全文获取类型
收费全文 | 40637篇 |
免费 | 3668篇 |
国内免费 | 1724篇 |
专业分类
电工技术 | 2227篇 |
技术理论 | 4篇 |
综合类 | 2586篇 |
化学工业 | 6824篇 |
金属工艺 | 2323篇 |
机械仪表 | 2686篇 |
建筑科学 | 3154篇 |
矿业工程 | 1058篇 |
能源动力 | 1080篇 |
轻工业 | 2820篇 |
水利工程 | 780篇 |
石油天然气 | 2206篇 |
武器工业 | 369篇 |
无线电 | 4455篇 |
一般工业技术 | 5408篇 |
冶金工业 | 2218篇 |
原子能技术 | 594篇 |
自动化技术 | 5237篇 |
出版年
2024年 | 207篇 |
2023年 | 696篇 |
2022年 | 1175篇 |
2021年 | 1548篇 |
2020年 | 1279篇 |
2019年 | 1109篇 |
2018年 | 1157篇 |
2017年 | 1384篇 |
2016年 | 1235篇 |
2015年 | 1764篇 |
2014年 | 2146篇 |
2013年 | 2545篇 |
2012年 | 2694篇 |
2011年 | 2645篇 |
2010年 | 2341篇 |
2009年 | 2173篇 |
2008年 | 2163篇 |
2007年 | 2096篇 |
2006年 | 2135篇 |
2005年 | 1902篇 |
2004年 | 1217篇 |
2003年 | 1115篇 |
2002年 | 1070篇 |
2001年 | 926篇 |
2000年 | 1004篇 |
1999年 | 1032篇 |
1998年 | 867篇 |
1997年 | 750篇 |
1996年 | 690篇 |
1995年 | 611篇 |
1994年 | 465篇 |
1993年 | 337篇 |
1992年 | 300篇 |
1991年 | 232篇 |
1990年 | 186篇 |
1989年 | 151篇 |
1988年 | 131篇 |
1987年 | 68篇 |
1986年 | 82篇 |
1985年 | 62篇 |
1984年 | 34篇 |
1983年 | 17篇 |
1982年 | 27篇 |
1981年 | 30篇 |
1980年 | 21篇 |
1979年 | 16篇 |
1977年 | 13篇 |
1976年 | 27篇 |
1975年 | 12篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
ATM技术能否在数据通信网中广泛采用取决于其是否能高效地支持现有业务,其中主要为非连接业务。本文介绍了几种基于ATM 的非连接业务支持方式和协议体系结构,对其进行了评述并对IP分组到ATM信元的封装效率进行了分析。 相似文献
32.
A structured genetic algorithm (SGA) approach is developed for robust controller design based on the concept of an H∞ loop-shaping technique and the method of inequalities. Such an SGA is capable of simultaneously searching the orders and coefficients of the precompensator and postcompensator for the weighted plant. It is, therefore, not necessary to predefine the order of compensators as in usual practice. A multiple objective ranking approach is also incorporated so that the design criteria of extreme plants can be easily achieved. The effectiveness of such a technique is illustrated by a high-purity distillation column design example 相似文献
33.
ATM局域网仿真体系结构的研究 总被引:4,自引:0,他引:4
本文在简要叙述了基于ATM技术进行局域网仿真的原理后,对局域网仿真体系结构作了一些探讨。考虑的重点是无连接服务和群播功能的实现 相似文献
34.
35.
由碳五馏分合成甲基叔戊基醚工艺的研究 总被引:1,自引:0,他引:1
以催化裂化C_5馏分与工业甲醇为原料,D005型大孔强酸型阳离子交换树脂为催化剂,采用筒式膨胀床双反应器,考察了甲基叔戊基醚的合成工艺条件。一阶反应器的操作条件为:循环比为2:1,醇烯比为1.2:1,入口温度为70℃,空速为6 h~(-1),平均转化率为53.63%;二阶反应器的操作条件为:入口温度为50℃,空速为1.2h~(-1),平均转化率为71.32%,全调合方案可以使催化裂化汽油的辛烷值平均提高0.55个单位。 相似文献
36.
37.
本文对激光结晶a-Si∶H SOI结构砷注入和快速退火行为作了研究.a-Si∶H激光结晶有Lp-LCR,OD,FCR-2,FCR-1四个结晶区.用剖面电镜观察了结晶区的结构.扩展电阻测量表明Lp-LCR区中有两种扩散机制,即杂质在晶粒体内扩散和沿缺陷扩散.OD区中有三种扩散形式,除有上述两种以外,还有沿缺陷的扩散.首次比较了沿晶界和缺陷的扩散速度. 相似文献
38.
This article presents a detailed investigation on the influence of the phosphorus element upon the laser sintering of a multicomponent
Cu-based metal powder system consisting of Cu, Cu-10Sn, and Cu-8.4P. Powder systems containing 0, 10, 15, and 20 wt pct CuP
were sintered in atmosphere at room temperature using the following optimal processing parameters: laser power of 350 W, scan
speed of 0.04 m/s, scan line spacing of 0.15 mm, and layer thickness of 0.25 mm. It was found that the relative density of
the sintered sample with 15 wt pct CuP increased by 24,4 pct as compared with the sample without phosphorus addition. A further
increase in the CuP content (≥20 wt pct), however, resulted in a poor densification with a serious delamination. The exact
metallurgical roles of the phosphorus element in the laser sintering process were addressed as follows. First, the phosphorus
could prevent the sintering system from oxidation by forming CuPO3, thereby improving the wetting characteristics and the sintering kinetics. Second, the phosphorus could decrease the surface
tension of molten materials, leading to a successive transition from highly discontinuous sintered tracks to fairly coherent
ones with increasing the phosphorus content. Third, the phosphorus could lower the melt viscosity, thereby improving the microstructural
homogeneity of the laser-sintered samples. 相似文献
39.
通过研究二连盆地赛汉塔拉凹陷中洼槽陡坡带的含鲕粒块状细砂岩从岩性特征、沉积结构及构造特征、粒度特征、测井曲线特征、地震反射特征以及对其形成机理的分析,认为赛83x含油砂岩体为在半深湖一深湖环境形成的滑塌浊积扇沉积.这种类型的滑塌浊积扇具备分选、磨圆度、物性较好等条件,尤其是此类砂岩体往往被形成于深湖一半深湖相还原环境的深灰色、灰黑色泥岩--成熟烃源岩所包围,易形成岩性圈闭,有利于油气的运移和聚集成藏,是断陷湖盆陡坡带油气勘探的重要目标. 相似文献
40.
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