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21.
22.
J Robert Huber 《Chemphyschem》2004,5(11):1663-1669
This Minireview gives an account of the photochemical decay of nitric acid HNO3 in the gas phase, which has been well investigated under bulk and molecular-beam conditions. Due to the importance of this molecule in atmospheric chemistry, attention was paid to the irradiation regions around 300 and 200 nm, where solar photolysis of HNO3 is expected to be particularly efficient. While the low-energy region is characterized by the products OH and NO2, the high-energy region gives rise to a variety of photochemical decay pathways, dominated by channels which lead to the products HONO + O in different electronic states. 相似文献
23.
Cushman M Yang D Gerhardt S Huber R Fischer M Kis K Bacher A 《The Journal of organic chemistry》2002,67(16):5807-5816
A series of 6-carboxyalkyl and 6-phosphonoxyalkyl derivatives of 7-oxo-8-D-ribityllumazine were synthesized as inhibitors of both Escherichia coli riboflavin synthase and Bacillus subtilis lumazine synthase. The compounds were designed to bind to both the ribitylpurine binding site and the phosphate binding site of lumazine synthase. In the carboxyalkyl series, maximum activity against both enzymes was observed with the 3'-carboxypropyl compound 22. Lengthening or shortening the chain linking the carboxyl group to the lumazine by one carbon resulted in decreased activity. In the phosphonoxyalkyl series, the 3'-phosphonoxypropyl compound 33 was more potent than the 4'-phosphonoxybutyl derivative 39 against lumazine synthase, but it was less potent against riboflavin synthase. Molecular modeling suggested that the terminal carboxyl group of 6-(3'-carboxypropyl)-7-oxo-8-D-ribityllumazine (22) may bind to the side chains of Arg127 and Lys135 of the enzyme. A hypothetical molecular model was also constructed for the binding of 6-(2'-carboxyethyl)-7-oxolumazine (15) in the active site of E. coli riboflavin synthase, which demonstrated that the active site could readily accommodate two molecules of the inhibitor. 相似文献
24.
Preparation of Acetatolead(1V) and Acetatotin(1V) Manganese Pentacarbonyls by Acidolysis of (C6H5)4?n M[Mn(CO)5]n (M ? Sn, Pb; n = 1, 2) with Acetic Acid By acidolysis of (C6H5)4?nM[Mn(CO)5]n (M ? Sn, Pb; n = 1, 2) with acetic acid no M? Mn bonds are broken, but M? C bonds. In this reaction (CH3COO)2M[Mn(CO)5]2 is formed from (C6H5)2M[Mn(CO)5]2, and (CH3COO)3SnMn(CO)5 and (CH3COO)2C6H5PbMn(CO)5 from (C6H5)3MMn-(CO)5. (CH3COO)2C6H5SnMn(CO)5 is prepared from Cl2C6H5SnMn(CO)5 and AgCH3COO. According to IR spectroscopic data the acetato ligands of the diacetato complexes are bidentate, while in (CH3COO)3SnMn(CO)5 bi- and monodentate carboxylate groups are present. For the central atoms Sn and Pb octahedral coordination is proposed. 相似文献
25.
Werner?Seebacher Reto?Brun Robert?Saf Robert?WeisEmail author 《Monatshefte für Chemie / Chemical Monthly》2003,134(10):1411-1420
Summary. 4-Aminobicyclo[2.2.2]octanones were converted to their N-oxides and to 4-aminobicyclo[2.2.2]octanes. Furthermore, the 6,7-bis-(4-methoxyphenyl) analogues were synthesized. All products were screened for their activities against Trypanosoma b. rhodesiense and Plasmodium falciparum. The pharmacological results were compared with those of formerly tested bicyclo[2.2.2]octanones and bicyclo[2.2.2]octanols. Structure-activity relationships are discussed.Received April 8, 2003; accepted April 14, 2003
Published online September 25, 2003 相似文献
26.
Robert Weis Reto Brun Robert Saf Werner Seebacher 《Monatshefte für Chemie / Chemical Monthly》2003,134(7):1019-1026
Summary. 4-Aminobicyclo[2.2.2]octanones which were prepared in one-pot-reactions from benzylidene acetone and dialkylammonium rhodanides
were reduced stereoselectively to their corresponding alcohols. The activities of the bicyclic compounds against causative
organisms of tropical deseases were examined. The 4-aminobicyclo[2.2.2]octan-2-ols were in general more active against Trypanosoma b. rhodesiense and Plasmodium falciparum than the corresponding keto compounds.
Corresponding author. E-mail: robert.weis@uni-graz.at
Received November 27, 2002; accepted December 2, 2002
Published online May 2, 2003 相似文献
27.
The aromatic thioketone xanthione has been investigated by means of the optically detected magnetic resonance (ODMR) technique in a n-hexane matrix at ≈ 1.1 K. It was established that the short-lived red emission, which is characteristic for many thione molecules, is phosphorescence. At high temperatures (77 K) this phosphorescence originates mainly (>80%) from the T1z (n, π*) sublevel (kz(r) >kx(r), ky(r). At low temperature (1.1 K) the intersystem crossing following S2 (π, π*) ← S0 excitation is a highly spin-sublevel selective process which populates predominantly the T1x and T1y, levels. Hence, the slow spin—lattice relaxation phosphorescence at low temperature originates from these sublevels. A value of 0.0611 cm?1 was obtained for the zero-field parameter |E|/hc. A lower limit of 0.66 cm?1 has been found for the zero-field parameter |D|/hc. This value is considerably larger than those observed for ketones, and it is shown that spin—orbit coupling contributes strongly to the zero-field splitting. 相似文献
28.
The electrochemical oxidation of a series of thils on the surface of a nickel oxide electrode is investigated in a flow-injection system. The background electrolyte is 0.1 M NaOH containing 5 × 10?65 M NiSO4 and the injected sample volume is 25 μl. The net peak current is observed at +0.46 V vs. SCE for thiols dissolved in pH 3.0 phthalate buffer. The upper limit of linearity extends to 10?3 M. The relative standard deviation for ten replicate measurements on 10?4 M ethanethiol is 1.6%. The lower limits of detection are between 3 × 10?5 and 2 × 10?4 M for a series of thiols. Peak shapes indicate that thiolate oxidation mediated by a higher oxide layer on the electrode rather than mass transport or adsorption / rearrangement is the rate-determining step. 相似文献
29.
While operational qualification (OQ) is a well-established term within equipment qualification, users of equipment often become unsure when it comes to implementation. The biggest problem is how to select procedures and acceptance criteria. Should these be the vendor's specifications or should the users define their own limits, and, if so, how? Should all instruments of the same type have the same values or should these be optimized for each individual instrument? This article will provide an overall strategy and specific examples for HPLC on how to select procedures and acceptance limits that are based on efficient use of resources, on practicality and on the intended use of the equipment. 相似文献
30.
Photosynthesis is one of the fascinating fields of current interdisciplinary research. It seems miraculous that nature, in the process of evolution, has managed to bring about the process of photosynthesis. The first step involves a charge separation at the reaction centers, which proceeds with 100% quantum yield from the photoexcited singlet state of the bacteriochlorophyll donor, despite the fact that the wasteful deactivation of the electron into the ground state should be highly favored. Biomimetic model compounds (that is, those which resemble the pigments nature has developed) have been constructed from porphyrins and quinones. These model systems have allowed the study of the factors contributing to the highly efficient charge separation. This report focuses on recent developments in the study of electron transfer in porphyrinoquinones. Some of the results of these investigations may not be not fully understood and are often the subject of controversial discussions. 相似文献