全文获取类型
收费全文 | 933篇 |
免费 | 47篇 |
国内免费 | 4篇 |
专业分类
化学 | 706篇 |
晶体学 | 3篇 |
力学 | 42篇 |
数学 | 138篇 |
物理学 | 95篇 |
出版年
2023年 | 7篇 |
2022年 | 30篇 |
2021年 | 33篇 |
2020年 | 20篇 |
2019年 | 31篇 |
2018年 | 37篇 |
2017年 | 10篇 |
2016年 | 32篇 |
2015年 | 38篇 |
2014年 | 32篇 |
2013年 | 76篇 |
2012年 | 68篇 |
2011年 | 60篇 |
2010年 | 42篇 |
2009年 | 30篇 |
2008年 | 52篇 |
2007年 | 66篇 |
2006年 | 49篇 |
2005年 | 45篇 |
2004年 | 34篇 |
2003年 | 32篇 |
2002年 | 34篇 |
2001年 | 15篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 8篇 |
1997年 | 8篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1991年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1977年 | 6篇 |
1975年 | 2篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1966年 | 2篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1961年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有984条查询结果,搜索用时 18 毫秒
831.
Elmetwally M. Elabbasy Taher S. Hassan Samir H. Saker 《Journal of Applied Mathematics and Computing》2006,21(1-2):99-118
In this paper, we study the oscillatory behavior of first order nonlinear neutral delay differential equations. Several new sufficient conditions which ensure that all solutions are oscillatory are given. The obtained results extend and improve several known results in the literature. Some examples are considered to illustrate the main results. 相似文献
832.
The syntheses of rebeccamycin analogues possessing a 7-azaindole moiety instead of an indole unit, and with both indole and azaindole moieties linked to the carbohydrate are described. In these bridged aza compounds, the oxygen of the pyranose heterocycle is oriented towards either the indole, or the azaindole unit. In these series, compounds bearing a free imide nitrogen were synthesized by coupling the corresponding aglycones with a sugar pre-tosylated in 2-position via a Mitsunobu reaction. To obtain a precursor for bridged aza-rebeccamycin analogues substituted in 6-position on the sugar moiety, a 2,6-ditosylated sugar was used. 相似文献
833.
Adnane Aouidate Adib Ghaleb Mounir Ghamali Samir Chtita Abdellah Ousaa M’barek Choukrad Abdelouahid Sbai Mohammed Bouachrine Tahar Lakhlifi 《Structural chemistry》2018,29(6):1609-1622
Kinase-related apoptosis-inducing kinase 2 (DRAK2) is a serine/threonine kinase and belongs to the death-associated protein kinase DPAK family, which is responsible for induction of apoptosis in many cell types. Thus, DRAK2 is regarded as a promising target for treatment of autoimmune diseases. To investigate the binding between DRAK2 and indirubin inhibitors and design potent inhibitors, a three-dimensional quantitative structure-activity relationship (3D-QSAR) and molecular docking were performed. Comparative Molecular Similarity Indices Analysis (CoMSIA) was developed using 33 molecules having pIC50 ranging from 8.523 to 5.000 (IC50 in nM). The best CoMSIA model gave a significant coefficient of determination (R2?=?0.93), as well as a (leave-one-out cross-validation coefficient Q2 of 0.81. The predictive ability of this model was evaluated by external validation using a test set of eight compounds and yielded a predicted coefficient of determination R2test of 0.94. The contour maps could provide structural features to improve inhibitory activity. Good consistency between contour maps and molecular docking strongly suggests that the molecular modeling is reliable. Based on these satisfactory results, we designed several new DRAK2 inhibitors and their inhibitory activities were predicted using different models, which are developed on different training and test sets. Additionally, these newly designed inhibitors showed promising results in the preliminary in silico ADMET evaluations compared to the best inhibitor from the studied dataset. This study could be useful in lead identification and optimization for early drug discovery of DRAK2 inhibitors. 相似文献
834.
