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991.
Mutational analysis of the leucine zipper-like motif of the human immunodeficiency virus type 1 envelope transmembrane glycoprotein. 总被引:19,自引:16,他引:3 下载免费PDF全文
The N-terminal region of the envelope (env) transmembrane protein of human immunodeficiency virus type 1 (HIV-1) has a leucine zipper-like motif. This highly conserved zipper motif, which consists of a heptad repeat of leucine or isoleucine residues, has been suggested to play a role in HIV-1 env glycoprotein oligomerization. This hypothesis was tested by replacing the highly conserved leucine or isoleucine residues in the zipper motif with a strong alpha-helix breaker, proline. We report here that such substitutions did not abolish the ability of env protein to form oligomers, indicating that this highly conserved zipper motif does not have a crucial role in env protein oligomerization. However, the mutant viruses all showed impaired infectivity, suggesting that this conserved zipper motif can have an important role in the virus life cycle. 相似文献
992.
Separation of the complex DNA binding domain of EBNA-1 into DNA recognition and dimerization subdomains of novel structure. 总被引:9,自引:4,他引:5 下载免费PDF全文
EBNA-1 is essential for replication of the latent episomal form of the Epstein-Barr virus genome and is involved in regulation of viral latency promoters. EBNA-1 activity is mediated through direct DNA binding. The DNA binding and dimerization functions of EBNA-1 have previously been located to a carboxy-terminal domain, amino acids (aa) 459 to 607. To identify and define the subdomains for these two functions, we created an extensive series of deletions and point mutations in an EBNA-1 (aa 408 to 641) background. The ability of the EBNA-1 mutants to heterodimerize with a wild-type EBNA-1 (aa 459 to 641) Immunoprecipitation assays with a monoclonal antibody, EBNA.OT1x, that recognizes EBNA-1 (aa 408 to 641) but not EBNA-1 (aa 459 to 641). These experiments revealed that mutations affecting dimerization occurred over two separate regions, aa 501 to 532 and aa 554 to 598. DNA binding was tested in mobility shift assays against a panel of oligonucleotide-binding sites. Dimerization was a prerequisite for DNA binding. The DNA recognition domain was localized to a separate region, aa 459 to 487, upstream of the dimerization domain. EBNA-1 variants carrying substitutions at aa 467 and 468 and at aa 477 gave a pattern of binding to mutant oligonucleotide probes that implicates these particular amino acids in DNA recognition. EBNA-1 appears to utilize novel mechanisms for both DNA recognition and dimerization since neither domain conforms to previously described structural motifs. 相似文献
993.
Streptavidin is an extracellular tetrameric protein produced by Streptomyces avidinii. A series of hybrid gene fusions consisting of Bacillus signal peptide coding regions fused to the mature streptavidin sequence were constructed. B. subtilis strains harboring these plasmids accumulate a tetrameric streptavidin in the growth medium. The properties of the streptavidin produced by B. subtilis are similar to those of the streptavidin produced by S. avidinii. B. subtilis strains carrying the various fusions can be grown to a high cell density in a biotin-free medium. Thus, B. subtilis represents an alternate host system for the production of streptavidin. 相似文献
994.
In an earlier paper which models the cell-cell (or virus-cell) fusion complex as two partial spherical vesicles joined at a narrow neck (Rubin, R. J., and Yi-der Chen. 1990. Biophys. J. 58:1157-1167), the redistribution by diffusion of lipid-like molecules through the neck between the two fused cell surfaces was studied. In this paper, we extend the study to the calculation of the kinetics of fluorescence increase in a single fusion complex when the lipid-like molecules are fluorescent and self-quenching. The formalism developed in this paper is useful in deducing fusion activation mechanisms from cuvette fluorescence measurements in cell-cell fusion systems. Two different procedures are presented: 1) an exact one which is based on the exact local density functions obtained from diffusion equations in our earlier study; and 2) an approximate one which is based on treating the kinetics of transfer of probes between the two fused cells as a two-state chemical reaction. For typical cell-cell fusion complexes, the fluorescence dequencing curves calculated from the exact and approximate procedures are very similar. Due to its simplicity, the approximate method should be very useful in future applications. The formalism is applied to a typical cell-cell fusion complex to study the sensitivity of dequenching curves to changes in various fusion parameters, such as the radii of the cells, the radius of the pore at the fusion junction, and the number of probes initially loaded to the complex. 相似文献
995.
Neutron structure factors of in-vivo deuterated amorphous protein C-phycocyanin 总被引:1,自引:1,他引:0 下载免费PDF全文
Neutron powder diffraction measurements of fully deuterated protein C-phycocyanin have been made at three temperatures, 295, 200, and 77 K, using dry and partially hydrated samples. The average coherent structure factors and the corresponding radial distribution functions d(r) are determined. The changes in d(r) functions observed in hydrated samples depend strongly on the level of hydration and most of these changes are due to water-protein interactions. At 0.365 gram D2O per gram of protein, the water crystallized into hexagonal ice at 200 K and below, but at 0.175 gram D2O per gram of protein, no crystallization of water was observed. At the higher hydration a peak appears in the radial distribution function which indicates that the average distance of the water molecule in the first hydration shell from the amino acid residues is 3.5 Å. 相似文献
996.
997.
