全文获取类型
收费全文 | 29439篇 |
免费 | 4671篇 |
国内免费 | 1611篇 |
专业分类
电工技术 | 735篇 |
综合类 | 1692篇 |
化学工业 | 9058篇 |
金属工艺 | 1996篇 |
机械仪表 | 1467篇 |
建筑科学 | 1268篇 |
矿业工程 | 326篇 |
能源动力 | 385篇 |
轻工业 | 738篇 |
水利工程 | 251篇 |
石油天然气 | 396篇 |
武器工业 | 200篇 |
无线电 | 3368篇 |
一般工业技术 | 4788篇 |
冶金工业 | 3450篇 |
原子能技术 | 158篇 |
自动化技术 | 5445篇 |
出版年
2024年 | 173篇 |
2023年 | 622篇 |
2022年 | 712篇 |
2021年 | 1284篇 |
2020年 | 1123篇 |
2019年 | 898篇 |
2018年 | 986篇 |
2017年 | 1131篇 |
2016年 | 1219篇 |
2015年 | 1358篇 |
2014年 | 1796篇 |
2013年 | 1843篇 |
2012年 | 1689篇 |
2011年 | 2094篇 |
2010年 | 1664篇 |
2009年 | 1837篇 |
2008年 | 1884篇 |
2007年 | 1954篇 |
2006年 | 1796篇 |
2005年 | 1550篇 |
2004年 | 1448篇 |
2003年 | 1229篇 |
2002年 | 1013篇 |
2001年 | 785篇 |
2000年 | 593篇 |
1999年 | 480篇 |
1998年 | 398篇 |
1997年 | 363篇 |
1996年 | 301篇 |
1995年 | 253篇 |
1994年 | 209篇 |
1993年 | 183篇 |
1992年 | 151篇 |
1991年 | 96篇 |
1990年 | 96篇 |
1989年 | 91篇 |
1988年 | 63篇 |
1987年 | 23篇 |
1986年 | 28篇 |
1985年 | 63篇 |
1984年 | 47篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1961年 | 6篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
71.
Nuclear magnetic resonance (n.m.r.) studies of 19F nuclei in a random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T2 components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T1 appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T1 were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals. 相似文献
72.
Arjunan Arulchakkaravarthi Rakesh Kumar Parthasarathy Santhanaraghavan Sivaramakrishnan Muralithar Rengasamy Gopalakrishanan Perumalsamy Ramasamy 《Materials Research Innovations》2002,6(5-6):273-276
Organic molecular scintillating crystals are noted for their good timing and particle discrimination process. Trans-stilbene
is one such candidate noted for its good particle detection characteristics for the past five decades. Progressive strengthening
of detection characteristics of trans-stilbene has been attempted by improving crystal perfection. A series of timing resolution
studies have been carried out for the Bridgman grown trans-stilbene crystals under different experimental conditions. The
results were compared with the previously reported values. Pulse shape discrimination process has been carried out for 241Am and 252Cf sources and good discrimination has been obtained for gamma-alpha and gamma-neutron sources from the grown organic phosphor
crystal.
Electronic Publication 相似文献
73.
Cis-1,4-polybutadiene (PB) in a 0.5% solution of a solvent mixture of dichloromethane and 1,2-dibromoethane or tetrahydrofuran was quantitatively brominated with elemental bromine at 0°C under careful exclusion of oxygen to head-to-head poly(vinyl bromide). Partially brominated PB has a structure of random or block sequences of butadiene units in the polymer depending on the bromination solvent but shows no stereospecificity in the CHBrCHBr-dyads. Partially brominated PB with block structure showed a microphase-separated morphology over a wide range of composition. Microphase separation is less pronounced for the more random structure of butadiene units. I.r and 13C n.m.r. spectroscopy of the partially brominated PB was used to follow the progress of the bromination. 相似文献
74.
精密陶瓷部件近净成型技术的发展 总被引:5,自引:0,他引:5
重点介绍了近十年发展起来的陶瓷部件的近净成型技术 ,主要包括直接凝固注模成型、凝胶注模成型、陶瓷注射成型、陶瓷无模成型和微注入成型。对这些新的成型方法的原理、工艺过程及应用特点进行了较全面的分析与比较。 相似文献
75.
