全文获取类型
收费全文 | 51828篇 |
免费 | 5336篇 |
国内免费 | 3627篇 |
专业分类
电工技术 | 1189篇 |
综合类 | 5886篇 |
化学工业 | 6378篇 |
金属工艺 | 6118篇 |
机械仪表 | 3865篇 |
建筑科学 | 10661篇 |
矿业工程 | 2956篇 |
能源动力 | 1278篇 |
轻工业 | 2647篇 |
水利工程 | 2554篇 |
石油天然气 | 2739篇 |
武器工业 | 432篇 |
无线电 | 1401篇 |
一般工业技术 | 8229篇 |
冶金工业 | 3202篇 |
原子能技术 | 349篇 |
自动化技术 | 907篇 |
出版年
2024年 | 214篇 |
2023年 | 697篇 |
2022年 | 2050篇 |
2021年 | 2122篇 |
2020年 | 1699篇 |
2019年 | 1607篇 |
2018年 | 1568篇 |
2017年 | 1850篇 |
2016年 | 1971篇 |
2015年 | 2006篇 |
2014年 | 3013篇 |
2013年 | 3276篇 |
2012年 | 3447篇 |
2011年 | 3808篇 |
2010年 | 2846篇 |
2009年 | 2963篇 |
2008年 | 2800篇 |
2007年 | 3272篇 |
2006年 | 2951篇 |
2005年 | 2498篇 |
2004年 | 2110篇 |
2003年 | 1760篇 |
2002年 | 1598篇 |
2001年 | 1370篇 |
2000年 | 1206篇 |
1999年 | 1030篇 |
1998年 | 856篇 |
1997年 | 746篇 |
1996年 | 624篇 |
1995年 | 517篇 |
1994年 | 455篇 |
1993年 | 360篇 |
1992年 | 337篇 |
1991年 | 223篇 |
1990年 | 192篇 |
1989年 | 193篇 |
1988年 | 115篇 |
1987年 | 94篇 |
1986年 | 52篇 |
1985年 | 50篇 |
1984年 | 47篇 |
1983年 | 27篇 |
1982年 | 33篇 |
1981年 | 11篇 |
1980年 | 28篇 |
1979年 | 35篇 |
1964年 | 10篇 |
1961年 | 6篇 |
1959年 | 8篇 |
1955年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
河口水流、波浪、潮流、泥沙、河床变形二维数学模型 总被引:19,自引:0,他引:19
根据河口“波浪掀沙,潮流输沙”的泥沙运动机制,引入“波浪幅射应力”反应波浪对水体和泥沙的驱动力.考虑波浪对底部泥沙作用力、波浪对水流挟沙能力的影响及风场对水流和泥沙运动的影响.同时考虑泥沙粒径大小、水体含盐度、含沙量及水流紊动程度等因素对絮凝沉速的影响.用ADI算法求解沿水深平均方程,破开算子法解悬移质不平衡输沙方程及河床变形方程,引入通度概念处理岸滩不规则边界,建立河口水流、波浪、潮流、泥沙、河床变形二维数学模型.通过实测资料及卫星摇感图像对所建数学模型进行检验,表明它可以较好地预测河口泥沙的运动 相似文献
32.
The bond strength and slip of epoxy-coated reinforcing bars in concrete have been evaluated by carrying out single pullout and double pullout tests. In extended single pullout tests, slip measurements were made while tensile force was applied to reinforcing bars embedded in concrete. In double pullout tests, 20 cycles of load were applied at levels of steel stress between zero and 0·5 times characteristic steel strength. Strains were measured by electrical resistance strain gauges glued inside the bars. Both epoxy-coated and uncoated bars were used in the investigation, to obtain comparative results. The strain gradient along the bar was found to be less for the coated reinforcement. In general, the epoxy coating was found to increase slip in bond and thereby reduce the bond performance of coated bars. 相似文献
33.
34.
35.
K.W. Allen S.M. Smith W.C. Wake A.O. van Raalte 《International Journal of Adhesion and Adhesives》1985,5(1):23-32
The effect of cyclic stressing on the strength of single lap adhesive joints has been studied and a considerable reduction in strength observed when the maximum stress exceeds about 40% of the ultimate tensile strength, but whether or not a true endurance limit exists is not proven. Fallacies are shown in some of the techniques which have been proposed for studying the fatigue behaviour of adhesive joints. 相似文献
36.
