全文获取类型
收费全文 | 3877篇 |
免费 | 109篇 |
国内免费 | 10篇 |
专业分类
化学 | 3141篇 |
晶体学 | 99篇 |
力学 | 171篇 |
数学 | 106篇 |
物理学 | 479篇 |
出版年
2023年 | 25篇 |
2022年 | 47篇 |
2021年 | 54篇 |
2020年 | 72篇 |
2019年 | 92篇 |
2018年 | 97篇 |
2017年 | 73篇 |
2016年 | 126篇 |
2015年 | 90篇 |
2014年 | 170篇 |
2013年 | 423篇 |
2012年 | 262篇 |
2011年 | 230篇 |
2010年 | 145篇 |
2009年 | 136篇 |
2008年 | 224篇 |
2007年 | 216篇 |
2006年 | 157篇 |
2005年 | 159篇 |
2004年 | 150篇 |
2003年 | 131篇 |
2002年 | 107篇 |
2001年 | 41篇 |
2000年 | 43篇 |
1999年 | 34篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 41篇 |
1995年 | 25篇 |
1994年 | 31篇 |
1993年 | 30篇 |
1992年 | 28篇 |
1991年 | 24篇 |
1990年 | 38篇 |
1989年 | 30篇 |
1988年 | 25篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 26篇 |
1981年 | 24篇 |
1980年 | 23篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 21篇 |
1976年 | 16篇 |
1975年 | 18篇 |
1974年 | 9篇 |
排序方式: 共有3996条查询结果,搜索用时 15 毫秒
951.
Srivari Chandrasekhar Birudaraju Saritha Police Naresh Marelli Udayakiran Chada Raji Reddy Bharatam Jagadeesh 《Helvetica chimica acta》2008,91(7):1267-1276
The conformational control of a 14‐helix nucleating template, cis‐β‐furanoid sugar amino acid (FSAA), over a flexible δ‐amino acid, ornithine is studied in a FSAA‐ornithine cyclic tetrapeptide. Extensive NMR and MD studies reveal that the cyclic peptide adopts a three‐dimentional bowl‐shape cavity, which promotes six‐ and seven‐membered intra‐ and inter‐residue H‐bonding, in polar and non‐polar solvents, respectively. 相似文献
952.
R. Kandan B. Prabhakara Reddy G. Panneerselvam 《Journal of Thermal Analysis and Calorimetry》2018,132(3):1639-1644
Enthalpy measurements have been taken on GdSmTi2O7 and DySmTi2O7 by using a high-temperature differential calorimeter at temperature between 800 and 1655 K. Thermodynamic function, such as heat capacity, entropy and Gibbs energy functions of GdSmTi2O7 and DySmTi2O7, was derived using the data obtained in this study. The results are presented and compared with the data available in the literature. The polynomial expression of enthalpy increments obtained for GdSmTi2O7(s) and DySmTi2O7(s) in the temperature range 298–1700 K is given as: \(\begin{aligned} H_{\text{T}}^{0} - H_{298}^{0} / {\text{J}}\,{\text{mol}}^{ - 1} & = 252.961\,T \, + 1.596 \times 10^{ - 2} \,T^{2} + 3.705 \times 10^{6} \,T^{ - 1} - 89{,}265\quad ({\text{GdSmTi}}_{2} {\text{O}}_{7} ) \\ H_{\text{T}}^{0} - H_{298}^{0} / {\text{J}}\,{\text{mol}}^{ - 1} & = 256.504\,T \, + 1.576 \times 10^{ - 2} \,T^{2} + 3.531 \times 10^{6} \,T^{ - 1} - 89{,}721\quad \left( {{\text{DySmTi}}_{2} {\text{O}}_{7} } \right). \\ \end{aligned}\) 相似文献
953.
