全文获取类型
收费全文 | 12840篇 |
免费 | 613篇 |
国内免费 | 765篇 |
专业分类
化学 | 13324篇 |
晶体学 | 138篇 |
力学 | 6篇 |
综合类 | 26篇 |
数学 | 152篇 |
物理学 | 572篇 |
出版年
2023年 | 103篇 |
2022年 | 258篇 |
2021年 | 298篇 |
2020年 | 422篇 |
2019年 | 339篇 |
2018年 | 281篇 |
2017年 | 275篇 |
2016年 | 366篇 |
2015年 | 264篇 |
2014年 | 333篇 |
2013年 | 751篇 |
2012年 | 1326篇 |
2011年 | 505篇 |
2010年 | 448篇 |
2009年 | 627篇 |
2008年 | 706篇 |
2007年 | 858篇 |
2006年 | 657篇 |
2005年 | 604篇 |
2004年 | 593篇 |
2003年 | 496篇 |
2002年 | 404篇 |
2001年 | 356篇 |
2000年 | 353篇 |
1999年 | 333篇 |
1998年 | 288篇 |
1997年 | 286篇 |
1996年 | 307篇 |
1995年 | 312篇 |
1994年 | 210篇 |
1993年 | 183篇 |
1992年 | 153篇 |
1991年 | 102篇 |
1990年 | 62篇 |
1989年 | 49篇 |
1988年 | 51篇 |
1987年 | 42篇 |
1986年 | 37篇 |
1985年 | 29篇 |
1984年 | 31篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 14篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Dr. Abdessamad Grirrane Dr. Eleuterio Álvarez Prof. Dr. Hermenegildo García Prof. Dr. Avelino Corma 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8810-8818
The cationic complex [(JohnPhos–Au)3(acetylide)][SbF6] (JohnPhos=(2-biphenyl)di-tert-butylphosphine, L1) has been characterised structurally and features an acetylide–trigold(I)–JohnPhos system; the trinuclear–acetylide unit, coordinated to the monodentate bulk phosphines, adopts an unprecedented μ,η1,η2,η1 coordination mode with an additional interaction between distal phenyl rings and gold centres. Other cationic σ,π-[(gold(I)L1)2] complexes have also been isolated. The reaction of trimethylsilylacetylene with various alcohols (iPrOH, nBuOH, n-HexOH) catalysed by cationic [AuIL1][SbF6] complexes in CH2Cl2 at 50 °C led to the formation of acetaldehyde acetals with a high degree of chemo- and regioselectivity. The reaction mechanism was studied, and several organic and inorganic intermediates have been characterised. A comparative study with the analogous cationic [CuIL1][PF6] complex revealed different behaviour; the copper metal is lost from the coordination sphere leading to the formation of cationic vinylphosphonium and copper nanoparticles. Additionally, a new catalytic approach for the formation of this high-value cationic vinylphosphonium has been established. 相似文献
142.
Ali El-Dissouky Eslam S. Abu-Elsoud Afaf Abdel Razik Mohamed K. Awad Hammed H.A.M. Hassan Amel F. Elhusseiny 《应用有机金属化学》2020,34(11):e5953
A series of nanometer-sized spherical sulfonamide imine ligands HL 1 -HL 5 and their copper and zinc complexes were synthesized and fully characterized based on elemental analyses, spectroscopic (UV/vis, FT-IR, NMR, EPR, SEM) studies, molar conductance and thermal analyses. Furthermore, computational studies of HL 1 -HL 5 were carried out by the DFT/B3LYP method. TD-DFT, HOMO and LUMO energy values, chemical hardness, electronegativity, electrophilic index, softness, and other parameters were calculated. Screening against several pathogenic microorganisms indicated that HL 1 exhibited high activity against the tested Gram-negative bacteria relative to other analogues and the inhibition activity is greater than the standard Gentamicin. Analogously, HL 2 exhibited high potent activity against the tested Gram-positive bacteria. Copper complexes exhibited a higher potent activity than zinc analogues. Noteworthy, inhibition activity of [Cu ( L 3 )(OAc)] complex is higher than that of the standard Ampicillin. [Cu ( L 2 )(OAc)] complex displayed a similar activity of the standard bactericides and fungicides in use. The complexes showed appreciated values of MIC against bacterial strains: B. subtilis (MIC = 0.4 μg / mL), E. coli and S. pneumonia (MIC = 1.95 μg / mL) and P. aeruginosa (MIC = 7.81 μg / mL). in vitro cytotoxic activities study proved that [Cu ( L 3 )(OAc)] complex exhibited appreciable activity versus (HEPG-2); IC50 = 4.8 μg/ml, while [Cu( L 2 )(OAc)] complex showed a high activity against (MCF-7); IC50 = 6.2 μg/ml. These results could be considered as new findings of promising antitumor candidates for experimental chemotherapy. 相似文献
143.
Kengo Sugita Prof. Dr. Makoto Yamashita 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4520-4523
The reaction between a dialkyl-substituted alumanyl anion and [Y(CH2SiMe3)2(thf)3][BPh4] resulted in the formation of (dialkylalumanyl)yttrium complex 2 , which exhibits the first 2-center–2-electron (2 c-2 e) Al−Y bond. The 1H and 13C NMR spectra of 2 together with an X-ray crystallographic analysis indicated a C2v symmetrical structure. DFT calculations on 2 revealed that its LUMO consists of overlapping 3 p- and 4 d-orbitals of the Al and Y atoms, respectively, and that the HOMO–LUMO gap is narrow. The UV/Vis spectrum of 2 exhibited a visible absorption at 432 nm, which suggests that the strong σ-donating and π-accepting character of the three-coordinate dialkylalumanyl ligand generates a colored d0-complex that does not contain any π-electrons. 相似文献
144.
