全文获取类型
收费全文 | 1953篇 |
免费 | 163篇 |
国内免费 | 165篇 |
专业分类
2281篇 |
出版年
2024年 | 6篇 |
2023年 | 19篇 |
2022年 | 65篇 |
2021年 | 89篇 |
2020年 | 79篇 |
2019年 | 74篇 |
2018年 | 92篇 |
2017年 | 59篇 |
2016年 | 98篇 |
2015年 | 109篇 |
2014年 | 134篇 |
2013年 | 155篇 |
2012年 | 178篇 |
2011年 | 143篇 |
2010年 | 92篇 |
2009年 | 77篇 |
2008年 | 93篇 |
2007年 | 98篇 |
2006年 | 77篇 |
2005年 | 69篇 |
2004年 | 95篇 |
2003年 | 79篇 |
2002年 | 71篇 |
2001年 | 55篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 13篇 |
1995年 | 9篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有2281条查询结果,搜索用时 15 毫秒
991.
The development time from zygote to late stage of planula larvaeon the oral arms of Aurelia aurita was found to be 270 and 170h at 12 and 22°C, respectively. The mean ratio of the diameterof the long axis to the short axis in newly released planulaewas 2.27. 相似文献
992.
993.
Oyama Takumi Komeno Shohei Ai Yuta Tamayama Wakana Sano Haruto Nakano Masao Nakachi Shuu Sunobe Tomoki Akagawa Izumi 《Ichthyological Research》2020,67(3):416-421
Ichthyological Research - Reproductive behavior of the blenniid fish Meiacanthus kamoharai was investigated in Tachibanaura Bay, Kochi Prefecture, Japan in 2016–2018. The species is sexually... 相似文献
994.
Zeyuan Chen Fandi Ai Junlin Zhang Xinzhi Ma Wenlu Yang Weiwei Wang Yutao Su Mingcheng Wang Yongzhi Yang Kangshan Mao Qingfeng Wang Martin Lascoux Jianquan Liu Tao Ma 《The Plant journal : for cell and molecular biology》2020,103(1):430-442
Species are becoming extinct at unprecedented rates as a consequence of human activity. Hence it is important to understand the evolutionary dynamics of species with already small population sizes. Populus ilicifolia is a vulnerable poplar species that is isolated from other poplar species and is uniquely adapted to the Tropics. It has a very limited size, reproduces partly clonally and is therefore an excellent case study for conservation genomics. We present here the first annotated draft genome of P. ilicifolia, characterize genome‐wide patterns of polymorphisms and compare those to other poplar species with larger natural ranges. P. ilicifolia experienced a more prolonged and severe decline of effective population size (Ne) and signs of genetic erosion than any other poplar species with which it was compared. At present, the species has the lowest genome‐wide genetic diversity, the highest abundance of long runs of homozygosity, high inbreeding levels as well as a high overall accumulation of deleterious variants. However, more effective purging of severely deleterious variants and adaptation to the Tropics may have contributed to its survival. Hence, in spite of its limited genetic variation, it is certainly worth pursuing the conservation efforts of this unique species. 相似文献
995.
Nguyen Tien Huy Yusuke Shima Atsushi Maeda Tran Thanh Men Kenji Hirayama Ai Hirase Atsuo Miyazawa Kaeko Kamei 《PloS one》2013,8(7)
Phospholipid membranes are thought to be one of the main inducers of hemozoin formation in Plasmodia and other blood-feeding parasites. The “membrane surrounding hemozoin” has been observed in infected cells but has not been observed in in vitro experiments. This study focused on observing the association of phospholipid membranes and synthetic β-hematin, which is chemically identical to hemozoin, and on a further exploration into the mechanism of phospholipid membrane-induced β-hematin formation. Our results showed that β-hematin formation was induced by phospholipids in the fluid phase but not in the gel phase. The ability of phospholipids to induce β-hematin formation was inversely correlated with gel-to-liquid phase transition temperatures, suggesting an essential insertion of heme into the hydrocarbon chains of the phospholipid membrane to form β-hematin. For this study, a cryogenic transmission electron microscope was used to achieve the first direct observation of the formation of a monolayer of phospholipid membrane surrounding β-hematin. 相似文献
996.
