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991.
AIMS: To evaluate the occurrence and abundance of phages that carry the stx(1) and stx(2) gene in water samples of different quality. METHODS AND RESULTS: Phages growing on the Shiga toxin-negative Escherichia coli O157:H7 (ATCC 43,888) strain were enumerated by a plaque assay in concentrated raw and treated waste water samples and river water samples. Plaques were investigated for the presence of stx(1) and stx(2) genes by a multiplex/nested PCR procedure. An overall number of 805 plaques were tested for the presence of stx-carrying phages. Stx genes could be demonstrated in 2% (stx(1)) and 16% (stx(2)) of the plaques. Stx-phages were eliminated with approximately the same efficiency in comparison with somatic coliphages during the waste water treatment process. CONCLUSIONS: Due to the low numbers of phages carrying the stx genes 1 and 2 in treated waste water and river water, the dilution and inactivation of host bacteria and the unsuitable conditions for the transduction of host organisms in aquatic environments, it is difficult to derive from the data the direct evidence for a public health problem. SIGNIFICANCE AND IMPACT OF THE STUDY: The results show the quantitative occurrence of stx-carrying phages in waste and river water and confirm the frequent circulation of these viruses in the aquatic environment. 相似文献
992.
Reaction centers (RCs) of purple bacteria are uniquely suited objects to study the mechanisms of the photosynthetic conversion of light energy into chemical energy. A recently introduced method of higher order derivative spectroscopy [I.K. Mikhailyuk, H. Lokstein, A.P. Razjivin, A method of spectral subband decomposition by simultaneous fitting the initial spectrum and a set of its derivatives, J. Biochem. Biophys. Methods 63 (2005) 10-23] was used to analyze the NIR absorption spectra of RC preparations from Rhodobacter (R.) sphaeroides strain 2R and Blastochloris (B.) viridis strain KH, containing bacteriochlorophyll (BChl) a and b, respectively. Q(y) bands of individual RC porphyrin components (BChls and bacteriopheophytins, BPheo) were identified. The results indicate that the upper exciton level P(y+) of the photo-active BChl dimer in RCs of R. sphaeroides has an absorption maximum of 810nm. The blue shift of a complex integral band at approximately 800nm upon oxidation of the RC is caused primarily by bleaching of P(y+), rather than by an electrochromic shift of the absorption band(s) of the monomeric BChls. Likewise, the disappearance of a band peaking at 842nm upon oxidation of RCs from B. viridis indicates that this band has to be assigned to P(y+). A blue shift of an absorption band at approximately 830nm upon oxidation of RCs of B. viridis is also essentially caused by the disappearance of P(y+), rather than by an electrochromic shift of the absorption bands of monomeric BChls. Absorption maxima of the monomeric BChls, B(B) and B(A) are at 802 and 797nm, respectively, in RCs of R. sphaeroides at room temperature. BPheo co-factors H(B) and H(A) peak at 748 and 758nm, respectively, at room temperature. For B. viridis RCs the spectral positions of H(B) and H(A) were found to be 796 and 816nm, respectively, at room temperature. 相似文献
993.
Iuchi S Marsch-Moreno M Velez-DelValle C Easley K Kuri-Harcuch W Green H 《Differentiation; research in biological diversity》2006,74(4):160-166
Human embryonic stem (ES) cells are usually co-cultivated with supporting cells consisting of short-term cultures of fibroblasts (not an immortalized line) in a medium lacking serum. This method has promoted important progress in the field, but suffers from certain disadvantages. By serial cultivation for 27 consecutive transfers and about 63 cell generations, we have evolved an immortalized line from fibroblastic cells of 12-13-day mouse embryos. This line (MMM) supports the multiplication of H9 cells better than the 3T3 line. It supports the growth of H9 cells as well as do available short-term fibroblast cultures, but maintains more effectively the stem cell character of the H9 cells, judging by their better retention of Oct4. We have made MMM cells resistant to blasticidin and zeocin, the most efficient antibiotics for selection of stable transformants. In the presence of zeocin, the resistant MMM were able to support multiplication and selection of ES cells transfected with an exogenous gene encoding zeocin resistance. 相似文献
994.
