全文获取类型
收费全文 | 1404篇 |
免费 | 80篇 |
国内免费 | 6篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 38篇 |
2021年 | 56篇 |
2020年 | 56篇 |
2019年 | 74篇 |
2018年 | 63篇 |
2017年 | 50篇 |
2016年 | 64篇 |
2015年 | 82篇 |
2014年 | 88篇 |
2013年 | 124篇 |
2012年 | 91篇 |
2011年 | 110篇 |
2010年 | 63篇 |
2009年 | 58篇 |
2008年 | 47篇 |
2007年 | 46篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 37篇 |
2003年 | 24篇 |
2002年 | 22篇 |
2001年 | 2篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 22篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1985年 | 9篇 |
1984年 | 14篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1975年 | 4篇 |
1957年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有1490条查询结果,搜索用时 31 毫秒
961.
962.
963.
Since differentiation therapy is one of the promising strategies for treatment of leukemia, universal efforts have been focused on finding new differentiating agents. In that respect, we used guanosine 5'-triphosphate (GTP) to study its effects on K562 cell line. GTP, at concentrations between 25-200 microM, inhibited proliferation (3-90%) and induced 5-78% increase in benzidine-positive cells after 6-days of treatments of K562 cells. Flow cytometric analyses of glycophorine A (GPA) showed that GTP can induce expression of this marker in more mature erythroid cells in a time- and dose-dependent manner. These effects of GTP were also accompanied with inhibition of DNA synthesis (measured by [3H]-thymidine incorporation) and early S-phase cell cycle arrest by 96 h of exposure. In contrast, no detectable effects were observed when GTP administered to unstimulated human peripheral blood lymphocytes (PBL). However, GTP induced an increase in proliferation, DNA synthesis and viability of mitogen-stimulated PBL cells. In addition, growth inhibition and differentiating effects of GTP were also induced by its corresponding nucleotides GDP, GMP and guanosine (Guo). In heat-inactivated medium, where rapid degradation of GTP via extracellular nucleotidases is slow, the anti-proliferative and differentiating effects of all type of guanine nucleotides (except Guo) were significantly decreased. Moreover, adenosine, as an inhibitor of Guo transporter system, markedly reduced the GTP effects in K562 cells, suggesting that the extracellular degradation of GTP or its final conversion to Guo may account for the mechanism of GTP effects. This view is further supported by the fact that GTP and Guo are both capable of impeding the effects of mycophenolic acid. In conclusion, our data will hopefully have important impact on pharmaceutical evaluation of guanine nucleotides for leukemia treatments. 相似文献
964.
新疆阿勒泰山两河源自然保护区地面生地衣的物种多样性 总被引:1,自引:0,他引:1
阿勒泰山地是我国著名水系额尔齐斯河和乌伦古河的发源地,该山地地衣植物的研究在中国乃至中亚都占有非常重要的科学地位。新疆阿勒泰山两河源自然保护区位于阿勒泰山东段,气候在新疆最为潮湿,其地衣植物种类十分丰富。作者在该保护区选择6个植被带类型,即山地荒漠带、山地草原带、针阔混交林带、针叶林带、亚高山草甸带、高山草甸带,研究了其地面生地衣植物的物种多样性特征。结果表明:阿勒泰山两河源自然保护区地衣植物区系成分丰富而且复杂,共有地面生地衣植物5科6属46种,以石蕊科种类最为丰富,约32种。该地区不同植被带类型下地面生地衣植物物种的S?renson相似性系数在0.200–0.739之间,以针阔混交林和针叶林带的相似性为最高(0.739),针阔混交林和高山草甸带地衣植物物种相似性最低(0.200)。各植被带地衣优势种中白边岛衣(Cetrarialaeuigata)、林鹿蕊(Cladoniaarbuscula)、佐木氏珊瑚枝(Stereocaulonsasakii)、鳞地卷(Peltigeralepido-phora)、喇叭粉石蕊(Cladoniachlorophaea)、东方鹿蕊(Cladinagrisea)等的重要值在0.5以上,其余优势种的重要值均在0.5以下;山地森林带地衣植物物种多样性最为丰富,在整个阿勒泰山两河源自然保护区地面生地衣植物群落中占据优势地位,为该地区地衣植物多样性的分布中心,是地衣植物多样性保护的关键地区。 相似文献
965.