Posttraumatic stress in children and adolescents exposed to family violence: I. Overview and issues.
Exposure to child physical abuse and parents' domestic violence can subject youth to pervasive traumatic stress and can lead to posttraumatic stress disorder (PTSD). This article presents evolving conceptualizations in the burgeoning field of trauma related to family violence exposure and describes how the often repeating and ongoing nature of family violence exposure can complicate a PTSD diagnosis. In addition, recent literature indicates that children exposed to family violence may experience problems in multiple domains of functioning and may meet criteria for multiple disorders in addition to PTSD. Considerations salient to the recognition of traumatic stress in this population and that inform assessment and treatment planning are presented. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
37.
In this study, distribution and history of residual stresses in plaque-like geometries are simulated based on linear thermoviscoelastic
model, which helps to understand the mechanics and evolution of the residual stresses in the injection molding process. The
numerical calculation of direction, combined with the specified boundary conditions. Results show that the stress variation
across the thickness exhibits a high surface tensile value changing to a compressive peak value close to the surface, with
the core region experiencing a parabolic tensile peak. Residual stress distribution throughout the thickness is almost same
along the flowpath and the final residual stresses value near the gate is lower than the value near the end of flowpath. 相似文献
38.
The primary aim of this paper is to present results describing in detail the behaviour of ±45° E-glass/MY750 (GRP) tubes, of various wall thicknesses, subjected to equal biaxial tension–compression loading, generated under combined internal pressure and axial compression. The role played by the non-linear lamina shear has also been assessed by comparing various shear stress–strain curves for embedded laminae (extracted from tests on ±45° tubes subjected to circumferential: axial stress ratios SR=1:0, 1:−1 and 2.3:−1) with that of an ‘isolated’ lamina (measured from torsion of 90° tubes). Extracted shear failure strains, for embedded laminae, were more than four fold larger than those measured at ultimate failure for an ‘isolated’ lamina. Soft characteristics were observed in the embedded lamina and these were believed to be due to interaction between early matrix damage initiation (and propagation) and shear. Factors affecting the behaviour of the tubes, such as bulging, scissoring, thermal stresses and stress variation through the thickness are discussed. 相似文献
39.
Koenen Karestan C.; Stellman Jeanne Mager; Stellman Steven D.; Sommer John F. Jr. 《Canadian Metallurgical Quarterly》2003,71(6):980
Risk factors affecting the course of posttraumatic stress disorder (PTSD) are poorly understood. As part of a larger study on characterizing exposure to herbicides in Vietnam, the authors investigated this issue in a random sample of 1,377 American Legionnaires who had served in Southeast Asia during the Vietnam War and were followed over a 14-year period. High combat exposure, perceived negative community attitudes at homecoming, minority race, depression symptoms at Time 1, and more anger at Time 1 predicted a more chronic course. Community involvement at Time 1 was protective and associated with decreased risk at Time 2. Discomfort in disclosing Vietnam experiences was associated with an increased risk for developing PTSD but did not predict its course. Combat exposure predicted PTSD course more strongly than any other risk factor. Findings suggest recovery from PTSD is significantly influenced by perceived social support. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
40.
曲轴激光喷丸强化试验研究 总被引:2,自引:2,他引:0
采用实验的方法,研究了激光冲击强化对175A型柴油机曲轴疲劳寿命的影响,取得了激光冲击强化试验条件下曲轴过渡圆角处残余应力场的数据。并将激光冲击强化工艺效果和曲轴滚压强化效果做了对比性分析,结果表明:虽然激光冲击强化效果不如曲轴滚压强化,但考虑到激光工艺参数精确可控、加工质量好、成本低以及可避免滚压强化所造成的表面疲劳、撕痕等,激光冲击强化工艺可望代替滚压强化成为新型的曲轴强化手段。通过此类激光冲击强化强化实验可优化激光冲击的相关参数,使曲轴过渡圆角产生有利的残余应力场。 相似文献