全文获取类型
收费全文 | 5645篇 |
免费 | 370篇 |
国内免费 | 357篇 |
出版年
2024年 | 6篇 |
2023年 | 72篇 |
2022年 | 82篇 |
2021年 | 300篇 |
2020年 | 170篇 |
2019年 | 209篇 |
2018年 | 235篇 |
2017年 | 175篇 |
2016年 | 226篇 |
2015年 | 358篇 |
2014年 | 389篇 |
2013年 | 492篇 |
2012年 | 549篇 |
2011年 | 430篇 |
2010年 | 277篇 |
2009年 | 244篇 |
2008年 | 252篇 |
2007年 | 249篇 |
2006年 | 235篇 |
2005年 | 217篇 |
2004年 | 141篇 |
2003年 | 117篇 |
2002年 | 117篇 |
2001年 | 118篇 |
2000年 | 90篇 |
1999年 | 119篇 |
1998年 | 50篇 |
1997年 | 63篇 |
1996年 | 53篇 |
1995年 | 29篇 |
1994年 | 36篇 |
1993年 | 31篇 |
1992年 | 41篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1966年 | 1篇 |
排序方式: 共有6372条查询结果,搜索用时 296 毫秒
181.
Involvement of antioxidant defense system in chill hardening-induced chilling tolerance in Jatropha curcas seedlings 总被引:1,自引:0,他引:1
Jatropha curcas L. is a sustainable energy plant with great potential for biodiesel production, and low temperature is an important limiting factor for its distribution and production. In this present work, chill hardening-induced chilling tolerance and involvement of antioxidant defense system were investigated in J. curcas seedlings. The results showed that chill hardening at 10 or 12 °C for 1 and 2 days greatly lowered death rate and alleviated electrolyte leakage as well as accumulation of the lipid peroxidation product malondialdehyde (MDA) of J. curcas seedlings under severe chilling stress at 1 °C for 1–7 days, indicating that the chill hardening significantly improved chilling tolerance of J. curcas seedlings. Measurement of activities of the antioxidant enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POD), and glutathione reductase (GR), and the levels of the antioxidants ascorbic acid (AsA) and glutathione (GSH) showed the chill hardening at 12 °C for 2 days could obviously increase the activities of these antioxidant enzymes and AsA and GSH contents in the hardened seedlings. When the hardened and non-hardening (control) seedlings were subjected to severe chilling stress at 1 °C for 1–7 days, the chill-hardened seedlings generally maintained significantly higher activities of the antioxidant enzymes SOD, APX, CAT, POD, and GR, and content of the antioxidants AsA and GSH as well as ratio of the reduced antioxidants to total antioxidants [AsA/(AsA + DHA) and GSH/(GSH + GSSG)], when compared with the control without chill hardening. All above-mentioned results indicated that the chill hardening could enhance the chilling tolerance, and the antioxidant defense system plays an important role in the chill hardening-induced chilling tolerance in J. curcas seedlings. 相似文献
182.
Zhong‐Fei Ni Zhi‐Wei Ma Ao‐Ji Xie Xiang‐Shu Cheng Qun Wang Jian‐Zhi Wang Gong‐Ping Liu 《Journal of neurochemistry》2013,124(3):388-396
Hyperhomocysteinemia (Hhcy) may induce memory deficits with β‐amyloid (Aβ) accumulation and tau hyperphosphorylation. Simultaneous supplement of folate and vitamin B12 partially restored the plasma homocysteine level and attenuated tau hyperphosphorylation, Aβ accumulation and memory impairments induced by Hhcy. However, folate and vitamin B12 treatment have no effects on Hhcy which has the methylenetetrahydrofolate reductase genotype mutation. In this study, we investigated the effects of simultaneous supplement of betaine on Alzheimer‐like pathological changes and memory deficits in hyperhomocysteinemic rats after a 2‐week induction by vena caudalis injection of homocysteine (Hcy). We found that supplementation of betaine could ameliorate the Hcy‐induced memory deficits, enhance long‐term potentiation (LTP) and increase dendritic branches numbers and the density of the dendritic spines, with up‐regulation of NR1, NR2A, synaptotagmin, synaptophysin, and phosphorylated synapsin I protein levels. Supplementation of betaine also attenuated the Hcy‐induced tau hyperphosphorylation at multiple AD‐related sites through activation protein phosphatase‐2A (PP2A) with decreased inhibitory demethylated PP2AC at Leu309 and phosphorylated PP2AC at Tyr307. In addition, supplementation of betaine also decreased Aβ production with decreased presenilin‐1 protein levels. Our data suggest that betaine could be a promising candidate for arresting Hcy‐induced AD‐like pathological changes and memory deficits. 相似文献
183.
Hong Wang Urmila Sreenivasan Da-Wei Gong Kelly A. O'Connell Erinne R. Dabkowski Peter A. Hecker Nicoleta Ionica Manige Konig Anup Mahurkar Yezhou Sun William C. Stanley Carole Sztalryd 《Journal of lipid research》2013,54(4):953-965
Presence of ectopic lipid droplets (LDs) in cardiac muscle is associated to lipotoxicity and tissue dysfunction. However, presence of LDs in heart is also observed in physiological conditions, such as when cellular energy needs and energy production from mitochondria fatty acid β-oxidation are high (fasting). This suggests that development of tissue lipotoxicity and dysfunction is not simply due to the presence of LDs in cardiac muscle but due at least in part to alterations in LD function. To examine the function of cardiac LDs, we obtained transgenic mice with heart-specific perilipin 5 (Plin5) overexpression (MHC-Plin5), a member of the perilipin protein family. Hearts from MHC-Plin5 mice expressed at least 4-fold higher levels of plin5 and exhibited a 3.5-fold increase in triglyceride content versus nontransgenic littermates. Chronic cardiac excess of LDs was found to result in mild heart dysfunction with decreased expression of peroxisome proliferator-activated receptor (PPAR)α target genes, decreased mitochondria function, and left ventricular concentric hypertrophia. Lack of more severe heart function complications may have been prevented by a strong increased expression of oxidative-induced genes via NF-E2-related factor 2 antioxidative pathway. Perilipin 5 regulates the formation and stabilization of cardiac LDs, and it promotes cardiac steatosis without major heart function impairment. 相似文献
184.
