全文获取类型
收费全文 | 121433篇 |
免费 | 12457篇 |
国内免费 | 7042篇 |
专业分类
电工技术 | 8870篇 |
技术理论 | 12篇 |
综合类 | 9016篇 |
化学工业 | 18322篇 |
金属工艺 | 7115篇 |
机械仪表 | 8151篇 |
建筑科学 | 9622篇 |
矿业工程 | 4119篇 |
能源动力 | 3667篇 |
轻工业 | 8407篇 |
水利工程 | 2560篇 |
石油天然气 | 6503篇 |
武器工业 | 1376篇 |
无线电 | 15062篇 |
一般工业技术 | 13475篇 |
冶金工业 | 5155篇 |
原子能技术 | 1691篇 |
自动化技术 | 17809篇 |
出版年
2024年 | 718篇 |
2023年 | 2280篇 |
2022年 | 4376篇 |
2021年 | 6156篇 |
2020年 | 4620篇 |
2019年 | 3553篇 |
2018年 | 4009篇 |
2017年 | 4543篇 |
2016年 | 4002篇 |
2015年 | 5748篇 |
2014年 | 7274篇 |
2013年 | 8454篇 |
2012年 | 9612篇 |
2011年 | 10018篇 |
2010年 | 8790篇 |
2009年 | 8202篇 |
2008年 | 7879篇 |
2007年 | 7186篇 |
2006年 | 6410篇 |
2005年 | 5264篇 |
2004年 | 3542篇 |
2003年 | 2651篇 |
2002年 | 2507篇 |
2001年 | 2050篇 |
2000年 | 1912篇 |
1999年 | 1825篇 |
1998年 | 1379篇 |
1997年 | 1185篇 |
1996年 | 1080篇 |
1995年 | 848篇 |
1994年 | 708篇 |
1993年 | 473篇 |
1992年 | 369篇 |
1991年 | 296篇 |
1990年 | 234篇 |
1989年 | 184篇 |
1988年 | 158篇 |
1987年 | 86篇 |
1986年 | 84篇 |
1985年 | 43篇 |
1984年 | 39篇 |
1983年 | 30篇 |
1982年 | 34篇 |
1981年 | 25篇 |
1980年 | 29篇 |
1979年 | 21篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1959年 | 15篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
12.
13.
14.
Lei Liu Ying Kong Hong Xu Jin P. Li Jin X. Dong Zhi Lin 《Microporous and mesoporous materials》2008,115(3):624-628
A three-dimensional zinc phosphate compound with DFT topology, designated as ZnPO4-EU1, has been synthesized by an ionothermal approach from the system HF-ZnO–P2O5-choline chloride-imidazolidone. Ethylenediamine, derived from decomposition of the imidazolidone component of the deep-eutectic solvent (DES) itself, is delivered to the synthesis and serves as an appropriate template for ZnPO4-EU1. Experiments in which the synthesis conditions were varied showed that ZnPO4-EU1 may be prepared over a wide molar ratio of P/Zn = 0.55–13.0. Powder X-ray diffraction patterns have been obtained at intervals to track the crystallization process of this material. The experimental data show that Zn3(PO4)2 · 4H2O (a dense phase) was first isolated from the DES after reaction for 1 h. Subsequently, the pure phase of ZnPO4-EU1 was obtained with increasing crystallization time from 12 h to 72 h. The experimental results show that the nucleation and crystallization take place with relatively low levels of solvent degradation, demonstrating that zinc phosphate with a three-dimensional framework can be synthesized by in situ generation of an appropriate template using an unstable DES at high temperatures (150–200 °C). 相似文献
15.
Dae-Son Kim Hyun-Young Oh Hong-Yeop Song 《Communications Letters, IEEE》2008,12(3):203-205
In parallel-architecture turbo codes, the constituent interleavers must avoid memory collision. This paper proposes a collision-free interleaver structure composed of a Latin square (LS) and pre-designed interleavers. Our proposed interleavers can be easily optimized for various information block sizes and for various degrees of parallelism. Their performances were evaluated by computer simulation. 相似文献
16.
