全文获取类型
收费全文 | 4659篇 |
免费 | 606篇 |
国内免费 | 423篇 |
专业分类
化学 | 2316篇 |
晶体学 | 33篇 |
力学 | 258篇 |
综合类 | 12篇 |
数学 | 333篇 |
物理学 | 1232篇 |
综合类 | 1504篇 |
出版年
2024年 | 25篇 |
2023年 | 102篇 |
2022年 | 169篇 |
2021年 | 201篇 |
2020年 | 188篇 |
2019年 | 156篇 |
2018年 | 154篇 |
2017年 | 145篇 |
2016年 | 211篇 |
2015年 | 206篇 |
2014年 | 250篇 |
2013年 | 283篇 |
2012年 | 388篇 |
2011年 | 394篇 |
2010年 | 258篇 |
2009年 | 235篇 |
2008年 | 248篇 |
2007年 | 260篇 |
2006年 | 222篇 |
2005年 | 186篇 |
2004年 | 152篇 |
2003年 | 132篇 |
2002年 | 102篇 |
2001年 | 77篇 |
2000年 | 80篇 |
1999年 | 103篇 |
1998年 | 95篇 |
1997年 | 105篇 |
1996年 | 112篇 |
1995年 | 69篇 |
1994年 | 69篇 |
1993年 | 64篇 |
1992年 | 57篇 |
1991年 | 42篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 26篇 |
1987年 | 9篇 |
1986年 | 20篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1957年 | 2篇 |
排序方式: 共有5688条查询结果,搜索用时 15 毫秒
51.
Wenxuan Jiang Wei Wei Tinglian Yuan Shasha Liu Ben Niu Hui Wang Wei Wang 《Chemical science》2021,12(24):8556
The inevitable microstructural defects, including cracks, grain boundaries and cavities, make a portion of the material inaccessible to electrons and ions, becoming the incentives for electrochemically inactive zones in single entity. Herein, we introduced dark field microscopy to study the variation of scattering spectrum and optical mass centroid (OMC) of single Prussian blue nanoparticles during electrochemical reaction. The “dark zone” embedded in a single electroactive nanoparticle resulted in the incomplete reaction, and consequently led to the misalignment of OMC for different electrochemical intermediate states. We further revealed the dark zones such as lattice defects in the same entity, which were externally manifested as the fixed pathway for OMC for the migration of potassium ions. This method opens up enormous potentiality to optically access the heterogeneous intraparticle dark zones, with implications for evaluating the crystallinity and electrochemical recyclability of single electroactive nano-objects.The schematic of single cubic-shaped Prussian blue (PB) mesocrystals formed by the oriented aggregation of small nanocrystals. The dark-field images of single PB nanoparticle at PB and Prussian white (PW) states, respectively. 相似文献
52.
Zhenbin Niu Xingyuan Zhang Jiabing Dai Heping Zhang 《Frontiers of Chemistry in China》2007,2(2):151-155
A new kind of ultraviolet (UV) curable waterborne polyurethane acrylate dispersion was synthesized based on hydroxyl-terminated
polybutadiene (HTPB), poly-(propylene glycol) (PPG), isophorene diisocyanate (IPDI), 2-hydroxy ethyl acrylate (HEA) and dimethylol
propionic acid (DMPA) after neutralizing by triethylamine (TEA). 2-Hydroxy-1-[4-2-hydroxyethoxy) phenyl]-2-methyl-1-propanone
(Irgacure 2959) was used as a photoinitiator and deionized water as a diluent. Fourier transform infrared (FTIR) analysis
was used to identify the chain structure of the UV-curable polyurethane prepolymer based on HTPB and the curing process. Effects
of relative content of HTPB and PPG on emulsion stability, resistance to water and ethanol, thermal stability, compatibility
of soft and hard segment, as well as the mechanical property of the cured film were investigated.
Translated from Polymer Materials Science and Engineering, 2006, 22(3): 199–203 (in Chinese) 相似文献
53.
