全文获取类型
收费全文 | 788篇 |
免费 | 6篇 |
国内免费 | 18篇 |
专业分类
系统科学 | 21篇 |
丛书文集 | 12篇 |
教育与普及 | 50篇 |
理论与方法论 | 1篇 |
现状及发展 | 198篇 |
研究方法 | 65篇 |
综合类 | 464篇 |
自然研究 | 1篇 |
出版年
2021年 | 3篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 18篇 |
2011年 | 28篇 |
2010年 | 22篇 |
2009年 | 58篇 |
2008年 | 36篇 |
2007年 | 35篇 |
2006年 | 31篇 |
2005年 | 30篇 |
2004年 | 88篇 |
2003年 | 31篇 |
2002年 | 18篇 |
2001年 | 79篇 |
2000年 | 67篇 |
1999年 | 55篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 6篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 8篇 |
1969年 | 8篇 |
1968年 | 4篇 |
1967年 | 4篇 |
1966年 | 2篇 |
1958年 | 2篇 |
1956年 | 2篇 |
排序方式: 共有812条查询结果,搜索用时 62 毫秒
201.
Han X 《Cellular and molecular life sciences : CMLS》2004,61(15):1896-1906
The critical roles of apolipoprotein E (apoE) in regulating plasma lipid and lipoprotein levels have been
extensively studied for over 2 decades. However, an understanding of the roles of apoE in the central nervous
system (CNS) is less certain. This review will summarize the available experimental results on the role of apoE
in CNS lipid homeostasis with respect to its modulation of sulfatide trafficking, alteration of CNS cholesterol
homeostasis and apoE-induced changes in phospholipid molecular species in specialized subcellular membrane
fractions. The results indicate that apoE mediates sulfatide trafficking and metabolism in the CNS. Moreover,
although apoE does not affect the cholesterol mass content or the phospholipid mass levels and composition in the
CNS as a whole, apoE modulates cholesterol and phospholipid homeostasis in selective subcellular membrane
compartments. Through elucidating the roles of apoE in CNS lipid metabolism, new insights into overall functions
of apoE in neurobiology can be accrued ultimately, leading to an increased understanding of CNS lipid metabolism
and the identification of novel therapeutic targets for CNS diseases.Received 9 January 2004; received after revision 28 February 2004; accepted 10 March 2004 相似文献
202.
Cattle call for gene targeting 总被引:1,自引:0,他引:1
203.
Room-temperature ferroelectricity in strained SrTiO3 总被引:1,自引:0,他引:1
Haeni JH Irvin P Chang W Uecker R Reiche P Li YL Choudhury S Tian W Hawley ME Craigo B Tagantsev AK Pan XQ Streiffer SK Chen LQ Kirchoefer SW Levy J Schlom DG 《Nature》2004,430(7001):758-761
Systems with a ferroelectric to paraelectric transition in the vicinity of room temperature are useful for devices. Adjusting the ferroelectric transition temperature (T(c)) is traditionally accomplished by chemical substitution-as in Ba(x)Sr(1-x)TiO(3), the material widely investigated for microwave devices in which the dielectric constant (epsilon(r)) at GHz frequencies is tuned by applying a quasi-static electric field. Heterogeneity associated with chemical substitution in such films, however, can broaden this phase transition by hundreds of degrees, which is detrimental to tunability and microwave device performance. An alternative way to adjust T(c) in ferroelectric films is strain. Here we show that epitaxial strain from a newly developed substrate can be harnessed to increase T(c) by hundreds of degrees and produce room-temperature ferroelectricity in strontium titanate, a material that is not normally ferroelectric at any temperature. This strain-induced enhancement in T(c) is the largest ever reported. Spatially resolved images of the local polarization state reveal a uniformity that far exceeds films tailored by chemical substitution. The high epsilon(r) at room temperature in these films (nearly 7,000 at 10 GHz) and its sharp dependence on electric field are promising for device applications. 相似文献
204.
Neurofilament proteins in neurodegenerative diseases 总被引:3,自引:0,他引:3
Liu Q Xie F Siedlak SL Nunomura A Honda K Moreira PI Zhua X Smith MA Perry G 《Cellular and molecular life sciences : CMLS》2004,61(24):3057-3075
The function of neurofilaments, the major component in large myelinated neurons, is not well understood even though they were discovered as structures over 100 years ago. Recent studies have suggested that neuro-filaments are closely related to many neurodegenerative diseases, such as amyotrophic lateral sclerosis, Parkinson disease Alzheimer disease, and diabetes. Using in vitro assays, cultures and transgenic mice, these studies provided new insights into neurofilament function. The function of each subunit, the relationship of neurofilaments with other cytoskeletal elements and their clinical significance are topics of increasing attention.Received 22 June 2004; received after revision 4 August 2004; accepted 19 August 2004 相似文献
205.
文章通过试验得出预混式气力喷雾系统的空气流量、排液量、系统压力及气液质量比与雾滴体积中径的关系,并对其影响因素进行分析。同时用回归法得出各参数与雾滴体积中径关系的二次回归方程,用以指导预混式气力喷雾系统的优化设计。 相似文献
206.
207.
徐诗豪 《科技情报开发与经济》2004,14(6):46-47
介绍了互联网上生命科学信息资源的获取方法,包括生物学数据库、搜索引擎、专业网站、研究机构、大专院校、学术机构、电子论坛等网站的网址、内容及其基本检索方法。 相似文献
208.
我国青贮玉米的研究现状及市场前景 总被引:17,自引:0,他引:17
青贮玉米作为饲料玉米既能大幅度地提高饲料产量,同时具有较高的营养价值,在国民经济和人民生活中占有越来越重要的地位。在借鉴欧美等发达国家对青贮玉米研究成果的基础上,分析了我国发展青贮玉米的优势和潜力,提出了青贮玉米的育种策略、育种目标和主要用于家畜饲养业的有效利用途径。 相似文献
209.
太原市二氧化硫污染状况及评价 总被引:1,自引:0,他引:1
通过对太原市不同季节、不同监测位点大气二氧化硫(SO2)浓度的监测,分析了太原市SO2污染状况,指出在太原市对SO2排放企业的治理和管理工作势在必行。 相似文献
210.
SU5416 sensitizes ovarian cancer cells to cisplatin through inhibition of nucleotide excision repair 总被引:5,自引:0,他引:5
SU5416 is reported to be a selective inhibitor of vascular endothelial growth factor, and it has metwith limited success in the clinic. In the present study, we investigated whether SU5416 could augment cisplatin-induced cytotoxicity in human ovarian cancer cells. When used as a single agent, 2-h exposures to SU5416 were not harmful to the cells up to doses of 100 microM. For 48-h exposures, the SU5416 IC20 and IC50 were 17 and 34 microM, respectively. When used with cisplatin, the effect of SU5416 was sequence dependent. SU5416 given first was subadditive, whereas cisplatin given first was supraadditive. Cisplatin was given as a 1-h exposure. Augmented cisplatin cytotoxicity was seen with 2-h exposures to SU5416 at doses of 17-34 microM. This was associated with a decrease in cisplatin-DNA adduct repair, as measured by atomic absorbance spectrometry. Treatment of the ovarian carcinoma cells with SU5416 was also associated with a reduced expression of ERCC-1 protein and c-jun mRNA, as well as a decrease in c-Jun and JNK activities. We conclude that SU5416 can be used to augment cisplatin-induced cell killing at doses that are non-toxic. This effect may occur through direct or indirect reduction of the activity of AP-1 and DNA repair. 相似文献