全文获取类型
收费全文 | 2795篇 |
免费 | 84篇 |
国内免费 | 12篇 |
专业分类
化学 | 2117篇 |
晶体学 | 28篇 |
力学 | 40篇 |
数学 | 154篇 |
物理学 | 552篇 |
出版年
2022年 | 30篇 |
2021年 | 22篇 |
2020年 | 39篇 |
2019年 | 47篇 |
2018年 | 32篇 |
2017年 | 19篇 |
2016年 | 48篇 |
2015年 | 34篇 |
2014年 | 51篇 |
2013年 | 113篇 |
2012年 | 119篇 |
2011年 | 161篇 |
2010年 | 73篇 |
2009年 | 88篇 |
2008年 | 148篇 |
2007年 | 146篇 |
2006年 | 156篇 |
2005年 | 143篇 |
2004年 | 119篇 |
2003年 | 96篇 |
2002年 | 83篇 |
2001年 | 67篇 |
2000年 | 52篇 |
1999年 | 46篇 |
1998年 | 30篇 |
1997年 | 34篇 |
1996年 | 48篇 |
1995年 | 37篇 |
1994年 | 25篇 |
1993年 | 34篇 |
1992年 | 46篇 |
1991年 | 29篇 |
1990年 | 32篇 |
1989年 | 35篇 |
1988年 | 41篇 |
1987年 | 34篇 |
1986年 | 29篇 |
1985年 | 63篇 |
1984年 | 37篇 |
1983年 | 30篇 |
1982年 | 33篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 40篇 |
1978年 | 33篇 |
1977年 | 28篇 |
1976年 | 22篇 |
1975年 | 24篇 |
1974年 | 27篇 |
1973年 | 25篇 |
排序方式: 共有2891条查询结果,搜索用时 15 毫秒
31.
Thermal nitrogen extrusion of 2-methylene-6,7-diazabicyclo[3.2.2]non-6-enes and 6,7- diazabicyclo[3.2.2]nona-2,6-diene,6 proceeded easily to give closure and cleavage products the corresponding 5-methylene-1,4-cycloheptylenes and 4-cyclohepten-1,3-ylenes, respectively. 相似文献
32.
Masao Kato Hiroyoshi Kamogawa 《Journal of polymer science. Part A, Polymer chemistry》1966,4(7):1773-1782
The polymerization behavior of o-hydroxystyrene with free-radical and cationic initiators and without an initiator was examined. The structures thus obtained were estimated. Although polymerization behavior of o-hydroxystyrene was rather complicated, according to the results, it appeared that each polymerization more or less might simultaneously follow the two types of mechanisms: normal vinyl polymerization and polymerization through the addition to benzene nuclei. The proportion of addition to benzene nuclei was considered to be highest in the polymerization with BF3·(OEt)2 and lowest in that with azobisisobutyronitrile. Degrees of polymerization of these polymers were low in all cases (42–82). Some brief experiments on copolymerization of o-hydroxystyrene were carried out. 相似文献
33.
Junko Kuwahara Hideo Akisada Tamaki Kato Norikazu Nishino 《Colloid and polymer science》2005,283(7):747-752
A series of peptides containing various hydrophobic amino acids [methionine (Met), leucine (Leu), norleucine (Nle), phenylalanine (Phe), 2-aminooctanoic acid (Aoc), and 2-aminodecanoic acid (Ade)] were synthesized and their conformations were studied using circular dichroism (CD) spectroscopy in different solvents such as water, methanol, and aqueous solution of ammonium tetradecanesulfonate. Peptides containing hydrophobic amino acids with linear side chains formed -sheets in water and methanol. Electrostatic interaction between the charged side chain (lysine) and a micelle consisting of an anionic surfactant, ammonium tetradecanesulfonate, is necessary for the formation of -helices in micellar environments. The conformational transition from -helix to -sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration. 相似文献
34.
A new entry for the synthesis of 3-alkyl substituted 5-vinyloxazolidin-2-one derivatives 2 from cis-2-butenylene-1,4-dicarbonate 1 and primary amines mediated by palladium-phosphine catalysts is described. The scope and limitation, a plausible mechanism, and an asymmetric version of the reaction are also discussed. 相似文献
35.
A nondestructive photon activation procedure with 30 MeV bremsstrahlung followed by high-resolution gamma-spectrometry has
been applied to the multielement determination in tobacco leaves and commercial cigarettes. The elements determined by this
method included essential minor elements such as Ca, Cl, K and Mg, essential trace elements such as Fe, Mn and Zn, and possibly
toxic elements such As and Sb. The NBS Orchard Leaves could successfully be used as a comparative standard. The method is
quite simple and gives good reproducible results for at least 12 elements. 相似文献
36.
