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31.
Roberta Pierattelli Lucia Banci D. L. Turner 《Journal of biological inorganic chemistry》1996,1(4):320-329
The chemical shifts of several 13C nuclei positioned α to the haems in oxidised cyanide complexes of horseradish peroxidase and lignin peroxidase are reported and analysed in terms
of π molecular orbitals with perturbed D4h symmetry. The additional contributions to the paramagnetic shifts of 13C nuclei in the vinyl groups which arise from conjugation with the porphyrin π molecular orbitals are discussed, and an empirical correction factor is derived from a number of other compounds which contain
haems b. The orbital mixing parameter which is obtained from the analysis of the experimental 13C shifts is compared with the orientation of the axial histidine ligands in X-ray structures of related compounds and found
to be close to the orientation of the normal to the histidine ring. Comparison with the magnetic axes determined by fitting
the dipolar shifts of several protons which have been assigned previously also shows close agreement with the negative in-plane
rotation of the magnetic y axis. It is therefore possible to obtain the approximate orientation of the magnetic axes from 13C resonances of the haem and hence to determine the dipolar shifts at any point in space with respect to the haem by using
these axes together with the anisotropy of the magnetic susceptibility, which can be obtained by extrapolation from EPR g values. Excellent agreement is found between dipolar shifts obtained by fitting an empirical magnetic susceptibility tensor
and predictions based on 13C NMR and EPR in the case of lignin peroxidase. The agreement is less good in the case of horseradish peroxidase, in which
the empirical magnetic z axis appears to be tilted significantly away from the haem normal, though this may be due in part to the lack of accurate
atomic coordinates. It is concluded that useful estimates of the magnetic susceptibility tensor may be obtained from 13C NMR and EPR studies even in large mammalian peroxidases for which no structural models are available.
Received: 27 December 1995 / Accepted: 17 April 1996 相似文献
32.
Umberto Belluco Roberta Bertani Rino A. Michelin Mirto Mozzon Franco Benetollo Gabriella Bombieri Robert J. Angelici 《Inorganica chimica acta》1995,240(1-2):567-574
The chloro complexes trans-[Pt(Me)(Cl)(PPh3)2], after treatment with AgBF4, react with 1-alkynes HC---C---R in the presence of NEt3 to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh3)2] (R = p-tolyl (1), Ph (2), C(CH3)3 (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH2)nCl (n = 2, 3) in the presence of 1 equiv. of HBF4 to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH2)nCl](CH2R) } (PPh3)2][BF4] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph)2(PMe2Ph)2] with 2 equiv. HBF4 and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH2CH2CH2Cl)(CH2Ph) } (PMe2Ph)2][BF4] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH2CH2Cl)(CH2Ph) } (PPh3)2][BF4] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh3)2], after treatment with AgBF4 in HOCH2CH2Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe2Ph)]2 with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl2{C(OCH2CH2CH2Cl)(CH2C6H4-p-Me}(PMe2Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna21, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) Å3 and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry. 相似文献
33.
34.
Roberta S. Wallace J. Andrew Teare Edward Diebold Margaret Michaels Mary Jo Willis 《Zoo biology》1995,14(4):311-316
To establish baseline hematologic and plasma biochemistry values in free-ranging Humboldt penguins (Spheniscus humboldti), heparinized blood samples were collected from 51 apparently healthy, adult Humboldt penguins residing at two colonies off the Chilean coast. Thirty samples were collected in April, 1992, from penguins inhabiting the Ex-islote de los Pájaros Niños in Algarrobo, Chile. In September, 1992, 21 samples were collected from birds inhabiting Isla de Cachagua, Chile. Hematologic values measured include packed cell volume, leucocyte count, leucocyte differential, and the presence of blood parasites. Plasma biochemistry values measured include glucose, blood urea nitrogen, creatinine, uric acid, calcium, inorganic phosphorous, sodium, potassium, chloride, total protein, albumin, globulin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin, and creatine kinase. Only the mean values for chloride and for the number of eosinophils differed significantly between the two sample groups. No blood parasites were seen. © 1995 Wiley-Liss, Inc. 相似文献
35.
Frank W. Crow Kenneth B. Tomer Michael L. Gross James A. McCloskey Donald E. Bergstrom 《Analytical biochemistry》1984,139(1):243-262
The positive and negative ion fast atom bombardment (FAB) mass spectra and fast atom bombardment collisionally activated decomposition (CAD) spectra of a series of nucleosides and two dinucleotides are reported. The nucleosides studied are substituted forms of guanosine, adenosine, nebularine, tubercidin, uridine, and related pyrimidines. The FAB and CAD data both contain similar information. The CAD spectra are found to provide some structural information not found in the FAB mass spectra. Tandem mass spectrometry also allows emphasis to be put on weak fragments which are either not observed in the FAB mass spectrum or are lost in the matrix ion signals. 相似文献
36.
