadlec F. 《Selected Areas in Communications, IEEE Journal on》2005,23(7):1378-1384
Due to their unique properties, electromagnetic bandgap (EBG) materials are of high interest for applications in communication technology for many frequency bands from microwave up to optical frequencies. We have investigated in both simulation and experiment a two dimensionally periodic EBG structure made by reactive ion etching of silicon with a bandgap for transverse magnetic waves in the millimeter wave range around 100 GHz. The structure comprises both a large bandgap and a high mechanical stability due to interconnecting dielectric bridges. 相似文献
62.
Summary Oligomers with different aromatic substituents (oligostyrenes, oligo-p-ethylstyrenes, oligo-p-methoxystyrenes and oligo-1-vinylnaphthalenes) were synthesized by living anionic polymerization using sec-butyllithium as initiator. Number average degrees of polymerization were varied between 2 and 16 and narrow homologuedistributions were obtained. In the case of the benzenic types the isolation into pure homologues from dimers to hexamers was carried out by preparative gel permeation chromatography (GPC). In a polymeranalogous heterogeneous catalytic hydrogenation reaction the aromatic compounds were converted into oligomers with saturated cyclic structures, the initial homologue-distributions not being changed. Characterization of all oligomers was performed by GPC and proton nuclear magnetic resonance (1H-NMR). In the case of oligostyrenes and oligo-p-ethylstyrenes the occurrence of the characteristic high field shift of the ortho-protons is observed in dependence of the degree of polymerization. Oligo-1-vinylnaphthalenes show three differently shielded aromatic resonance areas. 相似文献
63.
The quantum efficiency (QE) in HgCdTe photovoltaic pixel arrays employing a photon-trapping (PT) structure realized with a periodic array of pillars intended to provide broadband operation was investigated. It was found that the QE depends heavily on the passivation of the pillar surface. This is due to the presence of large fixed positive charge on the surface of pillars passivated with anodic oxide. A three-dimensional numerical simulation model was used to study the effect of the surface charge density and surface recombination velocity on the exterior of the pillars. Then, the QE of this structure was evaluated subject to different surface conditions. It was found that alone the surface charge density or surface recombination is detrimental to the QE but that the QE is recovered when both phenomena are present. Subsequently, the crosstalk was analyzed and the superior performance of the PT structure was demonstrated by evaluating the modulation transfer function. 相似文献
64.
H Sánchez T Fester S Kloska W Schr?der W Schuster 《Canadian Metallurgical Quarterly》1996,15(9):2138-2149
The discovery of disrupted rps19 genes in Arabidopsis mitochondria prompted speculation about the transfer to the nuclear compartment. We here describe the functional gene transfer of rps19 into the nucleus of Arabidopsis. Molecular cloning and sequence analysis of rps19 show that the nuclear gene encodes a long N-terminal extension. Import studies of the precursor protein indicate that only a small part of this extension is cleaved off during import. The larger part of the extension, which shows high similarity to conserved RNA-binding domains of the RNP-CS type, became part of the S19 protein. In the Escherichia coli ribosome S19 forms an RNA-binding complex as heterodimer with S13. By using immuno-analysis and import studies we show that a eubacterial-like S13 protein is absent from Arabidopsis mitochondria, and is not substituted by either a chloroplastic or a cytosolic homologue of this ribosomal protein. We therefore propose that either a highly diverged or missing RPS13 has been functionally replaced by an RNP domain that most likely derived from a glycine-rich RNA-binding protein. These results represent the first case of a functional replacement of a ribosomal protein by a common RNA-binding domain and offer a new view on the flexibility of biological systems in using well-adapted functional domains for different jobs. 相似文献
65.
The interaction of Ni and Fe-Ni base alloys with the reactive impurities H2O, CO, H2 and CH4 in simulated cooling gas of the primary circuit of the High Temperature Gas Cooled Reactor (HTGR) causes corrosion effects that can significantly influence the mechanical properties. Apart from the formation of surface scales (oxides, carbides or mixed oxides/carbides), structural changes of the alloys are observed; depending on gas composition, gas supply rate and test temperature, carburization or decarburization can occur. In this report it is shown that an interpretation of the basic corrosion effects is possible on the basis of a modified stability diagram for chromium provided that - the kinetics of elementary gas metal reactions are incorporated in the expressions for carbon activity and oxygen partial pressure of the atmosphere and - the gradients of the potentials across the surface scales are taken into account. The interpretation allows the derivation of the corrosion behaviour of NiCr-base alloys in different HTGR helium compositions and enables the limits for the formation of protective chromia surface scales to be given. The influence of alloying elements other than chromium can be explained qualitatively. The results can be transferred to other reactive gas mixtures, which are characterized by an oxygen partial pressure near to the dissociation pressure of the scale forming oxides. 相似文献
66.
