全文获取类型
收费全文 | 95374篇 |
免费 | 7724篇 |
国内免费 | 2034篇 |
出版年
2023年 | 1399篇 |
2022年 | 1351篇 |
2021年 | 2228篇 |
2020年 | 3072篇 |
2019年 | 3856篇 |
2018年 | 3534篇 |
2017年 | 2607篇 |
2016年 | 2575篇 |
2015年 | 2953篇 |
2014年 | 5385篇 |
2013年 | 6844篇 |
2012年 | 4161篇 |
2011年 | 5389篇 |
2010年 | 4706篇 |
2009年 | 4580篇 |
2008年 | 4838篇 |
2007年 | 4891篇 |
2006年 | 4280篇 |
2005年 | 3978篇 |
2004年 | 3616篇 |
2003年 | 3123篇 |
2002年 | 2552篇 |
2001年 | 1840篇 |
2000年 | 1518篇 |
1999年 | 1540篇 |
1998年 | 1286篇 |
1997年 | 1098篇 |
1996年 | 1104篇 |
1995年 | 1223篇 |
1994年 | 1155篇 |
1993年 | 1052篇 |
1992年 | 954篇 |
1991年 | 842篇 |
1990年 | 694篇 |
1989年 | 636篇 |
1988年 | 562篇 |
1987年 | 502篇 |
1986年 | 461篇 |
1985年 | 676篇 |
1984年 | 923篇 |
1983年 | 720篇 |
1982年 | 782篇 |
1981年 | 625篇 |
1980年 | 605篇 |
1979年 | 470篇 |
1978年 | 374篇 |
1977年 | 365篇 |
1976年 | 336篇 |
1975年 | 245篇 |
1973年 | 243篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Shuichi Nagashima Hiroaki Yagyu Ryuichi Tozawa Fumiko Tazoe Manabu Takahashi Tetsuya Kitamine Daisuke Yamamuro Kent Sakai Motohiro Sekiya Hiroaki Okazaki Jun-ichi Osuga Akira Honda Shun Ishibashi 《Journal of lipid research》2015,56(5):998-1005
Squalene synthase (SS) catalyzes the biosynthesis of squalene, the first specific intermediate in the cholesterol biosynthetic pathway. To test the feasibility of lowering plasma cholesterol by inhibiting hepatic SS, we generated mice in which SS is specifically knocked out in the liver (L-SSKO) using Cre-loxP technology. Hepatic SS activity of L-SSKO mice was reduced by >90%. In addition, cholesterol biosynthesis in the liver slices was almost eliminated. Although the hepatic squalene contents were markedly reduced in L-SSKO mice, the hepatic contents of cholesterol and its precursors distal to squalene were indistinguishable from those of control mice, indicating the presence of sufficient centripetal flow of cholesterol and/or its precursors from the extrahepatic tissues. L-SSKO mice showed a transient liver dysfunction with moderate hepatomegaly presumably secondary to increased farnesol production. In a fed state, the plasma total cholesterol and triglyceride were significantly reduced in L-SSKO mice, primarily owing to reduced hepatic VLDL secretion. In a fasted state, the hypolipidemic effect was lost. mRNA expression of liver X receptor α target genes was reduced, while that of sterol-regulatory element binding protein 2 target genes was increased. In conclusion, liver-specific ablation of SS inhibits hepatic cholesterol biosynthesis and induces hypolipidemia without increasing significant mortality. 相似文献
2.
3.
Polyphenols from green tea prevent antineuritogenic action of Nogo‐A via 67‐kDa laminin receptor and hydrogen peroxide 下载免费PDF全文
Usha Gundimeda Thomas H. McNeill Barsegh A. Barseghian William S. Tzeng David V. Rayudu Enrique Cadenas Rayudu Gopalakrishna 《Journal of neurochemistry》2015,132(1):70-84
Axonal regeneration after injury to the CNS is hampered by myelin‐derived inhibitors, such as Nogo‐A. Natural products, such as green tea, which are neuroprotective and safe for long‐term therapy, would complement ongoing various pharmacological approaches. In this study, using nerve growth factor‐differentiated neuronal‐like Neuroscreen‐1 cells, we show that extremely low concentrations of unfractionated green tea polyphenol mixture (GTPP) and its active ingredient, epigallocatechin‐3‐gallate (EGCG), prevent both the neurite outgrowth‐inhibiting activity and growth cone‐collapsing activity of Nogo‐66 (C‐terminal domain of Nogo‐A). Furthermore, a synergistic interaction was observed among GTPP constituents. This preventive effect was dependent on 67‐kDa laminin receptor (67LR) to which EGCG binds with high affinity. The antioxidants N‐acetylcysteine and cell‐permeable catalase abolished this preventive effect of GTPP and EGCG, suggesting the involvement of sublethal levels of H2O2 in this process. Accordingly, exogenous sublethal concentrations of H2O2, added as a bolus dose (5 μM) or more effectively through a steady‐state generation (1–2 μM), mimicked GTPP in counteracting the action of Nogo‐66. Exogenous H2O2 mediated this action by bypassing the requirement of 67LR. Taken together, these results show for the first time that GTPP and EGCG, acting through 67LR and elevating intracellular sublethal levels of H2O2, inhibit the antineuritogenic action of Nogo‐A.
4.
