全文获取类型
收费全文 | 20098篇 |
免费 | 3304篇 |
国内免费 | 3907篇 |
专业分类
化学 | 15550篇 |
晶体学 | 519篇 |
力学 | 926篇 |
综合类 | 385篇 |
数学 | 2689篇 |
物理学 | 7240篇 |
出版年
2024年 | 45篇 |
2023年 | 259篇 |
2022年 | 588篇 |
2021年 | 643篇 |
2020年 | 755篇 |
2019年 | 776篇 |
2018年 | 624篇 |
2017年 | 762篇 |
2016年 | 872篇 |
2015年 | 984篇 |
2014年 | 1179篇 |
2013年 | 1533篇 |
2012年 | 1797篇 |
2011年 | 1849篇 |
2010年 | 1541篇 |
2009年 | 1510篇 |
2008年 | 1748篇 |
2007年 | 1497篇 |
2006年 | 1395篇 |
2005年 | 1139篇 |
2004年 | 860篇 |
2003年 | 716篇 |
2002年 | 864篇 |
2001年 | 679篇 |
2000年 | 510篇 |
1999年 | 382篇 |
1998年 | 254篇 |
1997年 | 175篇 |
1996年 | 197篇 |
1995年 | 151篇 |
1994年 | 145篇 |
1993年 | 138篇 |
1992年 | 115篇 |
1991年 | 115篇 |
1990年 | 91篇 |
1989年 | 75篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 39篇 |
1985年 | 45篇 |
1984年 | 29篇 |
1983年 | 25篇 |
1982年 | 20篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 6篇 |
1973年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
The crystallization of calcium carbonate (CaCO3) controlled by Pluronic P123 in a room-temperature ionic liquid, ethylamine nitrate (EAN), was investigated. The CaCO3 aggregates were obtained by rapid mixing of ammonium carbonate ((NH4)2CO3) and calcium chloride (CaCl2). Cubic calcite, spherical vaterite, and bagel-like vaterite were obtained easily by changing P123 concentration and reaction temperature. The morphologies of the as-prepared CaCO3 aggregates were investigated by transmission electron microscopy and scanning electronic microscopy. The phase change of the obtained crystals was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. It was shown that higher P123 concentration and higher reaction temperature favor the formation of vaterite in EAN. Unusual bagel-like vaterite was first obtained at 60 °C in the presence of 5 g/L P123 in EAN. Mineralization of CaCO3 regulated by P123 in EAN is a simple, novel, and environment-friendly strategy for vaterite synthesis. 相似文献
882.
Streptococcus mutans (S. mutans) forms part of the commensal microflora and is deemed to be the major pathogen responsible for the generation of dental caries. The enzyme, sortase A enzyme, modulates the surface properties and cariogenicity of S. mutans. Curcumin has been reported to be an inhibitor of Staphylococcus aureus sortase A. In this study, inhibition of a purified S. mutans UA159 sortase A by curcumin was evaluated. Curcumin exerted strong inhibitory activity with a half maximal inhibitory concentration (IC50) of 10.2?±?0.7 μM which was lower than the minimum inhibitory concentration of 175 μM and the minimum bactericidal concentration of 350 μM. These results indicated that curcumin is a S. mutans UA159 sortase A inhibitor and therefore represents as a promising anticaries agent. 相似文献
883.
Suk Soon Choi Hyun Min Lee Jeong Hyub Ha Dong Gyun Kang Chang Sup Kim Jeong Hyun Seo Hyung Joon Cha 《Applied biochemistry and biotechnology》2013,171(5):1170-1177
During wastewater treatment, phosphate removal is an important and challenging process; thus, diverse technologies, including those derived from biological means, have been devised for efficient phosphate removal. Although conventional biological methods are effective in decreasing wastewater phosphate levels to ~1 mg/L, long periods of microbial adaptation are required for effective phosphate removal, and the removal efficiency of these methods is relatively poor at lower phosphate concentrations. In the present work, we constructed a recombinant Escherichia coli with periplasmic-expressed phosphate-binding protein (PBP) and investigated its biological removal ability for low phosphate levels. We found that the PBP-expressing recombinant E. coli cells showed efficient (> 94 %) removal of phosphate at low concentrations (0.2–1.0 mg/L) in a treated cell mass-dependent manner. Collectively, we propose that our PBP-expressing recombinant whole-cell system could be successfully used during wastewater treatment for the biological removal of low concentrations of phosphate. 相似文献
884.
