全文获取类型
收费全文 | 28151篇 |
免费 | 2717篇 |
国内免费 | 3750篇 |
出版年
2024年 | 80篇 |
2023年 | 415篇 |
2022年 | 754篇 |
2021年 | 1404篇 |
2020年 | 1095篇 |
2019年 | 1326篇 |
2018年 | 1168篇 |
2017年 | 912篇 |
2016年 | 1188篇 |
2015年 | 1916篇 |
2014年 | 2219篇 |
2013年 | 2297篇 |
2012年 | 2874篇 |
2011年 | 2522篇 |
2010年 | 1685篇 |
2009年 | 1550篇 |
2008年 | 1755篇 |
2007年 | 1529篇 |
2006年 | 1404篇 |
2005年 | 1117篇 |
2004年 | 954篇 |
2003年 | 864篇 |
2002年 | 716篇 |
2001年 | 409篇 |
2000年 | 370篇 |
1999年 | 335篇 |
1998年 | 271篇 |
1997年 | 192篇 |
1996年 | 168篇 |
1995年 | 143篇 |
1994年 | 175篇 |
1993年 | 97篇 |
1992年 | 116篇 |
1991年 | 94篇 |
1990年 | 61篇 |
1989年 | 60篇 |
1988年 | 38篇 |
1987年 | 55篇 |
1986年 | 37篇 |
1985年 | 43篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1976年 | 13篇 |
1975年 | 12篇 |
1973年 | 11篇 |
1972年 | 10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.
Ting‐Hang Liu Chia‐Lin Chyan Feng‐Yin Li Ying‐Jie Chen Jason T. C. Tzen 《Biotechnology progress》2011,27(6):1760-1767
It has been demonstrated that caleosin alone is sufficient to stabilize artificial oil bodies. A series of recombinant caleosins, mutated with 3, 5, 8, 11, 13, 15, and 17 extra Lys residues and over‐expressed in Escherichia coli, were used as carrier proteins to render biotin as a hapten on the surface of artificial oil bodies for antibody production. Biotinylation levels of the recombinant caleosins were step‐wisely elevated as the number of extra Lys residues increased, and the biotinylated Lys residues were identified by mass spectrometric analysis. Polyclonal antibodies against biotin were successfully generated in rats injected with artificial oil bodies constituted with each of the biotinylated caleosins. Moreover, those generated via the biotinylated caleosins with eight or more extra Lys residues no longer recognized caleosin. It appears that engineered Lys‐rich caleosins are suitable carrier proteins for the production of antibodies against small molecules. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011 相似文献
3.
4.
5.
6.
Semiparametric Regression in Size-Biased Sampling 总被引:1,自引:0,他引:1
Ying Qing Chen 《Biometrics》2010,66(1):149-158
Summary . Size-biased sampling arises when a positive-valued outcome variable is sampled with selection probability proportional to its size. In this article, we propose a semiparametric linear regression model to analyze size-biased outcomes. In our proposed model, the regression parameters of covariates are of major interest, while the distribution of random errors is unspecified. Under the proposed model, we discover that regression parameters are invariant regardless of size-biased sampling. Following this invariance property, we develop a simple estimation procedure for inferences. Our proposed methods are evaluated in simulation studies and applied to two real data analyses. 相似文献
7.
Fang Chang An Yan Li-Na Zhao Wei-Hua Wu Zhenbiao Yang 《植物学报(英文版)》2007,49(8):1261-1270
A tip-focused Ca^2+ gradient is tightly coupled to polarized pollen tube growth, and tip-localized influxes of extracellular Ca^2+ are required for this process. However the molecular identity and regulation of the potential Ca^2+ channels remains elusive. The present study has implicated CNGC18 (cyclic nucleotide-gated channel 18) in polarized pollen tube growth, because its overexpression induced wider and shorter pollen tubes. Moreover, CNGC18 overexpression induced depolarization of pollen tube growth was suppressed by lower extracellular calcium ([Ca^2+]ex). CNGC18-yellow fluorescence protein (YFP) was preferentially localized to the apparent post-Golgi vesicles and the plasma membrane (PM) in the apex of pollen tubes. The PM localization was affected by tip-localized ROP1 signaling. Expression of wild type ROP1 or an active form of ROP1 enhanced CNGC18-YFP localization to the apical region of the PM, whereas expression of RopGAP1 (a ROP1 deactivator) blocked the PM localization. These results support a role for PM-Iocalized CNGC18 in the regulation of polarized pollen tube growth through its potential function in the modulation of calcium influxes. 相似文献
8.
9.
Fei Mi Ying Zhang Dan Yang Xiaozhao Tang Pengfei Wang Xiaoxia He Yunrun Zhang Jianyong Dong Yang Cao Chunli Liu Ke-Qin Zhang Jianping Xu 《PloS one》2016,11(2)
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China. 相似文献
10.