全文获取类型
收费全文 | 1590篇 |
免费 | 63篇 |
国内免费 | 16篇 |
专业分类
化学 | 997篇 |
晶体学 | 25篇 |
力学 | 57篇 |
数学 | 235篇 |
物理学 | 355篇 |
出版年
2023年 | 10篇 |
2022年 | 49篇 |
2021年 | 45篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 55篇 |
2017年 | 56篇 |
2016年 | 71篇 |
2015年 | 55篇 |
2014年 | 68篇 |
2013年 | 160篇 |
2012年 | 98篇 |
2011年 | 136篇 |
2010年 | 80篇 |
2009年 | 87篇 |
2008年 | 100篇 |
2007年 | 99篇 |
2006年 | 69篇 |
2005年 | 58篇 |
2004年 | 45篇 |
2003年 | 44篇 |
2002年 | 34篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 10篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1669条查询结果,搜索用时 22 毫秒
991.
Shujaat Ahmad Manzoor Ahmad Mazen Almehmadi Syed Adnan Ali Shah Farman Ali Khan Nasir Mehmood Khan Asifullah Khan Zainab Mustafa Halawi Hanif Ahmad 《Molecules (Basel, Switzerland)》2022,27(14)
This study reports the isolation of three new C20 diterpenoid alkaloids, Chitralinine A–C (1–3) from the aerial parts of Delphinium chitralense. Their structures were established on the basis of latest spectral techniques and single crystal X-rays crystallographic studies of chitralinine A described basic skeleton of these compounds. All the isolated Compounds (1–3) showed strong, competitive type inhibition against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in comparison to standard allanzanthane and galanthamine however, chitralinine-C remained the most potent with IC50 value of 11.64 ± 0.08 μM against AChE, and 24.31 ± 0.33 μM against BChE, respectively. The molecular docking reflected a binding free energy of −16.400 K Cal-mol−1 for chitralinine-C, having strong interactions with active site residues, TYR334, ASP72, SER122, and SER200. The overall findings suggest that these new diterpenoid alkaloids could serve as lead drugs against dementia-related diseases including Alzheimer’s disease. 相似文献
992.
Qudsia Sarwer Muhammad Shoaib Amjad Ansar Mehmood Zakia Binish Ghazala Mustafa Atikah Farooq Mirza Faisal Qaseem Fozia Abasi Jos Manuel Prez de la Lastra 《Molecules (Basel, Switzerland)》2022,27(21)
Nanotechnology is the study and control of materials at length scales between 1 and 100 nanometers (nm), where incredible phenomena enable new applications. It affects all aspects of human life and is the most active research topic in modern materials science. Among the various metallic nanoparticles used in biomedical applications, silver nanoparticles (AgNPs) are among the most important and interesting nanomaterials. The aim of this study was to synthesize AgNPs from the leaf extract of Myrsine africana to investigate their antibacterial, antioxidant, and phytotoxic activities. When the leaf extract was treated with AgNO3, the color of the reaction solution changed from light brown to dark brown, indicating the formation of AgNPs. The UV-visible spectrum showed an absorption peak at 438 nm, confirming the synthesis of AgNPs. Scanning electron microscopy (SEM) showed that the AgNPs were spherical and oval with an average size of 28.32 nm. Fourier transform infrared spectroscopy confirms the presence of bio-compound functional groups on the surface of the AgNPs. The crystalline nature of the AgNPs was confirmed by XRD pattern. These biosynthesized AgNPs showed pronounced antibacterial activity against Gram-positive and Gram-negative bacteria, with higher inhibitory activity against Escherichia coli. At 40 µg/mL AgNPs, the highest antioxidant activity was obtained, which was 57.7% and an IC50 value of 77.56 µg/mL. A significant positive effect was observed on all morphological parameters when AgNPs were applied to wheat seedlings under constant external conditions at the different concentrations. The present study provides a cost-effective and environmentally friendly method for the synthesis of AgNPs, which can be effectively used in the field of therapeutics, as antimicrobial and diagnostic agents, and as plant growth promoters. 相似文献
993.
