全文获取类型
收费全文 | 4103篇 |
免费 | 26篇 |
国内免费 | 25篇 |
专业分类
系统科学 | 78篇 |
丛书文集 | 242篇 |
教育与普及 | 171篇 |
理论与方法论 | 11篇 |
现状及发展 | 406篇 |
研究方法 | 593篇 |
综合类 | 2651篇 |
自然研究 | 2篇 |
出版年
2018年 | 5篇 |
2014年 | 13篇 |
2013年 | 13篇 |
2012年 | 268篇 |
2011年 | 330篇 |
2010年 | 71篇 |
2009年 | 15篇 |
2008年 | 273篇 |
2007年 | 264篇 |
2006年 | 301篇 |
2005年 | 321篇 |
2004年 | 300篇 |
2003年 | 264篇 |
2002年 | 231篇 |
2001年 | 189篇 |
2000年 | 242篇 |
1999年 | 66篇 |
1998年 | 11篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 11篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 19篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 11篇 |
1986年 | 26篇 |
1985年 | 22篇 |
1984年 | 21篇 |
1983年 | 14篇 |
1982年 | 21篇 |
1981年 | 30篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1972年 | 4篇 |
1971年 | 16篇 |
1970年 | 28篇 |
1966年 | 15篇 |
1959年 | 68篇 |
1958年 | 124篇 |
1957年 | 89篇 |
1956年 | 66篇 |
1955年 | 87篇 |
1954年 | 83篇 |
1948年 | 25篇 |
1947年 | 4篇 |
1940年 | 4篇 |
排序方式: 共有4154条查询结果,搜索用时 22 毫秒
981.
982.
This article describes the most recent process of projecting population at the subnational level in England. It briefly explains the reasons why projecting population at the subnational level is important, describes the model and how it was used to produce the latest set of long-term subnational population projections in England published by the Office for National Statistics (ONS) in 1998. The article then discusses how the model may be applied to answer various 'what-if' questions about future population. 相似文献
983.
Gineitis A Treigyte G Savickiene J Shanbhag VP Stigbrand T 《Cellular and molecular life sciences : CMLS》1999,55(2):317-326
The two-dimensional electrophoretic patterns of nuclear proteins and their tyrosine phosphorylation were compared for HL-60
cells before and after differentiation induction to granulocytes by dimethyl sulfoxide, all-trans retinoic acid and N
6,O
2-dibutyryl adenosine 3′5′-cyclic monophosphate. Regardless of the inducer used, some nuclear proteins, which are tyrosine-phosphorylated
in proliferating HL-60 cells, undergo gradual dephosphorylation 12–72 h after induction of differentiation, followed by drastic
dephosphorylation during maturation to granulocytes. At least 13 nuclear proteins with a molecular mass of 35–110 kDa are
dephosphorylated, and 6 nuclear proteins undergo tyrosine phosphorylation. Analysis of the nuclear proteins differentially
extracted by salt and detergents indicates that changes in their tyrosine phosphorylation during the maturation stage of differentiating
granulocytes occur mainly in proteins which are abundant in nucleoplasm, chromatin and residual nuclear structures. The abundance
of these proteins, residing in the nuclear structures, and their long-term modification in phosphorylation during the maturation
stages of differentiation strongly suggest that tyrosine phosphorylation of these proteins is involved in reorganization of
the differentiating cell nucleus.
Received 21 September 1998; received after revision 24 November 1998; accepted 3 December 1998 相似文献
984.
Nitric oxide and cellular respiration 总被引:7,自引:0,他引:7
Brunori M Giuffrè A Sarti P Stubauer G Wilson MT 《Cellular and molecular life sciences : CMLS》1999,56(7-8):549-557
The role of nitric oxide (NO) as a signalling molecule involved in many pathophysiological processes (e.g., smooth muscle relaxation, inflammation, neurotransmission, apoptosis) has been elaborated during the last decade. Since NO has also been found to inhibit cellular respiration, we review here the available information on the interactions of NO with cytochrome c oxidase (COX), the terminal enzyme of the respiratory chain. The effect of NO on cellular respiration is first summarized to present essential evidence for the fact that NO is a potent reversible inhibitor of in vivo O2 consumption. This information is then correlated with available experimental evidence on the reactions of NO with purified COX. Finally, since COX has been proposed to catalyze the degradation of NO into either nitrous oxide (N2O) or nitrite, we consider the putative role of this enzyme in the catabolism of NO in vivo. 相似文献
985.
Pathophysiology of mitochondrial cell death control 总被引:3,自引:0,他引:3
Mitochondria have been recently recognized to play a major role in the control of apoptosis or programmed cell death. Permeabilization of mitochondrial membranes, a decisive feature of early cell death, is regulated by members of the Bcl-2 family which interact with the permeability transition pore complex (PTPC). Thus, the cytoprotective oncoprotein Bcl-2 stabilizes the mitochondrial membrane barrier function, whereas the tumor suppressor protein Bax permeabilizes mitochondrial membranes. The regulation of membrane permeabilization is intertwined with that of the bioenergetic and redox functions of mitochondria. The implications of alterations in the composition of the PTPC and in mitochondrial function for the pathophysiology of cancer (reduced apoptosis) and neurodegeneration (enhanced apoptosis) are discussed. 相似文献
986.
987.
Paolini M Cantelli-Forti G Perocco P Pedulli GF Abdel-Rahman SZ Legator MS 《Nature》1999,398(6730):760-761
988.
Ubiquitin tag for sperm mitochondria 总被引:29,自引:0,他引:29
989.
Mercader N Leonardo E Azpiazu N Serrano A Morata G Martínez C Torres M 《Nature》1999,402(6760):425-429
Vertebrate limbs grow out from the flanks of embryos, with their main axis extending proximodistally from the trunk. Distinct limb domains, each with specific traits, are generated in a proximal-to-distal sequence during development. Diffusible factors expressed from signalling centres promote the outgrowth of limbs and specify their dorsoventral and anteroposterior axes. However, the molecular mechanism by which limb cells acquire their proximodistal (P-D) identity is unknown. Here we describe the role of the homeobox genes Meis1/2 and Pbx1 in the development of mouse, chicken and Drosophila limbs. We find that Meis1/2 expression is restricted to a proximal domain, coincident with the previously reported domain in which Pbx1 is localized to the nucleus, and resembling the distribution of the Drosophila homologues homothorax (hth) and extradenticle (exd); that Meis1 regulates Pbx1 activity by promoting nuclear import of the Pbx1 protein; and that ectopic expression of Meis1 in chicken and hth in Drosophila disrupts distal limb development and induces distal-to-proximal transformations. We suggest that restriction of Meis1/Hth to proximal regions of the vertebrate and insect limb is essential to specify cell fates and differentiation patterns along the P-D axis of the limb. 相似文献
990.
<正> 我们研制了一种对耐火金属硅化物,铌和二氧化硅中痕量杂质,U,Th,Ca,Fe,Cr,Ni,Cu和Cd的测定方法,即同位素稀释质谱法(IDMS),该法是借助微电子设备的特性使其对铀、钍分析检出限降到最低为ppt级的水平,对其他元素可检测到ppb级或根据空白值的某些情况而衰减的高灵敏度和高准确度的方法.痕量组分与基体分离是采用选择色谱,萃取和电解步骤与热离子化质谱结合的方法,并对先进工艺的高纯材料(金属和硅化物粉末,致密的硅化物和二氧化硅)的不同样品进行了分析. 相似文献