全文获取类型
收费全文 | 3476篇 |
免费 | 173篇 |
国内免费 | 209篇 |
专业分类
电工技术 | 38篇 |
综合类 | 112篇 |
化学工业 | 591篇 |
金属工艺 | 241篇 |
机械仪表 | 422篇 |
建筑科学 | 348篇 |
矿业工程 | 238篇 |
能源动力 | 63篇 |
轻工业 | 105篇 |
水利工程 | 56篇 |
石油天然气 | 45篇 |
武器工业 | 69篇 |
无线电 | 76篇 |
一般工业技术 | 985篇 |
冶金工业 | 175篇 |
原子能技术 | 84篇 |
自动化技术 | 210篇 |
出版年
2024年 | 10篇 |
2023年 | 39篇 |
2022年 | 84篇 |
2021年 | 78篇 |
2020年 | 83篇 |
2019年 | 77篇 |
2018年 | 82篇 |
2017年 | 81篇 |
2016年 | 137篇 |
2015年 | 187篇 |
2014年 | 188篇 |
2013年 | 248篇 |
2012年 | 200篇 |
2011年 | 273篇 |
2010年 | 221篇 |
2009年 | 217篇 |
2008年 | 236篇 |
2007年 | 183篇 |
2006年 | 182篇 |
2005年 | 150篇 |
2004年 | 126篇 |
2003年 | 132篇 |
2002年 | 97篇 |
2001年 | 88篇 |
2000年 | 86篇 |
1999年 | 62篇 |
1998年 | 53篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 45篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 12篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有3858条查询结果,搜索用时 15 毫秒
1.
The paper is devoted to the effect of compressibility of the avalanche snow impacting an obstacle. Compression shocks generated by obstacle cause high pressure peaks at first instants of impact. That is why the account of compressibility is essential for the understanding of measurements and the design of structures. The main problem in calculation compression shocks in avalanches is to formulate an equation of state for moving snow in impact. Two different types of equations of state are proposed depending on the type of the avalanche (low-density and high-density flows). The approach is not totally new. It was earlier proposed mainly in Russian literature. Here a brief review of the previous work is given with discussion of some gaps in it. The theory is reformulated and further developed to account thermodynamical equations. The simplest case of a normal compression shock in an avalanche flow is studied. Examples of estimations of pressure and density behind a shock are given. It is important to emphasize that the Mach number plays an important role in the theory of compressible flows so it should be taken into account (together with the Froude number) in calculation and modelling an avalanche impact pressure. 相似文献
2.
Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs. 相似文献
3.
Thin hard coatings fracture propagation during the impact test 总被引:2,自引:0,他引:2
One of the most significant applications of the impact test is to investigate thin hard coatings fatigue properties. Herein the test conditions and duration up to the film damage initiation, are considered in order to determine the critical stresses associated with the coating fatigue strength. Moreover, the subsequent film damage propagation is a significant mechanism as well, since it refers to the ability of the coating to withstand loads after its fatigue damage initiation. In order to describe the film fracture propagation the failed area ratio was introduced and an algorithm to determine this magnitude developed, based on the analysis of imprint scanning electron microscopy graphs. The application of the coating failed area ratio will be demonstrated in various impact test film cases, also with superficial thin layers. The top layers do not affect, in general, the failure initiation of the basic coating. However, according to the obtained results, the superficial films influence the basic coating failure propagation rate during the impact test. 相似文献
4.
The shape of the impactor with the maximum depth of penetration (DOP) for a given impact velocity is found using a numerical procedure for solving a corresponding non-classical variational problem. It is shown that the optimum shape in a general case is close to a blunt cone. The variation of the optimal shape of the impactor and the dependence of the DOP vs. the initial (impact) velocity and friction coefficient is studied. The analysis is performed also for optimal conical impactors. 相似文献
5.
6.
7.
Kaushik A. Iyer 《International Journal of Fracture》2007,146(1-2):1-18
Internal fracture patterns developed in silicon carbide cylindrical targets as a result of dynamic indentation (63–500 m/s)
by tungsten carbide spheres are defined. Microscopy of recovered and sectioned targets delineate into three regions, each
associated with distinct cracking modes, i.e., shallow cone macrocracking at and near the impact surface, steep interior cone
macrocracks that radiate into the target from the impact region and local grain-scale microcracking directly underneath the
impact region. The observed fracture patterns are found to maintain a noticeable degree of self-similarity upto the impact
velocity of 500 m/s. Linear elastic analysis of the full (surface and interior) stress field developed under static (Hertz)
contact loading delineate the target into four regions, based on the number of principal stresses that are tensile (none,
1, 2 or all 3). A strong correlation is found between the principal stress conditions within each region and the forms of
cracking, their locations and orientations present therein. This correlation has a number of implications, including non-interaction
of crack systems, which are discussed. Illustrative linear elastic fracture mechanics analyses are performed for three regions,
and calculated and observed macrocrack lengths are found to be in reasonable agreement. 相似文献
8.
9.
10.
100m高烟囱拆除爆破冲击振动测试与分析 总被引:9,自引:5,他引:4
在新乡电厂百米钢筋混凝土烟囱爆破拆除工程中,布置了不同方向的两条测线共9个测点,量测了爆破和烟囱倒塌触地引起的地面质点振速和主振频率。从实测数据的分析认识到:烟囱顶部落地产生的冲击力最大,线状震源正前方测点的振速比其侧向测点的振速要大;烟囱倒塌触地产生的振动是各段筒体所产生的振动的叠加,它与各分段体的质量、位置高度、材质强度等因素有关;高大建(构)筑物落地冲击地振动的频率一般比爆破引起的地振动的频率要低;铺设缓冲材料、分段爆破等措施可减小触地冲击引起的地面振动强度。此外,利用实测数据进行拟合,得出了适用于描述本工程烟囱倒塌触地冲击地振动衰减规律的经验公式。 相似文献