全文获取类型
收费全文 | 2782篇 |
免费 | 82篇 |
国内免费 | 29篇 |
专业分类
化学 | 1739篇 |
晶体学 | 21篇 |
力学 | 57篇 |
数学 | 575篇 |
物理学 | 501篇 |
出版年
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 101篇 |
2020年 | 45篇 |
2019年 | 58篇 |
2018年 | 55篇 |
2017年 | 50篇 |
2016年 | 100篇 |
2015年 | 79篇 |
2014年 | 112篇 |
2013年 | 200篇 |
2012年 | 183篇 |
2011年 | 192篇 |
2010年 | 133篇 |
2009年 | 128篇 |
2008年 | 159篇 |
2007年 | 165篇 |
2006年 | 153篇 |
2005年 | 161篇 |
2004年 | 124篇 |
2003年 | 84篇 |
2002年 | 69篇 |
2001年 | 26篇 |
2000年 | 33篇 |
1999年 | 35篇 |
1998年 | 28篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 32篇 |
1994年 | 24篇 |
1993年 | 30篇 |
1992年 | 15篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 10篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 13篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 11篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1963年 | 2篇 |
排序方式: 共有2893条查询结果,搜索用时 31 毫秒
61.
T. Case K. M. Crowe K. Lou C. Petitjean W. H. Breunlich M. Jeitler P. Kammel B. Lauss J. Marton W. Prymas J. Zmeskal D. V. Balin V. N. Baturin Yu. S. Grigoriev A. I. Ilyin E. M. Maev G. E. Petrov G. G. Semenchuk Yu. V. Smirenin A. A. Vorobyov N. I. Voropaev P. Baumann H. Daniel F. J. Hartmann M. Mühlbauer W. Schott P. Wojciechowski 《Hyperfine Interactions》1993,82(1-4):295-302
Starting in 1989 an experiment was run at PSI to directly measure the final sticking probability in muon catalyzed dt fusion. This experiment was based on an active-target ionization chamber (IC) built at Gatchina, Russia, and an array of plastic neutron counters. In three runs approximately 5×106 isolated alpha signals were recorded with around one half of these occurring in the inner chamber region where we have more complete understanding of the systematic errors. Particularly from a long run in 1992 we were able to obtain a very clean sticking peak of some 5000 events. However, to reach an accurate value of sticking, all systematic effects and several major backgrounds had to be understood in detail. To this end a Monte Carlo code was written to simulate the full electrostatic environment of the IC and to recreate completely each signal type including the actual tritium decay noise from the live experiment. A slightly model dependent value of approx. 0.56±0.04% is obtained for final sticking. 相似文献
62.
W. Schott V. N. Baturin W. H. Breunlich T. Case H. Daniel F. J. Hartmann M. Jeitler P. Kammel K. Lou E. M. Maev J. Marton M. Mühlbauer C. Petitjean G. E. Petrov Yu. V. Petrov G. G. Semenchuk Yu. V. Smirenin A. A. Vorobyov P. Wojciechowski J. Zmeskal 《Hyperfine Interactions》1993,82(1-4):471-481
The triton energy of the muon capture reaction 3He t+v, where 3 He is the ground state of muonic3He, has been measured in order to investigate a possible heavy v admixture into the flavour with high sensitivity. 3 He has been formed via the pd fusion reaction by stopping – in an ionization chamber (IC) filled with an H/D gas mixture of 3% D concentration at a pressure of 161 bar. In a first short experiment 650 triton events were observed yielding an upper limit for the -heavy v mixing strength of 2.3×10–3 atE
0v=60 MeV. 相似文献
63.
P. Ackerbauer W. H. Breunlich M. Fuchs S. Fussy M. Jeitler P. Kammel B. Lauss J. Marton W. Prymas J. Werner J. Zmeskal K. Lou C. Petitjean P. Baumann H. Daniel F. J. Hartmann W. Schott T. von Egidy P. Wojciechowski D. Chatellard J. P. Egger E. Jeannet T. Case K. M. Crowe R. H. Sherman V. Markushin 《Hyperfine Interactions》1993,82(1-4):243-258
Complementary to the investigations of the most efficient dt cycle, also the other muon-induced fusion cycles in mixtures of hydrogen isotopes have been studied. The results of these dedicated experiments provide rich information about muon-induced few-body reactions and contribute significantly to a better overall understanding of CF. A summary of the recent progress will be presented. Special emphasis will be put on two characteristic examples, namely a new experimental approach to study the muonic cascade in H-D mixtures and the systematic study of hyperfine effects in muon-induced reactions. 相似文献
64.
We use an idea of countable separability of points and sets in topological spaces to prove results on intersection of measurable
multifunctions and an implicit function theorem. We generalize or extend in part some well known Himmelberg's theorems. 相似文献
65.
