全文获取类型
收费全文 | 1078篇 |
免费 | 38篇 |
国内免费 | 9篇 |
专业分类
化学 | 705篇 |
晶体学 | 30篇 |
力学 | 21篇 |
数学 | 160篇 |
物理学 | 209篇 |
出版年
2023年 | 5篇 |
2022年 | 22篇 |
2021年 | 52篇 |
2020年 | 24篇 |
2019年 | 26篇 |
2018年 | 31篇 |
2017年 | 33篇 |
2016年 | 47篇 |
2015年 | 23篇 |
2014年 | 54篇 |
2013年 | 63篇 |
2012年 | 80篇 |
2011年 | 81篇 |
2010年 | 56篇 |
2009年 | 46篇 |
2008年 | 60篇 |
2007年 | 60篇 |
2006年 | 54篇 |
2005年 | 55篇 |
2004年 | 51篇 |
2003年 | 34篇 |
2002年 | 20篇 |
2001年 | 14篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 1篇 |
1988年 | 6篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有1125条查询结果,搜索用时 15 毫秒
71.
Palladium‐Catalyzed Stereoselective Intramolecular Oxidative Amidation of Alkenes in the Synthesis of 1,3‐ and 1,4‐Amino Alcohols and 1,3‐Diamines 下载免费PDF全文
Prof. Dr. Andrei V. Malkov Dr. Darren S. Lee Dr. Maciej Barłóg Dr. Mark R. J. Elsegood Prof. Dr. Pavel Kočovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4901-4905
An efficient and practical Pd‐catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3‐ and 1,4‐amino alcohols and 1,3‐diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center 相似文献
72.
Dr. Wawrzyniec Kaszub Andrea Marino Dr. Maciej Lorenc Prof. Eric Collet Prof. Elena G. Bagryanskaya Prof. Evgeny V. Tretyakov Prof. Victor I. Ovcharenko Prof. Matvey V. Fedin 《Angewandte Chemie (International ed. in English)》2014,53(40):10636-10640
Molecular compounds with photoswitchable magnetic properties have been intensively investigated over the last decades due to their prospective applications in nanoelectronics, sensing and magnetic data storage. The family of copper‐nitroxide‐based molecular magnets represents a new promising type of photoswitchable compounds. We report the first study of these appealing systems using femtosecond optical spectroscopy. We unveil the mechanism of ultrafast (<50 fs) spin state photoswitching and establish its principal differences compared to other photoswitchable magnets. On this basis, we propose potential advantages of copper‐nitroxide‐based molecular magnets for the future design of ultrafast magnetic materials. 相似文献
73.
Maciej Jan Rybicki Anna Klimek-Turek Tadeusz Henryk Dzido 《Molecules (Basel, Switzerland)》2020,25(24)
Coccidiostats are drugs used against coccidiosis, a common disease among breeding animals. Their widespread application leads to the appearance of their residues in food, which is potentially harmful for human health and life. The European Union has established limits of concentrations of these drugs in premixtures and food. Nowadays, there are many methods for monitoring coccidiostats’ presence in market products, but their frequent weakness is sample preparation. Solvent Front Position Extraction is a planar chromatography-based sample preparation method that allows for effective assay of samples with coccidiostats when coupled with LC-MS/MS. The purpose of this research was to find common conditions for the effective isolation of eight coccidiostats from biological sample components with both lower and higher retention than the substances of interest. The acquired results were used for effective isolation of monensin and salinomycin from the premixture samples and allowed for their quantitative determination. The application of a semi-automatic device for the development of chromatograms positively impacted the results, confirming the effectiveness of the method for determining coccidiostats in biological samples. 相似文献
74.