Mustafa M. Aldfer Ibrahim A. Alfayez Hamza A. A. Elati Nilanjana Gayen Ehab Kotb Elmahallawy Ana Milena Murillo Sabrina Marsiccobetre Serge Van Calenbergh Ariel M. Silber Harry P. de Koning 《Molecules (Basel, Switzerland)》2022,27(22)
Among the scarce validated drug targets against Chagas disease (CD), caused by Trypanosoma cruzi, the parasite’s nucleoside salvage system has recently attracted considerable attention. Although the trypanocidal activity of tubercidin (7-deazapurine) has long been known, the identification of a class of 7-substituted tubercidin analogs with potent in vitro and in vivo activity and much-enhanced selectivity has made nucleoside analogs among the most promising lead compounds against CD. Here, we investigate the recently identified TcrNT2 nucleoside transporter and its potential role in antimetabolite chemotherapy. TcrNT2, expressed in a Leishmania mexicana cell line lacking the NT1 nucleoside transporter locus, displayed very high selectivity and affinity for thymidine with a Km of 0.26 ± 0.05 µM. The selectivity was explained by interactions of 2-oxo, 4-oxo, 5-Me, 3′-hydroxy and 5′-hydroxy with the transporter binding pocket, whereas a hydroxy group at the 2′ position was deleterious to binding. This made 5-halogenated 2′-deoxyuridine analogues good substrates but 5-F-2′-deoxyuridine displayed disappointing activity against T. cruzi trypomastigotes. By comparing the EC50 values of tubercidin and its 7-substituted analogues against L. mexicana Cas9, Cas9ΔNT1 and Cas9ΔNT1+TcrNT2 it was shown that TcrNT2 can take up tubercidin and, at a minimum, a subset of the analogs. 相似文献
994.
In this study, an impedimetric immunosensor based on polymer poly(thiophene)‐graft‐poly(methacrylamide) polymer (P(Thi‐g‐MAm)) modified indium tin oxide (ITO) electrode is developed for the detection of the Neuron Specific Enolase (NSE) cancer biomarker. First, the P(Thi‐g‐MAm) polymer is synthesized and coated on the ITO electrode by using a spin‐coating technique. P(Thi‐g‐MAm) polymer acts as an immobilization platform for immobilization of NSE‐specific monoclonal antibodies. Anti‐NSE antibodies are utilized as biosensing molecules and they bind to the amino groups of P(Thi‐g‐Mam) polymer via glutaraldehyde cross‐linking. Spin‐coating technique is employed for bioelectrode fabrication and this technique provides a thin and uniform film on the ITO electrode surface. This bioelectrode fabrication technique is simple and it generates a suitable platform for large‐scale loadings of anti‐NSE antibodies. This immunosensor exhibits a wide linear detection range from 0.02 to 4 pg mL?1 and with an ultralow detection limit of 6.1 fg mL?1. It reveals a good long‐term stability (after 8 weeks, 78% of its initial activity), an excellent reproducibility (1.29% of relative standard deviation (RSD)), a good repeatability (5.55% of RSD), and a high selectivity. In addition, the developed immunosensor is proposed as a robust diagnostic tool for the clinical detection of NSE and other cancer biomarkers. 相似文献
995.
Isik Aysen Oguz Mehmet Kocak Ahmet Yilmaz Mustafa 《Journal of inclusion phenomena and macrocyclic chemistry》2022,102(5-6):439-449
Journal of Inclusion Phenomena and Macrocyclic Chemistry - Cancer is one of the leading causes of death worldwide, and the limited success of currently used anticancer drugs is a driving force for... 相似文献
996.
