全文获取类型
收费全文 | 1743篇 |
免费 | 78篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 69篇 |
化学工业 | 347篇 |
金属工艺 | 56篇 |
机械仪表 | 61篇 |
建筑科学 | 25篇 |
矿业工程 | 1篇 |
能源动力 | 76篇 |
轻工业 | 151篇 |
水利工程 | 11篇 |
石油天然气 | 3篇 |
无线电 | 161篇 |
一般工业技术 | 309篇 |
冶金工业 | 313篇 |
原子能技术 | 36篇 |
自动化技术 | 204篇 |
出版年
2023年 | 27篇 |
2022年 | 25篇 |
2021年 | 49篇 |
2020年 | 20篇 |
2019年 | 28篇 |
2018年 | 47篇 |
2017年 | 36篇 |
2016年 | 64篇 |
2015年 | 30篇 |
2014年 | 63篇 |
2013年 | 97篇 |
2012年 | 71篇 |
2011年 | 82篇 |
2010年 | 75篇 |
2009年 | 75篇 |
2008年 | 74篇 |
2007年 | 62篇 |
2006年 | 65篇 |
2005年 | 65篇 |
2004年 | 37篇 |
2003年 | 33篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 29篇 |
1999年 | 43篇 |
1998年 | 124篇 |
1997年 | 62篇 |
1996年 | 66篇 |
1995年 | 45篇 |
1994年 | 40篇 |
1993年 | 29篇 |
1992年 | 17篇 |
1991年 | 17篇 |
1990年 | 27篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 10篇 |
1986年 | 18篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有1823条查询结果,搜索用时 578 毫秒
131.
J Sloan-Lancaster J Presley J Ellenberg T Yamazaki J Lippincott-Schwartz LE Samelson 《Canadian Metallurgical Quarterly》1998,143(3):613-624
The nonreceptor protein tyrosine kinase ZAP-70 is a critical enzyme required for successful T lymphocyte activation. After antigenic stimulation, ZAP-70 rapidly associates with T cell receptor (TCR) subunits. The kinetics of its translocation to the cell surface, the properties of its specific interaction with the TCRzeta chain expressed as a chimeric protein (TTzeta and Tzetazeta), and its mobility in different intracellular compartments were studied in individual live HeLa cells, using ZAP-70 and Tzetazeta fused to green fluorescent protein (ZAP-70 GFP and Tzetazeta-GFP, respectively). Time-lapse imaging using confocal microscopy indicated that the activation-induced redistribution of ZAP-70 to the plasma membrane, after a delayed onset, is of long duration. The presence of the TCRzeta chain is critical for the redistribution, which is enhanced when an active form of the protein tyrosine kinase Lck is coexpressed. Binding specificity to TTzeta was indicated using mutant ZAP-70 GFPs and a truncated zeta chimera. Photobleaching techniques revealed that ZAP-70 GFP has decreased mobility at the plasma membrane, in contrast to its rapid mobility in the cytosol and nucleus. Tzetazeta- GFP is relatively immobile, while peripherally located ZAP-70 in stimulated cells is less mobile than cytosolic ZAP-70 in unstimulated cells, a phenotype confirmed by determining the respective diffusion constants. Examination of the specific molecular association of signaling proteins using these approaches has provided new insights into the TCRzeta-ZAP-70 interaction and will be a powerful tool for continuing studies of lymphocyte activation. 相似文献
132.
BACKGROUND: The aim of this study was to obtain a more precise understanding of the mechanical properties of the periodontal ligament in continuously erupting incisors by comparing the shear stress-strain relations among teeth from four closely related species. METHODS: Four species of experimental animals (mice, hamsters, rats, and rabbits) were used. Transverse sections of the left mandibular incisors were cut from the incisal, middle, and basal regions of each incisor. The tooth was pushed out of the alveolar bone in an extrusive direction at 5 mm/min using a materials testing machine. The maximum shear stress, maximum shear strain, tangent modulus, and failure strain energy density were estimated from the resulting stress-strain curve. Polarized light microscopic observations of collagen fibers were also made. RESULTS: All the biomechanical measures tended to decrease from the incisal toward the basal regions in all species. There were large species differences, especially in the incisal region, with the greatest maximum shear stress and failure strain energy density in hamsters. The greatest tangent modulus and the smallest maximum shear strain were observed in mice. The birefringent fiber architectures of the periodontal ligaments in the four species appeared to be similarly organized; the incisal periodontal ligament appeared to have more organized and thicker collagen fibres than did the middle and basal ligaments in the four species. CONCLUSIONS: These results suggest that the regional differences in the biomechanical properties of the periodontal ligament depend upon the developmental stages of the periodontal collagen fibers that may be related to the general arrangement, diameters, and densities of the collagen fiber bundles and the fiber insertions into the alveolar bone and cementum. The species differences in the biomechanical properties may be due to differences in the width of the periodontal ligament and the waviness as well as the strength and stiffness of the periodontal collagen fibers. 相似文献
133.
