全文获取类型
收费全文 | 4775篇 |
免费 | 429篇 |
国内免费 | 509篇 |
专业分类
化学 | 4090篇 |
晶体学 | 22篇 |
力学 | 123篇 |
综合类 | 75篇 |
数学 | 577篇 |
物理学 | 826篇 |
出版年
2024年 | 7篇 |
2023年 | 44篇 |
2022年 | 179篇 |
2021年 | 171篇 |
2020年 | 159篇 |
2019年 | 121篇 |
2018年 | 106篇 |
2017年 | 125篇 |
2016年 | 163篇 |
2015年 | 179篇 |
2014年 | 190篇 |
2013年 | 281篇 |
2012年 | 305篇 |
2011年 | 212篇 |
2010年 | 205篇 |
2009年 | 234篇 |
2008年 | 252篇 |
2007年 | 266篇 |
2006年 | 275篇 |
2005年 | 236篇 |
2004年 | 197篇 |
2003年 | 190篇 |
2002年 | 262篇 |
2001年 | 127篇 |
2000年 | 137篇 |
1999年 | 118篇 |
1998年 | 143篇 |
1997年 | 118篇 |
1996年 | 84篇 |
1995年 | 66篇 |
1994年 | 65篇 |
1993年 | 64篇 |
1992年 | 61篇 |
1991年 | 26篇 |
1990年 | 35篇 |
1989年 | 28篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 16篇 |
1985年 | 31篇 |
1984年 | 32篇 |
1983年 | 13篇 |
1982年 | 37篇 |
1981年 | 24篇 |
1980年 | 9篇 |
1979年 | 37篇 |
1978年 | 14篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有5713条查询结果,搜索用时 15 毫秒
61.
Qiangzhe Zhang Dr. Ronnie H. Fang Dr. Weiwei Gao Dr. Liangfang Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10547-10551
Inhibition of phospholipase A2 (PLA2) has long been considered for treating various diseases associated with an elevated PLA2 activity. However, safe and effective PLA2 inhibitors remain unavailable. Herein, we report a biomimetic nanoparticle design that enables a “lure and kill” mechanism designed for PLA2 inhibition (denoted “L&K-NP”). The L&K-NPs are made of polymeric cores wrapped with modified red blood cell membrane with two inserted key components: melittin and oleyloxyethyl phosphorylcholine (OOPC). Melittin acts as a PLA2 attractant that works together with the membrane lipids to “lure” in-coming PLA2 for attack. Meanwhile, OOPC acts as inhibitor that “kills” PLA2 upon enzymatic attack. Both compounds are integrated into the L&K-NP structure, which voids toxicity associated with free molecules. In the study, L&K-NPs effectively inhibit PLA2-induced hemolysis. In mice administered with a lethal dose of venomous PLA2, L&K-NPs also inhibit hemolysis and confer a significant survival benefit. Furthermore, L&K-NPs show no obvious toxicity in mice. and the design provides a platform technology for a safe and effective anti-PLA2 approach. 相似文献
62.
Lars Müller Santina Hoof Matthias Keck Christian Herwig Prof. Dr. Christian Limberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(51):11851-11861
The design of biomimetic model complexes for the cysteine dioxygenase (CDO) and cysteamine dioxygenase (ADO) is reported, where the 3-His coordination of the iron ion is simulated by three pyrazole donors of a trispyrazolyl borate ligand (Tp) and protected cysteine and cysteamine represent substrate ligands. It is found that the replacement of phenyl groups—attached at the 3-positions of the pyrazole units in a previous model—by mesityl residues has massive consequences, as the latter arrange to a more spacious reaction pocket. Thus, the reaction with O2 proceeds much faster and afterwards the first structural characterization of an iron(II) η2-O,O-sulfinate product became possible. If one of the three Tp-mesityl groups is placed in the 5-position, an even larger reaction pocket results, which leads to yet faster rates and accumulation of a reaction intermediate at low temperatures, as shown by UV/Vis and Mössbauer spectroscopy. After comparison with the results of investigations on the cobalt analogues this intermediate is tentatively assigned to an iron(III) superoxide species. 相似文献
63.
Alexander V. Fejzagić Sebastian Myllek Fabian Hogenkamp Julian Greb Prof. Dr. Jörg Pietruszka Dr. Thomas Classen 《ChemistryOpen》2020,9(9):959-966
Screening for an interesting biocatalyst and its subsequent kinetic characterization depends on a reliable activity assay. In this work, a fluorometric assay based on the halogenation of 4-methyl-7-diethylamino-coumarin was established to monitor haloperoxidase-activity. Since haloperoxidases utilize hydrogen peroxide and halide ions to halogenate a broad range of substrates by releasing hypohalous acids, a direct quantification of haloperoxidase-activity remains difficult. With the system presented here, 3-bromo-4-methyl-7-diethylaminocoumarin is preferentially formed and monitored by fluorescence measurements. As starting material and product share similar spectroscopical properties, a two-dimensional calibration ap-proach was utilized to allow for quantification of each compound within a single measurement. To validate the system, the two-dimensional Michaelis-Menten kinetics of a vanadium-dependent chloroperoxidase from Curvularia inaequalis were recorded, yielding the first overall kinetic parameters for this enzyme. With limits of detection and quantification in the low μm range, this assay may provide a reliable alternative system for the quantification of haloperoxidase-activity. 相似文献
64.