氯化铁催化合成富马酸二甲酯 总被引:9,自引:0,他引:9
氯化铁可代替硫酸催化酯化反应,探讨了氯化铁催化合成富马酸二甲酯的条件,操作简便,反应温和,无腐蚀,减少了污染与产品纯化。 相似文献
17.
One requirement in designing and operating and operating system is to minimize the moisture change in stored grain. Moisture transfer during the aeration process is generally believed to be caused by the partial pressure difference between water in grain and water in air (P3-P4). A mathematical model was developed for rough rice, which predicts the partial pressure difference under various grain and ambient conditions. Observations of moisture change over 10 aeration tests confirmed the good correlation between sorption phenomena and partial pressure differences. Studies indicated that air relative humidity, air temperature, grain temperature and grain moisture are significant factors influencing the partial pressure differences and, thus, affecting 相似文献
18.
一种改进的共同进化遗传算法及其应用 总被引:2,自引:0,他引:2
将共同进化遗传算法应用于临床营养决策优化中,虽然取得了一定成果,但算法中仍存在早熟现象、局部搜索能量弱等问题,为此提出一种改进的共同进化模型。算法使用新的子群体划分方法和交叉算子,引入精英保留策略、信息交换原则和小生境技术。通过对糖尿病营养治疗的仿真表明,改进后的算法在保证群体多样性和避免早熟现象的前提下,提高了算法的局部和全局寻优能力,且膳食配方中营养素达标率符合要求,满足专家建议的糖尿病饮食需求。 相似文献
19.
Pattern search algorithms for nonlinear inversion of high-frequency Rayleigh-wave dispersion curves 总被引:1,自引:0,他引:1
Inversion of Rayleigh wave dispersion curves is challenging for most local-search methods due to its high nonlinearity and to its multimodality. In this paper, we implemented and tested a Rayleigh wave dispersion curve inversion scheme based on GPS Positive Basis 2N, a commonly used pattern search algorithm. Incorporating complete poll and complete search strategies based on GPS Positive Basis 2N into the inverse procedure greatly enhances the performance of pattern search algorithms because the two steps can effectively locate the promising areas in the solution space containing the global minima and significantly reduce the computation cost, respectively.The proposed inverse procedure was applied to nonlinear inversion of fundamental-mode Rayleigh wave dispersion curves for a near-surface shear (S)-wave velocity profile. The calculation efficiency and stability of the inversion scheme are tested on three synthetic models and a real example from a roadbed survey in Henan, China. Effects of the number of data points, the reduction of the frequency range of the considered dispersion curve, errors in P-wave velocities and density, the initial S-wave velocity profile as well as the number of layers and their thicknesses on inversion results are also investigated in the present study to further evaluate the performance of the proposed approach.Results demonstrate that pattern search algorithms applied to nonlinear inversion of high-frequency surface wave data should be considered good not only in terms of accuracy but also in terms of the computation effort due to their global and deterministic search process. 相似文献
20.
The intent of this paper is to design a high-frequency transformer that is to be incorporated into the DC/DC pulsewidth-modulated switch-mode power supplies by two different technical approaches: a conventional wound-coil magnetic using copper wires, and a planar magnetic with layered copper tracks on laminated printed circuit board. Comparisons will be made between the two approaches in terms of profile: mounting height and surface area, and performance: power losses and efficiency. Other indicators like temperature rise and leakage inductance that causes electromagnetic interference, and cost, materials, and process fluency are also to be looked into. A sandwiched configuration for primary and secondary windings is proposed for the planar type. Issues arising and typical phenomena encountered will be discussed in detail. Primarily, the dominating factor in performance, cost effectiveness, or circuit compactness that restrains the choice of a particular type is to be evaluated. 相似文献