全文获取类型
收费全文 | 22305篇 |
免费 | 1979篇 |
国内免费 | 2566篇 |
专业分类
26850篇 |
出版年
2024年 | 61篇 |
2023年 | 220篇 |
2022年 | 556篇 |
2021年 | 891篇 |
2020年 | 758篇 |
2019年 | 897篇 |
2018年 | 858篇 |
2017年 | 705篇 |
2016年 | 831篇 |
2015年 | 1296篇 |
2014年 | 1637篇 |
2013年 | 1768篇 |
2012年 | 2119篇 |
2011年 | 1970篇 |
2010年 | 1321篇 |
2009年 | 1172篇 |
2008年 | 1536篇 |
2007年 | 1295篇 |
2006年 | 1198篇 |
2005年 | 997篇 |
2004年 | 986篇 |
2003年 | 906篇 |
2002年 | 815篇 |
2001年 | 369篇 |
2000年 | 263篇 |
1999年 | 219篇 |
1998年 | 222篇 |
1997年 | 134篇 |
1996年 | 130篇 |
1995年 | 132篇 |
1994年 | 95篇 |
1993年 | 77篇 |
1992年 | 64篇 |
1991年 | 46篇 |
1990年 | 31篇 |
1989年 | 44篇 |
1988年 | 31篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 25篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 18篇 |
1981年 | 5篇 |
1977年 | 7篇 |
1971年 | 4篇 |
1969年 | 4篇 |
1967年 | 5篇 |
1965年 | 4篇 |
1962年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this study, we prepared nano-hydroxyapatite/polyamide 66/glass fibre (n-HA/PA66/GF) bioactive bone screws. The microstructure, morphology and coating of the screws were characterised, and the adhesion, proliferation and viability of MC3T3-E1 cells on n-HA/PA66/GF scaffolds were determined using scanning electron microscope, CCK-8 assays and cellular immunofluorescence analysis. The results confirmed that n-HA/PA66/GF scaffolds were biocompatible and had no negative effect on MC3T3-E1 cells in vitro. To investigate the in vivo biocompatibility, internal fixation properties and osteogenesis of the bioactive screws, both n-HA/PA66/GF screws and metallic screws were used to repair intercondylar femur fractures in dogs. General photography, CT examination, micro-CT examination, histological staining and biomechanical assays were performed at 4, 8, 12 and 24 weeks after operation. The n-HA/PA66/GF screws exhibited good biocompatibility, high mechanical strength and extensive osteogenesis in the host bone. Moreover, 24 weeks after implantation, the maximum push-out load of the bioactive screws was greater than that of the metallic screws. As shown by their good cytocompatibility, excellent biomechanical strength and fast formation and ingrowth of new bone, n-HA/PA66/GF screws are thus suitable for orthopaedic clinical applications. 相似文献
992.
Yong Lian Jing Zhao Peiyu Xu Yimei Wang Jun Zhao Li Jia Ze Fu Li Jing Gang Liu Shuangqing Peng 《PloS one》2013,8(8)
Isoniazid (INH) and Rifampicin (RFP) are widely used in the world for the treatment of tuberculosis, but the hepatotoxicity is a major concern during clinical therapy. Previous studies showed that these drugs induced oxidative stress in liver, and several antioxidants abated this effect. Metallothionein (MT), a member of cysteine-rich protein, has been proposed as a potent antioxidant. This study attempts to determine whether endogenous expression of MT protects against INH and RFP-induced hepatic oxidative stress in mice. Wild type (MT+/+) and MT-null (MT−/−) mice were treated intragastrically with INH (150 mg/kg), RFP (300 mg/kg), or the combination (150 mg/kg INH +300 mg/kg RFP) for 21 days. The results showed that MT−/− mice were more sensitive than MT+/+ mice to INH and RFP-induced hepatic injuries as evidenced by hepatic histopathological alterations, increased serum AST levels and liver index, and hepatic oxidative stress as evidenced by the increase of MDA production and the change of liver antioxidant status. Furthermore, INH increased the protein expression of hepatic CYP2E1 and INH/RFP (alone or in combination) decreased the expression of hepatic CYP1A2. These findings clearly demonstrate that basal MT provides protection against INH and RFP-induced toxicity in hepatocytes. The CYP2E1 and CYP1A2 were involved in the pathogenesis of INH and RFP-induced hepatotoxicity. 相似文献
993.
994.
995.