Adnane Aouidate Adib Ghaleb Mounir Ghamali Samir Chtita Abdellah Ousaa M’barek Choukrad Abdelouahid Sbai Mohammed Bouachrine Tahar Lakhlifi 《Structural chemistry》2018,29(4):1031-1043
Cell division cycle 7 (CDC7) is a serine/threonine kinase, which plays a vital role in the replication initiation of DNA synthesis. Overexpression of the CDC7 in various tumor growths and in cell proliferation makes it a promising target for treatment of cancers. To investigate the binding between the CDC7 and furanone inhibitors, and in order to design highly potent inhibitors, a three-dimensional quantitative structure activity relationship (3D-QSAR) with molecular docking was performed. The optimum CoMSIA model showed significant statistical quality on all validation methods with a determination coefficient (R2?=?0.945), bootstrapping R2 mean (BS-R2?=?0.960), and leave-one-out cross-validation (Q2) coefficient of 0.545. The predictability of this model was evaluated by external validation using a test set of nine compounds with a predicted determination coefficient R2test of 0.96, besides the mean absolute error (MAE) of the test set was 0.258 log units. The extracted contour maps were used to identify the important regions, where the modification was necessary to design a new molecule with improved activity. Furthermore, a good consistency between the molecular docking and contour maps strongly demonstrates that the molecular modeling is reliable. Based on those obtained results, we designed several new potent CDC7 inhibitors, and their inhibitory activities were validated by the molecular models. Additionally, those newly designed inhibitors showed promising results in the preliminary in silico ADMET evaluations. 相似文献
835.
Quaternary Germanides RE3TRh4Ge4 (RE = Ce,Pr, Nd; T = Nb,Ta) – A New Coloring Variant of the Aristotype AlB2 下载免费PDF全文
Rolf‐Dieter Hoffmann Daniel Voßwinkel Samir F. Matar Rainer Pöttgen 《无机化学与普通化学杂志》2016,642(18):979-986
The quaternary germanides RE3TRh4Ge4 (RE = Ce, Pr, Nd; T = Nb, Ta) were synthesized from the elements by arc‐melting and subsequent annealing in a muffle furnace. The structure of Ce3TaRh4Ge4 was refined from single‐crystal X‐ray diffractometer data: new type, Pbam, a = 719.9(2), b = 1495.0(3), c = 431.61(8), wR2 = 0.0678, 1004 F2 values, and 40 variables. Isotypy of the remaining phases was evident from X‐ray powder patterns. Ce3TaRh4Ge4 is a new superstructure variant of the aristotype AlB2 with an ordering of cerium and tantalum on the aluminum site, whereas the honey‐comb network is built up by a 1:1 ordering of rhodium and germanium. This crystal‐chemical relationship is discussed based on a group‐subgroup scheme. The distinctly different size of tantalum and cerium leads to a pronounced puckering of the [Rh4Ge4] network, which shows the shortest interatomic distances (253–271 pm Rh–Ge) within the Ce3TaRh4Ge4 structure. Another remarkable structural feature concerns the tantalum coordination with six shorter Ta–Rh bonds (265–266 pm) and six longer Ta–Ge bonds (294–295 pm). The [Rh4Ge4] network fully separates the tantalum and cerium atoms (Ce–Ce > 387 pm, Ta–Ta > 431 pm, and Ce–Ta > 359 pm). The electronic density of states DOS from DFT calculations show metallic behavior with large contributions of localized Ce 4f as well as itinerant ones from all constituents at the Fermi level but no significant magnetic polarization on Ce could be identified. The bonding characteristics described based on overlap populations illustrate further the crystal chemistry observations of the different coordination of Ce1 and Ce2 in Ce3TaRh4Ge4. The Rh–Ge interactions within the network are highlighted as dominant. The bonding magnitudes follow the interatomic distances and identify differences of Ta bonding vs. Ce1/Ce2 bonding with the Rh and Ge substructures. 相似文献
836.
A Bifunctional Electrocatalyst for Oxygen Evolution and Oxygen Reduction Reactions in Water 下载免费PDF全文
Prof. Dr. Wolfgang Schöfberger Dipl.‐Ing. Felix Faschinger Samir Chattopadhyay Snehadri Bhakta Biswajit Mondal Prof. Dr. Johannes A. A. W. Elemans Prof. Dr. Stefan Müllegger M. Sc. Stefano Tebi Prof. Dr. Reinhold Koch Priv.‐Doz. Dr. Florian Klappenberger Dipl.‐Chem. Mateusz Paszkiewicz Prof. Dr. Johannes V. Barth Dr. Eva Rauls Hazem Aldahhak Prof. Dr. Wolf Gero Schmidt Prof. Dr. Abhishek Dey 《Angewandte Chemie (International ed. in English)》2016,55(7):2350-2355
Oxygen reduction and water oxidation are two key processes in fuel cell applications. The oxidation of water to dioxygen is a 4 H+/4 e? process, while oxygen can be fully reduced to water by a 4 e?/4 H+ process or partially reduced by fewer electrons to reactive oxygen species such as H2O2 and O2?. We demonstrate that a novel manganese corrole complex behaves as a bifunctional catalyst for both the electrocatalytic generation of dioxygen as well as the reduction of dioxygen in aqueous media. Furthermore, our combined kinetic, spectroscopic, and electrochemical study of manganese corroles adsorbed on different electrode materials (down to a submolecular level) reveals mechanistic details of the oxygen evolution and reduction processes. 相似文献
837.
