全文获取类型
收费全文 | 23601篇 |
免费 | 2328篇 |
国内免费 | 1200篇 |
专业分类
耳鼻咽喉 | 168篇 |
儿科学 | 323篇 |
妇产科学 | 315篇 |
基础医学 | 4486篇 |
口腔科学 | 503篇 |
临床医学 | 1834篇 |
内科学 | 4604篇 |
皮肤病学 | 567篇 |
神经病学 | 1238篇 |
特种医学 | 444篇 |
外国民族医学 | 12篇 |
外科学 | 3039篇 |
综合类 | 3166篇 |
现状与发展 | 5篇 |
预防医学 | 900篇 |
眼科学 | 347篇 |
药学 | 2131篇 |
3篇 | |
中国医学 | 342篇 |
肿瘤学 | 2702篇 |
出版年
2024年 | 47篇 |
2023年 | 489篇 |
2022年 | 704篇 |
2021年 | 2041篇 |
2020年 | 1175篇 |
2019年 | 1437篇 |
2018年 | 1272篇 |
2017年 | 1010篇 |
2016年 | 819篇 |
2015年 | 961篇 |
2014年 | 1402篇 |
2013年 | 1279篇 |
2012年 | 1288篇 |
2011年 | 1458篇 |
2010年 | 1247篇 |
2009年 | 1301篇 |
2008年 | 1227篇 |
2007年 | 1131篇 |
2006年 | 1010篇 |
2005年 | 821篇 |
2004年 | 679篇 |
2003年 | 546篇 |
2002年 | 345篇 |
2001年 | 371篇 |
2000年 | 285篇 |
1999年 | 256篇 |
1998年 | 279篇 |
1997年 | 243篇 |
1996年 | 166篇 |
1995年 | 168篇 |
1994年 | 146篇 |
1993年 | 119篇 |
1992年 | 110篇 |
1991年 | 94篇 |
1990年 | 70篇 |
1989年 | 77篇 |
1988年 | 72篇 |
1987年 | 61篇 |
1986年 | 60篇 |
1985年 | 106篇 |
1984年 | 108篇 |
1983年 | 77篇 |
1982年 | 85篇 |
1981年 | 90篇 |
1980年 | 85篇 |
1979年 | 59篇 |
1978年 | 69篇 |
1977年 | 32篇 |
1976年 | 47篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
992.
Lu J Zhang C Baulcombe DC Chen ZJ 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(14):5529-5534
Seed size is important to crop domestication and natural selection and is affected by the balance of maternal and paternal genomes in endosperm. Endosperm, like placenta in mammals, provides reserves to the developing embryo. Interploidy crosses disrupt the genome balance in endosperm and alter seed size. Specifically, paternal-excess crosses (2 × 4) delay endosperm cellularization (EC) and produce larger seeds, whereas maternal-excess crosses (4 × 2) promote precocious EC and produce smaller seeds. The mechanisms for responding to the parental genome dosage imbalance and for gene expression changes in endosperm are unknown. In plants, RNA polymerase IV (PolIV or p4) encoded by NRPD1a is required for biogenesis of a major class of 24-nt small interfering RNAs (also known as p4-siRNAs), which are predominately expressed in developing endosperm. Here we show that p4-siRNA accumulation depends on the maternal genome dosage, and maternal p4-siRNAs target transposable elements (TEs) and TE-associated genes (TAGs) in seeds. The p4-siRNAs correlate negatively with expression levels of AGAMOUS-LIKE (AGL) genes in endosperm of interploidy crosses. Moreover, disruption of maternal NRPD1a expression is associated with p4-siRNA reduction and AGL up-regulation in endosperm of reciprocal crosses. This is unique genetic evidence for maternal siRNAs in response to parental genome imbalance and in control of transposons and gene expression during endosperm development. 相似文献
993.
Kröger C Dillon SC Cameron AD Papenfort K Sivasankaran SK Hokamp K Chao Y Sittka A Hébrard M Händler K Colgan A Leekitcharoenphon P Langridge GC Lohan AJ Loftus B Lucchini S Ussery DW Dorman CJ Thomson NR Vogel J Hinton JC 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(20):E1277-E1286
994.
