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141.
We have shown, in a preliminary report, that macrophages can induce strand breaks in the DNA of co-cultured tumor cells (Chong et al., 1988). The present study is designed to determine if oxygen-centered species generated by the cell-free enzyme-substrate combination of hypoxanthine and xanthine oxidase can induce similar lesions and to identify the specific mediator(s). We report that co-incubation of murine mammary tumor cell lines with hypoxanthine and xanthine oxidase leads to the induction of DNA-strand breaks as determined by fluorescence analysis of DNA unwinding (FADU) assay or alkaline elution techniques. This damage is preventable by catalase which removes hydrogen peroxide but no protection is provided by agents to remove or prevent the formation of superoxide anion (superoxide dismutase), or hydroxyl radical (mannitol or the iron chelator o-phenanthroline). Likewise, cyclooxygenase or lipoxygenase inhibitors of arachidonate metabolism (indomethacin, nordihydroguaiaretic acid, caffeic acid) or bromophenacyl bromide do not alter the degree of DNA scission. Treatment with higher doses of oxygen species leads to significant toxicity as determined by evaluation of cell growth potential or colony-forming ability. Again, toxicity is prevented only by the presence of catalase. Tumor cells are able to rejoin strand breaks at lower, less toxic doses. When comparing different tumor cell subpopulations at various stages of progression, i.e., metastatic vs. nonmetastatic, for sensitivity to hydrogen peroxide-induced strand breakage, we found that at lower concentrations (less than 5μM) metastatic populations are sensitive whereas nonmetastatic populations exhibit no significant breakage. At higher concentrations of hydrogen peroxide, all lines were sensitive, suggesting that a lower threshold of sensitivity may exist for more progressed tumour cell lines. 相似文献
142.
Basidiomycetous fungi, two saprophytes and three mycorrhizal, were used to assess the specificity of DNA hybridization for
distinguishing genera from one another. Interspecific comparisons were done with several isolates of mycorrhizal fungi,Laccaria bicolor andL. laccata, collected from diverse geographical sites. The DNAs were digested with four restriction nucleases and separated by gel electrophoresis
into patterns of DNA fragments called restriction fragment length polymorphisms (RFLPs). The RFLPs were hybridized with a
radioactively-labeled DNA probe encoding Basidiomycetous ribosomal RNA genes. The five genera were discernable using both
unprobed and probed RFLPs. Hybridization of probe DNA with RFLPs was isolate-specific for all nine Laccaria isolates examined.
The reclassification of aL. bicolor isolate is supported, demonstrating that hybridization of RFLPs offers an additional tool for taxonomy of ectomycorrhizal
fungi. The method may have field application for distinguishing known isolates if their DNA fingerprints are previously ascertained
and are distinct from RFLPs of indigenous organisms. 相似文献
143.
144.
The mouseIgK-VSer gene encodes an immunoglobulin light chain variable region which gives rise to two phenotypic polymorphisms of mouse chains. The nucleotide sequences of coding and flanking regions of theIgk-VSer
c
andIgk-VSer
d
alleles found in recently inbred strains of wild mice are compared with those of theIgk-VSer
a
andIgk-VSer
b
alleles described previously. Results suggest that the gene is evolving randomly and that framework 2 and complentarity determining region 2 are preserved, presumably for overall light chain structure. Results indicate that all four allels have an octamer motif upstream of the gene which should be functional and allow prediction of whether or not the product of the germ line gene will be detectable as either the IB-peptide or Ef1a phenotypic polymorphism. Southern hybridization of genomic DNA using as probe a 1-kbXba I-Xba I fragment located approximately 4 kb upstream of the BALB/cIgk-VSer
b
coding region demonstrated the presence of homologous DNA in mice bearing theIgk-VSer
a
allele and absence from mice bearing theIgk-VSer
c
andIgk-VSer
d
alleles. Nucleotide sequence comparison of BALB/c and SK/CamRk (Igk-VSer
d
) DNA in this region demonstrated that BALB/c contained an insertion 2.4 kb in length which was absent from SK/CamRk. Both strains contain DNA homologous to the reverse complement of the mouse Bam5 repetitive element at the point of the insertion, with BALB/c containing approximately 70 nucleotides more of the element than SK/CamRk. Surprisingly, the strains containing DNA related to theXba I-Xba I probe are not those determined to be the most similar by nucleotide sequence comparisons and by the Phylogenetic Analysis Using Parsimony program. The evolutionary relationship of the alleles and a possible basis for the inconsistency presented by theXba I-Xba
I fragment-related DNA are discussed. 相似文献
145.
