全文获取类型
收费全文 | 48370篇 |
免费 | 4086篇 |
国内免费 | 4094篇 |
出版年
2024年 | 72篇 |
2023年 | 533篇 |
2022年 | 802篇 |
2021年 | 2583篇 |
2020年 | 1727篇 |
2019年 | 2135篇 |
2018年 | 2138篇 |
2017年 | 1517篇 |
2016年 | 2075篇 |
2015年 | 3012篇 |
2014年 | 3596篇 |
2013年 | 3851篇 |
2012年 | 4472篇 |
2011年 | 3913篇 |
2010年 | 2470篇 |
2009年 | 2073篇 |
2008年 | 2527篇 |
2007年 | 2235篇 |
2006年 | 2019篇 |
2005年 | 1653篇 |
2004年 | 1483篇 |
2003年 | 1304篇 |
2002年 | 1225篇 |
2001年 | 1029篇 |
2000年 | 851篇 |
1999年 | 845篇 |
1998年 | 520篇 |
1997年 | 481篇 |
1996年 | 451篇 |
1995年 | 403篇 |
1994年 | 407篇 |
1993年 | 325篇 |
1992年 | 369篇 |
1991年 | 294篇 |
1990年 | 247篇 |
1989年 | 217篇 |
1988年 | 153篇 |
1987年 | 118篇 |
1986年 | 103篇 |
1985年 | 102篇 |
1984年 | 79篇 |
1983年 | 61篇 |
1982年 | 42篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 11篇 |
1976年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 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.
Z Zhong A Toukdarian D Helinski V Knauf S Sykes J E Wilkinson C O'Bryne T Shea C DeLoughery R Caspi 《Applied and environmental microbiology》2001,67(12):5771-5779
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results. 相似文献
3.
Minjuan Shen Mingli Lin Mengqi Zhu Wenxin Zhang Danyang Lu Huanhuan Liu Jingjing Deng Kehua Que Xu Zhang 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(1):167-181
Since their discovery, matrix vesicles (MVs) containing minerals have received considerable attention for their role in the mineralization of bone, dentin and calcified cartilage. Additionally, MVs' association with collagen fibrils, which serve as the scaffold for calcification in the organic matrix, has been repeatedly highlighted. The primary purpose of the present study was to establish a MVs–mimicking model (PEG-S-ACP/micelle) in vitro for studying the exact mechanism of MVs-mediated extra/intra fibrillar mineralization of collagen in vivo. In this study, high-concentration serine was used to stabilize the amorphous calcium phosphate (S-ACP), which was subsequently mixed with polyethylene glycol (PEG) to form PEG-S-ACP nanoparticles. The nanoparticles were loaded in the polysorbate 80 micelle through a micelle self-assembly process in an aqueous environment. This MVs–mimicking model is referred to as the PEG-S-ACP/micelle model. By adjusting the pH and surface tension of the PEG-S-ACP/micelle, two forms of minerals (crystalline mineral nodules and ACP nanoparticles) were released to achieve the extrafibrillar and intrafibrillar mineralization, respectively. This in vitro mineralization process reproduced the mineral nodules mediating in vivo extrafibrillar mineralization and provided key insights into a possible mechanism of biomineralization by which in vivo intrafibrillar mineralization could be induced by ACP nanoparticles released from MVs. Also, the PEG-S-ACP/micelle model provides a promising methodology to prepare mineralized collagen scaffolds for repairing bone defects in bone tissue engineering. 相似文献
4.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter
food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s
hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using
the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds
as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental
food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter
increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end
of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased
cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival
and spring social groups or population sizes of Mongolian gerbils. 相似文献
5.
6.
7.
Transcriptional regulatory network triggered by oxidative signals configures the early response mechanisms of japonica rice to chilling stress 总被引:3,自引:0,他引:3
8.
9.
10.