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11.
利用人粒细胞集落刺激因子(hG-CSF)cDNA3′端非翻译区(3′-UTR)中存在的DraⅠ酶切位点,通过部分酶切与完全酶切,删除3′-UTR不同长度,构建了四种hG-CSFcDNA瞬时重组表达质粒。转染COS-7细胞后,生物活性测定结果提示,hG-CSFcDNA3′-UTR对其表达起负调控作用,其关键性序列位于紧接终止密码子TGA下游的65bp范围内,3′-UTR对hG-CSFcDNA表达的影响与转录水平的差别有一定关系。 相似文献
12.
H A El-Dorry D K Chu A Dzugaj L H Botelho S Pontremoli B L Horecker 《Archives of biochemistry and biophysics》1977,182(2):763-773
Digestion of rabbit liver fructose 1,6-bisphosphatase with subtilisin followed by denaturation of the protein yields a peptide containing 60 amino acid residues, including the blocked NH2-terminus. This peptide has the following sequence: Ac-Ala-Asp-Lys-Ala-Pr o-Phe-Asp-Thr-Asp-Ile-Ser-Thr-Met-Thr-Arg-Phe-Val-Met-Glu-Glu-Gly-Arg-Ly s-Ala-Gly-Gly-Thr-Gly-Glu-Met-Thr-Gln-Leu-Leu-Asn-Ser-Leu-Cys-Thr-Ala-Va l-Lys-Ala-Ile-Ser-Thr-Ala-Val-Arg-Lys-Ala-Gly-Ile-Ala-His-Leu-Tyr-Gly-Ile-Ala. 相似文献
13.
14.
T-2 toxin in serum, urine, and saline was analyzed by a modified radioimmunoassay procedure. The specimens were added directly to the assay tubes without extraction steps. The reaction between antibody and ligands was optimal at 1 h. Albumin-coated charcoal was used to separate bound from free radioactivity. Quenching, which occurred with hemolyzed specimens, was corrected by a wet oxidation process with 60% perchloric acid and 30% hydrogen peroxide. The shorter incubation times resulted in an assay that takes less than 6 h to complete. The average affinity constant of the antibody (Km) was 1.75 X 10(10) liters/mol. The sensitivity was 1 ng per assay or 10 ng/ml. Among the other trichothecenes tested, only H-T-2 cross-reacted significantly (10.3%). 相似文献
15.
B C Trapnell P L Zeitlin C S Chu K Yoshimura H Nakamura W B Guggino J Bargon T C Banks W Dalemans A Pavirani 《The Journal of biological chemistry》1991,266(16):10319-10323
16.
To complete assignment of the 19F nuclear magnetic resonance (NMR) spectrum of 5-fluorouracil-substituted Escherichia coli tRNA(Val), resonances from 5-fluorouracil residues involved in tertiary interactions have been identified. Because these assignments could not be made directly by the base-replacement method used to assign 5-fluorouracil residues in loop and stem regions of the tRNA, alternative assignment strategies were employed. FU54 and FU55 were identified by 19F homonuclear Overhauser experiments and were then assigned by comparison of their 19F NMR spectra with those of 5-fluorouracil-labeled yeast tRNA(Phe) mutants having FU54 replaced by adenine and FU55 replaced by cytosine. FU8 and FU12, were assigned from the 19F NMR spectrum of the tRNA(Val) mutant in which the base triple G9-C23-G12 substituted for the wild-type A9-A23-FU12. Although replacement of the conserved U8 (FU8) with A or C disrupts the tertiary structure of tRNA(Val), it has only a small effect on the catalytic turnover number of valyl-tRNA synthetase, while reducing the affinity of the tRNA for enzyme. Analysis of the 19F chemical shift assignments of all 14 resonances in the spectrum of 5-fluorouracil-substituted tRNAVal indicated a strong correlation to tRNA secondary and tertiary structure. 5-Fluorouracil residues in loop regions gave rise to peaks in the central region of the spectrum, 4.4 to 4.9 parts per million (p.p.m.) downfield from free 5-fluorouracil. However, the signal from FU59, in the T-loop of tRNA(Val), was shifted more than 1 p.p.m. downfield, to 5.9 p.p.m., presumably because of the involvement of this fluorouracil in the tertiary interactions between the T and D-loops. The 19F chemical shift moved upfield, to the 2.0 to 2.8 p.p.m. range, when fluorouracil was base-paired with adenine in helical stems. This upfield shift was less pronounced for the fluorine of the FU7.A66 base-pair, located at the base of the acceptor stem, an indication that FU7 is only partially stacked on the adjacent G49 in the continuous acceptor stem/T-stem helix. An unanticipated finding was that the 19F resonances of 5-fluorouracil residues wobble base-paired with guanine were shifted 4 to 5 p.p.m. downfield of those from fluorouracil residues paired with A. In the 19F NMR spectra of all fluorinated tRNAs studied, the farthest downfield peak corresponded to FU55, which replaced the conserved pseudouridine normally found at this position. 相似文献
17.