Leckband D Chen YL Israelachvili J Wickman HH Fletcher M Zimmerman R 《Biotechnology and bioengineering》1993,42(2):167-177
The adhesion forces between various surfaces were measured using the "surface forces apparatus" technique. This technique allows for the thickness of surface layers and the adhesion force between them to be directly measured in controlled vapor or liquid environments. Three types of biological surfaces were prepared by depositing various lipid-protein monolayers (with thicknesses ranging from 1 to 4 nm) on the inert, molecularly smooth mica surface: (i) hydrophobic lipid monolayers; (ii) amphiphilic polyelectrolyte surfaces of adsorbed polylysine; and (iii) deposited bacterial S-layer proteins. The adhesion, swelling, and wetting properties of these surfaces was measured as a function of relative humidity and time. Initial adhesion is due mainly to the van der Waals forces arising from nonpolar (hydrophobic) contacts. Following adhesive contact, significant molecular rearrangements can occur which alter their hydrophobic-hydrophilic balance and increase their adhesion with time. Increased adhesion is generally enhanced by (i) increased relative humidity (or degree of hydration); (ii) increased contact time; and (iii) increased rates of separation. The results are likely to be applicable to the adhesion of many other biosurfaces, and show that the hydrophobicity of a lipid or protein surface is not an intrinsic property of that surface but depends on its environment (e.g., on whether it is in aqueous solution or exposed to the atmosphere), and on the relative humidity of the atmosphere. It also depends on whether the surface is in adhesive contact with another surface and-when considering dynamic (nonequilibrium) conditions-on the time and previous history of its interaction with that surface. (c) 1993 John Wiley & Sons, Inc. 相似文献
998.
A. Kleinhofs A. Kilian M. A. Saghai Maroof R. M. Biyashev P. Hayes F. Q. Chen N. Lapitan A. Fenwick T. K. Blake V. Kanazin E. Ananiev L. Dahleen D. Kudrna J. Bollinger S. J. Knapp B. Liu M. Sorrells M. Heun J. D. Franckowiak D. Hoffman R. Skadsen B. J. Steffenson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1993,86(6):705-712
A map of the barley genome consisting of 295 loci was constructed. These loci include 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism (SAP) markers. The RFLP-identified loci include 63 that were detected using cloned known function genes as probes. The map covers 1,250 centiMorgans (cM) with a 4.2 cM average distance between markers. The genetic lengths of the chromosomes range from 124 to 223 cM and are in approximate agreement with their physical lengths. The centromeres were localized to within a few markers on all of the barley chromosomes except chromosome 5. Telomeric regions were mapped for the short (plus) arms of chromosomes 1, 2 and 3 and the long (minus) arm of chromosomes 7.This research was also supported by other members of the NABGMP: K. Kasha, Department of Crop Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1; W. Kim, Agriculture Canada Research Station, 195 Dafoe Road, Winnipeg, Manitoba, Canada R3T 2M9; A. Laroche, Agriculture Canada Research Station, P.O. Box 3000 Main, Lethbridge, Alberta, Canada,TU 4B1; S. Molnar, Plant Research Centre Agriculture Canada, Central Experimental farm, Ottawa, Ontario, Canada K1A 0C6; G. Scoles, Department of Crop Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N OWOThis research is part of the North American Barley Genome Mapping Project, R. A. Nilan and K. Kasha, Coordinator and Associate Coordinator, respectively
Permanent address: Department of Plant Genetics, NI Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow 相似文献
999.
1000.
Sharon X. Chen Charles C. Hardin Harold E. Swaisgood 《Journal of Protein Chemistry》1993,12(5):613-625
Incubation of -lactoglobulin with immobilized trypsin at 5–10°C results in a time-dependent release of several fragments of the core domain in yields approaching 15%. Digests were fractionated by ion-exchange chromatography with a Mono Q HR5/5 column and analyzed after disulfide reduction by polyacrylamide gel electrophoresis in sodium dodecylsulfate. Three fragments with approximate molecular weights of 13.8, 9.6, and 6.7 kD were identified. The fraction from ion-exchange chromatography yielding the 6.7 kD fraction after disulfide reduction was further characterized because it was most homogeneous and gave the highest yield. The C-terminal cleavage site of the 6.7 kD core fragment appeared to be Lys100 or Lys101 as determined by C-terminal amino acid analysis. The exact masses, after reduction with dithiothreitol, are 6195 and 6926 as determined by laser desorption mass spectrometry, corresponding to residues 48–101 and 41–100. Prior to reduction, -lactoglobulin C-terminal residues 149–162 are connected to these core domain fragments as shown by C-terminal analysis and mass spectrometry. Structural studies indicate that these 7.9 and 8.6 kD core domain fragments released by immobilized trypsin retain much of their native structure. CD spectra indicate the presence of antiparallel -sheet structure similar to the native protein but the -helix is lost. Spectra in the aromatic region indicate the existence of tertiary structure. Moreover, structural transitions in urea are completely reversible as measured by CD spectra, although the extrapolated G
D
H20
and the urea concentration at the transition midpoint are lower than for the native protein. The core domain fragments also display apH-dependent binding to immobilizedtrans-retinal as does intact protein. A single endotherm is obtained for both core domain fragments and native protein upon differential scanning calorimetry, but again, the domain is less stable as indicated by a transition peak maxima of 56.9°C as compared with 81.1°C for native protein.Abbreviations used: CD, circular dichroism; CPG, controlled pore glass; DSC, differential scanning calorimetry; DTT, dithiothreitol; FPLC, fast flow liquid chromatography; HPLC, high-performance liquid chromatography; PITC, phenylisothiocyanate; SDS-PAGE, sodium dodecyl sulfate-polyacrylamide gel electrophoresis; TEA, triethylamine; UV, ultraviolet. 相似文献