Combined shape and sizing optimization of truss structures 总被引:1,自引:0,他引:1
In this paper, an evolutionary optimization method is presented for weight minimum problem of a 3-dimensional truss structure
in terms of nodal coordinates and element cross-sectional areas. The structure is subject to stress, local buckling and displacement
constraints. Two types of design variables with different natures are optimized separately: (1) a fully stressed design (FSD)
and scaling techniques are applied to sizing variables and (2) the evolutionary node shift method is applied to shape variables.
Alternating procedure is utilized to couple the two types of variables and to combine the results. The optimum solution is
achieved gradually from the initial configuration design. Two typical truss structures are examined to illustrate the validity
of the method.
Received: 22 October 2001 / Accepted: 04 June 2002
This research work is supported by the National Natural Science Foundation of China under the guarantees no. 10072050 and
10172072, respectively. 相似文献
76.
Temperature dependences of shrinkage forces appearing in oriented polymer samples when heated at constant length were recorded for polycarbonate, polyethylene terephthalate, polyethylene and polypropylene. The influence of various processing conditions on thermally stimulated shrinkage forces is demonstrated. A four-state model is proposed which qualitatively describes the temperature dependences of shrinkage forces in amorphous polymers. 相似文献
77.
D. Bogdal V. Yashchuk J. Pielichowski T. Ogul'Chansky M. Warzala V. Kudrya 《应用聚合物科学杂志》2002,84(9):1650-1656
The alkyl methacrylates with halogenated carbazolyl pendant groups were prepared, and the analysis of their absorption and emission spectra showed that the polymers containing monohalogenatged carbazole rings were capable of exhibiting a high singlet‐triplet (S‐T) conversion. The reasons that mainly triplet excitons could be observed in such polymers and additional bands appearance in the spectra of the polymers with dihalogenated carbazole rings are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1650–1656, 2002; DOI 10.1002/app.10469 相似文献
78.
A. Moran C. Madden R. Rebis R. Payne M. A. Matteson 《Journal of Thermal Spray Technology》1994,3(2):197-198
Over the past five years, the Annapolis Detachment, Carderock Division, Naval Surface Warfare Center (formerly David Taylor
Research Center) has established a state- of- the- art spray forming facility for the study and exploitation of this near
net shape manufacturing process. Spray forming is a single step gas atomization/deposition process which yields ferrous and
nonferrous, near final shape, near fully dense preforms that has proven to be a viable and cost effective alternative to conventional
metalworking technology for the production of material preforms with properties surpassing those of their cast and wrought
counterparts. Current programs at Carderock Divison Naval Surface Warfare Center are aimed at optimization of the process,
certification of the spray formed products and industrialization of the technology. 相似文献
79.
Rajiv Prakash 《应用聚合物科学杂志》2002,83(2):378-385
Polyaniline was electrochemically synthesized from an aqueous medium with various acid electrolytes via potentiodynamic and potentiostatic techniques. The electrochemical synthesis of polyaniline was studied over various substrates, including Pt, Ti, Ni, and SnO2 coated glass, and in various acid electrolytes. Cyclic voltammograms of electrochemically synthesized polyaniline were studied in HCl in a pH range of 1–4. Probable electrochemistry and chemical changes were deduced that occurred when polyaniline film was electrochemically oxidized and reduced between ?0.2 and 1.0 V versus a Ag/AgCl reference electrode in an acidic electrolyte at pH 1, and three corresponding oxidation and reduction peaks were described instead of two redox peaks (as observed by W. S. Huang, B. D. Humphrey, and A. G. MacDiarmid, J Chem Soc Faraday Trans 1 1986, 82, 2385). The electrochromic property was studied with changes in the chemical states of polyaniline during electrochemical oxidation and reduction. A new viscous electrolyte, aqueous AlCl3 (pH 2), saturated with AgCl was used for the construction of an electrochromic display device. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 378–385, 2002 相似文献
80.