全文获取类型
收费全文 | 1479401篇 |
免费 | 25850篇 |
国内免费 | 6999篇 |
专业分类
电工技术 | 34312篇 |
综合类 | 6510篇 |
化学工业 | 269507篇 |
金属工艺 | 63773篇 |
机械仪表 | 41971篇 |
建筑科学 | 45537篇 |
矿业工程 | 11420篇 |
能源动力 | 50174篇 |
轻工业 | 109972篇 |
水利工程 | 14800篇 |
石油天然气 | 37512篇 |
武器工业 | 186篇 |
无线电 | 195827篇 |
一般工业技术 | 280240篇 |
冶金工业 | 148410篇 |
原子能技术 | 33885篇 |
自动化技术 | 168214篇 |
出版年
2021年 | 15507篇 |
2020年 | 11804篇 |
2019年 | 14558篇 |
2018年 | 15348篇 |
2017年 | 14685篇 |
2016年 | 21030篇 |
2015年 | 17272篇 |
2014年 | 28616篇 |
2013年 | 87596篇 |
2012年 | 34692篇 |
2011年 | 46764篇 |
2010年 | 41885篇 |
2009年 | 50363篇 |
2008年 | 43808篇 |
2007年 | 40811篇 |
2006年 | 44167篇 |
2005年 | 38729篇 |
2004年 | 40979篇 |
2003年 | 40969篇 |
2002年 | 40072篇 |
2001年 | 36839篇 |
2000年 | 35350篇 |
1999年 | 34127篇 |
1998年 | 40117篇 |
1997年 | 36325篇 |
1996年 | 33481篇 |
1995年 | 29692篇 |
1994年 | 27995篇 |
1993年 | 27842篇 |
1992年 | 26072篇 |
1991年 | 23100篇 |
1990年 | 23414篇 |
1989年 | 22424篇 |
1988年 | 20960篇 |
1987年 | 19304篇 |
1986年 | 18687篇 |
1985年 | 21991篇 |
1984年 | 22284篇 |
1983年 | 20249篇 |
1982年 | 19201篇 |
1981年 | 19273篇 |
1980年 | 17852篇 |
1979年 | 18481篇 |
1978年 | 17703篇 |
1977年 | 17197篇 |
1976年 | 17762篇 |
1975年 | 15966篇 |
1974年 | 15538篇 |
1973年 | 15589篇 |
1972年 | 13039篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
271.
272.
273.
D. A. Kudryashov A. S. Gudovskikh A. M. Mozharov A. D. Bol’shakov I. S. Mukhin Zh. I. Alferov 《Technical Physics Letters》2015,41(12):1120-1123
Design and operation modes of double-junction monolithic lattice-matched solar cells based on the ZnSiP2/Si system of materials have been calculated. The effect of the photoactive region thickness and minority carrier lifetime in ZnSiP2 layers on the efficiency of conversion of the incident solar light energy into electrical power was determined. It is shown that solar cells based on ZnSiP2/Si heterostructures can provide efficiencies of 28.8% at AM1.5D, 100 mW/cm2, and 33.3% at AM1.5D, 200 W/cm2. 相似文献
274.
Temperature history can have a significant effect on the strength of water-saturated chalk.In this study,hydrostatic stress cycles are applied to understand the mechanical response of chalk samples exposed to temperature cycling between each stress cycle,compared to the samples tested at a constant temperature.The total accumulated strain during a stress cycle and the irreversible strain are reported.Chalk samples from Kansas(USA)and Mons(Belgium),with different degrees of induration(i.e.amount of contact cementation),were used.The samples were saturated with equilibrated water(polar)and nonpolar Isopar H oil to quantify water weakening.All samples tested during 10 stress cycles with varying temperature(i.e.temperature cycled in between each stress cycle)accumulated more strain than those tested at constant temperatures.All the stress cycles were performed at 30℃.The two chalk types behaved similarly when saturated with Isopar H oil,but differently when saturated with water.When saturated with water,the stronger Kansas chalk accumulated more total strain and more irreversible strain within each stress cycle than the weaker Mons chalk. 相似文献
275.
Sakizadeh Mohamad Mohamed Mohamed M. A. Klammler Harald 《Water Resources Management》2019,33(4):1425-1437
Water Resources Management - Overexploitation of groundwater in the Malayer Plain has resulted in a continuous decline of groundwater levels over recent years with associated risks to water... 相似文献
276.
Wireless Networks - The existing medium access control (MAC) protocols are not able to utilize the full opportunities from power-domain non-orthogonal multiple access (NOMA) technique in wireless... 相似文献
277.
Journal of Communications Technology and Electronics - A new method is proposed to represent electromagnetic field in inhomogeneous 2D periodic medium (PM) as a discrete set of amplitude vectors... 相似文献
278.
Hashim A.
Hashim 《国际强度与非线性控制杂志
》2020,30(10):3848-3870
》2020,30(10):3848-3870
This paper introduces two novel nonlinear stochastic attitude estimators developed on the Special Orthogonal Group with the tracking error of the normalized Euclidean distance meeting predefined transient and steady‐state characteristics. The tracking error is confined to initially start within a predetermined large set such that the transient performance is guaranteed to obey dynamically reducing boundaries and decrease smoothly and asymptotically to the origin in probability from almost any initial condition. The proposed estimators produce accurate attitude estimates with remarkable convergence properties using measurements obtained from low‐cost inertial measurement units. The estimators proposed in continuous form are complemented by their discrete versions for the implementation purposes. The simulation results illustrate the effectiveness and robustness of the proposed estimators against uncertain measurements and large initialization error, whether in continuous or discrete form. 相似文献
279.
Multicellular tumor spheroid models (MCTS) are often coined as 3D in vitro models that can mimic the microenvironment of tissues. MCTS have gained increasing interest in the nano‐biotechnology field as they can provide easily accessible information on the performance of nanoparticles without using animal models. Considering that many countries have put restrictions on animals testing, which will only tighten in the future as seen by the recent developments in the Netherlands, 3D models will become an even more valuable tool. Here, an overview on MCTS is provided, focusing on their use in cancer research as most nanoparticles are tested in MCTS for treatment of primary tumors. Thereafter, various types of nanoparticles—from self‐assembled block copolymers to inorganic nanoparticles, are discussed. A range of physicochemical parameters including the size, shape, surface chemistry, ligands attachment, stability, and stiffness are found to influence nanoparticles in MCTS. Some of these studies are complemented by animal studies confirming that lessons from MCTS can in part predict the behaviour in vivo. In summary, MCTS are suitable models to gain additional information on nanoparticles. While not being able to replace in vivo studies, they can bridge the gap between traditional 2D in vitro studies and in vivo models. 相似文献
280.
In order to improve the process effectiveness and joint quality, ultrasonic vibrations were integrated with friction stir lap welding. Effect of ultrasonic exertion on the process and joint quality of AA 6061-T6 were investigated. Upon ultrasonic exertion, joints owned larger effective lap width, shorter hooks and improved strength. Weld fracture mode changed from a ductile–brittle mixed mode to a more ductile mode while the fracture path shifted from lap interface to beyond the stir zone. Material flow and interface defects were characterised using lap welded dissimilar aluminium alloy joints. Ultrasonic vibration improved the material flow and reduced the interfacial defects. Variations in failure load of joints were found in accordance with the variations in material flow and interfacial defects. 相似文献