全文获取类型
收费全文 | 7517篇 |
免费 | 644篇 |
国内免费 | 26篇 |
出版年
2022年 | 57篇 |
2021年 | 132篇 |
2020年 | 54篇 |
2019年 | 74篇 |
2018年 | 115篇 |
2017年 | 83篇 |
2016年 | 180篇 |
2015年 | 333篇 |
2014年 | 372篇 |
2013年 | 480篇 |
2012年 | 643篇 |
2011年 | 575篇 |
2010年 | 329篇 |
2009年 | 284篇 |
2008年 | 375篇 |
2007年 | 377篇 |
2006年 | 355篇 |
2005年 | 317篇 |
2004年 | 320篇 |
2003年 | 294篇 |
2002年 | 255篇 |
2001年 | 177篇 |
2000年 | 169篇 |
1999年 | 138篇 |
1998年 | 83篇 |
1997年 | 70篇 |
1996年 | 63篇 |
1995年 | 54篇 |
1994年 | 55篇 |
1993年 | 63篇 |
1992年 | 109篇 |
1991年 | 86篇 |
1990年 | 76篇 |
1989年 | 83篇 |
1988年 | 70篇 |
1987年 | 82篇 |
1986年 | 51篇 |
1985年 | 39篇 |
1984年 | 43篇 |
1983年 | 39篇 |
1982年 | 31篇 |
1981年 | 29篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 29篇 |
1976年 | 31篇 |
1975年 | 30篇 |
1974年 | 29篇 |
1973年 | 36篇 |
1970年 | 31篇 |
排序方式: 共有8187条查询结果,搜索用时 375 毫秒
1.
2.
3.
D. Pangallo K. Chovanov H. Drahovska F. De Leo C. Urzì 《International biodeterioration & biodegradation》2009,63(7):868-872
The aim of this work was the evaluation of fluorescence ITS-PCR (f-ITS) as a molecular tool to analyze the microbial community involved in the biodeterioration of cultural heritage surfaces. As a case study we analyzed by f-ITS ninety-two bacterial strains isolated from a medieval fresco and the surrounding air environment. The internal transcribed spacer between the 16S and 23S rRNA genes was amplified, and then the fluorescently labeled PCR products were separated by capillary electrophoresis. Bacterial strains were identified by 16S rDNA sequencing. The f-ITS electropherograms showed different profiles coherent with the affiliation of the strains at the genus and species levels. Among the isolates obtained from the fresco surface, those belonging to the genus Bacillus were the most prevailing exhibiting 8 different f-ITS profiles. The airborne bacilli exhibited only 2 of these 8 profiles. Staphylococcus were mostly isolated from air and produced 4 different profiles. Pseudomonas isolates presented 3 different profiles, and one of them was typical of Pseudomonas putida. Members of the other genera produced their distinctive profiles. Our results show that f-ITS is a promising molecular tool for the rapid selection and clustering of strains isolated from different sources. 相似文献
4.
We here report the second record of a developmentally aberrant strain of a cellular slime mold from natural populations and demonstrate that this Dictyostelium mucoroides variant is capable of undergoing normal morphogenesis in the presence of the phycomycete fungus, Mucor hiemalis. The synergism is induced by an extracellular product(s) which is diffusable through thin agar membranes and is released by the fungus. The presence of the fungus not only induces stalk formation in this stalkless variant, but also increases the rate of sorocarp formation in 3 of 5 additional species of cellular slime molds assayed. 相似文献
5.
6.
Ohne Zusammenfassung 相似文献
7.
8.
S C Tsai R Adamik V C Manganiello M Vaughan 《Biochemical and biophysical research communications》1981,100(2):637-643
A new amino acid was isolated from the cuticle collagen of and characterized by ultraviolet, mass and nmr spectroscopies and chemical degradation. The results indicate that the compound is an isomer of trityrosine, having an ether linkage. The name “isotrityrosine” is proposed. Its structure suggests that it serves as a crosslink and plays a role in the organization of the collagen structure. 相似文献
9.
Hsuan-Hwai Lin Yi-Jen Peng Ming-Jiun Tsai Yi-Ying Wu Tsung-Neng Tsai Hsin-Hung Huang Yu-Lueng Shih Wei-Kuo Chang Tsai-Yuan Hsieh 《Journal of cellular physiology》2020,235(2):1689-1699
Activated hepatic stellate cells promote hepatocellular carcinoma (HCC) progression. Hepatic stellate cells play a key role in retinoid metabolism, and activation of stellate cells increases retinoic acid (RA) in the liver. However, the role of RA in HCC proliferation remains unclear. We aimed to analyse the mechanism of RA in HCC proliferation. Thirty-eight patients who had undergone hepatic resection for HCCs were recruited. Paired non-tumour tissues, adjacent and distal to HCCs, were collected, and the RA levels in the tissues were analysed. The mechanisms of RA and HCC proliferation were assessed in liver cancer cell lines by protein and gene expression analyses. Early recurrence of HCC was significantly higher in patients with a higher RA concentration than in those with a lower RA concentration in tissues adjacent to HCCs (61.1% vs. 20%, p = .010). RA promoted HCC cell proliferation and activated the expression of Amphiregulin, a growth factor in hepatocarcinogenesis. The promoter of Amphiregulin contained the binding sites of the RA receptor, RXRα. Wnt signalling also activated the expression of Amphiregulin, and the RA and Wnt pathways acted synergistically to increase the expression of Amphiregulin. Furthermore, RXRα interacted with β-catenin and then translocated to the nucleus to activate Amphiregulin. An increased RA concentration in the tissues adjacent to the tumour was associated with an early recurrence of HCC. RA activated the expression of Amphiregulin, and then promoted HCC proliferation, which might partly contribute to early recurrence of HCC after hepatic resection. 相似文献
10.
Kun-Nan Tsai Guang-Wu Chen Calvin Yu-Chian Chen 《Journal of biomolecular structure & dynamics》2013,31(5):1089-1099
Abstract The resonances of the protonated carbons of [d(TAGCGCTA)]2 have been assigned by the two-dimensional proton-detected double-quantum heteronuclear correlation experiment ([1H-l3C]-DQCOSY). 13C-coupled and l3C-decoupled versions of the experiment were used. The assignment method is discussed in detail. The deoxyribose cross peaks segregate into five well-resolved regions, and the base cross peaks have distinct features that are helpful for assignments. The cross peaks from the 1H-13C pairs at the Cyd5, Ado2 and ThdCH3 base positions fall in separate regions of the spectrum from each other; they also are resolved from the closely spaced Ado8, Guo8, Cyd6 and Thd6. Additional parameters for distinction of the base signals are their differing J-coupling values and long-range coupling patterns. 相似文献