全文获取类型
收费全文 | 15388篇 |
免费 | 966篇 |
国内免费 | 2篇 |
出版年
2022年 | 97篇 |
2021年 | 154篇 |
2020年 | 68篇 |
2019年 | 104篇 |
2018年 | 158篇 |
2017年 | 127篇 |
2016年 | 236篇 |
2015年 | 387篇 |
2014年 | 410篇 |
2013年 | 898篇 |
2012年 | 778篇 |
2011年 | 738篇 |
2010年 | 415篇 |
2009年 | 457篇 |
2008年 | 728篇 |
2007年 | 704篇 |
2006年 | 691篇 |
2005年 | 711篇 |
2004年 | 720篇 |
2003年 | 707篇 |
2002年 | 651篇 |
2001年 | 562篇 |
2000年 | 544篇 |
1999年 | 461篇 |
1998年 | 194篇 |
1997年 | 182篇 |
1996年 | 166篇 |
1995年 | 140篇 |
1994年 | 133篇 |
1993年 | 143篇 |
1992年 | 348篇 |
1991年 | 317篇 |
1990年 | 320篇 |
1989年 | 291篇 |
1988年 | 249篇 |
1987年 | 242篇 |
1986年 | 217篇 |
1985年 | 185篇 |
1984年 | 144篇 |
1983年 | 138篇 |
1982年 | 119篇 |
1981年 | 112篇 |
1980年 | 94篇 |
1979年 | 117篇 |
1978年 | 92篇 |
1977年 | 82篇 |
1976年 | 81篇 |
1975年 | 73篇 |
1974年 | 88篇 |
1973年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Y Hiraki N Endo M Takigawa A Asada H Takahashi F Suzuki 《Biochimica et biophysica acta》1987,931(1):94-100
Pulsed electromagnetic fields promote healing of delayed united and ununited fractures by triggering a series of events in fibrocartilage. We examined the effects of a pulsed electromagnetic field (recurrent bursts, 15.4 Hz, of shorter pulses of an average of 2 gauss) on rabbit costal chondrocytes in culture. A pulsed electromagnetic field slightly reduced the intracellular cyclic adenosine 3',5'-monophosphate (cAMP) level in the culture. However, it significantly enhanced cAMP accumulation in response to parathyroid hormone (PTH) to 140% of that induced by PTH in its absence, while it did not affect cAMP accumulation in response to prostaglandin E1 or prostaglandin I2. The effect on cAMP accumulation in response to PTH became evident after exposure of the cultures to the pulsed electromagnetic field for 48 h, and was dependent upon the field strength. cAMP accumulation in response to PTH is followed by induction of ornithine decarboxylase, a good marker of differentiated chondrocytes, after PTH treatment for 4 h. Consistent with the enhanced cAMP accumulation, ornithine decarboxylase activity induced by PTH was also increased by the pulsed electromagnetic field to 170% of that in cells not exposed to a pulsed electromagnetic field. Furthermore, stimulation of glycosaminoglycan synthesis, a differentiated phenotype, in response to PTH was significantly enhanced by a pulsed electromagnetic field. Thus, a pulsed electromagnetic field enhanced a series of events in rabbit costal chondrocytes in response to PTH. These findings show that exposure of chondrocytes to a pulsed electromagnetic field resulted in functional differentiation of the cells. 相似文献
52.
