全文获取类型
收费全文 | 1301篇 |
免费 | 48篇 |
专业分类
化学 | 841篇 |
晶体学 | 25篇 |
力学 | 46篇 |
数学 | 92篇 |
物理学 | 345篇 |
出版年
2023年 | 28篇 |
2022年 | 31篇 |
2021年 | 35篇 |
2020年 | 28篇 |
2019年 | 36篇 |
2018年 | 33篇 |
2017年 | 37篇 |
2016年 | 70篇 |
2015年 | 48篇 |
2014年 | 44篇 |
2013年 | 102篇 |
2012年 | 96篇 |
2011年 | 117篇 |
2010年 | 60篇 |
2009年 | 53篇 |
2008年 | 58篇 |
2007年 | 66篇 |
2006年 | 52篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 9篇 |
1996年 | 10篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 15篇 |
1982年 | 6篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1971年 | 7篇 |
1970年 | 6篇 |
排序方式: 共有1349条查询结果,搜索用时 0 毫秒
151.
152.
Binoy K. Saha 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o591-o593
The title compound, C9H15N3O3, which has crystallographically imposed threefold symmetry, crystallizes as a hexagonal columnar structure. The crystal structure is stabilized by a less common amide–amide synthon, where one amide group is hydrogen bonded to four others. The amide groups form cyclic amide–amide hexamers via N—H...O hydrogen bonds. 相似文献
153.
154.
Koushik Saha Benson Joseph Rongala Ramalakshmi Dr. R. S. Anju Dr. Babu Varghese Prof. Sundargopal Ghosh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(23):7871-7878
Thermolysis of [Cp*Ru(PPh2(CH2)PPh2)BH2(L2)] 1 (Cp*=η5‐C5Me5; L=C7H4NS2), with terminal alkynes led to the formation of η4‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)B{R‐C=CH2}(L)2] ( 2 a – c ) and η2‐vinylborane complexes [Cp*Ru(R‐C=CH2)BH(L)2] ( 3 a – c ) ( 2 a , 3 a : R=Ph; 2 b , 3 b : R=COOCH3; 2 c , 3 c : R=p‐CH3‐C6H4; L=C7H4NS2) through hydroboration reaction. Ruthenium and the HBCC unit of the vinylborane moiety in 2 a – c are linked by a unique η4‐interaction. Conversions of 1 into 3 a – c proceed through the formation of intermediates 2 a – c . Furthermore, in an attempt to expand the library of these novel complexes, chemistry of σ‐borane complex [Cp*RuCO(μ‐H)BH2L] 4 (L=C7H4NS2) was investigated with both internal and terminal alkynes. Interestingly, under photolytic conditions, 4 reacts with methyl propiolate to generate the η4‐σ,π‐borataallyl complexes [Cp*Ru(μ‐H)BH{R‐C=CH2}(L)] 5 and [Cp*Ru(μ‐H)BH{HC=CH‐R}(L)] 6 (R=COOCH3; L=C7H4NS2) by Markovnikov and anti‐Markovnikov hydroboration. In an extension, photolysis of 4 in the presence of dimethyl acetylenedicarboxylate yielded η4‐σ,π‐borataallyl complex [Cp*Ru(μ‐H)BH{R‐C=CH‐R}(L)] 7 (R=COOCH3; L=C7H4NS2). An agostic interaction was also found to be present in 2 a – c and 5 – 7 , which is rare among the borataallyl complexes. All the new compounds have been characterized in solution by IR, 1H, 11B, 13C NMR spectroscopy, mass spectrometry and the structural types were unequivocally established by crystallographic analysis of 2 b , 3 a – c and 5 – 7 . DFT calculations were performed to evaluate possible bonding and electronic structures of the new compounds. 相似文献
155.
New LS Saha S Ong MM Boelsterli UA Chan EC 《Rapid communications in mass spectrometry : RCM》2007,21(6):982-988
A rapid and sensitive ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and validated for the determination of troglitazone in mouse plasma. Troglitazone and its internal standard (IS), rosiglitazone, were separated on an ACQUITY UPLC BEH C(18) column (1.7 microm particle size, 50 x 2.1 mm i.d.) by gradient elution with water and methanol at a flow rate of 0.5 mL/min. The cycle time of each analysis was 2.5 min. Rosiglitazone and troglitazone eluted at 1.13 and 1.57 min, respectively, and were chromatographically resolved from the ion suppression and enhancement zones due to the biological matrix effect. Quantitation of the analytes was performed in electrospray negative ionization mode (ESI -ve) using multiple reaction monitoring (MRM) experiments. The weighted (1/x) calibration curve was quadratic over the plasma concentration range 1-2500 ng/mL with a correlation coefficient (r(2)) of 0.9966. The limit of quantitation (LOQ) of troglitazone in mouse plasma was lower than 1 ng/mL. The inter- and intra-day variations of the assay were lower than 12.1%; the overall accuracy ranged from 86.4-110.2% and recovery from spiked plasma was more than 60%. The developed method was successfully applied to determine troglitazone in mouse plasma after intraperitoneal administration. 相似文献
156.
