全文获取类型
收费全文 | 1842篇 |
免费 | 91篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 24篇 |
综合类 | 16篇 |
化学工业 | 564篇 |
金属工艺 | 30篇 |
机械仪表 | 31篇 |
建筑科学 | 138篇 |
矿业工程 | 3篇 |
能源动力 | 27篇 |
轻工业 | 171篇 |
水利工程 | 11篇 |
石油天然气 | 3篇 |
无线电 | 116篇 |
一般工业技术 | 373篇 |
冶金工业 | 68篇 |
原子能技术 | 16篇 |
自动化技术 | 347篇 |
出版年
2023年 | 27篇 |
2022年 | 49篇 |
2021年 | 65篇 |
2020年 | 36篇 |
2019年 | 47篇 |
2018年 | 43篇 |
2017年 | 42篇 |
2016年 | 51篇 |
2015年 | 47篇 |
2014年 | 73篇 |
2013年 | 97篇 |
2012年 | 89篇 |
2011年 | 157篇 |
2010年 | 99篇 |
2009年 | 111篇 |
2008年 | 102篇 |
2007年 | 84篇 |
2006年 | 85篇 |
2005年 | 73篇 |
2004年 | 68篇 |
2003年 | 53篇 |
2002年 | 51篇 |
2001年 | 44篇 |
2000年 | 42篇 |
1999年 | 41篇 |
1998年 | 29篇 |
1997年 | 27篇 |
1996年 | 18篇 |
1995年 | 20篇 |
1994年 | 27篇 |
1993年 | 14篇 |
1992年 | 10篇 |
1991年 | 23篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 7篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1967年 | 2篇 |
1939年 | 1篇 |
1931年 | 3篇 |
排序方式: 共有1938条查询结果,搜索用时 328 毫秒
991.
Polybrominated diphenyl ethers vs alternate brominated flame retardants and Dechloranes from East Asia to the Arctic 总被引:1,自引:0,他引:1
Möller A Xie Z Cai M Zhong G Huang P Cai M Sturm R He J Ebinghaus R 《Environmental science & technology》2011,45(16):6793-6799
Marine boundary layer air and seawater samples taken during a polar expedition cruise from East China Sea to the Arctic were analyzed in order to compare the occurrence, distribution, and fate of the banned polybrominated diphenyl ethers (PBDEs) with their brominated alternatives as well as the chlorinated Dechloranes. The sum of PBDEs (∑(10)PBDEs) in the atmosphere ranged from 0.07 to 8.1 pg m(-3) with BDE-209 being the dominating congener and from not detected (n.d.) to 0.6 pg L(-1) in seawater. Alternate brominated flame retardants (BFRs), especially hexabromobenzene (HBB), (2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE), pentabromotoluene (PBT), 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (EHTBB), bis-(2-ethylhexyl)-tetrabromophthalate (TBPH), were detected in higher concentrations than PBDEs, even in the high Arctic (0.6 to 15.4 pg m(-3) for sum of alternate BFRs), indicating the change of PBDEs toward alternate BFRs in the environmental predominance. In addition, Dechlorane Plus (DP) as well as Dechlorane 602, 603, and 604 were detected both in the atmosphere and in seawater. The highest concentrations as well as the highest compound variability were observed in East Asian samples suggesting the Asian continent as source of these compounds in the marine environment. The air-seawater exchange indicates strong deposition, especially of alternate BFRs, as well as dry particle-bound deposition of BDE-209 into the ocean. 相似文献
992.
Recently, biotin (vitamin H) has been described as a ligand for active targeting and it has been found that many cancer cells overexpress the biotin receptor. In this study a biotin-conjugated block copolymer, biotin-poly(2-ethyl-2-oxazoline)-block-poly{N '-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} (biotin-pEtOx-b-pASP(DEA) is synthesized by a living cationic polymerization of the pEtOx-block followed by the nucleophilic ringopening polymerization of the pASP-block. The biotin moiety is coupled to the pEtOx-b-pASP precursor by a Cu(I) mediated azide-alkyne click chemistry and finally, the diethylamine (DEA) side chain is introduced by a polymer analogous reaction. The final polymer P1 formed polyplexes in the presence of plasmid DNA that are characterized with respect to N/P ratio, size, zeta potential, and shape compared to a control polymer P2 without biotin. In addition, HEK293 cells are transfected with these polyplexes and the number of fluorescent HEK293 cells is evaluated to assess the influence of polymer nature on the activity of the micelles. Flow cytometric analysis revealed a significantly higher uptake of the biotin-PEtOx-PASP(DEA)/pDNA micelle than the PEtOx-PASP(DEA)/pDNA micelle against HEK293 cells at a low N/P ratio of 20, consistent with the transfection results whereas at higher N/P ratio no difference can be observed anymore between the two polymers. 相似文献
993.
