全文获取类型
收费全文 | 1708篇 |
免费 | 99篇 |
专业分类
1807篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 20篇 |
2019年 | 20篇 |
2018年 | 18篇 |
2017年 | 22篇 |
2016年 | 30篇 |
2015年 | 54篇 |
2014年 | 65篇 |
2013年 | 90篇 |
2012年 | 102篇 |
2011年 | 109篇 |
2010年 | 61篇 |
2009年 | 67篇 |
2008年 | 97篇 |
2007年 | 91篇 |
2006年 | 85篇 |
2005年 | 95篇 |
2004年 | 100篇 |
2003年 | 98篇 |
2002年 | 79篇 |
2001年 | 31篇 |
2000年 | 20篇 |
1999年 | 36篇 |
1998年 | 35篇 |
1997年 | 18篇 |
1996年 | 23篇 |
1995年 | 24篇 |
1994年 | 23篇 |
1993年 | 36篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 16篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 6篇 |
排序方式: 共有1807条查询结果,搜索用时 0 毫秒
21.
Mats Thulin 《Nordic Journal of Botany》2003,23(5):629-640
The six new species Convolvulus scopulatus, a shrub from gypseous semidesert coastal plains in northern Somalia, Astripomoea procera, a woody climber in Acacia-Commiphora bushland on sand in south-central Somalia, Ipomoea hiranensis, a prostrate or climbing shrublet in Acacia-Commiphora bushland in rocky places on sandstone in south-central Somalia, Ipomoea galhareriana, a woody climber in bushland on sand in central Somalia, Ipomoea pogonantha, a woody climber in bushland usually on red soil over limestone in eastern and southern Ethiopia, southern Somalia and northern Kenya, and Ipomoea corrugata, a herb with trailing stems in bushland on sandy soil in south-central Somalia, are described, and illustrations are provided for most of them. The new combinations Ipomoea ovatolanceolata (= I. adenoides var. ovatolanceolata) and Merremia obtusa (= M. ampelophylla subsp. obtusa) are made, and a new synonymy is provided for M. ampelophylla. Merremia ellenbeckii is neotypified and M. lobata is placed in synonymy. 相似文献
22.
23.
Mats Thulin 《Nordic Journal of Botany》1999,19(2):199-208
Pavonia friisii , sp. nov., from south-eastern Ethiopia and south-central and southern Somalia, P. nigrescens , sp. nov., from south-central and southern Somalia, P. matteiana , sp. nov., from south-central Somalia, P. longipilosa , sp. nov., from eastern Ethiopia, P. rotundifolia , sp. nov., from eastern Ethiopia and northern and central Somalia, P. marginata , sp. nov., from central Somalia, and P. paucibracteata , sp. nov., from central Somalia, are described and illustrated. 相似文献
24.
The rapidly growing body of sequenced DNA demands efficientcomputer programs for its analysis and storage. The programdescribed in this paper, SEQ-ED, has been designed to handlea large number of DNA sequences up to 200 kilobases [kb] longstored in a sequence library. In order to minimize the requiredstorage space, the sequences are stored in a compressed formatusing three binary digits per base. In the development of thisprogram, special care has been given to make it easy to usefor molecular biologists without any previous computer experience.
Received on September 10, 1984; accepted on October 30, 1984 相似文献
25.
26.
27.
28.
John Axelsson Javaid-ur Rehman Torbjorn Akerstedt Rolf Ekman Gregory E. Miller Caroline Olgart H?glund Mats Lekander 《PloS one》2013,8(12)
Background
Recent studies suggest that acute sleep deprivation disrupts cellular immune responses by shifting T helper (Th) cell activity towards a Th2 cytokine profile. Since little is known about more long-term effects, we investigated how five days of sleep restriction would affect pro-inflammatory, chemotactic, Th1- and Th2 cytokine secretion.Methods
Nine healthy males participated in an experimental sleep protocol with two baseline sleep-wake cycles (sleep 23.00 – 07.00 h) followed by 5 days with restricted sleep (03.00 – 07.00 h). On the second baseline day and on the fifth day with restricted sleep, samples were drawn every third hour for determination of cytokines/chemokines (tumor necrosis factor alpha (TNF-α), interleukin (IL) -1β, IL-2, IL-4 and monocyte chemoattractant protein-1 (MCP-1)) after in vitro stimulation of whole blood samples with the mitogen phytohemagglutinin (PHA). Also leukocyte numbers, mononuclear cells and cortisol were analysed.Results
5-days of sleep restriction affected PHA-induced immune responses in several ways. There was a general decrease of IL-2 production (p<.05). A shift in Th1/Th2 cytokine balance was also evident, as determined by a decrease in IL2/IL4 ratio. No other main effects of restricted sleep were shown. Two significant interactions showed that restricted sleep resulted in increased TNF-α and MCP-1 in the late evening and early night hours (p’s<.05). In addition, all variables varied across the 24 h day.Conclusions
5-days of sleep restriction is characterized by a shift towards Th2 activity (i.e. lower 1L-2/IL-4 ratio) which is similar to the effects of acute sleep deprivation and psychological stress. This may have implications for people suffering from conditions characterized by excessive Th2 activity like in allergic disease, such as asthma, for whom restricted sleep could have negative consequences. 相似文献29.
Mats F. Nilsson Helen Ritchie William S. Webster 《Birth defects research. Part B, Developmental and reproductive toxicology》2013,98(5):416-427
In this study, we compared the effects of four ion channel blockers on rat embryonic heart function during the organogenic period from gestational day (GD) 10 to 15, to determine the changes in dependence on ion channels during rat cardiac development. Rat embryos in culture were exposed to either the human ether‐á‐go‐go‐related gene potassium channel blocker, dofetilide (400 nM); the sodium channel blocker, lidocaine (250 μM); the L‐type calcium channel blocker, nifedipine (1.8 μM); or the multichannel blocker, phenytoin (200 μM). Lidocaine slowed the heart rate (HR) with the effect becoming more severe with increasing GD. Dofetilide slowed the embryonic HR and caused arrhythmias with the most severe effect on GD 11 to 13. Nifedipine primarily caused a negative inotropic effect except on GD 10 when it stopped the heart in most embryos. Phenytoin stopped the heart of most GD 10 to 12 embryos while on GD 13 to 15 phenytoin slowed the heart. The results demonstrate that as the rat heart develops during the organogenic period its functional dependence on ion channels changes markedly. These changes are important for understanding drug effects on the embryo during pregnancy and the methodology used provides a simple procedure for assessing drug effects on the developing heart. 相似文献
30.
Dipankar Ray Shirish Shukla Uday Sankar Allam Abigail Helman Susmita Gurjar Ramanand Linda Tran Michael Bassetti Pranathi Meda Krishnamurthy Matthew Rumschlag Michelle Paulsen Lei Sun Thomas P. Shanley Mats Ljungman Mukesh K. Nyati Ming Zhang Theodore S. Lawrence 《PloS one》2013,8(2)
The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For in vitro studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the in vivo relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from ttp (−/−) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTPSer178 phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT. 相似文献