Ayman A. Abdel Aziz Rania G. Mohamed Fatma M. Elantabli Samir M. El-Medani 《Journal of fluorescence》2016,26(6):1927-1938
A novel fluorimetric optode has been developed for the highly selective and sensitive for the determination of ultra trace amounts of Al3+ ions. The proposed fluorescent optode is based on the incorporation of a simple and effective fluorescent sensor tridentate NOS Schiff base N-(2-hydroxynaphthylidene)-2-aminothiophenol (H2L) in a plasticized PVC containing KTpClPB as a lipophilic anionic additive. H2L was synthesized by a facile one-step Schiff base reaction. The plasticized PVC-membrane displays a calibration response for Al3+ ions over a wide concentration range from 1.0 × 10?9 to 4.4 × 10?3 mol/L. The fluorescence signal of the optode membrane can be easily recovered by immersion in 0.01 M EDTA. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Al3+ ion with respect to common co-existing cations, particularly Ga3+and In3+. The proposed optode was applied successfully for determination of Al3+ in some real samples, including bottled drinking waters, bottled mineral waters and soft drinks. 相似文献
838.
In this paper, we study the well-posedness and stability analysis of set-valued Lur’e dynamical systems in infinite-dimensional Hilbert spaces. The existence and uniqueness results are established under the so-called passivity condition. Our approach uses a regularization procedure for the term involving the maximal monotone operator. The Lyapunov stability as well as the invariance properties are considered in detail. In addition, we give some sufficient conditions ensuring the robust stability of the system in finite-dimensional spaces. The theoretical developments are illustrated by means of two examples dealing with nonregular electrical circuits and an other one in partial differential equations. Our methodology is based on tools from set-valued and variational analysis. 相似文献
839.
Synthesis,Docking, and Evaluation of Antimicrobial Activity of a New Series of Acyclo C‐Nucleosides of 1, 2, 4‐Triazolo[4, 3‐a]quinoxaline Derivatives 下载免费PDF全文
Mohammed Salah Ayoup Hany Emary Ali Ahmed Abdel Moneim El Massry Samir Senior Sherine Nabil Khattab Seham Yassen Hassan Adel Amer 《Journal of heterocyclic chemistry》2016,53(1):153-163
In this study, 18 new 3‐benzylquinoxalinyl hydrazones bearing carbohydrate moiety and their corresponding triazoloquinoxalines were synthesized in order to investigate their possible antibacterial and antifungal activities. Some of these compounds such as 4b , 4c , 7b , 7c , and 7d showed promising antibacterial and antifungal activities and were found to have more potent activity compared with that of standard drugs. From structure–activity relationship point of view, increasing the size of the substitutions at position 6 or 7 on the quinoxaline nucleus decreased the antimicrobial activity, while the presence of the hydroxyl groups at C2 (R) and C3 (S) of sugar moieties enhanced the activity. Further, molecular docking studies of the active compounds were performed on different targets belonging to different microorganisms and showed good scoring with further understanding of the various interactions with the active sites of interesting enzymes compared with the co‐crystallized ligands. 相似文献
840.
Synthesis,Anti‐Microbial,and Cytotoxic Activities Evaluation of Some New Pyrido[2,3‐d]Pyrimidines 下载免费PDF全文
Samir Kamel Elsaedany Mohamed AbdEllatif Zein Elsayed Mohmoud AbedelRehim Reda Mohammed Keshk 《Journal of heterocyclic chemistry》2016,53(5):1534-1543
Novel pyridine derivatives 1d and 7 , pyrido[2,3‐d]pyrimidine derivatives 2a , 2b , 2c , 2d , 3a , 3b , 3c , 3d , 4a , 4b , 4c , 4d , 5a , 5b , 5c , 5d , 6a , 6b , 6c , 6d , 8a , 8b , and 9a , 9b were synthesized and screened for their anti‐microbial and cytotoxic activities. Compounds 2b , 2c , 3b , 3c , 5b , 5c , 6b , 6c , and 7 showed excellent anti‐microbial activities against all the tested bacteria and fungi compared to the reference drugs. Furthermore, they exhibited high safety profile in cytotoxicity test except 2c and 3c . The structures of the newly synthesized compounds were confirmed by spectral data and elemental analysis. 相似文献