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991.
Binary zirconium orthophosphates R1/3Zr2(PO4)3 and M1/4Zr2(PO4)3, where R = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu; M = Th, U, have been synthesized and studied by IR spectroscopy [structural family of NaZr2(PO4)3 (NZP)]. Vibrational analysis for the PO4 tetrahedron and investigation of symmetry relations among trigonal NZP phases showed that ordering of lanthanide atoms in structures of NaZr2(PO4)3 type with space group R
c leads to symmetry reduced to P
c. The lanthanide atoms occupy the 2b sites. The phosphorus atoms occupy two independent sites: 6f with C
2 symmetry and 12g with C
1 symmetry. Factor group analysis admits that the IR spectrum can contain eight v3 bands and two v1 bands of the stretching vibrations of the PO4 ions. The M atoms of actinides occupy statistical positions in the structure, and space group R
c is retained.Original Russian Text Copyright © 2004 by V. S. Kurazhkovskaya, D. M. Bykov, and A. I. Orlova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 1013–1019, November–December, 2004. 相似文献
992.
Summary A high-performance liquid chromatographic method for the separation and determination of gastrodin,p-hydroxybenzyl alcohol, vanillyl alcohol,p-hydroxylbenzaldehyde and vanillin in extract of Chinese herbal medicine tall gastrodia tuber (Chinese name: Tianma) was established.
The chromatographic conditions were optimized by means of computer-assisted method development technique. Dry-Lab software
was used to model the retention behavior of the compounds as a function of gradient conditions, based on the data from two
scouting gradient runs. Under the optimized conditions: column, Kromasil-C18, 5 μm, 15×0.46-cm; solvent A, water; solvent
B, methanol; gradient, 5/44/65/65% B at 0/9/12/15 min; flow rate, 1.00 mL min−1; temperature, ambient, the quality of tall gastrodia tubers from different sources and tianma injection were examined. 相似文献
993.
Ailing Zhu Yingying Guo Guangliang Liu Maoyong Song Yong Liang Yong Cai Yongguang Yin 《中国化学快报》2019,30(12):2241-2244
Dark formation of hydroxyl radical upon oxidation of reduced iron minerals plays an important role in the degradation and transformation of organic and inorganic pollutants. Herein, we compared the hydroxyl radical formation from various reduced iron minerals at different redox conditions. OH production was generally observed from the oxidation of reduced iron minerals, following the order: mackinawite (FeS) > reduced nontronite (iron-bearing smectite clay) > pyrite (FeS2) > siderite (FeCO3). Structural Fe2+ and dissolved O2 play critical roles in OH production from reduced iron minerals. OH production increases with decreasing pH, and Cl? has little effect on this process. More importantly, dissolved organic matter significantly enhances OH production, especially under O2 purging, highlighting the importance of this process in ambient environments. This sunlight-independent pathway in which OH forms during oxidation of reduced iron minerals is helpful for understanding the degradation and transformation of various inorganic and organic pollutants in the redox-fluctuation environments. 相似文献
994.
M. P. Shurygina S. A. Chesnokov M. A. Lopatin V. K. Cherkasov G. A. Abakumov 《Russian Chemical Bulletin》2004,53(11):2485-2489
A study of the kinetics of photoreduction of 9,10-phenanthrenequinone in the presence of hydrogen donors (para-substituted N,N-dimethylanilines and polymethylbenzenes) showed that plots of the quantum yield of photoreduction (H) and apparent reaction rate constant (k
H) vs. oxidation potential of hydrogen donors are extreme. In the presence of amines, k
H and H increase, as a whole, whereas they decrease in the presence of polymethylbenzenes. In coordinates H-G
e (G
e is the change in the free energy of electron transfer) for pairs quinone-H donor, H increases with G
e approaching to zero. For the amine series, this effect is mainly in the exothermic region of G
e (G
e < 0). For the series of polymethylbenzenes, this increase is observed in the endothermic region (G
e > 0).__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2381–2385, November, 2004. 相似文献
995.
Vanessa Gouge 《Tetrahedron letters》2004,45(4):773-776
2,2-Difluoro-3-(2-hydroxy-1 R-phenylethylamino)-3 S-phenylpropionic acid 3, obtained by a Reformatsky-type reaction of ethyl bromodifluoroacetate with (4R)-2,4-diphenyloxazolidine, was used as a classical carboxylic acid in the Ugi reaction to prepare various difluorinated pseudopeptides 5a-n. Compounds 5 were then deprotected by hydrogenolysis to furnish difluorinated pseudopeptides 6. 相似文献
996.
Differential scanning calorimetry (DSC) is the most widely used thermal analytical technique in food research and it has a great utility in quality assurance of food. Proteins are the most studied food components by thermal analysis including studies on conformation changes of food proteins as affected by various environmental factors, thermal denaturation of tissue proteins, food enzymes and enzyme preparations for the food industry, as well as effects of various additives on their thermal properties. Freezing-induced denaturation of food proteins and the effect of cryoprotectants are also monitored by DSC. Polymer characterization based on DSC of polysaccharides, gelatinization behaviour of starches and interaction of starch with other food components can be determined, and phase transitions during baking processes can be studied by DSC. Studies on crystallization and melting behaviour of fats observed by DSC indicate changes in lipid composition or help characterizing products. Thermal oxidative decomposition of edible oils examined by DSC can be used for predicting oil stability. Using DSC in the freezing range has a great potential for measuring and modelling frozen food thermal properties, and to estimate the state of water in foods and food ingredients. Research in food microbiology utilizes DSC in better understanding thermoadaptive mechanisms or heat killing of food-borne microorganisms. Isothermic microcalorimetric techniques provide informative data regarding microbial growth and microbial metabolism. 相似文献
997.
Tetrabutylammonium cyanide has been used as non-metallic catalyst for the diastereoselective cyanosilylation of α-hydroxyketones derived from the chiral pool. This affords α-substituted-α,β-dihydroxynitriles with high levels of asymmetric induction. 相似文献
998.
Three different types of SCD combustion source have been evaluated for use in the chromatographic analysis of atmospheric sulfur compounds. The conventional FID source and the newer inverted burner source were found to be less sensitive and less stable than the flameless design. Overall, the flameless source was superior for use with HRGC-SCD. 相似文献
999.
D. Harbach und H. Diehl 《Fresenius' Journal of Analytical Chemistry》1978,293(2):145-146
Ohne Zusammenfassung
Comparison of sample preparation methods for quantitative determination of heavy metals in fruit juices with flameless atomic absorption spectroscopy
Vortragender 相似文献
1000.
Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.Deceased July 31, 1996 相似文献