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101.
Fauhl C Wittkowski R Lofthouse J Hird S Brereton P Versini G Lees M Guillou C 《Journal of AOAC International》2004,87(5):1179-1188
The aim of the present study was to provide the official wine control authorities with an internationally validated method for the determination of 3-methoxy-1,2-propanediol (3-MPD) and cyclic diglycerols (CycDs)-both of which are recognized as impurities of technical glycerol-in different types of wine. Because glycerol gives a sweet flavor to wine and contributes to its full-body taste, an economic incentive is to add glycerol to a wine to mask its poor quality. Furthermore, it is known that glycerol, depending on whether it is produced from triglycerides or petrochemicals, may contain considerable amounts of 3-MPD in the first case or CycDs in the second. However, because these compounds are not natural wine components, it is possible to detect glycerol added to wine illegally by determining the above-mentioned by-products. To this end, one of the published methods was adopted, modified, and tested in a collaborative study. The method is based on gas chromatographic/mass spectrometric analysis of diethyl ether extracts after salting out with potassium carbonate. The interlaboratory study for the determination of 3-MPD and CycDs in wine was performed in 11 laboratories in 4 countries. Wine samples were prepared and sent to participants as 5 blind duplicate test materials and 1 single test material. The concentrations covered ranges of 0.1-0.8 mg/L for 3-MPD and 0.5-1.5 mg/L for CycDs. The precision of the method was within the range predicted by the Horwitz equation. HORRAT values obtained for 3-MPD ranged from 0.8 to 1.7, and those obtained for CycDs ranged from 0.9 to 1.3. Average recoveries were 104 and 109%, respectively. 相似文献
102.
Field SJ Thornton NP Anderson LJ Gates AJ Reilly A Jepson BJ Richardson DJ George SJ Cheesman MR Butt JN 《Dalton transactions (Cambridge, England : 2003)》2005,(21):3580-3586
Protein film voltammetry of Paracoccus pantotrophus respiratory nitrate reductase (NarGH) and Synechococcus elongatus assimilatory nitrate reductase (NarB) shows that reductive activation of these enzymes may be required before steady state catalysis is observed. For NarGH complementary spectroscopic studies suggest a structural context for the activation. Catalytic protein film voltammetry at a range of temperatures has allowed quantitation of the activation energies for nitrate reduction. For NarGH with an operating potential of ca. 0.05 V the activation energy of ca. 35 kJ mol-1 is over twice that measured for NarB whose operating potential is ca. -0.35 V. 相似文献
103.
Jones SC Hascall T Barlow S O'Hare D 《Journal of the American Chemical Society》2002,124(39):11610-11611
The bimetallic complexes [M(CO)(3)](2)(mu:eta(5):eta(5)-Pn) (Pn = pentalene, C(8)H(6); M = Mn, Re) have been synthesized and characterized crystallographically; the Mn compound was isolated as solely the anti-isomer, while the Re analogue was formed as a mixture of anti- and syn-isomers. [Mn(CO)(3)](2)(mu:eta(5):eta(5)-Pn) may be reduced chemically to its mono- and dianions; the mixed-valence Mn(I)/Mn(0) monoanion is shown by ESR, vibrational, and electronic spectroscopies to be a Robin-Day class III system with an exceptionally large electronic coupling between the metal centers. 相似文献
104.
James O'Donnell Bruno Rusterholz Barbara Aebersold Denise Rüegg Wilhelm Simon Ernö Pretsch 《Mikrochimica acta》1994,113(1-2):45-52
In an investigation of octamethylene bis(malonic acid diamides) and their selectivities for magnesium, it was found that presence of secondary amides within the particular ionophore played a considerable role in the enhancement of magnesium selectivity. Similar effects in other ionophores, i.e. tris(malonic acid diamides), were thus systematically looked at with the help of selectivity measurements with the hope of optimizing the number of secondary and tertiary amides so as to improve the magnesium selectivity. The syntheses of several investigated tris(malonic acid diamide) isologues are equally reported.Deceased in November 1992 相似文献
105.
The reaction of hydroxy peroxy radicals (RO(2)) with NO represents one of the most crucial tropospheric processes, leading to terrestrial ozone formation or NO(x)() removal and chain termination. We investigate the formation of hydroxy peroxy nitrites (ROONO) and nitrates (RONO(2)) from the OH-isoprene reactions using DFT and ab initio theories and variational RRKM/master equation (vRRKM/ME) formalism. The binding energies of ROONO from NO addition to RO(2) are determined to be in the range of 20-22 kcal mol(-)(1), and the bond dissociation energies of ROONO to form an alkoxy radical (RO) and NO(2) range from 6 to 9 kcal mol(-)(1). Isomerization of ROONO to RONO(2) is exothermic by 22-28 kcal mol(-)(1). The entrance and exit channels of the RO(2)-NO reaction are found to be barrierless, and the rate constants to form ROONO are calculated to be 3 x 10(-)(12) to 2 x 10(-)(11) cm(3) molecule(-)(1) s(-)(1) using the canonical variational transition state theory. The vRRKM/ME analysis reveals negligible stabilization of excited ROONO and provides an assessment of ROONO isomerization to RONO(2). 相似文献
106.
