全文获取类型
收费全文 | 296篇 |
免费 | 26篇 |
专业分类
化学 | 278篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 18篇 |
物理学 | 23篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 16篇 |
2020年 | 16篇 |
2019年 | 24篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 26篇 |
2015年 | 10篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 33篇 |
2011年 | 25篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 12篇 |
2007年 | 20篇 |
2006年 | 16篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有322条查询结果,搜索用时 15 毫秒
91.
92.
93.
Postsynthetic Stille cross-coupling for functionalization of oligonucleotides on solid support was applied on iodo modified RNA utilizing different protecting group strategies. As result, the otherwise very successful ACE [bis(acetoxyethyloxy)-methyl orthoester] chemistry was found to be limited since methylated side-products formed as was investigated via enzymatic degradation of RNA and various monomer model reactions. Enzymatic digestion of poly uridine sequences revealed presence of considerable amounts of N3-methylated uridine derivatives due to migration of methyl as phosphate protecting group used in ACE strategy. Monomer test reactions mimicking conditions on RNA clearly indicated an enhanced methylation effect correlated to the Stille coupling procedure. 相似文献
94.
Andre Wichmann Günter Schnurpfeil Jana Backenköhler Lena Kolke Vladimir A. Azov Dieter Wöhrle Marcus Bäumer Arne Wittstock 《Tetrahedron》2014
Nanoporous gold (npAu) was employed as high surface area substrate for immobilization of redox- and photooxidative-active organic molecules. A two-step synthetic routine is demonstrated as a versatile and robust method for immobilization of various molecules. First, self-assembled monolayers (SAMs) of thiols containing an azide moiety were prepared on npAu substrates. Then, alkyne-modified ferrocene, tetrathiafulvalene, and zinc(II)phthalocyanine derivatives were covalently bound via the click reaction to this linker. Following the provided synthetic procedures high performance composite materials are generated for electrochemistry and photochemistry. The robust bonding between the organic functional group and the gold support provides stability even under strongly oxidizing conditions (applied potential or singlet oxygen). 相似文献
95.
Alexander Schoth Caroline Wagner Lena L. Hecht Svenja Winzen Rafael Muñoz-Espí Heike P. Schuchmann Katharina Landfester 《Colloid and polymer science》2014,292(10):2427-2437
Hydrophilic silica particles need to be hydrophobized to be encapsulated in a polymeric environment, which can be achieved by different methods. We report on the relationship between different hydrophobization techniques of silica and the final structure of poly(methyl methacrylate)/silica hybrid nanoparticles obtained by miniemulsion polymerization. Hydrophobization by cetyltrimethylammonium chloride (CTMA-Cl) uses the ionic interaction between the positively charged ammonium salt and the negatively charged silica surface, as shown by isothermal titration calorimetry. In this case, the interaction between polymer and silica surface needs to be enhanced, so 4-vinylpyridine (4-VP) was used as a co-monomer. Alternatively, the condensation reactions of 3-methacryloxypropyltrimethoxysilane (MPS) and octadecyltrimethoxysilane (ODTMS) were used to provide a covalent bond to the silica surface. The condensation reaction of the trimethoxysilane groups onto the silica surface was proven by Fourier transform infrared spectroscopy and thermogravimetric analysis. Hybrid nanoparticles were successfully formed with silica particles functionalized with the different functionalization agents. However, the structure of the resulting hybrid particles (i.e., the distribution of the silica particles within the polymer matrix) depends on the agent. The MPS-functionalized silica particles copolymerize with poly(methyl methacrylate), leading to a fixation of the silica particles inside the polymer and to a homogeneous distribution. The CTMA-Cl- and ODTMS-functionalized silica particles cannot copolymerize, but aggregate at the interface, leading to a Janus-like structure. 相似文献
96.
Giovanni Di Lena Davide Franco Mario Martelli Basilio Messano 《Mediterranean Journal of Mathematics》2011,8(4):473-489
The main purpose of this paper is to investigate dynamical systems
F : \mathbbR2 ? \mathbbR2{F : \mathbb{R}^2 \rightarrow \mathbb{R}^2} of the form F(x, y) = (f(x, y), x). We assume that
f : \mathbbR2 ? \mathbbR{f : \mathbb{R}^2 \rightarrow \mathbb{R}} is continuous and satisfies a condition that holds when f is non decreasing with respect to the second variable. We show that for every initial condition x0 = (x
0, y
0), such that the orbit
O(x0) = {x0, x1 = F(x0), x2 = F(x1), . . . }, O({\rm{x}}_0) = \{{\rm{x}}_0, {\rm{x}}_1 = F({\rm{x}}_0), {\rm{x}}_2 = F({\rm{x}}_1), . . . \}, 相似文献
97.
