全文获取类型
收费全文 | 173812篇 |
免费 | 21902篇 |
国内免费 | 9927篇 |
专业分类
电工技术 | 11918篇 |
技术理论 | 3篇 |
综合类 | 14046篇 |
化学工业 | 26218篇 |
金属工艺 | 23849篇 |
机械仪表 | 12929篇 |
建筑科学 | 12613篇 |
矿业工程 | 7532篇 |
能源动力 | 8714篇 |
轻工业 | 9355篇 |
水利工程 | 5136篇 |
石油天然气 | 7300篇 |
武器工业 | 3733篇 |
无线电 | 12911篇 |
一般工业技术 | 19656篇 |
冶金工业 | 9886篇 |
原子能技术 | 2275篇 |
自动化技术 | 17567篇 |
出版年
2024年 | 553篇 |
2023年 | 2941篇 |
2022年 | 5862篇 |
2021年 | 8028篇 |
2020年 | 6278篇 |
2019年 | 5221篇 |
2018年 | 5348篇 |
2017年 | 6899篇 |
2016年 | 8594篇 |
2015年 | 9503篇 |
2014年 | 12242篇 |
2013年 | 11937篇 |
2012年 | 12799篇 |
2011年 | 13225篇 |
2010年 | 9799篇 |
2009年 | 9916篇 |
2008年 | 8832篇 |
2007年 | 11736篇 |
2006年 | 10913篇 |
2005年 | 8839篇 |
2004年 | 6979篇 |
2003年 | 5850篇 |
2002年 | 4610篇 |
2001年 | 3635篇 |
2000年 | 2980篇 |
1999年 | 2282篇 |
1998年 | 1693篇 |
1997年 | 1403篇 |
1996年 | 1276篇 |
1995年 | 989篇 |
1994年 | 854篇 |
1993年 | 584篇 |
1992年 | 496篇 |
1991年 | 413篇 |
1990年 | 409篇 |
1989年 | 331篇 |
1988年 | 175篇 |
1987年 | 121篇 |
1986年 | 124篇 |
1985年 | 109篇 |
1984年 | 124篇 |
1983年 | 83篇 |
1982年 | 87篇 |
1981年 | 51篇 |
1980年 | 74篇 |
1979年 | 34篇 |
1964年 | 35篇 |
1962年 | 64篇 |
1959年 | 46篇 |
1951年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
912.
913.
K. Gunnarsson P.E. Roy S. Felton J. Pihl P. Svedlindh S. Berner H. Lidbaum S. Oscarsson 《Advanced materials (Deerfield Beach, Fla.)》2005,17(14)
Structured magnetic surfaces enabling programmable motion of single micrometer‐sized magnetic particles are reported on p. 1730 by Gunnarsson and co‐workers. Patterns of thin‐film magnetic elements are tailored to form transport lines with junctions for the separation of individual particles. This method has the potential to improve and generate new applications in biotechnology. The cover shows a schematic of the transportation and separation of magnetic particles functionalized with antibodies capable of selectively capturing the corresponding analytes from a sample. 相似文献
914.
Simultaneous HPLC quantification of total cholesterol,tocopherols and β-carotene in Barrosã-PDO veal 总被引:1,自引:0,他引:1
José A. Mestre Prates Mário A. Gonçalves Quaresma Rui J. Branquinho Bessa Carlos M.G. Andrade Fontes Cristina M.P. Mateus Alfaia 《Food chemistry》2006
A simple, rapid and sensitive procedure for the simultaneous determination of total cholesterol, tocopherols and β-carotene in meat is described. The method involves a direct saponification of the meat, a single n-hexane extraction and the analysis of the extracted compounds by normal-phase HPLC, using fluorescence (tocopherols) and UV–Vis photodiode array (cholesterol and β-carotene) detections in tandem. Rates of recovery of spiked meat samples were 93% for cholesterol, 83–86% for (α-, β- and -γ) tocopherols and 89% for β-carotene. Repeatabilities were high (CV < 6%) for all determined compounds, except for δ-tocopherol. This tocopherol, which is not usually present in meat, showed a much lower recovery percentage (73%) and repeatability (12.8%). This methodology was applied for the quantification of total cholesterol, tocopherols and β-carotene in three muscles (longissimus thoracis, longissimus lumborum and semitendinosus) of the Portuguese traditional Barrosã-PDO veal, obtained from autochthonous calves fed extensively during summer (with the least abundant green pastures) and slaughtered in early autumn (October). Barrosã-PDO veal showed median contents of total cholesterol (0.50–0.56 mg/g) and, depending on the analysed muscle, moderate to high contents of α-tocopherol (3.3–3.9 μg/g) and β-carotene (0.07–0.09 μg/g), suggesting an high sensorial and hygienic quality. 相似文献
915.
