全文获取类型
收费全文 | 43891篇 |
免费 | 143篇 |
国内免费 | 290篇 |
专业分类
系统科学 | 533篇 |
丛书文集 | 1033篇 |
教育与普及 | 142篇 |
理论与方法论 | 245篇 |
现状及发展 | 17790篇 |
研究方法 | 1644篇 |
综合类 | 22115篇 |
自然研究 | 822篇 |
出版年
2013年 | 441篇 |
2012年 | 790篇 |
2011年 | 1656篇 |
2010年 | 505篇 |
2009年 | 461篇 |
2008年 | 960篇 |
2007年 | 1033篇 |
2006年 | 1076篇 |
2005年 | 1010篇 |
2004年 | 814篇 |
2003年 | 769篇 |
2002年 | 776篇 |
2001年 | 1243篇 |
2000年 | 1207篇 |
1999年 | 821篇 |
1992年 | 732篇 |
1991年 | 607篇 |
1990年 | 626篇 |
1989年 | 610篇 |
1988年 | 613篇 |
1987年 | 614篇 |
1986年 | 589篇 |
1985年 | 723篇 |
1984年 | 618篇 |
1983年 | 501篇 |
1982年 | 455篇 |
1981年 | 444篇 |
1980年 | 569篇 |
1979年 | 1232篇 |
1978年 | 1055篇 |
1977年 | 1069篇 |
1976年 | 755篇 |
1975年 | 855篇 |
1974年 | 1218篇 |
1973年 | 1058篇 |
1972年 | 1059篇 |
1971年 | 1307篇 |
1970年 | 1640篇 |
1969年 | 1292篇 |
1968年 | 1228篇 |
1967年 | 1295篇 |
1966年 | 1106篇 |
1965年 | 819篇 |
1959年 | 486篇 |
1958年 | 708篇 |
1957年 | 567篇 |
1956年 | 475篇 |
1955年 | 440篇 |
1954年 | 468篇 |
1948年 | 246篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Lubelski J Rink R Khusainov R Moll GN Kuipers OP 《Cellular and molecular life sciences : CMLS》2008,65(3):455-476
This review discusses the state-of-the-art in molecular research on the most prominent and widely applied lantibiotic, i.e., nisin. The developments in understanding its complex biosynthesis and mode of action are highlighted. Moreover, novel applications
arising from engineering either nisin itself, or from the construction of totally novel dehydrated and/or lanthionine-containing
peptides with desired bioactivities are described. Several challenges still exist in understanding the immunity system and
the unique multiple reactions occurring on a single substrate molecule, carried out by the dehydratase NisB and the cyclization
enzyme NisC. The recent elucidation of the 3-D structure of NisC forms the exciting beginning of further 3-D-structure determinations
of the other biosynthetic enzymes, transporters and immunity proteins. Advances in achieving in vitro activities of lanthionine-forming enzymes will greatly enhance our understanding of the molecular characteristics of the
biosynthesis process, opening up new avenues for developing unique and novel biocatalytic processes.
Received 9 April 2007; received after revision 31 August 2007; accepted 28 September 2007 相似文献
942.
943.
944.
Navarro S Aleu J Jiménez M Boix E Cuchillo CM Nogués MV 《Cellular and molecular life sciences : CMLS》2008,65(2):324-337
Human eosinophil cationic protein (ECP)/ ribonuclease 3 (RNase 3) is a protein secreted from the secondary granules of activated
eosinophils. Specific properties of ECP contribute to its cytotoxic activities associated with defense mechanisms. In this
work the ECP cytotoxic activity on eukaryotic cell lines is analyzed. The ECP effects begin with its binding and aggregation
to the cell surface, altering the cell membrane permeability and modifying the cell ionic equilibrium. No internalization
of the protein is observed. These signals induce cell-specific morphological and biochemical changes such as chromatin condensation,
reversion of membrane asymmetry, reactive oxygen species production and activation of caspase-3-like activity and, eventually,
cell death. However, the ribonuclease activity component of ECP is not involved in this process as no RNA degradation is observed.
In summary, the cytotoxic effect of ECP is attained through a mechanism different from that of other cytotoxic RNases and
may be related with the ECP accumulation associated with the inflammatory processes, in which eosinophils are present.
Received 26 October 2007; accepted 23 November 2007 相似文献
945.
Shin JM Vagin O Munson K Kidd M Modlin IM Sachs G 《Cellular and molecular life sciences : CMLS》2008,65(2):264-281
Inhibition of gastric acid secretion is the mainstay of the treatment of gastroesophageal reflux disease and peptic ulceration;
therapies to inhibit acid are among the best-selling drugs worldwide. Highly effective agents targeting the histamine H2 receptor
were first identified in the 1970s. These were followed by the development of irreversible inhibitors of the parietal cell
hydrogen-potassium ATPase (the proton pump inhibitors) that inhibit acid secretion much more effectively. Reviewed here are
the chemistry, biological targets and pharmacology of these drugs, with reference to their current and evolving clinical utilities.