T Yamazaki T Kimoto K Higuchi Y Ohta S Kawato S Kominami 《Canadian Metallurgical Quarterly》1998,139(12):4765-4771
o-Nitrophenyl sulfenyl-modified ACTH (NPS-ACTH) stimulated steroidogenesis acutely in bovine fasciculata-reticularis cells without increase in cellular cAMP synthesis. Application of NPS-ACTH to the cultured cells induced Ca2+ signals in individual cells as detected by video-enhanced microscopic fluorescence measurements. The percentage of Ca2+ signaling cells corresponded well with the increase of steroidogenesis induced by NPS-ACTH below 1 nM. Treatment of the cells with nicardipine, a Ca2+ channel blocker, suppressed the Ca2+ signals except for the transient increase just after the addition of NPS-ACTH and also blocked completely the stimulative effect on the steroidogenesis of NPS-ACTH below 1 nM. At a dosage of NPS-ACTH higher than 10 nM, the stimulative effect of steroidogenesis was partly suppressed by nicardipine and also by AA-861, a lipoxygenase inhibitor. The action of NPS-ACTH might be mediated by both Ca2+ and lipoxygenase metabolite(s) of arachidonic acid as dual second messengers. The effect of ACTH in pM range on the steroidogenesis was suppressed completely by the treatment with nicardipine and AA-861 at the same time, indicating that the action was mediated by both Ca2+ and the lipoxygenase metabolite(s) but not by cAMP. cAMP plays a significant role as a second messenger for ACTH action only at ACTH concentrations greater than 10 pM. 相似文献
134.
135.
Juhachi Oda Kouetsu Yamazaki 《International journal for numerical methods in engineering》1980,15(7):1095-1105
In this paper, a procedure for obtaining a fully stresses shape of elastic continuum under arbitrary design conditions is proposed, by using the optimum distribution of the material properties such as the Young's modulus or the plate thickness. By using this technique, the optimum multiple-connected shape can be created from the original shape of simply body. The optimum shape of a road-pole subjected to an uniformly distributed load is determined by using the technique, and from the results the effectiveness of the technique is examined numerically. 相似文献
136.
Teramura H. Ono K. Ando S. Yamazaki Y. Yamamoto S. Matsuo K. 《Communications, IEEE Transactions on》1981,29(12):1942-1951
The use of the public data network for facsimile communication has remarkable advantages with regard to high speed and reliable transmission and, in addition, it is well applicable to provide value added facilities for future service extension. The Research and Development Laboratories of Kokusai Denshin Denwa (KDD) Company, Ltd. have developed an experimental facsimile communication system on the packet switched data network (PSDN). The system is composed of packet switching exchanges (PSE), high speed digital facsimile terminal equipment, a facsimile communication processor (FCP), and facsimile packet assembly/ disassembly equipment (FAX-PAD). The facsimile equipment in the system adopts a two-dimensional modified READ code and has the interface protocol to the PSDN. The FCP provides the store-and-forward facilities to provide such services as delayed delivery, multiaddress delivery, and mailbox service. The FAX-PAD realizes the interworking between facsimile equipments on the public switched telephone network (PSTN) and those on PSDN. After various experiments including international field tests, it was confirmed that the system is useful for future advanced facsimile service. 相似文献
137.
