全文获取类型
收费全文 | 10395篇 |
免费 | 1959篇 |
国内免费 | 1356篇 |
专业分类
化学 | 6909篇 |
晶体学 | 129篇 |
力学 | 829篇 |
综合类 | 121篇 |
数学 | 1337篇 |
物理学 | 4385篇 |
出版年
2024年 | 44篇 |
2023年 | 200篇 |
2022年 | 345篇 |
2021年 | 402篇 |
2020年 | 383篇 |
2019年 | 358篇 |
2018年 | 335篇 |
2017年 | 366篇 |
2016年 | 472篇 |
2015年 | 477篇 |
2014年 | 555篇 |
2013年 | 760篇 |
2012年 | 844篇 |
2011年 | 952篇 |
2010年 | 690篇 |
2009年 | 669篇 |
2008年 | 737篇 |
2007年 | 610篇 |
2006年 | 634篇 |
2005年 | 495篇 |
2004年 | 406篇 |
2003年 | 316篇 |
2002年 | 312篇 |
2001年 | 309篇 |
2000年 | 255篇 |
1999年 | 233篇 |
1998年 | 198篇 |
1997年 | 192篇 |
1996年 | 185篇 |
1995年 | 149篇 |
1994年 | 133篇 |
1993年 | 122篇 |
1992年 | 104篇 |
1991年 | 74篇 |
1990年 | 88篇 |
1989年 | 78篇 |
1988年 | 55篇 |
1987年 | 38篇 |
1986年 | 40篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 17篇 |
1981年 | 4篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
41.
Yong Sun Bo-Qiao Fu Ming-Wu Ding 《Phosphorus, sulfur, and silicon and the related elements》2013,188(6):1437-1443
The isothiocyanates 2, obtained from aza-Wittig reactions of vinyliminophosphoranes 1 with CS 2 , reacted with hydrazine to give 3-amino-2-thioxo-4-imidazolidinones 4. One-pot reactions of 4, aromatic isocyanates, Ph 3 P, C 2 Cl 6 , and Et 3 N generated imidazo[2,1-b]-1,3,4-thiadiazol-5(6H)-ones 7. Compound 7 exhibited good fungicidal activities, especially against Sclerotinia sclerotiorum de Bary and Botrytis Cinerea Pers. 相似文献
42.
Fu-Jun Duan Jin-Chang Ding Hong-Juan Deng Ding-Ben Chen Jiu-Xi Chen Miao-Chang Liu Hua-Yue Wu 《中国化学快报》2013,24(9):793-796
An efficient and facile method for the synthesis of N-substituted pyrroles in moderate to good yields by the Paal–Knorr reaction of γ-diketones with amines in the presence of β-cyclodextrin in aqueous media has been developed.Moreover,this process tolerated diamines(e.g.,para-,meta- or orthophenylenediamine)to construct bis-pyrrole or mono-pyrrole derivates.β-Cyclodextrin can be recovered easily after the reactions and reused without evident loss in activity. 相似文献
43.
We investigate the uniform piecewise linearizing question for a family of Lorenz maps. Let f be a piecewise linear Lorenz map with different slopes and positive topological entropy, we show that f is conjugate to a linear mod one transformation and the conjugacy admits a dichotomy: it is either bi-Lipschitz or singular depending on whether f is renormalizable or not. f is renormalizable if and only if its rotation interval degenerates to be a rational point. Furthermore, if the endpoints are periodic points with the same rotation number, then the conjugacy is quasisymmetric. 相似文献
44.
45.
Na[cyclo‐(P5tBu4)] ( 1 ) reacts with [FeBr2(CO)4] (2:1) to give the first homoleptic iron(II) complex [Fe{cyclo‐(P5tBu4)}2] ( 2 ) containing two tridentate cyclo‐(P5tBu4)– ligands. Thermolysis of 2 up to 500 °C produces a new phosphorus‐rich iron phosphide, calculated as FeP6 according to the mass change. 相似文献
46.
Shi-Ji Xiao Xin-Xiang Lei Bing Xia Dan-Qing Xu Hong-Ping Xiao Hong-Xi Xu Fang Chen Li-Sheng Ding Yan Zhou 《Tetrahedron letters》2014
Two novel lignans, gymnothespirolignans A (1) and B (2), possessing a rare polycyclic spiro skeleton, were isolated from the endemic plant of Gymnotheca involucrata Pei. Their structures were determined by spectroscopic evidences and the absolute configurations were confirmed by single crystal X-ray diffraction analysis. Compounds 1 and 2 showed promising antiviral activities against RSV with an IC50 value of 31.87 and 17.51 μM, respectively. 相似文献
47.
