全文获取类型
收费全文 | 12483篇 |
免费 | 658篇 |
国内免费 | 2644篇 |
专业分类
化学 | 14265篇 |
晶体学 | 101篇 |
力学 | 55篇 |
综合类 | 124篇 |
数学 | 154篇 |
物理学 | 1086篇 |
出版年
2024年 | 19篇 |
2023年 | 184篇 |
2022年 | 1054篇 |
2021年 | 805篇 |
2020年 | 704篇 |
2019年 | 578篇 |
2018年 | 524篇 |
2017年 | 519篇 |
2016年 | 685篇 |
2015年 | 614篇 |
2014年 | 589篇 |
2013年 | 1064篇 |
2012年 | 901篇 |
2011年 | 721篇 |
2010年 | 523篇 |
2009年 | 706篇 |
2008年 | 646篇 |
2007年 | 697篇 |
2006年 | 528篇 |
2005年 | 488篇 |
2004年 | 438篇 |
2003年 | 359篇 |
2002年 | 510篇 |
2001年 | 209篇 |
2000年 | 235篇 |
1999年 | 220篇 |
1998年 | 184篇 |
1997年 | 150篇 |
1996年 | 136篇 |
1995年 | 129篇 |
1994年 | 122篇 |
1993年 | 89篇 |
1992年 | 70篇 |
1991年 | 71篇 |
1990年 | 44篇 |
1989年 | 68篇 |
1988年 | 45篇 |
1987年 | 17篇 |
1986年 | 19篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 19篇 |
1981年 | 5篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Chemical Fixation of CO2 and Other Heterogeneous Catalytic Studies by Employing a Layered Cu‐Porphyrin Prepared Through Single‐Crystal to Single‐Crystal Exchange of a Zn Analogue 下载免费PDF全文
A solvothermal reaction of Zn(NO3)2 ? 6 H2O, tetra‐(4‐pyridyl)porphyrin (H2TPyP), and 4,4′‐oxybis(benzoic acid) (H2OBA) resulted in a new two‐dimensional Zn‐ porphyrin metal–organic framework compound, [Zn2(C40H24N8)0.5(C14H8O5)(DMA)](DMA)(H2O)6 ( 1 ; DMA=N,N‐dimethylacetamide). The ZnII ions present in 1 could be exchanged by using a solution of Cu(NO3)2 ? 3 H2O in DMA at room temperature to give [Cu2(C40H24N8)0.5(C14H8O5)(DMA)](DMA)(H2O)3 ( Cu∈1 ). The extra‐framework solvent molecules have been shown to be reversibly removed or exchanged without collapse of the framework. Solvent‐free Cu∈1 was explored as an active heterogeneous catalyst towards three different organic reactions: 1) the chemical fixation of CO2 into cyclic carbonate at room temperature and 1 atm; 2) the nitroaldol reaction under solvent‐free conditions, and 3) the three‐component coupling of aminopyridine, benzaldehyde, and aryl alkynes followed by 5‐exo‐dig cyclization to produce the important pharmacophore imidazopyridine. 相似文献
992.
Tuning the Electronic Properties and Acid‐Response Behavior of N‐Heteroacene‐Based π‐Conjugated Liquids by Changing the Number of π‐Conjugated Substituents 下载免费PDF全文
Yuika Sato Dr. Yuichiro Mutoh Dr. Daisuke Matsukuma Makoto Nakagawa Prof. Takeshi Kawai Dr. Kyosuke Isoda 《化学:亚洲杂志》2018,13(18):2619-2625
We have designed and synthesized two room‐temperature‐fluorescent π‐conjugated liquids based on the N‐heteroacene framework ( 1 and 2 ). These two π‐conjugated liquids, which contained one and two thiophene rings, respectively, exhibited different electronic properties and rheology behaviors. Single‐crystal X‐ray analysis of dithiophene‐appended compound 4 revealed that two thiophene rings hindered the interactions of the imino N atoms with acids through the formation of interactions between the S atoms of the thiophene rings and the imino N atoms of the pyrazine group. On the other hand, monothiophene‐appended molecules 1 and 3 each contained an unhindered imino N atom on the opposite site to the thiophene ring. Upon dissolving various acids with different pKa values in compounds 1 and 2 , these slight structural differences gave rise to marked differences in their acid‐response behaviors, thereby resulting in the emission of variously colored fluorescence in the liquid state. Furthermore, when acids with lower pKa values was dissolved in compounds 1 and 2 , phase transition occurred from an isotropic liquid state to a self‐organized liquid‐crystalline phase. 相似文献
993.