Nidogen‐1 is a common target of microRNAs MiR‐192/215 in the pathogenesis of Hirschsprung's disease 下载免费PDF全文
Dongmei Zhu Hua Xie Hongxing Li Peng Cai Hairong Zhu Chao Xu Pingfa Chen Ankur Sharan Yankai Xia Weibing Tang 《Journal of neurochemistry》2015,134(1):39-46
Recent studies have emphasized the important role of microRNA (miRNA) clusters and common target genes in disease progression. Despite the known involvement of the miR‐192/215 family in many human diseases, its biological role in Hirschsprung disease (HSCR) remains undefined. In this study, we explored the role of the miR‐192/215 family in the pathogenesis of HSCR. Quantitative real‐time PCR and western blotting measured relative expression levels of miRNAs, mRNAs, and proteins in 80 HSCR patients and 77 normal colon tissues. Targets were evaluated by dual‐luciferase reporter assays, and the functional effects of miR‐192/215 on human 293T and SH‐SY5Y cells were detected by the Transwell assay, CCK8 assay and flow cytometry. MiR‐192/215 was significantly down‐regulated in HSCR tissue samples, and their knockdown inhibited cell migration and proliferation in the human 293T and SH‐SY5Y cell lines. Nidogen 1 (NID1) was confirmed as a common target gene of miR‐192/215 by dual‐luciferase reporter gene assay and its expression was inversely correlated with that of miR‐192/215 in tissue samples and cell lines. Silencing of NID1 could rescue the extent of the suppressing effects by miR‐192/215 inhibitor. The down‐regulation of miR‐192/215 may contribute to HSCR development by targeting NID1.
5.
6.
To increase the menaquinone (MK) content of an Elizabethkingia meningoseptica, site-directed mutagenesis was generated to suppress 4-hydroxybenzoate octaprenyl transferase (UbiA) activity and subsequently blocked the ubiquinone (UQ) biosynthesis pathway. Fourteen conserved residues except L174 and G211 were mutated to analyze the effect of site-directed mutagenesis. The expression of UbiA in twelve mutants was decreased in both mRNA and protein levels, which resulted in the decrease of UQ concentration. Based on MenA expression level, 12 mutants were divided into two groups. Second group such as N72A, D76A, K81A, L139A, and D198A enhanced the expression of MenA, which increased MK production by 127.1%, 87.9%, 96.2%, 109.7% and 130.0% in wt-EmUbiA, respectively. In general, blocking UQ synthesis pathway for by site-directed mutagenesis of the active site of UbiA in E. meningoseptica was a promising strategy to increase MK production in E. meningoseptica. 相似文献
7.
8.
9.
C. Lawrence Kien Dwight E. Matthews Matthew E. Poynter Janice Y. Bunn Naomi K. Fukagawa Karen I. Crain David B. Ebenstein Emily K. Tarleton Robert D. Stevens Timothy R. Koves Deborah M. Muoio 《Journal of lipid research》2015,56(9):1795-1807
Palmitic acid (PA) is associated with higher blood concentrations of medium-chain acylcarnitines (MCACs), and we hypothesized that PA may inhibit progression of FA β-oxidation. Using a cross-over design, 17 adults were fed high PA (HPA) and low PA/high oleic acid (HOA) diets, each for 3 weeks. The [1-13C]PA and [13-13C]PA tracers were administered with food in random order with each diet, and we assessed PA oxidation (PA OX) and serum AC concentration to determine whether a higher PA intake promoted incomplete PA OX. Dietary PA was completely oxidized during the HOA diet, but only about 40% was oxidized during the HPA diet. The [13-13C]PA/[1-13C]PA ratio of PA OX had an approximate value of 1.0 for either diet, but the ratio of the serum concentrations of MCACs to long-chain ACs (LCACs) was significantly higher during the HPA diet. Thus, direct measurement of PA OX did not confirm that the HPA diet caused incomplete PA OX, despite the modest, but statistically significant, increase in the ratio of MCACs to LCACs in blood. 相似文献
10.
Identification of P‐glycoprotein co‐fractionating proteins and specific binding partners in rat brain microvessels 下载免费PDF全文
Margaret E. Tome Charles P. Schaefer Leigh M. Jacobs Yifeng Zhang Joseph M. Herndon Fabian O. Matty Thomas P. Davis 《Journal of neurochemistry》2015,134(2):200-210
Drug delivery to the brain for the treatment of pathologies with a CNS component is a significant clinical challenge. P‐glycoprotein (PgP), a drug efflux pump in the endothelial cell membrane, is a major factor in preventing therapeutics from crossing the blood‐brain barrier (BBB). Identifying PgP regulatory mechanisms is key to developing agents to modulate PgP activity. Previously, we found that PgP trafficking was altered concomitant with increased PgP activity and disassembly of high molecular weight PgP‐containing complexes during acute peripheral inflammatory pain. These data suggest that PgP activity is post‐translationally regulated at the BBB. The goal of the current study was to identify proteins that co‐localize with PgP in rat brain microvessel endothelial cell membrane microdomains and use the data to suggest potential regulatory mechanisms. Using new density gradients of microvessel homogenates, we identified two unique pools (1,2) of PgP in membrane fractions. Caveolar constituents, caveolin1, cavin1, and cavin2, co‐localized with PgP in these fractions indicating the two pools contained caveolae. A chaperone (Hsc71), protein disulfide isomerase and endosomal/lysosomal sorting proteins (Rab5, Rab11a) also co‐fractionated with PgP in the gradients. These data suggest signaling pathways with a potential role in post‐translational regulation of PgP activity at the BBB.