Michael E. Tauchert Jun Okuda 《Angewandte Chemie (International ed. in English)》2020,59(11):4214-4215
A six‐coordinate [ML3Z3]‐type transition‐metal complex with a hexagonal planar geometry has been isolated and characterized, extending the scope of six‐coordinate metal coordination compounds to those with a geometry beyond octahedral and trigonal prismatic. 相似文献
145.
Dr. Aleksandra Markovic Luca Gerhards Dr. Pia Sander Dr. Carsten Dosche Prof. Dr. Thorsten Klüner Prof. Dr. Rüdiger Beckhaus Prof. Gunther Wittstock 《Chemphyschem》2020,21(22):2506-2514
Multinuclear transition metal complexes bridged by ligands with extended π-electronic systems show a variety of complex electronic transitions and electron transfer reactions. While a systematic understanding of the photochemistry and electrochemistry has been attained for binuclear complexes, much less is known about trinuclear complexes such as hexaphenyl-5,6,11,12,17,18-hexaazatrinaphthylene-tristitanocene [(Cp2Ti)3HATN(Ph)6]. The voltammogram of [(Cp2Ti)3HATN(Ph)6] shows six oxidation and three reduction waves. Solution spectra of [(Cp2Ti)3HATN(Ph)6] and of the electrochemically formed oxidation products show electronic transitions in the UV, visible and the NIR ranges. Density functional theory (DFT) and linear response time-dependent DFT show that the three formally titanium(II) centers transfer an electron to the HATN ligand in the ground state. The optically excited transitions occur exclusively between ligand-centered orbitals. The charged titanium centers only provide an electrostatic frame to the extended π-electronic system. Complete active self-consistent field (CASSCF) calculation on a structurally simplified model compound, which considers the multi-reference character imposed by the three titanium centers, can provide an interpretation of the experimentally observed temperature-dependent magnetic behavior of the different redox states of the title compound in full consistency with the interpretation of the electronic spectra. 相似文献
146.
Gaspar Ana B. Ksenofontov Vadim Spiering Hartmut Reiman Sergey Real José A. Gütlich Philipp 《Hyperfine Interactions》2002,144(1-4):297-306
This article reports on the study of the interplay between magnetic coupling and spin transition in 2,2′-bipyrimidine (bpym)-bridged
iron(II) dinuclear compounds. Coexistence of both phenomena has been observed in [Fe(bpym)(NCS)2]2bpym, [Fe(bpym)(NCSe)2]2bpym and [Fe(bt)(NCS)2]2bpym (bpym = 2,2′-bipyrimidine, bt = 2,2′-bithiazoline) by the action of external physical factors namely pressure or electromagnetic
radiation. Competition between magnetic exchange and spin crossover has been studied in [Fe(bpym)(NCS)2]2bpym at 6.3 kbar. LIESST experiments carried out in [Fe(bpym)(NCSe)2]2bpym and [Fe(bt)(NCS)2]2bpym at 4.2 K have shown that is possible to achieve dinuclear molecules with different spin states in this class of compounds.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
147.
V. A. Smirnov 《Mathematical Notes》2005,78(1-2):251-257
Homotopy theories of algebras over operads, including operads over “little n-cubes,” are defined. Spectral sequences are constructed and the corresponding homotopy groups are calculated.__________Translated from Matematicheskie Zametki, vol. 78, no. 2, 2005, pp. 278–285.Original Russian Text Copyright © 2005 by V. A. Smirnov. 相似文献
148.
XIAO Jie ZHANG Guanglian'''' & ZHU Bin Department of Mathematical Sciences Tsinghua University Beijing China Department of Mathematics Yancheng Teachers College Yancheng China 《中国科学A辑(英文版)》2005,48(8):1033-1045
We define the BGP-reflection functors in the derived categories and the root categories. By Ringel's Hall algebra approach, the BGP-reflection functor is applicable to obtain the classical Weyl group action on the Lie algebra. 相似文献
149.
《Journal of Pure and Applied Algebra》2022,226(12):107136
We adapt a construction due to Troesch to the category of strict polynomial superfunctors in order to construct complexes of injective objects whose cohomology is isomorphic to Frobenius twists of the (super)symmetric power functors. We apply these complexes to construct injective resolutions of the even and odd Frobenius twist functors, to investigate the structure of the Yoneda algebra of the Frobenius twist functor, and to compute other extension groups between strict polynomial superfunctors. By an equivalence of categories, this also provides cohomology calculations in the category of left modules over Schur superalgebras. 相似文献
150.
Abstract Fourier transform infrared (4000-200 cm1) and Raman (3500-50 cm?1) spectra are reported for metal(II) halide 3,5-lutidine (3,5-dimethylpyridine) complexes of the following stoichiometries: M(3,5L)4X2 M=Co or Ni, X=C1 or Br; M=Mn or Cu, X=Br; M=Cd, X=I; M(3,5L)3X2 M=Fe, X=C1; M=Cu, X=Br; Hg(3,5L) X2 X=C1 or Br. Vibrational assignments are given for all the observed bands. Some structure- spectra correlations are found. For a given series of isomorphous complexes the sum of the difference between the liquid and ligand values of the vibrational modes of 3,5-lutidine is found to increase in the order of the second ionization potentials of the metals. The frequency shifts are also found to depend on the halogen. 相似文献