18.
I-Chian Li Diane A. Blake Irwin J. Goldstein Ernest H. Y. Chu 《Experimental cell research》1980,129(2)
Stable and heritable variants of Chinese hamster ovary (CHO) cells which are resistant to different levels (0.1, 1.0 and 10 μg/ml) of the toxin abrin have been isolated and characterized. The frequency of resistant colonies to abrin was increased with the concentration of a chemical mutagen. There was no effect of cell density or cross-feeding on the recovery of variants. In experiments using fluorescein-labeled abrin and ricin which bind to terminal (non-sialylated) galactose residues of cell-surface oligosaccharides, parental cells exhibited strong binding toward both toxins, whereas no fluorescence was observed in the resistant clones. A fluorescein-conjugated lectin, BS II, which is specific for terminal N-acetyl-
-glucosaminyl residues, did not interact with the parental cells, but did with the resistant clones. This suggests that on the surface of resistant cells the number of terminal galactosyl residues of oligosaccharide chains in glycoproteins was reduced, exposing the penultimate N-acetyl-
-glucosaminyl residues. The number of available endogenous acceptor sites for galactosyl transferase in the abrin-resistant clones was directly proportional to the degree of resistance. In the presence of great excess of exogenous acceptor, the rates of galactosyl transfer were similar in all the abrin-resistant cell types tested, with levels ranging from 1.4 to 1.7 times parental cell values. Studies with tetraploid cell hybrids reveal that resistance was a recessive trait. Fluctuation analysis showed that abrin resistance occurred in CHO cell populations at a rate of 4−7 × 10−8/cell/generation. The system may serve as a new marker for quantitative mutagenesis studies. 相似文献
19.
Phenacylcobalamin has been synthesized and characterized by thin-layer chromatography and uv-visible spectroscopy, as well as identification of the cobalt-containing and organic products of its cleavage in acid and base and by aerobic photolysis. The major organic product from all three cleavage reactions is acetophenone and the cobalt-containing product is aquacobalamin (or hydroxocobalamin, its conjugate base). In aqueous acidic solution (pH 0 to 7.3, ionic strength 1.0 M, and 25.0 degrees C), the kinetics of the formation of aquacobalamin are biphasic representing the linear sum of two exponential terms. The pH dependence of the first-order rate constant of both phases shows a first-order dependence on proton concentration but with an inflection point ot pH 3.55 for the faster phase and at pH 4.03 for the slower phase. This behavior is interpreted in terms of the specific acid catalyzed formation of an intermediate from both "base on" and "base off" phenacylcobalamin with different second-order rate constants for each form, followed by an intermediate decompotion step with a similar formal mechanism. The nature of the intermediate is discussed and it is concluded to be a pi-complex between cob(III)alamin and the enol of acetophenone. 相似文献
20.
This study describes the ultrastructural characteristics of the middle cerebral artery and its related neural elements in the squirrel monkey and baboon. The cytoarchitecture of the M-1 segment as well as that of the smaller extracerebral and intracerebral vessels is comparable in both animals.Smooth muscle elements are occasionally found within the intimai lining. The nerve bundles associated with vessels contain fewer myelinated fibers as the vessel diameter decreases. The cytological relationship between the neural structures and the smooth muscle cells are discussed. 相似文献