The solvent extraction of copper(II) with trimethylacetic acid using benzene and 1-octanol as solvents was performed at 25 degrees C and 0.1 mole. dm(-3) ionic strength in the aqueous phase. In contrast to the extraction of copper(II) with a saturated straight-chain carboxylic acid in benzene, the dimeric copper(II) trimethylacetate was observed to dissociate into the monomer, even at a moderately high concentration of copper(II) in the benzene phase. In the system using 1-octanol as a solvent, both the monomeric and dimeric copper(II) species are suggested to be solvated by some 1-octanol molecules. It has been found that the dimerization and adduct formation of copper(II) species in benzene may more effectively enhance the extractability of copper(II) than the solvation by 1-octanol molecules. 相似文献
37.
A method for the enantiomeric determination of 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxy chroman (LLU-alpha, gamma-CEHC) in rat plasma was developed using high-performance liquid chromatography (HPLC) with a fluorimetric derivatization with 4-N, N-dimethylaminosulfonyl-7-piperazino-2,1,3-benzoxadiazole (DBD-PZ) followed by O-acetylation with acetyl chloride. The proposed HPLC system used two non-chiral columns (phenyl and octadecylsilica) and a chiral column (a modified cellulose type), which were connected via two column-switching valves. A derivatized sample prepared from rat plasma was first separated on the phenyl column, and the fraction including LLU-alpha derivative was introduced to the octadecylsilica column to quantify the concentration of the mixture of S- and R-LLU-alpha. Finally, the LLU-alpha derivative was directly injected into the chiral column to obtain the ratio of the enantiomers. The proposed HPLC system was applied to the enantiomeric determination of LLU-alpha in plasma after intravenous administration of racemic LLU-alpha. S-LLU-alpha was eliminated faster than R-LLU-alpha, and its concentration in plasma decreased to one-third at 2 min after dosing. 相似文献
38.
Yoshio Kato Katsuo Komiya Yuuzi Sawada Hiroo Sasaki Tsutomu Hashimoto 《Journal of chromatography. A》1980,190(2)
The purification of enzymes was investigated by high-speed gel filtration on TSK-GEL G3000SWG columns packed with porous silica gel deactivated by chemically bonded hydrophilic compounds. Crude β-galactosidase from bacterial cells and commercial urease were purified ca. 15-fold in a single gel filtration. These enzymes were eluted within an hour from the column and the recoveries of enzymatic activity were almost 100% although the operation was carried out at room temperature (22°). Samples up to 100 mg could be applied to the column without loss of separation efficiency. 相似文献
39.
Electron-phonon interactions in the photoinduced excited electronic states in molecular systems such as phenanthrene-edge-type hydrocarbons are discussed and compared with those in the monoanions and cations. The complete phase patterns difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) (the atomic orbitals between two neighboring carbon atoms combined in phase (out of phase) in the HOMO are combined out of phase (in phase) in the LUMO) are the main reason that the C-C stretching modes around 1500 cm(-1) afford much larger electron-phonon coupling constants in the excited electronic states than in the charged electronic states. The frequencies of the vibrational modes that play an essential role in the electron-phonon interactions for the excited electronic states are similar to those for the monoanions and cations in phenanthrene-edge-type hydrocarbons. Possible electron pairing and Bose-Einstein condensation in the photoinduced excited electronic states as well as those in the monoanions and cations in molecular systems such as phenanthrene-edge-type hydrocarbons are also discussed. 相似文献
40.
S Sakurai K Mitani S Hashimoto K Morikawa S Yasuda E Koshinaka H Kato Y Ito 《Chemical & pharmaceutical bulletin》1992,40(6):1443-1451
To find a novel alpha-blocker with high alpha-blocking selectivity against dopamine D2-receptor affinity, we performed structural modification of the alkylene chains and the substituents on two benzene rings of 2-alkoxy-5-[(phenoxyalkylamino)alkyl]benzenesulfonamide derivatives. The modification of the alkylene chain between the amino moiety in the center of the molecule and the benzene ring (ring A) was found to be the most significant. 5-[2-[[2-(5-Fluoro-2-methoxyphenoxy)ethyl]amino]propyl]-2- methoxybenzenesulfonamide (II-4), which possesses 1-methylethyl as the alkylene chain, exhibited high alpha-blocking selectivity as well as potent alpha-blocking activity. 相似文献