全文获取类型
收费全文 | 3305篇 |
免费 | 576篇 |
国内免费 | 523篇 |
专业分类
化学 | 2509篇 |
晶体学 | 34篇 |
力学 | 150篇 |
综合类 | 29篇 |
数学 | 393篇 |
物理学 | 1289篇 |
出版年
2024年 | 17篇 |
2023年 | 85篇 |
2022年 | 141篇 |
2021年 | 152篇 |
2020年 | 157篇 |
2019年 | 165篇 |
2018年 | 146篇 |
2017年 | 134篇 |
2016年 | 174篇 |
2015年 | 210篇 |
2014年 | 199篇 |
2013年 | 249篇 |
2012年 | 287篇 |
2011年 | 296篇 |
2010年 | 231篇 |
2009年 | 224篇 |
2008年 | 239篇 |
2007年 | 180篇 |
2006年 | 172篇 |
2005年 | 152篇 |
2004年 | 96篇 |
2003年 | 65篇 |
2002年 | 83篇 |
2001年 | 49篇 |
2000年 | 52篇 |
1999年 | 60篇 |
1998年 | 31篇 |
1997年 | 50篇 |
1996年 | 62篇 |
1995年 | 60篇 |
1994年 | 44篇 |
1993年 | 37篇 |
1992年 | 19篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1965年 | 3篇 |
1936年 | 1篇 |
排序方式: 共有4404条查询结果,搜索用时 15 毫秒
41.
Xiao-Yu Miao Yong-Ji Hu Fu-Rao Liu Yuan-Yuan Sun Die Sun An-Xin Wu Yan-Ping Zhu 《Molecules (Basel, Switzerland)》2022,27(19)
A cascade 6-endo-dig cyclization reaction was developed for the switchable synthesis of halogen and non-halogen-functionalized pyrazolo[3,4-b]pyridines from 5-aminopyrazoles and alkynyl aldehydes via C≡C bond activation with silver, iodine, or NBS. In addition to its wide substrate scope, the reaction showed good functional group tolerance as well as excellent regional selectivity. This new protocol manipulated three natural products, and the arylation, alkynylation, alkenylation, and selenization of iodine-functionalized products. These reactions demonstrated the potential applications of this new method. 相似文献
42.
从有电荷转移络合物参与的共聚体系增长基元反应出,提出一种有CTC参与的共聚体系竞聚率的求法,从中得到4个竞聚率,自由单体和CTC的相对活性等信息。 相似文献
43.
Hydrophobically associating copolymers of acrylamide (AM) with a small amount of 4-(omega-propenoyloxyethoxy) benzoic acid (PEBA, <2.5%) were synthesized by template copolymerization in the presence of poly(allylammonium chloride) (PAAC) as a template in an aqueous medium. These template copolymers exhibited remarkable thickening properties due to the effective hydrophobic association, which were similar to those copolymers with a multiblock structure obtained by the micellar process. The pH of the reaction medium and the molecular weight of the template strongly influenced the thickening properties of the products. In the experimental range, the higher the PEBA content, the larger the thickening capacity of these hydrophobic copolymers. The aggregate behaviors of these copolymers were studied by fluorescence, transmission electron microscopy (TEM), and light scattering techniques. The apparent critical interpolymer aggregate concentration (cac) of the copolymer solution was about 0.5 g/dL. As the concentration of the copolymer became higher than the cac, the aggregates changed their morphology from small hollow spheres to big flower-shaped aggregates. All the above results indicated that the template copolymerization gave access to a very simple and powerful means for the preparation of hydrophobically associating copolymers and other functional polymer materials. 相似文献
44.
Miao Du Zhi‐Hui Zhang Yan‐Ping You 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(9):o574-o576
Co‐crystallization of hemimellitic acid (benzene‐1,2,3‐tricarboxylic acid) dihydrate (H3HMA·2H2O) with 4,4′‐bipyridine (4,4′‐bpy) affords the 1:1 co‐crystal benzene‐1,2,3‐tricarboxylic acid–4,4′‐bipyridine (1/1), H3HMA·4,4′‐bpy or C9H6O6·C10H8N2. Strong O—H⋯O hydrogen bonds connect the acid molecules to form a one‐dimensional zigzag chain, around which the 4,4′‐bpy components are fixed as arms via O—H⋯N interactions, resulting in a ladder motif. Through weak C—H⋯O non‐covalent forces, the resulting acid layers are extended into a three‐dimensional pillar‐layered architecture supported by rod‐like 4,4′‐bpy components. The influence on hydrogen‐bonding models is also discussed, with the discovery of an unexpected interaction motif that does not follow the routine hydrogen‐bonded hierarchical rule in the construction of an acid–base co‐crystal. 相似文献
45.
