全文获取类型
收费全文 | 603763篇 |
免费 | 7490篇 |
国内免费 | 1793篇 |
专业分类
电工技术 | 11259篇 |
综合类 | 506篇 |
化学工业 | 87734篇 |
金属工艺 | 26990篇 |
机械仪表 | 21341篇 |
建筑科学 | 13296篇 |
矿业工程 | 3692篇 |
能源动力 | 15694篇 |
轻工业 | 42465篇 |
水利工程 | 6709篇 |
石油天然气 | 11471篇 |
武器工业 | 23篇 |
无线电 | 70420篇 |
一般工业技术 | 124629篇 |
冶金工业 | 108773篇 |
原子能技术 | 13063篇 |
自动化技术 | 54981篇 |
出版年
2021年 | 4999篇 |
2020年 | 3770篇 |
2019年 | 4863篇 |
2018年 | 13929篇 |
2017年 | 14268篇 |
2016年 | 12128篇 |
2015年 | 5974篇 |
2014年 | 9355篇 |
2013年 | 26563篇 |
2012年 | 16744篇 |
2011年 | 25996篇 |
2010年 | 21709篇 |
2009年 | 22943篇 |
2008年 | 23365篇 |
2007年 | 24533篇 |
2006年 | 16442篇 |
2005年 | 17254篇 |
2004年 | 15419篇 |
2003年 | 15163篇 |
2002年 | 13598篇 |
2001年 | 13157篇 |
2000年 | 12591篇 |
1999年 | 13031篇 |
1998年 | 33255篇 |
1997年 | 23061篇 |
1996年 | 17801篇 |
1995年 | 13169篇 |
1994年 | 11749篇 |
1993年 | 11591篇 |
1992年 | 8522篇 |
1991年 | 8037篇 |
1990年 | 7842篇 |
1989年 | 7578篇 |
1988年 | 7232篇 |
1987年 | 6358篇 |
1986年 | 6136篇 |
1985年 | 6975篇 |
1984年 | 6381篇 |
1983年 | 5853篇 |
1982年 | 5304篇 |
1981年 | 5520篇 |
1980年 | 5033篇 |
1979年 | 5027篇 |
1978年 | 5015篇 |
1977年 | 5683篇 |
1976年 | 7532篇 |
1975年 | 4323篇 |
1974年 | 4080篇 |
1973年 | 4146篇 |
1972年 | 3436篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Effect of Thermohydrogen Treatment on the Structure and Properties of Titanium Alloy Castings 总被引:2,自引:0,他引:2
Il'in A. A. Skvortsova S. V. Mamonov A. M. Permyakova G. V. Kurnikov D. A. 《Metal Science and Heat Treatment》2002,44(5-6):185-189
Metal Science and Heat Treatment - 相似文献
972.
Metal Science and Heat Treatment - 相似文献
973.
Yamanaka N. Kawano R. Oki E. Yasukawa S. Okazaki K. 《Advanced Packaging, IEEE Transactions on》2002,25(1):65-72
A 640-Gb/s high-speed ATM switching system that is based on the technologies of advanced MCM-C, 0.25-μm CMOS, and optical wavelength-division-multiplexing (WDM) interconnection is fabricated for future broadband backbone networks. A 40-layer, 160×114 mm ceramic MCM forms the basic ATM switch module with 80-Gb/s throughput. It consists of 8 advanced 0.25-μm CMOS LSIs and 32 I/O bipolar LSIs. The MCM has a 7-layer high-speed signal line structure having 50-Ω strip lines, high-speed signal lines, and 33 power supply layers formed using 50-μm thick ceramic layers to achieve high capacity. A uniquely structured closed-loop-type liquid cooling system for the MCM is used to cope with its high power dissipation of 230 W. A three-stage ATM switch is made using the optical WDM interconnection between high-performance MCMs. For WDM interconnection, newly developed compact 10-Gb/s, 8-WDM optical transmitter and receiver modules are used. These modules are each only 80×120×20 mm and dissipate 9.65 W and 22.5 W, respectively. They have a special chassis for cooling, which contains high-performance heat-conductive plates and micro-fans. An optical WDM router based on an arrayed waveguide router is used for mesh interconnection of boards. The optical WDM interconnect has 640-Gb/s throughput and simple interconnection 相似文献
974.
