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1.
2.
This minireview makes an initial assessment of the progress made using anisotropy decay measurements for investigating the conformational changes and molecular dynamics in soluble systems. A critical analysis of available data is presented. The anisotropy decays of the tryptophan fluorescence of staphylococcal nuclease, adrenocorticotropin, melittin and of labeled transfer RNA were studied for investigating the functional conformational changes of these systems. The emissions of variously labeled immunoglobulins have been used to elucidate the conformations of these proteins before and after the binding of specific antibodies. Labeled myosin and its fragments have given information on the functional motions of the protein domains. The anisotropy decays of labeled and natural hemoglobin systems have been utilized for exploring the allosteric behavior of these molecules. The data suggest a wide applicability of this technique to the study of protein dynamics and conformational changes of macromolecules. 相似文献
3.
E Bucci H Malak C Fronticelli I Gryczynski G Laczko J R Lakowicz 《Biophysical chemistry》1988,32(2-3):187-198
We used front-face illumination to examine the steady-state and time-resolved emission from the intrinsic tryptophan emission of human hemoglobin (Hb). Experimental conditions were identified which eliminated all contributions of scattered light. The sensitivity obtained using front-face optics was adequate to allow measurement of the wavelength-dependent frequency response of the emission to 2 GHz. The intensity decays displayed pico- and nanosecond components in the emission at all wavelengths from 315 to 380 nm. The contribution of the picosecond component decreased from 72 to 37% over this range of wavelengths. Frequency-domain measurements were used to calculate the time-resolved emission spectra and decay-associated emission spectra. These spectra indicate that the picosecond components of the emission display maxima near 320 nm, whereas the nanosecond components are centered at longer wavelengths near 335 nm. The nanosecond components appear to be due to residual impurities which remain even in highly purified samples of Hb. However, we cannot eliminate the possibility that some of these components are due to Hb itself. 相似文献
4.
Claudio Fortis Elisabetta Ferrero Mauro Biffi Silvia Heltai Carlo Besana Eraldo Bucci Moreno Tresoldi Claudio Rugarli 《Cancer immunology, immunotherapy : CII》1991,34(2):128-132
Summary Burkitt lymphoma (BL) lines can be grouped according to phenotypic characteristics. Group I cells exhibit the phenotype of resting B cells and grow as single cells. Such lines can be Epstein-Barr-virus(EBV)-negative or -positive. Group II and group III cells are always EBV-positive, they express B cell activation markers, grow in aggregates and resemble in varying degrees lymphoblastoid cell lines (LCL). We studied three groups of BL lines for their capacity to interact with allogeneic lymphocytes. The results showed that as long as the lines have the group I phenotype, they do not stimulate allogeneic T lymphocytes irrespective whether they carry the EBV genome. The group II and III cells are stimulatory. Generally there was no correlation between sensitivity to lymphocyte-mediated lysis and the phenotype of the lines. In one set of lines, the group I cells had higher sensitivity to both natural killer and lymphokine-activated killer effectors compared to the group II or III lines. However, such correlation could not be seen with the other two sets of lines. Among the phenotypic features investigated, expression of the adhesion molecules LFA-1 and LFA-3 correlated with the tendency for cell aggregation. 相似文献
5.
F Panicucci G Angeloni S Arrighi E Bucci G DiMambro L Lecchini S Pitruzzello M Positano 《Journal of biological standardization》1985,13(2):115-121
Two secondary standards for use in routine assays of Factor VIII in therapeutic concentrates and in patients, plasmas, respectively, have been established in a multicenter collaborative study. In order to assess the effect of the adoption of these preparations as common Secondary Standards a comparative assay has been performed: one sample of a Factor VIII concentrate of intermediate purity and one plasma sample have been tested in two laboratories for Factor VIII:C activity using as reference, among others, the common working standard. Analysis of the results shows that with the plasma sample the differences of the estimates obtained with any of the references in our two laboratories were not statistically significant (P greater than 0.3), while with the concentrate sample the differences were always statistically significant (P less than 0.005). The study shows that the adoption of common working standards (besides the uniformity in assay method, reagents and basic equipment) is not sufficient to eliminate interlaboratory variation in the measurement of Factor VIII:C. 相似文献
6.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
7.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
8.
Solvent regulation of oxygen affinity in hemoglobin. Sensitivity of bovine hemoglobin to chloride ions 总被引:1,自引:0,他引:1
Under physiological conditions of pH (7.4) and chloride concentration (0.15 M), the oxygen affinity of bovine hemoglobin is substantially lower than that of human hemoglobin. Also, the Bohr effect is much more pronounced in bovine hemoglobin. Numerical simulations indicate that both phenomena can be explained by a larger preferential binding of chloride ions to deoxyhemoglobin in the bovine system. Also, they show that the larger preferential binding may be produced by a decreased affinity of the anions for oxyhemoglobin, thereby stressing the potential relevance of the oxy conformation in regulating the functional properties of the protein. The conformation of the amino-terminal end of the beta subunits appears to regulate the interaction of hemoglobin with solvent components. The pronounced sensitivity of the oxygen affinity of bovine hemoglobin to chloride concentration and to pH suggests that in bovine species these are the modulators of oxygen transport in vivo. 相似文献
9.
Functional studies on human semi-hemoglobin 总被引:1,自引:0,他引:1
10.