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991.
Summary A method for the gas chromatographic trace analysis of underivatized nitrophenols in ground-water is presented. Using a highly
de-activated separation system a satisfactory precision for their quantitative GC analysis could be achieved by avoiding condensation
of the solvent and by fast injection of the sample. The reproducibility of the peak areas of eleven nitrophenols in ethylacetate
was <5 % RSD. Using a nitrogen-phosphorus detector detection limits were in a range from 10 to 30 pg. Within the concentration
range from 0.1 to 10 ng μl−1 the calibrations were linear with correlation coefficients >0.992.
The approach described was applied to the analysis of nitrophenols in ground-water near a former ammunition plant, after preconcentration
by continuous liquid/liquid extraction with ethylacetate. Using a GC-MS technique and retention times various nitrophenols
were identified and then quantified in the μg/L-range by applying NPD. 相似文献
992.
Ghandi K Addison-Jones B Brodovitch JC McCollum BM McKenzie I Percival PW 《Journal of the American Chemical Society》2003,125(32):9594-9595
Muoniated free radicals have been detected in muon-irradiated aqueous solutions of acetone at high temperatures and pressures. At temperatures below 250 degrees C, the radical product is consistent with muonium addition to the keto form of acetone. However, at higher temperatures, a different radical was detected, which is attributed to muonium addition to the enol form. Muon hyperfine coupling constants have been determined for both radicals over a wide range of temperatures, significantly extending the range of conditions under which these radicals and the keto-enol equilibrium have been studied. 相似文献
993.
994.
35Cl NQR spectra of dichlorophosphates Me(PO2Cl2)2 · 2D (Me = Mg, Ca, Mn; D = CH3COOC2H5, CH3COCH3, POCl3) are studied in the temperature range 77 ? T (K) ? 305. It is shown that the three compounds with CH3COOC2H5 as donor are isomorphic at 77 K, the crystal structure of Mn(PO2Cl2)2· 2CH3COOC2H5. The structure of Mg(PO2Cl2)2?· 2CH3COCH3 and of Mg(PO2Cl2)2 · 2POCl3 probably consists of infinite chains as found for Mn(PO2Cl2)2· 2CH3COOC2H5. Mg(PO2Cl2)2· 2CH3COOC2H5 shows phase transformations and a complicated dynamical behaviour leading to strong deviations from a Bayertype NQR function v = f(T). The donor capacity of POCl3 in Mg(PO2Cl2)2· 2POCl3 is comparable with the donor strength in AsCl3 · POCl3 · A dπ-pπ overlap of the P-O bond influences the P-Cl bond. 相似文献
995.
Ronald N. Warrener Richard P. Johnson Charles W. Jefford David A. Ralph 《Tetrahedron letters》1979,20(31):2939-2942
Structural assignments are made to the three adducts derived from the title reaction. 1H-n.m.r., 13C-n.m.r. and euroshift data are used to support the new structures. 相似文献
996.
Episulfidation of (E)-cyclooctene and (E)-cyclononene was achieved with elemental sulfur by using a catalytic amount of a molybdenum oxo complex. 相似文献
997.
Dolashka-Angelova P Hristova R Stoeva S Voelter W 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1999,55(14):2927-2934
Hemocyanin (Hc) of Carcinus aestuarii contains three major and one minor electrophoretically separable polypeptide chains which were purified by fast protein liquid chromatography (FPLC) ion exchange chromatography. N-terminal amino acid sequences of four structural subunits (SSs) from C. aestuarii were compared with known N-terminal sequences from other arthropodan hemocyanins. The conformational changes, induced by various treatments, were monitored by far UV, CD and fluorescence spectroscopy. The critical temperatures for the structural subunits, Tc, determined by fluorescence spectroscopy, are in the region of 52-59 degrees C and coincide with the melting temperatures, Tm (49-55 degrees C), determined by CD spectroscopy. The free energy of stabilization in water, delta GDH2O, toward guanidinium hydrochloride is about 1.3 times higher for the dodecameric Hc as compared to the isolated subunits and about one time higher for Cal, comparing with other SSs. The studies reveal that the conformational stability of the native dodecamer towards various denaturants (temperature and guanidinium hydrochloride) indicate that the quaternary structure is stabilized by oligomerization between structural subunits, and the possibility of a structural role of the sugar mojeties cannot be excluded. 相似文献
998.
999.
1000.
During direct liquid introduction (DLI) liquid chromatography-mass spectrometry (LC-MS), the detectability of acetone is shown to be predictable, based on consideration of the gas-phase acidities and basicities of solvents methanol and acetonitrile and modifiers formic acid and ammonium formate. Consequently, ion formation in DLI LC-MS resembles gas-phase chemical ionization processes; since the order of acidities is altered in solution, solution ionization must be much less important than gas-phase. Ion populations could be predicted on the basis of gas-phase proton affinities and acidities: acetone could be detected in all solvent mixture by positive ions, but it was not readily detected by negative ions when acid was also present. In solvents without additives it was always detected. 相似文献