全文获取类型
收费全文 | 121656篇 |
免费 | 10665篇 |
国内免费 | 5566篇 |
专业分类
电工技术 | 7299篇 |
技术理论 | 13篇 |
综合类 | 8119篇 |
化学工业 | 19940篇 |
金属工艺 | 6745篇 |
机械仪表 | 7515篇 |
建筑科学 | 9488篇 |
矿业工程 | 3540篇 |
能源动力 | 3544篇 |
轻工业 | 9042篇 |
水利工程 | 2427篇 |
石油天然气 | 6428篇 |
武器工业 | 1068篇 |
无线电 | 14218篇 |
一般工业技术 | 14722篇 |
冶金工业 | 5979篇 |
原子能技术 | 1485篇 |
自动化技术 | 16315篇 |
出版年
2024年 | 569篇 |
2023年 | 2086篇 |
2022年 | 3710篇 |
2021年 | 5125篇 |
2020年 | 3945篇 |
2019年 | 3275篇 |
2018年 | 3720篇 |
2017年 | 3956篇 |
2016年 | 3773篇 |
2015年 | 4935篇 |
2014年 | 6156篇 |
2013年 | 7163篇 |
2012年 | 8073篇 |
2011年 | 8671篇 |
2010年 | 7359篇 |
2009年 | 7038篇 |
2008年 | 6857篇 |
2007年 | 6415篇 |
2006年 | 6075篇 |
2005年 | 5223篇 |
2004年 | 3910篇 |
2003年 | 3503篇 |
2002年 | 3417篇 |
2001年 | 3022篇 |
2000年 | 2867篇 |
1999年 | 3146篇 |
1998年 | 2483篇 |
1997年 | 2016篇 |
1996年 | 1959篇 |
1995年 | 1651篇 |
1994年 | 1361篇 |
1993年 | 995篇 |
1992年 | 784篇 |
1991年 | 559篇 |
1990年 | 471篇 |
1989年 | 396篇 |
1988年 | 318篇 |
1987年 | 201篇 |
1986年 | 167篇 |
1985年 | 106篇 |
1984年 | 85篇 |
1983年 | 57篇 |
1982年 | 65篇 |
1981年 | 40篇 |
1980年 | 40篇 |
1979年 | 22篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1974年 | 12篇 |
1970年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
Recently, Timmermann and Nowak developed algorithms for estimating the means of independent Poisson random variables. The algorithms are based on a multiscale model where certain random variables are assumed to obey a beta-mixture density function. Timmermann and Nowak simplify the density estimation problem by assuming the beta parameters are known and only one mixture parameter is unknown. They use the observed data and the method of moments to estimate the unknown mixture parameter. Taking a different approach, we generate training data from the observed data and compute maximum likelihood estimates of all of the beta-mixture parameters. To assess the improved performance obtained by the proposed modification, we consider a denoising application using Poisson data. 相似文献
152.
Since most end-of-life electronics equipment contain hazardous materials such as lead solder alloys or lead-impregnated glass, it is important to divert them from landfills. For end-of-life products that are not repairable and do not contain reusable parts, bulk recycling is an alternative to recover base materials. In this paper, we contrast production and recycling planning and distribution decisions, activities, and costs. We reveal that while a traditional production facility connects suppliers and customers, a recycling facility connects both "input" and "output" customers. As a result, decisions in short-term bulk recycling planning include what products to accept, what products to process and reprocess, and what products to carry in inventory. Many recyclers set prices to receive "input" based on experience. For various prices to receive "input", we use a new analytical model to investigate the sensitivity of the short-term bulk recycling planning decisions in products from two different sources: industrial returns versus residential returns. The results of the case study show that different decisions are recommended for the industrial returns versus the residential returns when the total quantity of the incoming products is equal. 相似文献
153.
154.
In this paper, a new vectorial boundary element method is introduced and applied to the modal analysis of dielectric waveguides with piecewise homogeneous refractive indexes. The procedure, which is free of spurious modes, determines the full field distribution from the longitudinal fields at the refractive index boundaries. Singular kernels are evaluated through series solutions while the electric field discontinuity at corners is accommodated through either a grid refinement technique or a semianalytic approach. Our formalism generates propagation constants and modal field distributions for several representative refractive index profiles with far higher accuracy than standard finite-difference or finite-element procedures. 相似文献
155.
156.
157.
An account is given of some principal observations made from a series of experiments in which three-span pipe beams were subjected to central impact by indenters with different nose shapes. These pipes were filled and pre-pressurized with water in order to identify the main effects produced by the fluid–structure interaction. In comparison, the impact experiments of the pipes with no water were also carried out. The perforation failure modes and corresponding critical impact energies were obtained in different test conditions. The experimental results indicated that the critical perforation energy and the deformation of the wall of the pipe were significantly influenced by the presence of the water and the pressure. 相似文献
158.
董志武 《高分子材料科学与工程》1992,8(6):72-78
用TMA方法研究了双向拉伸PET膜和容器的热收缩特性,讨论了热收缩和分子结构的关系和各种影响因素。实验结果表明,TMA是研究和测试取向聚合物材料热收缩的简便有效方法。 相似文献
159.
一种有机化合物名称编码与亚结构检索方法 总被引:1,自引:0,他引:1
本文以 IUPAC 为基础,考虑有机化合物母体和取代基的关联,采用库中已有的化合物名称进行亚结构检索,这种检索方法,由于由化合物名称所劈裂的编码数量较少,所以索引文件小,检索速度较快。另外,这种方法是侧重在化学上有意义的母体和宫能团,它可以和碎片编码亚结构检索方法互相补充。 相似文献
160.
用差热、热重法对原丝的热性能及由不同预处理方法所引起的PVA纤维的热行为变化进行了研究;并通过模拟脱水条件,用不同升温速率,求出了经不同预处理纤维的脱水反应活化能。结果表明,PVA原丝在230℃有一软化点,三种预处理都不同程度地影响了原丝的热效应变化;纤维在180~340℃主要为脱水反应;原丝及经脱水剂、O_3和O_3综合脱水剂处理的纤维,其脱水反应的表观活化能分别为:164.3kJ/mol,92.9kJ/mol,130.5kJ/mol和117.6kJ/mol。 相似文献