全文获取类型
收费全文 | 1085篇 |
免费 | 46篇 |
国内免费 | 4篇 |
专业分类
化学 | 773篇 |
晶体学 | 20篇 |
力学 | 32篇 |
数学 | 76篇 |
物理学 | 234篇 |
出版年
2024年 | 7篇 |
2023年 | 15篇 |
2022年 | 20篇 |
2021年 | 26篇 |
2020年 | 36篇 |
2019年 | 28篇 |
2018年 | 23篇 |
2017年 | 27篇 |
2016年 | 45篇 |
2015年 | 22篇 |
2014年 | 50篇 |
2013年 | 59篇 |
2012年 | 79篇 |
2011年 | 99篇 |
2010年 | 41篇 |
2009年 | 42篇 |
2008年 | 60篇 |
2007年 | 56篇 |
2006年 | 53篇 |
2005年 | 16篇 |
2004年 | 35篇 |
2003年 | 41篇 |
2002年 | 25篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 14篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 4篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1135条查询结果,搜索用时 15 毫秒
921.
Stefan Zimmermann Dr. Mohammad Akbarzadeh Felix Otte Prof. Dr. Carsten Strohmann Dr. Muthukumar Gomathi Sankar Dr. Slava Ziegler Dr. Axel Pahl Dr. Sonja Sievers Dr. Kamal Kumar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(68):15498-15503
A “branching–folding” synthetic strategy that affords a range of diverse cyclic benzo-sulfonamide scaffolds is presented. Whereas different annulation reactions on common ketimine substrates build the branching phase of the scaffold synthesis, a common hydrogenative ring-expansion method, facilitated by an increase of the ring-strain during the branching phase, led to sulfonamides bearing medium-sized rings in a folding pathway. Cell painting assay was successfully employed to identify tubulin targeting sulfonamides as novel mitotic inhibitors. 相似文献
922.
Jyoti Bhomia Jyoti Sharma Rucha Lakhne Rachna Sharma R.S. Gupta Ram Avatar Sharma Yashpal Singh 《应用有机金属化学》2018,32(1)
Some new mononuclear organoboron derivatives of the type PhBL1–5(OH) ( 1a – 1e ) were synthesized by the reaction of PhB(OH)2 and LH (LH = OC(NH2)NH:NC(CH3)4C6H4R, where R = H (L1H); CH3(L2H); OCH3(L3H); Cl (L4H); Br (L5H)) in 1:1 molar ratio in refluxing tetrahydrofuran (THF). This was followed by the reactions of PhBL1–5(OH) with NH(SiMe3)2 in 2:1 molar ratio in THF to yield new heterodinuclear derivatives of the type PhBL1–5(OSiMe3) ( 2a – 2e ). All these newly synthesized complexes were characterized using elemental analyses and their probable structure was proposed on the basis of infrared, 1H NMR, 13C NMR, 11B NMR and 29Si NMR spectral data and mass spectrometry. Semicarbazone ligands and their corresponding mono‐ and heterodinuclear boron derivatives were screened against pathogenic bacteria (E. coli and P. aeruginosa) and fungi (A. niger and P. peniculosum) to examine their antimicrobial activities. Representative compounds of each series of mono‐ and heterodinuclear boron derivatives and a ligand were screened for their antifertility activity on male adult Wistar rats. 相似文献
923.
924.
925.
Upadhayaya RS Shinde PD Sayyed AY Kadam SA Bawane AN Poddar A Plashkevych O Földesi A Chattopadhyaya J 《Organic & biomolecular chemistry》2010,8(24):5661-5673
Prompted by our discovery of a new class of conformationally-locked indeno[2,1-c]quinolines as anti-mycobacterials, compounds 2a and 3a (Fig. 1; MIC < 0.39 μg mL(-1) and 0.78 μg mL(-1), respectively)(14) with a freely rotating C2-imidazolo substituent, we herein describe the synthesis of pentacyclic azole-fused quinoline derivatives 4 and 5, in which we have restricted the rotation of the C2-imidazolo moiety by fusing it to the adjacent quinoline-nitrogen to give a five-membered fused azole heterocycle. The idea of locking the flexibility of the system by conformational constraint was simply to reduce its entropy, thereby reducing the overall free-energy of its binding to the target receptor. Out of 22 different azole-fused indeno[2,1-c]quinoline derivatives, seven structurally distinct compounds, 9, 15, 17, 25, 27, 28 and 29, have shown 79-99% growth inhibition of Mycobacterium tuberculosis H37Rv at a fixed dose of 6.25 μg mL(-1). The efficacies of these compounds were evaluated in vitro for 8/9 consecutive days using the BACTEC radiometric assay upon administration of single dose on day one. Of these, two compounds, 9 and 28, inhibited growth of M. tuberculosis very effectively at MIC < 0.39 μg mL(-1) (0.89 μM and 1 μM, respectively). These active compounds 9, 15, 17, 25, 27, 28 and 29 were screened for their cytotoxic effect on mammalian cells (human monocytic cell line U937), which showed that the human cell survival is almost unperturbed (100% survival), except for compound 25, hence these new compounds with new scaffolds have been identified as potent anti-mycobacterials, virtually with no toxicity. Thus these "hit" molecules constitute our important "leads" for further optimization by structure-activity relationship against TB. 相似文献
926.