Rong Wang Barbara C. McGrath Richard F. Kopp Michael W. Roe Xin Tang Gong Chen Douglas R. Cavener 《The Journal of biological chemistry》2013,288(47):33824-33836
Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) (EIF2AK3) is essential for normal development and function of the insulin-secreting β-cell. Although genetic ablation of PERK in β-cells results in permanent neonatal diabetes in humans and mice, the underlying mechanisms remain unclear. Here, we used a newly developed and highly specific inhibitor of PERK to determine the immediate effects of acute ablation of PERK activity. We found that inhibition of PERK in human and rodent β-cells causes a rapid inhibition of secretagogue-stimulated subcellular Ca2+ signaling and insulin secretion. These dysfunctions stem from alterations in store-operated Ca2+ entry and sarcoplasmic endoplasmic reticulum Ca2+-ATPase activity. We also found that PERK regulates calcineurin, and pharmacological inhibition of calcineurin results in similar defects on stimulus-secretion coupling. Our findings suggest that interplay between calcineurin and PERK regulates β-cell Ca2+ signaling and insulin secretion, and that loss of this interaction may have profound implications in insulin secretion defects associated with diabetes. 相似文献
185.
Takahiro Seki Lijie Gong Aislinn J. Williams Norio Sakai Sokol V. Todi Henry L. Paulson 《The Journal of biological chemistry》2013,288(24):17145-17155
The functional diversity of deubiquitinating enzymes (DUBs) is not well understood. The MJD family of DUBs consists of four cysteine proteases that share a catalytic “Josephin” domain. The family is named after the DUB ATXN3, which causes the neurodegenerative disease Machado-Joseph disease. The two closely related Josephin domain-containing (JosD) proteins 1 and 2 consist of little more than the Josephin domain. To gain insight into the properties of Josephin domains, we investigated JosD1 and JosD2. JosD1 and JosD2 were found to differ fundamentally in many respects. In vitro, only JosD2 can cleave ubiquitin chains. In contrast, JosD1 cleaves ubiquitin chains only after it is monoubiquitinated, a form of posttranslational-dependent regulation shared with ATXN3. A significant fraction of JosD1 is monoubiquitinated in diverse mouse tissues. In cell-based studies, JosD2 localizes to the cytoplasm whereas JosD1 preferentially localizes to the plasma membrane, particularly when ubiquitinated. The membrane occupancy by JosD1 suggests that it could participate in membrane-dependent events such as cell motility and endocytosis. Indeed, time-lapse imaging revealed that JosD1 enhances membrane dynamics and cell motility. JosD1 also influences endocytosis in cultured cells by increasing the uptake of endocytic markers of macropinocytosis while decreasing those for clathrin- and caveolae-mediated endocytosis. Our results establish that two closely related DUBs differ markedly in activity and function and that JosD1, a membrane-associated DUB whose activity is regulated by ubiquitination, helps regulate membrane dynamics, cell motility, and endocytosis. 相似文献
186.
187.
188.
189.
L. Gong B. S. Hulke T. J. Gulya S. G. Markell L. L. Qi 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2013,126(1):93-99
Sunflower production in North America has recently suffered economic losses in yield and seed quality from sunflower rust (Puccinia helianthi Schwein.) because of the increasing incidence and lack of resistance to new rust races. RHA 464, a newly released sunflower male fertility restorer line, is resistant to both of the most predominant and most virulent rust races identified in the Northern Great Plains of the USA. The gene conditioning rust resistance in RHA 464 originated from wild Helianthus annuus L., but has not been molecularly marked or determined to be independent from other rust loci. The objectives of this study are to identify molecular markers linked to the rust resistance gene and to investigate the allelism of this gene with the unmapped rust resistance genes present in HA-R6, HA-R8 and RHA 397. Virulence phenotypes of seedlings for the F2 population and F2:3 families suggested that a single dominant gene confers rust resistance in RHA 464, and this gene was designated as R 12 . Bulked segregant analysis identified ten markers polymorphic between resistant and susceptible bulks. In subsequent genetic mapping, the ten markers covered 33.4 cM of genetic distance on linkage group 11 of sunflower. A co-dominant marker CRT275-11 is the closest marker distal to R 12 with a genetic distance of 1.0 cM, while ZVG53, a dominant marker linked in the repulsion phase, is proximal to R 12 with a genetic distance of 9.6 cM. The allelism test demonstrated that R 12 is not allelic to the rust resistance genes in HA-R6, HA-R8 and RHA 397, and it is also not linked to any previously mapped rust resistance genes. Discovery of the R 12 novel rust resistance locus in sunflower and associated markers will potentially support the molecular marker-assisted introgression and pyramiding of R 12 into sunflower breeding lines. 相似文献
190.