Mercedes Ferrando Xinhai Wan Roberto Meiss Jun Yang Adriana De Siervi Nora Navone Elba Vazquez 《PloS one》2013,8(11)
Prostate cancer (PCa) is a leading cause of death among males. It is currently estimated that inflammatory responses are linked to 15-20% of all deaths from cancer worldwide. PCa is dominated by complications arising from metastasis to the bone where the tumor cells interact with the bone microenvironment impairing the balance between bone formation and degradation. However, the molecular nature of this interaction is not completely understood. Heme oxygenase-1 (HO-1) counteracts oxidative damage and inflammation. Previous studies from our laboratory showed that HO-1 is implicated in PCa, demonstrating that endogenous HO-1 inhibits bone derived-prostate cancer cells proliferation, invasion and migration and decreases tumor growth and angiogenesis in vivo. The aim of this work was to analyze the impact of HO-1 modulated PCa cells on osteoblasts proliferation in vitro and on bone remodeling in vivo. Using a co-culture system of PC3 cells with primary mice osteoblasts (PMOs), we demonstrated that HO-1 pharmacological induction (hemin treatment) abrogated the diminution of PMOs proliferation induced by PCa cells and decreased the expression of osteoclast-modulating factors in osteoblasts. No changes were detected in the expression of genes involved in osteoblasts differentiation. However, co-culture of hemin pre-treated PC3 cells (PC3 Hem) with PMOs provoked an oxidative status and activated FoxO signaling in osteoblasts. The percentage of active osteoblasts positive for HO-1 increased in calvarias explants co-cultured with PC3 Hem cells. Nuclear HO-1 expression was detected in tumors generated by in vivo bone injection of HO-1 stable transfected PC3 (PC3HO-1) cells in the femur of SCID mice. These results suggest that HO-1 has the potential to modify the bone microenvironment impacting on PCa bone metastasis. 相似文献
996.
997.
Mutualisms are common in nature, though these symbioses can be quite permeable to cheaters in situations where one individual parasitizes the other by discontinuing cooperation yet still exploits the benefits of the partnership. In the Rhizobium-legume system, there are two separate contexts, namely nodulation and nitrogen fixation processes, by which resident Rhizobium individuals can benefit by cheating. Here, we constructed reversible and irreversible mutations in key nodulation and nitrogen-fixation pathways of Rhizobium etli and compared their interaction with plant hosts Phaseolus vulgaris to that of wild type. We show that R. etli reversible mutants deficient in nodulation factor production are capable of intra-specific cheating, wherein mutants exploit other Rhizobium individuals capable of producing these factors. Similarly, we show that R. etli mutants are also capable of cheating inter-specifically, colonizing the host legume yet contributing nothing to the partnership in terms of nitrogen fixation. Our findings indicate that cheating is possible in both of these frameworks, seemingly without damaging the stability of the mutualism itself. These results may potentially help explain observations suggesting that legume plants are commonly infected by multiple bacterial lineages during the nodulation process. 相似文献
998.
【目的】通过基因组挖掘的方法,研究红树林来源白骨壤链霉菌Streptomyces avicenniae 9-9中多环稠合大环内酰胺(PTMs)类化合物的结构多样性。【方法】通过生物信息学分析白骨壤链霉菌基因组序列,寻找PTMs类化合物的生物合成相关基因;利用UPLC-MS/MS技术对该菌的次级代谢产物进行分析。【结果】在白骨壤链霉菌基因组中发现PTMs生物合成基因簇(aviA-D);从菌液提取物中鉴定出5个PTMs类化合物,其中包括ikarugamycin(化合物1)和capsimycin B(化合物2);基于PTMs类化合物5-6-5环类型的MS/MS碎裂规律,对化合物3–5的结构进行了推测。【结论】红树林来源白骨壤链霉菌S.avicenniae 9-9具有产生5-6-5环类型的PTMs类化合物的能力。 相似文献
999.
Macroautophagy/autophagy is a conserved intracellular degradation system that traffics substrates including protein aggregates, defunct or disused organelles and invading pathogens to lysosomes via double-membrane vesicles called autophagosomes. BECN1/Beclin 1 functions as a key protein in autophagy initiation and progression; however, the role of BECN1 in innate immunity has not been fully investigated. Recently, we have found that USP19 affects the ubiquitination of BECN1, hence promoting the formation of autophagosomes and inhibiting DDX58/RIG-I-mediated type I interferon signaling. 相似文献
1000.
Luqiao?Wang Hangfei?Fu Gayani?Nanayakkara Yafeng?Li Ying?Shao Candice?Johnson Jiali?Cheng William?Y.?Yang Fan?Yang Muriel?Lavallee Yanjie?Xu Xiaoshu?Cheng Hang?Xi Jonathan?Yi Jun?Yu Eric?T.?Choi Hong?Wang Xiaofeng?Yang