全文获取类型
收费全文 | 26930篇 |
免费 | 2259篇 |
国内免费 | 2535篇 |
出版年
2024年 | 40篇 |
2023年 | 201篇 |
2022年 | 401篇 |
2021年 | 952篇 |
2020年 | 812篇 |
2019年 | 966篇 |
2018年 | 955篇 |
2017年 | 792篇 |
2016年 | 987篇 |
2015年 | 1555篇 |
2014年 | 1949篇 |
2013年 | 2108篇 |
2012年 | 2597篇 |
2011年 | 2389篇 |
2010年 | 1589篇 |
2009年 | 1409篇 |
2008年 | 1873篇 |
2007年 | 1561篇 |
2006年 | 1454篇 |
2005年 | 1214篇 |
2004年 | 1175篇 |
2003年 | 1074篇 |
2002年 | 967篇 |
2001年 | 495篇 |
2000年 | 388篇 |
1999年 | 327篇 |
1998年 | 258篇 |
1997年 | 161篇 |
1996年 | 150篇 |
1995年 | 153篇 |
1994年 | 114篇 |
1993年 | 94篇 |
1992年 | 90篇 |
1991年 | 69篇 |
1990年 | 45篇 |
1989年 | 57篇 |
1988年 | 36篇 |
1987年 | 31篇 |
1986年 | 37篇 |
1985年 | 28篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 8篇 |
1977年 | 9篇 |
1974年 | 9篇 |
1969年 | 7篇 |
1967年 | 9篇 |
1966年 | 7篇 |
1965年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
清香桂碱D和矮陀陀胺碱A,B的结构 总被引:9,自引:0,他引:9
本文报道从国产清香桂(Sarcococca ruscifolta)和金丝矮陀陀(Pachysandra axillaria)植物中分得的三个胺碱型新甾体生物碱清香桂碱 D 和矮陀陀胺碱 A、B 的化学结构,并首次归属了它们的~(13)C NMR 数据。 相似文献
72.
73.
S H Oh H Y Steiner D K Dougall D M Roberts 《Archives of biochemistry and biophysics》1992,297(1):28-34
Carrot cell cultures were used to study the dynamics of calmodulin protein levels, calmodulin methylation, and calmodulin-binding proteins during plant growth and development. Comparisons of proliferating and nonproliferating wild carrot cells show that, while calmodulin protein levels does not vary significantly, substantial variation in post-translational methylation of calmodulin on lysine-115 is observed. Calmodulin methylation is low during the lag and early exponential stages, but increases substantially as exponential growth proceeds and becomes maximal in the postexponential phase. Unmethylated calmodulin quickly reappears within 12 h of reinoculation of cells into fresh media, suggesting that the process is regulated according to the cell growth state. Calmodulin and calmodulin-binding proteins were also analyzed during the formation and germination of domestic carrot embryos in culture. Neither calmodulin methylation nor calmodulin protein levels varied significantly during somatic embryogenesis. However, upon germination of embryos, the level of calmodulin protein doubled. By calmodulin overlay analysis, we have detected a major 54,000 M(r) calmodulin-binding protein that also increased during embryo germination. This protein was purified from carrot embryo extracts by calmodulin-Sepharose chromatography. Overall, the data suggest that calmodulin methylation is regulated depending upon the state of cell growth and that calmodulin and its target proteins are modulated during early plant development. 相似文献
74.
A L Houseman B H Oh M C Kennedy C Fan M M Werst H Beinert J L Markley B M Hoffman 《Biochemistry》1992,31(7):2073-2080
The benefits of performing ENDOR experiments at higher microwave frequency are demonstrated in a Q-band (35 GHz) ENDOR investigation of a number of proteins with [nFe-mS] clusters, n = 2, 3, 4. Each protein displays several resonances in the frequency range of 0-20 MHz. In all instances, features are seen near v approximately 13 and 8 MHz that can be assigned, respectively, to "distant ENDOR" from 13C in natural-abundance (1.1%) and from 14N (the delta m1 = +/- 2 transitions); the nuclei involved in this phenomenon are remote from and have negligible hyperfine couplings to the cluster. In addition, a number of proteins show local 13C ENDOR signals with resolved hyperfine interactions; these are assigned to the beta carbons of cysteines bound to the cluster [A(13C) approximately 1.0 MHz]. Five proteins show resolved, local delta m1 = +/- 2 ENDOR signals from 14N with an isotropic hyperfine coupling, 0.4 less than or equal to A(14N) less than or equal to 1.0, similar to those seen in ESEEM studies; these most likely are associated with N-H...S hydrogen bonds to the cluster. Anabaena ferredoxin further shows a signal corresponding to A(14N) approximately 4 MHz. Quadrupole coupling constants are derived for both local and distant 14N signals. The interpretation of the data is supported by studies on 15N- and 13C-enriched ferredoxin (Fd) from Anabaena 7120, where the 15N signals can be clearly correlated with the corresponding 14N signals and where the 13C signals are strongly enhanced. Thus, the observation of 14N delta m1 = +/- 2 signals at Q-band provides a new technique for examining weak interactions with a cluster.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
75.