65.
Illanes A Wilson L Caballero E Fernández-Lafuente R Guisán JM 《Applied biochemistry and biotechnology》2006,133(3):189-202
Crosslinked enzyme aggregates (CLEAs) of a partially purified penicillin acylase from a recombinant Escherichia coli strain have been produced as a novel type of biocatalysts well endowed to perform in organic media. Different protein precipitants
were studied and glutaraldehyde was used as the crosslinking agent. Precipitation curves were obtained for all precipitants
to determine the concentrations at which all the protein precipitated out of the solution. The effect of the glutaraldehyde-to-protein
ratio was studied with respect to process recovery and the specific activity and stability of the biocatalyst. Recovery of
penicillin acylase activity was moderately high, about 50%; major losses of enzyme activity were produced at the precipitation
step. Specific activities of all CLEAs were very high, which is one of the advantages of using nonsupported biocatalysts.
Ammonium sulfate and tert-butyl alcohol were the best precipitants at a glutaraldehyde-protein mass ratio of 2 and were selected to perform the kinetically
controlled synthesis of ampicillin in 60% (v/v) ethylene glycol medium. At comparable conversion yields, volumetric and specific
antibiotic productivity were much higher for CLEAs than for carrier-bound penicillin acylases. 相似文献
66.
V. I. Isaeva Zh. L. Dykh L. I. Lafer V. I. Yakerson V. Z. Sharf 《Russian Chemical Bulletin》1992,41(1):49-54
The structure of Rh(II) complexes with vigorous ligands immobilized on -aminopropyl-containing silicagel (-AMPS) and polymers containing 3(5)-methyl-pyrazole and imidazole groups, was investigated. It was shown by IR spectroscopy that the ligand surroundings are maintained after application only for the Rh(II) acetate complex. For the acetonitrile and hexafluoroacetylacetonate complexes there is a replacement of the ligands by amino groups of the carrier. [Rh2(O2CCH3)4] is significantly more active than other metal complexes immobilized on -AMPS in the hydrodehalogenation of p-bromotoluene by transfer of hydrogen from NaBH4 and propanol-2.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 65–70, January, 1992. 相似文献
67.
68.
69.
Yuanqi Gui Baian Ji Gaoyi Yi Xiuju Li Kailian Zhang Qifeng Fu 《Molecules (Basel, Switzerland)》2021,26(6)
Herein, a novel L-arginine (L-Arg)-modified polydopamine (PDA)-coated capillary (PDA/L-Arg@capillary) was firstly fabricated via the basic amino-acid-induced PDA co-deposition strategy and employed to constitute a new chiral ligand exchange capillary electrochromatography (CLE-CEC) method for the high-performance enantioseparation of D,L-amino acids (D,L-AAs) with L-Arg as the immobilized chiral ligand coordinating with the central metal ion Zn(II) as running buffer. Assisted by hydrothermal treatment, the robust immobilization of L-Arg on the capillary inner wall could be facilely achieved within 1 h, prominently improving the synthesis efficiency and simplifying the preparation procedure. The successful preparation of PDA/L-Arg coatings in the capillary was systematically characterized and confirmed using several methods. In comparison with bare and PDA-functionalized capillaries, the enantioseparation capability of the presented CLE-CEC system was significantly enhanced. Eight D,L-AAs were completely separated and three pairs were partially separated under the optimal conditions. The prepared PDA/L-Arg@capillary showed good repeatability and stability. The potential mechanism of the greatly enhanced enantioseparation performance obtained by PDA/L-Arg@capillary was also explored. Moreover, the proposed method was further utilized for studying the enzyme kinetics of L-glutamic dehydrogenase, exhibiting its promising prospects in enzyme assays and other related applications. 相似文献
70.
Eduardo Rosado Paloma Delgado-Fernndez Blanca de las Rivas Rosario Muoz Francisco Javier Moreno Nieves Corzo Cesar Mateo 《Molecules (Basel, Switzerland)》2022,27(4)
The synthesis of β-galactosyl xylitol derivatives using immobilized LacA β-galactosidase from Lactobacillus plantarum WCFS1 is presented. These compounds have the potential to replace traditional sugars by their properties as sweetener and taking the advantages of a low digestibility. The enzyme was immobilized on different supports, obtaining immobilized preparations with different activity and stability. The immobilization on agarose-IDA-Zn-CHO in the presence of galactose allowed for the conserving of 78% of the offered activity. This preparation was 3.8 times more stable than soluble. Since the enzyme has polyhistidine tags, this support allowed the immobilization, purification and stabilization in one step. The immobilized preparation was used in synthesis obtaining two main products and a total of around 68 g/L of β-galactosyl xylitol derivatives and improving the synthesis/hydrolysis ratio by around 30% compared to that of the soluble enzyme. The catalyst was recycled 10 times, preserving an activity higher than 50%. The in vitro intestinal digestibility of the main β-galactosyl xylitol derivatives was lower than that of lactose, being around 6 and 15% for the galacto-xylitol derivatives compared to 55% of lactose after 120 min of digestion. The optimal amount immobilized constitutes a very useful tool to synthetize β-galactosyl xylitol derivatives since it can be used as a catalyst with high yield and being recycled for at least 10 more cycles. 相似文献