全文获取类型
收费全文 | 112325篇 |
免费 | 13846篇 |
国内免费 | 7254篇 |
专业分类
电工技术 | 9184篇 |
技术理论 | 3篇 |
综合类 | 11886篇 |
化学工业 | 12595篇 |
金属工艺 | 8406篇 |
机械仪表 | 11259篇 |
建筑科学 | 12823篇 |
矿业工程 | 6306篇 |
能源动力 | 6746篇 |
轻工业 | 1823篇 |
水利工程 | 4253篇 |
石油天然气 | 5872篇 |
武器工业 | 3822篇 |
无线电 | 8165篇 |
一般工业技术 | 10468篇 |
冶金工业 | 3101篇 |
原子能技术 | 1742篇 |
自动化技术 | 14971篇 |
出版年
2024年 | 284篇 |
2023年 | 1640篇 |
2022年 | 3452篇 |
2021年 | 4029篇 |
2020年 | 4152篇 |
2019年 | 2959篇 |
2018年 | 2902篇 |
2017年 | 3871篇 |
2016年 | 4575篇 |
2015年 | 5001篇 |
2014年 | 7747篇 |
2013年 | 7416篇 |
2012年 | 9089篇 |
2011年 | 10009篇 |
2010年 | 7017篇 |
2009年 | 7105篇 |
2008年 | 6655篇 |
2007年 | 8147篇 |
2006年 | 7038篇 |
2005年 | 5694篇 |
2004年 | 4765篇 |
2003年 | 3804篇 |
2002年 | 3061篇 |
2001年 | 2587篇 |
2000年 | 2038篇 |
1999年 | 1691篇 |
1998年 | 1296篇 |
1997年 | 1028篇 |
1996年 | 873篇 |
1995年 | 728篇 |
1994年 | 596篇 |
1993年 | 420篇 |
1992年 | 341篇 |
1991年 | 290篇 |
1990年 | 224篇 |
1989年 | 226篇 |
1988年 | 151篇 |
1987年 | 82篇 |
1986年 | 84篇 |
1985年 | 51篇 |
1984年 | 60篇 |
1983年 | 40篇 |
1982年 | 29篇 |
1981年 | 20篇 |
1980年 | 26篇 |
1979年 | 21篇 |
1977年 | 6篇 |
1959年 | 28篇 |
1955年 | 5篇 |
1951年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
21.
The calcium pump (sarco/endoplasmic reticulum Ca2+-ATPase, SERCA) plays a major role in calcium homeostasis in muscle cells by clearing cytosolic Ca2+ during muscle relaxation. Active Ca2+ transport by SERCA involves the structural transition from a low-Ca2+ affinity E2 state toward a high-Ca2+ affinity E1 state of the pump. This structural transition is accompanied by the countertransport of protons to stabilize the negative charge and maintain the structural integrity of the transport sites and partially compensate for the positive charges of the two Ca2+ ions passing through the membrane. X-ray crystallography studies have suggested that a hydrated pore located at the C-terminal domain of SERCA serves as a conduit for proton countertransport, but the existence and function of this pathway have not yet been fully characterized. We used atomistic simulations to demonstrate that in the protonated E2 state and the absence of initially bound water molecules, the C-terminal pore becomes hydrated in the nanosecond timescale. Hydration of the C-terminal pore is accompanied by the formation of water wires that connect the transport sites with the cytosol. Water wires are known as ubiquitous proton-transport devices in biological systems, thus supporting the notion that the C-terminal domain serves as a conduit for proton release. Additional simulations showed that the release of a single proton from the transport sites induces bending of transmembrane helix M5 and the interaction between residues Arg762 and Ser915. These structural changes create a physical barrier against full hydration of the pore and prevent the formation of hydrogen-bonded water wires once proton transport has occurred through this pore. Together, these findings support the notion that the C-terminal proton release pathway is a functional element of SERCA and also provide a mechanistic model for its operation in the catalytic cycle of the pump. 相似文献
22.
23.
