全文获取类型
收费全文 | 9832篇 |
免费 | 944篇 |
国内免费 | 1038篇 |
专业分类
化学 | 7588篇 |
晶体学 | 140篇 |
力学 | 61篇 |
综合类 | 32篇 |
数学 | 2956篇 |
物理学 | 1037篇 |
出版年
2023年 | 115篇 |
2022年 | 98篇 |
2021年 | 155篇 |
2020年 | 259篇 |
2019年 | 311篇 |
2018年 | 233篇 |
2017年 | 249篇 |
2016年 | 281篇 |
2015年 | 407篇 |
2014年 | 470篇 |
2013年 | 942篇 |
2012年 | 620篇 |
2011年 | 619篇 |
2010年 | 537篇 |
2009年 | 602篇 |
2008年 | 700篇 |
2007年 | 635篇 |
2006年 | 535篇 |
2005年 | 531篇 |
2004年 | 481篇 |
2003年 | 422篇 |
2002年 | 306篇 |
2001年 | 238篇 |
2000年 | 220篇 |
1999年 | 195篇 |
1998年 | 193篇 |
1997年 | 184篇 |
1996年 | 148篇 |
1995年 | 120篇 |
1994年 | 127篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 68篇 |
1990年 | 69篇 |
1989年 | 79篇 |
1988年 | 58篇 |
1987年 | 44篇 |
1986年 | 43篇 |
1985年 | 52篇 |
1984年 | 46篇 |
1983年 | 27篇 |
1982年 | 34篇 |
1981年 | 33篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 13篇 |
1976年 | 10篇 |
1974年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 231 毫秒
41.
Shivanand Gajare Megha Jagadale Altafhusen Naikwade Prakash Bansode Gajanan Rashinkar 《应用有机金属化学》2019,33(6)
Ferrocene tethered N‐heterocyclic carbene‐copper complex anchored on graphene ([GrFemImi]NHC@Cu complex) has been synthesized by covalent grafting of ferrocenyl ionic liquid in the matrix of graphene followed by metallation with copper (I) iodide. The [GrFemImi]NHC@Cu complex has been characterized by fourier transform infrared (FT‐IR), fourier transform Raman (FT‐Raman), CP‐MAS 13C NMR spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), energy dispersive X‐ray (EDX) analysis, X‐ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) surface area analysis and X‐ray diffractometer (XRD) analysis. This novel complex served as a robust heterogeneous catalyst for the synthesis of bioactive N‐aryl sulfonamides from variety of aryl boronic acids and sulfonyl azides in ethanol by Chan‐Lam coupling. Recyclability experiments were executed successfully for six consecutive runs. 相似文献
42.
Mahmoud Nasrollahzadeh Mohaddeseh Sajjadi Hartmut Komber Hossein Ali Khonakdar S. Mohammad Sajadi 《应用有机金属化学》2019,33(7)
In the present work, for the first time we have designed a novel approach for the synthesis of N‐benzyl‐N‐aryl‐5‐amino‐1H‐tetrazoles using reduced graphene oxide (rGO) decorated with Cu‐Ni bimetallic nanoparticles (NPs). In situ synthesis of Cu/Ni/rGO nanocomposite was performed by a cost efficient, surfactant‐free and environmentally benign method using Crataegus azarolus var. aronia L. leaf extract as a stabilizing and reducing agent. Phytochemicals present in the extract can be used to reduce Cu2+ and Ni2+ ions and GO to Cu NPs, Ni NPs and rGO, respectively. Analyses by means of FT‐IR, UV–Vis, EDS, TEM, FESEM, XRD and elemental mapping confirmed the Cu/Ni/rGO formation and also FT‐IR, NMR, and mass spectroscopy as well as elemental analysis were used to characterize the tetrazoles. The Cu/Ni/rGO nanocomposite showed the superior catalytic activity for the synthesis of N‐benzyl‐N‐aryl‐5‐amino‐1H‐tetrazoles within a short reaction time and high yields. Furthermore, this protocol eliminates the need to handle HN3. 相似文献
43.