本文将用放射性磷32标记法测得的二(2-乙基己基)磷酸在碱金属氯化物水溶液(LiCl、NaCl、KCl、RbCl、CsCl和NH_4Cl)中的溶解度数据~[1], 分别用Pitzer(1973年)方程和Pitzer-Li(1983年)方程进行活度系数的关联. 计算结果表明, 由于Pitzer-Li方程考虑了溶质-溶剂间的短程作用能, 所得参数更能反映盐效应的本质, 故优于Pitzer方程. 同时还表明, 上述体系中离子-水之间的作用能远大于离子-有机化合物之间的作用能。 相似文献
54.
Yan-Ping Liu Li-Li Sun Xiang-Lin Zhang Hai-Yuan Niu Zheng-Hong Pan 《Natural product research》2020,34(16):2295-2300
Abstract A phytochemical investigation on the stems of Mappianthus iodoides led to the isolation of a new naturally occurring prenylated isoflavone, mappianthone A (1), together with seven known analogues (2?8). The structure of 1 was elucidated by extensive spectroscopic methods and the known compounds were identified by comparison with data reported in the literature. All isolated compounds were evaluated for their antiproliferative activities against five human cancer cell lines: HL-60, SMMC-7721, A-549, MCF-7 and SW480 in vitro. Compounds 1?8 showed significant antiproliferative effects against several human cancer cell lines with IC50 values ranging from 0.16 to 12.68?μM. 相似文献
55.
累托石/聚丙烯插层纳米复合材料的制备与性能 总被引:19,自引:0,他引:19
采用熔融共混法制备了有机改性累托石 (OREC)粘土 均聚聚丙烯 (PP)纳米复合材料 ,以X 射线衍射分析 (XRD)及透射电子显微镜分析 (TEM)观察了复合材料的相貌结构 ,研究了复合材料的力学性能及热性能 .结果表明 ,OREC在添加份数较少时可与均聚聚丙烯熔融插层形成插层型聚丙烯纳米复合材料 ,该复合材料与纯PP相比 ,具有较高的拉伸强度、断裂伸长率及冲击强度 .在有机粘土添加 2 %时 ,复合材料的拉伸强度、断裂伸长率、冲击强度最高 ,与纯PP相比 ,2 %添加量的聚丙烯纳米复合材料拉伸强度提高 6 5 7% ,断裂伸长率提高 2 89 3% ,冲击强度提高 14 1% ,10 %失重率时对应的热分解温度提高 50K . 相似文献
56.
The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10–56.0×10–4molL–1 and 5.0×10–6 2.0×10–4molL–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10–7 and 1.3×10–7molL–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results. 相似文献
57.
Ruojie Tao Shuangquan Zang Chongzhen Mei Qinglun Wang Benyong Lou Jingyang Niu Yanxiang Cheng Daizheng Liao 《Journal of Cluster Science》2003,14(4):459-469
Two heterometallic trinuclear complexes {[Cu(oxbp)]2Co(H2O)2}1.5DMF0.5H2O (complex 1) and {[Cu(oxbm)]2Co(H2O)2}2DMF (complex 2) were obtained from the self-organization of two new dissymmetrical oxamidato-bridged copper(II) building blocks [Cu(oxbp)]– and [Cu(oxbm)]–[H3oxbp=N-benzoato-N'-(3-aminopropyl)oxamido, H3oxbm=N-benzoato-N'-(2-amino-2-methylethyl)oxamido, DMF=dimethylformamide]. The crystal structure of complex 1 has been determined. Complex 1 crystallize in triclinic system, space group P-1, a=8.0609(16) Å, b=10.661(2) Å, c=22.279(5) Å, =85.32(3), =86.64(3), =70.90(3), and Z=1. The crystal structure of complex 1 consists of neutral trinuclear complex units, and hydrogen bond involved DMF and water molecules. Through the hydrogen bonds, weak coordination and CuCu weak interactions, complex 1 features a 2-D supramolecular structure. Magnetic susceptibility measurements (5–100 K) indicate that the central Co(II) and terminal copper metal ions are antiferromagnetically coupled with J=–28.09 and J=–29.70 cm–1 for complex 1 and 2, respectively. 相似文献
58.
