全文获取类型
收费全文 | 240265篇 |
免费 | 1792篇 |
国内免费 | 673篇 |
专业分类
化学 | 117926篇 |
晶体学 | 3270篇 |
力学 | 8356篇 |
综合类 | 6篇 |
数学 | 23308篇 |
物理学 | 64804篇 |
无线电 | 25060篇 |
出版年
2021年 | 1904篇 |
2020年 | 2204篇 |
2019年 | 2521篇 |
2018年 | 3492篇 |
2017年 | 3352篇 |
2016年 | 4585篇 |
2015年 | 2530篇 |
2014年 | 4147篇 |
2013年 | 9801篇 |
2012年 | 7292篇 |
2011年 | 8910篇 |
2010年 | 6566篇 |
2009年 | 6686篇 |
2008年 | 9013篇 |
2007年 | 9275篇 |
2006年 | 8699篇 |
2005年 | 7908篇 |
2004年 | 7136篇 |
2003年 | 6576篇 |
2002年 | 6460篇 |
2001年 | 6844篇 |
2000年 | 5666篇 |
1999年 | 4300篇 |
1998年 | 3853篇 |
1997年 | 3790篇 |
1996年 | 3532篇 |
1995年 | 3010篇 |
1994年 | 3128篇 |
1993年 | 3083篇 |
1992年 | 3211篇 |
1991年 | 3306篇 |
1990年 | 3190篇 |
1989年 | 3082篇 |
1988年 | 2958篇 |
1987年 | 2683篇 |
1986年 | 2609篇 |
1985年 | 3297篇 |
1984年 | 3434篇 |
1983年 | 2779篇 |
1982年 | 3024篇 |
1981年 | 2866篇 |
1980年 | 2690篇 |
1979年 | 2880篇 |
1978年 | 2976篇 |
1977年 | 2998篇 |
1976年 | 2959篇 |
1975年 | 2814篇 |
1974年 | 2797篇 |
1973年 | 2929篇 |
1972年 | 1997篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
991.
All the second-order density matrix spin components for the spin-projected Slater determinant are presented as expansions in direct products of powers of unprojected spin- and residual electron density matrices. Spin components of the second-order transition density matrices between spin-projected Slater determinants built of orthogonal orbitals are also obtained. 相似文献
992.
N Sayem-el-Daher R E Simard L L'Heureux A G Roberge 《Journal of chromatography. A》1983,256(2):313-321
A fully automated, rapid and sensitive method was developed to analyze fourteen different biogenic amines in food. Using a Technicon C4 ion-exchange resin column (20 m X 0.5 cm), adapted to an automatic Technicon TSM amino acid analyzer, the following amines were separated and quantified: adrenaline, noradrenaline, 1,3-diaminopropane, putrescine, cadaverine, histamine, spermidine, dopamine, spermine, agmatine, tyramine, serotonin, phenethylamine and tryptamine. Five buffers were required to elute the amines using a gradient of pH from 5.6 to 12.7; the column temperature was maintained at 65 degrees C. The method was also assayed on ground beef, cheese and wine samples. Amines from cheese and ground beef samples were extracted with 0.6 M perchloric acid. No extraction of wine samples was necessary. 相似文献
993.
A simple method for the separation of hemoglobin chains from hemolysate or globin, by sodium dodecyl sulfate polyacrylamide gel electrophoresis, is described. The alpha, beta, and gamma chains can be clearly separated from each other. The alpha chain has the highest mobility, the beta chain has a slower mobility than the gamma chain, while the delta chain has about the same mobility as the beta chain. Hemoglobins with elongated chains can easily be detected by this method. Tak-beta, elongated by 11 residues, moves much more slowly than betaA but is much faster than alpha Constant Spring which is elongated by 31 residues. Screening of several individuals with slow-moving hemoglobins using this method led to the finding of a case with Hb Tak-beta thalassemia and other carriers of Hb Tak. 相似文献
994.
Abstract— Picosecond 530 nm actinic and 1242 nm probe light pulses have been used to measure the kinetics of energy transfer and photooxidation in Rhodopseudomonas sphaeroides R-26 reaction centers. The energy transfer rate between bacteriopheophytin and the bacteriochlorophyll dimer is 1.0 ± 0.3 ± 1011 s-l and photooxidation of the dimer occurs within 5 ps after the dimer reaches the first excited singlet state. Using these parameters in a simple model we are able to explain the odd result that the number of reaction centers oxidized by a saturating 530 nm actinic picopulse is only 60% of the number oxidized by a saturating CW light source. 相似文献
995.
Procedures are proposed for the determination of phosphorus and silicon in the ppM range, by extraction of phosphomolybdic and silicomolybdic acids with organic solvent, decomposition of the complex and spectrophotometric determination of its molybdenum content. 相似文献
996.
I.R. Spectra of the Phases A B Te3O8 (A = Fe, In, Sc; B = Nb, Ta) and UTe3O9 The infrared spectra of the title compounds have been recorded and discussed in comparison to formerly investigated MIVTe3O8 phases. The spectrum of UTe3O9 (synthetic cliffordite) confirms the presence of uranyl groups and the structural relation of this compound to the fluorite. 相似文献
997.
A rapid non-destructive neutron-activation method for the determination of uranium in rocks is described. The method is based on activation with epithermal neutrons and subsequent measurement of the 74 keV gamma-ray of (239)U. Results given for some standard rocks are in good agreement with literature data. The precision of the method is about 5 % and the limit of detection is of the order of 0.1 ppm in silicate rocks. 相似文献
998.
E. Schnell 《Monatshefte für Chemie / Chemical Monthly》1962,93(5):1136-1141
Zusammenfassung Die Verbindung SiF4·N(CH3)3 ist in Benzol löslich und daraus in nadelförmigen Kristallen erhältlich, während SiF4·2 N(CH3)3 als in Petroläther schwer löslicher Niederschlag gewonnen werden kann. IR-Spektren beider Verbindungen werden mitgeteilt.Mit 2 Abbildungen 相似文献
999.
Model chromophores of 1.10-dihydroflavin and its 10.10a-ring opened derivative have been isolated. By comparison with enzymatic intermediates, reaction mechanisms of flavin-dependent oxygenase and luciferase are discussed in terms of chemical structure. 相似文献
1000.
Summary The previously described method yielding apolar, chemically bonded methyl polysiloxane glass capillary columns was extended to the production of capillary systems of controlled polarity. The approach involved prior synthesis of a reactive methyl-phenyl polysiloxane polymer by copolymerisation of a mixture of dimethyl and diphenyl chlorosilanes. The polymer was then chemically bonded to the capillary glass surface to yield remarkably stable, high resolution analytical systems which were shown to be particularly well suited to the separation of biochemical mixtures at the subnanogram level. The principle of copolymerisation of differently substituted silanes confers to the method a considerable flexibility which could be used to devise polar capillary systems tailor made for a given analytical problem. 相似文献