Shiding Miao Dr. Hugo Leeman Steven De Feyter Prof. Robert A. Schoonheydt Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2461-2469
The Langmuir–Blodgett (L–B) technique has been employed for the construction of hybrid films consisting of three components: surfactant, clay, and lysozyme (Lys). The surfactants are octadecylammonium chloride (ODAH) and octadecyl ester of rhodamine B (RhB18). The clays include saponite and laponite. Surface pressure versus area isotherms indicate that lysozyme is adsorbed by the surfactant–clay L–B film at the air–water interface without phase transition. The UV‐visible spectra of the hybrid film ODAH–saponite–Lys show that the amount of immobilized lysozyme in the hybrid film is (1.3±0.2) ng mm?2. The average surface area (Ω) per molecule of lysozyme is approximately 18.2 nm2 in the saponite layer. For the multilayer film (ODAH–saponite–Lys)n, the average amount of lysozyme per layer is (1.0±0.1) ng mm?2. The amount of lysozyme found in the hybrid films of ODAH–laponite–Lys is at the detection limit of about 0.4 ng mm?2. Attenuated total reflectance (ATR) FTIR spectra give evidence for clay layers, ODAH, lysozyme, and water in the hybrid film. The octadecylammonium cations are partially oxidized to the corresponding carbamate. A weak 1620 cm?1 band of lysozyme in the hybrid films is reminiscent of the presence of lysozyme aggregates. AFM reveals evidence of randomly oriented saponite layers of various sizes and shapes. Individual lysozyme molecules are not resolved, but aggregates of about 20 nm in diameter are clearly seen. Some aggregates are in contact with the clay mineral layers, others are not. These aggregates are aligned in films deposited at a surface pressure of 20 mN m?1. 相似文献
46.
A novel and sensitive electrochemical method for determination of mercury (II) ions (Hg2+) based on the formation of thymine–Hg2+–thymine complexes and gold nanoparticle-mediated signal amplification is reported. Two 5′ end thiolated complementary oligonucleotides containing six strategically placed thymine–thymine mistakes were introduced in this work. One of the two oligonucleotides was immobilized on a gold electrode and the other one on gold nanoparticles (AuNPs). Due to six thymine–thymine mistakes the two oligonucleotides were not able to be hybridized, so AuNPs could not be immobilized onto the electrode surface after the electrode was immersed in the DNA–AuNPs solution. However, if Hg2+ existed, T–Hg2+–T complexes could be formed and AuNPs could be immobilized onto the electrode surface. Meanwhile, large numbers of [Ru(NH3)6]3+ molecules as electrochemical species could be localized onto the electrode surface. The Hg2+ detection limit of this assay could be as low as 10 nM, which is the US Environmental Protection Agency (EPA) limit of Hg2+ for drinkable water. This method is proven to be simple, convenient, high sensitive and selective. 相似文献
47.
Redox Processes Involving Quinones on Poly-3,4-ethylenedioxythiophene-Modified Glassy Carbon Surface
Miao S. Tolstopyatova E. G. Kondratiev V. V. 《Russian Journal of General Chemistry》2019,89(2):266-270
Russian Journal of General Chemistry - Redox transformations involving quinone/hydroquinone redox pair on a glassy carbon electrode (pristine and modified with poly-3,4-ethylenedioxythiophene film)... 相似文献
48.
Health or environmental issue caused by abnormal level of metal ions like Zn2+ or Cd2+ is a worldwide concern. Developing an inexpensive and facile detection method for Zn2+ and Cd2+ is in urgent demand. Due to their super optical properties, fluorescent quantum dots (QDs) have been developed as a promising alternative for organic dyes in fluorescence analysis. In this study, a CdTe QDs-based sensitive and selective probe for Zn2+ and Cd2+ in aqueous media was reported. The proposed probe worked in fluorescence “turn-on” mode. The initial bright fluorescence of CdTe QDs was effectively quenched by sulfur anions (S2−). The presence of Zn2+ (or Cd2+) can “turn-on” the weak fluorescence of QDs quenched by S2− due to the formation of ZnS (or CdS) passivation shell. Under optimal conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ (or Cd2+) could be obtained in the range from 1.6 to 35 μM (1.3–25 μM for Cd2+). The limit of detection (LOD) for Zn2+ and Cd2+ were found to be 1.2 and 0.5 μM, respectively. Furthermore, the present probe exhibited a high selectivity for Zn2+ and Cd2+ over other metal ions and was successfully used in the detection of Zn2+ or Cd2+ in real water samples. 相似文献
49.
An enantioselective Biginelli reaction has been developed by using a bifunctional primary amine-thiourea-TfOH (BPAT·TfOH) as a chiral phase-transfer catalyst and t-BuNH(2)·TFA as an additive in saturated brine at room temperature. The corresponding dihydropyrimidines were obtained in moderate-to-good yields with up to 99% ee under mild conditions. A plausible transition state has been proposed to explain the origin of the activation and the asymmetric induction. 相似文献
50.
Bin Wang Zhi-Wei Miao Ru-Yu Chen 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2739-2748
A series of naphthoquinone-fused phosphorus heterocycles was synthesized via a three-component Mannich-type reaction. 2-Chloroethoxylphosphorodichloridite was used as a phosphorus substrate to explore the structure–activity relationships of the 2-position of the heterocycles. One spiral heterocycle compound was structurally characterized by a single-crystal X-ray diffraction analysis. 相似文献