全文获取类型
收费全文 | 7119篇 |
免费 | 297篇 |
国内免费 | 426篇 |
专业分类
系统科学 | 1353篇 |
丛书文集 | 177篇 |
教育与普及 | 38篇 |
理论与方法论 | 11篇 |
现状及发展 | 78篇 |
综合类 | 6184篇 |
自然研究 | 1篇 |
出版年
2024年 | 25篇 |
2023年 | 63篇 |
2022年 | 111篇 |
2021年 | 113篇 |
2020年 | 121篇 |
2019年 | 95篇 |
2018年 | 91篇 |
2017年 | 127篇 |
2016年 | 106篇 |
2015年 | 213篇 |
2014年 | 349篇 |
2013年 | 261篇 |
2012年 | 455篇 |
2011年 | 445篇 |
2010年 | 340篇 |
2009年 | 427篇 |
2008年 | 446篇 |
2007年 | 632篇 |
2006年 | 583篇 |
2005年 | 526篇 |
2004年 | 441篇 |
2003年 | 382篇 |
2002年 | 315篇 |
2001年 | 293篇 |
2000年 | 205篇 |
1999年 | 179篇 |
1998年 | 109篇 |
1997年 | 81篇 |
1996年 | 54篇 |
1995年 | 49篇 |
1994年 | 43篇 |
1993年 | 31篇 |
1992年 | 19篇 |
1991年 | 26篇 |
1990年 | 14篇 |
1989年 | 27篇 |
1988年 | 19篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 2篇 |
1981年 | 3篇 |
排序方式: 共有7842条查询结果,搜索用时 15 毫秒
11.
Hellgren M Strömberg P Gallego O Martras S Farrés J Persson B Parés X Höög JO 《Cellular and molecular life sciences : CMLS》2007,64(4):498-505
The metabolism of all-trans- and 9-cis-retinol/ retinaldehyde has been investigated with focus on the activities of human, mouse and rat alcohol dehydrogenase 2
(ADH2), an intriguing enzyme with apparently different functions in human and rodents. Kinetic constants were determined with
an HPLC method and a structural approach was implemented by in silico substrate dockings. For human ADH2, the determined Km values ranged from 0.05 to 0.3 μM and kcat values from 2.3 to 17.6 min−1, while the catalytic efficiency for 9-cis-retinol showed the highest value for any substrate. In contrast, poor activities
were detected for the rodent enzymes. A mouse ADH2 mutant (ADH2Pro47His) was studied that resembles the human ADH2 setup.
This mutation increased the retinoid activity up to 100-fold. The Km values of human ADH2 are the lowest among all known human retinol dehydrogenases, which clearly support a role in hepatic
retinol oxidation at physiological concentrations.
Received 12 October 2006; received after revision 6 December 2006; accepted 8 January 2007 相似文献
12.
WANG Xibo ZHOU Benhai YU Gei LI Qian 《武汉大学学报:自然科学英文版》2007,12(5):946-950
μC/OS-Ⅱ is an open source real-time kernel adopting priority preemptive schedule strategy. Aiming at the problem of μC/OS-Ⅱ failing to support homology priority tasks scheduling, an approach for solution is proposed. The basic idea is adding round-robin scheduling strategy in its original scheduler in order to schedule homology priority tasks through time slice roundrobin. Implementation approach is given in detail. Firstly, the Task Control Block (TCB) is extended. And then, a new priority index table is created, in which each index pointer points to a set of homology priority tasks. Eventually, on the basis of reconstructing μC/OS-Ⅱ real-time kernel, task scheduling module is rewritten. Otherwise, schedulability of homology task supported by modified kernel had been analyzed, and deadline formula of created homology tasks is given. By theoretical analysis and experiment verification, the modified kernel can support homology priority tasks scheduling, meanwhile, it also remains preemptive property of original μC/OS-Ⅱ. 相似文献
13.
14.
在未来空间作战中,航天器将成为重要的作战装备,同时也将是敌对双方重点打击的对象.通过投影形状确定航天器类型或者航天器毁伤部位的毁伤度,可以为及时采取相应的措施提供决策依据.结合航天器的三维空间实体描述,给出了航天器投影多边形的误差带模型以及航天器毁伤部位投影多边形的面积误差模型.通过实例仿真分析得出,通过构建航天器及其毁伤部位多方位投影形状数据库,建立多边形面元不确定性模型,结合先进的计算机技术和人工智能技术,确定航天器类型及其可能毁伤部位的毁伤度是可行的. 相似文献
16.
总线周期精确事务级建模能解决系统设计中的仿真精度和速度之间的矛盾。以北桥中的总线设计为背景,采用SystemC中接口方法调用的原理,实现了对Wishbone总线的周期精确事物级建模,并给出了具体的实现方法和测试方法,具有一定的通用性。 相似文献
17.
权立枝 《科技情报开发与经济》2006,16(20):189-191
指出山西民营企业品牌塑造与价值提升是山西民营企业发展以及山西经济发展的需要,并从多方面探讨了这种需要的有利之处。 相似文献
18.
The interleukin 1β (IL-1β) cDNA was cloned from the red seabream (Pagrus major) by homology cloning strategy. A cDNA fragment was amplified by PCR using two degenerated primers, which were designed according to the conserved regions of other known IL-1β sequences, and elongated by 3' ends and 5' ends RACE PCR to get the full length coding sequence of red seabream IL-1β (RS IL-1β). The sequence contained 1252 nucleotides that included a 5' untranslated region (UTR) of 84bp, a 3' UTR of 410 bp and an open reading frame (ORF) of 759 nucleotides which could be translated into a putative peptide of 253 amino acids with molecular weight of 28.6 kD and putative isoelectric point pI of 5.29. The deduced peptide contained two potential N-glycosylation sites and an identifiable IL1 family signature, but lacked the signal peptide and the clear ICE cut site, which were common in other nonmammalian IL-1β genes. The RS IL-1β had the highest homology with piscine IL-1β according to phylogenetic tree analysis. 相似文献
19.
20.
本介绍了一种利用电视机遥控器作为单片机输入键秀的接口原理和方法,并讨论了如何使用单片机来指令的解码,实践证明这种接口方式可以节省单片机的硬件资源,缩小单片机系统的体积,同时也方便了单片机的操作,尤其是某些需要远距离操作场合。 相似文献