Sreenu Pavurala Krishnaiah Vaarla Rajeshkumar Kesharwani Lieve Naesens Sandra Liekens 《合成通讯》2018,48(12):1494-1503
A series of novel 3,3′-(3,3′-(dihydroxy/hydroxyethane-1,2-diyl)bis(7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-6,3-diyl))bis(2H-chromen-2-ones) were prepared by the condensation of thiocarbohydrazide with tartaric acid or malic acid followed by various 3-(2-bromoacetyl)-2H-chromen-2-ones in two steps with good yields. All the synthesized compounds were characterized by analytical and spectral (IR, 1H NMR, 13C NMR, and mass) data. These synthesized bis(triazolothiadiazinyl coumarin) compounds were evaluated for broad spectrum of antiviral activity. Among all the tested compounds, compound 5f exhibited antiviral activity against H1N1 virus. The molecular docking studies of these compounds against H1N1 neuraminidase enzyme were performed. The binding affinity and binding values were compared with standard drugs. 相似文献
994.
Ummuhan Solmaz Gun Binzet Omer Celik Gulten Kavak Balci Aylin Dogen 《Journal of Coordination Chemistry》2018,71(2):200-218
N,N-Di-R-N′-(4-chlorobenzoyl)thiourea (Di-R: diethyl, di-n-propyl, di-n-butyl and diphenyl) ligands (HL1–4) and their Pt(II) complexes (cis-[Pt(L1–4-S,O)2]) have been synthesized and structurally characterized by elemental analyses, FT-IR and NMR spectroscopy. HL2 ligand and cis-[Pt(L4-S,O)2] metal complex have been also characterized by a single-crystal X-ray diffraction study. HL2, C14H19ClN2OS, crystallizes in the monoclinic space group P21/n (no. 14), with Z = 4, and unit cell parameters, a = 11.1405(16) Å, b = 9.7015(12) Å, c = 14.790(2) Å, β = 106.547(7)°. The cis-[Pt(L4-S,O)2], C40H28Cl2N4O2PtS2: triclinic, space group P-1 (no. 2), a = 8.9919(3) Å, b = 14.7159(6) Å, c = 15.7954(6) Å, α = 113.9317(18)°, β = 97.4490(18)°, and γ = 105.0492(16)°. Single crystal analysis of complex, cis-[Pt(L1–4-S,O)2], revealed that a square planar coordination geometry is formed around the platinum atom by two sulfur and two oxygen atoms of the related ligands, which are in a cis configuration. In addition, the thiourea derivative ligands and their complexes were evaluated for both their in-vitro antibacterial and antifungal activity. The results have been reported, explained, and compared with fluconazole and ampicillin, used as reference drugs. 相似文献
995.
Kesheng Shen Xintong Han Chuang Li Guozhen Huang Shanshan Mao Xinkui Shi 《Journal of Coordination Chemistry》2018,71(7):980-990
N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline (EtAIDB) and its transition metal complexes, [Cu(EtAIDB)Br2]·EtOH {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] copper(II) ethanol} (1) and [Zn(EtAIDB)Br2] {dibromo[N,N-bis(N-methyl-2-ylmethylbenzimidazole)aniline] zinc(II)} (2), have been synthesized and characterized by elemental analysis, molar conductivity, UV–visible, and IR spectroscopy. The X-ray crystallographic studies of 1 and 2 have shown two different arrangements: 1 is distorted square-based pyramidal, while 2 can be treated as distorted tetrahedral. The cyclic voltammogram of 1 represents quasi-reversible Cu2+/Cu+ pairs. In vitro antioxidant tests showed that 1 had significant antioxidant activity against superoxide and hydroxy radicals. 相似文献
996.
M. A. Salam Mahbubul Alam Sohug Sarker Mohammed M. Rahman 《Journal of Coordination Chemistry》2018,71(10):1593-1605
Three new diorganotin(IV) complexes, [Me2Sn(BDET] (2), [Bu2Sn(BDET)] (3), and [Ph2Sn(BDET)] (4), were synthesized by reacting R2SnCl2 (R = Me, Bu, and Ph) with 5-bromo-2-hydroxybenzaldehyde-N(4)-ethylthiosemicarbazone [H2BDET, (1)] in the presence of KOH in absolute methanol. The newly synthesized complexes were characterized by elemental analysis, molar conductivity, UV–vis, FT-IR, 1H, 13C, and 119Sn NMR spectroscopies. The molecular structure of 4 was confirmed by X-ray crystallography. X-ray crystallography revealed that the doubly deprotonated O,N,S-tridentate thiosemicarbazone coordinates to tin(IV), resulting in a distorted trigonal bipyramidal geometry. Their 1H, 13C, and 119Sn NMR spectra support a five-coordinate tin(IV) in solution for all complexes, in accord with the solid-state X-ray structure determined for 4. Compounds 1–4 were evaluated for their antibacterial activities against Staphylococcus aureus, Enterobacter aerogenes, Escherichia coli, and Salmonella typhi. The results exhibited that 2–4 were active with comparable potency compared to the standard drug. Antibacterial studies also indicated that the complexes have potential for biological evaluation. 相似文献
997.
