全文获取类型
收费全文 | 4899篇 |
免费 | 104篇 |
国内免费 | 13篇 |
专业分类
化学 | 3600篇 |
晶体学 | 59篇 |
力学 | 78篇 |
数学 | 182篇 |
物理学 | 1097篇 |
出版年
2021年 | 29篇 |
2020年 | 56篇 |
2019年 | 57篇 |
2018年 | 52篇 |
2017年 | 33篇 |
2016年 | 67篇 |
2015年 | 77篇 |
2014年 | 95篇 |
2013年 | 228篇 |
2012年 | 196篇 |
2011年 | 241篇 |
2010年 | 166篇 |
2009年 | 141篇 |
2008年 | 243篇 |
2007年 | 274篇 |
2006年 | 274篇 |
2005年 | 236篇 |
2004年 | 198篇 |
2003年 | 205篇 |
2002年 | 194篇 |
2001年 | 123篇 |
2000年 | 149篇 |
1999年 | 96篇 |
1998年 | 62篇 |
1997年 | 67篇 |
1996年 | 65篇 |
1995年 | 49篇 |
1994年 | 54篇 |
1993年 | 63篇 |
1992年 | 60篇 |
1991年 | 54篇 |
1990年 | 46篇 |
1989年 | 58篇 |
1988年 | 65篇 |
1987年 | 49篇 |
1986年 | 46篇 |
1985年 | 61篇 |
1984年 | 76篇 |
1983年 | 58篇 |
1982年 | 69篇 |
1981年 | 56篇 |
1980年 | 65篇 |
1979年 | 60篇 |
1978年 | 52篇 |
1977年 | 53篇 |
1976年 | 28篇 |
1975年 | 33篇 |
1974年 | 39篇 |
1973年 | 26篇 |
1967年 | 27篇 |
排序方式: 共有5016条查询结果,搜索用时 31 毫秒
61.
Tsutomu Oishi Kensoh Kagawa Minoru Fujimoto 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1341-1352
Two types of optically active N-[N′-(α-methylbenzyl)amino/carbonyl-n-alkyl]maleimides (MBAC) were synthesized from maleic anhydride, 6-amino-n-caproic acid (or 12-amino-n-dodecanoic acid), and (R)-(+)-α-methylbenzylamine. Radical homopolymerizations of MBAC were performed in several solvents at 60 and 110°C for 24 h to give optically active polymers. Radical copolymerizations of MBAC were performed with styrene (ST) and methyl methacrylate (MMA) in dioxane at 60°C. The monomer reactivity ratios and the Alfrey-Price Q-e values were determined. Chiroptical properties of the polymers and copolymers were investigated. © 1995 John Wiley & Sons, Inc. 相似文献
62.
Tetsuo Miyazaki Shigeru Nagasaka Isao Maeda Takuro Matsumoto Shinji Koyama Seiji Kodama Masami Watanabe 《Radiation Physics and Chemistry》1996,47(6):817-819
Emission from high-energy-electron-irradiated golden hamster embryo (GHE) cells has been studied over the temperature range 12–300 K both by a one-shot-single-photon-counting method and by photocurrent measurements with an oscilloscope. Emission from the irradiated phosphate buffered saline (PBS) also has been studied. The emission spectra from PBS at 12 and 77 K show a maximum around 330 and 380 nm, respectively, which are the same spectra as those from irradiated pure H2O. The emission from irradiated GHE consists of the new band at 480 nm in addition to the emission from H2O. The 480 nm emission is observed at the temperature range of 12–300 K, though the emission at 300 K is much lower than that at low temperature. The 480 nm emission is ascribed to the transition from excited organic substances in GHE cells. The intensity of 480 nm emission at 300 K increases linearly with increasing irradiation-dose in the range of 11–600 Gy. 相似文献
63.
Both enantiomers of 1,1-diethoxyethyl(aminomethyl)phosphinates were prepared through chromatographic separation of a diastereomeric mixture derived from (S)-phenylethylamine and 1,1-diethoxyethyl-H-phosphinate. The individual enantiomer was transformed into α-substituted α-amino-H-phosphinate with high enantiomeric purity by a highly diastereoselective alkylation at the α-carbon on the basis of our previously developed method. 相似文献
64.
Masatoshi Sakae Masanori Katsurada Mayumi Watanabe Fumio Yoneda Sadao Nishigaki Toshimasa Ishida 《Journal of heterocyclic chemistry》1997,34(1):157-160
The reaction of 2-bromoethylamine 1 with methylisothiocyanate 2 under mild condition gave 2-methyl-amino-2-thiazoline 3 as the major product together with two kinds of byproducts, 3-(N-methylthiocar-bamoyl)-2-methyliminothiazolidine 4 and N,N′-dimethyl-N-(2-thiazolin-2-yl)thiourea 5. Thermal isomer-ization of 5 to 4 was observed. The structures of the byproducts were confirmed by X-ray crystallography. 相似文献
65.
