全文获取类型
收费全文 | 16879篇 |
免费 | 37篇 |
国内免费 | 77篇 |
专业分类
系统科学 | 53篇 |
丛书文集 | 173篇 |
教育与普及 | 67篇 |
理论与方法论 | 49篇 |
现状及发展 | 7664篇 |
研究方法 | 664篇 |
综合类 | 8165篇 |
自然研究 | 158篇 |
出版年
2012年 | 197篇 |
2011年 | 338篇 |
2009年 | 100篇 |
2008年 | 264篇 |
2007年 | 290篇 |
2006年 | 269篇 |
2005年 | 285篇 |
2004年 | 330篇 |
2003年 | 288篇 |
2002年 | 281篇 |
2001年 | 466篇 |
2000年 | 491篇 |
1999年 | 338篇 |
1994年 | 304篇 |
1992年 | 268篇 |
1991年 | 224篇 |
1990年 | 278篇 |
1989年 | 254篇 |
1988年 | 262篇 |
1987年 | 284篇 |
1986年 | 290篇 |
1985年 | 340篇 |
1984年 | 235篇 |
1983年 | 258篇 |
1982年 | 213篇 |
1981年 | 205篇 |
1980年 | 246篇 |
1979年 | 508篇 |
1978年 | 436篇 |
1977年 | 390篇 |
1976年 | 314篇 |
1975年 | 387篇 |
1974年 | 476篇 |
1973年 | 422篇 |
1972年 | 431篇 |
1971年 | 562篇 |
1970年 | 610篇 |
1969年 | 531篇 |
1968年 | 532篇 |
1967年 | 460篇 |
1966年 | 408篇 |
1965年 | 294篇 |
1964年 | 128篇 |
1959年 | 166篇 |
1958年 | 322篇 |
1957年 | 253篇 |
1956年 | 202篇 |
1955年 | 200篇 |
1954年 | 193篇 |
1948年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Shiga toxin and some other protein toxins that act on targets in the cytosol have previously been shown to enter the trans-Golgi network. Transport by this route may be necessary for translocation of the toxin to the cytosol and for intoxication, but it is not known whether the enzymatically active part of the toxins actually enters the cytosol from the trans-Golgi network. It has been suggested that such toxins are transported in a retrograde manner to the endoplasmic reticulum and that translocation occurs in this organelle, but retrograde transport of endocytosed material beyond the trans-Golgi network has never been demonstrated. Here we show that in butyric acid-treated A431 cells endocytosed Shiga toxin is not only transported to the trans-Golgi network, but also to all Golgi stacks, to the endoplasmic reticulum and to the nuclear envelope. Furthermore, butyric acid sensitizes the cells to Shiga toxin, which is consistent with the possibility that retrograde transport is required for translocation of the toxin to the cytosol. 相似文献
32.
33.
H R Brenner 《Nature》1985,317(6038):572-573
34.
35.
Summary Traces of nor-adrenaline restore the vascular action of adrenaline altered in epinephrectomized dogs to the reaction of the normal animal. Therefore it is claimed that the adrenals discharge one or several substances into the blood stream, which are necessary for the usual peripheral vascular action of adrenaline. Further investigations are in progress. 相似文献
36.
David H. Hubel 《自然科学进展(英文版)》2007,17(13):1-3
The visual field is topographically mapped onto the primary visual cortex (V1), forming a retinotopic map which is far more detailed for the foveal regions than for the periphery. We found that receptive field (RF) size in monkey V1 increases with eccentricity, and that a 1—2 m2 V1 region contains roughly a complete set of machinery necessary to analyze a visual-field area whose size is about that of the RFs of the cells. This allows V1 to be anatomically uniform, and is in sharp contrast with the retina. 相似文献
37.
Sobacchi C Frattini A Guerrini MM Abinun M Pangrazio A Susani L Bredius R Mancini G Cant A Bishop N Grabowski P Del Fattore A Messina C Errigo G Coxon FP Scott DI Teti A Rogers MJ Vezzoni P Villa A Helfrich MH 《Nature genetics》2007,39(8):960-962
Autosomal recessive osteopetrosis is usually associated with normal or elevated numbers of nonfunctional osteoclasts. Here we report mutations in the gene encoding RANKL (receptor activator of nuclear factor-KB ligand) in six individuals with autosomal recessive osteopetrosis whose bone biopsy specimens lacked osteoclasts. These individuals did not show any obvious defects in immunological parameters and could not be cured by hematopoietic stem cell transplantation; however, exogenous RANKL induced formation of functional osteoclasts from their monocytes, suggesting that they could, theoretically, benefit from exogenous RANKL administration. 相似文献
38.
Rogaeva E Meng Y Lee JH Gu Y Kawarai T Zou F Katayama T Baldwin CT Cheng R Hasegawa H Chen F Shibata N Lunetta KL Pardossi-Piquard R Bohm C Wakutani Y Cupples LA Cuenco KT Green RC Pinessi L Rainero I Sorbi S Bruni A Duara R Friedland RP Inzelberg R Hampe W Bujo H Song YQ Andersen OM Willnow TE Graff-Radford N Petersen RC Dickson D Der SD Fraser PE Schmitt-Ulms G Younkin S Mayeux R Farrer LA St George-Hyslop P 《Nature genetics》2007,39(2):168-177
The recycling of the amyloid precursor protein (APP) from the cell surface via the endocytic pathways plays a key role in the generation of amyloid beta peptide (Abeta) in Alzheimer disease. We report here that inherited variants in the SORL1 neuronal sorting receptor are associated with late-onset Alzheimer disease. These variants, which occur in at least two different clusters of intronic sequences within the SORL1 gene (also known as LR11 or SORLA) may regulate tissue-specific expression of SORL1. We also show that SORL1 directs trafficking of APP into recycling pathways and that when SORL1 is underexpressed, APP is sorted into Abeta-generating compartments. These data suggest that inherited or acquired changes in SORL1 expression or function are mechanistically involved in causing Alzheimer disease. 相似文献
39.
Péterfy M Ben-Zeev O Mao HZ Weissglas-Volkov D Aouizerat BE Pullinger CR Frost PH Kane JP Malloy MJ Reue K Pajukanta P Doolittle MH 《Nature genetics》2007,39(12):1483-1487
Hypertriglyceridemia is a hallmark of many disorders, including metabolic syndrome, diabetes, atherosclerosis and obesity. A well-known cause is the deficiency of lipoprotein lipase (LPL), a key enzyme in plasma triglyceride hydrolysis. Mice carrying the combined lipase deficiency (cld) mutation show severe hypertriglyceridemia owing to a decrease in the activity of LPL and a related enzyme, hepatic lipase (HL), caused by impaired maturation of nascent LPL and hepatic lipase polypeptides in the endoplasmic reticulum (ER). Here we identify the gene containing the cld mutation as Tmem112 and rename it Lmf1 (Lipase maturation factor 1). Lmf1 encodes a transmembrane protein with an evolutionarily conserved domain of unknown function that localizes to the ER. A human subject homozygous for a deleterious mutation in LMF1 also shows combined lipase deficiency with concomitant hypertriglyceridemia and associated disorders. Thus, through its profound effect on lipase activity, LMF1 emerges as an important candidate gene in hypertriglyceridemia. 相似文献
40.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n... 相似文献