全文获取类型
收费全文 | 16419篇 |
免费 | 2476篇 |
国内免费 | 1705篇 |
专业分类
化学 | 12037篇 |
晶体学 | 199篇 |
力学 | 863篇 |
综合类 | 72篇 |
数学 | 1627篇 |
物理学 | 5802篇 |
出版年
2024年 | 60篇 |
2023年 | 320篇 |
2022年 | 563篇 |
2021年 | 590篇 |
2020年 | 649篇 |
2019年 | 652篇 |
2018年 | 590篇 |
2017年 | 516篇 |
2016年 | 746篇 |
2015年 | 795篇 |
2014年 | 994篇 |
2013年 | 1241篇 |
2012年 | 1447篇 |
2011年 | 1500篇 |
2010年 | 1081篇 |
2009年 | 930篇 |
2008年 | 1075篇 |
2007年 | 987篇 |
2006年 | 871篇 |
2005年 | 758篇 |
2004年 | 572篇 |
2003年 | 474篇 |
2002年 | 447篇 |
2001年 | 311篇 |
2000年 | 308篇 |
1999年 | 256篇 |
1998年 | 227篇 |
1997年 | 201篇 |
1996年 | 188篇 |
1995年 | 152篇 |
1994年 | 196篇 |
1993年 | 137篇 |
1992年 | 125篇 |
1991年 | 99篇 |
1990年 | 97篇 |
1989年 | 86篇 |
1988年 | 47篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 24篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1980年 | 21篇 |
1979年 | 14篇 |
1976年 | 13篇 |
1974年 | 12篇 |
1973年 | 11篇 |
1968年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
901.
Gangwei Sun Wenhua Song Xiaojun Liu Wenming Qiao Donghui Long Licheng Ling 《Journal of Solid State Electrochemistry》2012,16(3):1263-1270
Mesoporous carbide-derived carbons (CDC) with hierarchical pore structure were fabricated by chlorine etching of mesoporous
titanium carbides. Their capacitive behaviors for electrochemical capacitor were investigated in comparison to those of purely
microporous CDC. The as-prepared mesoporous CDC exhibited not only uniform micropores formed by leaching out titanium atoms
but a 3-D mesoporous network inherited from their parent carbides. These mesoporous CDC could deliver a high specific capacitance
of 120 F g−1 in 1 M tetraethylammonium tetrafluoroborate dissolved in propylene carbonate. Moreover, they owned excellent frequency response
and superior rate capability with capacitance retention ratio of 91% at current density of 10 A g−1. A high energy density of 16.3 Wh kg−1 was obtained even though power density was raised up to 4,300 W kg−1. The distinctive capacitive performance of mesoporous CDC would be attributed to their superior microstructure, in which
the uniform micropores contributed to high charge storage while the 3-D mesoporous network and nanometer-scaled dimension
of particles facilitated ions transfer as well as shortened electrolyte diffusion distance. 相似文献
902.
Byoung-Kee Jo Hyun-Don Kim Chun-Hag Jang Ki-Won Song Jang-Oo Lee 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):2293-2310
Abstract Interpolymer complex formation between basic polypeptides, poly(L- proline) Form I [PLP(I)], Form II [PLP(II)] and poly-4-hydroxy-L-proline (PHLP), and acidic polypeptides, poly(L-glutamic acid) (PLGA), poly(D- glutamic acid) (PDGA) and poly(L-aspartic acid) (PLAA), has been studied in water-methanol (1:2 v/v) mixed-solvent by viscometry, potentiometry, light scattering and circular dichroism (CD) measurements. It has been found that polymer complexes between basic- and acidic- polypeptides are formed via hydrogen bonding with a stoichiometric ratio of basic/acidic polypeptides =1:2 (in unit mole ratio) and that PLP(II) forms polymer complex more favorably with PLGA than with PLAA, and the complex of PLP(II) with PLGA is also more favorable than the complex formation of PHLP with PLGA. In addition, the complex formation is highly dependent on the conformation, especially the optical structure of the component polymers, i.e., the stereoselective complexation is observed. The PLGA having a right-handed helix at pH 3.2 formed the complex favorably and quickly with left-handed helix PLP(II), whereas PDGA having a left-handed helix at pH 3.2 favorably formed the complex with right-handed helix PLP(I). 相似文献
903.