Xiaoyi Yang Binbin Zhang Chaohua Guo Jianbo Li Xingang Wang 《Journal of Dispersion Science and Technology》2018,39(10):1518-1523
The present work aimed at research the physic-chemical properties of the interaction of N-decyl-O-chitosan sulfate (an amphiphilic chitosan derivative, C10-OCHS) with cetyltrimetylammonium bromide (CTAB) by the steady-state fluorescent, static/dynamic surface tension, turbidity and transmission electron microscopy (TEM). The results showed that the complex of C10-OCHS/CTAB had high surface activity and lower critical aggregation concentration. Besides, the C10-OCHS/CTAB could self-assemble into various aggregates like irregular spherical aggregates, vesicles or polydisperse aggregates from lower to higher concentrations of CTAB with a mixed C10-OCHS concentration of 200?mg/L. 相似文献
998.
Integrated Transmission Electron and Single‐Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle 下载免费PDF全文
Frank C. Hendriks Sajjad Mohammadian Dr. Zoran Ristanović Dr. Sam Kalirai Dr. Florian Meirer Prof. Dr. Eelco T. C. Vogt Dr. Pieter C. A. Bruijnincx Prof. Dr. Hans C. Gerritsen Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2018,57(1):257-261
Establishing structure–activity relationships in complex, hierarchically structured nanomaterials, such as fluid catalytic cracking (FCC) catalysts, requires characterization with complementary, correlated analysis techniques. An integrated setup has been developed to perform transmission electron microscopy (TEM) and single‐molecule fluorescence (SMF) microscopy on such nanostructured samples. Correlated structure–reactivity information was obtained for 100 nm thin, microtomed sections of a single FCC catalyst particle using this novel SMF‐TEM high‐resolution combination. High reactivity in a thiophene oligomerization probe reaction correlated well with TEM‐derived zeolite locations, while matrix components, such as clay and amorphous binder material, were found not to display activity. Differences in fluorescence intensity were also observed within and between distinct zeolite aggregate domains, indicating that not all zeolite domains are equally active. 相似文献
999.
Back Cover: Integrated Transmission Electron and Single‐Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle (Angew. Chem. Int. Ed. 1/2018) 下载免费PDF全文
1000.
A new Schiff base ligand (HL) was prepared via a condensation reaction of quinoline‐2‐carboxaldhyde with 2‐aminophenol in a molar ratio of 1:1. Its transition metal mixed ligand complexes with 1,10‐phenanthroline (1,10‐phen) as co‐ligand were also synthesized in a 1:1:1 ratio. HL and its mixed ligand complexes were characterized using elemental analysis, infrared, 1H NMR, mass and UV–visible spectroscopies, molar conductance, magnetic measurements, solid reflectance, thermal analysis, electron spin resonance and X‐ray diffraction. Molar conductance measurements showed that all complexes have an electrolytic nature, except Cd(II) complex. From elemental and spectral data, the formulae [M(L)(1,10‐phen)(H2O)]Clx?nH2O (where M = Cr(III) (x = n = 2), Mn(II) and Ni(II) (x = 1, n = 2), Fe(III) (x = n = 2), Co(II), Cu(II) and Zn(II) (x = 1, n = 2)) and [Cd(L)(1,10‐phen)Cl]?3H2O for the metal complexes have been proposed. The geometric structures of complexes were found to be octahedral. Powder X‐ray diffraction reflected the crystalline nature of the complexes; however, the Schiff base is amorphous. HL and its mixed ligand complexes were screened against Gram‐positive bacteria (Streptococcus pneumoniae and Bacillus subtilis) and Gram‐negative bacteria (Pseudomonas aeruginosa and Escherichia coli). Antifungal activity was determined against Aspergillus fumigatus and Candida albicans, the data showing that most complexes had activity less than that of the Schiff base while Mn(II), Fe(III) and Ni(II) complexes showed no significant antifungal activity. The anticancer activity of HL and its metal complexes was also studied against breast and colon cell lines. The metal complexes showed IC50 higher than that of HL, especially the Cu(II) complex which showed the highest IC50 against breast cell line. 相似文献