全文获取类型
收费全文 | 63357篇 |
免费 | 6387篇 |
国内免费 | 3011篇 |
出版年
2023年 | 753篇 |
2022年 | 957篇 |
2021年 | 2563篇 |
2020年 | 2364篇 |
2019年 | 2715篇 |
2018年 | 2520篇 |
2017年 | 2001篇 |
2016年 | 2778篇 |
2015年 | 4040篇 |
2014年 | 4868篇 |
2013年 | 5042篇 |
2012年 | 6001篇 |
2011年 | 5380篇 |
2010年 | 3292篇 |
2009年 | 3000篇 |
2008年 | 3383篇 |
2007年 | 3051篇 |
2006年 | 2599篇 |
2005年 | 2147篇 |
2004年 | 1776篇 |
2003年 | 1647篇 |
2002年 | 1270篇 |
2001年 | 1037篇 |
2000年 | 1002篇 |
1999年 | 914篇 |
1998年 | 552篇 |
1997年 | 487篇 |
1996年 | 477篇 |
1995年 | 444篇 |
1994年 | 443篇 |
1993年 | 340篇 |
1992年 | 466篇 |
1991年 | 343篇 |
1990年 | 292篇 |
1989年 | 264篇 |
1988年 | 196篇 |
1987年 | 189篇 |
1986年 | 171篇 |
1985年 | 151篇 |
1984年 | 96篇 |
1983年 | 108篇 |
1982年 | 65篇 |
1980年 | 35篇 |
1979年 | 56篇 |
1978年 | 33篇 |
1977年 | 34篇 |
1976年 | 46篇 |
1974年 | 54篇 |
1973年 | 45篇 |
1972年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
1.
2.
Robert Fitzgerald Breann DeSantiago Danielle Y. Lee Guangdong Yang Jae Yeon Kim D. Brian Foster Yee Chan-Li Maureen R. Horton Reynold A. Panettieri Rui Wang Steven S. An 《Biochemical and biophysical research communications》2014
Here we explored the impact of hydrogen sulfide (H2S) on biophysical properties of the primary human airway smooth muscle (ASM)–the end effector of acute airway narrowing in asthma. Using magnetic twisting cytometry (MTC), we measured dynamic changes in the stiffness of isolated ASM, at the single-cell level, in response to varying doses of GYY4137 (1–10 mM). GYY4137 slowly released appreciable levels of H2S in the range of 10–275 μM, and H2S released was long lived. In isolated human ASM cells, GYY4137 acutely decreased stiffness (i.e. an indicator of the single-cell relaxation) in a dose-dependent fashion, and stiffness decreases were sustained in culture for 24 h. Human ASM cells showed protein expressions of cystathionine-γ-lyase (CSE; a H2S synthesizing enzyme) and ATP-sensitive potassium (KATP) channels. The KATP channel opener pinacidil effectively relaxed isolated ASM cells. In addition, pinacidil-induced ASM relaxation was completely inhibited by the treatment of cells with the KATP channel blocker glibenclamide. Glibenclamide also markedly attenuated GYY4137-mediated relaxation of isolated human ASM cells. Taken together, our findings demonstrate that H2S causes the relaxation of human ASM and implicate as well the role for sarcolemmal KATP channels. Finally, given that ASM cells express intrinsic enzymatic machinery of generating H2S, we suggest thereby this class of gasotransmitter can be further exploited for potential therapy against obstructive lung disease. 相似文献
3.
Ya-Chung Tian Yi-Jung Li Hua-Chien Chen Hsin-Hsu Wu Cheng-Hao Weng Yung-Chang Chen Cheng-Chia Lee Ming-Yang Chang Hsiang-Hao Hsu Tzung-Hai Yen Cheng-Chieh Hung Chih-Wei Yang 《Biochemical and biophysical research communications》2014
Polyomavirus BK (BKV) infection is an important cause of renal allograft failure. Viral microRNAs are known to play a crucial role in viral replication. This study investigated the expression of BKV-encoded microRNAs (miR-B1) in patients with polyomavirus-associated nephropathy (PVAN) and their role in viral replication. Following BKV infection in renal proximal tubular cells, the 3p and 5p miR-B1 levels were significantly increased. Cells transfected with the vector containing the miR-B1 precursor (the miR-B1 vector) showed a significant increase in expression of 3p and 5p miR-B1 and decrease in luciferase activity of a reporter containing the 3p and 5p miR-B1 binding sites, compared to cells transfected with the miR-B1-mutated vector. Transfection of the miR-B1 expression vector or the 3p and 5p miR-B1 oligonucleotides inhibited expression of TAg. TAg-enhanced promoter activity and BKV replication were inhibited by miR-B1. In contrast, inhibition of miR-B1 expression by addition of miR-B1 antagomirs or silencing of Dicer upregulated the expression of TAg and VP1 proteins in BKV-infected cells. Importantly, patients with PVAN had significantly higher levels of 3p and 5p miR-B1 compared to renal transplant patients without PVAN. In conclusion, we demonstrated that (1) miR-B1 expression was upregulated during BKV infection and (2) miR-B1 suppressed TAg-mediated autoregulation of BKV replication. Use of miR-B1 can be evaluated as a potential treatment strategy against BKV infection. 相似文献
4.