A sample pretreatment involving only the dilution (1 + 19) of two 0.2–0.4 ml sample aliquots with 0.5 M hydrochloric acid, with a standard addition to one of the aliquots, precedes the injection of each sample. The computer-controlled flow system used automatically executes a pre-programmed number of cycles on each sample pair before presenting the final result. Each cycle, which has a duration of 80 or 135 s for lead(II) and cadmium(II), respectively, involves the display of the derivative stripping signal on a printer/plotter and integration of the stripping peaks generated. For lead(II), striping is done in 0.5 M hydrochloric acid, which eliminates interferences from copper, though at the cost of a relatively high stripping rate, compared to the 5 M calcium chloride used for cadmium(II). The flow cell consists of a silver chloride-lined silver tube which acts as both reference and counter electrode, and a disposable carbon-fibre working electrode mounted in a PVC tube, which normally will operate for 50–200 cycles. The method was verified for whole blood reference standards and by comparison with results obtained by atomic absorption spectrometry. 相似文献
98.
Alexander Swoboda Lukas Johannes Pfeifenberger Zerina Duhović Moritz Bürgler Dr. Isabel Oroz-Guinea Klara Bangert Florian Weißensteiner Lena Parigger Katharina Ebner Prof. Dr. Anton Glieder Prof. Dr. Wolfgang Kroutil 《Angewandte Chemie (International ed. in English)》2023,62(46):e202312721
Identifying (bio)catalysts displaying high enantio-/stereoselectivity is a fundamental prerequisite for the advancement of asymmetric catalysis. Herein, a high-throughput, stereoselective screening assay is reported that gives information on enantioselectivity, stereopreference and activity as showcased for peroxygenase-catalyzed hydroxylation. The assay is based on spectrophotometric analysis of the simultaneous formation of NAD(P)H from the alcohol dehydrogenase catalyzed enantioselective oxidation of the sec-alcohol product formed in the peroxygenase reaction. The assay was applied to investigate a library comprising 44 unspecific peroxygenases (UPOs) containing 25 UPOs not reported yet. Thereby, previously non-described wild-type UPOs displaying (S)- as well as (R)-stereoselectivity for the hydroxylation of representative model substrates were identified, reaching up to 98 % ee for the (R)- and 94 % ee for the (S)-enantiomer. Homology models with concomitant docking studies indicated the structural reason for the observed complementary stereopreference. 相似文献
99.
Yannick Branson Simone Söltl Carolin Buchmann Dr. Ren Wei Dr. Lena Schaffert Dr. Christoffel P. S. Badenhorst Dr. Lukas Reisky Dr. Gernot Jäger Prof. Dr. Uwe T. Bornscheuer 《Angewandte Chemie (International ed. in English)》2023,62(9):e202216220
Enzymatic degradation and recycling can reduce the environmental impact of plastics. Despite decades of research, no enzymes for the efficient hydrolysis of polyurethanes have been reported. Whereas the hydrolysis of the ester bonds in polyester-polyurethanes by cutinases is known, the urethane bonds in polyether-polyurethanes have remained inaccessible to biocatalytic hydrolysis. Here we report the discovery of urethanases from a metagenome library constructed from soil that had been exposed to polyurethane waste for many years. We then demonstrate the use of a urethanase in a chemoenzymatic process for polyurethane foam recycling. The urethanase hydrolyses low molecular weight dicarbamates resulting from chemical glycolysis of polyether-polyurethane foam, making this strategy broadly applicable to diverse polyether-polyurethane wastes. 相似文献
100.
Christine Farthing Don Farthing Donald F. Brophy Terri Larus Lena Maynor Itaf Fakhry Todd W. B. Gehr 《Chromatographia》2008,67(5-6):365-368
A simple high-performance liquid chromatographic (HPLC) method was developed for the simultaneous determination of cefepime
and cefazolin in human plasma and dialysate. For component separation, the method utilized a C18 column with an aqueous mobile phase of dibasic potassium hydrogen phosphate (pH 7.0) and methanol gradient at a flow rate
of 1 mL min−1. The method demonstrated linearity from 2.0 to 100.0 μg mL−1 (r > 0.999) with detection limit of 1 μg mL−1 for both cefepime and cefazolin. The method was utilized for evaluation of plasma and dialysate samples in a clinical study
evaluating the dialyzer clearance of cefepime and cefazolin using high-flux hemodialysis with varying blood flow rates in
chronic kidney failure patients undergoing hemodialysis and peritoneal dialysis treatment. 相似文献
|