全文获取类型
收费全文 | 1651篇 |
免费 | 170篇 |
专业分类
1821篇 |
出版年
2022年 | 7篇 |
2021年 | 17篇 |
2020年 | 8篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 35篇 |
2014年 | 41篇 |
2013年 | 119篇 |
2012年 | 89篇 |
2011年 | 95篇 |
2010年 | 39篇 |
2009年 | 32篇 |
2008年 | 82篇 |
2007年 | 101篇 |
2006年 | 91篇 |
2005年 | 80篇 |
2004年 | 64篇 |
2003年 | 84篇 |
2002年 | 62篇 |
2001年 | 61篇 |
2000年 | 57篇 |
1999年 | 52篇 |
1998年 | 22篇 |
1997年 | 30篇 |
1996年 | 21篇 |
1995年 | 14篇 |
1994年 | 19篇 |
1993年 | 22篇 |
1992年 | 30篇 |
1991年 | 38篇 |
1990年 | 28篇 |
1989年 | 50篇 |
1988年 | 35篇 |
1987年 | 26篇 |
1986年 | 25篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1974年 | 11篇 |
1973年 | 6篇 |
1971年 | 7篇 |
1968年 | 8篇 |
排序方式: 共有1821条查询结果,搜索用时 15 毫秒
991.
Guan JZ Maeda T Sugano M Oyama J Higuchi Y Makino N 《Molecular and cellular biochemistry》2007,304(1-2):353-360
Telomeres play a role in cellular aging and they may also contribute to the genetic basis of human aging and longevity. A
gradual loss of the telomeric repeat sequences has been reported in adult tissue specimens. This study determined the percentage
of telomere restriction fragment in various molecular-sized regions in addition to measuring the average telomere length.
Mean telomere restriction fragment (TRF) length was determined by Southern blot analysis using a longer telomeric repeat probe
with higher sensitivity. A significant decrease in longer telomere fragments and a quick increase in the shortest fragments
were observed, especially in male subjects. There was a tendency that the age-adjusted telomere length was longer in females
than that observed in males, while males lose the telomeric sequence faster than females. These data indicated that the percentage
of longer telomeres fragments decreased, while the shortest fragments increased quickly with age. In addition, the longest
telomere fragments decreased and the short fragments increased with a relatively stable frequency with age. There was also
a significant difference in the longest telomere fragment percentage between males and female in their 40s and 50s, whereas
no difference was observed in the mean TRF length. Interestingly, the changing rate of the longest and the shortest range
group of TRF percentage associated with aging seemed quite different between before and after 50-year old with a gender-related
contrast. This contrast implies a drastic change around the age of 50 of unknown factors that affect telomere attrition.
The first two authors equally contributed to this article. 相似文献
992.
An asymmetric hydrogen-transfer biocatalyst consisting of mutated Rhodococcus phenylacetaldehyde reductase (PAR) or Leifsonia alcohol dehydrogenase (LSADH) was applied for some water-soluble ketone substrates. Among them, 4-hydroxy-2-butanone was
reduced to (S)/(R)-1,3-butanediol, a useful intermediate for pharmaceuticals, with a high yield and stereoselectivity. Intact Escherichia coli cells overexpressing mutated PAR (Sar268) or LSADH were directly immobilized with polyethyleneimine or 1,6-diaminehexane
and glutaraldehyde and evaluated in a batch reaction. This system produced (S)-1,3-butanediol [87% enantiomeric excess (e.e.)] with a space time yield (STY) of 12.5 mg h−1 ml−1 catalyst or (R)-1,3-butanediol (99% e.e.) with an STY of 60.3 mg h−1 ml−1 catalyst, respectively. The immobilized cells in a packed bed reactor continuously produced (R)-1,3-butanediol with a yield of 99% (about 49.5 g/l) from 5% (w/v) 4-hydroxy-2-butanoate over 500 h. 相似文献
993.
Asakura H Panutdaporn N Kawamoto K Igimi S Yamamoto S Makino S 《Microbiology and immunology》2007,51(9):875-881
Enterohemorrhagic Escherichia coli (EHEC) O157 strain F2, a food isolate of an outbreak, is resistant to oxidative stress, but has increased stress-sensitivity after passage through mice. The stress-sensitive variant of F2 (designated MP37) has decreased culturability, but retains membrane integrity under stress conditions, indicating that the cells enter a viable but non-culturable (VBNC) state. Proteomic analyses revealed that MP37 in the VBNC state had decreased levels of some oxidation-responsive factors (AhpCF, AceF), but it markedly increased levels of outer membrane protein W (OmpW). Because F2 expressed higher levels of some ribosome-associated proteins (RaiA, S6, Bcp) than MP37, the effect of animal passage on the induction of the VBNC state in the EHEC O157 cells might be due to ribosomal activity. 相似文献
994.
995.
Suzuki Yuji Konno Yume Takegahara-Tamakawa Yuki Miyake Chikahiro Makino Amane 《Photosynthesis research》2022,153(1-2):83-91
Photosynthesis Research - As chloroplast phosphoglycerate kinase (cpPGK) is one of the enzymes which has the highest capacity among the Calvin–Benson cycle enzymes, it has not been regarded... 相似文献
996.
