全文获取类型
收费全文 | 16787篇 |
免费 | 1301篇 |
国内免费 | 587篇 |
专业分类
18675篇 |
出版年
2024年 | 28篇 |
2023年 | 145篇 |
2022年 | 359篇 |
2021年 | 559篇 |
2020年 | 410篇 |
2019年 | 526篇 |
2018年 | 596篇 |
2017年 | 491篇 |
2016年 | 686篇 |
2015年 | 1033篇 |
2014年 | 1125篇 |
2013年 | 1300篇 |
2012年 | 1545篇 |
2011年 | 1364篇 |
2010年 | 891篇 |
2009年 | 771篇 |
2008年 | 950篇 |
2007年 | 853篇 |
2006年 | 724篇 |
2005年 | 632篇 |
2004年 | 588篇 |
2003年 | 504篇 |
2002年 | 457篇 |
2001年 | 254篇 |
2000年 | 250篇 |
1999年 | 237篇 |
1998年 | 120篇 |
1997年 | 132篇 |
1996年 | 117篇 |
1995年 | 96篇 |
1994年 | 90篇 |
1993年 | 83篇 |
1992年 | 106篇 |
1991年 | 111篇 |
1990年 | 73篇 |
1989年 | 61篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 42篇 |
1985年 | 43篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 12篇 |
1981年 | 17篇 |
1979年 | 18篇 |
1978年 | 20篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1972年 | 13篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper
culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs
from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is
still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell
differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis. 相似文献
2.
A recombinant cell line (NIH3T3:pLtkSN) was made by infecting parental cells (NIH3T3) with a recombinant retrovirus (pLtkSN) encoding herpes simplex virus thymidine kinase (HSVtk) gene. The cells expressing HSVtk (NIH3T3:pLtkSN) grew 2.3 times more than the parental cells (NIH3T3) in Dulbecco's Modified Eagles Media containing 10% (v/v) horse serum. The NIH3T3:pLtkSN cells also showed a significant enhancement in the maximal cell concentration and the specific growth rate even at 2.5% serum concentration. The specific O2 uptake rate of NIH3T3 was 2.1 times greater than that of NIH3T3:pLtkSN. Under both O2-limited and O2-unlimited conditions, it appears that HSVtk plays an important role in enhancing the growth characteristics of animal cells. 相似文献
3.
4.
Michael D. Jensen Ji?í Bajnárek Sang Yeoup Lee Soren Nielsen Christina Koutsari 《Journal of lipid research》2009,50(9):1863-1869
The relationship between overnight postabsorptive (fasting) respiratory exchange ratio (RER) and plasma FFA concentrations was addressed using data from three separate protocols, each of which involved careful control of the antecedent diet. Protocol 1 examined the relationship between fasting RER and the previous daytime RER. In Protocol 2 fasting, RER and plasma palmitate concentrations were measured in 29 women and 31 men (body mass index <30 kg·m−2). Protocol 3 analyzed data from Nielsen et al. (Nielsen, S., Z. K. Guo, J. B. Albu, S. Klein, P. C. O''Brien, M. D. Jensen. 2003. Energy expenditure, sex and endogenous fuel availability in humans. J. Clin. Invest. 111: 981-988.) to understand how fasting RER and palmitate concentrations relate within individuals during four consecutive measurements. The results were as follows: 1) Fasting RER was correlated (r = 0.74, P < 0.001) with the previous day''s average RER, and less so with RER variability. 2) Fasting RER was correlated (r = −0.39, P = 0.007) with fasting plasma palmitate concentrations. 3) The pattern of the RER/palmitate relationship was similar within individuals and between individuals; a negative slope was observed significantly more often than a positive slope (χ2 test; P < 0.001). Our findings suggest that, despite a fixed food quotient, the slight departures from energy equilibrium in a controlled General Clinical Research Center environment can effect plasma FFA concentrations. We suggest that including indirect calorimetry as part of FFA metabolism studies may aid in data interpretation. 相似文献
5.
Zenghui Hu Yingbai Shen Fanyi Shen Youqing Luo Xiaohua Su 《Trees - Structure and Function》2009,23(5):1003-1011
Interplant communication has been widely demonstrated in plants, especially in herbaceous plants. In this study, mechanical
damage was shown to affect the levels of pyrochatechol, chlorogenic acid, gallic acid and p-hydroxyl benzoic acid in poplar (Populus simonii × P. pyramidalis ‘Opera 8277’) cuttings, indicating the activation of defense response. In neighboring intact cuttings, the levels of those
phenolics also varied when compared to the control, suggesting the interplant communication between poplar cuttings. Three
volatiles, methyl jasmonate, methyl salicylate and benzothiazole, were detected in volatiles emitted from mechanically damaged
poplar cuttings. All of them can induce changes in the levels of four phenolics. Therefore, they could act as airborne signals
between P. simonii × P. pyramidalis ‘Opera 8277’ cuttings. The different change patterns of phenolic contents induced by different volatiles imply that the defense
response activated in neighboring plants may be regulated by multiple signaling pathways. The results also suggest that the
entire defense response of plants involves a variety of airborne signals in wound-induced volatiles. 相似文献
6.
7.
8.
9.
10.
Association of viral and plasmid DNA with the nuclear matrix during productive infection 总被引:1,自引:0,他引:1
The association of simian virus 40 (SV40) DNA or plasmid DNA in subcellular fractions from either infected or transfected cells was examined. In lytically infected cells, approx. 25% of viral specific DNA during the infection cycle was retained in nuclei after washing with low ionic strength buffer and 1% Triton X-100. Viral replicating DNA found in the nuclear matrix was capable of performing limited DNA synthesis by the endogenous DNA polymerase in vitro. Viral DNA synthesized in vitro hybridized preferentially to SV40 Hind-III B and C fragments which are in proximity to the origin of replication. In plasmid-transfected COS-7 cells (SV40-transformed cells), the amount of plasmid DNA found in the nuclear matrix was related to its replication efficiency in cells. More than 80% of the plasmid DNA was tightly associated with subnuclear structures. Little or no plasmid DNA was found in the cytoplasmic fraction. The results suggest that, in extrachromosomal model systems, the association of DNA with nuclear matrix is important for the regulation of DNA replication. 相似文献