全文获取类型
收费全文 | 319篇 |
免费 | 9篇 |
国内免费 | 11篇 |
专业分类
系统科学 | 3篇 |
丛书文集 | 1篇 |
教育与普及 | 9篇 |
现状及发展 | 8篇 |
研究方法 | 11篇 |
综合类 | 307篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 15篇 |
2016年 | 15篇 |
2015年 | 22篇 |
2014年 | 6篇 |
2013年 | 11篇 |
2012年 | 12篇 |
2011年 | 17篇 |
2010年 | 17篇 |
2009年 | 28篇 |
2008年 | 23篇 |
2007年 | 30篇 |
2006年 | 23篇 |
2005年 | 23篇 |
2004年 | 21篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 1篇 |
1998年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 3篇 |
1986年 | 1篇 |
排序方式: 共有339条查询结果,搜索用时 15 毫秒
1.
2.
Development ofPostgraduate Education There were only postgraduates were honored master degree from the year to in old China. While after the establishment of new China the postgraduate educationhas developed in a certain degree there were postgraduates were enrolled from to there were no postgraduates during the period of to due to the"culture revolution".…… 《广西师范大学学报(自然科学版)》2003,21(Z1):231-232
1 Development of Postgraduate Education
There were only 200 postgraduates were honored master degree from the year 1935 to 1949 in old China. While, after the establishment of new China, the postgraduate education has developed in a certain degree, there were 23,000 postgraduates were enrolled from 1950 to 1965, and there were no postgraduates during the period of 1966 to 1977 due to the "culture revolution". 相似文献
3.
In modernindustry thin film on the substratc has much important role to decide the properties ofproduct especially for electrical optical wear-resistant etc production. There aresome technical methods to prepare thin film including plasma spray physical vapordeposition 《广西师范大学学报(自然科学版)》2003,21(Z4):284-285
In modern industry,thin film on the substratc has much important role to decide the properties of product, especially for electrical, optical and wear-resistant etc, production. There are some technical methods to prepare thin film,including plasma spray,physical vapor deposition (PVD),chemical vapor deposition (CVD) and sol-gel,etc. Among of them,sol-gel method has been developed a popular tech nique for preparing thin films. 相似文献
4.
在流体相平衡理论基础上,综合考虑压力、温度的相互影响及动能变化的影响,同时将流体偏差系数考虑为压力和温度的函数,建立了新的凝析气井井筒压力分布计算模型.计算时将井筒分成若干段,在每段中进行迭代求解.新的压力计算模型与常用的平均温度和平均偏差系数计算方法的实例对比表明,新计算模型具有较高的精度,可用于深度超过4000 m的高温高压凝析气井井筒压力分布计算. 相似文献
5.
探讨气顶油藏屏障注水提高油藏开发效果的机理,并优化屏障注水参数。以国外某气顶油藏的储层特征为基础,通过油藏数值模拟方法,对气顶油藏屏障注水运移规律及作用机理进行分析。结果表明,屏障形成前,屏障水以径向流的运移规律向气顶和油环流动,分别补充油区与气区地层能量,延长开发年限,有效抑制气顶膨胀能,减缓油气界面运移速度,降低油井生产油气比,提高油井开发效果。当屏障形成后,屏障切断油区与气区的通道,将气顶油环分为一个大气顶小油环与小气顶大油环,实现气顶油环单独开采,有效防止油气互窜。结合该油藏的开发政策,优化气顶油环屏障注水参数及开发方式,分别从油侵损失量和气顶油环采出程度两个方面综合考虑,最优屏障井位置随着注采比的增加逐渐往气顶方向移动,并最终稳定在一定位置。 相似文献
6.
Five advanced high-strength transformation-induced plasticity(TRIP) steels with different chemical compositions were studied to correlate the retained austenite and nonmetallic inclusion content with their physical properties and the characteristics of the resistance spot welding nuggets. Electrical and thermal properties and equilibrium phases of TRIP steels were predicted using the JMatPro? software. Retained austenite and nonmetallic inclusions were quantified by X-ray diffraction and saturation magnetization techniques. The nonmetallic inclusions were characterized by scanning electron microscopy. The results show that the contents of Si, C, Al, and Mn in TRIP steels increase both the retained austenite and the nonmetallic inclusion contents. We found that nonmetallic inclusions affect the thermal and electrical properties of the TRIP steels and that the differences between these properties tend to result in different cooling rates during the welding process. The results are discussed in terms of the electrical and thermal properties determined from the chemical composition and their impact on the resistance spot welding nuggets. 相似文献
7.