966.
Barron L Dooms H Hoyer KK Kuswanto W Hofmann J O'Gorman WE Abbas AK 《Journal of immunology (Baltimore, Md. : 1950)》2010,185(11):6426-6430
IL-2 controls the survival of regulatory T cells (Tregs), but it is unclear whether IL-2 also directly affects Treg suppressive capacity in vivo. We have found that eliminating Bim-dependent apoptosis in IL-2- and CD25-deficient mice restored Treg numbers but failed to cure their lethal autoimmune disease, demonstrating that IL-2-dependent survival and suppressive activity can be uncoupled in Tregs. Treatment with IL-2-anti-IL-2-Ab complexes enhanced the numbers and suppressive capacity of IL-2-deprived Tregs with striking increases in CD25, CTLA-4, and CD39/CD73 expression. Although cytokine treatment induced these suppressive mechanisms in both IL-2(-/-) and IL-2(-/-)Bim(-/-) mice, it only reversed autoimmune disease in the latter. Our results suggest that successful IL-2 therapy of established autoimmune diseases will require a threshold quantity of Tregs present at the start of treatment and show that the suppressive capacity of Tregs critically depends on IL-2 even when Treg survival is independent of this cytokine. 相似文献
967.
968.
969.
Bahman Ebrahimi Seyed Abbas Shojaosadati Seyyed Mohammad Mousavi 《Biotechnology and Bioprocess Engineering》2010,15(3):383-391
A flow-through system based on acetylcholineesterase (AChE) was studied. The system was prepared by mixing AChE and a multiwall
carbon nanotube (MWCNT). Two important parameters, the ratios of AChE:MWCNT (X1) and AChE-MWCNT:sol-gel (X2) were optimized using response surface methodology. The results revealed that an enzyme immobilized within the MWCNT-sol-gel
was more effective compared to one conducted with sol-gel. The optimum feed flow rate was 0.4 mL/min and ATChI concentration
was found to be 1 mM. The optimum ratios of X1 and X2 for immobilization on ceramic packing were 1.07 and 0.43, respectively. The sensitivity of this flow-through system was 1.82
× 10−5/μM and long-term stability analyzed after 120 days was 74% of initial absorbance. With respect to an incubation time of 14
min, the detection limit for paraoxon was 7.3 × 10−12 mol. 相似文献
970.
Hasan Kouchakzadeh Seyed Abbas Shojaosadati Amir Maghsoudi Ebrahim Vasheghani Farahani 《AAPS PharmSciTech》2010,11(3):1206-1211
Chemical coupling of polyethylene glycol (PEG) to proteins or particles (PEGylation), prolongs their circulation half-life
by greater than 50-fold, reduces their immunogenicity, and also promotes their accumulation in tumors due to enhanced permeability
and retention effect. Herein, phase separation method was used to prepare bovine serum albumin (BSA) nanoparticles. PEGylation
of BSA nanoparticles was performed by SPA activated mPEG through their free amino groups. Effect of process variables on PEGylation
efficiency of BSA nanoparticles was investigated and optimized through response surface methodology with the amount of free
amino groups as response. Optimum conditions was found to be 32.5 g/l of PEG concentration, PEG-nanoparticle incubation time
of 10 min, incubation temperature of 27°C, and pH of 7 for 5 mg of BSA nanoparticles in 1 mL phosphate buffer. Analysis of
data showed that PEG concentration had the most noticeable effect on the amount of PEGylated amino groups, but pH had the
least. Mean diameter and zeta potential of PEGylated nanoparticles under these conditions were 217 nm and −14 mV, respectively.
In conclusion, PEGylated nanoparticles demonstrated reduction of the negative surface charge compared to the non modified
particles with the zeta potential of −31.7 mV. Drug release from PEGylated nanoparticles was almost slower than non-PEGylated
ones, probably due to existence of a PEG layer around PEGylated particles which makes an extra resistance in opposition to
drug diffusion. 相似文献