Future directions in the development of acid inhibitory drugs include modifications of current agents and the emergence of
a novel class of agents, the acid pump antagonists.
Received 30 May 2007; received after revision 15 August 2007; accepted 13 September 2007 相似文献
946.
Dolezel D Zdechovanova L Sauman I Hodkova M 《Cellular and molecular life sciences : CMLS》2008,65(6):964-969
Current models state that insect peripheral oscillators are directly responsive to light, while mammalian peripheral clock
genes are coordinated by a master clock in the brain via intermediate factors, possibly hormonal. We show that the expression
levels of two circadian clock genes, period (per) and Par Domain Protein 1 (Pdp1) in the peripheral tissue of an insect model species, the linden bug Pyrrhocoris apterus, are inversely affected by contrasting photoperiods. The effect of photoperiod on per and Pdp1 mRNA levels was found to be mediated by the corpus allatum, an endocrine gland producing juvenile hormone. Our results
provide the first experimental evidence for the effect of an endocrine gland on circadian clock gene expression in insects.
Received 31 October 2007; received after revision 7 January 2008; accepted 9 January 2008
D. Dolezel, L. Zdechovanova: These authors contributed equally to this work. 相似文献
947.
雪灵芝水溶性多糖提取工艺优化及其数学模型的建立 总被引:2,自引:0,他引:2
目的 优化雪灵芝水溶性多糖的提取工艺,并建立数学模型.方法 采用水提醇沉法提取雪灵芝水溶性多糖;运用苯酚-硫酸法测定多糖含量;通过单因素实验研究浸提时间、加水比、浸提温度及乙醇浓度对多糖提取率的影响;采用响应面分析法优化提取条件,运用sas软件分析实验数据,建立回归模型.结果 得到雪灵芝水溶性多糖提取的优化工艺参数的最佳取值范围为:浸提温度(94.5~97.5℃);浸提时间(2~2.5h);加水比(43~51v/w).结论 为雪灵芝水溶性多糖提取工艺的优化提供了一定的技术依据,也为其后续研究奠定了基础. 相似文献
948.
圆筒直线感应电机研究综述 总被引:2,自引:0,他引:2
圆筒型直线感应电动机与普通电动机的区别在于圆筒型直线电动机存在纵向端部效应.在这篇文章中,简要介绍圆筒直线感应电机的发展与结构后,分析了国内外直线电机特别是圆筒直线电机的研究现状,根据分析得出圆筒直线感应电机需要进一步研究的方向. 相似文献
949.
Many notions regarding the function, structure and regulation of cholera toxin expression have remained essentially unaltered
in the last 15 years. At the same time, recent findings have generated additional perspectives. For example, the cholera toxin
genes are now known to be carried by a non-lytic bacteriophage, a previously unsuspected condition. Understanding of how the
expression of cholera toxin genes is controlled by the bacterium at the molecular level has advanced significantly and relationships
with cell-density-associated (quorum-sensing) responses have recently been discovered. Regarding the cell intoxication process,
the mode of entry and intracellular transport of cholera toxin are becoming clearer. In the immunological field, the strong
oral immunogenicity of the non-toxic B subunit of cholera toxin (CTB) has been exploited in the development of a now widely
licensed oral cholera vaccine. Additionally, CTB has been shown to induce tolerance against co-administered (linked) foreign
antigens in some autoimmune and allergic diseases.
Received 25 October 2007; accepted 12 December 2007 相似文献
950.
Hochrainer K Kroismayr R Baranyi U Binder BR Lipp J 《Cellular and molecular life sciences : CMLS》2008,65(13):2105-2117
Small HERC proteins are defined by the presence of one RCC1-like domain and a HECT domain. Having evolved out of one common ancestor, the four members of the family exhibit a high degree of homology in genomic organization and amino acid sequence, thus it seems possible that they might accomplish similar functions. Here we show that small HERC proteins interact with each other and localize to the same cellular structures, which we identify as late endosomes and lysosomes. We demonstrate interaction of HERC3 with the ubiquitin-like proteins hPLIC-1 and hPLIC-2 and we establish interaction of HERC5 with the metastasis suppressor Nm23B. While hPLIC proteins are not ubiquitinated by HERC3, HERC5 plays an important role in ubiquitination of Nm23B. In summary, although small HERC proteins are highly homologous showing the same subcellular distribution, they undergo different molecular interactions. 相似文献