全文获取类型
收费全文 | 10080篇 |
免费 | 306篇 |
国内免费 | 719篇 |
专业分类
系统科学 | 479篇 |
丛书文集 | 256篇 |
教育与普及 | 204篇 |
理论与方法论 | 35篇 |
现状及发展 | 53篇 |
研究方法 | 38篇 |
综合类 | 10038篇 |
自然研究 | 2篇 |
出版年
2024年 | 39篇 |
2023年 | 77篇 |
2022年 | 189篇 |
2021年 | 186篇 |
2020年 | 132篇 |
2019年 | 77篇 |
2018年 | 109篇 |
2017年 | 116篇 |
2016年 | 149篇 |
2015年 | 288篇 |
2014年 | 391篇 |
2013年 | 375篇 |
2012年 | 421篇 |
2011年 | 449篇 |
2010年 | 451篇 |
2009年 | 502篇 |
2008年 | 605篇 |
2007年 | 550篇 |
2006年 | 474篇 |
2005年 | 465篇 |
2004年 | 380篇 |
2003年 | 405篇 |
2002年 | 609篇 |
2001年 | 580篇 |
2000年 | 393篇 |
1999年 | 465篇 |
1998年 | 269篇 |
1997年 | 284篇 |
1996年 | 278篇 |
1995年 | 227篇 |
1994年 | 220篇 |
1993年 | 202篇 |
1992年 | 168篇 |
1991年 | 138篇 |
1990年 | 123篇 |
1989年 | 112篇 |
1988年 | 106篇 |
1987年 | 59篇 |
1986年 | 29篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
771.
新一代开放系统及互操作性研究 总被引:2,自引:0,他引:2
经历 2 0世纪 90年代的持续实践 ,采用“开放系统”的思想来集成大型的计算机系统已成为技术界不争的事实。然而 ,技术的发展使得传统的开放系统面临严峻的挑战 ,需要新的标准、技术来使开放系统体现高度的智能协作性及移动性。基于完善的开放系统的实际形成有赖于“互操作性”的实现这一原因 ,以互操作性为研究对象 ,以移动agent为研究工具 ,探讨了新一代开放系统实现机制以及未来发展的前景。 相似文献
772.
教育是产业,是个人(或家庭)与国家为主要投资主体的产业,是增加社会效用和个人满足感的部门。对教育进行投资的过程就是人力资本和物力资本的积累过程。居民教育支出的主要功能,是实现未来收益的、积累”,而非“消费”。国家和个人或家庭确定自己的投资计划,定位自己的成本--收益曲线的过程,实际上就是国家政府和个人通过党校进行博弈的过程。教育的边际效用是递增的,教育“产业化”不等于“市场化”。国家应加大对初、中等教育的投资力度,建立新型的政府与民间合作投资的“混合制度”,以促进教育产业的健康发展。 相似文献
773.
基于对等网络的信任模型 总被引:4,自引:0,他引:4
在Client/Server网络架构得到普遍应用的格局中,对等网络却异军突起迅速发展。针对这种新兴架构提出了与传统架构不同的一种安全信任模型。它依据网络的推荐值建立节点间的信任关系,更好地保证网络的安全性和避免恶意攻击。给出了求解信任值的数学模型和具体算法,并对信任模型的安全性能进行了理论评测。 相似文献
774.
对履带式推土机行走机构的振动特性进行测试 ,建立起推土机缓冲系统模型 ,经对模型特性参数对传递率影响的分析 ,确定出参数的合理值域。把阻尼材料诺模图曲线数字化 ,做到了计算机对诺模图动态曲线的自动查询 ,实现了阻尼缓冲结构的动态优化。掌握了阻尼缓冲结构的设计理论和方法 ,已应用于 2 4 2kW履带式推土机粘弹性悬挂机构的开发。 相似文献
775.