Studies over the past decade show that some people are receiving more care than they need, and some are receiving less. Simple averages from a number of studies indicate that 50 percent of people received recommended preventive care; 70 percent, recommended acute care; 30 percent, contraindicated acute care; 60 percent, recommended chronic care; and 20 percent, contraindicated chronic care. These studies strongly suggest that the care delivered in the United States often does not meet professional standards. Efforts to measure quality and report routinely on the results to the public at large would allow more definitive assessments of the status of the nation's health care and would enable us to single out the areas in need of improvement. 相似文献
67.
The less common methods of medication administration that used to be used only in the hospital are also now used in alternate settings. Understanding the treatment modalities, care requirements, and complications of these alternate routes of administration is important for nurses who participate in the care of patients receiving infusions. Several alternate routes of administration are discussed, with emphasis on the more commonly used methods: intra-arterial, intraspinal, intraventricular, intraperitoneal, intraosseous, and several other routes. 相似文献
68.
Using atomic force microscopy (AFM), we have investigated neutron-induced DNA double-strand breaks in plasmids in aqueous solution. AFM permits direct measurement of individual DNA molecules with an accuracy of a few nanometers. Furthermore, the analysis of the DNA fragment size distribution is non-parametric, whereas other methods are dependent on the model. Neutron irradiation of DNA results in the generation of many short fragments, an observation not made for damage induced by low-LET radiation. These data provide clear experimental evidence for the existence of clustered DNA double-strand breaks and demonstrate that short DNA fragments may be produced by such radiations in the absence of a nucleosomal DNA structure. 相似文献
69.
DM Schuster 《Canadian Metallurgical Quarterly》1996,2(4):503-514
The nature of the inhibition of camel retina acetylcholinesterase (AChE) activity by tetrahydro-aminoacridine (THA, tacrine) has been investigated in the present study. The non-significant change of the percent inhibition of AChE by THA with respect to various lengths of the preincubation period showed the type of the reversible inhibition. THA reversibly inhibited AChE activity in a concentration dependent manner; IC50 was 0.23 microM while the IC100 was 14.22 microM. The K(m) for the hydrolysis of acetylthiocholine iodide was found to be 62.6 microM in the control system; a value increased in the THA treated systems. The Vmax was 0.472 mumole/min/mg protein for the control system, while it decreased in the THA treated systems. Dixon, as well as Lineweaver-Burk, plots and their secondary replots indicated that the nature of the inhibition is of the linear mixed type, which is considered to be a partial competitive and pure non-competitive mixture. The values of Ki(slope) and K'i(intercept) were estimated as 0.068 microM and 0.181 microM, respectively. The K'i was greater than Ki indicating that THA has a greater affinity of binding for the peripheral site than the active site of the camel retina AChE. The use of camel retina as a good experimental animal model may open new avenues for studying acetylcholine and AChE metabolism. 相似文献
70.
We show that archaebacterial DNA polymerases are strongly inhibited by the presence of small amounts of uracil-containing DNA. Inhibition appears to be competitive, with the DNA polymerase exhibiting approximately 6500-fold greater affinity for binding the inhibitor than a DNase I-activated DNA substrate. All six archaebacterial DNA polymerases tested were inhibited, while no eubacterial, eukaryotic, or bacteriophage enzymes showed this effect. Only a small inhibition resulted when uracil was present as the deoxynucleoside triphosphate, dUTP. The rate of DNA synthesis was reduced by approximately 40% when dUTP was used in place of dTTP for archaebacterial DNA polymerases. Furthermore, an incorporated dUMP served as a productive 3'-primer terminus for subsequent elongation. In contrast, the presence of an oligonucleotide containing as little as a single dUrd residue was extremely inhibitory to DNA polymerase activity on other primer-template DNA. 相似文献