Shinichi Yamabe Noriko Tsuchida Tsutomu Minato Takahisa Machiguchi 《Theoretical chemistry accounts》2005,113(2):95-106
Cheletropic additions forming cyclopropane rings were studied theoretically. Ten addition paths were traced by means of density-functional-theory calculations. Two 1,4-dienes, 1,4-pentadiene, and tricyclo[5.3.1.04,9]undeca-2,5-diene were adopted as substrates. CO, SO2, C2H5PCl2, CCl2 and SiCl2 were employed as cheletropic reagents (Xs). An orbital correlation diagram of the Woodward–Hoffmann (W–H) rule and frontier molecular orbital (FMO) interactions between them were investigated in detail. The FMO interactions, HOMO (1,4-diene)lumo (X) and homo (X)LUMO (diene), work reasonably for the progress of the reactions. Those cause the formation of two C–X bonds and a cyclopropane ring, and alternation of double bonds to single bonds. All the additions are concerted. The easiness of the ring formation depends upon the energy gap between HOMO and lumo and that between homo and LUMO, and the spatial directions of HOMO and LUMO extensions. Symmetry conservation of the W–H rule does not hold necessarily for those addition paths. The symmetry-breaking was discussed in terms of FMO interactions.Acknowledgement This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture, Japan and by Nishida Memorial Foundation for Fundamental Chemical Research. 相似文献
66.
Umetsu K Tanaka M Yuasa I Adachi N Miyoshi A Kashimura S Park KS Wei YH Watanabe G Osawa M 《Electrophoresis》2005,26(1):91-98
We present a reliable, rapid, and economical multiplex amplified product-length polymorphism (APLP) method for analyzing the haplogroup-diagnostic mitochondrial single-nucleotide polymorphisms (mtSNPs) in East Asian populations. By examining only 36 haplogroup-specific mtSNPs in the coding region by using four 9-multiplex polymerase chain reaction (PCR) and subsequent electrophoresis, we could safely assign 1815 individuals from 8 populations of Japanese, Korean, Chinese, and Germans to 45 relevant haplogroups. This multiplex APLP analysis of coding-region mtSNPs for haplogrouping is especially useful not only for molecular phylogenetic studies but also for large-scale association studies due to its rapid and economical nature. This is the first panel of mtSNPs in the coding region to be used for haplogrouping of East Asian populations. 相似文献
67.
Heterogeneous structure of silk fibers from Bombyx mori resolved by 13C solid-state NMR spectroscopy
Asakura T Yao J Yamane T Umemura K Ulrich AS 《Journal of the American Chemical Society》2002,124(30):8794-8795
The molecular conformation of silk fibrion is characterized by solid-state 13C NMR before spinning (silk I structure) and after spinning (silk II structure). We compare native silk fibers with the quasi-crystalline Cp-fraction and a synthetic model peptide (Ala-Gly)15, both of which can be converted either into silk I by dialysis from 9 M LiBr or into silk II by treatment with formic acid. Our results demonstrate that silk II fibers are intrinsically heterogeneous, consisting of beta-sheets, distorted beta-turns, and distorted beta-sheets. This higher-order heterogeneity is revealed by the 13C-NMR Cbeta-peak of Ala, indicating that the Ala side chains are stacked partially in parallel and partially face-to-face, at a ratio of 1:2. 相似文献
68.
Akio Okamoto Eiichi Watanabe Itaru Mita 《Journal of polymer science. Part A, Polymer chemistry》1979,17(8):2483-2490
The deactivation of α-methylstyryl and styryl carbanions followed by spectral change and titration was studied kinetically. First-order rate constants were obtained for the deactivation of oligo-α-methylstyryl lithium, disodium, and dipotassium in tetrahydrofuran and of polystyryl potassium in varying degrees of polymerization in benzene that contained a small amount of tetrahydrofuran and n-hexane. It was observed that the addition of cryptate [222] exerts a significant effect on the system of oligo-α-methylstyryl disodium in tetrahydrofuran. The effect of dilution, degree of polymerization of the polymer, and counterions on the rate of deactivation of carbanions was discussed. 相似文献
69.
Otaka A Yukimasa A Watanabe J Sasaki Y Oishi S Tamamura H Fujii N 《Chemical communications (Cambridge, England)》2003,(15):1834-1835
Gamma-acetoxy-alpha,beta-enoates were easily reduced by samarium diiodide (SmI2) in THF to generate samarium dienolates which were kinetically trapped with ease at their alpha-positions by electrophiles (proton, aldehydes or ketones) to yield (E)-alkene dipeptide isosteres or gamma-amino acid derivatives in high chemical yields. 相似文献
70.
Enzyme heterobilayer-modified electrodes were fabricated by successively covalently binding to the surface of a tin(IV) oxide plate horseradish peroxidase (HRP), then an oxidase (lactate, pyruvate or cholesterol oxidase or uricase), which liberates hydrogen peroxide by reaction with the respective substrate. The cooperative action of oxidase-HRP leads to an efficient amperometric sensor system with the minimum amount of enzyme immobilized on an electrode. 相似文献