全文获取类型
收费全文 | 13328篇 |
免费 | 1977篇 |
国内免费 | 1582篇 |
专业分类
化学 | 8989篇 |
晶体学 | 199篇 |
力学 | 811篇 |
综合类 | 151篇 |
数学 | 1907篇 |
物理学 | 4830篇 |
出版年
2024年 | 37篇 |
2023年 | 218篇 |
2022年 | 387篇 |
2021年 | 398篇 |
2020年 | 540篇 |
2019年 | 504篇 |
2018年 | 483篇 |
2017年 | 455篇 |
2016年 | 622篇 |
2015年 | 729篇 |
2014年 | 784篇 |
2013年 | 1087篇 |
2012年 | 1196篇 |
2011年 | 1202篇 |
2010年 | 898篇 |
2009年 | 869篇 |
2008年 | 932篇 |
2007年 | 809篇 |
2006年 | 694篇 |
2005年 | 591篇 |
2004年 | 432篇 |
2003年 | 349篇 |
2002年 | 361篇 |
2001年 | 244篇 |
2000年 | 249篇 |
1999年 | 178篇 |
1998年 | 111篇 |
1997年 | 107篇 |
1996年 | 98篇 |
1995年 | 91篇 |
1994年 | 76篇 |
1993年 | 74篇 |
1992年 | 54篇 |
1991年 | 52篇 |
1990年 | 53篇 |
1989年 | 40篇 |
1988年 | 60篇 |
1987年 | 28篇 |
1986年 | 40篇 |
1985年 | 38篇 |
1983年 | 32篇 |
1982年 | 34篇 |
1980年 | 39篇 |
1979年 | 35篇 |
1978年 | 52篇 |
1977年 | 41篇 |
1976年 | 44篇 |
1975年 | 35篇 |
1974年 | 34篇 |
1968年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
941.
Romana Krištof Suzana Košenina Benjamin Zorko Jasmina Kožar Logar 《Journal of Radioanalytical and Nuclear Chemistry》2017,314(2):675-679
The aim of the research was to obtain first results of tritium in the organic matter of environmental samples in the vicinity of Kr?ko NPP. The emphasis was on the layout of suitable sampling network of crops and fruits in nearby agricultural area. Method for determination of tritium in organic matter in the form of Tissue Free Water Tritium (TFWT) and Organically Bound Tritium (OBT) has been implemented. Capabilities of the methods were tested on real environmental samples and its findings were compared to modeled activities of tritium from atmospheric releases and literature based results of TFWT and OBT. 相似文献
942.
943.
944.
This study has investigated the migration of stabilizers from three polypropylene materials: a polypropylene homopolymer, a polypropylene block copolymer, and a polypropylene random copolymer in 10% ethanol, 3% acetic acid, 20% ethanol, 50% ethanol, and isooctane according to Regulation (EU) No. 10/2011. Measurements were performed at 20, 40, and 70°C and migration was evaluated from 10?min to 10 days. Measurements were performed by high-performance liquid chromatography (HPLC) with external calibration. The HPLC method provided high correlation coefficients, good precision, good accuracy, and suitable reproducibility. Diffusion coefficients for stabilizers were obtained using a rigorous model based on Fick’s second law and the values were between 6.1?×?10?13 and 3.8?×?10?9?cm2?s?1. By applying an Arrhenius-type equation to the diffusion coefficients, an estimation of activation energy of the diffusion was obtained. The activation energies were from 39.97 to 98.75?kJ?mol?1 for the stabilizers. The results indicate that the polypropylene material structure influenced the migration rate, which decreased in the order of the increasing crystallinity in the materials. The diffusion coefficients for stabilizers in the polypropylene random copolymer were higher than in the polypropylene block copolymer and polypropylene homopolymer. The random polypropylene copolymer had the lowest activation energy. These results show that a higher diffusion coefficient indicates a higher migration rate, and a system with a lower activation energy allows more migration. 相似文献
945.
