全文获取类型
收费全文 | 1114篇 |
免费 | 32篇 |
国内免费 | 1篇 |
专业分类
化学 | 858篇 |
晶体学 | 10篇 |
力学 | 2篇 |
数学 | 19篇 |
物理学 | 258篇 |
出版年
2023年 | 12篇 |
2022年 | 8篇 |
2021年 | 9篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 21篇 |
2013年 | 49篇 |
2012年 | 44篇 |
2011年 | 50篇 |
2010年 | 33篇 |
2009年 | 27篇 |
2008年 | 66篇 |
2007年 | 55篇 |
2006年 | 63篇 |
2005年 | 52篇 |
2004年 | 52篇 |
2003年 | 58篇 |
2002年 | 33篇 |
2001年 | 40篇 |
2000年 | 22篇 |
1999年 | 16篇 |
1998年 | 8篇 |
1997年 | 15篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 16篇 |
1993年 | 13篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 12篇 |
1987年 | 15篇 |
1986年 | 7篇 |
1985年 | 21篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 12篇 |
1977年 | 11篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1974年 | 12篇 |
1973年 | 6篇 |
排序方式: 共有1147条查询结果,搜索用时 234 毫秒
21.
Mass spectra of ginsenoside-Rg1 deca-acetate 1 Siehe Lit.2. and the related dammaran-type triterpene saponin acetates have been studied and a comment is given on the structure of panaxoside A (=ginsenoside-Rg1) proposed by Elyakov, et al . 相似文献
22.
23.
T Sato T Fujiwara Y Abe M Itoh H Fukuda J Hatazawa K Kubota T Ido T Matsuzawa 《Radioisotopes》1989,38(1):7-12
We investigated glucose and amino acid metabolism in tumors and other organs using whole body autoradiography with a short-lived positron emitter and a long-lived beta emitter. The radioactive compounds used were 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) with a half life of 109.8 min and L-[methyl-14C]-methionine (14C-MET) with a half life of 5,730 years. A Donryu rat weighing about 150 g was subcutaneously inoculated at the back with experimental tumors of AH109A and AH272. 74 MBq (2 mCi) of 18F-FDG and 740 kBq (20 microCi) of 14C-MET was administered and after 30 min, the rat was sacrificed. Whole body frozen sections were obtained using autocryotome. For the 18F-FDG autoradiogram, the frozen sections were exposed to an X-ray film for 6 h. After seven days, these frozen sections were again exposed to 14C-MET for a week. Cross-contamination was minimized by adjusting the exposure time, the interval of exposures and the administered dose. The accumulation of the tracers was represented as the optical density ratio of the tissue of interest to the muscle. The tumor ratios were 12.5 for 18F-FDG and 8.6 for 14C-MET showing the highest accumulation in the whole body autoradiogram. In contrast the inflammatory tissue ratios were 1.27 for 18F-FDG and 0.77 for 14C-MET showing very low amino acid metabolism. With the present double tracer whole body autoradiogram, 18F-FDG accumulation was seen in the brain and the heart but not to the liver as against 14C-MET accumulation which was seen to the liver but not to the brain and the heart. 相似文献
24.
25.
The molecular displacements on the M011-->M101 phase transition of n-hexatriacontane (n-C36H74) have been investigated with an IR microscope designed for the oblique infrared transmission method. It has been clarified that two polytypic structures of the M011 modification, single-layered structure (Mon) and double-layered one (Orth II), both transform to the M101 modification of single-layered structure with their respective mechanisms. On the M011(Mon)-->M101 transition, the inclination direction of molecular axis is changed by 90 degrees through an intermediate state in which the molecular chain is set perpendicular to the basal plane of the single crystal. On the other hand, a polymorphic-polytypic composite structural change on the M011(Orth II)-->M101 transition is accomplished through two kinds of molecular displacements occurring alternately along the stacking direction of molecular layers. 相似文献
26.
Suzuki Y Yamauchi K Muramatsu K Sato M 《Chemical communications (Cambridge, England)》2004,(23):2770-2771
Chiral N-heterocyclic carbenes, which are derived from C2-symmetric 1,3-bis(1-arylethyl)imidazolium salts, catalyze enantioselective acylation of racemic secondary alcohols. 相似文献
27.
Hideaki Hioki Yumiko Ohnishi Miwa Kubo Emi Nashimoto Yukinori Kinoshita Miho Samejima Mitsuaki Kodama 《Tetrahedron letters》2004,45(3):561-564
A fluorescence-labeled calix[4]arene library substituted with peptides at the upper rim was synthesized. Screening of the library for binding a dye-labeled oligopeptide indicated that some peptidocalix[4]arenes selectively bind the oligopeptide. The chemosensitivity of the library members for a target peptide was also investigated. 相似文献
28.
The thermodynamic properties of the two polytypes of n-hexatriacontane (n-C36H74), single-layered structure Mon and double-layered structure Orth II have been investigated by means of solubility measurements and incoherent inelastic neutron scattering. The solubility measurements reveal that Orth II is more stable than Mon by 1.2 kJ/mol because of the advantage of larger entropy. The neutron scattering measurements show that the vibrational modes of Orth II shift to the lower frequencies compared with those of Mon in the frequency region below 120 cm(-1). The advantage of Orth II in vibrational entropy due to the low-frequency shifts is estimated to be 9.6 J K(-1)/mol at 288 K under the harmonic approximation, which nearly agrees with the entropy difference of 6.8 J K(-1)/mol between Mon and Orth II determined by solubility measurements. These results suggest that the difference in vibrational entropy due to low-frequency modes mainly contributes to the relative thermodynamic stabilities of polytypic structures of long-chain compounds. From the frequency of methyl torsional mode, it is suggested that the cohesive force at the lamellar interface is stronger in Mon than in Orth II. 相似文献
29.
M. Kubota 《Journal of Radioanalytical and Nuclear Chemistry》1983,78(2):295-305
Ion exchange resins are widely used in the field of nuclear industry. The present work aimed at the development of a method
for complete decomposition of cation exchange resins with H2O2 in the presence of Fe3+ ion. The decomposition reaction proceeded at ambient temperature and decomposition time was greatly shortened with increasing
concentration of Fe3+ ion rather than that of H2O2. The catalytic action of Fe3+ ion was suppressed with increase of HNO3 concentration. As much as 4 g of the air-dried resin could be decomposed with 8 ml of 30% H2O2, and the use of about 60 ml of 30% H2O2 resulted in the complete decomposition of organic carbon to CO2. Absence of any orgnaic carbon in the residual solution will simplify the final disposal. 相似文献
30.
Edwards KW Ogg M Bellerive A Britton DI Hyatt ER MacFarlane DB Patel PM Spaan B Sadoff AJ Ammar R Baringer P Bean A Besson D Coppage D Copty N Davis R Hancock N Kelly M Kotov S Kravchenko I Kwak N Lam H Kubota Y Lattery M Momayezi M Nelson JK Patton S Poling R Savinov V Schrenk S Wang R Alam MS Kim IJ Ling Z Mahmood AH O'Neill JJ Severini H Sun CR Wappler F Crawford G Daubenmier CM Fulton R Fujino D Gan KK Honscheid K Kagan H Kass R Lee J Sung M White C Wolf A Zoeller MM Butler F Fu X Nemati B 《Physical review letters》1995,74(17):3331-3335