Objective
Ultrasonographic studies have demonstrated transient reduction in spleen volume in relation to apnea diving. We measured spleen volume under various respiratory conditions by MR imaging to accurately determine the influence of ordinary breath holding on spleen volumetry.Materials and Methods
Twelve healthy adult volunteers were examined. Contiguous MR images of the spleen were acquired during free breathing and during respiratory manipulations, including breath holding at the end of normal expiration, breath holding at deep inspiration, and the valsalva maneuver, and spleen volume was measured from each image set based on the sum-of-areas method. Acquisition during free breathing was performed with respiratory triggering. The duration of each respiratory manipulation was 30 s, and five sets of MR images were acquired serially during each manipulation.Results
Baseline spleen volume before respiratory manipulation was 173.0 ± 79.7 mL, and the coefficient of variance for two baseline measures was 1.4% ± 1.6%, suggesting excellent repeatability. Spleen volume decreased significantly just after the commencement of respiratory manipulation, remained constant during the manipulation, and returned to the control value 2 min after the cessation of the manipulation, irrespective of manipulation type. The percentages of volume reduction were 10.2% ± 2.9%, 10.2% ± 3.5%, and 13.3% ± 5.7% during expiration breath holding, deep-inspiration breath holding, and the valsalva maneuver, respectively, and these values did not differ significantly.Conclusions
Spleen volume is reduced during short breath-hold apnea in healthy adults. Physiological responses of the spleen to respiratory manipulations should be considered in the measurement and interpretation of spleen volume. 相似文献997.
Ai‐ran Liu Le Liu Song Chen Yi Yang Hong‐jie Zhao Ling Liu Feng‐mei Guo Xiao‐min Lu Hai‐bo Qiu 《Journal of cellular physiology》2013,228(6):1270-1283
The differentiation of mesenchymal stem cells (MSCs) into type II alveolar epithelial (AT II) cells in vivo and in vitro, is critical for reepithelization and recovery in acute lung injury (ALI), but the mechanisms responsible for differentiation are unclear. In the present study, we investigated the role of the canonical wnt pathway in the differentiation of mouse bone marrow‐derived MSCs (mMSCs) into AT II cells. Using a modified co‐culture system with murine lung epithelial‐12 (MLE‐12) cells and small airway growth media (SAGM) to efficiently drive mMSCs differentiation, we found that GSK 3β and β‐catenin in the canonical wnt pathway were up‐regulated during differentiation. The levels of surfactant protein (SP) C, SPB, and SPD, the specific markers of AT II cells, correspondingly increased in mMSCs when Wnt3a or LiCl was added to the co‐culture system to activate wnt/β‐catenin signaling. The expression of these factors was depressed to some extent by inhibiting the pathway with the addition of DKK 1. The differentiation rate of mMSCs also depends on their abilities to accumulate and survive in inflammatory tissue. Our results suggested that the activation of wnt/β‐catenin signaling promoted mMSCs migration towards ALI mouse‐derived lung tissue in a Transwell assay, and ameliorated the cell death and the reduction of Bcl‐2/Bax induced by H2O2, which simultaneously caused reduced GSK 3β and β‐catenin in mMSCs. These data supports a potential mechanism for the differentiation of mMSCs into AT II cells involving canonical wnt pathway activation, which may be significant to their application in ALI. J. Cell. Physiol. 228: 1270–1283, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
998.
999.
1000.
Wellner N Tsuboi K Madsen AN Holst B Diep TA Nakao M Tokumura A Burns MP Deutsch DG Ueda N Hansen HS 《Biochimica et biophysica acta》2011,1811(9):508-512
N-acyl-phosphatidylethanolamine is a precursor phospholipid for anandamide, oleoylethanolamide, and other N-acylethanolamines, and it may in itself have biological functions in cell membranes. Recently, N-palmitoyl-phosphatidylethanolamine (NAPE) has been reported to function as an anorectic hormone secreted from the gut and acting on the brain (Gillum et al., [5]). In the current study, two of our laboratories independently investigated whether NAPE metabolites may be involved in mediating the anorectic action of NAPE i.p. injected in mice. Thus, the anorectic activity of a non-hydrolysable NAPE analogue, having ether bonds instead of ester bonds at sn1 and sn2 was compared with that of NAPE in molar equivalent doses. Furthermore, the anorectic effect of NAPE in NAPE-hydrolysing phospholipase D knockout animals was investigated. As negative controls, the NAPE precursor phosphatidylethanolamine and the related phospholipids phosphatidylcholine and phosphatidic acid were also tested. All compounds except one were found to inhibit food intake, raising the possibility that the effect of NAPE is non-specific. 相似文献