Chiaki Iwamura Kenta Shinoda Yusuke Endo Yukiko Watanabe Damon John Tumes Shinichiro Motohashi Kazuyoshi Kawahara Yuki Kinjo Toshinori Nakayama 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(42):16992-16997
To develop more effective vaccines and strategies to regulate chronic inflammatory diseases, it is important to understand the mechanisms of immunological memory. Factors regulating memory CD4+ T helper (Th)-cell pool size and function remain unclear, however. We show that activation of type I invariant natural killer T (iNKT) cells with glycolipid ligands and activation of type II natural killer T (NKT) cells with the endogenous ligand sulfatide induced dramatic proliferation and expansion of memory, but not naïve, CD4 T cells. NKT cell-induced proliferation of memory Th1 and Th2 cells was dependent largely on the production of IL-2, with Th2-cell proliferation also affected by loss of IL-4. Type II NKT cells were also required for efficient maintenance of memory CD4 T cells in vivo. Activation of iNKT cells resulted in up-regulation of IFN-γ expression by memory Th2 cells. These IFN-γ–producing memory Th2 cells showed a decreased capability to induce Th2 cytokines and eosinophilic airway inflammation. Thus, activated NKT cells directly regulate memory CD4 T-cell pool size and function via the production of cytokines in vivo. 相似文献
995.
P Wang CM Chan D Christensen C Zhang K Selvadurai RH Huang 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(33):13248-13253
Ribotoxins cleave essential RNAs for cell killing in vivo, and the bacterial polynucleotide kinase-phosphatase (Pnkp)/hua enhancer 1 (Hen1) complex has been shown to repair ribotoxin-cleaved RNAs in vitro. Bacterial Pnkp/Hen1 is distinguished from other RNA repair systems by performing 3'-terminal 2'-O-methylation during RNA repair, which prevents the repaired RNA from repeated cleavage at the same site. To ensure the opportunity of 2'-O-methylation by bacterial Hen1 during RNA repair and, therefore, maintain the quality of the repaired RNA, Pnkp/Hen1 has evolved to require the participation of Hen1 in RNA ligation, because Pnkp alone is unable to carry out the reaction despite possessing all signature motifs of an RNA ligase. However, the precise role of Hen1 in RNA ligation is unknown. Here, we present the crystal structure of an active RNA ligase consisting of the C-terminal half of Pnkp (Pnkp-C) and the N-terminal half of Hen1 (Hen1-N) from Clostridium thermocellum. The structure reveals that the N-terminal domain of Clostridium thermocellum (Cth) Hen1, shaped like a left hand, grabs the flexible insertion module of CthPnkp and locks its conformation via further interaction with the C-terminal addition module of CthPnkp. Formation of the CthPnkp-C/Hen1-N heterodimer creates a ligation pocket with a width for two strands of RNA, depth for two nucleotides, and the adenosine monophosphate (AMP)-binding pocket at the bottom. The structure, combined with functional analyses, provides insight into the mechanism of how Hen1 activates the RNA ligase activity of Pnkp for RNA repair. 相似文献
996.
997.
Höchsmann B Leichtle R von Zabern I Kaiser S Flegel WA Schrezenmeier H 《Vox sanguinis》2012,102(2):159-166
Background/Objectives Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by intravascular haemolysis with a negative direct antiglobulin test (DAT). Eculizumab is a humanized monoclonal antibody that inhibits complement component C5 and is approved for PNH treatment. Recent publications demonstrated that some patients with PNH develop a positive DAT during eculizumab treatment. These published clinical trials investigated a highly selected patient population. Therefore, it seems important to study this topic in a general PNH patient population with a longer follow‐up. Materials and Methods We analysed haemolytic activity, RBC transfusion requirement, effect on DAT and ferritin levels in 41 patients with PNH before and during eculizumab therapy with a median follow‐up of 24 months (range 1–63 months). Results During eculizumab therapy, median LDH decreased (1657–258 U/l; P < 0·0001), while median haemoglobin increased (9·2–10·3 g/dl). Eighteen of 32 pts (56%) who previously required regular transfusions became transfusion independent. DAT was positive for C3d in 72·4% of 21 eculizumab‐treated pts with available DAT. Ferritin levels increased (69–348 ng/ml, P < 0·0001). This increase was more pronounced in pts with ongoing transfusion dependency during eculizumab therapy. Conclusion Eculizumab therapy for PNH should be added to the list of possible causes for a positive DAT. Intravascular haemolysis was inhibited by eculizumab, but signs of extravascular haemolysis should be monitored. Because renal iron loss was stopped, eculizumab‐treated pts can be prone to iron overload and therefore ferritin concentrations should be monitored closely. 相似文献
998.
检测20例正常口腔黏膜和43例口腔鳞状细胞癌患者MAC30蛋白的表达情况。MAC30蛋白在口腔鳞状细胞癌中的表达较正常黏膜明显增加(P<0.05);低分化组和淋巴结转移组较高分化组及淋巴结无转移组阳性表达率明显增高(P<0.05);MAC30蛋白在口腔鳞状细胞癌的发生、发展、分化及转移过程中可能起着重要作用,并可作为一个预测肿瘤转移的新的分子生物学指标。 相似文献
999.
1000.