全文获取类型
收费全文 | 3563篇 |
免费 | 345篇 |
国内免费 | 368篇 |
专业分类
化学 | 2513篇 |
晶体学 | 44篇 |
力学 | 222篇 |
综合类 | 37篇 |
数学 | 434篇 |
物理学 | 1026篇 |
出版年
2024年 | 5篇 |
2023年 | 55篇 |
2022年 | 101篇 |
2021年 | 113篇 |
2020年 | 121篇 |
2019年 | 132篇 |
2018年 | 111篇 |
2017年 | 90篇 |
2016年 | 128篇 |
2015年 | 133篇 |
2014年 | 174篇 |
2013年 | 230篇 |
2012年 | 256篇 |
2011年 | 290篇 |
2010年 | 206篇 |
2009年 | 169篇 |
2008年 | 211篇 |
2007年 | 219篇 |
2006年 | 203篇 |
2005年 | 183篇 |
2004年 | 106篇 |
2003年 | 98篇 |
2002年 | 123篇 |
2001年 | 91篇 |
2000年 | 60篇 |
1999年 | 54篇 |
1998年 | 65篇 |
1997年 | 57篇 |
1996年 | 68篇 |
1995年 | 61篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 51篇 |
1991年 | 30篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 23篇 |
1987年 | 19篇 |
1986年 | 13篇 |
1985年 | 16篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1975年 | 3篇 |
1961年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4276条查询结果,搜索用时 0 毫秒
71.
叙述了CAHN-2000磁天平(美国)调试过程中如何解决液氮温区的测试,自制了磁天平与计算机的接口,编写了数据采集、处理和控制等高原 软件,节省了几万美元,部分指标超过原配套水平,三年来仪器在对国同外开放过程中,液氮温区的工作一直正常,实测了上千个样品,提供的数据已撰写数十篇文章在国内外刊物上发表。由此说明,要充分发挥进口仪器的使用效率,必须对仪器的工作原理、结构特点有透乇的了解,同时要有相当的自 相似文献
72.
Cotton FA Liu CY Murillo CA Villagrán D Wang X 《Journal of the American Chemical Society》2003,125(44):13564-13575
Reactions of Mo(2)(O(2)CCH(3))(DAniF)(3), DAniF = N,N'-di-p-anisylformamidinate, with oxamidate dianions [ArNC(O)C(O)NAr](2-), Ar = C(6)H(5) and p-anisyl, give pairs of isomeric compounds where the [Mo(2)] units are bridged by the oxamidate anions. For the alpha isomers, the C-C unit of the dianion is nearly perpendicular to the Mo-Mo bonds, and these are essentially perpendicular to each other. For the beta isomers, the corresponding C-C unit and the Mo-Mo bonds are essentially parallel to each other. Each type of isomer is stable in solution. The electronic communication as measured by the DeltaE(1/2) for the oxidation of each of the Mo(2) units is significantly better for the beta isomers. This is supported also by the appearance of what is conventionally called an intervalence charge-transfer band in the near infrared region upon oxidation of the beta isomers but not the alpha isomers. Molecular mechanics and DFT calculations help explain the relative conformations in the alpha isomers and the relative energy differences between the alpha and beta isomers. 相似文献
73.
In this paper, pressurized CEC was used for the separation and determination of seven fluoroquinolones (FQs). The effect of different experimental conditions, such as the concentration and pH of the buffer, the organic modifier concentration, the surfactant and ion-paring agents added to the electrolyte, and applied voltage were studied. All the seven FQs were baseline separated using mobile phase containing 27% v/v ACN, 5 mmol/L Na2HPO4 buffer (pH 4.0 adjusted using citric acid), 11 mmol/L SDS, and 0.01% TEA v/v at detection wavelength of 287 nm and at an applied voltage of -10 kV. The calibration curves were linear (r>0.9991) over a concentration range of 1.0-50.0 mg/L for norfloxacin (NFLX); 2.5-50.0 mg/L for fleroxacin (FLX), ciprofloxacin (CPFX), and lomefloxacin (LMX); and 5.0-50.0 mg/L for enoxacin (ENX), ofloxacin (OFLX), and gatifloxacin (GFLX). The detection limits (S/N = 3) for ENX, OFLX, FLX, NFLX, CPFX, LMX, and GFLX were 0.5, 0.8, 0.4, 0.2, 0.4, 0.5, and 1.0 mg/L, respectively. The method is simple, rapid, and reproducible. It was successfully applied to the analysis of fish muscle samples spiked with FQs. Mean recoveries ranged from 81.6 to 97.6%. 相似文献
74.