Summary X-inactivation patterns were studied by replication analyses both in lymphocytes and skin fibroblasts of two patients carrying balanced X-autosome translocations, t(X;10)-(pter;q11) and t(X;17)(q11;q11), and one patient with an unbalanced translocation t(X;22)(p21;q11). Preferential late replication of the normal X chromosome was found in lymphocytes of both patients carrying balanced translocations and in skin fibroblasts of the patient carrying the translocation t(X;17). However, skin fibroblasts of the patient with a translocation t(X;10) showed preferential late replication of the abnormal der(X) chromosome with no spreading of late replication to the autosomal segment. In the case of unbalanced translocation t(X;22) there was preferential late replication of the der(X) chromosome both in lymphocytes and skin fibroblasts. The abnormal phenotype of the patients is discussed in relation to the observed X-inactivation patterns and the variability of the patterns in different tissues. 相似文献
37.
Rino Cella Roberta Colombo Maria Grazia Galli Erik Nielsen Franco Rollo Francesco Sala 《Physiologia plantarum》1982,55(3):279-284
Rice ( Oryza sativa L.) cells returning to in vitro culture after preservation at superlow temperature in liquid nitrogen are characterized by a number of physiological alterations. These include: reduction in respiration and glucose uptake, loss of intracellular potassium, decrease in the cellular level of key metabolites (ATP, glucose-6-phosphate and pyruvate) and fragility of protoplasts following the action of cell wall-degrading enzymes.
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献
38.
Guanine aminohydrolase (GAH) (E.C. 3.5.4.3) was purified by affinity chromatography on 9-(p-β-aminoethoxyphenyl)guanine-Sepharose to a specific activity of 35.5 units/mg. The molecular weight of the enzyme was estimated to be 110,000 by gel filtration. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS) showed that the enzyme was composed of subunits with molecular weights of approximately 52,000. Data from SDS-gel electrophoresis in a discontinuous buffer system and from isoelectric focusing in the presence of 8-m urea indicated that more than one type of subunit were present. This was consistent with multiple forms of the native enzyme seen by electrophoresis and isoelectric focusing in polyacrylamide gels. The isoelectric points for the different forms of GAH were in the range of 4.65–4.85. Amino acid analyses showed cysteine to be the minimum amino acid and gave a calculated molecular weight for GAH of 53,016 when the assumption that there were four cysteines per subunit was made. Guanine, 8-azaguanine, and 6-thioguanine served as substrates for the enzyme but 3-deazaguanine, a potent competitive inhibitor of GAH, did not. Fluoride ion inhibited the enzyme in a noncompetitive manner, and this inhibition decreased as pH increased. Variation of the kinetic parameters with pH suggested that hydroxide ion might be the second substrate and that a functional group on the enzyme with a pKa near 5.6 was involved in the reaction. The enzyme was inactivated by treatment with p-hydroxymercurobenzoate and by photooxidation in the presence of rose bengal. Two plausible mechanisms are proposed for the reaction catalyzed by GAH. 相似文献
39.
In the study of chemical modification of enzymes and other biologically active proteins, plots of fractional residual activity
as a function of number of groups modified per enzyme molecule are often used to establish a correlation between the chemical
modification and enzyme inactivation reactions and to determine the stoichiometry of the modification reaction. This paper
presents a critical examination of the underlying theoretical framework of such graphs. Whereas these plots are usually presented
as linear functions, it is shown here that the general equation describing the relationship between inactivation and modification
contains an exponential term; therefore, in the general case, the plot is actually a curve. It is suggested that caution be
exercised in the interpretation of such plots and that equations such as those derived in the text be used to fit theoretical
curves to the data, in order to maximize the information gained from chemical modification experiments. 相似文献
40.
Somatic embryoids differentiated in suspension cultures of G. klotzschianum after 3–4 weeks of culture in a liquid medium containing glutamine (optimally, 10–15 mM). Embryogenesis occurred after a preculture of callus on a medium containing 10 mg/l of the cytokinin, 2iP. The embryoids had meristematic regions, a well formed epidermis, and formed roots and vestigial leaves. Asparagine was much less effective than glutamine in promoting embryoid differentiation. The presence of 2,4-D in the medium resulted in increased vigor of the suspension cultures and subsequently in the formation of many embryoids, but does not seem to be necessary for somatic embryogenesis in cotton.Technical Article 14646 from the Texas Agricultural Experiment Station 相似文献