Ambarish Mondal Rajat K. Tripathy Parul Dutta Manas Kumar Santra Anvarhusein A. Isab Christopher W. Bielawski Hemanta K. Kisan Swapan K. Chandra Joydev Dinda 《应用有机金属化学》2019,33(1)
The syntheses, structures, and chemotherapeutic activities of Ag(I)‐, Au(I)‐, and Ru(II)‐complexes ligated to a novel N‐heterocyclic carbene ligand, 2‐(4‐nitrophenyl)imidazo[1,5‐a]pyridin‐2‐ylidene ( 1 ), are described. The corresponding complexes, [Ag( 1 )2][PF6], [Au( 1 )2][PF6] ( 3 ), and [Ru( 1 )(p‐cymene)Cl][PF6] ( 4 ), were prepared using convenient transmetallation chemistry and characterized using a range of spectroscopic and analytical techniques. X‐ray crystallography revealed that complexes 2 and 3 adopted linear structures whereas 4 exhibited a prototypical “piano‐stool”‐like geometry; the structural assignments were further supported by DFT calculations. A series of in vitro studies revealed that while the aforementioned Ag(I), Au(I) and Ru(II) complexes exhibited significant cytotoxicities against the human colon adenocarcinoma (HCT 116), lung cancer (A549), and breast cancer (MCF7) cell lines, the Ru derivative was most prominent. 相似文献
44.
Wenjie Tao Xiaoming Wang Shingo Ito Kyoko Nozaki 《Journal of polymer science. Part A, Polymer chemistry》2019,57(3):474-477
Herein, we report the synthesis of palladium complexes bearing an N‐heterocyclic carbene (NHC)‐sulfonamide bidentate ligand and their application in ethylene oligomerization and ethylene/polar monomer cooligomerization. These catalysts could smoothly catalyze ethylene oligomerization and ethylene/methyl acrylate cooligomerization albeit the performance was lower compared to that of a NHC–phenoxide catalyst. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 474–477 相似文献
45.
We study the well‐posedness of the fractional differential equations with infinite delay on Lebesgue–Bochner spaces and Besov spaces , where A and B are closed linear operators on a Banach space X satisfying , and . Under suitable assumptions on the kernels a and b, we completely characterize the well‐posedness of in the above vector‐valued function spaces on by using known operator‐valued Fourier multiplier theorems. We also give concrete examples where our abstract results may be applied. 相似文献
46.
A cheap synthesis of the so‐called ‘decalin‐1,8‐diones’ started with the conjugate (1,4‐) addition of cyclohex‐2‐en‐1‐one derivatives to the γ‐position of the dilithium derivative (buta‐1,3‐diene‐1,1‐bis(olate)) of crotonic acid. Hydrogenation of these ‘1,4‐γ’ adducts and final cyclization afforded the enol tautomers of decalin‐1,8‐diones. Nucleophilic substitutions at these 3‐oxoenols by NH3 or primary amines created only monoamino products (namely, 3‐oxoenamines) whose reactions with OPCl3 yielded dihydro(1,3,2)oxazaphosphinin‐2‐one derivatives. The two regioisomers of a trimethyl‐3‐oxoenamine served as models for the constitutional assignments of the two rapidly interconverting (hence, individually NMR‐invisible), tautomeric trimethyl‐3‐oxoenols. Such methyl substitutions served to break the ‘pretended’ symmetry of ‘decalin‐1,8‐dione’. Hydrazine and 3‐oxoenols furnished oxygen‐free indazole derivatives whose N?H bonds exchanged with t1/2=ca. 0.00035 s at ca. ?58(9) °C. 相似文献
47.
