全文获取类型
收费全文 | 43926篇 |
免费 | 2191篇 |
国内免费 | 44篇 |
专业分类
电工技术 | 355篇 |
综合类 | 57篇 |
化学工业 | 9458篇 |
金属工艺 | 902篇 |
机械仪表 | 925篇 |
建筑科学 | 1609篇 |
矿业工程 | 94篇 |
能源动力 | 912篇 |
轻工业 | 6441篇 |
水利工程 | 409篇 |
石油天然气 | 176篇 |
武器工业 | 6篇 |
无线电 | 1937篇 |
一般工业技术 | 7413篇 |
冶金工业 | 8748篇 |
原子能技术 | 212篇 |
自动化技术 | 6507篇 |
出版年
2023年 | 381篇 |
2022年 | 575篇 |
2021年 | 1161篇 |
2020年 | 878篇 |
2019年 | 979篇 |
2018年 | 1643篇 |
2017年 | 1571篇 |
2016年 | 1705篇 |
2015年 | 1287篇 |
2014年 | 1686篇 |
2013年 | 3307篇 |
2012年 | 2481篇 |
2011年 | 2462篇 |
2010年 | 1922篇 |
2009年 | 1862篇 |
2008年 | 1782篇 |
2007年 | 1651篇 |
2006年 | 1200篇 |
2005年 | 1011篇 |
2004年 | 958篇 |
2003年 | 867篇 |
2002年 | 776篇 |
2001年 | 569篇 |
2000年 | 566篇 |
1999年 | 581篇 |
1998年 | 2571篇 |
1997年 | 1825篇 |
1996年 | 1173篇 |
1995年 | 729篇 |
1994年 | 578篇 |
1993年 | 669篇 |
1992年 | 278篇 |
1991年 | 278篇 |
1990年 | 223篇 |
1989年 | 240篇 |
1988年 | 214篇 |
1987年 | 195篇 |
1986年 | 185篇 |
1985年 | 215篇 |
1984年 | 197篇 |
1983年 | 154篇 |
1982年 | 189篇 |
1981年 | 197篇 |
1980年 | 207篇 |
1979年 | 124篇 |
1978年 | 124篇 |
1977年 | 333篇 |
1976年 | 691篇 |
1975年 | 99篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Ivan Fortelný Monika Lapčíková František Lednický Zdeněk Starý Zdeněk Kruliš 《Polymer Engineering and Science》2008,48(3):564-571
This article is focused on the phase structure development in immiscible polymer blends during melt mixing. Nonuniformity of the phase structure, i.e., the coexistence of areas containing particles with markedly different size distribution, was detected in quenched and compression molded samples of a number of various blends prepared by long and intensive mixing in the chamber of a Plasticorder. The same effect was found also for polystyrene/polyamide blends prepared in a twin‐screw extruder. It was shown that neglecting nonuniformity of the phase structure can lead to considerable error in evaluation of the effect of system parameters on the blend morphology. The reasons for the effect were discussed and it was found that inhomogeneous flow field in mixers is a plausible explanation of the nonuniform phase structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers 相似文献
32.
The new emerging area of Enterprise Wide Optimization (EWO) has focused the attention in effectively solving the combined production/distribution scheduling problem. The importance of logistic activities performed in multi-site environments comes from the relative magnitude of the associated transportation costs and the good chance of getting large savings on such expenses. This paper first develops an exact MILP mathematical formulation for the multiple vehicle time-window-constrained pickup and delivery (MVPDPTW) problem. The approach is able to account for many-to-many transportation requests, pure pickup and delivery tasks, heterogeneous vehicles and multiple depots. Optimal solutions for a variety of benchmark problems with cluster/random distributions of pickup and delivery locations and limited sizes in terms of customer requests and vehicles have been discovered. However, the computational cost exponentially grows with the number of requests. For large-scale m-PDPTW problems, a local search improvement algorithm steadily providing a better solution through two evolutionary steps is also presented. A neighborhood structure around the starting solution is generated by first allowing multiple request exchanges among nearby trips and then permitting the reordering of nodes on every individual route. If a better set of routes is found, both steps are repeated until no improved solution is discovered. Compact MILP mathematical formulations for both sub-problems have been developed and solved through an efficient branch-and-bound algorithm. A significant number of large-scale m-PDPTW benchmark problems, some of them including up to 100 transportation requests, were successfully solved in reasonable CPU times. 相似文献
33.
Vanesa Rodríguez-Amor Juan P. Fernández-Blázquez Antonio Bello Ernesto Pérez María L. Cerrada 《Polymer Bulletin》2008,60(1):89-96
Summary The effect of molecular weight on the uniaxial orientation process has been analyzed in two samples of thermotropic poly(diethylene
glycol p,p′-bibenzoate), evaluating the influence of that parameter on the type of orientation obtained. Several strain rates and deformation
temperatures have been tested in order to map out the conditions for obtaining the two different kinds of orientation. The
results show that in the lower molecular weight PDEB sample (Mw=31200) it is rather easy to get exclusively perpendicular “anomalous” orientation, with the molecular axes aligned transversely
to the stretching direction. However, it is extremely difficult to obtain 100% parallel “normal” orientation. On the contrary,
either type of orientation or a mixture of them can be easily developed for the higher molecular weight PDEB sample (Mw=102900). 相似文献
34.
35.
36.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
37.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
38.
Jürgen Schönbeçk 《NTM》2004,12(2):80-99
Thomas Fincke (January 6th, 1561–April 24th, 1656), born in Flensburg (Germany), was one of the very most important and significant scientists in Denmark during the
seventeenth century, a mathematician and astrologer and physician in the beginning of modern science, a representative of
humanism and an influentual academic organizer. He studied in Strasbourg (since 1577) and Padua (since 1583) and received
his M.D. in Basel (1587), he practised as a physician throughout his life (since 1587 or 1590) and became a professor at Copenhagen
(1591). But he was best known because of his Geometriae rotundi libri XIIII (1583), a famous book on plane and spherical trigonometry, based not on Euclid but on Petrus Ramus. In this influentual work,
in which Fincke introduced the terms tangent and secant and probable first noticed the Law of Tangents and the so-called Newton-Oppel-Mauduit-Simpson-Mollweide-Gauss-formula,
he showed himself to be „abreast of the mathematics of his time“.
相似文献
39.
40.
Toughening mechanism for a rubber-toughened epoxy resin with rubber/matrix interfacial modification 总被引:1,自引:0,他引:1
For a rubber-toughened piperidine-DGEBA epoxy resin, the interface between the rubber particle and the epoxy resin matrix was modified by an epoxide end-capped carboxyl terminated butadiene and acrylonitrile random copolymer (CTBN). The end-capping epoxides used were a rigid diglycidyl ether of bisphenol-A (Epon 828), a short-chain flexible diglycidyl ether of propylene glycol (DER 736), and a long-chain flexible diglycidyl ether of propylene glycol (DER 732). The microstructures and the fracture behaviour of these rubber-modified epoxy resins were studied by transmission electron microscopy and scanning electron microscopy. Their thermal and mechanical properties were also investigated. In the rubber-modified epoxy resins, if the added CTBNs were end-capped by a flexible diglycidyl ether of propylene glycol (DER 732 or DER 736) before curing, the interfacial zone of the undeformed rubber particle, the degree of cavitation of the cavitated rubber particle on the fracture surface and the fracture energy of the toughened epoxy resin were all significantly increased. The toughening mechanism based on cavitation and localized shear yielding was considered and a mechanism for the interaction between cavitation and localized shear yielding that accounts for all the observed characteristics is proposed. 相似文献