全文获取类型
收费全文 | 4905篇 |
免费 | 283篇 |
国内免费 | 485篇 |
专业分类
化学 | 3683篇 |
晶体学 | 33篇 |
力学 | 116篇 |
综合类 | 9篇 |
数学 | 73篇 |
物理学 | 1053篇 |
无线电 | 706篇 |
出版年
2024年 | 33篇 |
2023年 | 337篇 |
2022年 | 131篇 |
2021年 | 171篇 |
2020年 | 172篇 |
2019年 | 172篇 |
2018年 | 133篇 |
2017年 | 157篇 |
2016年 | 166篇 |
2015年 | 167篇 |
2014年 | 211篇 |
2013年 | 310篇 |
2012年 | 377篇 |
2011年 | 293篇 |
2010年 | 238篇 |
2009年 | 287篇 |
2008年 | 278篇 |
2007年 | 286篇 |
2006年 | 232篇 |
2005年 | 192篇 |
2004年 | 204篇 |
2003年 | 149篇 |
2002年 | 90篇 |
2001年 | 96篇 |
2000年 | 87篇 |
1999年 | 104篇 |
1998年 | 109篇 |
1997年 | 79篇 |
1996年 | 65篇 |
1995年 | 51篇 |
1994年 | 46篇 |
1993年 | 47篇 |
1992年 | 37篇 |
1991年 | 36篇 |
1990年 | 20篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 8篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1978年 | 1篇 |
1975年 | 14篇 |
1968年 | 1篇 |
排序方式: 共有5673条查询结果,搜索用时 0 毫秒
161.
Acrylamide complexes of metal nitrates: [M(O‐OC(NH2)CHCH2)n(H2O)m][NO3]2 (M = Co( 1 ), Ni( 2 ) (n = 6 and m = 0) and Zn( 3 ) (n = 4 and m = 2)) have been determined by using single crystal X‐ray diffraction analysis. All complexes crystallize in the triclinic space group . The structures of 1 and 2 represent octahedral species [M(AAm)6]2+ (AAm = O‐OC(NH2)CHCH2 and M = Co or Ni) and uncoordinated nitrate ions. The structure of 3 involves the octahedral cation [Zn(AAm)4(H2O)2]2+ in which the Zn2+ environment includes oxygen atoms of four acrylamide and two water molecules that are stabilized using ionic nitrate ions. The observations of the solid‐state IR spectroscopic vibrational frequencies of these acrylamide complexes are in agreement with the crystal structures. 相似文献
162.
Jinhua Hong Shunsuke Kobayashi Akihide Kuwabara Yumi H. Ikuhara Yasuyuki Fujiwara Yuichi Ikuhara 《Molecules (Basel, Switzerland)》2021,26(12)
Solid electrolytes, such as perovskite Li3xLa2/1−xTiO3, LixLa(1−x)/3NbO3 and garnet Li7La3Zr2O12 ceramic oxides, have attracted extensive attention in lithium-ion battery research due to their good chemical stability and the improvability of their ionic conductivity with great potential in solid electrolyte battery applications. These solid oxides eliminate safety issues and cycling instability, which are common challenges in the current commercial lithium-ion batteries based on organic liquid electrolytes. However, in practical applications, structural disorders such as point defects and grain boundaries play a dominating role in the ionic transport of these solid electrolytes, where defect engineering to tailor or improve the ionic conductive property is still seldom reported. Here, we demonstrate a defect engineering approach to alter the ionic conductive channels in LixLa(1−x)/3NbO3 (x = 0.1~0.13) electrolytes based on the rearrangements of La sites through a quenching process. The changes in the occupancy and interstitial defects of La ions lead to anisotropic modulation of ionic conductivity with the increase in quenching temperatures. Our trial in this work on the defect engineering of quenched electrolytes will offer opportunities to optimize ionic conductivity and benefit the solid electrolyte battery applications. 相似文献
163.