Bacterivorous nanoflagellates (microflagellates) have been routinely enumerated in marine and freshwater samples using either a Most Probable Number (MPN) culture method or by a direct microscopical counting method (DC). These two techniques typically yield highly disparate estimates of the density of nanoflagellates in natural samples. We compared these methods with seawater and marine snow (macroscopic detrital aggregate) samples collected from surface waters throughout the North Atlantic and in freshwater samples collected at three stations in Lake Ontario. Densities of nanoflagellates determined by the two methods differed by as much as four orders of magnitude; the MPN estimate rarely exceeded 10% of the microscopical count, and averaged 1% of this count. The MPN estimate constituted a higher percentage of the DC value in environments with high concentrations of nanoflagellates relative to environments with low concentrations of nanoflagellates. The ratio of the culture count to the microscopical count (MPNDC) increased along an environmental gradient from oligotrophy to eutrophy, and was positively correlated with the density of bacteria in the samples. In laboratory experiments with two species of bacterivorous nanoflagellates, the MPN count constituted a much greater percentage of the DC count during the exponential growth phase of the nanoflagellate than during the stationary growth phase. Differences in the estimates of nanoflagellate density obtained with these two techniques probably can be explained by the trophic mode of these protozoa, their growth stage, and the amenability of these species to laboratory culture. 相似文献
146.
A major myristylated substrate of protein kinase C and protein kinase C itself are differentially regulated during murine B- and T-lymphocyte development and activation. 总被引:2,自引:0,他引:2 下载免费PDF全文
P Hornbeck H Nakabayashi B J Fowlkes W E Paul D Kligman 《Molecular and cellular biology》1989,9(9):3727-3735
The regulation and expression of protein kinase C (PKC) and phosphomyristin C (PMC) (a principal substrate of PKC which is the major myristylated protein in lymphocyte and glioma lines that express it) in murine B and T lymphocytes were investigated. Both PMC and PKC are differentially regulated during T-cell development. The level of PMC expression is highest in CD4-8-, intermediate in CD4+8+, and lowest in J11d-, CD4, or CD8 single-positive thymocytes. PKC is equally expressed by all three thymic populations. In striking contrast to thymocytes, resting peripheral lymph node T cells and T-cell clones express little if any PMC and reduced levels of PKC. Neither PKC nor PMC is significantly induced upon the activation of lymph node T cells: treatment with anti-CD3 antibodies or anti-CD3 and interleukin-2 fails to induce PKC, whereas PMC is not induced by anti-CD3 alone and is only slightly induced by anti-CD3 and interleukin-2. In contrast to the situation with T cells, PMC and PKC are constitutively expressed at moderate levels in mature B cells. PMC is greatly increased in B-cell blasts generated by cross-linking the antigen receptor with anti-immunoglobulin. These results demonstrate that PMC and PKC are differentially regulated during the development and activation of B and T cells, suggesting that cellular events that rely upon PKC and PMC may differ during ontogeny and activation of different lymphocyte subsets. 相似文献
147.