Estimating the pore size distribution of activated carbons from adsorption data of different adsorbates by various methods 总被引:1,自引:0,他引:1
Gauden PA Terzyk AP Rychlicki G Kowalczyk P Cwiertnia MS Garbacz JK 《Journal of colloid and interface science》2004,273(1):39-63
Experimental adsorption isotherms of four adsorbates (N2, Ar, C6H6, and CCl4) as well as adsorption enthalpy (C6H6 and CCl4) measured on two strictly microporous carbons are used to evaluate the porosity of adsorbents (i.e., pore size distributions (PSDs) and average pore diameter ( Lav )). The influence of the diameter of adsorbates ( dA) as well as of the temperature ( T ) is analyzed in order to explain the differences or similarities between the above-mentioned quantities for all systems. Proposed previously, the general relationships between the parameters of the Dubinin-Astakhov (DA) isotherm equation (the characteristic energy of adsorption ( E0 ) and the exponent of this equation ( n )) and the average slit-width of carbon micropores are investigated. Moreover, the thermodynamic verification of the Horvath-Kawazoe (HK) theory and the ND model is presented based on data of the adsorption and enthalpy of adsorption of benzene and carbon tetrachloride on two carbons. Finally, the pore diameters calculated from calorimetry data using the Everett and Powl method and those calculated applying the recently developed equations are compared. In our opinion the change of apparent PSD should be monitored by performing a series of isotherm measurements from high (equal and higher than room temperature) to low temperatures (ca. 77.5 K) as was presented in the current study. Moreover, the analysis of the experimental data leads to the conclusion that the entropy of C6H6 and CCl4 can approach to the values characteristic of quasi-solid (a partially ordered structure). Therefore, this behavior of the adsorbate should be taken into consideration in the theoretical assumptions of model and its thermodynamic verification. 相似文献
66.
Dzygiel A Rzeszotarska B Masiukiewicz E Cmoch P Kamieński B 《Chemical & pharmaceutical bulletin》2004,52(2):192-198
Methyl 5-amino-1H-[1,2,4]triazole-3-carboxylate hydrochloride (1). and free ester (2). were obtained and 2 was reacted with Ac(2)O to give the acetylated products 3-6. Compounds 1-6 were studied using HPLC, GC-MS, FTIR and multinuclear NMR spectroscopy, including the cross-polarisation magic angle spinning (CPMAS) technique. The results of the acetylation of 2 were compared to those of the acetylation of 5-amino-1H-[1,2,4]triazole, and for 2 a significant decrease in the susceptibility to acetylation was found. The reaction of 2 with Ac(2)O at 20 degrees C, regardless of the amount and the concentration of the latter, including neat Ac(2)O, proceeds fully regioselectively and leads to one product: methyl 1-acetyl-5-amino-1H-[1,2,4]triazole-3-carboxylate (3). In sharp contrast to 5-amino-1H-[1,2,4]triazole, neither an additional monoacetylated isomer, whether annular or exocyclic, nor any diacetylated derivative could be detected. The diacetylation of 2 requires the process to be carried out in neat boiling Ac(2)O and, as in the case of 5-amino-1H-[1,2,4]triazole, gives two diacetylated isomers. These are methyl 1-acetyl-3-(acetylamino)-1H-[1,2,4]triazole-5-carboxylate (4) and 1-acetyl-5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (5). Hypothetical pathways of their formation have been suggested. A mixture of 4 and 5 upon hydrolysis of the ring acetyl group gives the monoacetylated derivative methyl 5-(acetylamino)-1H-[1,2,4]triazole-3-carboxylate (6). The spectroscopic, structural and conformational characteristics of compounds 1-6 have been given and methods for their preparation have been provided. 相似文献
67.
Fiammengo R Wojciechowski K Crego-Calama M Timmerman P Figoli A Wessling M Reinhoudt DN 《Organic letters》2003,5(19):3367-3370
[structure: see text] Water-soluble models of heme-protein active sites are obtained via the self-assembly of cationic porphyrins 1 and tetrasulfonato calix[4]arene 2 (K(1.2)() = 10(5) M(-)(1)). Selective binding of ligands either outside or inside the cavity of assemblies 1.2 via coordination to the zinc center has been observed. Small ligands such as 4-methylpyridine and 1-methylimidazole are encapsulated, while the bulkier caffeine is bound outside. Assemblies Co-1.2, in which the Zn porphyrin moiety has been replaced by a Co(II) porphyrin, can act as O(2) carriers. 相似文献
68.
3H-1,2-Benzoxathiole 2,2-dioxides (benzosultones) undergo thermal extrusion of sulfur dioxide to form ortho-quinone methides that enter Diels-Alder reaction with maleimides to form chroman 2,3-dicarboxylic acid derivatives. 相似文献
69.
5'-O-DMT-deoxyribonucleoside-3'-O-(2-selena-4,4-pentamethylene-1,3,2-oxathiaphospholane) monomers, derivatives of dA, dC, dG, and T, can be resolved into pure P-diastereomers by silica gel column chromatography. They have been used for DBU-promoted, either solution- or solid-phase synthesis of P-stereodefined phosphoroselenoate analogues of oligodeoxyribonucleotides. Fast- and slow-eluting monomers are precursors of phosphoroselenoate internucleotide linkage of R(P) and S(P) absolute configuration, respectively. [reaction: see text] 相似文献
70.
Piotr Kirszensztejn Wlodzimierz Zmierczak 《Reaction Kinetics and Catalysis Letters》1994,52(2):467-474
This study is concerned with the effect of various amounts of Sn species in modifying the dispersity of Al2O3–SnO2 supported platinum catalysts by application of hydrogen chemisorption in a pulse chromatographic system, as well as determination of activity in water-gas shift reaction (WGS). 相似文献