全文获取类型
收费全文 | 476篇 |
免费 | 25篇 |
国内免费 | 12篇 |
专业分类
化学 | 377篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 56篇 |
物理学 | 63篇 |
出版年
2024年 | 1篇 |
2023年 | 9篇 |
2022年 | 15篇 |
2021年 | 14篇 |
2020年 | 28篇 |
2019年 | 18篇 |
2018年 | 27篇 |
2017年 | 16篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 28篇 |
2013年 | 56篇 |
2012年 | 27篇 |
2011年 | 30篇 |
2010年 | 29篇 |
2009年 | 21篇 |
2008年 | 28篇 |
2007年 | 18篇 |
2006年 | 20篇 |
2005年 | 24篇 |
2004年 | 14篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 1篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有513条查询结果,搜索用时 31 毫秒
91.
Mina Mazzeo Marina Lamberti Daniela Pappalardo Liana Annunziata Claudio Pellecchia 《Journal of molecular catalysis. A, Chemical》2009,297(1):9-17
New fluorinated bis(phenoxy-imine)zirconium complexes bearing halogen substituents in the ortho and para positions of the phenolate rings, bis[N-(3,5-dibromosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (1) and bis[N-(3,5-dichlorosalycilidene)-2,3,4,5,6-pentafluoroaniline]-Zr(IV) dichloride (2) have been synthesized and used as precatalysts in the polymerization of propylene and 1-hexene. Their catalytic behaviour was compared with that of the analogous fluorinated zirconium complexes bearing alkyl groups in the same positions of the phenolate rings to investigate the effects produced by the introduction of additional electron-withdrawing halogen substituents. Complexes 1 and 2 produce stereoirregular, slightly syndiotactic enriched polypropylenes showing enhanced catalytic activities and an improved primary regioselectivity. Both catalysts promote efficiently the oligomerization of 1-hexene to atactic and regioregular oligomers. Interestingly for both the studied monomers it is possible to control the molecular weights and the structures of end groups of the produced polymeric chains by an appropriate choice of the cocatalyst. Functionalization reactions of the unsaturated polymeric chains selectively produced are also reported. 相似文献
92.
Ohkawa K Hayashi S Kameyama N Yamamoto H Yamaguchi M Kimoto S Kurata S Shinji H 《Macromolecular bioscience》2009,9(1):79-92
A synthetic route is described for collagen-like polypeptides constructed from O-phospho-L-hydroxyproline [Hyp(PO(3)H(2))] residues. Using the synthetic polypeptides and a natural protein, gelatin, fine fibers and their network structures (ESNWs) were prepared via electrospinning. The composite ESNWs can induce the mineralization of calcium phosphate. The phosphoryl groups of the Hyp(PO(3)H(2)) residues affect both the crystalline phase and amount of the calcium phosphate, depending on the chemical structure in the repeating sequence. The composite ESNWs can be developed as a biocompatible replacement of the extracellular matrix of hard tissues, and thus can be applied as dental materials for restoration of dental cavities or as a sealant for pits and fissures. 相似文献
93.
Sara Nourizadeh Adeleh Divsalar Mina Fekri Behafarid Ghalandari Mahbubeh Eslami-Moghadam Ali Akbar Saboury Saba Abbasi 《Journal of fluorescence》2018,28(2):551-559
In the present study, the biological activities of a new synthesized Pt(II)-complex, 2,2′ bipyridinphenyl isopentylglycin Pt(II) nitrate was investigated via its interaction with the most important blood carrier protein of human serum albumin (HSA), using fluorescence and Far-UV circular dichroism (CD) spectroscopic techniques and also molecular docking. Moreover, cytotoxicity activity of the complex was studied against breast cancer cell line of MDA MB231 using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The Pt(II)-complex has a strong ability to quench the intrinsic fluorescence of HSA through a static quenching mechanism. According fluorescence quenching data, the binding parameters of the interaction were calculated and showed that hydrophobic interaction has an important role. The molecular docking results in coherent with fluorescence measurements illustrated that Pt(II) complex can bind to HSA at one position that located in the hydrophobic cavity of groove between drug site I and II. Also, experimental data on driving force in binding site was confirmed whereas theoretical results demonstrated Pt(II) complexinteract to HSA by hydrophobic interaction. Far-UV-CD results showed that Pt(II)-complex induced an increasing in the content of α-helical structure of the protein and stabilized it. Also, MTT assay represented growth inhibitory effect of the complex toward the breast cancer cell line. 相似文献
94.