Zongxia Guo Yubao Song Ruiying Gong Youbing Mu Yi Jiang Ming Li 《Supramolecular chemistry》2013,25(5-6):383-391
Biomolecule-directed self-assembly of π-conjugated oligomers has attracted great attention in the past decade. In this contribution, two conjugates composed of quaterthiophene and tetrapeptide (Gly-Val-Gly-Val) were synthesised, namely peptide–thiophene–peptide (PTP) and thiophene–peptide–thiophene (TPT), to investigate the influence of peptide content ratio and its location in the molecular structures on the nanostructures and properties of the assemblies. Both conjugates formed organogels consisting of left-handed twisted nanostructures; however, anti-parallel β-sheets were observed in PTP while parallel β-sheets were obtained for TPT, although in both cases oligothiophenes adopted an H-like stacking mode. Obvious solvent-induced supramolecular chirality inversion from the oligothiophene segment was observed for PTP while such phenomenon was not clear for TPT. PTP and TPT gels also showed different stabilities towards temperature increase, as evidenced by variable-temperature circular dichroism study. From the data, it is suggested that the rational design of the location and ratio of peptide plays a key role in constructing materials with determined properties based on peptide–thiophene conjugates. 相似文献
904.
905.
耐盐性聚丙烯酸盐类高吸水树脂的制备 总被引:20,自引:0,他引:20
耐盐性聚丙烯酸盐类高吸水树脂的制备宋彦凤,崔占臣,陈欣芳(吉林大学材料科学系长春130023)关键词丙烯酸钠,丙烯酰胺,丙烯酸羟乙酯,共聚物,吸水树脂,耐酸性高吸水树脂是一种应用比较广的功能性高分子材料[1~5].它的吸水率可高达几百倍乃至几千倍。但... 相似文献
906.
低硫可膨胀石墨的制备 总被引:18,自引:0,他引:18
低硫可膨胀石墨的制备宋克敏,路文义,高淑英,阎秋燕(河北教育学院石家庄050091)关键词低硫可膨胀石墨,制备,过氧化氢,硫酸柔性石墨具有耐高温、耐酸碱、抗拉、抗压、抗辐射、回弹性等优良性能,被广泛应用于化工、机械、肮天、原子能等领域。但其原材料可膨... 相似文献
907.
聚氯乙烯—丁腈橡胶—氯丁橡胶三元共混物的研究 总被引:1,自引:0,他引:1
测定了聚氯乙烯(PVC)-丁脯橡胶(NBR-29)-氯丁橡胶(CR)三元共混物的冲击性能和应力-应变行为,用动态力分析、扫描电和透射电镜研究了共混物的相容性和形态结构。结果表明,NBR-29对PVC,CR有良好的增容作用,三元共混物是部分相容的二相体系,具有良好的抗冲击性能。 相似文献
908.
909.
Hai Pham Tuan Hans-Gerd Janssen Ellen M. Kuiper-van Loo Harm Vlap 《Journal of separation science》1995,18(9):525-534
Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m3. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL. 相似文献
910.
Song YJ Hyun MY Lee JH Lee HG Kim JH Jang SP Noh JY Kim Y Kim SJ Lee SJ Kim C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):6094-6101
A mononuclear nonheme cobalt(III) complex of a tetradentate ligand containing two deprotonated amide moieties, [Co(bpc)Cl(2)][Et(4)N] (1; H(2)bpc = 4,5-dichloro-1,2-bis(2-pyridine-2-carboxamido)benzene), was prepared and then characterized by elemental analysis, IR, UV/Vis, and EPR spectroscopy, and X-ray crystallography. This nonheme Co(III) complex catalyzes olefin epoxidation upon treatment with meta-chloroperbenzoic acid. It is proposed that complex 1 shows partitioning between the heterolytic and homolytic cleavage of an O-O bond to afford Co(V)=O (3) and Co(IV)=O (4) intermediates, proposed to be responsible for the stereospecific olefin epoxidation and radical-type oxidations, respectively. Moreover, under extreme conditions, in which the concentration of an active substrate is very high, the Co-OOC(O)R (2) species is a possible reactive species for epoxidation. Furthermore, partitioning between heterolysis and homolysis of the O-O bond of the intermediate 2 might be very sensitive to the nature of the solvent, and the O-O bond of the Co-OOC(O)R species might proceed predominantly by heterolytic cleavage, even in the presence of small amounts of protic solvent, to produce a discrete Co(V) ?O intermediate as the dominant reactive species. Evidence for these multiple active oxidants was derived from product analysis, the use of peroxyphenylacetic acid as the peracid, and EPR measurements. The results suggest that a less accessible Co(V)=O moiety can form in a system in which the supporting chelate ligand comprises a mixture of neutral and anionic nitrogen donors. 相似文献