全文获取类型
收费全文 | 293327篇 |
免费 | 23324篇 |
国内免费 | 15086篇 |
专业分类
电工技术 | 23702篇 |
技术理论 | 52篇 |
综合类 | 38963篇 |
化学工业 | 29656篇 |
金属工艺 | 10414篇 |
机械仪表 | 15111篇 |
建筑科学 | 41247篇 |
矿业工程 | 16151篇 |
能源动力 | 10130篇 |
轻工业 | 14753篇 |
水利工程 | 24064篇 |
石油天然气 | 12015篇 |
武器工业 | 2666篇 |
无线电 | 18748篇 |
一般工业技术 | 19716篇 |
冶金工业 | 16064篇 |
原子能技术 | 2977篇 |
自动化技术 | 35308篇 |
出版年
2024年 | 921篇 |
2023年 | 2861篇 |
2022年 | 5522篇 |
2021年 | 6674篇 |
2020年 | 7081篇 |
2019年 | 5915篇 |
2018年 | 5502篇 |
2017年 | 6784篇 |
2016年 | 8049篇 |
2015年 | 9045篇 |
2014年 | 16759篇 |
2013年 | 14788篇 |
2012年 | 19726篇 |
2011年 | 20955篇 |
2010年 | 16450篇 |
2009年 | 17227篇 |
2008年 | 16115篇 |
2007年 | 20883篇 |
2006年 | 19740篇 |
2005年 | 17195篇 |
2004年 | 14731篇 |
2003年 | 13301篇 |
2002年 | 10902篇 |
2001年 | 9228篇 |
2000年 | 7811篇 |
1999年 | 6381篇 |
1998年 | 4824篇 |
1997年 | 4170篇 |
1996年 | 3907篇 |
1995年 | 3328篇 |
1994年 | 2922篇 |
1993年 | 2165篇 |
1992年 | 1897篇 |
1991年 | 1396篇 |
1990年 | 1201篇 |
1989年 | 1082篇 |
1988年 | 858篇 |
1987年 | 591篇 |
1986年 | 448篇 |
1985年 | 370篇 |
1984年 | 351篇 |
1983年 | 247篇 |
1982年 | 226篇 |
1981年 | 181篇 |
1980年 | 139篇 |
1979年 | 120篇 |
1978年 | 68篇 |
1977年 | 76篇 |
1976年 | 56篇 |
1975年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
Evaluating the Wisdom of Strangers: The Perceived Credibility of Online Consumer Reviews on Yelp 下载免费PDF全文
This study examined the effects of review valence, the reviewer profile, and the receiver's familiarity with the platform (user/nonuser) on the perceived credibility of a review on Yelp.com and on the receiver's attitude toward the reviewed object. The results demonstrated a difference in cue‐taking between users and nonusers. For users, there was an interaction effect of 2 profile cues (number of friends and number of reviews) on competence. Users interpreted the cues in combination, whereas non‐users were not influenced by them. The friends × reviews × platform familiarity interaction indirectly affected attitude through competence. Further, review valence was positively associated with perceived credibility and attitude. The findings support and extend the social information processing theory and cue combination literature. 相似文献
992.
Orientations of proteins in the membranes are crucial to their function and stability. Unfortunately the exact positions of these proteins in the lipid bilayer are mostly undetermined. Here, the spatial orientation of membrane proteins within the lipid membrane was evaluated using a Poisson–Boltzmann solvent continuum approach to calculate the electrostatic free energy of the protein solvation at various orientations in an implicit bilayer. The solvation energy was obtained by computing the difference in electrostatic energies of the protein in water and in lipid/water environments, treating each as an implicit solvent model. The optimal position of transmembrane proteins (TMP) in a lipid bilayer is identified by the minimum in the “downhill” pathway of the solvation energy landscape. The energy landscape pattern was considerably conserved in various TMP classes. Evaluation of the position of 1060 membrane proteins from the orientations of proteins in membranes (OPM) database revealed that most of the polytopic and β-barrel proteins were in good agreement with those of the OPM database. The study provides a useful scheme for estimating the membrane solvation energy made by lipid-exposed amino acids in membrane proteins. In addition, our results tested with the bacterial potassium channel model demonstrated the potential usefulness of the approach in assessing the quality of membrane protein models. The present approach should be applicable for constructing transmembrane proteins–lipid configuration suitable for membrane protein simulations and will have utility for the structural modeling of membrane proteins. 相似文献
993.
This paper investigates epidemic dynamics over dynamic networks via the approach of semi-tensor product of matrices. First, a formal susceptible-infected-susceptible epidemic dynamic model over dynamic networks (SISED-DN) is given. Second, based on a class of determinate co-evolutionary rule, the matrix expressions are established for the dynamics of individual states and network topologies, respectively. Then, all possible final spreading equilibria are obtained for any given initial epidemic state and network topology by the matrix expression. Third, a sufficient and necessary condition of the existence of state feedback vaccination control is presented to make every individual susceptible. The study of illustrative examples shows the effectiveness of our new results. 相似文献
994.
