全文获取类型
收费全文 | 2598篇 |
免费 | 278篇 |
国内免费 | 164篇 |
专业分类
电工技术 | 152篇 |
综合类 | 334篇 |
化学工业 | 400篇 |
金属工艺 | 72篇 |
机械仪表 | 200篇 |
建筑科学 | 175篇 |
矿业工程 | 48篇 |
能源动力 | 74篇 |
轻工业 | 531篇 |
水利工程 | 90篇 |
石油天然气 | 39篇 |
武器工业 | 18篇 |
无线电 | 175篇 |
一般工业技术 | 146篇 |
冶金工业 | 43篇 |
原子能技术 | 24篇 |
自动化技术 | 519篇 |
出版年
2024年 | 10篇 |
2023年 | 35篇 |
2022年 | 94篇 |
2021年 | 114篇 |
2020年 | 86篇 |
2019年 | 86篇 |
2018年 | 79篇 |
2017年 | 76篇 |
2016年 | 101篇 |
2015年 | 104篇 |
2014年 | 153篇 |
2013年 | 139篇 |
2012年 | 207篇 |
2011年 | 197篇 |
2010年 | 142篇 |
2009年 | 141篇 |
2008年 | 127篇 |
2007年 | 161篇 |
2006年 | 138篇 |
2005年 | 113篇 |
2004年 | 99篇 |
2003年 | 86篇 |
2002年 | 77篇 |
2001年 | 62篇 |
2000年 | 58篇 |
1999年 | 51篇 |
1998年 | 38篇 |
1997年 | 41篇 |
1996年 | 27篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 17篇 |
1990年 | 17篇 |
1989年 | 13篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1960年 | 1篇 |
1956年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3040条查询结果,搜索用时 15 毫秒
21.
Soo-In Sohn Jae-Hyung Ahn Subramani Pandian Young-Ju Oh Eun-Kyoung Shin Hyeon-Jung Kang Woo-Suk Cho Youn-Sung Cho Kong-Sik Shin 《International journal of molecular sciences》2021,22(11)
Bacterial communities in rhizosphere and root nodules have significant contributions to the growth and productivity of the soybean (Glycine max (L.) Merr.). In this report, we analyzed the physiological properties and dynamics of bacterial community structure in rhizosphere and root nodules at different growth stages using BioLog EcoPlate and high-throughput sequencing technology, respectively. The BioLog assay found that the metabolic capability of rhizosphere is in increasing trend in the growth of soybeans as compared to the bulk soil. As a result of the Illumina sequencing analysis, the microbial community structure of rhizosphere and root nodules was found to be influenced by the variety and growth stage of the soybean. At the phylum level, Actinobacteria were the most abundant in rhizosphere at all growth stages, followed by Alphaproteobacteria and Acidobacteria, and the phylum Bacteroidetes showed the greatest change. But, in the root nodules Alphaproteobacteria were dominant. The results of the OTU analysis exhibited the dominance of Bradyrhizobium during the entire stage of growth, but the ratio of non-rhizobial bacteria showed an increasing trend as the soybean growth progressed. These findings revealed that bacterial community in the rhizosphere and root nodules changed according to both the variety and growth stages of soybean in the field. 相似文献
22.
关于对称矩阵的美韵,笔者已经撰文做过研究,而反对称矩阵的美韵并不亚于对称矩阵。本文对反对称矩阵之美亦从“内”与“外”进行分析和探索。 相似文献
23.
Abstract. It is now well known that how the initial observation is generated can have a significant effect on the power of a unit‐root test. In this article, we show that by taking a simple data‐dependent weighted average of the initial condition‐robust test of Elliott and Müller [Journal of Econometrics (2006), forthcoming] and the standard augmented Dickey–Fuller test, we are able to produce a new unit‐root test that can improve power, both asymptotically and in finite samples, over a wide range of possibilities governing the generation of the initial observation. 相似文献
24.
25.
油松作为一种植根于黄土地区的常见植物,在提高黄土强度方面起重要作用。为了弄清油松根系在黄土地区的固土效应,本文采用离散单元法(Distinct Element Method)模拟根系拉拔试验,分析了法向压力、根系埋深、含水率对根-黄土界面摩擦力学特性的影响。结果表明:拉拔试验中,根-黄土界面峰值强度、残余强度随着法向力的增大而增大;峰值强度、残余强度随着根系埋深的增加而增大;随着含水率的降低,根-黄土界面峰值强度、残余强度呈增大的趋势。 相似文献
26.
孙滨刘林 《计算机与数字工程》2014,(2):187-189,209
论文提出一个基于语义的文本间的相似度算法,以文本的特征词相似度为基础,来计算文本间的相似度,利用聚类算法对文本簇进行聚类.实验结果证明基于知网的文本语义相似度方法在对文本相似度计算以及文本聚类方面,能有效提高聚类的效果. 相似文献
27.
3D objects can be stored in computer of different describing ways, such as point set, polyline, polygonal surface and Euclidean distance map. Moment invariants of different orders may have the different magnitude. A method for normalizing moments of 3D objects is proposed, which can set the values of moments of different orders roughly in the same range and be applied to different 3D data formats universally. Then accurate computation of moments for several objects is presented and experiments show that this kind of normalization is very useful for moment invariants in 3D objects analysis and recognition. 相似文献
28.
Modelling water flow,nitrogen transport and root uptake including physical non-equilibrium and optimization of the root water potential 总被引:3,自引:0,他引:3
F. Lafolie 《Nutrient Cycling in Agroecosystems》1991,27(2-3):215-231
A model is presented for the simulation of water flow, heat flow, and nitrate and ammonium transport. Two approaches are used for modelling plant water uptake as well as for plant nitrogen uptake. Nitrogen transformations are accounted for in a very simple way. This paper focuses mainly on water flow modelling, solute transport, and water uptake. Richards' equation is used to model water flow in layered soil profiles with a great variety of boundary conditions. Solute transport is simulated with either a simple convection dispersion equation or with a two-region physical non-equilibrium model to distinguish between mobile and immobile water and solute exchange between these two regions. A macroscopic sink term is added to Richards' equation to account for plant water uptake. This term can be calculated along two different approaches, one of which is based on the concept of root water potential. The root water potential is then continuously optimized to minimize the difference between the climatic demand and the uptake rate.Simulation results are compared with field data from the Netherlands to illustrate the degree to which the model is able to predict water flow, solute transport and plant water uptake. The root water potential optimization model seems to provide the best prediction of water distribution. In particular the shape of the profile, revealing uptake patterns, is quite well reproduced with this model. Comparison of simulated and observed water content profiles seems also to reveal the presence of preferential pathways. The comparisons show also how predicted solute distributions can be improved by using a two-region approach rather than a simple convection-dispersion model. 相似文献
29.
30.
Leslie矩阵模型在带年龄结构的种群动力学中具有重要地位,研究成果表明当Leslie矩阵为素矩阵时,目标种群将趋向一稳定的年龄分布。该文给出了一个无需通过烦琐的矩阵幂运算来判定Leslie矩阵是素矩阵的充分必要条件,它为Leslie模型的实际应用提供了很大方便。 相似文献