Yosuke Tanaka Kazuhiko Aoyagi Keiko Minashi Rie Komatsuzaki Masayuki Komatsu Fumiko Chiwaki Masashi Tamaoki Takao Nishimura Naoki Takahashi Ichiro Oda Yuji Tachimori Tokuzo Arao Kazuto Nishio Shigehisa Kitano Kenta Narumi Kazunori Aoki Satoshi Fujii Atsushi Ochiai Teruhiko Yoshida Manabu Muto Yasuhide Yamada Hiroki Sasaki 《PloS one》2015,10(12)
Definitive chemoradiotherapy (CRT) is a less invasive therapy for esophageal squamous cell carcinoma (ESCC). Five-year survival rate of locally advanced ESCC patients by definitive CRT were 37%. We previously reported that tumor-specific cytotoxic T-lymphocyte (CTL) activation signatures were preferentially found in long-term survivors. However, it is unknown whether the CTL activation is actually driven by CRT. We compared gene expression profiles among pre- and post-treatment biopsy specimens of 30 ESCC patients and 121 pre-treatment ESCC biopsy specimens. In the complete response (CR) cases, 999 overexpressed genes including at least 234 tumor-specific CTL-activation associated genes such as IFNG, PRF1, and GZMB, were found in post-treatment biopsy specimens. Clustering analysis using expression profiles of these 234 genes allowed us to distinguish the immune-activated cases, designating them as I-type, from other cases. However, despite the better CR rate in the I-type, overall survival was not significantly better in both these 30 cases and another 121 cases. Further comparative study identified a series of epithelial to mesenchymal transition-related genes overexpressed in the early relapse cases. Importantly, the clinical outcome of CDH2-negative cases in the I-type was significantly better than that of the CDH2-positive cases in the I-type. Furthermore, NK cells, which were activated by neutrophils-producing S100A8/S100A9, and CTLs were suggested to cooperatively enhance the effect of CRT in the CDH2-negative I-type. These results suggested that CTL gene activation may provide a prognostic advantage in ESCCs with epithelial characteristics. 相似文献
997.
When pollinators use flower color to locate food sources, a distinct color can serve as a reproductive barrier against co-flowering species. This anti-interference function of flower color may result in a community assembly of plant species displaying mutually different flower colors. However, such color dispersion is not ubiquitous, suggesting a variable selection across communities and existence of some opposing factors. We conducted a 30-week study in a plant community and measured the floral reflectances of 244 species. The reflectances were evaluated in insect color spaces (bees, swallowtails, and flies), and the dispersion was compared with random expectations. We found that co-existing colors were overdispersed for each analyzed pollinator type, and this overdispersion was statistically significant for bees. Furthermore, we showed that exclusion of 32 aliens from the analysis significantly increased the color dispersion of native flowers in every color space. This result indicated that aliens disturbed a native plant–pollinator network via similarly colored flowers. Our results demonstrate the masking effects of aliens in the detection of color dispersion of native flowers and that variations in pollinator vision yield different outcomes. Our results also support the hypothesis that co-flowering species are one of the drivers of color diversification and affect the community assembly. 相似文献
998.
Muneko Nishijo Pham The Tai Nguyen Thi Nguyet Anh Tran Ngoc Nghi Hideaki Nakagawa Hoang Van Luong Tran Hai Anh Yuko Morikawa Tomoo Waseda Teruhiko Kido Hisao Nishijo 《PloS one》2015,10(1)
In our previous study of 3-year-old children in a dioxin contamination hot spot in Vietnam, the high total dioxin toxic equivalent (TEQ-PCDDs/Fs)-exposed group during the perinatal period displayed lower Bayley III neurodevelopmental scores, whereas the high 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-exposed group displayed increased autistic traits. In autistic children, urinary amino acid profiles have revealed metabolic alterations in the amino acids that serve as neurotransmitters in the developing brain. Therefore, our present study aimed to investigate the use of alterations in urinary amino acid excretion as biomarkers of dioxin exposure-induced neurodevelopmental deficits in highly exposed 3-year-old children in Vietnam. A nested case-control study of urinary analyses was performed for 26 children who were selected from 111 3-year-old children whose perinatal dioxin exposure levels and neurodevelopmental status were examined in follow-up surveys conducted in a dioxin contaminated hot spot. We compared urinary amino acid levels between the following 4 groups: (1) a high TEQ-PCDDs/Fs and high TCDD-exposed group; (2) a high TEQ-PCDDs/Fs but low TCDD-exposed group; (3) a low TEQ-PCDDs/Fs exposed and poorly developed group; and (4) a low TEQ-PCDDs/Fs exposed and well-developed group. Urinary levels of histidine and tryptophan were significantly decreased in the high TEQ-PCDDs/Fs and high TCDD group, as well as in the high TEQ-PCDDs/Fs but low TCDD group, compared with the low TEQ-PCDDs/Fs and well-developed group. However, the ratio of histidine to glycine was significantly lower only in the high TEQ-PCDDs/Fs and high TCDD group. Furthermore, urinary histidine levels and the ratio of histidine to glycine were significantly correlated with neurodevelopmental scores, particularly for language and fine motor skills. These results indicate that urinary histidine is specifically associated with dioxin exposure-induced neurodevelopmental deficits, suggesting that urinary histidine may be a useful marker of dioxin-induced neurodevelopmental deficits and that histaminergic neurotransmission may be an important pathological contributor to dioxin-mediated neurotoxicity. 相似文献
999.
1000.
Anisaldehyde, a melanogenesis potentiator 总被引:1,自引:0,他引:1
Nitoda T Fan MD Kubo I 《Zeitschrift für Naturforschung. C, Journal of biosciences》2007,62(1-2):143-149
Anisaldehyde (4-methoxybenzaldehyde), previously reported as a tyrosinase inhibitor, did not inhibit melanogenesis in cultured B16-F10 melanoma cells but rather enhanced it. This adverse effect of anisaldehyde was accompanied by melanocytotoxicity in a dose-dependent manner up to 2 mM. The melanin content per cell at 1 mM was increased 5-fold compared to control and morphological observations showed the deposition of melanin pigments. Anisaldehyde was also examined against cultured human A375 melanoma cells. 相似文献