Chen Z Heine T Jiao H Hirsch A Thiel W Schleyer Pv 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(4):963-970
Hybrid B3LYP and density-functional-based tight-binding (DFTB) computations on the solid-state structures and electronic properties of the C(20) fullerene monomer and oligomers are reported. C(20) cages with C(2), C(2h), C(i), D(3d), and D(2h) symmetries have similar energies and geometries. Release of the very high C(20) strain is, in theory, responsible for the ready oligomerization and the formation of different solid phases. Open [2+2] bonding is preferred both in the oligomers and in the infinite one-dimensional solids; the latter may exhibit metallic character. Two types of three-dimensional solids, the open [2+2] simple cubic and the body-centered cubic (bcc) forms, are proposed. The energy of the latter is lower due to the better oligomer bonding. The open [2+2] simple cubic solid should be a conductor, whereas the bcc solids are insulators. The most stable three-dimensional solid-state structure, an anisotropically compressed form of the bcc solid, has a HOMO-LUMO gap of approximately 2 eV and a larger binding energy than that of the proposed C(36) solid. 相似文献
59.
T. Nakamura S. Kojima T. Ohta M. Nishida A. Rakowski A. Ikeda H. Oda E. Niu 《Journal of Radioanalytical and Nuclear Chemistry》2007,273(2):327-332
14C variations of atmospheric CO2 as well as carbonaceous fraction of living materials, such as collagen from tooth and bone, tissue, skin, hair, nail, etc.,
of modern humans are influenced by 14C produced artificially by nuclear bomb tests in the atmosphere from late 1950s to early 1960s. By careful investigation of
14C concentration of tree rings and human body samples formed in this time intervals, we can establish a relationship of their
14C concentrations with calendar year. By applying this relation to a sample whose 14C concentration can be measured, we can estimate the formation age of the sample. In addition, sources of the chemicals that
were used in some criminal cases can be possibly identified, by their carbon isotope ratios (13C/12C and 14C/12C). This method of age determination has been applied to a forensic study, i.e., two criminal cases of murder. For each case,
by comparing the measured 14C abundances of several pieces of hair and one tooth (the third molar) from the body with the annual change on concentrations
of bomb-produced 14C, the time of death of the body and the age of the victim were estimated. The estimated values were consistent with the real
ones that were revealed by the confession of the real murderers. 相似文献
60.
Three novel Schiff base cadmium(II) complexes, derived from the end‐on (μ‐1,1‐N3) azide or end‐to‐end (μ‐1,3‐NCS) thio cyanate bridges and similar tridentate Schiff base ligands, have been synthesized under similar synthetic procedures and their crystal structures determined by X‐ray diffraction methods. They are the dinuclear double end‐on azide‐bridged [Cd2(L1)2(N3)2(μ‐1,1‐N3)2] ( 1 ), the dinuclear double end‐on azide‐bridged [Cd2(L2)2(N3)2(μ‐1,1‐N3)2] ( 2 ), and the dinuclear double end‐to‐end thiocyanate‐bridged [Cd2(L3)2(NCS)2(μ1,3‐NCS)2] ( 3 ), where L1, L2 and L3 are three similar tridentate Schiff bases obtained by condensation of 2‐pyridylaldehyde with N,N‐diethylethane‐1,2‐diamine, of 2‐pyridylaldehyde with N‐isopropylethane‐1,2‐diamine, and of 2‐pyridylaldehyde with N,N‐dimethylpropane‐1,3‐diamine, respectively. Each cadmium(II) centre in the complexes is in a distorted octahedral coordination. There is a crystallographic inversion centre in each of the complexes. The similar small ligands used as the secondary ligands in the preparation of the cadmium(II) complexes with similar Schiff bases can result in similar structures. 相似文献