Linkui Bai Linxiang Cai Qinghua Liu Yunxu Qian Bo Yang 《Journal of Coordination Chemistry》2017,70(22):3759-3768
A series of novel dinuclear platinum(II) complexes with a chiral tetradentate ligand, (1R,1′R,2R,2′R)-N1,N1′-(1,2-phenylenebis(methylene))dicyclohexane-1,2-diamine (HL), and mono-carboxylic acid derivatives as ligands have been designed, synthesized, and characterized. In vitro cytotoxicity evaluation of synthesized complexes against human HepG-2, A549, HCT-116, and MCF-7 cancer cell lines has been conducted by MTT assays. All compounds showed antitumor activity to HepG-2 and HCT-116 cell lines. Compound L2 exhibited better cytotoxicity than that of carboplatin against HepG-2 and A549 cell lines and also showed comparable activity against HCT-116 cell line. 相似文献
946.
Atisane‐type diterpenoids are the principal constituent of tetracyclic C20‐diterpenoids, widely isolated from the plant kingdom with varying degrees of structural complexity and pharmacological activity. The tetracarbocyclic system with the unique bicyclo[2.2.2]octane skeleton of this natural product family has generated interest within the synthetic community. Divergent total synthesis is an effective tactic to synthesize several atisane‐type diterpenoids using structural interconversion from a common intermediate. This account summarizes the divergent total synthesis of atisane‐type diterpenoids. 相似文献
947.
Roman Boča 《Theoretical chemistry accounts》1982,61(2):179-192
The perturbative configuration interaction using localized orbitals (the PCILO method) was extended in the way that current limitations to the two-centre bond approach were overcome. The localized molecular orbitals contain an arbitrary number of the basis set components; this follows from the a priori stated localized bonding model of a molecule. The extended PCILO method was formulated for the CNDO, INDO and NDDO Hamiltonian approximations. The configuration interaction was performed using the Rayleigh-Schrödinger many-body perturbation theory with the Møller-Plesset type of Hamiltonian partitioning, similar to that used in the so-called modified PCILO method. Applications to molecules with semi-localized and/or semi-delocalized bonds, as benzene or diborane, are presented. 相似文献
948.
The paper presents the results of a study of M
2
I
M
II(SO4)2 compounds withM
I= K, Rb, Cs or Tl, andM
II=Cu or Ni, in the interval from room temperature to the melting temperature. All the compounds studied show endo- or exothermic excursions in their DTA curves, corresponding to phase transitions connected with colour changes of the compounds. For M
2
I
Cu(SO4)2, whereM
I is K or Tl, several modifications could be prepared at laboratory temperature, probably distortion isomers. No modifications of this type could be prepared, however, for M
2
I
Ni(SO4)2 compounds.
Zusammenfassung Die Ergebnisse einer Untersuchung von M 2 I M II(SO4)2-Verbindungen Cs, Tl;M II=Cu, Ni) im Temperaturbereich von Raum- bis Schmelztemperatur werden beschrieben. Alle untersuchten Verbindungen zeigen in ihren DTA-Kurven mit Farbänderungen einhergehende, durch Phasenumwandlungen bedingte endo- und exotherme Peaks. Bei Laboratoriumstemperatur konnten verschiedene Modifikationen von M 2 I Cu(SO4)2 (mitM I gleich K oder Tl) hergestellt werden, wobei es sich wahrscheinlich um Distorsionsisomere handelt. Keine Modifikationen dieses Typs konnten jedoch für M 2 I Ni(SO4)2 erhalten werden.
M 2 I M II(SO4)2, 1-, Rb, Cs Tl, aM 11-Cu Ni, . - -, , . M 2 I Cu(SO4)2, 1- l, , , , . , M i 2 Ni(SO4)2 .相似文献
949.
Summary A comparison of three binary mobile phases in LC separation of C60 and C70 fullerences on chemically bonded 2,4-dinitroanilinopropyl (DNAP) stationary phase was carried out, n-Hexane-benzene has been found to be the best mobile phase for efficient separation of the all-carbon molecules permitting high loads in preparative LC. 相似文献
950.
用X射线衍射、X射线光电子能谱、俄歇电子能谱和扫描电子显微术等考察了石墨炉升温过程中Sr(NO3)2在石墨探针表面上的形态变化,阐明了它的原子化机理.加热过程中Sr(NO3)2首先分解为SrO(s),再还原为SrC2,后者进一步分解为Sr(s).锶的原子化源于金属蒸发. 相似文献