Hongxu Wu Shifang Yang Xiaojie Wu Junling Zhao Jianping Zhao Qin Ning Yongjian Xu Jungang Xie 《Biochemical and biophysical research communications》2014
Interleukin-33 is a newly described member of the interleukin-1 family. Recent research suggests that IL-33 is increased in lungs and plays a critical role in chronic airway inflammation in cigarette smoke-induced chronic obstructive pulmonary disease (COPD) mice. To determine the role of IL-33 in systemic inflammation, we induced COPD mice models by passive cigarette smoking and identified the IL-33 expression in bronchial endothelial cells and peripheral blood mononuclear cells (PBMCs) of them. After isolation, PBMCs were cultured and stimulated in vitro. We measured expressions of interleukin-6 and interleukin-8 in PBMCs in different groups. The expression of IL-33 in bronchial endothelial cells and PBMCs of COPD mice were highly expressed. Stimulated by cigarette smoke extract (CSE), the expression of IL-6 and IL-8 were induced and enhanced by IL-33. PBMCs of COPD mice produced more IL-6 and IL-8 stimulated by CSE and IL-33. Expression of IL-6 and IL-8 were decreased when stimulated by IL-33 together with soluble ST2. The mRNA production of ST2 in IL-33 stimulated PBMCs was increased. Being pretreated with several kinds of MAPK inhibitors, the secretions of IL-6 and IL-8 in PBMCs did not decrease except for the p38 MAPK inhibitor. We found that IL-33 could induce and enhance the expression of IL-6 and IL-8 in PBMCs of COPD mice via p38 MAPK pathway, and it is a promoter of the IL-6 and IL-8 production in systemic inflammation in COPD mice. 相似文献
5.
A Gram-stain negative, motile, rod-shaped bacterium, designated strain WM-2T, was isolated from a forest soil in Sihui City, South China, and characterized by means of a polyphasic approach. Growth occurred with 0–5 % (w/v) NaCl (optimum 0–1 %) and at pH 5.0–10.5 (optimum pH 8.5) and 4–40 °C (optimum 30 °C) in Luria–Bertani medium. Comparative 16S rRNA gene sequence analyses showed that strain WM-2T is a member of the genus Pseudomonas and most closely related to P. guguanensis, P. oleovorans subsp. lubricantis, P. toyotomiensis, P. alcaliphila and P. mendocina with 97.1–96.6 % sequence similarities. In terms of gyrB and rpoB gene sequences, strain WM-2T showed the highest similarity with the type strains of the species P. toyotomiensis and P. alcaliphila. The DNA–DNA relatedness values of strain WM-2T with P. guguanensis and P. oleovorans subsp. lubricantis was 48.7 and 37.2 %, respectively. Chemotaxonomic characteristics (the main ubiquinone Q-9, major fatty acids C18:1 ω7c/C18:1 ω6c, C16:0 and C16:1 ω7c/C16:1 ω6c and DNA G+C content 65.2 ± 0.7 mol%) were similar to those of members of the genus Pseudomonas. Polar lipids consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unknown aminophospholipid, an unknown phospholipid and five unknown lipids. According to the results of polyphasic analyses, strain WM-2T represents a novel species in the genus Pseudomonas, for which the name Pseudomonas sihuiensis sp. nov. is proposed. The type strain is WM-2T (=KCTC 32246T=CGMCC 1.12407T). 相似文献
6.
7.
8.
Reactive oxygen species (ROS) including hydrogen peroxide (H2O2) exhibit both pro-survival and pro-death signaling in leukemic cells. We examined the effect of exogenous H2O2 on Fas ligand (FasL) -induced apoptosis in Jurkat cells. H2O2 applied prior to (pre-conditioning) and during (post-conditioning) FasL stimulation attenuated early apoptosis through activation of EKR5. H2O2 increased the activated caspase-8 sequestered in the mitochondria thereby decreasing cell death through the extrinsic apoptotic pathway. In addition, inhibition of a protein tyrosine phosphatase likely explains the post-conditioning requirement for H2O2. Given that chemotherapeutic agents used for the treatment of acute lymphoblastic leukemia are thought to work partly through production of ROS, a simultaneous inhibition of the ERK5 pathway may abrogate the ROS-initiated pro-survival signaling for an enhanced cell kill. 相似文献
9.
Hydrogen gas (H2) was recently proposed as a therapeutic antioxidant and signaling molecule in clinical trials. However, the underlying physiological roles of H2 in plants remain unclear. In the present study, hydrogen-rich water (HRW) was used to characterize the physiological roles of H2 in enhancing the tolerance of Brassica campestris against cadmium (Cd). The results showed that both 50 μM CdCl2 and 50%-saturated HRW induced an increase of endogenous H2 in Brassica campestris seedlings, and HRW alleviated Cd toxicity related to growth inhibition and oxidative damage. Seedlings supplied with HRW exhibited increased root length and reduced lipid peroxidation, similar to plants receiving GSH post-treatment. Additionally, seedlings post-treated with HRW accumulated higher levels of reduced glutathione (GSH) and ascorbic acid (AsA) and showed increased GST and GPX activities in roots. Molecular evidence illustrated that the expression of genes such as GS, GR1 and GR2, which were down-regulated following the addition of Cd, GSH or BSO, could be reversed to varying degrees by the addition of HRW. Based on these results, it could be proposed that H2 might be an important regulator for enhancing the tolerance of Brassica campestris seedlings against Cd, mainly by governing reduced glutathione homeostasis. 相似文献
10.
Study on Environmental Causes and SNPs of MTHFR,MS and CBS Genes Related to Congenital Heart Disease
Hui Shi Shiwei Yang Yan Liu Peng Huang Ning Lin Xiaoru Sun Rongbin Yu Yuanyuan Zhang Yuming Qin Lijuan Wang 《PloS one》2015,10(6)