Khalifah P Nelson KD Jin R Mao ZQ Liu Y Huang Q Gao XP Ramirez AP Cava RJ 《Nature》2001,411(6838):669-671
Understanding the complexities of electronic and magnetic ground states in solids is one of the main goals of solid-state physics. Transition-metal oxides have proved to be particularly fruitful in this regard, especially for those materials with the perovskite structure, where the special characteristics of transition-metal-oxygen orbital hybridization determine their properties. Ruthenates have recently emerged as an important family of perovskites because of the unexpected evolution from high-temperature ferromagnetism in SrRuO3 to low-temperature superconductivity in Sr2RuO4 (refs 1, 2). Here we show that a ruthenate in a different structural family, La4Ru6O19, displays a number of highly unusual properties, most notably non-Fermi-liquid behaviour. The properties of La4Ru6O19 have no analogy among the thousands of previously characterized transition-metal oxides. Instead, they resemble those of CeCu6-xAux-a widely studied f-electron-based heavy fermion intermetallic compound that is often considered as providing the best example of non-Fermi-liquid behaviour. In the ruthenate, non-Fermi-liquid behaviour appears to arise from just the right balance between the interactions of localized electronic states derived from Ru-Ru bonding and delocalized states derived from Ru-O hybridization. 相似文献
776.
基于ACIS ,以InteSolid作为开发平台 ,运用数据库与参数化相结合的方法 ,采用“同构树”的装配模型 ,实现了注塑模标准模架的三维参数化设计 相似文献
777.
Mechanism of silk processing in insects and spiders 总被引:1,自引:0,他引:1
Silk spinning by insects and spiders leads to the formation of fibres that exhibit high strength and toughness. The lack of understanding of the protein processing in silk glands has prevented the recapitulation of these properties in vitro from reconstituted or genetically engineered silks. Here we report the identification of emulsion formation and micellar structures from aqueous solutions of reconstituted silkworm silk fibroin as a first step in the process to control water and protein-protein interactions. The sizes (100-200 nm diameter) of these structures could be predicted from hydrophobicity plots of silk protein primary sequence. These micelles subsequently aggregated into larger 'globules' and gel-like states as the concentration of silk fibroin increased, while maintaining solubility owing to the hydrophilic regions of the protein interspersed among the larger hydrophobic regions. Upon physical shearing or stretching structural transitions, increased birefringence and morphological alignment were demonstrated, indicating that this process mimics the behaviour of similar native silk proteins in vivo. Final morphological features of these silk materials are similar to those observed in native silkworm fibres. 相似文献
778.
Melanoma mouse model implicates metabotropic glutamate signaling in melanocytic neoplasia 总被引:3,自引:0,他引:3
Pollock PM Cohen-Solal K Sood R Namkoong J Martino JJ Koganti A Zhu H Robbins C Makalowska I Shin SS Marin Y Roberts KG Yudt LM Chen A Cheng J Incao A Pinkett HW Graham CL Dunn K Crespo-Carbone SM Mackason KR Ryan KB Sinsimer D Goydos J Reuhl KR Eckhaus M Meltzer PS Pavan WJ Trent JM Chen S 《Nature genetics》2003,34(1):108-112
779.
A real-size experiment on 11 tubes was done to study the performance of centrifugal concrete-filled steel tubes under bending and torsion. This paper first introduces the relevant operating method, equipment, subjects and processes. The factors that affect deformation and stiffness and the break mechanism under different loading were studied. Experimental stress analysis showed that the values of practical critical stress of steel tubes accorded well with the MISES Yielding Rule. The correlative equation (on the bearing capacity of a structural member under bending and torsion) deduced in this study may provide valuable reference for the desima of this structural member. 相似文献
780.
Geochronology of source materials from high-pressure and ultrahigh-pressure metamorphic rocks in Jurassic sedimentary rocks of Hefei Basin 总被引:4,自引:0,他引:4
LI Renwei SANG Haiqing ZHANG Renhu CHU Zhuyin LI Shuangyin JIN Fuquan & JIANG Maosheng . Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Department of Resource Environment Sciences Hefei Industrial University Hefei China 《科学通报(英文版)》2003,48(6):605-610
Eclogite cobbles were discovered by Wang et al. (2001) in the Fenghuangtai Formation of the northern margin of Dabie Mountains in the Dushan area of Anhui Province, China[1]. They proposed that after the formation during the Triassic, the high-pressure (HP) and ultra-high-pressure (UHP) metamorphic rocks reached the sur-face through exhumation and uplifting before the late Ju-rassic. However, they have not provided any evidence about isotopic ages. One kind of cobbles of HP-UHP rocks w… 相似文献