全文获取类型
收费全文 | 580篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
化学 | 403篇 |
晶体学 | 15篇 |
力学 | 21篇 |
数学 | 28篇 |
物理学 | 132篇 |
出版年
2024年 | 4篇 |
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 17篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 18篇 |
2017年 | 23篇 |
2016年 | 28篇 |
2015年 | 17篇 |
2014年 | 44篇 |
2013年 | 68篇 |
2012年 | 37篇 |
2011年 | 41篇 |
2010年 | 23篇 |
2009年 | 21篇 |
2008年 | 23篇 |
2007年 | 27篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1973年 | 6篇 |
1971年 | 1篇 |
排序方式: 共有599条查询结果,搜索用时 15 毫秒
171.
The Eupatorium odoratum leaf peroxidase exists as at least seven distinct isozymes (three cationic, three anionic, and one neutral). These isozymes
were identified and separated by preparative iso-electric focusing. Thermal stability, including the activation enthalpy (ΔH
*), free energy of inactivation (ΔG
*) and activation entropy (ΔS
*), and kinetic studies of two isozymes, one having a pI of 5.0 (E5) and another one having a pI of 7.0 (E7) with mol mass
of 43 and 50 kD, respectively, were studied in detail. Of the molecular weight of E5 and E7, 25 and 32% correspond to the
carbohydrate content of the isozymes. Optimal pH was in the acidic range of 3.6–3.8 for E5 and 3.8 for E7 with the oxidation
of ABTS. E7 and E5 showed activation energy for inactivation, 194.8 and 145.4 kJ/mol, respectively. Both the isozymes showed
distinct substrate specificity. The catalytic specificity constant for E5 and E7 were 112×105 and 124×105/s·M, respectively, when 2,2′-azino-bis-(3-ethylbenz-thiazoline-6 sulfonic acid) was used as the substrate. Maximum affinity (i.e., lowest K
m value) to H2O2 was shown by E5 and E7 along with Pyrogallol and was 0.02 and 0.05/s·M, respectively. 相似文献
172.
A new library of C-16 modified artemisinin analogs and evaluation of their anti-parasitic activities
Menon RB Kannoth MM Tekwani BL Gut J Rosenthal PJ Avery MA 《Combinatorial chemistry & high throughput screening》2006,9(10):729-741
A library of C-16 modified artemisinin analogs was prepared and their antimalarial as well as antileishmanial activities were evaluated. Synthesis of these compounds involved the conversion of artemisinin to its phenol derivatives 7 and 12, and subsequent parallel derivatization by introducing new chemical groups through ester, carbamate, sulfate, phosphate and isourea linkages. Comparison of in vitro antimalarial activities showed that C9-beta artemisinin analogs (8a-f) are more potent than the corresponding C9-alpha diastereomers (9a-f); however, their antileishmanial activities were in the same range. Many of the 10-deoxoartemisinin analogs studied here showed promising antiparasitic activities. For example, compounds 13a-e are approximately three times more active against drug resistant W2 strain of P. falciparum, compared to artemisinin (IC(50), approximately 0.2 - 0.6 nM; cf. artemisinin = 1.6 nM). Further, a number of compounds in this series were notably leishmanicidal, with activities comparable to or better than pentamidine (e.g., 13g and 13j). Detailed in vivo studies involving these active compounds are underway to identify lead candidates for further development. 相似文献
173.
Prof. Dr. Tarlok S. Lobana Poonam Kumari Gagandeep Bawa Geeta Hundal Ray J. Butcher Francisco J. Fernandez Jerry P. Jasinski James A. Golen 《无机化学与普通化学杂志》2012,638(5):804-810
Complexes of pyrrole‐2‐carbaldehyde thiosemicarbazones, [(C4H4N4)(H)C2=N3–N2(H)–C1(=S)–N1HR; R = Ph, H2L1; Me, H2L2; H, H2L3] with nickel(II) and palladium(II) are described. The reaction of nickel(II) acetate with H2L1 in methanol in 1:1 molar ratio yielded a complex of composition, [Ni(κ2‐N3,S‐HL1)2] ( 1 ). Likewise reaction of NiCl2 with H2L2 in 1:1 molar ratio in acetonitrile in the presence of triethylamine base followed by the addition of pyridine did not yield the anticipated [Ni(κ3‐N4,N3,S‐L2)(py)] complex, moreover a bis‐square‐planar complex, [Ni(κ2‐N3,S‐HL2)2] ( 2 ) was formed. However, in the presence of bipyridine (bipy), it yielded the addition product, [Ni(κ2‐N3,S‐HL2)2(κ2‐N, N‐bipy)] ( 3 ). Reaction of PdCl2(κ2‐P, P–PPh2–CH2–PPh2) with H2L3 in toluene in the presence of triethylamine has yielded a complex of stoichiometry, [Pd(κ3‐N4,N3,S–L3)(κ1‐P–PPh2–CH2–P(O)Ph2] ( 4 ). The ligands (HL1)– and (HL2)– are chelating to NiII metal atom as anions binding through N3,S‐donor atoms with pendant pyrrole groups, and (L3)2– is chelating to the PdII metal atom as dianion through N4,N3,S‐donor atoms (pyrrole is N4‐bonded). Fourth site in 4 is bonded to one P‐donor atom of PPh2–CH2–P(O)Ph2, whose pendant –PPh2 group involves auto oxidation to –P(O)PPh2 during reaction. These complexes were characterized using analytical data, IR, NMR (1H, 31P) spectroscopy and X‐ray crystallography. Complexes 1 , 2 , and 4 have square‐planar arrangement, whereas complex 3 is octahedral. 相似文献
174.