Podma Pollov Sarmah Bibek Jyoti Borah Alexandra M.Z. Slawin Dipak Kumar Dutta 《Journal of organometallic chemistry》2010,695(24):2603-2608
The dimeric rhodium precursor [Rh(CO)2Cl]2 reacts with quinoline (a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde (b), quinoline-3-carboxaldehyde (c), and quinoline-4-carboxaldehyde (d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)2Cl(L)] (1a-1d), where L = a-d. The complexes 1a-1d have been characterised by elemental analyses, mass spectrometry, IR and NMR (1H, 13C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh?Rh = 3.573 Å). 1a-1d undergo oxidative addition (OA) with different electrophiles such as CH3I, C2H5I and I2 to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = -CH3 (2a-2d), R = -C2H5 (3a-3d)} and [Rh(CO)Cl(L)I2] (4a-4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a-1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551-1735 h−1] compared to that of the well known Monsanto’s species [Rh(CO)2I2]− (TOF = 1000 h−1) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a-1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity. 相似文献
927.
Bhaskar Jyoti Sarmah 《Journal of organometallic chemistry》2010,695(6):781-785
The complex [Ru(CO)2(triphos-κ2P)Cl2] (1) underwent decarbonylation in dichloromethane solution under air over a period of about two weeks to afford the chelated monocarbonyl complex [Ru(CO)(triphos-κ3P)Cl2] (2). The Single Crystal X-ray structure of 2 showed a slightly distorted metal centred complex. The catalytic activity of one of the complexes [Ru(CO)(triphos-κ3P)Cl2] (2) was examined in the transfer hydrogenation of aromatic carbonyl compounds and was found to be efficient with conversion up to 100% in the presence of isopropanol/NaOH. 相似文献
928.
Govindarajan Sankar 《European Polymer Journal》2009,45(3):911-922
Two series of N-methylaniline-blocked isocyanates based on monomeric diisocyanates such as 4,4′-methylene bis(phenyl isocyanate), toluene-2,4-diisocyanate, isophorone diisocyanate and 1,6-diisocyanato hexane and their NCO terminated polyurethane prepolymer (polyisocyanates) were prepared and characterized thoroughly by FTIR, 1H NMR, 13C NMR and EI-Mass spectroscopic methods. The blocking reaction of N-methylaniline with aromatic isocyanates and aromatic polyisocyanates occur faster when compared to the aliphatic isocyanates. The deblocking reactions of blocked isocyanates were carried out under dynamic and isothermal conditions using hot-stage FTIR spectrophotometer. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate kinetics and thermodynamics parameters. Cure reactions of blocked isocyanates with hydroxyl-terminated polybutadiene were also followed to establish the structure-property relationship of the N-methylaniline-blocked isocyanates. The deblocking studies of blocked isocyanates reveal that the aromatic isocyanates undergo deblocking easily compared to aliphatic isocyanates. The rate of deblocking reaction of N-methylaniline-blocked aromatic polyisocyanates was found to be higher compared to N-methylaniline-blocked aromatic monomeric diisocyanate adducts. On the other hand, this trend was just reverse in the cure-reaction studies. The dissolution behavior of N-methylaniline-blocked isocyanates in Terathane-2000, polypropylene glycol-2000, polycaprolactone diol-2000 and hydroxyl-terminated polybutadiene-2500 was also studied and found that all adducts are soluble in these polyols. 相似文献
929.
Jyoti Prasad Chakraborty Deepak Kunzru 《Journal of Analytical and Applied Pyrolysis》2009,86(1):44-52
Pyrolysis of n-heptane was investigated in a tubular reactor in the temperature range of 793–953 K and pressure range of 0.1–2.93 MPa. At all conditions, the main products were methane, ethylene, ethane, propylene, 1-butene, 1-pentene and 1-hexene. With an increase in pressure, the selectivities of hydrogen, methane, ethylene and propylene decreased and that of propane, n-butane and 1-butene increased. To explain the product distribution at high pressure, the Rice–Kossiakoff theory was modified by including the bimolecular reactions of alkyl radicals with the parent hydrocarbon. The initial product selectivities, calculated using the modified R–K mechanism, were in good agreement with the experimental selectivities. The overall kinetics of n-heptane pyrolysis was determined by non-linear analysis. The optimum values of the kinetic parameters at each pressure were determined by minimizing the difference between the calculated and experimental conversions. At each pressure, the reaction order was close to unity and the activation energy ranged between 209 and 219 kJ mol−1. 相似文献
930.
The complexes [Co(N^O)2] (1) and [Cu(N^O)2] (2) {N^O = η2-(N,O) coordinated 2-pyrazinecarboxylic acid} have been synthesized and characterized by elemental (including metal) analyses, FT-IR spectroscopy and powder X-ray diffraction. The molecular structure of complex 2 was determined by single X-ray crystallography. In the molecule, the Cu atom occupies the center of a square planar geometry, which consists of two trans-O atoms and two trans-N atoms of two 2-pyrazinecarboxylic acid ligands. The complexes 1 and 2 were well encapsulated into zeolite–Y super-cage to yield the corresponding zeolite–Y encapsulated metal complexes, abbreviated herein as [Co(N^O)2]–Y (3) and [Cu(N^O)2]–Y (4). Similarly, the metal complexes 1 and 2 were immobilized on alumina and organically modified silica surfaces to lead to the formation of immobilized metal complexes [Co(N^O)2]–Al2O3 (5); [Cu(N^O)2]–Al2O3 (6); [Co(N^O)2]–AMPS (7) and [Cu(N^O)2]–AMPS (8) (AMPS = aminopropyl silica). Elemental (including metal) analyses, FT-IR spectroscopy, powder X-ray diffraction and thermal analysis have been used to characterize these materials. The catalytic activity of all the catalysts 1–8 towards the oxidation of cyclohexene into different chemically and pharmaceutically important products were evaluated under homogeneous and heterogeneous conditions. In order to obtain a maximum conversion of cyclohexene, the reaction parameters, like reaction temperature and time, were optimized. Under the optimized conditions, a maximum of 90.47% cyclohexene conversion was achieved with [Cu(N^O)2]–Y (4) with a 1:2 molar ratio reaction of cyclohexene and H2O2. 相似文献