The syntheses, crystal structures and characterizations of two new divalent metal carboxylate-phosphonates, namely, Zn(H3L)·2H2O (1) and Pb(H3L)(H2O)2 (2) (H5L4-HO2C–C6H4–CH2N(CH2PO3H2)2) have been reported. Compound 1 features a 1D column structure in which the Zn(II) ions are tetrahedrally coordinated by four phosphonate oxygen atoms from four phosphonate ligands, and neighboring such 1D building blocks are further interconnected via hydrogen bonds into a 3D network. The carboxylate group of H3L anion remains non-coordinated. Compound 2 has a 2D layer structure. Pb(II) ion is 7-coordinated by four phosphonate oxygen atoms from four phosphonate ligands and three aqua ligands. The interconnection of Pb(II) ions via bridging H3L anions results in a 001 layer. The carboxylate group of the H3L anion also remains non-coordinated and is oriented toward the interlayer space. Solid state luminescent spectrum of compound 1 exhibits a strong broad blue fluorescent emission band at 455 nm under excitation at 365 nm at room temperature. 相似文献
164.
Donna Leamy Fiona Regan 《International journal of environmental analytical chemistry》2013,93(10):867-877
The potential of an optical sensing material for determination of metal ions in wastewater streams is presented. The initial results in the development of a chromo-ionophore-based optical sensor for metal ions are detailed. An azo dye species, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (BrPADAP), together with an ionophore and plasticiser was immobilised in a film of poly(vinyl chloride) (PVC). Initial investigations using the dye-impregnated sensing film showed a reproducible and reversible response to Pb(II) ions in aqueous solution. The response of this sensing film to Pb(II) at pH 6 was found to be linear in the 0.1-10 mg/L range, with a %RSD of 1.55%. The film can be regenerated by immersion in a low-pH buffer solution. The authors demonstrate how this method shows potential for analysis using once-off sensing probes. The sensing film response for Pb(II) occurs within 30 s. 相似文献
165.
Nasser M. Hosny Farid I. El-Dossoki Mohsen M. Mostafa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):402-410
New metal complexes derived from the reaction of N-[(phenylamino)thioxomethyl] hydrazino carbonyl methyl pyridinium chloride (H2L; PTHMPC) with some metal salts of the general formula MX2 [(X = Cl? and/or CH3COO?; M = Cd(II), UO2(II), Mn(II) and Zr(IV)] were synthesized and characterized by elemental analyses, spectral analyses (IR, UV-vis., 1H NMR), thermal analyses (TGA, DTG), and conductance and magnetic measurements. The results showed that the ligand exists in metal complexes either in the keto form or in the enol form. Moreover, the IR spectral data suggest that the acetate ion behaves in a monodentate manner. Semi-empirical calculations ZINDO/1, PM3, and AM1 have been used to study the molecular geometry and the harmonic vibrational spectra of the ligand and its metal complexes with the purpose of assisting the experimental assignment of the complexes. Generally, there is an agreement between the observed and the calculated spectra. Finally, the thermodynamic parameters (ΔE*, ΔH, ΔG, and ΔS) have been calculated from the data of thermal analyses (TGA and DTG). Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献
166.
Rainer Bartsch Christian Müller Axel Fischer Peter G. Jones 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Syntheses and structures of penta- and hexaphosphorus analogues of ferrocene have been described recently1. Unlike their simple ferrocene analogues, these complexes have further ligating potential towards other transition metal centres by virtue of the availability of the ring phosphorus lone-pair electrons that are not involved in the η5-coordination. We now describe the first examples of coordination compounds of the triphospha-ferrocene [Fe(η5-C5Me5) (η5-C2 tBu2P3]. In the ruthenium complex [Fe(η5-C5Me5)(η5-C2 tBu2P3) Ru3(CO)9] 2 two adjacent phosphorus atoms of the η5-C2 tBu2P3 ring are interlinked by a ruthenium carbonyl cluster in which all three ruthenium atoms interact with the phosphorus atoms. The tetrametallic nickel complex [Fe(η5-C5Me5)(η5-C2 tBu2P3)Ni(CO)2]2 3 represents the first example of intermolecular interlinkage of two phospha-ferrocene systems by two metal centres. 相似文献
167.
