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991.
Development of an analytical procedure for determination of selected estrogens and progestagens in water samples 总被引:1,自引:0,他引:1
An analytical procedure has been developed for determination of eight selected natural and synthetic hormonal steroids in surface water and in effluent samples. Several methodological points have been investigated and are discussed; they include the choice of the solid-phase extraction sorbent, the influence of flow rate on recovery, the breakthrough volume for a given sorbent (Env+ and Oasis HLB), sample clean up, and sample storage. As regards the latter point, it was found that when no preservative was added to effluent from a sewage-treatment plant, severe loss of steroids occurred—85% of progesterone and about 30% of both estrone and estradiol were found to be degraded in 24 h. The procedure developed was applied to samples from the Seine river estuary. Sex steroids were not detected in surface water; estrone was the most commonly detected steroid in sewage-treatment plant effluent, with levels ranging from 1.8 to 8.3 ng L–1. Synthetic estrogens (ethynylestradiol and mestranol) and progestagens (levonorgestrel and norethindrone) were never detected, whatever the sampling season. Overall, for 162 out of 168 measurements levels were below the detection limits of the developed procedure. 相似文献
992.
Zhu Q Hensen EJ Mojet BL van Wolput JH van Santen RA 《Chemical communications (Cambridge, England)》2002,(11):1232-1233
Fe-oxide species in Fe/ZSM-5 (prepared by chemical vapor deposition of FeCl3)--active in N2O decomposition--react with zeolite protons during high temperature calcination to give highly active cationic Fe species, this transformation being reversible upon exposure to water vapor at lower temperature. 相似文献
993.
Fang-Hui?Wu Guang-Chao?ZhaoEmail author Xian-Wen?Wei Zhou-Sheng?Yang 《Mikrochimica acta》2004,144(4):243-247
Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5×10–7 to 1.0×10–4molL–1, and the detection limit is 2.7×10–8molL–1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity. 相似文献
994.
995.
Blake AJ Brett MT Champness NR Khlobystov AN Long DL Wilson C Schröder M 《Chemical communications (Cambridge, England)》2001,(21):2258-2259
4,4'-Bipyridine N,N'-dioxide (L) acts as a hydrogen-bond acceptor in the compounds ([M(NO3)2(H2O)4].L2) (M = Co, Ni) to form doubly-interpenetrated framework materials with sixfold topological connectivity. 相似文献
996.
Age K. Smilde Piet Hein van der Graaf Durk A. Doornbos Ton Steerneman Anita Sleurink 《Analytica chimica acta》1990
When retention measurements are available for a set of solutes on different stationary phases, with varying mobile phase compositions, the resulting data set can be represented by a three-way array. Models that describe the systematic variation in this training set sufficiently, can be used to calibrate a new stationary phase. Two models are tested for this purpose: three-way partial least squares and parallel factor analysis. 相似文献
997.
J. van Katwijk 《Fresenius' Journal of Analytical Chemistry》1958,164(1):73-80
Zusammenfassung Apparatur und Analysengang für die massenspektrometrische Analyse von Gasgemischen mit bis zwanzig Komponenten unter Benutzung eines analog-to-digital converter und einer elektronischen Rechenmaschine werden beschrieben. Die Methode wird mit der normalen massenspektrometrischen Analyse mit photographischer Registrierung der Peaks verglichen, vor welcher sie bei gleicher Genauigkeit den Vorteil größerer Schnelligkeit hat. 相似文献
998.
Tromp M van Bokhoven JA Arink AM Bitter JH van Koten G Koningsberger DC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(24):5667-5678
Herein we describe a structural characterisation with EXAFS of copper(I) arenethiolate complexes in both the solid and liquid state. Previously noted difficulties in the detection of the Cu-Cu interaction have been attributed to anti-phase behaviour of different Cu-Cu neighbour contributions. A data analysis procedure solely based on EXAFS parameters is presented which resolves these problems. A careful analysis of the individual coordination shells and the use of different k-weightings during the data analysis are shown to be an absolute necessity to obtain reliable results. During R-space fitting, the difference file technique is used to separate, examine and compare the individual contributions. Using this technique their statistical significance and correctness can be determined. Anti-phase behaviour can be detected and accounted for in this way. An additional mixed organocopper aggregate [Cu4(SAr)2(Mes)2] with different Cu sites is analysed, which proves the value of the analysis procedure described above. Moreover, this newly developed EXAFS data analysis procedure is applicable to any other EXAFS spectrum obtained. The structural analysis of these organocopper complexes with EXAFS provides information about their actual structure and dynamic behaviour in solution. The technique can now be used to obtain insights into the reactivity of these complexes and the way in which they form catalytic reaction intermediates. 相似文献
999.
Wong JW Maleknia SD Downard KM 《Journal of the American Society for Mass Spectrometry》2005,16(2):225-233
The calcium-dependent interaction of calmodulin and melittin is studied through the application of a radical probe approach in which solutions of the protein and peptide and protein alone are subjected to high fluxes of hydroxyl and other oxygen radicals on millisecond timescales. These radicals are generated by an electrical discharge within an electrospray ion source of a mass spectrometer. Condensation of the electrosprayed droplets followed by proteolytic digestion of both calmodulin and melittin has identified residues in both which participate in the interaction and/or are shielded from solvent within the protein complex. Consistent with other theoretical models and available experimental data, the tryptophan residue of melittin at position 19 is shown to be critical to the formation of the complex with the C-terminal domain of peptide enveloped by and protected from oxidation upon binding to the protein. Furthermore, the N-terminal domain (to residue 36) and tyrosine at position 99 in calmodulin are significantly protected from limited oxidation upon the binding of melittin while exposing the phenylalanine residue at position 92 of the flexible loop domain. The N-terminus (through residue 36) of calmodulin is shown to lie in closer proximity to the melittin helix than its C-terminal counterpart (residues 127-148) based upon the protection levels measured at reactive residues within these segments of the protein. 相似文献
1000.