The coordination chemistry of platinum(II) with a series of thiosemicarbazones {R(H)C2=N3‐N2(H)‐C1(=S)‐N1H2, R = 2‐hydroxyphenyl, H2stsc; pyrrole, H2ptsc; phenyl, Hbtsc} is described. Reactions of trans‐PtCl2(PPh3)2 precursor with H2stsc (or H2ptsc) in 1 : 1 molar ratio in the presence of Et3N base yielded complexes, [Pt(η3‐ O, N3, S‐stsc)(PPh3)] ( 1 ) and [Pt(η3‐ N4, N3, S‐ptsc)(PPh3)] ( 2 ), respectively. Further, trans‐PtCl2(PPh3)2 and Hbtsc in 1 : 2 (M : L) molar ratio yielded a different compound, [Pt(η2‐ N3, S‐btsc)(η1‐S‐btsc)(PPh3)] ( 3 ). Complex 1 involved deprotonation of hydrazinic (‐N2H‐) and hydroxyl (‐OH) groups, and stsc2? is coordinating via O, N3, S donor atoms, while complex 2 involved deprotonation of hydrazinic (‐N2H‐) and ‐N4H groups and ptsc2? is probably coordinating via N4, N3, S donor atoms. Reaction of PdCl2(PPh3)2 with Hbtsc‐Me {C6H5(CH3)C2=N3‐N2(H)‐C1(=S)‐N1H2} yielded a cyclometallated complex [Pd(η3‐C, N3, S‐btsc‐Me)(PPh3)] ( 4 ). These complexes have been characterized with the help of analytical data, spectroscopic techniques {IR, NMR (1H, 31P), U.V} and single crystal X‐ray crystallography ( 1 , 3 and 4 ). The effects of substituents at C2 carbon of thiosemicarbazones on their dentacy and cyclometallation are emphasized. 相似文献
175.
L-N(omega)-nitroarginine and L-arginine were coupled with N-(Cbz-alpha-aminoacyl)benzotriazoles and N-Cbz-dipeptidoylbenzotriazoles to provide arginine LL-dipeptides 9a-e, 11a-d; LLL-tripeptides 18a-c, 20; and diastereomeric mixtures (9b+9b'), (9c+9c'), (11b+11b') and (18c+18c') [compound numbers written within parentheses represent a diastereomeric mixture or racemate; compound numbers without parentheses represent an achiral compound or a single enantiomer] by extension at the N-terminus of arginine, in isolated yields of 66-95% with complete retention of chirality as evidenced by NMR and HPLC analysis. Arginine LL-dipeptides 15a-d were synthesized by extension at the C-terminus of arginine in isolated yield of 66-80%, using benzotriazole activated arginine L-(omega)NO2-Arg-Bt, 13. Our methodology has also been used to synthesize the protected RGD peptide (Cbz(alpha)-L-(omega)NO2-Arg-Gly-L-Asp-(OH)2) 21. 相似文献
176.
Tarlok S. Lobana Sonia Khanna Geeta Hundal Ray J. Butcher Alfonso Castineiras 《Polyhedron》2009,28(18):3899-3906
Reactions of copper(I) halides with a series of thiosemicarbazones, namely, benzaldehyde thiosemicarbazone (R1R2CN–NH–C(S)–NH2, R1 = Ph, R2 = H; Hbtsc), 2-benzoylpyridine thiosemicarbazone (R1 = Ph, R2 = py; Hbpytsc), and acetone thiosemicarbazone (R1 = R2 = Me; Hactsc), in the presence of PPh3 has formed dimeric complexes, viz. sulfur bridged [Cu2(μ-S-Hbtsc)2Br2(PPh3)2]·2H2O (1), iodo-bridged [Cu2(μ-I)2(η1-S-Hbtsc)2(PPh3)2] (2), and heterobridged [Cu2(μ3-S,N3-Hactsc)(η1-Br)(μ-Br)(PPh3)2] (3), as well as mononuclear complexes [CuX(η1-S-Hbpytsc)(PPh3)2]·CH3CN (X = Br, 4; Cl, 5). Complexes 1, 2, 4 and 5 involve thiosemicarbazone ligands in η1-S bonding mode while in compound 3, ligand acts in N3, S-chelation-cum-S-bridging mode (μ3-S,N3 mode). The intermolecular interactions such as, N2H?X, HN1H?X (X = S, Br, Cl), CH?π interactions lead to 2D networks. All the complexes have been characterized with the help of elemental analyses, IR, 1H, and 31P NMR spectroscopy, and single crystal X-ray crystallography. The role of a solvent in alteration of nuclearity and bonding modes of complexes has been highlighted. 相似文献
177.
