全文获取类型
收费全文 | 252725篇 |
免费 | 4050篇 |
国内免费 | 437篇 |
专业分类
电工技术 | 4413篇 |
综合类 | 264篇 |
化学工业 | 42159篇 |
金属工艺 | 9535篇 |
机械仪表 | 7697篇 |
建筑科学 | 6077篇 |
矿业工程 | 1437篇 |
能源动力 | 5442篇 |
轻工业 | 27044篇 |
水利工程 | 2564篇 |
石油天然气 | 5126篇 |
武器工业 | 32篇 |
无线电 | 26003篇 |
一般工业技术 | 46921篇 |
冶金工业 | 46081篇 |
原子能技术 | 5997篇 |
自动化技术 | 20420篇 |
出版年
2021年 | 2512篇 |
2019年 | 2359篇 |
2018年 | 3937篇 |
2017年 | 3875篇 |
2016年 | 4286篇 |
2015年 | 2736篇 |
2014年 | 4554篇 |
2013年 | 11373篇 |
2012年 | 7157篇 |
2011年 | 9115篇 |
2010年 | 7154篇 |
2009年 | 7834篇 |
2008年 | 8231篇 |
2007年 | 8273篇 |
2006年 | 7395篇 |
2005年 | 6398篇 |
2004年 | 6140篇 |
2003年 | 5865篇 |
2002年 | 5944篇 |
2001年 | 5716篇 |
2000年 | 5532篇 |
1999年 | 5417篇 |
1998年 | 12695篇 |
1997年 | 9010篇 |
1996年 | 6960篇 |
1995年 | 5415篇 |
1994年 | 4823篇 |
1993年 | 4699篇 |
1992年 | 3725篇 |
1991年 | 3437篇 |
1990年 | 3631篇 |
1989年 | 3513篇 |
1988年 | 3332篇 |
1987年 | 2922篇 |
1986年 | 2963篇 |
1985年 | 3412篇 |
1984年 | 3268篇 |
1983年 | 2918篇 |
1982年 | 2767篇 |
1981年 | 2847篇 |
1980年 | 2750篇 |
1979年 | 2657篇 |
1978年 | 2699篇 |
1977年 | 2964篇 |
1976年 | 3821篇 |
1975年 | 2381篇 |
1974年 | 2256篇 |
1973年 | 2391篇 |
1972年 | 1974篇 |
1971年 | 1864篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
Prof. Dr. Hans-René Bjørsvik Prof. Dr. Bjørn Tore Gjertsen Dr. Vijayaragavan Elumalai 《ChemMedChem》2020,15(10):862-870
A previously designed and developed 12-step total synthesis that includes [1,1′-biphenyl]-2-amine and carbazole intermediates and that ultimately produces the carbazole alkaloid carbazomycin G was exploited as a screening compound library with the goal of identifying potential lead compound(s) with cytotoxic effect. These compounds were investigated by using in-vitro tests involving the two human cell lines HL-60 and MOLM-13, which both model acute myeloid leukaemia (AML). The in-vitro biological test results were used together with the molecular structures of the various intermediates in a concise SAR analysis. Several of the intermediates revealed cytotoxicity (IC50<10−4 M), although the final natural product carbazomycin G did not reveal cytotoxicity versus the two said human cell lines. 相似文献
134.
135.
136.
A. E. Kudryashov Zh. V. Eremeeva E. A. Levashov V. Yu. Lopatin A. V. Sevost’yanova E. I. Zamulaeva 《Surface Engineering and Applied Electrochemistry》2018,54(5):437-445
Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings. 相似文献
137.
138.
139.
140.
Wyatt L. Brown Douglas A. Day Harald Stark Demetrios Pagonis Jordan E. Krechmer Xiaoxi Liu Derek J. Price Erin F. Katz Peter F. DeCarlo Catherine G. Masoud Dongyu S. Wang Lea Hildebrandt Ruiz Caleb Arata David M. Lunderberg Allen H. Goldstein Delphine K. Farmer Marina E. Vance Jose L. Jimenez 《Indoor air》2021,31(1):141-155
Understanding the sources and composition of organic aerosol (OA) in indoor environments requires rapid measurements, since many emissions and processes have short timescales. However, real-time molecular-level OA measurements have not been reported indoors. Here, we present quantitative measurements, at a time resolution of five seconds, of molecular ions corresponding to diverse aerosol-phase species, by applying extractive electrospray ionization mass spectrometry (EESI-MS) to indoor air analysis for the first time, as part of the highly instrumented HOMEChem field study. We demonstrate how the complex spectra of EESI-MS are screened in order to extract chemical information and investigate the possibility of interference from gas-phase semivolatile species. During experiments that simulated the Thanksgiving US holiday meal preparation, EESI-MS quantified multiple species, including fatty acids, carbohydrates, siloxanes, and phthalates. Intercomparisons with Aerosol Mass Spectrometer (AMS) and Scanning Mobility Particle Sizer suggest that EESI-MS quantified a large fraction of OA. Comparisons with FIGAERO-CIMS shows similar signal levels and good correlation, with a range of 100 for the relative sensitivities. Comparisons with SV-TAG for phthalates and with SV-TAG and AMS for total siloxanes also show strong correlation. EESI-MS observations can be used with gas-phase measurements to identify co-emitted gas- and aerosol-phase species, and this is demonstrated using complementary gas-phase PTR-MS observations. 相似文献