We apply the recently developed adaptive ensemble optimization technique to simulate dense Lennard-Jones fluids and a particle-solvent model by broad-histogram Monte Carlo techniques. Equilibration of the simulated fluid is improved by sampling an optimized histogram in radial coordinates that shifts statistical weight towards the entropic barriers between the shells of the liquid. Interstitial states in the vicinity of these barriers are identified with unprecedented accuracy by sharp signatures in the quickly converging histogram and measurements of the local diffusivity. The radial distribution function and potential of mean force are calculated to high precision. 相似文献
107.
Density functional theory (DFT) calculations have been used to investigate the effect of intermetallic electron transfer on the mode of magnetic coupling in the face-shared bimetallic complexes MWCl(9)(n-) (M = V, Cr, Mn; all with a nominal d(3) valence electronic configuration on each metal atom). These calculations illustrate a simple rule: when the oxidation state of M is lower than that of W, antiferromagnetic coupling is preferred, while ferromagnetism (via crossed exchange pathways) is favored when M has the higher oxidation state. This underlying trend in intermetallic interactions is seen to depend on the interplay among ligand field splitting, spin polarization splitting of alpha- and beta-spin orbitals, and the relative energies of the M and W valence d orbitals, and is mirrored in the results seen in a wider survey of mixed-metal, face-shared complexes. 相似文献
108.
P. Rauschenbach und H. Simon 《Fresenius' Journal of Analytical Chemistry》1971,255(5):337-344
Zusammenfassung Nach Verbrennung im Sauerstoffkolben zeigen die Szintillationsproben häufig über Stunden eine ansteigende Zählrate. Auch danach unterscheiden sich identisch präparierte Proben noch statistisch signifikant stärker, als aufgrund von Wäge- und Pipettierfehlern zu erwarten ist. Die zeitliche Inkonstanz und die Unterschiede von Probe zu Probe lassen sich durch Löschkorrekturkurven (Abhängigkeit der Zählausbeute und des externen Standardkanalverhältnisses von der Sauerstoffkonzentration) weitgehend eliminieren. Die so erhaltenen dpm-Werte haben geringere Standardabweichungen als die durch interne Standardisierung erhaltenen. Das Verfahren der externen Standardisierung wird einer Fehleranalyse für einzel- und doppelmarkierte Proben unterworfen. Ein Toluol/Methanol/Phenäthylamin-System absorbiert Kohlendioxid und Wasser quantitativ. Für einzelmarkierte Proben können mit diesem Gemisch für 3H 25% und für 14C 85% Zählausbeute erhalten werden. Bei 3H/14C-Markierung werden bei einer Kanaloptimierung nach Klein und Eisler noch 15% Zählausbeute für 3H neben 10% für 14C erhalten.
Symbole und Abkürzungen ESKV Externes Standard-Kanal-Verhältnis - ESKV-ESKV0 - ESKV0 Beginn der Gültigkeit der Löschfunktion, stärkst gelöschte Probe - ZA auf 1,0 bezogene Zählausbeute - S Standardabweichung - cpm Impulsrate (min–1) - dpm Zerfallsrate (min–1) - A bzw. B nieder- bzw. höherenergetisches Nuklid - (A) Meßkanal A - k,l,m,n Eichfaktoren 相似文献
Comparison of errors in liquid scintillation counting after quench correction by external or internal standardisation applied for oxygen flask combustion of 3H- and/or 14C-labelled samples
After oxygen flask combustion scintillation samples often show an increase in counting rates for several hours. Even after such a time identically prepared samples are statistically significantly more different as one should expect by weighing and pipetting errors. The inconstant cpm values during the first hours and the differences between the samples can mostly be eliminated by quench correction curves (dependence of counting efficiency and external channel ratio upon oxygen concentration). The dpm values achieved according to this method show smaller standard deviations than by internal standardisation. The procedure of the external standardisation was examined for error propagation. A system of toluene/methanol/phenethylamine absorbs carbon dioxide and water quantitatively. With this mixture the following counting efficiencies are achieved: 25% for 3H, 85% for 14C and for samples containing 3H and 14C 15% for 3H and 10% for 14C if the 3H channel is adjusted according to Klein and Eisler.
Symbole und Abkürzungen ESKV Externes Standard-Kanal-Verhältnis - ESKV-ESKV0 - ESKV0 Beginn der Gültigkeit der Löschfunktion, stärkst gelöschte Probe - ZA auf 1,0 bezogene Zählausbeute - S Standardabweichung - cpm Impulsrate (min–1) - dpm Zerfallsrate (min–1) - A bzw. B nieder- bzw. höherenergetisches Nuklid - (A) Meßkanal A - k,l,m,n Eichfaktoren 相似文献
109.
Chemical sensors have been widely used for the analysis of volatile organic compounds. Employing chemical sensors in an array format with pattern recognition provides a higher degree of selectivity and reversibility leading to an extensive range of applications. When such systems are used for odour analysis they are termed electronic noses. Application of electronic noses ranges from the food industry, medical industry to environmental monitoring and process control. Many types of different gas sensors have been employed in the array. These include conducting polymers, metal oxide semiconductors, piezoelectric, optical fluorescence and amperometric gas sensors The transducer principle of these sensors is varied and is discussed in detail within this review. Examples of the current trends in sensor array technology as well as the applications to which the sensor-based noses have been applied are also discussed. 相似文献
110.