全文获取类型
收费全文 | 99254篇 |
免费 | 8178篇 |
国内免费 | 4193篇 |
专业分类
电工技术 | 5572篇 |
技术理论 | 6篇 |
综合类 | 6228篇 |
化学工业 | 16240篇 |
金属工艺 | 6110篇 |
机械仪表 | 6947篇 |
建筑科学 | 7972篇 |
矿业工程 | 3349篇 |
能源动力 | 2904篇 |
轻工业 | 6251篇 |
水利工程 | 1643篇 |
石油天然气 | 7248篇 |
武器工业 | 805篇 |
无线电 | 10598篇 |
一般工业技术 | 11419篇 |
冶金工业 | 5898篇 |
原子能技术 | 1004篇 |
自动化技术 | 11431篇 |
出版年
2024年 | 352篇 |
2023年 | 1652篇 |
2022年 | 2782篇 |
2021年 | 4150篇 |
2020年 | 3225篇 |
2019年 | 2616篇 |
2018年 | 2851篇 |
2017年 | 3216篇 |
2016年 | 2990篇 |
2015年 | 4079篇 |
2014年 | 4880篇 |
2013年 | 5798篇 |
2012年 | 6298篇 |
2011年 | 6719篇 |
2010年 | 5766篇 |
2009年 | 5506篇 |
2008年 | 5363篇 |
2007年 | 5078篇 |
2006年 | 5408篇 |
2005年 | 4709篇 |
2004年 | 2990篇 |
2003年 | 2832篇 |
2002年 | 2657篇 |
2001年 | 2413篇 |
2000年 | 2330篇 |
1999年 | 2659篇 |
1998年 | 2392篇 |
1997年 | 1950篇 |
1996年 | 1815篇 |
1995年 | 1461篇 |
1994年 | 1200篇 |
1993年 | 803篇 |
1992年 | 647篇 |
1991年 | 451篇 |
1990年 | 361篇 |
1989年 | 306篇 |
1988年 | 233篇 |
1987年 | 145篇 |
1986年 | 124篇 |
1985年 | 81篇 |
1984年 | 45篇 |
1983年 | 44篇 |
1982年 | 50篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 16篇 |
1978年 | 4篇 |
1977年 | 33篇 |
1976年 | 70篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In distributed computing such as grid computing, online users submit their tasks anytime and anywhere to dynamic resources. Task arrival and execution processes are stochastic. How to adapt to the consequent uncertainties, as well as scheduling overhead and response time, are the main concern in dynamic scheduling. Based on the decision theory, scheduling is formulated as a Markov decision process (MDP). To address this problem, an approach from machine learning is used to learn task arrival and execution patterns online. The proposed algorithm can automatically acquire such knowledge without any aforehand modeling, and proactively allocate tasks on account of the forthcoming tasks and their execution dynamics. Under comparison with four classic algorithms such as Min–Min, Min–Max, Suffrage, and ECT, the proposed algorithm has much less scheduling overhead. The experiments over both synthetic and practical environments reveal that the proposed algorithm outperforms other algorithms in terms of the average response time. The smaller variance of average response time further validates the robustness of our algorithm. 相似文献
992.
Rongliang Chen Yuqi Wu Zhengzheng Yan Yubo Zhao Xiao-Chuan Cai 《Journal of scientific computing》2014,58(2):275-289
Numerical simulation of three-dimensional incompressible flows at high Reynolds number using the unsteady Navier–Stokes equations is challenging. In order to obtain accurate simulations, very fine meshes are necessary, and such simulations are increasingly important for modern engineering practices, such as understanding the flow behavior around high speed trains, which is the target application of this research. To avoid the time step size constraint imposed by the CFL number and the fine spacial mesh size, we investigate some fully implicit methods, and focus on how to solve the large nonlinear system of equations at each time step on large scale parallel computers. In most of the existing implicit Navier–Stokes solvers, segregated velocity and pressure treatment is employed. In this paper, we focus on the Newton–Krylov–Schwarz method for solving the monolithic nonlinear system arising from the fully coupled finite element discretization of the Navier–Stokes equations on unstructured meshes. In the subdomain, LU or point-block ILU is used as the local solver. We test the algorithm for some three-dimensional complex unsteady flows, including flows passing a high speed train, on a supercomputer with thousands of processors. Numerical experiments show that the algorithm has superlinear scalability with over three thousand processors for problems with tens of millions of unknowns. 相似文献
993.
In the present study, the stability condition for semi-discrete difference schemes of hyperbolic conservation laws obtained from Fourier analysis is simplified. This stability condition can be applied only to linear difference schemes with constant coefficients implemented with periodic boundary treatment. It could often give useful results for other cases, such as schemes with variable coefficients, schemes for nonperiodic problem and nonlinear problem. However, this condition usually leads to a trigonometric inequality, which makes it not convenient to use. For explicit difference schemes on uniform grids, this trigonometric inequality can be converted to polynomial form. Furthermore, if the scheme is a high-order one, the polynomial can be factorized into a simple form. Thus, it is much easier to solve than the inequality obtained directly from Fourier analysis. For compact difference schemes and conservative schemes, similar results are obtained. Some applications of this new stability criterion are shown, including judging the stability of two schemes, proving the upstream central schemes to be stable, constructing a stable upwind dissipation relation preserving (DRP) scheme and constructing an optimized weighted essentially non-oscillatory (WENO) scheme. Since WENO schemes are nonlinear schemes, the stability analysis in the present study is performed on their underlying linear schemes. According to the numerical tests, the underlying linear scheme should be stable, otherwise the corresponding WENO scheme may display instability. These applications demonstrate that this criterion is convenient and efficient for judging the linear stability of semi-discrete difference schemes and constructing stable upwind difference schemes. 相似文献
994.
995.
996.
997.
以Fe(NO3)3、煤矸石和NaOH为原料,采用沸腾回流法制得了一系列不同质量比的α-Fe2O3/煤矸石复合光催化剂。采用场发射扫描电子显微镜(FESEM)、X射线衍射仪(XRD)及紫外-可见漫反射光谱(UV-Vis DRS)等多种手段对产物做了表征。以五氯酚为目标降解物,考察了模拟太阳光照下样品的光催化效果。结果表明,将球形α-Fe2O3负载于改性煤矸石表面可有效提高其光催化活性,且α-Fe2O3/煤矸石复合光催化剂的性能与α-Fe2O3的含量有关,当α-Fe2O3与煤矸石的质量比为30∶100时,样品的光催化效果最佳,180 min内即可将五氯酚降解完全。此外,α-Fe2O3/煤矸石复合光催化剂还具有可重复使用的特点。 相似文献
998.
大掺量粉煤灰对混凝土渗透性的影响 总被引:1,自引:0,他引:1
以粉煤灰代替30%的水泥,在水胶比为0.30、0.33、0.36及0.39的情况下,分别试验了用水量及胶凝材料用量变化下混凝土的强度和渗透性。试验结果表明,与不掺粉煤灰的混凝土比较,掺粉煤灰混凝土的渗透性都明显降低,30天龄期时最大可降低至50.7%,70天时可降低至22.3%;为了获得较低的渗透性而采取较低的水胶比时,不掺粉煤灰的混凝土应用降低用水量的办法有利,掺粉煤灰的混凝土用提高总胶凝材料用量的办法更好 相似文献
999.
1000.