全文获取类型
收费全文 | 334530篇 |
免费 | 4011篇 |
国内免费 | 1270篇 |
专业分类
电工技术 | 5560篇 |
综合类 | 2504篇 |
化学工业 | 47288篇 |
金属工艺 | 14107篇 |
机械仪表 | 10542篇 |
建筑科学 | 8198篇 |
矿业工程 | 1431篇 |
能源动力 | 8392篇 |
轻工业 | 24630篇 |
水利工程 | 3421篇 |
石油天然气 | 3581篇 |
武器工业 | 15篇 |
无线电 | 43408篇 |
一般工业技术 | 65451篇 |
冶金工业 | 51180篇 |
原子能技术 | 5326篇 |
自动化技术 | 44777篇 |
出版年
2022年 | 1503篇 |
2021年 | 2246篇 |
2020年 | 1624篇 |
2019年 | 1967篇 |
2018年 | 17282篇 |
2017年 | 16197篇 |
2016年 | 13066篇 |
2015年 | 2829篇 |
2014年 | 4236篇 |
2013年 | 11762篇 |
2012年 | 9281篇 |
2011年 | 17657篇 |
2010年 | 14883篇 |
2009年 | 13301篇 |
2008年 | 14932篇 |
2007年 | 15815篇 |
2006年 | 7516篇 |
2005年 | 7684篇 |
2004年 | 7361篇 |
2003年 | 7679篇 |
2002年 | 6576篇 |
2001年 | 6628篇 |
2000年 | 6157篇 |
1999年 | 6472篇 |
1998年 | 16587篇 |
1997年 | 11468篇 |
1996年 | 8865篇 |
1995年 | 6649篇 |
1994年 | 5935篇 |
1993年 | 5880篇 |
1992年 | 4153篇 |
1991年 | 4053篇 |
1990年 | 3867篇 |
1989年 | 3659篇 |
1988年 | 3585篇 |
1987年 | 3030篇 |
1986年 | 2949篇 |
1985年 | 3227篇 |
1984年 | 2948篇 |
1983年 | 2836篇 |
1982年 | 2649篇 |
1981年 | 2553篇 |
1980年 | 2476篇 |
1979年 | 2314篇 |
1978年 | 2114篇 |
1977年 | 2621篇 |
1976年 | 3581篇 |
1975年 | 1772篇 |
1974年 | 1733篇 |
1973年 | 1673篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Stanisic B.R. Verghese N.K. Rutenbar R.A. Carley L.R. Allstot D.J. 《Solid-State Circuits, IEEE Journal of》1994,29(3):226-238
This paper describes new techniques for the simulation and power distribution synthesis of mixed analog/digital integrated circuits considering the parasitic coupling of noise through the common substrate. By spatially discretizing a simplified form of Maxwell's equations, a three-dimensional linear mesh model of the substrate is developed. For simulation, a macromodel of the fine substrate mesh is formulated and a modified version of SPICE3 is used to simulate the electrical circuit coupled with the macromodel. For synthesis, a coarse substrate mesh, and interconnect models are used to couple linear macromodels of circuit functional blocks. Asymptotic Waveform Evaluation (AWE) is used to evaluate the electrical behavior of the network at every iteration in the synthesis process. Macromodel simulations are significantly faster than device level simulations and compare accurately to measured results. Synthesis results demonstrate the critical need to constrain substrate noise and simultaneously optimize power bus geometry and pad assignment to meet performance targets 相似文献
992.
V. V. Veremey A. A. Kostenko I. K. Kuz'michev A. E. Poyedinchuk G. I. Khlopov 《Journal of Infrared, Millimeter and Terahertz Waves》1994,15(7):1283-1295
Reported here are the results on level and structure of the radiated field of an open resonator at and off resonance. On the basis of the modelling problem rigorous solution and the measurements at 4-millimeter wavelength we find there are no ways to compensate the radiated field from an open electromagnetic structure at resonance. Analysis of open resonator excitation efficiency shows that the mismatch loss of a slot-fed open resonator runs to 34% while at the aperture-feed excitation this is not more than 6% for the same-geometry resonator. 相似文献
993.
994.
