全文获取类型
收费全文 | 11098篇 |
免费 | 1878篇 |
国内免费 | 950篇 |
专业分类
化学 | 2476篇 |
晶体学 | 187篇 |
力学 | 816篇 |
综合类 | 86篇 |
数学 | 994篇 |
物理学 | 3750篇 |
无线电 | 5617篇 |
出版年
2024年 | 26篇 |
2023年 | 89篇 |
2022年 | 192篇 |
2021年 | 205篇 |
2020年 | 253篇 |
2019年 | 195篇 |
2018年 | 193篇 |
2017年 | 333篇 |
2016年 | 411篇 |
2015年 | 370篇 |
2014年 | 657篇 |
2013年 | 697篇 |
2012年 | 814篇 |
2011年 | 706篇 |
2010年 | 606篇 |
2009年 | 631篇 |
2008年 | 880篇 |
2007年 | 994篇 |
2006年 | 755篇 |
2005年 | 714篇 |
2004年 | 719篇 |
2003年 | 579篇 |
2002年 | 455篇 |
2001年 | 341篇 |
2000年 | 297篇 |
1999年 | 265篇 |
1998年 | 242篇 |
1997年 | 200篇 |
1996年 | 156篇 |
1995年 | 152篇 |
1994年 | 131篇 |
1993年 | 105篇 |
1992年 | 118篇 |
1991年 | 73篇 |
1990年 | 51篇 |
1989年 | 57篇 |
1988年 | 48篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 7篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1973年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
V. P. Bubnov I. S. Krainskii E. E. Laukhina E. B. Yagubskii 《Russian Chemical Bulletin》1994,43(5):746-750
The effect of the parameters of the electric arc (helium pressure, current and voltage, clearance between electrodes) and of the peculiarities of the setup design (arrangement of electrodes, distance between the arc and the cooling surface, temperature of the soot condensation surface) on the yield of fullerenes has been studied. Conditions for producing soot with a C60 and C70 content up to 43% (toluene extract) have been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 805–809, May, 1994.The authors are grateful to N. G. Spitsyna and A. V. Dubovitskii for the determination of the content of C60 and C70 fullerenes in the extract.The work was financially supported by the Russian Foundation for Basic Research (Project 93-03-18705). 相似文献
82.
T. Hayashita T. Kurosawa T. Miyata K. Tanaka M. Igawa 《Colloid and polymer science》1994,272(12):1611-1619
The cationic azo-surfactants possessing different spacers and tail alkyl chain lengths have been synthesized by azocoupling ofp-alkylaniline orop-ethoxyaniline with phenol, followed by alkylation and quaternalization with dibromoalkane and trimethylamine, respectively. These surfactants showed a good solubility in water. A reversibletrans-cis isomerization of the azosurfactants by photoirradiation was assessed by UV-Vis absorption spectra. Due to a difference in HLB between thetrans- andcis-surfactants, the observed critical micelle concentration (CMC) values and the electric conductivity of the surfactant solution at above the CMC were significantly affected by the photoinducedtrans-cis isomerization. The azo-surfactants bearing moderate alkyl chain lengths such as surfactants 6 (R2=C2H4, R3=C4H9) and 9 (R2=C4H8, R3=C2H5) were found to be effective to achieve large CMC changes (3.6 mmol/L for 6 and 5.9 mmol/L for 9) by UV-light irradiation. The replacement of the tail chain species also affected the photoresponsive function. The surfactant 12, possessingp-ethoxy group as the tail chain, was found to form a stable micelle aggregation as compared with the structurally related surfactant 10 having ethyl unit as its tail group, but it exhibited a large CMC change (5.3 mmol/L) by UV-light irradiation. 相似文献
83.
由于面临越来越严重的激光制导武器的威胁 ,对来袭威胁进行早期预警日趋重要。概要介绍了微弱激光辐射探测技术国外研究现状及发展趋势。对微弱激光辐射探测关键技术进行了研究探讨。 相似文献
84.
S. C. Joshi M. P. Singh V. P. Pandey B. S. Rajput 《International Journal of Theoretical Physics》2002,41(6):1107-1125
In four-dimensional N = 4 supersymmetric gauge theory, we obtain an exact metric on the moduli space of quantum vacua and analyze the spectra of BPS states in weak as well as in strong coupling regions. Identifying the hypermultiplet of the dyonic state as a string stretched between D3-brane probe and a 7-brane, we demonstrate that the two hypermultiplets, which become massless at two singularities in supersymmetric theory, correspond to open strings beginning on the D3-brane and ending on the respective 7-brane. 相似文献
85.
Comparison of Two Reformulation-Linearization Technique Based Linear Programming Relaxations for Polynomial Programming Problems 总被引:3,自引:0,他引:3
In this paper, we compare two strategies for constructing linear programmingrelaxations for polynomial programming problems using aReformulation-Linearization Technique (RLT). RLT involves an automaticreformulation of the problem via the addition of certain nonlinear impliedconstraints that are generated by using the products of the simple boundingrestrictions (among other products), and a subsequent linearization based onvariable redefinitions. We prove that applying RLT directly to the originalpolynomial program produces a bound that dominates in the sense of being atleast as tight as the value obtained when RLT is applied to the jointcollection of all equivalent quadratic problems that could be constructed byrecursively defining additional variables as suggested by Shor. 相似文献
86.
87.
88.
89.
90.