Donglin Mao Tingting Li Huarong Liu Zichao Li Hong Shao Min Li 《Colloid and polymer science》2013,291(7):1649-1656
PolyHIPEs are highly porous, crosslinked polymer foams typically synthesized within high internal-phase emulsions (HIPEs). Two kinds of polyHIPEs including poly(styrene-divinylbenzene) [P(St-DVB)] and poly(methyl methacrylate-divinylbenzene) [P(MMA-DVB)] foams are synthesized in this work, which are fabricated from HIPEs template via radiation-induced polymerization at room temperature. Traditional free radical polymerization initiated by potassium peroxydisulfate (KPS) at 60 °C for producing polyHIPE P(St-DVB) foams is also conducted for comparison. It is found that the amount of emulsifier can be reduced greatly in the radiation-induced polymerization of HIPEs at room temperature, compared with the traditional polymerization approach. Besides, P(MMA-DVB) PolyHIPE foams with a fine microstructure of highly interconnected pores have been successfully fabricated via radiation-induced polymerization in this work, which is usually difficult to be prepared by thermal-initiation method because of the intermediate hydrophobicity of methyl methacrylate monomer. The influences of the fraction of internal aqueous phase and the concentration of emulsifier on the structure and performance of foams are carefully explored. The structure and compression strength of the foams are characterized by scanning electron microscopy and a mechanical testing machine, respectively. Figure
Macroporous poly(styrene-divinylbenzene) and poly(methyl methacrylate-divinylbenzene) foams are synthesized from HIPEs template via radiation-induced polymerization at room temperature using a common surfactant Span 80. 相似文献
885.
A new metallomicellar system containing cerium(III), a macrocylic polyamine ligand, and the nonionic surfactant Brij35(polyoxyethylene(23) lauryl ether) was prepared and used as a catalyst in the hydrolysis of bis(4-nitrophenyl) phosphate (BNPP). Catalytic rate of the BNPP hydrolysis was measured kinetically using the UV-VIS spectrophotometric method. The results indicate that the metallomicellar system has relatively high stability and excellent catalytic function in the BNPP hydrolysis; also, the reaction rate of the BNPP catalytic hydrolysis increased by a factor of ca. 1 × 1010 compared to the BNPP spontaneous hydrolysis due to the catalytic effect of the active species and the local concentration effect of the micelles in the metallomicellar system. Experimental results also showed that the mono-hydroxy complex containing the macrocyclic polyamine ligand and cerium(III) is the real active species in the BNPP catalytic hydrolysis, and that the micelles provide a useful catalytic environment for the reaction. On basis of the research results, the reaction mechanism of BNPP catalytic hydrolysis has been proposed. 相似文献
886.
Sojung Park Junhong Min 《International journal of environmental analytical chemistry》2013,93(6):655-664
A fast and sensitive chemiluminescent enzyme-linked immunosorbent assay method to measure pathogenic bacteria, Escherichia coli O157:H7, on immuno-chromatographic membrane was studied. Non-specific binding of proteins on membrane strip was controlled to attain the best performance of immunosensor by optimising the composition of a running buffer. The specificity of the proposed immunostrip was confirmed by conducting experiments for four different micro-organisms. A chemiluminescent signal could be successfully generated from a proposed immunostrip sensing system, and a significant change in the chemiluminescent light intensity with the concentration of target microbes was obtained. E. coli O157:H7 could be quantitatively measured in the range of 1.1?×?103?–1.1?×?107 CFU (colony forming units) mL?1 within 16?min by using the developed chemiluminescent immunostrip. 相似文献
887.