Maeva Delcroix Dr. Anil Reddy Marri Stéphane Parant Dr. Philippe C. Gros Dr. Mathilde Bouché 《欧洲无机化学杂志》2023,26(27):e202300138
Significant effort focused on developing photoactivatable theranostics for localized image guided therapy of cancer by thermal ablation. In this context iron complexes were recently identified as photoactivatable theranostic agents with adequate biocompatibility and body clearance. Herein, a series of FeII complexes bearing polypyridine or N-heterocyclic carbenes is reported that rely on rational complex engineering to red-shift their MLCT based excited-state deactivation via a straightforward approach. The non-radiative decay of their MLCT upon irradiation is exploited for theranostic purposes by combining both tracking in photoacoustic imaging (PA) and photothermal therapy (PTT). The influence of structural modifications introduced herein on the solubility and stability of the complexes in biorelevant aqueous media is discussed. The relationship between complexes’ design, production of contrast in photoacoustic and photothermal efficiency are explored to develop tailored PA/PTT theranostic agents. 相似文献
954.
Chidrawar Ajay Devulapally Yogananda Chary Dr. Sridhar Balasubramanian Dr. Basi V. Subba Reddy 《European journal of organic chemistry》2023,26(13):e202201361
Rh(III)-catalyzed C−H bond annulation of 2-arylquinoxalines with cyclic 2-diazo-1,3-diketones has been accomplished for the first time to synthesize a novel series of 2,3-dihydrodibenzo[a,c]phenazin-4(1H)-one frameworks by means of carbene insertion followed by condensation. The reaction proceeds through the C−H bond activation and functionalization of 2-arylquinoxalines using Rh(III)/AgSbF6 complex to produce highly substituted 2,3-dihydrodibenzo[a,c]phenazin-4(1H)-one and benzo[5,6][1,2,4]thiadiazino[2,3-f]phenanthridin-5(6H)-one-10,10-dioxide derivatives in good to excellent yields. 相似文献
955.
Smriti Moi Shamasoddin Shekh K. Kasi Amarnath Reddy Pooja Dhurjad Rajesh Sonti Konkallu Hanumae Gowd 《Photochemistry and photobiology》2023,99(3):911-919
Photostabilizers have been used to impart stability to an FDA-approved chemical UV-A filter avobenzone against the UV-A radiations and sunlight. The thiol group of glutathione plays a critical role in imparting the photostabilization activity of glutathione on avobenzone. The current report aims to evaluate the photostabilization activity of multiple thiols containing cysteine peptides on avobenzone. Cysteine-tripeptide and cysteine-pentapeptide were chemically synthesized and characterized using mass spectrometry. Synthetic peptides were assessed for their photostabilization activity on the enolic-form of the avobenzone under natural sunlight using UV spectroscopy in both protic and aprotic solvents. Unlike glutathione, which has pronounced activity in protic solvents, cysteine-pentapeptide exhibits similar photoprotection activity in both protic and aprotic solvents. Computational calculations using DFT suggest that peptide cysteine thiols may assist in the reversal of the photoketonization process of avobenzone thereby exhibiting the photoprotection activity to the enolic-form of avobenzone. Peptide cysteine thiols lower the activation energy barrier of keto-to-enol tautomerization of avobenzone by 30 kcal mol−1 by assisting the proton shuttle through a six-membered transition state. The current report emphasizes the applications of peptide thiols in cosmetics and may help in the development of peptides as aesthetic medicines. 相似文献
956.
Vamshikrishna Reddy Sammeta Brian M. Anderson John D. Norris Chad D. Torrice Carstyn Joiner Shubin Liu Haoxi Li Konstantin I. Popov Sean W. Fanning Donald P. McDonnell Timothy M. Willson 《Helvetica chimica acta》2023,106(9):e202300097
Synthetic, structural, and computational approaches were used to solve the puzzle as to how a phenolic nonsteroidal estrogen 1 with only a single H-bond to its receptor was more potent than an isomer 2 which formed an intricate network of H-bonds. Synthesis of a series of substituted phenols revealed that pKa was not a determinant of estrogenic activity. First-principles calculation also failed to explain the difference in activity of 1 and 2 . Molecular dynamics revealed that 1 formed a more stable receptor complex compared to 2 , which may explain its increased activity despite forming fewer apparent H-bonds with the protein. 相似文献
957.