Radioadaptive response: Efficient repair of radiation-induced DNA damage in adapted cells 总被引:13,自引:0,他引:13
To verify the hypothesis that the induction of a novel, efficient repair mechanism for chromosomal DNA breaks may be involved in the radioadaptive response, the repair kinetics of DNA damage has been studied in cultured Chinese hamster V79 cells with single-cell gel electrophoresis. The cells were adapted by priming exposure with 5 cGy of γ-rays and 4-h incubation at 37°C. There were no indication of any difference in the initial yields of DNA double-strand breaks induced by challenging doses from non-adapted cells and from adapted cells. The rejoining of DNA double-strand breaks was monitored over 120 min after the adapted cells were challenged with 5 or 1.5 Gy, doses at the same level to those used in the cytogenetical adaptive response. The rate of DNA damage repair in adapted cells was higher than that in non-adapted cells, and the residual damage was less in adapted cells than in non-adapted cells. These results indicate that the radioadaptive response may result from the induction of a novel, efficient DNA repair mechanism which leads to less residual damage, but not from the induction of protective functions that reduce the initial DNA damage. 相似文献
76.
Hiroyuki Tsunoda Toshio Ohshima Jun Tohyama Masayuki Sasaki Norio Sakuragawa Frank Martiniuk 《Human genetics》1996,97(4):496-499
We report a missense mutation in an adult Japanese patient with acid alpha-glucosidase (GAA) deficiency. A TC to GT transition
at nucleotides 1585–1586, was identified. This transition resulted in an amino acid substitution of Ser-529 to Val (S529V)
in exon 11. We also have demonstrated that the S529V mutation abolishes the catalytic activity of the enzyme. Our data suggest
that this mutation is the cause of the clinical manifestation known as adult-onset GAA deficiency. The missense mutation described
here is a new mutation, and the first identified in Japanese patients with GAA deficiency.
Received: 23 May 1995 相似文献
77.
78.
可育的抗除草剂溴苯腈转基因小麦 总被引:21,自引:0,他引:21
报道了采用微粒轰击(Microprojectile bom bardm ent) 幼胚将除草剂抗性基因导入小麦(Triticumaestivum L.)的转化研究。实验共使用了13 个小麦品种, 从开花后14~18 d 的籽粒中剥取幼胚, 植物表达质粒含有CaMV 35S启动子控制的除草剂溴苯腈抗性基因bxn 以及筛选标记基因NTPⅡ。采用高压放电基因枪,用质粒DNA 包被的钨粒轰击预培养3 d 的幼胚。在含有卡那霉素类似物geneticin G418sulphate 的MS培养基上, 经过多步骤筛选和分化, 从800 多个幼胚中获得了16 株转化苗。除草剂抗性鉴定和Southern 杂交分析证明, 其中4 株为转基因植物,具有溴苯腈抗性, 并且自交可育。转化工作从分离幼胚到转化苗鉴定完毕, 最短时间为6 个月, 因此, 该方法是一项快速有效的基因导入技术 相似文献
79.
Summary Cell growth increased proportionally to the initial concentration of ammonium ion, however, methylan production was significantly inhibited at the high concentration of ammonium ion. The control of ammonium ion within the desired level(usually 0.45 g/l) was needed to reduce the inhibition. Methylan production was increased to 12.5 g/l by maintaining ammonium ion below 0.15 g/l. 相似文献
80.
Dong-Woog Choi Jai Young Song Man-Ho Oh Jong Seob Lee Jinho Moon Se Won Suh Sang-Gu Kim 《Plant molecular biology》1996,30(5):1059-1066
A root-specific cDNA clone, PVR3, was isolated from a bean (Phaseolus vulgaris L.) root cDNA library by a differential screening procedure. The nucleotide sequence of PVR3 contains an open reading frame coding for an 11.14 kDa polypeptide of 102 amino acid residues; the first 25 amino acids correspond to the sequence characteristic of a signal peptide. Comparison of the deduced PVR3 polypeptide sequence with the polypeptide sequences of previously cloned genes indicates that PVR3 may encode a ns-LTP-like protein. Molecular modelling of the PVR3 protein predicts that it has a three-dimensional structure that is similar to the three-dimensional model determined from the maize ns-LTP. The PVR3 mRNA accumulated mainly in the roots of young seedlings. It can be detected at low levels in flowers, but it is not detected in other organs. Genomic Southern blot analysis indicates that the genomic DNA corresponding to PVR3 cDNA is encoded by a single gene or small gene family in the bean genome. 相似文献