Joe W. Dorner Richard J. Cole Timothy H. Sanders Paul D. Blankenship 《Mycopathologia》1989,105(2):117-128
Samples of Florunner peanuts were collected throughout a period of late-season drought stress with mean geocarposphere temperatures of 29 and 25 °C, and determinations of maturity, kernel water activity (aw), percent moisture, capacity for phytoalexin production, and aflatoxin contamination were made. Results showed an association between the loss of the capacity of kernels to produce phytoalexins and the appearance of aflatoxin contamination. Kernel aw appeared to be the most important factor controlling the capacity of kernels to produce phytoalexins. Mature peanuts possessed additional resistance to contamination that could not be attributed solely to phytoalexin production. Kernel moisture loss was accelerated in the 29 °C treatment compared to the 25 °C treatment, and data indicated that the higher soil temperature also favored growth and aflatoxin production by Aspergillus flavus in peanuts susceptible to contamination.Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. 相似文献
148.
Absorbance changes induced by 25-ps laser flashes were measured in membranes of Heliobacterium chlorum at 15 K. Absorbance difference spectra, measured at various times after the flash showed negative bands in the Qy region at 812, 793 and 665 nm. The first of these bands was attributed to the formation of excited singlet states of a long-wavelength form of antenna bacteriochlorophyll g (BChl g 808). Absorbance changes of shorter wavelength absorbing antenna BChls g were at least an order of magnitude smaller, indicating rapid excitation energy transfer (i.e. within the time resolution of the apparatus) from these BChls to BChl g 808. Excited BChl g 808 showed a bi-exponential decay with time constants of 50 and 200 ps. The bands at 793 and 665 nm may be attributed to the primary charge separation and reflect the photooxidation of the primary electron donor P-798 and photoreduction of a primary electron acceptor absorbing near 670 nm, presumably a BChl c or Chl a-like pigment. The bleaching of this pigment reversed with a time constant of 300 ps at 15 K and of 800 ps at 300 K. This indicates that electron transfer from the primary to the secondary electron acceptor is approximately 2.5 times faster at 15 K than at room temperature.Abbreviations BChl
bacteriochlorophyll
- FWHM
full width at half maximum
- P-798
primary electron donor
- Tris
tris(hydroxymethyl)amino methane 相似文献
149.
Kees W. Rodenburg Marcel J. A. de Groot Rob A. Schilperoort Paul J. J. Hooykaas 《Plant molecular biology》1989,13(6):711-719
In relation to the question which DNA form (single- or double-stranded) is transferred by Agrobacterium tumefaciens to plant cells, we studied the behaviour of single-stranded DNA, as compared to double-stranded DNA, when it is introduced into plant protoplasts by electroporation. To this end, we cloned a construct with a plant NPTII gene as well as a CAT gene in the M13 vectors tg130 and tg131. We found that both complementary single-stranded molecules gave rise to substantial CAT activity in plant protoplasts, suggesting that single-stranded DNA is converted into double-stranded DNA by the plant cell replication machinery. Unexpectedly, we found that single-stranded DNA leads to a 3–10 fold higher frequency of stable transformation (selection for kanamycin resistance) than double-stranded DNA. These results indicate that the use of single-stranded DNA might be considered in experiments in which optimal transformation frequencies are needed, e.g. with protoplasts form recalcitrant plant species.Abbreviations ss
single-stranded
- ds
double-stranded
- CAT
chloramphenicol acetyl transferase
- NPTII
neomycin phosphotransferase II
- RT
room temperature 相似文献
150.
Frank van Engelenburg Ralf Smit Theo Goosen Henk van den Broek Paul Tudzynski 《Applied microbiology and biotechnology》1989,30(4):364-370
Summary To develop a DNA-mediated transformation system for Claviceps purpurea a vector was constructed using a bleomycin-resistance gene (bleo
R) fused in frame to the Aspergillus nidulans trp C promoter as a dominant selection marker. The construct was shown to be functional in Aspergillus nidulans and Aspergillus niger and used to transform a wild strain of Claviceps purpurea. Transformats were obtained at low frequencies; they were shown to contain transforming DNA integrated into the chromosomal DNA, probably in multimeric copies and at multiple sites. Combined Southern, Northern and resistance level analysis indicate that the A. nidulans promoter is functional in C. purpurea.Dedicated to Professor Dr. Dr. h. c. K. Esser on the occasion of his 65th birthday 相似文献