全文获取类型
收费全文 | 70871篇 |
免费 | 7669篇 |
国内免费 | 4424篇 |
专业分类
电工技术 | 3591篇 |
综合类 | 6142篇 |
化学工业 | 11546篇 |
金属工艺 | 6214篇 |
机械仪表 | 6958篇 |
建筑科学 | 5902篇 |
矿业工程 | 2128篇 |
能源动力 | 2284篇 |
轻工业 | 7247篇 |
水利工程 | 2152篇 |
石油天然气 | 2284篇 |
武器工业 | 779篇 |
无线电 | 5905篇 |
一般工业技术 | 10225篇 |
冶金工业 | 2879篇 |
原子能技术 | 977篇 |
自动化技术 | 5751篇 |
出版年
2024年 | 380篇 |
2023年 | 1390篇 |
2022年 | 2428篇 |
2021年 | 2719篇 |
2020年 | 2710篇 |
2019年 | 2490篇 |
2018年 | 2347篇 |
2017年 | 2790篇 |
2016年 | 2831篇 |
2015年 | 2960篇 |
2014年 | 3919篇 |
2013年 | 4737篇 |
2012年 | 5116篇 |
2011年 | 5424篇 |
2010年 | 3757篇 |
2009年 | 3851篇 |
2008年 | 3577篇 |
2007年 | 4371篇 |
2006年 | 3998篇 |
2005年 | 3288篇 |
2004年 | 2670篇 |
2003年 | 2282篇 |
2002年 | 1964篇 |
2001年 | 1646篇 |
2000年 | 1473篇 |
1999年 | 1256篇 |
1998年 | 1036篇 |
1997年 | 924篇 |
1996年 | 805篇 |
1995年 | 647篇 |
1994年 | 565篇 |
1993年 | 482篇 |
1992年 | 395篇 |
1991年 | 270篇 |
1990年 | 278篇 |
1989年 | 192篇 |
1988年 | 181篇 |
1987年 | 101篇 |
1986年 | 107篇 |
1985年 | 95篇 |
1984年 | 84篇 |
1983年 | 59篇 |
1982年 | 66篇 |
1981年 | 19篇 |
1980年 | 40篇 |
1979年 | 37篇 |
1965年 | 15篇 |
1964年 | 19篇 |
1963年 | 16篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 3 毫秒
101.
聚合物-金属界面相形貌的研究 总被引:1,自引:0,他引:1
环氧树脂在 Al 合金表面生成纤维状的界面相结构,其形成、发展和特征与树脂的体系、交联反应条件以及 Al 合金的表面状态有关。环氧树脂的基础相为颗粒状的超结构组织。聚合物界面相的力学破坏表现为纤维体的拉伸、变形和断裂,而基础相在纯剪切受力时出现在45°方向的裂纹,并发展导致连接层的破坏。 相似文献
102.
X-ray diffraction analysis shows that the transformation during heat treatment from amorphous to crystalline phases of bismuth-borate glass samples takes place in sequences. After a short heat treatment, 5 min at 550 °C, a layered structure with a preferred orientation of crystallites on the surface is observed. After a long heat treatment, 8 h at the same temperature, normal polycrystalline bulk samples are obtained. 相似文献
103.
Labouvie-Vief Gisela; Lumley Mark A.; Jain Elizabeth; Heinze Hillary 《Canadian Metallurgical Quarterly》2003,3(2):115
This research reports age and gender differences in cardiac reactivity and subjective responses to the induction of autobiographical memories related to anger, fear, sadness, and happiness. Heart rate (HR) and subjective state were assessed at baseline and after the induction of each emotion in 113 individuals (61 men, 52 women; 66% European American, 34% African American) ranging in age from 15 to 88 years (M = 50.0; SD = 20.2). Cardiac reactivity was lower in older individuals; however, for anger and fear, these age effects were significantly more pronounced for the women than the men. There were no gender differences in subjective responses, however, suggesting that the lower cardiac reactivity found among older people is dependent on gender and the specific emotion assessed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
105.
Kathryn Kromroy Kathleen Ward Paul Castillo Jennifer Juzwik 《Landscape and urban planning》2007,80(4):375-385
Urbanization was associated with loss and transformation of the oak forest in the Twin Cities (Minneapolis and St. Paul) metropolitan area (TCMA) over a recent 7-year interval. Between 1991 and 1998, urbanization increased based on several indicators: population density, area of developed land, and area of impervious surface—total impervious area and area within three classes of increasing degree of imperviousness (protected, affected, and degraded). We quantified relationships between changes in urbanization and changes in several parameters describing the oak forest at the scale of ecological subsection. Increased total and affected impervious area were strongly correlated with decreased area of oak forest when changes of the urbanization indicators and oak were expressed as percentages of the subsection area. Relationships were reversed when changes were expressed as percentages of the 1991 values. Increased population density was strongly correlated with increased loss in numbers and increased isolation of oak patches, but weakly correlated with loss of oak forest area. This is the first study to quantify relationships between changes in urbanization and changes in a specific forest cover type. Our results demonstrate complexities of urbanization impacts on a metropolitan forest resource, and highlight the importance of selected variables, spatial and temporal scales, and expressions of change when quantifying these relationships. 相似文献
106.
本文探讨了60Si2Mn合金钢发蓝原理,针对其膜层泛红问题,分析了热处理、表面前处理、发蓝及浸油等过程对发蓝质量的影响,由此采取了相应的技术措施,生产实践证明发蓝质量稳定,生产效率明显提高。 相似文献
107.
阴离子表面活性剂测定方法的探讨 总被引:8,自引:0,他引:8
本文对“阴离子表面活性剂的测定方法”进行探讨,优化了显色剂、萃取剂的用量及萃取频率等分析条件,有效地降低了方法的检出浓度,提高了分析精度及准确度,节约大量试剂。本法最低检出浓度的0.019mL/L。 相似文献
108.
L. M. CRUZ-ORIVE 《Journal of microscopy》2005,219(1):18-28
A new principle is presented to generate isotropic uniform random (IUR) test lines hitting a geometric structure in three-dimensional space (3D). The principle therefore concerns the estimation of surface area, volume, membrane thickness, etc., of arbitrary structures with piecewise smooth boundary. The principle states that a point-sampled test line on an isotropic plane through a fixed point in 3D is effectively an invariant test line in 3D. Particular attention is devoted to the stereology of particles, where an alternative to the surfactor method is obtained to estimate surface area. An interesting case arises when the particle is convex. The methods are illustrated with synthetic examples. 相似文献
109.
Cathy Lawson Douglas C. Montgomery 《Quality and Reliability Engineering International》2006,22(8):971-984
Variation exists in all processes. Significant work has been done to identify and remove sources of variation in manufacturing processes resulting in large returns for companies. However, business process optimization is an area that has a large potential return for a company. Business processes can be difficult to optimize due to the nature of the output variables associated with them. Business processes tend to have output variables that are binary, nominal or ordinal. Examples of these types of output include whether a particular event occurred, a customer's color preference for a new product and survey questions that assess the extent of the survey respondent's agreement with a particular statement. Output variables that are binary, nominal or ordinal cannot be modeled using ordinary least‐squares regression. Logistic regression is a method used to model data where the output is binary, nominal or ordinal. This article provides a review of logistic regression and demonstrates its use in modeling data from a business process involving customer feedback. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
110.