《Journal of Dispersion Science and Technology》2013,34(3-4):305-341
Abstract Plasma treatment of polymers encompasses a variety of plasma technologies and polymeric materials for a wide range of applications and dates back to at least the 1960s. In this article we provide a brief review of the United States patent literature on plasma surface modification technologies and a brief review of the scientific literature on investigations of the effects of plasma treatment, the nature of the plasma environment, and the mechanisms that drive the plasma–surface interaction. We then discuss low‐radio‐frequency capacitively coupled nitrogen plasmas and their characteristics, suggesting that they provide significant plasma densities and populations of reactive species for effective plasma treatments on a variety of materials, particularly when placing the sample surface in the cathode sheath region. We further discuss surface chemical characterization of treated polymers, including some results on polyesters treated in capacitively coupled nitrogen plasmas driven at 40 kHz. Finally, we connect plasma characterization with surface chemical analysis by applying a surface sites model to nitrogen uptake of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) treated in a 40 kHz nitrogen plasma. This example serves to suggest an interesting practical approach to comparisons of plasma treatments. In addition, it suggests an approach to defining the investigations required to conclusively identify the underlying treatment mechanisms. 相似文献
168.
《Journal of Dispersion Science and Technology》2013,34(3-4):517-525
Abstract Sorption of ions may lead to variations in interparticle forces and, thus, changes in the stability of colloidal particles. Chemical interactions between metal ions and colloidal particles modify the molecular structure of the surface, the surface charge, and the electrical potential between colloidal particles. These modifications to the surface and to the electrical double layer due to metal ion sorption are reflected in the interaction force between a particle and another surface, which is measured in this study by atomic force microscopy (AFM). Specifically, AFM is used to investigate the sorption of copper ions from aqueous solutions by silica particles. The influence of metal ion concentration and solution ionic strength on surface forces is studied under transient conditions. Results show that as the metal ion concentration is decreased, charge reversal occurs and a longer period of time is required for the system to reach equilibrium. The ionic strength has no significant effect on sorption kinetics. Furthermore, neither metal concentration nor ionic strength exhibits any effect on sorption equilibria, indicating that for the experimental conditions used in this study, the surface sites of the silica particle are fully occupied by copper ions. 相似文献
169.
ZnO nanocrystals, rod-, carnation-, and flower-like structures, have been synthesized in a high yield through low-temperature synthetic methods. Well-aligned ZnO nanorods having hexagonal wurtzite structure were grown on the ZnO thin films assembled by a spin-coating method. The morphologies of ZnO seed films are affected by pHs of sol–gel solutions, resulting smaller sizes and homogeneous roughness at higher pHs and higher number of spin-coating times. The carnation-like structures, average size of about 2–3 μm, were assembled by tens of uniform ZnO nanosheet petals of ∼50 nm in thickness when a different volume ratio of the precursory solution was used. ZnO nanocrystals on the facets of the compact ZnO nanorods have grown to linear nanorods having an average diameter of ∼500 nm and length of ∼2 μm. Furthermore, a noticeable difference in the growth of ZnO nanocrystals in the presence of various surfactants, polyvinylpyrrolidone, polyvinylsulphonic acid, and polyethyleneimine, has been observed and discussed. 相似文献
170.
采用在线富集/高效液相色谱(HPLC)与电感耦合等离子体质谱(ICP-MS)联用技术,建立了玩具中超痕量可迁移六价铬的测定方法。以10 mmol/L硝酸铵为流动相,样品在Agilent BIO WAX NP5阴离子交换柱(4.6 mm×50 mm,5μm)中富集,再通过阀切换,以75 mmol/L硝酸铵将六价铬洗脱至Dionex AG7阴离子柱(4.0 mm×50 mm,10μm)中分离,最后经ICP-MS进行分析。优化得到在线富集时间为4 min,进样量为900μL,富集流速为0.4 mL/min,洗脱流速为0.6 mL/min。结果显示,六价铬在2~20 ng/L范围内线性良好,检出限为1.93 ng/L,相对标准偏差(RSD)为3.9%。与直接进样相比,浓缩因子约为8.1倍,富集效率约为90%。对欧盟玩具安全指令2009/48/EC规定的3类玩具材料在5、10 ng/L的浓度水平下进行加标回收,回收率为93.4%~111%。 相似文献