The effect of the addition of certain low molecular weight compounds to highly crosslinked epoxy resins was investigated. The behavior which is known as antiplasticization, such as increases in modulus and yield strength and the elimination of β-transition, was observed in the highly crosslinked system as well as in the reported cases of thermoplastics—poly(vinyl chloride), bisphenol A polycarbonate, and polysulfone. Chlorinated biphenyl was found to be one of the most effective antiplasticizers examined in the present paper. However, the remarkable reduction in compressive strain at break and impact strength was not recognized for the highly antiplasticized samples. These phenomena have been interpreted on the basis of free volume concept. 相似文献
138.
Piao Y Yamashita M Kawaraichi N Asegawa R Ono H Murooka Y 《Journal of Bioscience and Bioengineering》2004,98(3):167-173
Since the chemical synthesis of vitamin B12 requires more than 70 steps, the production of vitamin B12 has been achieved by microorganism fermentation with additional brief chemical modifications. In an effort to increase the productivity of vitamin B12, we tried to express 10 genes belonging to the hem, cob and cbi gene families involved in the synthesis of vitamin B12 in Propionibacterium freudenreichii, which is a known producer of vitamin B12. In a recombinant P. freudenreichii clone that harbored the expression vector containing a cobA, cbiLF, or cbiEGH, we obtained an increase in vitamin B12 production of 1.7-, 1.9-, and 1.5-fold higher, respectively, than that in the microorganism without any cloned genes in the expression vector pPK705. The cobU and cobS genes caused a slight increase in the production of vitamin B12. Furthermore, we achieved multigene expression in P. freudenreichii. In a recombinant P. freudenreichii clone that harbored an exogenous gene, hemA, from Rhodobacter sphaeroides and endogenous hemB and cobA genes, we successfully achieved the production of about 1.7 mg/l vitamin B12, 2.2-fold higher than that produced by P. freudenreichii harboring pPK705. 相似文献
139.
Takemitsu Kunio Tatsuya Yamazaki Eiji Ohta Makoto Sakata 《Solid-state electronics》1983,26(2):155-160
The transient capacitance technique has been used to study the chromium-related levels in the silicon band gap. Chromium was diffused at temperature of 1100 and 1150°C for 0.5 and 3 hr. Five different levels at Ec?0.11 eV, Ec?0.21 eV, Ec?0.28 eV, Ec?0.36 eV and Ec?0.45 eV were obtained from the Arrheniu plots of the electron thermal-emission rates. The number of levels in the upper half of the band gap decreased from five to two with an increase of Cr-diffusion period. Two levels were located at Ec?0.20 eV (donor) and Ec?0.43 eV (acceptor). A donor level was also observed at Ev + 0.25 eV. The donor level was not affected by the diffusion condition. The majority carrier capture cross sections of the three dominant levels have been measured by the transient capacitance technique modified by the pulse transformer. The values were σn = 4.1 × 10?15 cm2 for the upper donor at Ec?0.20 eV, σn = 2.0 × 10?16 cm2 for the acceptor at Ec ?0.43 eV and σp = 9.1 × 10?18 cm2 for the lower donor at Ev + 0.25 eV, and were independent of temperature. The three dominant levels are due to distinct chromium centers. 相似文献
140.
A recirculating system of aqueous trichloroethylene (TCE) solutions through the packed bed reactor with TiO2 pellets has been developed in order to mineralize TCE without difficulties for filtration and recovery of catalyst. The TiO2 pellets prepared by sol gel method have photocatalytic activity similar to commercially available PC-101 and PC-102 in the powder form and to ST-B11 pellets. In batch experiments with TiO2 powders, Degussa P-25 is the most active photocatalyst, which indicates that specific surface area is not an important factor controlling the photocatalytic activity in aqueous solutions. The degradation rates of TCE in the recirculating system with TiO2 pellets decreased in the presence of H2O2, while were remarkably accelerated by adding S2O8(2-). The presence of S2O8(2-) ions more than 0.01 mol dm(-3) completely suppressed hole-electron recombination and mineralized 50 ppm TCE with the 2 h irradiation. In a reactor without TiO2 photocatalysts, TCE was photodegraded by SO4- radicals which produced by photodissociation of S2O8(2-). The degradation rates increased with increase of the initial S2O8(2-) concentration. However, TCE was not mineralized but converted to intermediates which were slowly degraded to Cl- by continuing the irradiation. 相似文献