全文获取类型
收费全文 | 22298篇 |
免费 | 111篇 |
国内免费 | 252篇 |
专业分类
系统科学 | 413篇 |
丛书文集 | 426篇 |
教育与普及 | 75篇 |
理论与方法论 | 79篇 |
现状及发展 | 8511篇 |
研究方法 | 928篇 |
综合类 | 11654篇 |
自然研究 | 575篇 |
出版年
2014年 | 156篇 |
2013年 | 297篇 |
2012年 | 533篇 |
2011年 | 1110篇 |
2010年 | 385篇 |
2009年 | 370篇 |
2008年 | 607篇 |
2007年 | 712篇 |
2006年 | 688篇 |
2005年 | 614篇 |
2004年 | 482篇 |
2003年 | 375篇 |
2002年 | 408篇 |
2001年 | 612篇 |
2000年 | 687篇 |
1999年 | 472篇 |
1992年 | 350篇 |
1991年 | 303篇 |
1990年 | 301篇 |
1989年 | 281篇 |
1988年 | 248篇 |
1987年 | 284篇 |
1986年 | 254篇 |
1985年 | 340篇 |
1984年 | 297篇 |
1983年 | 214篇 |
1982年 | 222篇 |
1981年 | 207篇 |
1980年 | 254篇 |
1979年 | 559篇 |
1978年 | 450篇 |
1977年 | 481篇 |
1976年 | 364篇 |
1975年 | 435篇 |
1974年 | 574篇 |
1973年 | 474篇 |
1972年 | 451篇 |
1971年 | 552篇 |
1970年 | 695篇 |
1969年 | 555篇 |
1968年 | 529篇 |
1967年 | 579篇 |
1966年 | 494篇 |
1965年 | 366篇 |
1959年 | 219篇 |
1958年 | 306篇 |
1957年 | 250篇 |
1956年 | 178篇 |
1955年 | 195篇 |
1954年 | 182篇 |
排序方式: 共有10000条查询结果,搜索用时 406 毫秒
21.
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
22.
研究了Al3+离子的固溶对C-S-H表面吸附Na+离子量的影响.实验结果表明,Al3+离子固溶于C-S-H结构中将使C-S-H表面所带的负电量增大,因而也就增大了C-S-H表面对Na+离子的吸附能力. 相似文献
23.
R. Poggioli A. V. Vergoni A. Bertolini 《Cellular and molecular life sciences : CMLS》1985,41(2):265-266
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma. 相似文献
24.
25.
1 Results Pyrimidinones (PMs) are a class of important heterocycles which have been well documented throughout the literature due to their biological importance. They exhibit a wide range of pharmaceutical and therapeutic properties[1].A rapid and efficient one-pot method for the synthesis of 4,6-diarylpyrimidin-2(1H)- ones and related heterocycles is described.The condensation of acetophenone derivatives,aldehydes and urea in the presence of sulfamic acid was employed to synthesize a variety of pyrimid... 相似文献
26.
27.
吕玉芳 《济源职业技术学院学报》2002,1(1):48-51
中国共产党始终代表中国先进生产力的发展要求的论断,是站在历史唯物主义的角度,揭示出我们党兴旺发达的根本动力. 相似文献
28.
Nuclear localization and signalling activity of phosphoinositidase C beta in Swiss 3T3 cells. 总被引:14,自引:0,他引:14
The hydrolysis of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) is a widespread receptor-coupled signalling system at the plasma membrane of most eukaryotic cells. The existence of an entirely separate nuclear phosphoinositide signalling system is suggested from evidence that purified nuclei synthesize PtdInsP2 and phosphatidylinositol 4-phosphate (PtdInsP) in vitro and that a transient decrease in the mass of these lipids occurs when Swiss 3T3 cells are cultured in the presence of insulin-like growth factor-1 (IGF-1). These IGF-1-dependent changes in inositol lipids coincide with an increase in nuclear diacyglycerol and precede translocation to the nucleus and activation of protein kinase C (refs 5, 6). Circumstantial evidence that links these changes with mitosis comes from the isolation of a 3T3 clone that expresses the type-1 IGF receptor and binds IGF-1 peptide but does not respond mitogenically or show transient mass changes in nuclear inositol lipids. A key question is how IGF-1 initiates the rapid breakdown of PtdInsP and PtdInsP2 in the nucleus. Here we present evidence that nuclei of 3T3 cells contain the beta-isozyme of phosphoinositidase C, whereas the gamma-isozyme is confined to the cytoplasm and that IGF-1 treatment stimulates exclusively the activity of nuclear phosphoinositidase C. 相似文献
29.
Growth hormone signal transduction 总被引:1,自引:0,他引:1
Growth hormone (GH) promotes animal growth by stimulating bone and cartilage cell proliferation, and influences carbohydrate and lipid metabolism. Some of these effects are brought about indirectly via somatomedin induction in hepatocytes, others by acting directly on the target cells. In either case, GH first binds to specific receptors on cells to trigger a sequence of biochemical events culminating in a biological response. Recently much has been learnt about the molecular structure of GH receptor, its binding to ligand, and the ensuing signal transduction events. 相似文献
30.
We recently reported on a linkage study within a Quarter Horse lineage segregating hyperkalaemic periodic paralysis (HYPP), an autosomal dominant condition showing potassium-induced attacks of skeletal muscle paralysis. HYPP co-segregated with the equine adult skeletal muscle sodium channel alpha subunit gene, the same gene that causes human HYPP. We now describe the Phe to Leu mutation in transmembrane domain IVS3 which courses the horse disease. This represents the first application of molecular genetics to an important horse disease, and the data will provide an opportunity for control or eradication of this condition. 相似文献