Aleksandra Bocian Adam Gorczyski Dawid Marcinkowski Grzegorz Dutkiewicz Violetta Patroniak Maciej Kubicki 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(4):367-374
The intermolecular interactions in the structures of a series of Schiff base ligands have been thoroughly studied. These ligands can be obtained in different forms, namely, as the free base 2‐[(2E)‐2‐(1H‐imidazol‐4‐ylmethylidene)‐1‐methylhydrazinyl]pyridine, C10H11N5, 1 , the hydrates 2‐[(2E)‐2‐(1H‐imidazol‐2‐ylmethylidene)‐1‐methylhydrazinyl]‐1H‐benzimidazole monohydrate, C12H12N6·H2O, 2 , and 2‐{(2E)‐1‐methyl‐2‐[(1‐methyl‐1H‐imidazol‐2‐yl)methylidene]hydrazinyl}‐1H‐benzimidazole 1.25‐hydrate, C13H14N6·1.25H2O, 3 , the monocationic hydrate 5‐{(1E)‐[2‐(1H‐1,3‐benzodiazol‐2‐yl)‐2‐methylhydrazinylidene]methyl}‐1H‐imidazol‐3‐ium trifluoromethanesulfonate monohydrate, C12H13N6+·CF3O3S?·H2O, 5 , and the dicationic 2‐{(2E)‐1‐methyl‐2‐[(1H‐imidazol‐3‐ium‐2‐yl)methylidene]hydrazinyl}pyridinium bis(trifluoromethanesulfonate), C10H13N52+·2CF3O3S?, 6 . The connection between the forms and the preferred intermolecular interactions is described and further studied by means of the calculation of the interaction energies between the neutral and charged components of the crystal structures. These studies show that, in general, the most important contribution to the stabilization energy of the crystal is provided by π–π interactions, especially between charged ligands, while the details of the crystal architecture are influenced by directional interactions, especially relatively strong hydrogen bonds. In one of the structures, a very interesting example of the nontypical F…O interaction was found and its length, 2.859 (2) Å, is one of the shortest ever reported. 相似文献
75.
Patrycja Wytrych Jzef Utko Julia Kak Maciej Ptak Mariusz Stefanski Tadeusz Lis Jolanta Ejfler ukasz John 《Molecules (Basel, Switzerland)》2022,27(1)
In alkali metal and lanthanide coordination chemistry, triphenylsiloxides seem to be unduly underappreciated ligands. This is as surprising as that such substituents play a crucial role, among others, in stabilizing rare oxidation states of lanthanide ions, taking a part of intramolecular and molecular interactions stabilizing metal-oxygen cores and many others. This paper reports the synthesis and characterization of new lithium [Li4(OSiPh3)4(THF)2] (1), and sodium [Na4(OSiPh3)4] (2) species, which were later used in obtaining novel gadolinium [Gd(OSiPh3)3(THF)3]·THF (3), and erbium [Er(OSiPh3)3(THF)3]·THF (4) configuration, it can result in res were determined for all 1–4 compounds, and in addition, IR, Raman, absorption spectroscopy studies were conducted for 3 and 4 lanthanide compounds. Furthermore, direct current (dc) variable-temperature magnetic susceptibility measurements on polycrystalline samples of 3 and 4 were carried out in the temperature range 1.8–300 K. The 3 shows behavior characteristics for the paramagnetism of the Gd3+ ion. In contrast, the magnetic properties of 4 are dominated by the crystal field effect on the Er3+ ion, masking the magnetic interaction between magnetic centers of neighboring molecules. 相似文献
76.
Jakub Trawiski Micha Wroski Maciej Gawlik Robert Skibiski 《Molecules (Basel, Switzerland)》2022,27(3)
In this study, the phase I hepatic metabolism pathway of a cardiovascular drug nebivolol was proposed on the basis of a human liver microsomes assay with the use of LC-HR-MS coupled with the chemometric method. Six biotransformation products were found with the assistance of chemometric analysis. Five of them were identified as the previously reported products of alicyclic hydroxylation and dihydroxylation, aromatic hydroxylation, as well as alicyclic oxidation of the parent compound. Moreover, one metabolite, not reported so far, was found to be a product of N-dealkylation of nebivolol—2-amino-1-(6-fluoro-3,4-dihydro-2H-1-benzopyran-2-yl)ethan-1-ol. The novel metabolite was submitted to an in silico toxicity analysis to assess its biological properties. The applied computational methods indicated a significantly elevated risk of its mutagenic activity, compared to the parent molecule. Several metabolites of the nebivolol described in the literature were not detected in this study, indicating their non-hepatic origin. 相似文献
77.