Synthesis and Cytotoxic Evaluation of Novel 1,2,3‐Triazole‐4‐Linked (2E,6E)‐2‐Benzylidene‐6‐(4‐nitrobenzylidene)cyclohexanones
下载免费PDF全文
![点击此处可从《Helvetica chimica acta》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mohammad Mahdavi Maryam Akhbari Mina Saeedi Maryam Karimi Niloufar Foroughi Elahe Karimpour‐Razkenari Heshmatollah Alinezhad Alireza Foroumadi Abbas Shafiee Tahmineh Akbarzadeh 《Helvetica chimica acta》2016,99(3):175-180
This work describes the synthesis of novel 1,2,3‐triazole‐4‐linked (2E,6E)‐2‐benzylidene‐6‐(4‐nitrobenzylidene)cyclo‐hexanones starting from cyclohexanone. 1‐(Cyclohex‐1‐en‐1‐yl)piperidine, the enamine from cyclohexanone and piperidine, reacted with 4‐nitrobenzaldehyde to obtain 2‐(4‐nitrobenzylidene)cyclohexanone. Condensation of the latter compound with (prop‐2‐yn‐1‐yloxy)benzaldehyde derivatives under acidic conditions gave (4‐nitrobenzylidene)‐[(prop‐2‐yn‐1‐yloxy)‐benzylidene]cyclohexanones. Finally, ‘click reaction’ of these derivatives and various organic azides led to the title compounds. All compounds were examined by MTT assay for cytotoxic activity in one human breast cancer cell line, MDA‐MB‐231. 相似文献
95.
Fatemeh Esmaeili‐Marandi Mina Saeedi Issa Yavari Mohammad Mahdavi Abbas Shafiee 《Helvetica chimica acta》2016,99(1):37-40
A synthesis of isoindolo[2,1‐a]quinazolinedione derivatives, coupled with a 1,2,3‐triazole ring system, via the reaction of isatoic anhydride, HC?CCH2NH2, and 2‐formylbenzoic acid is described, which led to the formation of the isoindolo[2,1‐a]quinazoline‐5,11‐dione scaffold having a C?C bond that participated in a click reaction with various organic azides. 相似文献
96.
Task-specific ionic liquid, [bmim]N3 was used as an effective catalyst and reaction medium for the direct oxidative esterification of arylaldehydes with alcohols. The oxidative esterification reaction of a variety of arylaldehydes took place smoothly with some primary and secondary alcohols in [bmim]N3. Satisfactory results were obtained with arylaldehydes containing electron withdrawing groups. Tertiary alcohols did not react under these conditions. 相似文献
97.
The title compound 3-(4-bromobenzyloxy)-6-morpholinopyridazine(C15H16BrN3O2) was synthesized,and its crystal structure was studied.It crystallizes in the triclinic system,space group P with a = 8.3408(17),b = 8.8620(18),c = 10.832(2) ,α = 108.09(3),β = 91.28(3),γ = 100.90(3)°,Dc = 1.562 g/cm3,Z = 2,λ = 0.71073 ,μ(MoKα) = 2.769 mm-1,Mr = 350.22,V = 744.5(3) 3,F(000) = 356,the final R = 0.0522 and wR = 0.1366 for 2016 observed reflections with I > 2σ(I).In the crystal structure,the morpholine ring adopts a chair conformation with O(2) and N(3) atoms at the flap positions-0.656(7) and 0.622(6) out of the mean plane formed by the other four C atoms,respectively.These molecules generate centro-symmetric dimers through intermolecular π-π interaction. 相似文献
98.
Maryam Sadat Hosseini-ZareMohammad Mahdavi Mina SaeediMehdi Asadi Shahrzad JavanshirAbbas Shafiee Alireza Foroumadi 《Tetrahedron letters》2012,53(27):3448-3451
We describe a new one-pot synthesis of 2,3-diaryl-5H-imidazo[2,1-a]isoindol-5-ones via the reaction of 1,2-diketones, 2-formylbenzoic acids, and ammonium acetate in acetic acid under reflux conditions and in the absence of a catalyst. 相似文献
99.
Mohammad Ali Rasouli Mohammad Mahdavi Parviz Rashidi Ranjbar Mina Saeedi Abbas Shafiee Alireza Foroumadi 《Tetrahedron letters》2012,53(52):7088-7092
This work describes a green and efficient one-pot synthesis of N-alkyl-2-(2-oxoazepan-1-yl)-2-arylacetamide derivatives via an Ugi four-center, three-component reaction of 6-aminohexanoic acid, aromatic aldehydes, and isocyanide derivatives in water under reflux conditions in the absence of a catalyst. 相似文献
100.
Lab-on-a-chip (LOC) technologies can take advantage of sheath flows for particle/cell focusing before sensing or sorting. The integration of focusing with other microscale manipulation techniques (e.g., sorting) creates a trade-off between the throughput of the device and its performance. Therefore, exploring the effective parameters for cells/particles focusing enables us to improve the desired output of LOC devices. A common configuration for sheath-assisted focusing is Y junctions, which are parametrically studied in this paper. First, a computational model was developed and validated by comparing it with our experimental results. Using COMSOL Multiphysics modeling, the effects of multiple parameters were studied. These parameters include the sheath flow ratio (sheath flow over total flow), width ratio (width of the sheath inlet over the total width), junction angles, and particle size on the focusing width and the distribution of the particles within the focusing region. Then, the numerical data were used to develop two generalized linear models to predict the focusing width of the particles and the standard deviation of the position of the particles. The results showed that the focusing width is greatly impacted by the sheath flow rate ratio. Further, the standard deviation of the position of the particles, which represents the concentration of the particles, is mostly dependent on the flow rate ratio, width ratio, and particle size. Our results provide a better understanding of how the device geometrical and operational factors affect the position of the particles in the development of high-performance on-chip sensing and sorting of both cells and particles. 相似文献