全文获取类型
收费全文 | 41514篇 |
免费 | 4721篇 |
国内免费 | 2357篇 |
专业分类
电工技术 | 3750篇 |
技术理论 | 2篇 |
综合类 | 3040篇 |
化学工业 | 5970篇 |
金属工艺 | 2485篇 |
机械仪表 | 2785篇 |
建筑科学 | 3291篇 |
矿业工程 | 1444篇 |
能源动力 | 1243篇 |
轻工业 | 2728篇 |
水利工程 | 944篇 |
石油天然气 | 1834篇 |
武器工业 | 494篇 |
无线电 | 5226篇 |
一般工业技术 | 4694篇 |
冶金工业 | 1851篇 |
原子能技术 | 535篇 |
自动化技术 | 6276篇 |
出版年
2024年 | 291篇 |
2023年 | 808篇 |
2022年 | 1647篇 |
2021年 | 2414篇 |
2020年 | 1698篇 |
2019年 | 1301篇 |
2018年 | 1534篇 |
2017年 | 1554篇 |
2016年 | 1494篇 |
2015年 | 2136篇 |
2014年 | 2448篇 |
2013年 | 2859篇 |
2012年 | 3123篇 |
2011年 | 3160篇 |
2010年 | 2738篇 |
2009年 | 2610篇 |
2008年 | 2422篇 |
2007年 | 2338篇 |
2006年 | 2074篇 |
2005年 | 1672篇 |
2004年 | 1150篇 |
2003年 | 1054篇 |
2002年 | 1027篇 |
2001年 | 842篇 |
2000年 | 730篇 |
1999年 | 620篇 |
1998年 | 525篇 |
1997年 | 459篇 |
1996年 | 422篇 |
1995年 | 323篇 |
1994年 | 231篇 |
1993年 | 179篇 |
1992年 | 144篇 |
1991年 | 106篇 |
1990年 | 88篇 |
1989年 | 84篇 |
1988年 | 49篇 |
1987年 | 40篇 |
1986年 | 42篇 |
1985年 | 30篇 |
1984年 | 20篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1959年 | 8篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
健康住宅正在走近我们 总被引:1,自引:1,他引:0
人类居住健康的问题越来越受到全世界居住者和舆论的关注.长期以来人类过于不当的城市建设行为,人口的过于集中,城市建筑的高层化倾向,过分的人造环境造成土地失水性严重、热岛现象衍生.城市作为人类居住生活的功能区,在很大程度上被削弱,居住条件恶化、环境受到污染.让城市功能朝着人居、健康的目标发展,包括生理和心理的、社会的和人文的、近期的和长期的多层次的健康,是我们今天的历史责任. 相似文献
12.
A feasibility analysis methodology adopted from reactive distillation is applied to membrane reactors. A model is formulated to depict the reactive liquid phase composition on the retentate side of a continuous type membrane reactor. The effects of both the chemical reaction kinetics and the membrane mass transfer kinetics on the feasible products are elucidated by means of retentate phase diagrams and bifurcation analysis. The proposed method can be applied to various membrane processes, independent of the specific structure of the membrane. Two quaternary reaction systems are considered to illustrate the methodology. In the first hypothetical system, it is shown how selective membranes can influence the sequence of effective volatilities which in turn affects the feasible products of the system. In the second example of practical importance, i.e. the heterogeneously catalysed synthesis of propyl acetate coupled with permeation through a porous polycarbonate membrane, the dusty gas model is applied to describe the component fluxes through the membrane. For the latter reaction system, the existence of reactive arheotrope is demonstrated. Arheotropes represent mass transfer controlled feasible products of membrane separation process. 相似文献
13.
The paper proposes a novel method of forecasting short-term electricity price based on a two-stage hybrid network of self-organised map (SOM) and support-vector machine (SVM). In the first stage, a SOM network is applied to cluster the input-data set into several subsets in an unsupervised manner. Then, a group of SVMs is used to fit the training data of each subset in the second stage in a supervised way. With the trained network, one can predict straightforwardly the next-day hourly electricity prices. To confirm its effectiveness, the proposed model has been trained and tested on the data of historical energy prices from the New England electricity market. 相似文献
14.
15.
在人类文明史上,中华民族文明是全球九个独立起源的文明之一(其余八个为古埃及文明、两河流域文明、古印度文明、爱琴-米诺斯文明、南俄文明、奥尔梅克文明、玛雅文明、查文文明)。在世界文化史上,中华民族文化是世界五大文化圈之一(其余四个是西方基督教文化圈、东方东正教文化圈、伊斯兰教文化圈和印度 相似文献
16.
Calculations and detailed first principle and thermodynamic analyses have been performed to understand the formation mechanism of K2Ti6O13 nanowires (NWs) by a hydrothermal reaction between bulk Na2Ti3O7 crystals and a KOH solution. It is found that direct ion exchange between K+ and Na+ plus H+ interactions with [TiO6] octahedra in Na2Ti3O7 promote the formation of an intermediate H2K2Ti6O14 phase. The large lattice mismatch between this intermediate phase and the bulk Na2Ti3O7 structure, and the large energy reduction associated with the formation of this intermediate phase, drive the splitting of the bulk crystal into H2K2Ti6O14 NWs. However, these NWs are not stable because of large [TiO6] octahedra distortion and are subject to a dehydration process, which results in uniform K2Ti6O13 NWs with narrowly distributed diameters of around 10 nm. 相似文献
17.
镁钴铝类水滑石催化合成安息香甲醚 总被引:1,自引:0,他引:1
采用共沉淀法制备了镁钴铝类水滑石化合物(MgCoAl-HTLcs),并用 X 射线衍射、扫描电子显微镜、NH_3程序升温脱附等方法对 MgCoAl-HTLcs 进行了表征,并以 MgCoAl-HTLcs 为催化剂催化苯甲醛与甲醇反应合成安息香甲醚,研究了n(Mg):n(Co):n(Al)、催化剂用量、原料配比、反应温度、反应时间对合成反应的影响。表征结果显示,MgCoAl-HTLcs 的晶相完整,表面主要为弱酸、弱碱性。催化合成安息香甲醚的适宜条件为:MgCoAl-HTLcs 催化剂用量0.10 g(约为原料总质量的0.23%),n(Mg):n(Co):n(Al)=0.4:1.6:1.0,V(苯甲醛):V(甲醇)=3:50,反应温度50℃,反应时间150 min。在此条件下,苯甲醛的平衡转化率达77.49%,安息香甲醚选择性接近100%。为洁净合成安息香甲醚开辟了一条新的途径。 相似文献
18.
19.
In this paper, we present a static load balancing method for mapping production rules in an expert system onto processors of a message-passing multicomputer. The method uses simulated annealing to achieve a nearly optimal allocation of production rules onto processor nodes. The approach balances the initial rule distribution to avoid higher communication demand among processor nodes at run time. A formal mapping model is developed and a new cost function is defined for the annealing process. New heuristic swap functions and cooling policies are provided to ensure the quality of the annealing process. A software load balancing package, SIMAL, was implemented on a SUN workstation to carry out the benchmark experiments. The overhead associated with this mapping method is O(m In m), where m is the number of rules in the production system. Two benchmark production systems, Toru-waltz and Tourney, are mapped onto a hypercube computer with 32 nodes. Experimental benchmark results verify the effectiveness of the rule mapping method. The method can be applied for distributed artificial intelligence processing or for the parallel execution of cooperating expert systems on a message-passing multicomputer. 相似文献
20.