No authorship indicated 《Canadian Metallurgical Quarterly》2007,61(4):345
Presents a collection of abstracts from the 2007 Canadian Society for Brain, Behaviour and Cognitive Science (CSBBCS) Annual Meeting. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
916.
917.
This paper presents results of numerical simulations for impact effects in panel-like structures using solid and shell element modeling techniques. Three examples from experiments in literature have been numerically analyzed. The nonlinear transient dynamic analysis code, LS-DYNA is used in the simulations to model projectiles and panel-like targets. It is found that models established for panel-like targets using solid shell elements cannot only save significant computational effort, but also produce good results as long as the panel-like targets satisfy certain conditions. A criterion that governs the validity of modeling panel-like targets with shell elements is proposed in the paper. 相似文献
918.
Bionanoparticles of starch obtained by submitting native potato starch granules to acid hydrolysis conditions. The resulted starch nanoparticles were used as core or macro initiator for polymerization of ε‐caprolactone (CL). Starch nanoparticle‐g‐polycaprolactone was synthesized through ring‐opening polymerization (ROP) of CL in the presence of Sn(Oct)2 as initiator. The detailed microstructure of the resulted copolymer was characterized with NMR spectroscopy. Thermal characteristic of the copolymer was investigated using DSC and TGA. By introducing PCL, the range of melting temperature for starch was increased and degradation of copolymer occurred in a broader region. X‐ray diffraction and TEM micrographs confirmed that there was no alteration of starch crystalline structure and morphology of nanoparticles, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
919.
The rheological behavior, thermal properties, and molecular mobility of a series of maleic anhydride (MA) grafted high‐density polyethylenes were characterized and evaluated. The rheological behavior was studied with a Haake minilaboratory. The viscosity of the samples in their melt state decreased with an increase in the graft yield, and this could be attributed to the higher molecular mobility for samples with a higher degree of grafting. The thermal properties were investigated with dynamic mechanical analysis and differential scanning calorimetry. Positron annihilation lifetime measurements were used to study the effect of the degree of grafting on the chemical environment and the atomic‐scale free‐volume properties. It was found that the grafted MA group played a significant chemical inhibition role in positronium formation when the graft yield was low. The results also indicated that the higher the degree of grafting was, the broader the free‐volume distribution was. The relationship between the microstructure and rheological behavior is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
920.
Yongxian Zhao Baochen Huang Wei Yao Hailin Cong Huafeng Shao Aihua Du 《应用聚合物科学杂志》2008,107(5):2986-2993
A new organic‐solvent‐free water‐phase suspension method was used to synthesize partially epoxidized high trans‐1,4‐polyisoprene (TPI) to improve its properties, including oil resistance and wet‐skid resistance. The epoxidation was conducted in an aqueous peracetic acid solution and on the TPI granules prepared by a bulk precipitation method with supported titanium catalyst. The effects of the synthesis conditions, including reaction temperature, reaction time, and pH value, on the epoxy content were investigated. Epoxidized trans‐1,4‐polyisoprene (ETPI) with epoxy contents between 10 and 80% were obtained within 4 h. Both the amorphous and crystalline regions of TPI were epoxidized. The crystallization properties decreased with increasing epoxy content. ETPIs possessed lower mechanical properties than TPI but could be enhanced by vulcanization. The oil resistance and wet‐skid resistance were significantly improved after epoxidation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献