O. Perat J. M. Dorkel E. Scheid P. Temple Boyer Y. S. Chung A. Peyre-Lavigne M. Zecri P. Tounsi 《Microelectronics Reliability》2002,42(7):1053-1058
Reliability of thermomechanical simulations is critically linked to the accuracy of the mechanical properties that govern the behaviour of structure, like Young's modulus (E) and coefficient of thermal expansion (CTE). For many cases, the values found in literatures are dealing with bulk properties without detailed information on temperature effects. To address such issues, it is necessary to measure the materials parameters as a function of temperature. The measurement of CTE is usually accomplished by evaluating the thermal deflections of a subjected material layer deposited on a substrate, providing that E is known at a specific temperature of experiment. A bilayer method, based on theory of elasticity, is proposed to determine both E and CTE for a given temperature with a good resolution. This paper presents the theoretical analysis, the design and process of the microsystem test structures, and the main calculation results. 相似文献
975.
G.D. Wignall R.W. Hendricks W.C. Koehler J.S. Lin M.P. Wai E.L. Thomas R.S. Stein 《Polymer》1981,22(7):886-889
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow. 相似文献
976.
The properties of a spinel copper cobaltite obtained by thermal decomposition of mixed nitrates of both metals at 350°C and normal pressure are described. It has been shown that the maximum copper content (x) in the spinel CuxCo3?xO4 does not exceed 0.9. When the copper amount in the initial mixture is higher a second phase CuO is formed. The copper ions are distributed over the A- and the B-sites of the spinel lattice, i.e. the spinel is partially inverted. Such a model explains well the data obtained about the lattice parameter, IR-absorption and the magnetic susceptibility of the samples with different x. 相似文献
977.
978.
Dynamic mechanical properties have been investigated for interpenetrating-network systems based on polyol-cured polyurethanes (PU) and 2 to 1 n-butyl acrylate-n-butyl methacrylate (Ac) networks. The systems were formed simultaneously (SIN) from all of the precursors and reactants for both networks in the same vessel, and sequentially (SIPN) by swelling a precured PU with the reactants that will form the Ac network. If the Ac network is formed after gelation of the PU, the IPNs are transparent and appear to have single T (tan δmax) between those of the homonetworks; visible-phase separation occurs if the Ac is intentionally polymerized prior to PU gelation. Damping curves were lower and broader and the T (tan δmax) and rubber moduli were higher for the SIN than for the SIPN systems. Up to 65 percent Ac, the T (tan δmax) data for both SIN and SIPN fit the Gordon-Taylor equation if a T (tan δmax) for the Ac homonetwork 7°C higher than observed is used, suggesting a higher crosslink density for the Ac network under these conditions. The differences in properties of the SIN and SIPN are assumed to be dependent on sample homogeneity and upon the presence of a tin catalyst in the SIN preparation. This can result in limited Ac-network formation and consequent phase separation before PU gelation has occurred, and the catalyst may also increase the extent of interaction, such as grafting or hydrogen-bond formation between the networks. 相似文献
979.
Critical-point drying and freeze drying were compared both quantitatively and qualitatively as preparative procedures for scanning electron microscopy. Isolated hepatocytes were used as model cells. Nomarski differential interference contrast microscopy was used for light microscopic measurements of the hepatocytes in the unfixed, the glutaraldehyde fixed, the glutaraldehyde + OsO4 fixed, the critical-point dried and the freeze dried states. Critical-point dried hepatocytes were found to shrink to 38% of glutaraldehyde + OsO4 fixed volume, whereas optimal freeze dried hepatocytes (frozen in water saturated with chloroform and freeze dried at 183 K for 84 h) were found to shrink to 51% of glutaraldehyde + OsO4 fixed volume. Transmission and scanning electron micrographs of the critical-point dried cells showed well-preserved ultrastructure and surface structure. Micrographs of the freeze dried cells showed ultrastructure destroyed by internal ice crystals and surface structure destroyed by external ice crystals. Double-fixed isolated hepatocytes were shown to swell during storage in buffer and to shrink during storage after critical-point drying. For low magnification scanning electron microscopy (up to about 3000 times) both critical-point drying and freeze drying can be used. However, for high magnification scanning electron microscopy, critical-point drying is superior to freeze drying. 相似文献
980.
A. A. Konstantinov N. V. Kurenkov A. B. Malinin T. E. Sazonova S. V. Sepman 《Atomic Energy》1989,67(3):696-698
Translated from Atomnaya Énergiya, Vol. 67, No. 3, pp. 215–216, September, 1989. 相似文献