Ang Han Wei Chan Aik Hui Ghaffar Mahumm Rybczyński Maciej Wilk Grzegorz Włodarczyk Zbigniew 《The European Physical Journal A - Hadrons and Nuclei》2020,56(4):1-8
The European Physical Journal A - The transverse momentum ($$p_{T}$$) distribution of strange hadrons ($$K_{S}^{0}$$ and $$\varLambda $$) and multi-strange hadrons( $$\varXi $$ and $$\varOmega $$)... 相似文献
78.
Hieronim Maciejewski Agnieszka Sydor Maciej Kubicki 《Journal of organometallic chemistry》2004,689(19):3075-3081
Reactions of the nickel(0) complexes [Ni(cod)2] (in the presence of PP or [Ni(PPh3)2C2H4] with vinyl-siloxanes, -silanes or -silazanes yield, by displacement of alkene ligand, the new nickel π-complexes [Ni(PPh3)2(η-CH2CHSi(OSiMe3)3)] (2), [{Ni(PPh3)}2{μ-(η-{(CH2CH)2SiMe}2O})] (4), [Ni(PPh3){η4-CH2CHSi(Me)(μ-O)}3] (5), [{Ni(η-CH2CHSiMe2)2O}(η-CH2CHSiMe3)] (7) and the known complexes [Ni(PPh3)2(η-CH2CHSiMe3)] (1), [{Ni(PPh3)}2{μ-(η-(CH2CH)4Si})] (3), [{Ni(PPh3)(η-CH2CHSiMe2)2NH}] (6) obtained by a simple one pot synthesis, more efficiently than in hitherto published reports. The X-ray crystal structure of (1) shows a trigonal planar environment around the nickel atom. 相似文献
79.
Guanidinoamidized linear polyethyleneimine for gene delivery 总被引:1,自引:0,他引:1
Guanidine was introduced to low molecular weight linear polyethyleneimine(LPEI) via amide groups, to explore the effect of both guanidine degree and pendant chain length on its transfection behavior. The resulting guanidinoamidized LPEIs(GLPEIs) could dramatically reduce LPEI's toxicity, enhance its DNA-packaging capability, cellular uptake and therefore transfection efficiency. These polyplexes were taken up very efficiently via caveolae-mediated endocytosis and their transfection efficiencies in ovarian cancer cells were significantly improved compared to native LPEI10 k polyplexes. Among these GLPEIs, LPEI-C3-G100 showed higher DNA affinity even than LPEI25 k and the highest transfection efficiency, probably due to the optimization of polymer chain flexibility. Of notice, LPEI-C3-G100 polyplexes could more effectively accumulate into cytoplasm than LPEI25 k, although the transfection efficiency of LPEI-C3-G100 polyplexes was not superior to that of LPEI25 k polyplexes, which would be probably attributed to the more efficient release of LPEI25 k polyplexes than LPEI-C3-G100 polyplexes in the cytoplasm. 相似文献
80.
Ireneusz Sowa Magdalena Wójciak-Kosior Piotr Drączkowski Maciej Strzemski Ryszard Kocjan 《Analytica chimica acta》2013
The new sorbent for non-suppressed ion chromatography based on silica gel coated with a film of polyaniline (PANI) was obtained in a process of in situ polymerization of aniline by oxidation with ammonium peroxydisulfate. Raman analyses performed using a Thermo Scientific DXR confocal Raman Microscope equipped with the Omnic 8 software from Thermo Fisher Scientific have proved a uniform distribution of PANI on the surface of chromatographic beads and in the pores of the particle. 相似文献