全文获取类型
收费全文 | 76659篇 |
免费 | 5813篇 |
国内免费 | 3113篇 |
专业分类
电工技术 | 4479篇 |
综合类 | 7235篇 |
化学工业 | 14438篇 |
金属工艺 | 5870篇 |
机械仪表 | 4653篇 |
建筑科学 | 9361篇 |
矿业工程 | 3387篇 |
能源动力 | 1865篇 |
轻工业 | 4787篇 |
水利工程 | 2245篇 |
石油天然气 | 5772篇 |
武器工业 | 590篇 |
无线电 | 3493篇 |
一般工业技术 | 7425篇 |
冶金工业 | 4534篇 |
原子能技术 | 939篇 |
自动化技术 | 4512篇 |
出版年
2024年 | 90篇 |
2023年 | 538篇 |
2022年 | 1207篇 |
2021年 | 1658篇 |
2020年 | 1721篇 |
2019年 | 1358篇 |
2018年 | 1384篇 |
2017年 | 1868篇 |
2016年 | 1927篇 |
2015年 | 2087篇 |
2014年 | 4466篇 |
2013年 | 4069篇 |
2012年 | 5424篇 |
2011年 | 4872篇 |
2010年 | 3991篇 |
2009年 | 4499篇 |
2008年 | 4277篇 |
2007年 | 5952篇 |
2006年 | 5981篇 |
2005年 | 4840篇 |
2004年 | 3413篇 |
2003年 | 3414篇 |
2002年 | 2869篇 |
2001年 | 2528篇 |
2000年 | 2149篇 |
1999年 | 1769篇 |
1998年 | 1340篇 |
1997年 | 1138篇 |
1996年 | 902篇 |
1995年 | 788篇 |
1994年 | 635篇 |
1993年 | 452篇 |
1992年 | 400篇 |
1991年 | 312篇 |
1990年 | 235篇 |
1989年 | 219篇 |
1988年 | 147篇 |
1987年 | 98篇 |
1986年 | 68篇 |
1985年 | 89篇 |
1984年 | 85篇 |
1983年 | 61篇 |
1982年 | 65篇 |
1981年 | 39篇 |
1980年 | 38篇 |
1979年 | 44篇 |
1978年 | 20篇 |
1977年 | 17篇 |
1976年 | 11篇 |
1975年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The aim of this study is to describe the development and application of a web-based decision support tool (ViRTUE) for performing climate risk evaluations of water supply systems. The tool is designed for small-scale water utilities in the northeastern United States that may lack the resources for detailed climate change risk investigations. Development of this tool demonstrates a relatively new approach to web application development using the Shiny framework for the R programming language to create an interactive environment for stakeholders and water managers to explore climate vulnerabilities. Using a decision-scaling framework, the tool allows the user to perform a climate stress test to evaluate the performance and vulnerability to water supply shortfalls of local reservoir systems over a wide range of potential climate change scenarios using a generic systems model. Probabilities of future climate conditions derived from climate projections then help inform utility operators of impending risk. 相似文献
102.
Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure. 相似文献
103.
This paper deals with the investigation of the effect of hygrothermal conditions on the bending of nanoplates using Levy type solution model employing the state-space concept. The nanoplates are assumed to be subjected to a hygrothermal environment. The two-unknown function plate theory is used to derive the governing differential equations on the basis of Eringen's nonlocal elasticity theory. The governing equations contain the small scale effect as well as hygrothermal and mechanical effects. These equations are converted into a set of first-order linear ordinary differential equations with constant coefficients. Analytical solution of bending response for nanoplates under combinations of simply supported, clamped and free boundary conditions is obtained. Comparison of the results with those being in the open literature is made. The influences played by small scale parameter, temperature rise, the degree of moisture concentration, boundary conditions, plate aspect ratio and side-to-thickness ratio are studied. 相似文献
104.
This paper presents a direct traction boundary integral equation method (DTBIEM) for two-dimensional crack problems of materials. The traction boundary integral equation was collocated on both the external boundary and either side of the crack surfaces. The displacements and tractions were used as unknowns on the external boundary, while the relative crack opening displacement (RCOD) was chosen as unknowns on either side of crack surfaces to keep the single-domain merit. Only one side of the crack surfaces was concerned and needed to be discretized, thus the proposed method resulted in a smaller system of algebraic equations compared with the dual boundary element method (DBEM). A new set of crack-tip shape functions was constructed to represent the strain field singularity exactly, and the SIFs were evaluated by the extrapolation of the RCOD. Numerical examples for both straight and curved cracks are given to validate the accuracy and efficiency of the presented method. 相似文献
105.
106.
基于声发射和高斯混合模型的灰岩破裂特征识别研究 总被引:3,自引:0,他引:3
通过单轴压缩条件下灰岩破裂过程的声发射试验研究,利用高斯混合模型(GMM)对加载过程声发射信号波形特征进行深入分析,探索性识别灰岩破裂失稳过程的裂纹模式及其前兆特征。分析结果表明,灰岩在单轴加载过程中先后主要存在张拉和剪切两种破裂模式。其中,张拉破裂的声发射信号波形特征在AF-RA坐标空间呈现低A_F值、高R_A值分布;剪切破裂的声发射信号波形特征在AF-RA坐标空间呈现低R_A值、高A_F值,且随着应力的增加分布中心向A_F轴靠拢。GMM分析结果揭示了灰岩在整个应力加载过程中以张拉裂纹为主,在加载前中期几乎全为张拉裂纹,临近破坏阶段过渡到剪切破坏为主。剪切裂纹所占比例的最大值出现在(0.8~0.9)σ_c阶段,也是AF-RA坐标轴分布呈现最大A_F值时。研究结果可为预测早期灰岩破裂失稳提供参考,同时为深入研究识别岩石破裂失稳前兆信号特征提供了一种分析方法。 相似文献
107.
Muntasir Hashim Farnoosh Farhad David Smyth‐Boyle Robert Akid Xiang Zhang Philip J. Withers 《工业材料与腐蚀》2019,70(11):2009-2019
The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits. 相似文献
108.
109.
110.
采用动态硫化法制备了高密度聚乙烯(HDPE)/丁苯橡胶(SBR)热塑性硫化胶(TPV),研究了橡塑比、定型温度、回复温度及增容剂苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)对HDPE/SBR TPV形状记忆性能的影响,观察了其微观结构,提出了形状记忆行为机制。结果表明,HDPE/SBR TPV具有典型的"海-岛"结构,拉伸后其表面存在明显的取向结构;SBS能显著提高HDPE/SBR TPV的形状记忆性能,当SBS用量为6份、定型温度和回复温度均为120℃时,HDPE/SBR TPV的形状记忆性能最佳。 相似文献