磁共振弹性成像技术可以量化人体组织弹性属性。磁共振弹性成像的弹性波激励方式有稳态和瞬态两种。由于人体组织的特殊性,弹性波在组织中传播情况复杂。文章通过建立一个磁共振弹性成像的有限元仿真平台,对瞬态磁共振弹性成像技术进行数值建模,并针对瞬态磁共振弹性成像设计了基于到达时间的弹性重构算法。通过 MATLAB编程处理仿真得到的瞬态磁共振弹性成像数据,最终导出瞬态磁共振弹性成像的结果。数值平台仿真的稳态和瞬态磁共振弹性成像对比实验表明,瞬态磁共振弹性成像对于反射和衍射具有较好的抗干扰能力,对于深处的小尺寸组织,具有较高的灵敏度和较好的精准度,而基于到达时间的算法能够实现瞬态磁共振弹性成像的弹性重构。 相似文献
995.
本文研究了不同厚度淤沙对混凝土重力坝地震响应的影响以及一定厚度层状淤沙的不同分布形式对混凝土重力坝的地震响应的影响。基于饱和多孔液固两相介质的压力波动方程,设层状淤沙各层厚度不同,将层状淤沙分为三种不同分布形式,在每种分布形式每层的物理参数相同和物理参数不同两种情况下,确定了淤沙对混凝土重力坝地震响应的影响大小。通过算例分析表明,相同物理性质不同的分布形式对地震响应的影响不显著,而不同的分布形式对坝体的地震响应影响较大。 相似文献
996.
回顾了南水北调中线工程水价形成过程,指出了现行水价方案存在的问题。对真实水价形成机制进行了论述,认为制定水价应遵循公平负担、成本回收、合理利润、价格调整和水资源配置原则;同一水质、同类用户、不同水源的用水,应执行统一的水价;不同行业实行不同水价。鼓励受水区各省市间开展水量配额交易,最大限度发挥工程效益。供水水价既要反映水资源的稀缺程度和水环境治理成本,促进资源的节约使用和环境保护,提高全民节水意识,又要保证供水管理单位能够正常持续经营,具备自我积累、自我发展的能力。 相似文献
997.
基于线性地基反力法和土体的弹塑性本构关系,对桩顶水平反力系数不为零时的水平受荷桩进行了研究,给出了桩顶土屈服临界荷载(水平力、弯矩)的耦合关系式。研究结果表明,当荷载大于临界荷载时,桩顶土发生塑性屈服,其塑性屈服深度随荷载的增加而增加,但其塑性区扩展速率随桩顶荷载的增加而逐渐减小。给出了弹性区与塑性区桩内力耦合的矩阵方程及其迭代求解格式;利用曲面拟合软件给出了塑性区换算深的计算公式。通过工程算例验证,证明该方法可靠快捷,便于手算,值得推广。
相似文献
998.
999.
Leyla Dogruel Sven Joeckel Nicholas D. Bowman 《Behaviour & Information Technology》2015,34(11):1052-1063
Research on elderly people's ICT acceptance and use often relies on the technology acceptance model (TAM) framework, but has been mostly limited to task-oriented uses. This article expands approaches in technology acceptance and use by developing a model to explain entertainment-related uses of new media technology by elderly people. On a theoretical level, we expand the TAM perspective by adding concepts that act as barriers and/or facilitators of technology acceptance, namely technophobia, self-efficacy and previous experience and expertise with technology. We develop an expanded TAM by testing the role of these concepts in two studies on entertainment media technology. In Study 1, we investigate behavioural intention to use 3D cinema among N?=?125 German elderly media users (Age 50+). In Study 2, we focus the actual use of a computer game simulation by N?=?115 German and US elderly media users (Age 50+). Findings in both studies point towards the central role of perceived usefulness, here modelled as enjoyment, as the reason for elderly people's use and acceptance of entertainment media technology. Perceived ease of use is seen as a precondition for enjoyment, particularly for interactive media. 相似文献
1000.
J. Kratt M. Spicker A. Guayaquil M. Fiser S. Pirk O. Deussen J. C. Hart B. Benes 《Computer Graphics Forum》2015,34(2):361-372
We present a botanical simulation of secondary (cambial) tree growth coupled to a physical cracking simulation of its bark. Whereas level set growth would use a fixed resolution voxel grid, our system extends the deformable simplicial complex (DSC), supporting new biological growth functions robustly on any surface polygonal mesh with adaptive subdivision, collision detection and topological control. We extend the DSC with temporally coherent texturing, and surface cracking with a user‐controllable biological model coupled to the stresses introduced by the cambial growth model. 相似文献