Junichi Ishihara Nagahiro Saijo Yasutsuna Sasaki Hidehiko Nakano Akira Ozaki Hidenobu Takahashi Masanori Sakurai Kazuhiko Nakagawa Masaaki Iigo Fumihiko Kanzawa Akio Hoshi Weon Seon Hong James R. Jett Terumi Takahashi 《Cancer immunology, immunotherapy : CII》1987,24(3):185-189
Summary The antitumor effect of recombinant human tumor necrosis factor (rH-TNF) on two clones of rat fibrosarcoma with different metastatic potential to lymph nodes was examined. The colony formation of clone A, which has high metastatic potential, was completely inhibited by continuous exposure to rH-TNF at 50 U/ml. In contrast, colony formation of clone G, which has low metastatic potential, was not inhibited by high concentrations of rH-TNF (10,000 U/ml). The inhibitory effect of rH-TNF on colony formation by clone A was also observed with a 1-h exposure to rH-TNF. This effect was time and concentration dependent, as determined by the colony assay, 3H-thymidine uptake assay, and 51Cr-release assay. 3H-thymidine and 3H-uridine uptake per cell of clone A exposed to rH-TNF was not decreased. This suggests that the mechanisms of the antitumor effect of rH-TNF were not due to inhibition of DNA and RNA synthesis of tumor cells. In vivo growth and lymph node metastases of clone A inoculated i.p. to Donryu strain rats were completely suppressed by 14 consecutive i.p. injections of 105 or 106 U/kg per day of rH-TNF. On the other hand the growth of clone G was not influenced by rH-TNF administration. 相似文献
53.
54.
Nishizono Hiromi; Watanabe Takemasa; Orii Tokiko; Suzuki Shizuo 《Plant & cell physiology》1989,30(4):565-569
A metal-tolerant fern, Athyrium yokoscense, is capable of growingin highly copper-contaminated soil, but cupric chloride inhibitedthe activities of some enzymes extracted from the fern. Thefunction in the detoxification of copper of two copper-bindingsubstances was investigated by examination of their effectson various enzymes assayed in vitro, i.e. acid phosphatase (orthophosphoric-monoesterphosphohydrolase [acid optimum], EC 3.1.3.2
[EC]
), glucose-6-phosphatedehydrogenase (D-glucose-6-phosphate: NADP+ 1-oxidoreductase,EC 1.1.1.49
[EC]
) and isocitrate dehydrogenase (threo-Ds-isocitrate:NADP+ oxidoreductase [decarboxylating], EC 1.1.1.42
[EC]
). The twocopper-binding substances, whose apparent molecular weightsare 9.5 kDa and 2 kDa, were previously obtained from the solublecytoplasmic fraction of the fern root. The 9.5-kDa substance,which is a cysteine-rich peptide induced as a result of exposureof the fern to copper, was found to suppress almost entirelythe inhibitory effects of the metal on the enzymes. The suppressoractivity of the peptide was nearly as effective as that of ethylenediaminetetraaceticacid. The 2-kDa substance, which is also found in fern thathas not been exposed to copper, had a more modest suppressoractivity. These results indicate that the 9.5-kDa substancemay contribute to the copper-tolerance of the fern growing incopper-contaminated soil. (Received August 26, 1988; Accepted March 17, 1989) 相似文献
55.
Photosynthetic characteristics of four high-CO2-requiring mutants of Chlamydomonas reinhardtii were compared to those of wild type before and after a 24-hour exposure to limiting CO2 concentrations. The four mutants represent two loci involved in the CO2-concentrating system of this unicellular alga. All mutants had a lower photosynthetic affinity for inorganic carbon than did the wild type when grown at an elevated CO2 concentration, indicating that the genetic lesion in each is expressed even at elevated CO2 concentrations. Wild type and all four mutants exhibited adaptive responses to limiting CO2 characteristic of the induction of the CO2-concentrating system, resulting in an increased affinity for inorganic carbon only in wild type. Although other components of the CO2-concentrating system were induced in these mutants, the defective component in each was sufficient to prevent any increase in the affinity for inorganic carbon. It was concluded that the genes corresponding to the ca-1 and pmp-1 loci exhibit at least partially constitutive expression and that all components of the CO2-concentrating system may be required to significantly affect the photosynthetic affinity for inorganic carbon. 相似文献
56.
Defense mechanisms in invertebrates and fish 总被引:6,自引:0,他引:6
57.
58.
