全文获取类型
收费全文 | 331588篇 |
免费 | 4057篇 |
国内免费 | 1888篇 |
专业分类
化学 | 168864篇 |
晶体学 | 4213篇 |
力学 | 16079篇 |
综合类 | 65篇 |
数学 | 61879篇 |
物理学 | 86433篇 |
出版年
2021年 | 2234篇 |
2020年 | 2407篇 |
2019年 | 2616篇 |
2018年 | 13071篇 |
2017年 | 12948篇 |
2016年 | 10754篇 |
2015年 | 4318篇 |
2014年 | 4978篇 |
2013年 | 11356篇 |
2012年 | 13445篇 |
2011年 | 21688篇 |
2010年 | 13491篇 |
2009年 | 13637篇 |
2008年 | 17114篇 |
2007年 | 19118篇 |
2006年 | 10498篇 |
2005年 | 10671篇 |
2004年 | 9757篇 |
2003年 | 9130篇 |
2002年 | 7965篇 |
2001年 | 7634篇 |
2000年 | 5935篇 |
1999年 | 4325篇 |
1998年 | 3634篇 |
1997年 | 3547篇 |
1996年 | 3666篇 |
1995年 | 3100篇 |
1994年 | 3173篇 |
1993年 | 3024篇 |
1992年 | 3215篇 |
1991年 | 3239篇 |
1990年 | 3026篇 |
1989年 | 2890篇 |
1988年 | 2827篇 |
1987年 | 2775篇 |
1986年 | 2787篇 |
1985年 | 3605篇 |
1984年 | 3683篇 |
1983年 | 3018篇 |
1982年 | 3286篇 |
1981年 | 3039篇 |
1980年 | 2845篇 |
1979年 | 2988篇 |
1978年 | 3173篇 |
1977年 | 3193篇 |
1976年 | 3202篇 |
1975年 | 2919篇 |
1974年 | 2998篇 |
1973年 | 3079篇 |
1972年 | 2392篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Results are presented of an analytic construction and investigation of adaptive data classification algorithms for intermittent turbulence. A decision making rule is presented, relationships are derived to estimate the classification accuracy. A three-level procedure is described for processing the intermittency, including the calculation algorithms for the initial point, self-teaching, and optimal classification. It is shown that the method proposed permits realization of total automation of intermittency data processing.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 18, pp. 119–123, 1987. 相似文献
992.
The reactions of furan and a number of its derivatives (furfural, furan-2-carboxylic acid, 2-furfuryl alcohol, and others), in systems containing H2O2 and vanadium compounds, proceed through a mechanism of radical hydoxylation of the furan ring with the formation of 5-hydroxy-2(5H)-furanone and maleic acid. The total yield and ratio of the synthesized compounds depend on the reaction conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1462–1467, November, 1991. 相似文献
993.
994.
995.
Ana L. Montero Luis A. Montero Ricardo Martínez S. Spange 《Journal of Molecular Structure》2006,770(1-3):99-106
A quantum chemical model (Abinitio HF-MO and DFT-B3LYP) of polyfurfuryl alcohol crosslinking is shown. Two pathways were considered: (a) a Diels–Alder (D–A) reaction between a dihydrofuran moiety and a furan ring; (b) the addition reaction of electrophilic specimens on conjugated double bonds. The ability for the formation of D–A adducts (dienes and dienophiles) was investigated by the frontier molecular orbital (FMO) theory. Energy gaps between the FMO's of diene and dienophile structures suggest that the occurrence of the D–A reaction is possible. The results suggest that the carbons of the exo double bonds attached to dihydrofuran rings are the sites most likely to be attacked by electrophilic species, while the C3 and C4 atoms display the opposite tendency due to their low HOMO electron densities. Results of a thermochemical approach to these reactions at the MP2 level was in agreement with reactivity modelled by MO predictions. 相似文献
996.
A file ofn records can be sorted in linear time givenO(log(n)) processors. Four such algorithms are presented and analyzed. All of them have reasonable hardware requirements; no memory access conflicts are generated; a constant number of communication lines per processor are needed (except for one case); and the space requirements areO(n) orO(n log(log(n))). 相似文献
997.
Reported to the 5th All-Union Conference on High-Temperature Plasma Diagnostics (June 18–22, 1990, Minsk). 相似文献
998.
Zbigniew Jaskólski 《Communications in Mathematical Physics》1991,139(2):353-375
Following the general scheme of the convariant path integral quantization of gauge systems, two alternative formulations of
the first quantized closed bosonic string in a position representation are presented. In both approaches the covariant path
integral representations of the propagator and of the higher order off-shell amplitudes are constructed. For a wide class
of gauges the explicit formulae for off-shell amplitudes are obtained. This paper is the continuation of our previous work
where the corresponding problems in the open string case were considered [20]. 相似文献
999.
Near-infrared calibrations for water, reducing sugar, glycerin, propylene glycol, nicotine, and menthol in tobacco blends were first obtained with a monochromator instrument. Transfer of calibrations to a tilting-filter instrument for factory trials is shown to be facilitated greatly by the computer-assisted scheme MTRAN. By means of this software, calibration equations were established for a Neotec 51A instrument that is sufficiently rugged for factory use. The predictive capabilities of the transferred calibrations are similar to those of the research monochromator. 相似文献
1000.