8.
Cdk1 is sufficient to drive the mammalian cell cycle 总被引:1,自引:0,他引:1
Santamaría D Barrière C Cerqueira A Hunt S Tardy C Newton K Cáceres JF Dubus P Malumbres M Barbacid M 《Nature》2007,448(7155):811-815
9.
Aeschlimann M Bauer M Bayer D Brixner T García de Abajo FJ Pfeiffer W Rohmer M Spindler C Steeb F 《Nature》2007,446(7133):301-304
Adaptive shaping of the phase and amplitude of femtosecond laser pulses has been developed into an efficient tool for the directed manipulation of interference phenomena, thus providing coherent control over various quantum-mechanical systems. Temporal resolution in the femtosecond or even attosecond range has been demonstrated, but spatial resolution is limited by diffraction to approximately half the wavelength of the light field (that is, several hundred nanometres). Theory has indicated that the spatial limitation to coherent control can be overcome with the illumination of nanostructures: the spatial near-field distribution was shown to depend on the linear chirp of an irradiating laser pulse. An extension of this idea to adaptive control, combining multiparameter pulse shaping with a learning algorithm, demonstrated the generation of user-specified optical near-field distributions in an optimal and flexible fashion. Shaping of the polarization of the laser pulse provides a particularly efficient and versatile nano-optical manipulation method. Here we demonstrate the feasibility of this concept experimentally, by tailoring the optical near field in the vicinity of silver nanostructures through adaptive polarization shaping of femtosecond laser pulses and then probing the lateral field distribution by two-photon photoemission electron microscopy. In this combination of adaptive control and nano-optics, we achieve subwavelength dynamic localization of electromagnetic intensity on the nanometre scale and thus overcome the spatial restrictions of conventional optics. This experimental realization of theoretical suggestions opens a number of perspectives in coherent control, nano-optics, nonlinear spectroscopy, and other research fields in which optical investigations are carried out with spatial or temporal resolution. 相似文献
10.
Genome sequence and analysis of the tuber crop potato 总被引:11,自引:0,他引:11
Potato Genome Sequencing Consortium Xu X Pan S Cheng S Zhang B Mu D Ni P Zhang G Yang S Li R Wang J Orjeda G Guzman F Torres M Lozano R Ponce O Martinez D De la Cruz G Chakrabarti SK Patil VU Skryabin KG Kuznetsov BB Ravin NV Kolganova TV Beletsky AV Mardanov AV Di Genova A Bolser DM Martin DM Li G Yang Y Kuang H Hu Q Xiong X Bishop GJ Sagredo B Mejía N Zagorski W Gromadka R Gawor J Szczesny P Huang S Zhang Z Liang C He J Li Y He Y Xu J Zhang Y Xie B Du Y Qu D Bonierbale M Ghislain M 《Nature》2011,475(7355):189-195
Potato (Solanum tuberosum L.) is the world's most important non-grain food crop and is central to global food security. It is clonally propagated, highly heterozygous, autotetraploid, and suffers acute inbreeding depression. Here we use a homozygous doubled-monoploid potato clone to sequence and assemble 86% of the 844-megabase genome. We predict 39,031 protein-coding genes and present evidence for at least two genome duplication events indicative of a palaeopolyploid origin. As the first genome sequence of an asterid, the potato genome reveals 2,642 genes specific to this large angiosperm clade. We also sequenced a heterozygous diploid clone and show that gene presence/absence variants and other potentially deleterious mutations occur frequently and are a likely cause of inbreeding depression. Gene family expansion, tissue-specific expression and recruitment of genes to new pathways contributed to the evolution of tuber development. The potato genome sequence provides a platform for genetic improvement of this vital crop. 相似文献