This electron microscopical study was performed in order to follow the endocytic pathway of horseradish peroxidase and colloidal gold tracers and to determine the involvement of endocytosis in postnatal differentiation in superficial cells of the mouse urinary bladder epithelium. Morphometric analyses of late endosomes/multivesicular bodies from day of birth to day 25 were performed. The internalisation and intracellular transport of luminal plasmalemma to multivesicular bodies via endocytic vesicles, early endosomes and pleomorphic compartments was established. Dynamic changes in endocytic activity took place within the first few days of postnatal differentiation. During this period the number of multivesicular bodies changed in an inverse ratio to their size. After the third day endocytic activity gradually approached the low rate of adult urothelium. 相似文献
995.
Affiliate of the L. Ya. Karpov Scientific-Research Institute of Physical Chemistry. Translated from Atomnaya énergiya, Vol.
76, No. 5, pp. 422–428, May, 1994. 相似文献
996.
Antigen-induced arthritis in guinea pigs was used as a model to investigate the pathogenic mechanisms responsible for cartilage destruction in chronic joint inflammation. The activation of macrophages, their effects on cartilage metabolism, and the development of autoimmunity to cartilage constituents were studied during the progression of arthritis. The results show that in arthritic animals the macrophages are systemically activated, with a peak in the early phase of inflammation. Interleukin 1, produced by the activated cells, suppresses the proteoglycan synthesis in cartilage explants and cultured chondrocytes and increases the proliferation of the cells in vitro. During the progression of arthritis humoral and cell-mediated immune responses to collagen type II and cartilage proteoglycans occur correlating with the severity of arthritis. It is concluded that different immunological mechanisms may be involved in cartilage destruction during antigen-induced arthritis. Mediator-induced metabolic reactions dominate in the early phase, whereas autoimmunity to cartilage might play an essential role in later phases of arthritis. 相似文献
997.
Thomas L. Landers Melinda K. Beavers Malik Sadiq Don E. Stuart 《Computers & Industrial Engineering》1994,27(1-4):245-248
This paper describes an approach, conceptual framework, and software architecture for dynamic reconfiguration of the order picking system. The research and development project was sponsored by the Material Handling Research Center (MHRC), a National Science Foundation sponsored Cooperative Industry/University Research Center. The storage configuration is assumed to be an in-the-aisle order picking system in which stockkeeping units (SKUs) can occupy variable capacity storage locations and stock-splitting is allowed among zones (clusters). The product mix may include multiple product families with different life cycles, correlated demand within families and commonality of demand across families. 相似文献
998.
Arylsulfate sulfotransferase purified from Eubacterium A-44 has higher specific activity than the enzymes from Klebsiella K-36 and Haemophilus K-12. Propylparaben and butylparaben were good substrates among several parabens. The antibacterial activity of parabens was reduced by the sulfation of the phenolic hydroxy group. Tyrosine-containing peptides, kyotorphin, enkephalin and cholecystokinin non-sulfate, were effective as acceptor substrates by A-44, K-36 and K-12 sulfotransferases. 相似文献
999.
1000.
OBJECTIVE: To determine the characteristics and long-term outcome of radiation-induced thyroid cancer in children. DESIGN: Retrospective review of a cohort of 4296 irradiated patients who received childhood radiation treatment to the head and neck area at the same hospital. PATIENTS: Forty-one children who were younger than 20 years when thyroid cancer developed in them and 77 adults in whom thyroid cancer developed. All 118 cases were diagnosed before 1974 and were followed up for a median of 19.4 years. RESULTS: Children presented with clinically palpable lymph nodes more often than adults (30.7% vs 15.1%, P = .05) and had more recurrences (39% vs 16%, P = .05). Despite these frequent recurrences, only one patient (an adult) died of thyroid cancer. Seventy percent of the recurrences occurred during the first 10 years of follow-up, but recurrences continued after 20 years. The adults had previously identified factors that predicted the risk of recurrences, but none could be identified in the children. CONCLUSION: The presentation and relatively good outcome of radiation-induced thyroid cancer in children is similar to that in nonirradiated children. Frequent and late recurrences call for lifelong follow-up. 相似文献