Min Lu Michael A. Phillips 《International journal of environmental analytical chemistry》2013,93(2):213-227
Antimony is an element of significant environmental concern, yet has been neglected relative to other heavy metals in electroanalysis. As such very little research has been reported on the electroanalytical determination of antimony at unmodified carbon electrodes. In this paper we report the electrochemical determination of Sb(III) in HCl solutions using unmodified carbon substrates, with focus on non-classical carbon materials namely edge plane pyrolytic graphite (EPPG), boron doped diamond (BDD) and screen-printed electrodes (SPE). Using differential pulse anodic stripping voltammetry, EPPG was found to give a considerably greater response towards antimony than other unmodified carbon electrodes, allowing highly linear ranges in nanomolar concentrations and a detection limit of 3.9?nM in 0.25?M HCl. Furthermore, the sensitivity of the response from EPPG was 100 times greater than for glassy carbon (GC). Unmodified GC gave a comparable response to previous results using the bare substrate, and BDD gave an improved, yet still very high limit of detection of 320?nM compared to previous analysis using an iridium oxide modified BDD electrode. SPEs gave a very poor response to antimony, even at high concentrations, observing no linearity from standard additions, as well as a major interference from the ink intrinsic to the working electrode carbon material. Owing to its superior performance relative to other carbon electrodes, the EPPG electrode was subjected to further analytical testing with antimony. The response of the electrode for a 40?nM concentration of Sb(III) was reproducible with a mean peak current of 1.07?µA and variation of 8.4% (n?=?8). The effect of metals copper, bismuth and arsenic were investigated at the electrode, as they are common interferences for stripping analysis of antimony. 相似文献
888.
Li‐Wei Zhao Hui‐Min Shi Zhe An Jiu‐Zhao Wang Prof. Jing He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(37):12350-12355
Effectively enhancing the enantioselectivity is a persistent challenge in heterogeneous asymmetric catalysis. Here, the validity of a layered double hydroxides (LDH) nanosheet as an efficient planar substituent to enhance the enantioselectivity has been investigated theoretically; first in vanadium‐catalyzed asymmetric epoxidation of allylic alcohols, and then in zinc‐catalyzed direct asymmetric aldol addition. The computational predication is further confirmed experimentally in zinc‐catalyzed direct asymmetric aldol addition by controlling the location of catalytic sites. 相似文献
889.
Dr. Ke‐Rang Wang Yue‐Qing Wang Hong‐Wei An Jin‐Chao Zhang Prof. Dr. Xiao‐Liu Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(8):2903-2909
A new triazatruxene‐based fluorescent glycocluster has been designed, synthesized, and fully characterized by NMR spectroscopy and mass spectrometry. Furthermore, its specific and selective binding properties with concanavalin A (Con A) have been investigated by fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and turbidity assay. The obtained results showed that the multivalent mannose‐modified triazatruxene exhibited specific binding with Con A, but no binding to peanut agglutinin (PNA) lectin or bovine serum albumin (BSA), corresponding to a two‐orders‐of‐magnitude higher affinity than that of monovalent mannose ligands. Most interestingly, a fluorescence enhancement of the triazatruxene‐based glycocluster was observed upon binding with Con A because of hydrophobic interactions involving sites close to the triazatruxene moiety. Furthermore, the inhibitory ability of the triazatruxene‐based glycocluster against ORN178‐ induced haemagglutination has been investigated by haemagglutination inhibition assay. The results indicated selective binding with ORN178. 相似文献
890.
Ran Choi Dr. Sang‐Il Choi Dr. Chang Hyuck Choi Dr. Ki Min Nam Prof. Seong Ihl Woo Prof. Joon T. Park Prof. Sang Woo Han 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8190-8198
Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs. 相似文献