Qingpei Xiang Dongfeng Tian Fanhua Hao Chengsheng Chu Ge Ding Jun Zeng Fei Luo 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(3):1439-1445
In recent years, the cerium-doped lanthanum bromide, LaBr3 (Ce = 5 %) detector is increasingly playing an important role in radiation measurements because of its higher energy resolution (~3 % at 662 keV), faster luminescence decay time (~35 ns) and higher detection efficiency compared to 7.65 cm × 7.65 cm NaI(Tl) detector. Intrinsic spectra between 1,800 and 3,000 keV derived from internal radioactivity within LaBr3(Ce) scintillators have been investigated in some literatures, and these results are confirmed by the experiments in this work. In this paper, a new method for LaBr3(Ce) detector energy calibration from 100 to 2,000 keV is proposed using the intrinsic spectra (self-calibration) instead of the standard gamma sources. Proof-of-concept experiment results show that self-calibration can guarantee energy accuracy of better than 0.815 % and can be applied outside the laboratory. The stability and applicability of this method are also investigated systematically. 相似文献
48.
In order to reduce greenhouse gas emissions, developing flame retardants from bio-based resources has aroused extensive interest in recent years. In this work, we utilized furfural(biomass) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO) to synthesize a biobased co-curing agent(FGD) to combine with 4,4'-diaminodiphenyl methane(DDM) for obtaining a low-phosphorus loading flame-retardant epoxy thermosets. The introduction of FGD decreased the activation energy of the curing progress, enhanced the mechanical properties of the epoxy thermosets, and did not affect the glass transition temperature of the epoxy thermosets. EP-5.0 had a lower thermal degradation rate and a doubled char yield compared with EP-0. The phosphorus content of EP-5.0 was only 0.45 wt%, while EP-5.0 reached the UL-94 V-0 rating with a high LOI value of 32%. Compared with EP-0, the PHRR of EP-2.5 and EP-5.0 decreased by 22.3% and 31.3%, respectively. The SEM results showed that the addition of FGD made the char residues more uniform and denser, which could effectively prevent combustible volatiles from escaping from the degradation area to the flame area and isolate the heat transfer so that the epoxy thermosets had an excellent flame-retardant performance. 相似文献
49.
Ding Congming Yuan Meini Cao Xiaochen Zheng Lirong Wang Kai 《Journal of Solid State Electrochemistry》2022,26(11):2445-2455
Journal of Solid State Electrochemistry - In order to meet the growing energy demand, it is of great significance to develop high-performance electrochemical energy storage materials. In this... 相似文献
50.
Joseph Israel Gurti Prof. Xun-Lei Ding Ya-Ya Wang Yan Chen Dr. Wei Li Dr. Xin Wang 《Chemphyschem》2022,23(14):e202200124
The reaction of N2 with trinuclear niobium and tungsten sulfide clusters Nb3Sn and W3Sn (n=0–3) was systematically studied by density functional theory calculations with TPSS functional and Def2-TZVP basis sets. Dissociations of N−N bonds on these clusters are all thermodynamically allowed but with different reactivity in kinetics. The reactivity of Nb3Sn is generally higher than that of W3Sn. In the favorite reaction pathways, the adsorbed N2 changes the adsorption sites from one metal atom to the bridge site of two metal atoms, then on the hollow site of three metal atoms, and at that place, the N−N bond dissociates. As the number of ligand S atoms increases, the reactivity of Nb3Sn decreases because of the hindering effect of S atoms, while W3S and W3S2 have the highest reactivity among four W3Sn clusters. The Mayer bond order, bond length, vibrational frequency, and electronic charges of the adsorbed N2 are analyzed along the reaction pathways to show the activation process of the N−N bond in reactions. The charge transfer from the clusters to the N2 antibonding orbitals plays an essential role in N−N bond activation, which is more significant in Nb3Sn than in W3Sn, leading to the higher reactivity of Nb3Sn. The reaction mechanisms found in this work may provide important theoretical guidance for the further rational design of related catalytic systems for nitrogen reduction reactions (NRR). 相似文献