Identification of the cell surface molecule involved in sexual cell fusion of Dictyostelium discoideum 总被引:6,自引:0,他引:6
Kazuyoshi Suzuki Kaichiro Yanagisawa 《Differentiation; research in biological diversity》1989,40(3):159-165
Dictyostelium discoideum was used as a model system for elucidating the molecular mechanism of sexual cell fusion. In heterothallic strains NC4 and HM1 of D. discoideum, complements in mating type, amoeboid cells acquire fusion competence only under certain environmental conditions, such as the presence of excess water and a certain period of darkness, to fuse sexually. The surface of cells which acquired fusion competence was found to possess specific antigens. Monovalent antibodies prepared from rabbit antiserum against fusion-competent NC4 cells inhibit the sexual cell fusion of these cells completely. Two specific antigenic proteins, 39 and 138 k Da in relative molecular mass and specific for fusion-competent cells, were detected. Only one, the 138-k Da protein, was capable of neutralizing the fusion-inhibitory activity of the monovalent antibody. These results show that the 139-k Da protein is the one involved in the sexual cell fusion of NC4 and HM1 strains in D. discoideum. 相似文献
59.
M Suzuki 《The EMBO journal》1989,8(3):797-804
A new DNA-binding unit of a protein different from the alpha-helix, the beta-sheet and the Zn-finger is proposed based on the analysis of the structure of the N-terminus of sea urchin spermatogenous histone H1. DNA-binding arms of the sea urchin spermatogenous histones, H1 and H2B, are composed of repeats of Ser-Pro-Lys(Arg)-Lys(Arg) (SPKK) residues. A six-times repeat of SPKK (S6 peptide) was isolated from H1 and the competition of S6 for DNA binding with a DNA-binding dye, Hoechst 33258, was analysed. The S6 peptide is shown to be a competitive inhibitor of Hoechst 33258, and it is concluded that the SPKK repeat binds to DNA in its minor groove with a binding constant, KS6 = 1.67 X 10(10) M-1. The circular dichroism (CD) spectrum of a synthetic peptide, SPRKSPRK (S2 peptide), is quite different from those of both the alpha-helix and the beta-sheet and resembles that of a random coil. From statistical consideration of protein structures it is proposed that SPKK forms a compact beta-turn stabilized by an additional hydrogen bond. Since a repeated chain of such turn of SPKK offers a repeat of amides of Ser residues at a distance similar to that of DNA-binding amides of the drugs, Hoechst 33258 and netropsin, and since the amides of these drugs bind to DNA replacing the spine of hydration in a minor groove, it is proposed that a repeat of SPKK binds to DNA in the minor groove using similar hydrogen bonds. 相似文献
60.
Rat pineal S-antigen: sequence analysis reveals presence of alpha-transducin homologous sequence 总被引:2,自引:0,他引:2
T Abe K Yamaki M Tsuda V K Singh S Suzuki R McKinnon D C Klein L A Donoso T Shinohara 《FEBS letters》1989,247(2):307-311
S-antigen (S-Ag) is a soluble, highly antigenic protein, the administration of which induces autoimmune uveitis. This protein is found in the retina and pineal. Retinal S-Ag from three species has been sequenced. In this study rat pineal S-Ag was sequenced. Clones were isolated from a rat pineal lambda gt11 cDNA library by probing with a 300 bp fragment of mouse retinal S-Ag cDNA containing the 5'-coding region. The largest clone isolated (RPS-118; 1364 bp) contained the entire coding sequence. Comparison of the rat pineal and mouse retinal S-Ag nucleotide sequences indicated a high homology (95%). The deduced amino acid sequence was found to contain 403 residues (congruent to 44 992 Da). Comparison of the rat pineal and mouse retinal S-Ag amino acid sequences also revealed high homology (97%). The similarity of both the nucleotide and amino acid sequences of rat pineal and mouse retinal S-Ag indicates that expression of the S-Ag gene in both tissues is similar. Further analysis of the rat pineal S-Ag sequence indicated that it contained essentially the same major uveitopathogenic region of S-Ag present in bovine retina; minor uveitopathogenic sites were somewhat different. As is true of retinal S-Ag, rat pineal S-Ag contains the same consensus phosphoryl-binding site present in many GTP/GDP-binding proteins and a homologous sequence found in the C-terminus of alpha-transducin. These sequences may play a role in the action of pineal S-Ag in transmembrane signal transduction. 相似文献