Chelation of vanadium(V) by difluoromethylene bisphosphonate, a structural analogue of pyrophosphate
Crans DC Holder AA Saha TK Prakash GK Yousufuddin M Kultyshev R Ismail R Goodman MF Borden J Florian J 《Inorganic chemistry》2007,46(16):6723-6732
The structural and functional analogy between difluoromethylene bisphosphonate (CF2PP) and pyrophosphate (PPi) is investigated in a reaction with V(V) in the form of vanadate. The reaction of CF2PP with vanadate was investigated using 1.00 M KCl as supporting electrolyte over the ranges 3 < or = [CF2PP] < or = 60 mM and 2.06 < or = pH < or = 11.80. 51V, 19F, and 31P NMR spectroscopic studies showed that a 1:1 species was formed with an H+-dependent formation constant of 110 M-1 at pH 7.22. Results of solution experiments and ab initio calculations are consistent with CF2PP coordinating V(V) in a bidentate manner, as previously reported for PPi. Below pH 4, a minor complex forms, which is consistent with a 1:2 stoichiometry. This complex was also observed with pyrophosphate. The X-ray crystal structure of the monoprotonated difluoromethylene bisphosphonate anion (H[CF2PP]3-)-toludine complex is presented. The H[CF2PP]3- anion crystallized in the triclinic space group P with a = 12.7629(7) A, b = 13.3992(7) A, c = 17.1002(9) A, and V = 2584.4(2) A3, and Z = 2. Sheets of the layers of anions are connected through a network of H-bonds and separated by a layer of toludine cations. The structural features are investigated, and the CF2PP anion was found to be longer and wider than the corresponding PPi. Given the larger size of this anion compared to PPi, the chelation affinity upon CF2 substitution was found to be 4-5-fold reduced at neutral pH. 相似文献
157.
Biswajit Saha 《Tetrahedron letters》2007,48(8):1379-1383
A mild and efficient protocol for the Pictet-Spengler reaction in water using an acid catalyst has been described. The condensation of tryptophan, tryptamine, and Nb-benzyl tryptophan with different aldehydes having both electron-withdrawing and -donating substituents in the presence of a catalytic amount of TFA in water furnished tetrahydro-β-carbolines in good isolated yields. A salient feature of the water mediated Pictet-Spengler reaction was the general trend observed during the condensation of Trp-OMe and aryl/aliphatic aldehydes furnishing diastereomeric mixtures with a preference for the cis-isomer. 相似文献
158.
The present study for the first time explores the use of Central composite design (CCD) of RSM to optimize the process parameters of biosynthesis of AgNPs from rhizome extract of Curculigo orchioides based on the absorbance of surface plasmon resonance (SPR) band at 430 nm that corresponds to the synthesis of mono-disperse, spherical AgNPs. A polynomial model was established as a functional relationship between the synthesis of AgNPs and four independent variables such as concentration of AgNO3, % rhizome extract, pH and temperature. The optimum conditions for maximum AgNPs synthesis were 2 mM concentration of AgNO3, 20 % rhizome extract, pH 8, and temperature of 60 °C. A significant correlation (R 2 = 0.8947) was observed between the experimental data and the predicted values indicating the adequacy of the model. Transmission electron microscopy (TEM) revealed spherical particles with size range of 5–28 nm. Selected area electron diffraction pattern and X-ray diffraction analysis confirmed the face-centered cubic structure of metallic silver. The plausible mechanism for the reduction of AgNO3 to AgNPs was proposed following the identification of functional groups by FTIR. The antioxidative activity of AgNPs was demonstrated with scavenging of hydrogen peroxide (H2O2), 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and superoxide radicals. 相似文献
159.
Pinki Saha Jnan Prakash Naskar Arnab Bhattacharya Rakesh Ganguly Baptu Saha 《Journal of Coordination Chemistry》2016,69(2):303-317
The reactions of equimolar amounts of trans-[ReOC13(PPh3)2] or trans-[Re(NPh)(PPh3)2Cl3] with a Schiff base formed by condensation of 2-hydroxy-4-methoxybenzaldehyde and ethanolamine (H2L) result in the formation of cis-[ReO(HL)PPh3Cl2] (1a) and trans-[Re(NPh)(HL)(PPh3)Cl2] (2b), respectively, in good yields. 1a and 2b have been characterized by a range of spectroscopic and analytical techniques. The X-ray crystal structures of 1a and 2b reveal that 1a is an octahedral cis-Cl,Cl oxorhenium(V) complex, while 2b is a trans-Cl,Cl phenylimidorhenium(V) complex. The complexes are weakly emissive at room temperature with quantum yields of 10?4. Density functional theory calculations of the electronic properties of the complexes were performed and are in agreement with the experimental results. The complexes display quasi-reversible Re(V)/Re(VI) redox couples in acetonitrile. There is reasonable agreement between the experimental and calculated redox potentials of 1a and 2b. 相似文献
160.
A noble interaction: An assessment of noble gas binding ability of metal oxides (metal = Cu,Ag, Au) 下载免费PDF全文
Sudip Pan Ranajit Saha Anand Kumar Ashutosh Gupta Gabriel Merino Pratim K. Chattaraj 《International journal of quantum chemistry》2016,116(13):1016-1024
An in silico study is performed on the structure and the stability of noble gas (Ng) bound MO complexes (M = Cu, Ag, Au). To understand the stability of these Ng bound complexes, dissociation energies, dissociation enthalpy, and dissociation free energy change are computed. The stability of NgMO is also compared with that of the experimentally detected NgMX (X= F, Cl, Br). It is found that MO has lower Ng binding ability than that of MX. All the dissociation processes producing Ng and MO are endothermic in nature and for the Kr‐Rn bound MO (M = Cu, Au), and Xe and Rn bound AgO cases, the corresponding dissociation processes are turned out to be endergonic in nature at standard state. The Wiberg bond indices of Ng? M bonds and Ng→M electron transfer gradually increase from Ar to Rn and for the same Ng they follow the order of NgAuO > NgCuO > NgAgO. Energy decomposition analysis shows that the Ng? M bonds in NgMO are partly covalent and partly electrostatic in nature. Electron density analysis further highlights the partial covalent character in Ng? M bonds. © 2016 Wiley Periodicals, Inc. 相似文献