全文获取类型
收费全文 | 12266篇 |
免费 | 1015篇 |
国内免费 | 1365篇 |
出版年
2024年 | 30篇 |
2023年 | 189篇 |
2022年 | 499篇 |
2021年 | 756篇 |
2020年 | 539篇 |
2019年 | 643篇 |
2018年 | 584篇 |
2017年 | 401篇 |
2016年 | 556篇 |
2015年 | 822篇 |
2014年 | 951篇 |
2013年 | 980篇 |
2012年 | 1203篇 |
2011年 | 1094篇 |
2010年 | 616篇 |
2009年 | 585篇 |
2008年 | 697篇 |
2007年 | 544篇 |
2006年 | 476篇 |
2005年 | 392篇 |
2004年 | 319篇 |
2003年 | 254篇 |
2002年 | 194篇 |
2001年 | 160篇 |
2000年 | 132篇 |
1999年 | 170篇 |
1998年 | 103篇 |
1997年 | 119篇 |
1996年 | 86篇 |
1995年 | 68篇 |
1994年 | 69篇 |
1993年 | 54篇 |
1992年 | 61篇 |
1991年 | 52篇 |
1990年 | 52篇 |
1989年 | 37篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 13篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
101.
102.
W. F. Li J. Ji G. Wang H. Y. Wang B. L. Niu T. L. Josine 《Russian Journal of Genetics》2011,47(9):1039-1046
Many natural proteins have been developed into drugs and produced for direct application. Identifying improved hosts to achieve
high-level heterologous protein production is a challenge in the study of heterologous protein expression in recombinant yeast.
In this study, a novel high-throughput assay to screen such overproducing Saccharomyces cerevisiae strains was systematically developed. The protocol designed was based on screening host strain derivatives with increased
superoxide dismutase dependent resistance to oxidative stress. Yeast cells transformed with recombinant plasmid carrying SOD1 gene as a reporter responded exquisitely to oxidative stress induced by elevated concentrations of paraquat. Improved yeast
strains resulting from screening clones subjected to genome shuffling through selective pressure argue for a more effective
screening system compared with traditonal selection. Moreover, this approach can be employed in general biochemical analysis
without utilization of flow cytometry or well plate reader. Therefore, it is expected that the high-throughput assay would
make superior strains producing heterologous proteins. 相似文献
103.
Focal adhesion kinase (FAK) functions as a key enzyme in the integrin-mediated adhesion-signalling pathway. Here, we aimed to investigate the effects of FAK on adhesion of human dental pulp (HDP) cells. We transfected lentiviral vectors to silence or overexpress FAK in HDP cells ex vivo. Early cell adhesion, cell survival and focal contacts (FCs)-related proteins (FAK and paxillin) were examined. By using immunofluorescence, the formation of FCs and cytoskeleton was detected, respectively. We found that both adhesion and survival of HDP cells were suppressed by FAK inhibition. However, FAK overexpression slightly inhibited cell adhesion and exhibited no change in cell survival compared with the control. A thick rim of cytoskeleton accumulated and smaller dot-shaped FCs appeared in FAK knockdown cells. Phosphorylation of paxillin (p-paxillin) was inhibited in FAK knockdown cells, verifying that the adhesion was inhibited. Less cytoskeleton and elongated FCs were observed in FAK-overexpressed cells. However, p-paxillin had no significant difference compared with the control. In conclusion, the data suggest that FAK maintains cell adhesion, survival and cytoskeleton formation, but excessive FAK has no positive effects on these aspects. 相似文献
104.
105.
106.
107.
Research has revealed that most chlorophyllous explants/plants in vitro have the ability to grow photoautotrophically (without
sugar in the culture medium), and that the low or negative net photosynthetic rate of plants in vitro is not due to poor photosynthetic
ability, but to the low CO2 concentration in the air-tight culture vessel during the photoperiod. Moreover, numerous studies have been conducted on improving
the in vitro environment and investigating its effects on growth and development of cultures/plantlets on nearly 50 species
since the concept of photoautotrophic micropropagation was developed more than two decades ago. These studies indicate that
the photoautotrophic growth in vitro of many plant species can be significantly promoted by increasing the CO2 concentration and light intensity in the vessel, by decreasing the relative humidity in the vessel, and by using a fibrous
or porous supporting material with high air porosity instead of gelling agents such as agar. This paper reviews the development
and characteristics of photoautotrophic micropropagation systems and the effects of environmental conditions on the growth
and development of the plantlets. The commercial applications and the perspective of photoautotrophic micropropagation systems
are discussed. 相似文献
108.
Before cell division in many bacteria, the ParBs spread on a large segment of DNA encompassing the origin-proximal parS site(s) to form the partition assembly that participates in chromosome segregation. Little is known about the structural organization of chromosomal partition assembly. We report solution X-ray and neutron scattering data characterizing the size parameters and internal organization of a nucleoprotein assembly formed by the mycobacterial chromosomal ParB and a 120-meric DNA containing a parS-encompassing region from the mycobacterial genome. The cross-sectional radii of gyration and linear mass density describing the rod-like ParB-DNA assembly were determined from solution scattering. A “DNA outside, protein inside” mode of partition assembly organization consistent with the neutron scattering hydrogen/deuterium contrast variation data is discussed. In this organization, the high scattering DNA is positioned towards the outer region of the partition assembly. The new results presented here provide a basis for understanding how ParBs organize the parS-proximal chromosome, thus setting the stage for further interactions with the DNA condensins, the origin tethering factors and the ParA. 相似文献
109.
Christopher M. Barker Tianchan Niu William K. Reisen David M. Hartley 《PLoS neglected tropical diseases》2013,7(11)
Rift Valley Fever virus (RVFV) is an enzootic virus that causes extensive morbidity and mortality in domestic ruminants in Africa, and it has shown the potential to invade other areas such as the Arabian Peninsula. Here, we develop methods for linking mathematical models to real-world data that could be used for continent-scale risk assessment given adequate data on local host and vector populations. We have applied the methods to a well-studied agricultural region of California with 1 million dairy cattle, abundant and competent mosquito vectors, and a permissive climate that has enabled consistent transmission of West Nile virus and historically other arboviruses. Our results suggest that RVFV outbreaks could occur from February–November, but would progress slowly during winter–early spring or early fall and be limited spatially to areas with early increases in vector abundance. Risk was greatest in summer, when the areas at risk broadened to include most of the dairy farms in the study region, indicating the potential for considerable economic losses if an introduction were to occur. To assess the threat that RVFV poses to North America, including what-if scenarios for introduction and control strategies, models such as this one should be an integral part of the process; however, modeling must be paralleled by efforts to address the numerous remaining gaps in data and knowledge for this system. 相似文献
110.