Pascal V. Grundler 《Inorganica chimica acta》2006,359(6):1795-1806
The ruthenium(II) hexaaqua complex [Ru(H2O)6]2+ reacts with dihydrogen under pressure to give the η2-dihydrogen ruthenium(II) pentaaqua complex [Ru(H2)(H2O)5]2+.The complex was characterized by 1H, 2H and 17O NMR: δH = −7.65 ppm, JHD = 31.2 Hz, δO = −80.4 ppm (trans to H2) and δO = −177.4 ppm (cis to H2).The H-H distance in coordinated dihydrogen was estimated to 0.889 Å from JHD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by 1H and 2H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: kf = (1.7 ± 0.2) × 10−3 kg mol−1 s−1 and Keq = 4.0 ± 0.5 mol kg−1.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (Id).In deuterated water, one can observe that [Ru(H2)(H2O)5]2+ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η2-dihydrogen ligand was determined as k1 = (0.24 ± 0.04) × 10−3 s−1.The upper and lower limits of the pKa of the coordinated dihydrogen ligand have been estimated:3 < pKa < 14. 相似文献
995.
996.
Polyanichko AM Chikhirzhina EV Andrushchenko VV Vorob'ev VI Wieser H 《Biopolymers》2006,83(2):182-192
The interactions were studied of DNA with the nonhistone chromatin protein HMGB1 and histone H1 in the presence of manganese(II) ions at different protein to DNA and manganese to DNA phosphate ratios by using absorption and optical activity spectroscopy in the electronic [ultraviolet (UV) and electronic circular dichroism ECD)] and vibrational [infrared (IR) and vibrational circular dichroism (VCD)] regions. In the presence of Mn2+, the protein-DNA interactions differ from those without the ions and cause prominent DNA compaction and formation of large intermolecular complexes. At the same time, the presence of HMGB1 and H1 also changed the mode of interaction of Mn2+ with DNA, which now takes place mostly in the major groove of DNA involving N7(G), whereas interactions between Mn2+ and DNA phosphate groups are weakened by histone molecules. Considerable interactions were also detected of Mn2+ ions with aspartic and glutamic amino acid residues of the proteins. 相似文献
997.
A new derivative of racemic gossypol with 2-thiophenecarbohydrazide (GHHT) and its complexes with monovalent cations have been synthesized and studied by electrospray ionization-mass spectroscopy (ESI-MS), multinuclear nuclear magnetic resonance (NMR), as well as by the Parametric Method 5 (PM5) methods. It is demonstrated that GHHT forms stable complexes of 1:1 stoichiometry with monovalent metal cations. The structures of the complexes are stabilized by three types of intramolecular hydrogen bonds. The spectroscopic methods have provided clear evidence that GHHT and its complexes exist in the DMSO-d6 solution in the N-imine-N-imine tautomeric forms. The structures of the GHHT and its complexes with Li+, Na+, K+, Rb+, and Cs+ cations are visualized and discussed in detail. 相似文献
998.
Monensin A methyl ester complexes with Li+, Na+, and K+ cations studied by ESI-MS, 1H- and 13C-NMR, FTIR, as well as PM5 semiempirical method 总被引:1,自引:0,他引:1
Monensin A methyl ester (MON1) was synthesized by a new method and its ability to form complexes with Li+, Na+, and K+ cations was studied by electrospray ionization-mass spectroscopy (ESI-MS), 1H and 13C nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), and PM5 semiempirical methods. It is shown that MON1 with monovalent metal cations forms stable complexes of 1:1 stoichiometry. The structures of the complexes are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. In the structure of MON1, the oxygen atom of the C=O ester group is involved in very weak bifurcated intramolecular hydrogen bonds with two hydroxyl groups, whereas in the complexes of MON1 with monovalent metal cations the C=O ester group is not engaged in any intramolecular hydrogen bonds. Furthermore, it is demonstrated that the strongest intramolecular hydrogen bonds are formed within the MON1-Li+ complex structure. The structures of the MON1 and its complexes with Li+, Na+, and K+ cations are visualized and discussed in detail. 相似文献
999.
Covalent linkages between wall polysaccharides and lignin, especially linkage between cellulose and lignin were discussed by carboxymethylation technique of whole cell walls of coniferous and nonconiferous woods. Hydroxyl groups of plant cell walls polysaccharides were highly substituted, but not those of lignin by carboxymethyl groups under the used conditions, and separated into water-soluble and insoluble fractions by water extraction. Carboxymethylated wall polysaccharides linked covalently with lignin were distributed into the water-insoluble fractions. Composition of carboxymethylated sugar residues in the both fractions was analyzed quantitatively by 1H NMR spectroscopy after hydrolyzation with D2SO4 in D2O. More than half of cellulose linked covalently with lignin in coniferous wood, but only one-sixth of cellulose was involved in the linkage in nonconiferous wood. The major noncellulosic wall polysaccharides of coniferous wood also linked significantly with lignin. On the other hand, noncellulosic wall polysaccharides of nonconiferous wood were involved slightly in the covalent linkage with lignin. The situation of linkage between wall polysaccharides containing cellulose and lignin was visualized by scanning electron micrographs. 相似文献
1000.