Ralf Endres Tillmann KraussFrank Wessely Udo Schwalke 《Microelectronic Engineering》2011,88(12):3393-3398
In this work, we present MOS capacitors and field effect transistors with a crystalline gadolinium oxide (Gd2O3) gate dielectric and metal gate electrode (titanium nitride) fabricated in a gentle damascene gate last process. Details of the gate last process and initial results on MOS devices with equivalent oxide thicknesses (EOT) of 3.0 nm and 1.5 nm, respectively, are shown. 相似文献
994.
Qingqing Chen Daxin Li Zhihua Yang Dechang Jia Yu Zhou Ralf Riedel 《Ceramics International》2021,47(16):22839-22853
Tris(dichloromethylsilylethyl)borane is a compound containing a B–C bond and Cl and H elements. Herein, we propose a novel method to synthesize polyborosilazanes using tris(dichloromethylsilylethyl)borane and boron trichlorosilane as boron sources and hexamethyldisilazane as a nitrogen source. The microstructure and chemical composition of the as-synthesized polyborosilazanes and as-annealed SiBCN ceramics were investigated using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, Raman spectroscopy, scanning electron microscope, and transmission electron microscope methods. The organic precursors were converted entirely into inorganic ceramics at 800 °C, and the ceramic yield of the polyborosilazanes was 88% at 1000 °C. SiBCN ceramics with irregular shapes contained chemical bonds of B–N, Si–N, and Si–C at 1500 °C and retained an amorphous structure below 1600 °C. After the first cycle, the fabricated SiBCN ceramic anodes exhibited a reversible capacity of 261.3 mA h/g, which was 2.6 times that reported in the literature (101 mA h/g). The discharge capacity decreased to 157.6 mA h/g after 30 cycles. The satisfactory electrochemical performance of the resulting SiBCN ceramic anodes can be attributed to the formation of conductive carbon species favoring the transport properties of lithium ion. 相似文献
995.
Viatcheslav Malikov Ralf Ossenbrink Bernd Viehweger Vesselin Michailov 《The International Journal of Advanced Manufacturing Technology》2012,61(5-8):449-455
The nonparametric location–scale statistic is introduced for a change-point problem. A combination of the Wilcoxon and Mood statistics is extended to the change-point setting. The limiting distribution of proposed statistic is derived for testing the null hypothesis of no change. The finite sample critical value of the suggested statistic is estimated by simulation studies. The accuracy of detecting a change point is investigated by simulation studies for various distributions. The method is illustrated by the analysis of real data. 相似文献
996.
Schäffer Michael Sturm Ralf Friedrich Horst E. 《International Journal of Mechanics and Materials in Design》2019,15(1):43-60
International Journal of Mechanics and Materials in Design - A challenge in the design and optimization of vehicle structures is the high computational costs required for crash analysis. In this... 相似文献
997.
Sheng Naicheng Horke Katharina Meyer Andreas Rettig Ralf Singer Robert F. 《Oxidation of Metals》2019,91(1-2):113-129
Oxidation of Metals - The oxidation behavior of superalloy IN 713 fabricated by metal injection molding (MIM) was investigated and compared with standard cast material plus hot isostatic pressing... 相似文献
998.
999.
Philipp Mertmann Denis Eremin Thomas Mussenbrock Ralf Peter Brinkmann Peter Awakowicz 《Computer Physics Communications》2011,(10):2161-2167
Particle-in-cell (PIC) simulations with Monte-Carlo collisions are used in plasma science to explore a variety of kinetic effects. One major problem is the long run-time of such simulations. Even on modern computer systems, PIC codes take a considerable amount of time for convergence. Most of the computations can be massively parallelized, since particles behave independently of each other within one time step. Current graphics processing units (GPUs) offer an attractive means for execution of the parallelized code. In this contribution we show a one-dimensional PIC code running on NVIDIA® GPUs using the CUDA™ environment. A distinctive feature of the code is that size of the cells that the code uses to sort the particles with respect to their coordinates is comparable to size of the grid cells used for discretization of the electric field. Hence, we call the corresponding algorithm “fine-sorting”. Implementation details and optimization of the code are discussed and the speed-up compared to classical CPU approaches is computed. 相似文献
1000.
Dr. Frank Wendland Dr. Georg Berthold Dr. Johann-Gerhard Fritsche Dr. Frank Herrmann Dr. Ralf Kunkel Prof.?Dr. Hans-J��rgen Voigt Prof.?Dr. Harry Vereecken 《Grundwasser》2011,16(3):163-176
A regional scale conceptual hydrogeological model has been developed for evaluating residence times of groundwater in the upper aquifers and unsaturated zone within the Federal State of Hessen (Germany). The model is based on digitally available data bases and was applied with a spatial resolution of 60?m×60?m. Typical residence times for areas of unconsolidated deposits ranged between 10 and 25 years, whereas residence times of less than 5?years were found in areas of consolidated rock. Within the EU-Water Framework Directive, these results may help in assessing temporal and regional impacts of measures to reduce mass loading from the surface to groundwater. This will lead to better decisions, for instance whether additional measures to reach the environmental objectives should be applied. 相似文献