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61.
Ultraviolet action spectra for DNA dimer induction, lethality, and mutagenesis in Escherichia coli with emphasis on the UVB region 总被引:4,自引:0,他引:4
Abstract —Ultraviolet (UV) action spectra were obtained for lethality and mutagenesis (reversion to tryptophan independence) in Escherichia coli WP2s for wavelengths 254–405 nm with detailed analysis in the UVB region (290–320 nm). Parallel chemical assay yields of pyrimidine dimers in DNA of E. coli RT4 were determined at the same wavelengths. Spectral regions isolated from a Xe arc and resonance lines from a high-pressure Hg-Xe arc lamp were both used for irradiation. In all cases, precise energy distributions throughout the isolated Xe bands regions were defined.
Lethality, mutagenesis, and dimer induction all decreased in efficiency in a similar fashion as the wavelengths of the radiation increased. Between 300 and 320 nm, all characteristics measured showed differences of about two and a half orders of magnitude. Between these wavelengths, the values of the three end points used either coincide with or parallel the absorption spectrum of DNA. The mutagenesis action spectrum coincides closely with the absorption spectrum of DNA. The lethality spectrum is closely parallel to the mutagenicity spectrum; the points, however, consistently occur at about 2 nm longer wavelengths. A calculation derived from the slope of the UVB spectra reveals that a 1-nm shift of the solar UV spectrum to shorter wavelengths would result in a 35% increase in its mutagenic potential. At 325 nm, both biological action spectra show sharp decreases in slope. In addition, above 325 nm the spectra for lethality. mutagenicity, and dimer formation diverge sharply; lethalities at these UVA wavelengths were approximately tenfold greater relative to mutagenicity than at shorter wavelengths. The relative yield of dimer formation by 365 nm radiation is intermediate between the yields for lethality and mutagenesis. 相似文献
Lethality, mutagenesis, and dimer induction all decreased in efficiency in a similar fashion as the wavelengths of the radiation increased. Between 300 and 320 nm, all characteristics measured showed differences of about two and a half orders of magnitude. Between these wavelengths, the values of the three end points used either coincide with or parallel the absorption spectrum of DNA. The mutagenesis action spectrum coincides closely with the absorption spectrum of DNA. The lethality spectrum is closely parallel to the mutagenicity spectrum; the points, however, consistently occur at about 2 nm longer wavelengths. A calculation derived from the slope of the UVB spectra reveals that a 1-nm shift of the solar UV spectrum to shorter wavelengths would result in a 35% increase in its mutagenic potential. At 325 nm, both biological action spectra show sharp decreases in slope. In addition, above 325 nm the spectra for lethality. mutagenicity, and dimer formation diverge sharply; lethalities at these UVA wavelengths were approximately tenfold greater relative to mutagenicity than at shorter wavelengths. The relative yield of dimer formation by 365 nm radiation is intermediate between the yields for lethality and mutagenesis. 相似文献
62.
Arylspiroborates Derived from 4‐tert‐Butylcatechol and 3,5‐Di‐tert‐butylcatechol and Their Antimicrobial Activities 下载免费PDF全文
Michael I. Webb Nathan R. Halcovitch Eric G. Bowes Graham M. Lee Michael J. Geier Christopher M. Vogels Taryn O'Neill Haoxin Li Andrew Flewelling Andreas Decken Christopher A. Gray Stephen A. Westcott 《Journal of heterocyclic chemistry》2014,51(1):157-161
A family of arylspiroborates has been prepared by the addition of either 4‐tert‐butylcatechol or 3,5‐di‐tert‐butylcatechol to boric acid and an alkali metal hydroxide. All compounds were characterized fully using multinuclear NMR spectroscopy and by elemental analyses. A single crystal X‐ray diffraction was carried out on potassium (bis‐(3,5‐di‐tertbutyl[1,2‐benzenediolato(2‐)‐O,O′]borate)) ( 8 ). All compounds displayed appreciable anti‐microbial activities. 相似文献
63.