M. L. P. Reddy 《Journal of Chemical Sciences》1991,103(2):95-98
The extraction behaviour of Cu(II) from hydrochloric acid and lithium chloride solutions with di-n-pentyl sulphoxide (DPSO) and di-n-octyl sulphoxide (DOSO) has been investigated over a wide range of conditions. At a given strength of the extradant, the
extraction increases with increase in HCl and LiCl concentrations. The extraction of the metal also increases with increase
in extractant concentration at constant [HCl] or [LiCl]. The species extracted would appear to be CuCl2·2DPSO/2DOSO and CuCl
4
2−
·2DPSO. The extraction of the metal decreases with increase in initial aqueous metal concentration and also with increase
in temperature. The extraction also depends on the nature of the diluent employed. 相似文献
958.
Macrocyclic divalent transition metal complexes of acetylacetone buckled with two different diamines
Metal-mediated condensation of o-phenylenediamine with bisacetylacetone-ethylenediimine yields 14-membered tetraaza macrocyclic six-coordinate complexes of the type [M(mac)Cl2],[M(mac)SO4·H2O] (where M = FeII, CoII and CuII; MAC = macrocyclic ligand formed in the template reaction). The metal ions are coordinated by four azomethine nitrogen atoms bridged by acetylacetone moieties. The electrical conductance magnetic moments, electronic and IR spectral data of all complexes are discussed. 相似文献
959.
Differential pulse polarographic (DPP) method of determination of cephalosporins has been developed based on the electrochemistry of the azomethine group in the drugs in universal buffers of pH 2.0-12.0. Quantitative measurements were successful in the concentration range of 1.0 x 10(-5) M-2.5 x 10(-8) M, the lower concentration representing the detection limit by DPP. The described procedure has been applied for the determination of these drugs individually in pharmaceutical formulations and urine samples as well as for simultaneous determination in a single run. 相似文献
960.
Roshan M. Borkar Shankar Gajji Soheb A. Mohammed Mithul Srivastava Velma Ganga Reddy Aishwarya Jala Shailendra Asthana Ahmed Kamal Sanjay K. Banerjee Srinivas Ragampeta 《Journal of mass spectrometry : JMS》2021,56(2)
The progression of diabetic complications can be prevented by inhibition of aldose reductase and fidarestat considered to be highly potent. To date, metabolites of the fidarestat, toxicity, and efficacy are unknown. Therefore, the present study on characterization of hitherto unknown in vitro and in vivo metabolites of fidarestat using liquid chromatography–electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS) is undertaken. In vitro and in vivo metabolites of fidarestat have been identified and characterized by using LC/ESI/MS/MS and accurate mass measurements. To identify in vivo metabolites, plasma, urine, and feces samples were collected after oral administration of fidarestat to Sprague–Dawley rats, whereas for in vitro metabolites, fidarestat was incubated in human S9 fraction, human liver microsomes, and rat liver microsomes. Furthermore, in silico toxicity and efficacy of the identified metabolites were evaluated. Eighteen metabolites have been identified. The main in vitro phase I metabolites of fidarestat are oxidative deamination, oxidative deamination and hydroxylation, reductive defluroniation, and trihydroxylation. Phase II metabolites are methylation, acetylation, glycosylation, cysteamination, and glucuronidation. Docking studies suggest that oxidative deaminated metabolite has better docking energy and conformation that keeps consensus with fidarestat whereas the rest of the metabolites do not give satisfactory results. Aldose reductase activity has been determined for oxidative deaminated metabolite (F‐1), and it shows an IC50 value of 0.44 μM. The major metabolite, oxidative deaminated, did not show any cytotoxicity in H9C2, HEK, HEPG2, and Panc1 cell lines. However, in silico toxicity, the predication result showed toxicity in skin irritation and ocular irritancy SEV/MOD versus MLD/NON (v5.1) model for fidarestat and its all metabolites. In drug discovery and development research, it is distinctly the case that the potential for pharmacologically active metabolites must be considered. Thus, the active metabolites of fidarestat may have an advantage as drug candidates as many drugs were initially observed as metabolites. 相似文献