M. Mustafa Cetin Sara Shafiei-Haghighi Jiazhen Chen Sheng Zhang Amanda C. Miller Daniel K. Unruh Dominick J. Casadonte Jr Tracy L. Lohr Tobin J. Marks Michael F. Mayer J. Fraser Stoddart Michael Findlater 《Journal of polymer science. Part A, Polymer chemistry》2020,58(8):1130-1143
The syntheses of the 2,9-dimesityl-1,10-phenanthroline ( dmesp ) metal complexes, [Cu(dmesp)(MeCN)]PF6 ( 1 ), [Cu(dmesp)2]PF6 ( 2 ), Fe(dmesp)Cl2 ( 3 ), Co(dmesp)Cl2 ( 4 ), Ni(dmesp)Cl2 ( 5 ), Zn(dmesp)Cl2 ( 6 ), Pd(dmesp)MeCl ( 7 ), Cu(dmesp)Cl ( 8 ), and Pd(dmesp)2Cl2 ( 9 ), in good to high yields are described. These complexes were characterized by 1H and 13C NMR spectroscopy, HR–MS (ESI and/or APPI), and elemental analysis (CHN). The solid-state structures of complexes 1 – 8 were determined by single-crystal X-ray analysis and their photophysical properties were also characterized. To demonstrate the versatility of this new platform, complexes 3 – 5 , 8 , and 9 were employed in the catalytic oligomerization of ethylene using modified methyl aluminoxane (MMAO) as the cocatalyst, where Co(II) and Ni(II) complexes ( 4 and 5 , respectively) were found to exhibit moderate selectivity for catalytic dimerization of ethylene to butenes over tri- or tetramerization. Complex 8 is an effective catalyst of both the commonly encountered “click” reaction and amine arylation chemistries. Complexes 6 and 9 were found to be excellent catalysts for Friedel-Crafts alkylation and Suzuki-Miyaura coupling, respectively. 相似文献
997.
998.
Mustafa Yasa Aybuke Deniz Mehrdad Forough Erol Yildirim Ozgul Persil Cetinkol Yasemin Arslan Udum Levent Toppare 《Journal of polymer science. Part A, Polymer chemistry》2020,58(23):3336-3348
Phenolic compounds used in food industries and pesticide industry, are environmentally toxic and pollute the rivers and ground water. For that reason, detection of phenolic compounds such as catechol by using simple, efficient and cost-effective devices have been becoming increasingly popular. In this study, a suitable and a novel matrix was composed using a novel conjugated polymer, namely poly[1-(5-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)furan-2-yl)-5-(2-ethylhexyl)-3-(furan-2-yl)-4H thieno[3,4-c]pyrrole-4,6(5H)-dione] (PFTBDT) and carbon dots (CDs) to detect catechol. PFTBDT and CDs were synthesized and the optoelectronic properties of PFTBDT were investigated via electrochemical and spectroelectrochemical studies. Laccase enzyme was immobilized onto the constructed film matrix on the graphite electrode. The proposed biosensor was found to have a low detection limit (1.23 μM) and a high sensitivity (737.44 μA/mM.cm−2) with a linear range of 1.25–175 μM. Finally, the applicability of the proposed enzymatic biosensor was evaluated in a tap water sample and a satisfactory recovery (96–104%) was obtained for catechol determination. 相似文献
999.
Mustafa Sertçelik Füreya Elif Özbek Parham Taslimi Murat Durman Mücahit Özdemir Bahattin Yalçın Hacali Necefoğlu Tuncer Hökelek 《应用有机金属化学》2020,34(9):e5802
A novel Ni(II) complex containing 2-fluorobenzoate and 3-hydroxypyridine ligands was synthesized and characterized using elemental analysis, Fourier transform infrared (FT-IR) spectroscopy and single-crystal X-ray diffraction. FT-IR peaks show that the carboxylate group from 2-fluorobenzoate has a monodentate coordination mode. The coordination environment around the Ni2+ ion is of distorted octahedral geometry. The octahedral geometry consists of a total of four oxygen atoms from two carboxylate groups of two fluorobenzoate anions, two water molecules and two nitrogen atoms from two 3-hydroxypyridine ligands. The complex shows excellent inhibitory effects against some metabolic enzymes. Ki values for the complex were found as 108.17 ± 25.63, 124.88 ± 36.20, 28.11 ± 2.87, 20.95 ± 5.65 and 32.63 ± 9.67 μM against human carbonic anhydrase I, human carbonic anhydrase II, α-glycosidase, acetylcholinesterase and butyrylcholinesterase, respectively. In addition, geometry optimization and vibration frequencies were calculated, and single point energy was studied based on optimization. Experimental and theoretical data were compared. The B3LYP/6-31G(d,p) basis set was used for all calculations. 相似文献
1000.