178.
An Elegant Synthesis of a New Class of 1‐(Substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxides by Microwave Irradiation 下载免费PDF全文
Radha Rani Chinthaparthi Chandra Sekhar Reddy Gangireddy Madhu Kumar Reddy Kandula Satheesh Krishna Balam Suresh Reddy Cirandur 《Journal of heterocyclic chemistry》2015,52(6):1876-1882
A simple and efficient one‐pot microwave‐assisted click formation of 1‐(substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxide derivatives via Huisgen regioselective [3+2]‐cycloaddition of an in situ generated organic azides and diphenyl(prop‐2‐yn‐1‐yl)phosphine oxide in highly polar DMSO‐H2O medium. This synthetic protocol is mild, requires shorter reaction time, and afforded products in excellent yields with high regioselectivity. 相似文献
179.
Synthesis,Spectroscopy, and Structures of Mono‐ and Dinuclear Copper(I) Halide Complexes with 1,3‐Imidazolidine‐2‐thiones 下载免费PDF全文
Simran Walia Supreet Kaur Jaspreet Kaur Amanpreet K. Sandhu Tarlok S. Lobana Geeta Hundal Jerry P. Jasinski 《无机化学与普通化学杂志》2015,641(10):1728-1736
Copper(I) halides with triphenyl phosphine and imidaozlidine‐2‐thiones (L ‐NMe, L ‐NEt, and L ‐NPh) in acetonitrile/methanol (or dichloromethane) yielded copper(I) mixed‐ligand complexes: mononuclear, namely, [CuCl(κ1‐S‐L ‐NMe)(PPh3)2] ( 1 ), [CuBr(κ1‐S‐L ‐NMe)(PPh3)2] ( 2 ), [CuBr(κ1‐S‐L ‐NEt)(PPh3)2] ( 5 ), [CuI(κ1‐S‐L ‐NEt)(PPh3)2] ( 6 ), [CuCl(κ1‐S‐L ‐NPh)(PPh3)2] ( 7 ), and [CuBr(κ1‐S‐L ‐NPh)(PPh3)2] ( 8 ), and dinuclear, [Cu2(κ1‐I)2(μ‐S‐L ‐NMe)2(PPh3)2] ( 3 ) and [Cu2(μ‐Cl)2(κ1‐S‐L ‐NEt)2(PPh3)2] ( 4 ). All complexes were characterized with analytical data, IR and NMR spectroscopy, and X‐ray crystallography. Complexes 2 – 4 , 7 , and 8 each formed crystals in the triclinic system with P$\bar{1}$ space group, whereas complexes 1 , 5 , and 6 crystallized in the monoclinic crystal system with space groups P21/c, C2/c, and P21/n, respectively. Complex 2 has shown two independent molecules, [(CuBr(κ1‐S‐L ‐NMe)(PPh3)2] and [CuBr(PPh3)2] in the unit cell. For X = Cl, the thio‐ligand bonded to metal as terminal in complex 4 , whereas for X = I it is sulfur‐bridged in complex 3 . 相似文献
180.
M. Priya Rani K. G. Raghu Mangalam S. Nair K. P. Padmakumari 《Applied biochemistry and biotechnology》2014,173(4):946-956
Stereospermum colais (family Bignoniaceae) is a well-known pharmacologically potent medicinal plant reported in traditional systems of medicine. Phytochemical investigation of the roots of S. colais resulted in the isolation of seven compounds, and the metabolites were screened for its α-glucosidase enzyme inhibition and anti-glycation property. The compounds identified were β-sitosterol (1), 2-(4′-hydroxyphenyl) ethyl undecanoate (2), 2-(4′-hydroxyphenyl)ethyl pentadecanoate (3), 5α-ergosta-7,22-dien-3β-ol (4), ursolic acid (5), lapachol (6), and pinoresinol (7). Ursolic acid, lapachol, and pinoresinol possessed IC50 values of 119.01, 130.29, and 125.62 nM, respectively, compared to standard ascorbic acid with an IC50 value of 201.01 nM. The other compounds failed to show the activity. Results of the current study showcased the possible exploration of this medicinal plant for the treatment of type 2 diabetes in line with the development of phytopharmaceutical industry. 相似文献