全文获取类型
收费全文 | 3178篇 |
免费 | 90篇 |
国内免费 | 13篇 |
专业分类
系统科学 | 117篇 |
丛书文集 | 3篇 |
教育与普及 | 2篇 |
理论与方法论 | 26篇 |
现状及发展 | 1014篇 |
研究方法 | 32篇 |
综合类 | 2076篇 |
自然研究 | 11篇 |
出版年
2024年 | 17篇 |
2023年 | 28篇 |
2022年 | 10篇 |
2020年 | 12篇 |
2017年 | 9篇 |
2016年 | 30篇 |
2015年 | 57篇 |
2014年 | 28篇 |
2013年 | 24篇 |
2012年 | 153篇 |
2011年 | 167篇 |
2008年 | 6篇 |
2007年 | 13篇 |
2006年 | 14篇 |
2005年 | 201篇 |
2004年 | 505篇 |
2003年 | 467篇 |
2002年 | 141篇 |
2001年 | 75篇 |
2000年 | 138篇 |
1999年 | 75篇 |
1992年 | 37篇 |
1991年 | 25篇 |
1990年 | 35篇 |
1989年 | 34篇 |
1988年 | 32篇 |
1987年 | 17篇 |
1986年 | 26篇 |
1985年 | 35篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 15篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 61篇 |
1978年 | 39篇 |
1977年 | 30篇 |
1976年 | 29篇 |
1975年 | 38篇 |
1974年 | 56篇 |
1973年 | 49篇 |
1972年 | 51篇 |
1971年 | 66篇 |
1970年 | 54篇 |
1969年 | 68篇 |
1968年 | 59篇 |
1967年 | 41篇 |
1966年 | 55篇 |
1965年 | 41篇 |
1964年 | 11篇 |
排序方式: 共有3281条查询结果,搜索用时 203 毫秒
111.
Good MF 《Cellular and molecular life sciences : CMLS》2011,68(7):1105-1113
Malaria presents a challenge to world health that to date has been beyond the abilities of researchers to conquer. This critique
presents some of the strategies employed by the parasite to overcome immunity and the immunological challenges that we face
to develop vaccines. A conclusion is that a vaccine must identify novel antigens or epitopes that are not normally immunogenic
and which are therefore not under immune pressure and most likely to be conserved between different strains. Such antigens
are most likely to be targets of cellular immunity. The case for a whole parasite blood stage vaccine is presented based on
these premises. 相似文献
112.
Marsango S Bonaccorsi di Patti MC Barra D Miele R 《Cellular and molecular life sciences : CMLS》2011,68(17):2919-2929
Prokineticins are proteins that regulate diverse biological processes including gastrointestinal motility, angiogenesis, circadian
rhythm, and innate immune response. Prokineticins bind two closed related G-protein coupled receptors (GPCRs), PKR1 and PKR2.
In general, these receptors act as molecular switches to relay activation to heterotrimeric G-proteins and a growing body
of evidence points to the fact that GPCRs exist as homo- or heterodimers. We show here by Western-blot analysis that PKR2
has a dimeric structure in neutrophils. By heterologous expression of PKR2 in Saccharomyces cerevisiae, we examined the mechanisms of intermolecular interaction of PKR2 dimerization. The potential involvement of three types
of mechanisms was investigated: coiled-coil, disulfide bridges, and hydrophobic interactions between transmembrane domains.
Characterization of differently deleted or site-directed PKR2 mutants suggests that dimerization proceeds through interactions
between transmembrane domains. We demonstrate that co-expressing binding-deficient and signaling-deficient forms of PKR2 can
re-establish receptor functionality, possibly through a domain-swapping mechanism. 相似文献
113.
114.
提出了一种用于时分多址突发通信系统中的IJF-OQPSK调制信号解调方法.介绍了电路的组成及原理,分析了系统的性能.该方法具有电路结构简单、数据恢复快、相位抖动小的优点,对提高突发通信系统的效率有显著作用.实验结果表明在时分多址突发通信系统中,该方法具有很好的使用价值. 相似文献
115.
An inflammatory drug prospect. 总被引:2,自引:0,他引:2
116.
Angela M. Ortega-León Maricela Villagrán-Santa Cruz J. Jamie Zú?iga-Vega Raúl Cueva-del Castillo Fausto R. Méndez-de la Cruz 《西北部美国博物学家》2011,69(1)
Asynchronous reproduction is a common phenomenon in high-elevation populations of lizards from Central México. Sperm storage in the reproductive tract of females is the mechanism for making oocyte fertilization possible. Our study addresses questions related to functional oviductal sperm storage of females mating on different dates throughout the reproductive season. A population of Sceloporus mucronatus with copulation in the summer and ovulation in the fall was chosen for this experiment. Eleven females that copulated in the field during June and 13 females that copulated in captivity during August were maintained in the laboratory until parturition. The number of pregnant females and the litter sizes produced in each experimental group were indicative of the viability of the stored sperm. Sperm stored in the reproductive tract of females were able to fertilize eggs after 4 months. No significant differences were found in the number of pregnant females between the 2 experimental groups nor in the litter sizes that they produced. We found that the amount of time sperm were held in the female reproductive tract (ca. 3 months) had no effect on the capacity of sperm to fertilize eggs. Histological examination of 8 oviducts collected before the mating season eliminated the possibility of sperm storage from one year to the next. In this system, sperm retention could have evolved as a response mechanism to deal with the asynchrony between sexes in the reproductive cycles. However, we cannot rule out alternative hypotheses. 相似文献
117.
118.
Putative transcription activator with alternative isoforms encoded by human ZFX gene 总被引:9,自引:0,他引:9
A Schneider-G?dicke P Beer-Romero L G Brown G Mardon S W Luoh D C Page 《Nature》1989,342(6250):708-711
119.
120.
Bcl-2 is an inner mitochondrial membrane protein that blocks programmed cell death 总被引:174,自引:0,他引:174
The t(14; 18) chromosomal translocation of human follicular B-cell lymphoma juxtaposes the bcl-2 gene with the immunoglobulin heavy chain locus. The bcl-2 immunoglobulin fusion gene is markedly deregulated resulting in inappropriately elevated levels of bcl-2 RNA and protein. Transgenic mice bearing a bcl-2 immunoglobulin minigene demonstrate a polyclonal expansion of resting yet responsive IgM-IgD B cells which display prolonged cell survival but no increase in cell cycling. Moreover, deregulated bcl-2 extends the survival of certain haematopoietic cell lines following growth-factor deprivation. By using immunolocalization studies we now demonstrate that Bcl-2 is an integral inner mitochondrial membrane protein of relative molecular mass 25,000 (25k). Overexpression of Bcl-2 blocks the apoptotic death of a pro-B-lymphocyte cell line. Thus, Bcl-2 is unique among proto-oncogenes, being localized to mitochondria and interfering with programmed cell death independent of promoting cell division. 相似文献