全文获取类型
收费全文 | 51098篇 |
免费 | 6372篇 |
国内免费 | 3840篇 |
专业分类
电工技术 | 4712篇 |
综合类 | 5131篇 |
化学工业 | 7175篇 |
金属工艺 | 3205篇 |
机械仪表 | 3339篇 |
建筑科学 | 3840篇 |
矿业工程 | 1709篇 |
能源动力 | 1468篇 |
轻工业 | 5639篇 |
水利工程 | 1538篇 |
石油天然气 | 1775篇 |
武器工业 | 692篇 |
无线电 | 5715篇 |
一般工业技术 | 4993篇 |
冶金工业 | 1837篇 |
原子能技术 | 1220篇 |
自动化技术 | 7322篇 |
出版年
2024年 | 301篇 |
2023年 | 970篇 |
2022年 | 2319篇 |
2021年 | 3064篇 |
2020年 | 2082篇 |
2019年 | 1624篇 |
2018年 | 1648篇 |
2017年 | 1832篇 |
2016年 | 1575篇 |
2015年 | 2573篇 |
2014年 | 3004篇 |
2013年 | 3407篇 |
2012年 | 4044篇 |
2011年 | 4318篇 |
2010年 | 3812篇 |
2009年 | 3830篇 |
2008年 | 3787篇 |
2007年 | 3502篇 |
2006年 | 3105篇 |
2005年 | 2591篇 |
2004年 | 1826篇 |
2003年 | 1364篇 |
2002年 | 1361篇 |
2001年 | 1263篇 |
2000年 | 854篇 |
1999年 | 410篇 |
1998年 | 165篇 |
1997年 | 128篇 |
1996年 | 110篇 |
1995年 | 79篇 |
1994年 | 67篇 |
1993年 | 59篇 |
1992年 | 27篇 |
1991年 | 32篇 |
1990年 | 19篇 |
1989年 | 24篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 17篇 |
1985年 | 6篇 |
1984年 | 6篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 7篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1959年 | 27篇 |
1951年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
邱文平 《理化检验(物理分册)》2003,39(8):409-410
介绍了一种用三点弯曲试验法测定高性能大尺寸粘接永磁体粘合强度的方法,及利用布氏硬度计的加载系统,实现100%检验粘接质量的方法。 相似文献
42.
Three-dimensional models, or pharmacophores, describing Euclidean constraints on the location on small molecules of functional
groups (like hydrophobic groups, hydrogen acceptors and donors, etc.), are often used in drug design to describe the medicinal
activity of potential drugs (or ‘ligands’). This medicinal activity is produced by interaction of the functional groups on
the ligand with a binding site on a target protein. In identifying structure-activity relations of this kind there are three
principal issues: (1) It is often difficult to “align” the ligands in order to identify common structural properties that
may be responsible for activity; (2) Ligands in solution can adopt different shapes (or `conformations’) arising from torsional
rotations about bonds. The 3-D molecular substructure is typically sought on one or more low-energy conformers; and (3) Pharmacophore
models must, ideally, predict medicinal activity on some quantitative scale. It has been shown that the logical representation
adopted by Inductive Logic Programming (ILP) naturally resolves many of the difficulties associated with the alignment and
multi-conformation issues. However, the predictions of models constructed by ILP have hitherto only been nominal, predicting
medicinal activity to be present or absent. In this paper, we investigate the construction of two kinds of quantitative pharmacophoric
models with ILP: (a) Models that predict the probability that a ligand is “active”; and (b) Models that predict the actual
medicinal activity of a ligand. Quantitative predictions are obtained by the utilising the following statistical procedures
as background knowledge: logistic regression and naive Bayes, for probability prediction; linear and kernel regression, for
activity prediction. The multi-conformation issue and, more generally, the relational representation used by ILP results in
some special difficulties in the use of any statistical procedure. We present the principal issues and some solutions. Specifically,
using data on the inhibition of the protease Thermolysin, we demonstrate that it is possible for an ILP program to construct
good quantitative structure-activity models. We also comment on the relationship of this work to other recent developments
in statistical relational learning.
Editors: Tamás Horváth and Akihiro Yamamoto 相似文献
43.
The estimation of the link capacity and its available bandwidth in an end-to-end path is crucial for network management, admission
control and flow control for adaptive applications. This paper introduces an estimation mechanism able to accurately estimate
the available bandwidth of all links in an end-to-end path, through its capacity and cross-traffic estimation. The estimation
procedures resort to the dispersions of packet pairs and trains using the concepts of ICMP Timestamp and Traceroute that,
efficiently used together, enable the measurement of the dispersions in all links in the path. These mechanisms were evaluated
through simulation experiments, where we analyzed the influence of the several network parameters on each estimation mechanism.
The results show that these estimation methods are able to accurately estimate both the capacity and the cross-traffic of
all links in a path with moderate length and with low overhead. 相似文献
44.
玻璃微珠的表面化学镀银及红外辐射性能研究 总被引:6,自引:1,他引:5
采用化学镀方法在玻璃微珠表面镀银,考察了预处理条件、反应温度和反应时间等因素对玻璃微珠表面镀银的影响,并通过扫描电镜和X-射线衍射分析仪,对镀银后玻璃微珠的表面形貌和结构进行了观察和表征。将镀银玻璃微珠用于涂料中,考察了玻璃微珠在涂料中的应用及其红外辐射率的变化,探讨了化学镀条件对涂料红外辐射率的影响,结果表明,在控制反应温度和浓度的条件下,可使镀银玻璃微珠的红外辐射率由原来的1.02降为0.70,将其应用于涂料后,涂层的红外辐射率为0.80。 相似文献
45.
46.
47.
48.
49.
随着光电器件的广泛应用,微机械光开关成为核心光交换器件的主流。在研发过程中,其器件检测手段成为人们所关注的话题。本文介绍了一种新颖的测量平台,通过高幅值利用单片机控制脉冲频率的方法来选择器件。与当前同类方法相比,具有精度高、可靠性强、成本低、易操作等特点,具有广阔的使用前景。 相似文献
50.