Dr. Lingxing Zeng Biyu Kang Fenqiang Luo Yixing Fang Cheng Zheng Junbin Liu Renpin Liu Xinye Li Prof. Dr. Qinghua Chen Prof. Dr. Mingdeng Wei Prof. Dr. Qingrong Qian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(58):13411-13421
Sodium/potassium-ion batteries (SIBs/PIBs) arouse intensive interest on account of the natural abundance of sodium/potassium resources, the competitive cost and appropriate redox potential. Nevertheless, the huge challenge for SIBs/PIBs lies in the scarcity of an anode material with high capacity and stable structure, which are capable of accommodating large-size ions during cycling. Furthermore, using sustainable natural biomass to fabricate electrodes for energy storage applications is a hot topic. Herein, an ultra-small few-layer nanostructured MoSe2 embedded on N, P co-doped bio-carbon is reported, which is synthesized by using chlorella as the adsorbent and precursor. As a consequence, the MoSe2/NP-C-2 composite represents exceedingly impressive electrochemical performance for both sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). It displays a promising reversible capacity (523 mAh g−1 at 100 mA g−1 after 100 cycles) and impressive long-term cycling performance (192 mAh g−1 at 5 A g−1 even after 1000 cycles) in SIBs, which are some of the best properties of MoSe2-based anode materials for SIBs to date. To further probe the great potential applications, full SIBs pairing the MoSe2/NP-C-2 composite anode with a Na3V2(PO4)3 cathode also exhibits a satisfactory capacity of 215 mAh g−1 at 500 mA g−1 after 100 cycles. Moreover, it also delivers a decent reversible capacity of 131 mAh g−1 at 1 A g−1 even after 250 cycles for PIBs. 相似文献
48.
Oliver Back Dr. Christoph Förster Prof. Dr. Thomas Basché Prof. Dr. Katja Heinze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(26):6542-6552
2-Iminopyrroles [HtBuL, 4-tert-butyl phenyl(pyrrol-2-ylmethylene)amine] are non-fluorescent π systems. However, they display blue fluorescence after deprotonation with alkali metal bases in the solid state and in solution at room temperature. In the solid state, the alkali metal 2-imino pyrrolates, M(tBuL), aggregate to dimers, [M(tBuL)(NCR)]2 (M=Li, R=CH3, CH(CH3)CNH2), or polymers, [M(tBuL)]n (M=Na, K). In solution (solv=CH3CN, DMSO, THF, and toluene), solvated, uncharged monomeric species M(tBuL)(solv)m with N,N′-chelated alkali metal ions are present. Due to the electron-rich pyrrolate and the electron-poor arylimino moiety, the M(tBuL) chromophore possesses a low-energy intraligand charge-transfer (ILCT) excited state. The chelated alkali cations rigidify the chromophore, restricting intramolecular motions (RIM) by the chelation-enhanced fluorescence (CHEF) effect in solution and, consequently, switch-on a blue fluorescence emission. 相似文献
49.
Bei-Bei Guo Dr. Yue-Jian Lin Prof. Guo-Xin Jin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9721-9727
Four flexible ligands with different lengths, degrees of flexibility, and steric bulk were synthesized and used to prepare metal-directed assemblies. Interestingly, minor differences among the ligands led to products with dramatically different topologies: a binuclear D -shaped macrocycle, tetranuclear rectangles, and hexanuclear trefoil knots. The interconversion of the trefoil-shaped complexes was also investigated. This contribution introduces a rare ligand-controlled trefoil–rectangle shape transformation in solution. 相似文献
50.
Dr. Weixin Zou Lixia Xu Yu Pu Haojie Cai Xiaoqian Wei Yidan Luo Dr. Lulu Li Prof. Dr. Bin Gao Prof. Dr. Haiqin Wan Prof. Dr. Lin Dong 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(19):5058-5064
Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C3N4 sample has superior activity to Ag/g-C3N4 and Pd/g-C3N4 photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C3N4, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H2O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H2O dissociation to radical species on the AgPd/g-C3N4 photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C3N4, that is, Pdδ−⋅⋅⋅Agδ+, and the activation energy of H2O molecule dissociation on AgPd/g-C3N4 is the lowest, which is the main contributor to the enhanced photocatalytic H2 evolution. 相似文献