Chuqiao Tu Kazimierz Surowiec Richard A. Bartsch 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(3-4):361-366
A di-ionizable p-tert-butylcalix[4]arene-1,3-thiacrown-5 ether extractant was synthesized. Its cone conformation and polyether ring attachment
regioselectivity were verified by NMR spectroscopy. The metal ion-complexing properties of this ligand were evaluated by solvent
extractions of metal cations from aqueous solutions into chloroform. The ligand was found to be an efficient extractant with
Ba2+ selectivity in competitive solvent extraction of alkaline earth metal cations. It also exhibits high extraction ability for
Pb2+ and for Hg2+ in single species solvent extractions. 相似文献
75.
Two compounds of a new type, [Mo(2)](CH(3)O)(2)M(CH(3)O)(2)[Mo(2)] where [Mo(2)] is an abbreviation for Mo(2)[(p-MeOC(6)H(4))NCHN(p-MeOC(6)H(4))](3) and M = Zn (1) and Co (2), are reported. Discrete [M(OR)(4)](2-) ions, either as such or in the mu(2),eta(4) role, have not heretofore been described. In these compounds they have distorted tetrahedral structures and bridge two [Mo(2)] groups in much the same way as did SO(4)(2-), MoO(4)(2-), and WO(4)(2-) ions in other recently reported compounds (Cotton, F. A.; Donahue, J. P.; Murillo, C. A. Inorg. Chem. 2001, 40, 2229). The (1)H NMR spectrum of 1 and the visible spectrum and magnetic properties of 2 are consistent with these structures. The M(OCH(3))(4) bridges are moderately effective in coupling the two [Mo(2)] redox centers. Compounds 1 and 2 may also be viewed as having Zn(II) and Co(II) centers tetrahedrally coordinated by the bidentate ligand [Mo(2)[(p-MeOC(6)H(4))NCHN(p-MeOC(6)H(4))](3)(OMe)(2)](-). From that point of view they may be compared with Zn(DPM)(2) and Co(DPM)(2) (3), where DPM is the anion of dipivaloylmethane. For purposes of comparison, 3 has been fully characterized structurally, spectroscopically, and magnetically. Close analogies between 2 and 3 are shown to exist. 相似文献
76.
A series of 1,4‐diarylquinoline derivatives were synthesized by the reaction of arylmethylidenemalononitriles or 2‐cyano‐3‐aryl‐1‐acrylate and 3‐arylamino‐5,5‐dimethylcyclohex‐2‐enone in aqueous media at 100 °C catalyzed by TEBAC. Meanwhile, the water medium was chosen as green solvent. 相似文献
77.
New quaternary intermetallic phases REMGa(3)Ge (1) (RE = Y, Sm, Tb, Gd, Er, Tm; M = Ni, Co) and RE(3)Ni(3)Ga(8)Ge(3) (2) (RE = Sm, Gd) were obtained from exploratory reactions involving rare-earth elements (RE), transition metal (M), Ge, and excess liquid Ga the reactive solvent. The crystal structures were solved with single-crystal X-ray and electron diffraction. The crystals of 1 and 2 are tetragonal. Single-crystal X-ray data: YNiGa(3)Ge, a = 4.1748(10) A, c = 23.710(8) A, V = 413.24(2) A(3), I4/mmm, Z = 4; Gd(3)Ni(3)Ga(8)Ge(3), a = 4.1809(18) A, c = 17.035(11) A, V = 297.8(3) A(3), P4/mmm, Z = 1. Both compounds feature square nets of Ga atoms. The distribution of Ga and Ge atoms in the REMGa(3)Ge was determined with neutron diffraction. The neutron experiments revealed that in 1 the Ge atoms are specifically located at the 4e crystallographic site, while Ga atoms are at 4d and 8g. The crystal structures of these compounds are related and could be derived from the consecutive stacking of disordered [MGa](2) puckered layers, monatomic RE-Ge planes and [MGa(4)Ge(2)] slabs. Complex superstructures with modulations occurring in the ab-plane and believed to be associated with the square nets of Ga atoms were found by electron diffraction. The magnetic measurements show antiferromagnetic ordering of the moments located on the RE atoms at low temperature, and Curie-Weiss behavior at higher temperatures with the values of mu(eff) close to those expected for RE(3+) free ions. 相似文献
78.
屠树江   朱晓彤   房芳   章晓镜   朱松磊   李团结   史达清 王香善   纪顺俊 《中国化学》2005,23(5):596-598
A simple effective synthesis of bis(dihydropyrimidinone-4-yl)benzene derivatives, using boric acid as catalyst,from isophthalic aldehyde or terephthalic aldehyde, 1,3-dicarbonyl compounds and urea or thiourea in glacial acetic acid was described. As the expansion of the classical Biginelli reaction, this method has the advantage of excellent yields 83%-94% and short reaction time 0.5-1.5 h. 相似文献
79.
One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF6 was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated. 相似文献
80.