为了研究综采工作面巷道内瓦斯运移规律,摸清瓦斯流动的状态,采用理论分析、数值模拟和现场试验相结合的方法,理论分析得到了工作面风流特性及瓦斯运移规律,数值模拟得到了瓦斯异常释放后工作面瓦斯浓度分布变化情况及工作面正常工作瓦斯浓度分布,然后进行现场试验,试验结果和数值模拟结果相似。研究为工作面瓦斯治理提供了技术支持。 相似文献
24.
Amino acid modified polyaspartic acids were evaluated as calcium-scale inhibitors. Feasibility of scale inhibition experiments was analyzed by molecular dynamics simulation and Gaussian optimization, and the scale inhibition mechanism was theoretically analyzed. Scale inhibition performance was studied by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, static scale inhibition experiments, and electrochemical performance testing, which provided an experimental basis for the molecular dynamics simulation. The experimental results showed that Arg-SA-PASP has better scale inhibition and corrosion inhibition performance than His-SA-PASP. The scale inhibition effect increased with increasing concentration. Electrochemical tests indicated that Arg-SA-PASP is an excellent scale and corrosion inhibitor. 相似文献
25.
26.
隐患采空区是目前影响露天开采矿山安全生产的主要危害源之一。随着台阶开采的不断剥离,露天开采境界内各台阶与地下空区群的隔离层厚度越来越薄,随时有可能发生采空区顶板坍塌事故。考虑到露天矿采空区地质赋存条件和围岩稳固性等特征,以弓长岭露天铁矿浅层采空区为工程背景,运用现场监测和数值模拟相结合的手段综合分析了浅层采空区的稳定性。将液体静力水准地表沉降监测系统的监测数据与FLAC数值模拟结果对比,调整蠕变参数使得数值模拟的蠕变速率与现场监测结果一致,而后据此进行未来结果的预测。最终根据地表沉降数据确定的蠕变参数取值为A=1.0×10^-12、m=1.75、n=0.35。研究表明:静力水准测点地表最大沉降位移为-9.8 mm,蠕变计算结果顶板最大垂直位移约20.4 mm,应力最大值约25 MPa,综合分析显示该采空区较稳定。上述研究提供了一种基于采空区现场监测数据的数值模拟蠕变分析方法,可为类似矿山采空区稳定性分析提供借鉴。 相似文献
27.
28.
《Ceramics International》2020,46(4):4857-4863
Assessment of mechanical properties of glass/metal joints is a challenging process, especially when the application relevant conditions of the joints have to be considered in the test design. In this study, a finite element method (FEM) is implemented to analyze a torsional shear strength test designed for glass-ceramic/steel joints aiming towards solid oxide fuel/electrolysis cells application. Deviations from axial symmetry of the square flanges (ends) of respective hourglass-shaped specimens and also supporting and loading sockets of the test set-up are included in the model to simulate conditions close to reality. Undesirable tensile stress and also shear stress concentration appear at the outer edge of glass-ceramic layers, which are less for the hollow-full specimen. The simulation results show that for a specimen with either 9 mm thick square- or 6 mm thick triangular-flanges, locally enhanced tensile stresses almost disappear, resulting in a symmetric shear stress distribution. The difference between the analytically derived nominal shear strength and the real critical shear stress derived via simulation reduces with decreasing the fracture torque. 相似文献
29.
以重庆市甄子岩29号危岩体为研究对象,基于现场调查和分析解剖,建立UDEC离散元数值计算模型,对其演化变形过程进行模拟分析。研究表明,在巨大的自重作用下,由于基座岩体岩质软,岩体较破碎,且基座外侧为直立的陡崖,具有完整的临空面,从而使基座岩体易发生压缩流变及剪切流变,进而使危岩体存在滑移垮塌的危险。 相似文献
30.
目的研究蛋类礼盒包装结构的缓冲性能。方法以蛋类尺寸为基础,建立可发性聚乙烯(expandable polyethylene. EPE)缓冲单元结构和组合结构,进行静态仿真分析和实验验证,比较结构在形状、叠合层数、组合形式等参数变化时的载荷与位移。结果结构层数变化相同时,单元结构的极限载荷从143N增加到236 N,组合结构的极限载荷从224 N增加到476 N,均呈近线性增长。结论蛋类礼盒包装中,组合结构的承载能力优于单元结构,通过单元结构的组合,可满足不同蛋类的包装要求。 相似文献