Y. Leon P. Sciau P. Goudeau N. Tamura S. Webb A. Mehta 《Applied Physics A: Materials Science & Processing》2010,99(2):419-425
In addition to the red terra sigillata production, the largest Gallic workshop (La Graufesenque) made a special type of terra sigillata, called “marbled” by the archaeologists. Produced exclusively at this site, this pottery is characterized by a surface finish
made of a mixture of yellow and red slips. Because the two slips are intimately mixed, it is difficult to obtain the precise
composition of one of the two constituents without contamination from the other. In order to obtain very precise correlation
at the appropriate scale between the color aspect and the elemental and mineralogical phase distributions in the slip, combined
electron microprobe, X-ray micro spectroscopies and micro diffraction on cross-sectional samples were performed. The aim of
this study is to discover how potters were able to produce this unique type of terra sigillata and especially this particular slip of an intense yellow color. Results show that the yellow component of marbled sigillata was made from a titanium-rich clay preparation. The color is due to the formation of a pseudobrookite (TiFe2O5) phase in the yellow part of the slip, the main characteristics of that structure being considered nowadays as essential
for the fabrication of stable yellow ceramic pigments. Its physical properties such as high refractive indices and a melting
point higher than that of most silicates widely used as ceramic colorants are indeed determinant for this kind of application.
Finally, the red parts have a similar composition (elementary and mineralogical) to the one of standard red slip. 相似文献
64.
65.
66.
The collision processes responsible for populating and de-populating upper and lower levels of the cw He-Hg ion laser are investigated using flowing afterglow techniques. It is shown that the superior performance of the laser at 6150 Å compared to that at 7945 Å is not due to a difference in excitation mechanism — both are excited by charge transfer from He+ — but instead reflects a greater effectiveness of second kind collisions of electrons in depopulating the 7p2P upper level of the 7945 Å transition. The charge transfer, excitation rate constants for several Hg II levels are compared, and values for the rate constant for the electron collision de-excitation process are deduced. 相似文献
67.
M. L. Martin M. L. Filleux-Blanchard G. J. Martin G. A. Webb 《Magnetic resonance in chemistry : MRC》1980,13(6):396-402
Rotational barriers and 15N chemical shifts have been measured in a number of ureas and thioureas. As anticipated on the basis of the 15N shifts, several previously unobserved rotational barriers could be detected by using lanthanide reagents or a high field spectrometer. Nearly constant effects on both the rotational activation energy and the 15N shift are produced on going from ureas to the corresponding thioureas, and correlations are found between the ΔG? and δ15N values. The results are discussed in terms of lone pair delocalization, and anomalies with respect to the general behaviour are tentatively explained in the light of the effect of steric torsion in crowded structures on the 15N shifts and rotation barriers. 相似文献
68.
69.
L. Baksay A. Boehm H. Foeth A. Staude W. Lockman M. Medinnis T. Meyer J. Rander P. Schlein T. Trippe R. Webb R. Ellis B. Naroska P. Strolin 《Physics letters. [Part B]》1975,53(5):484-488
In a single-arm magnetic spectrometer experiment at the CERN Intersecting Storage Rings (ISR), a prominent diffractive enhancement is observed for inclusive production of (pπ+π?) systems near x ~ 1 at √s = 53 and 35 GeV. In testing limiting fragmentation and scaling for this system, inclusive pπ+π? diffractive excitation into a fixed invariant mass range is found to possess a cross-section independent of s to within (3 ± 5)%. The main component in the (pπ+π?) system is Δ(1236)π, with a charge structure compatible with the break-up of an isotopic spin system. 相似文献
70.
The shape and moments of the F+ absorption band in SrO have been measured between 4.2K and 300K. Analysis of the moments gives the effective frequency of the vibrational modes interacting with the centre as , and the Huang-Rhys factors for cubic and non-cubic modes as SC = 3 ± 1 and SNC = 4 ± 1 respectively. 相似文献