全文获取类型
收费全文 | 58882篇 |
免费 | 4373篇 |
国内免费 | 2019篇 |
专业分类
电工技术 | 938篇 |
综合类 | 7690篇 |
化学工业 | 3813篇 |
金属工艺 | 3052篇 |
机械仪表 | 1487篇 |
建筑科学 | 28906篇 |
矿业工程 | 1481篇 |
能源动力 | 892篇 |
轻工业 | 275篇 |
水利工程 | 5394篇 |
石油天然气 | 714篇 |
武器工业 | 284篇 |
无线电 | 440篇 |
一般工业技术 | 7268篇 |
冶金工业 | 1851篇 |
原子能技术 | 155篇 |
自动化技术 | 634篇 |
出版年
2024年 | 169篇 |
2023年 | 414篇 |
2022年 | 1074篇 |
2021年 | 1246篇 |
2020年 | 1384篇 |
2019年 | 1033篇 |
2018年 | 1111篇 |
2017年 | 1486篇 |
2016年 | 1614篇 |
2015年 | 1993篇 |
2014年 | 3684篇 |
2013年 | 2631篇 |
2012年 | 3919篇 |
2011年 | 4243篇 |
2010年 | 3426篇 |
2009年 | 4176篇 |
2008年 | 3957篇 |
2007年 | 4817篇 |
2006年 | 3922篇 |
2005年 | 3502篇 |
2004年 | 2704篇 |
2003年 | 2417篇 |
2002年 | 2131篇 |
2001年 | 1711篇 |
2000年 | 1441篇 |
1999年 | 1080篇 |
1998年 | 811篇 |
1997年 | 710篇 |
1996年 | 520篇 |
1995年 | 418篇 |
1994年 | 341篇 |
1993年 | 248篇 |
1992年 | 220篇 |
1991年 | 154篇 |
1990年 | 132篇 |
1989年 | 125篇 |
1988年 | 73篇 |
1987年 | 46篇 |
1986年 | 14篇 |
1985年 | 19篇 |
1984年 | 31篇 |
1983年 | 34篇 |
1982年 | 37篇 |
1981年 | 6篇 |
1980年 | 28篇 |
1979年 | 14篇 |
1975年 | 2篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
31.
V. P. Naumenko 《Strength of Materials》1996,28(1):10-18
The adoption of unified fracture mechanics terminology (UFMT) will promote efficient communication between specialists in different fields of fracture research, harmonization of national and international standards relating to fracture mechanics, and last but not least improvement of the existing methodology for teaching and education in fatigue and fracture. In this paper the definitions of some basic and related terms included in different standards on fracture mechanics terminology are confronted with one another. Alternative definitions of the same terms are offered. By this strategy the author tries to show that the definitions of basic and related terms appropriate for the UFMT should emerge as a consequence of harmonizing a crack model with an actual crack and then both taken together with a fracture model, laboratory test methods, and failure assessment codes.Published in Problemy Prochonsti, No. 1, pp. 17–29, January, 1996.This paper is published as a matter of discussion. 相似文献
32.
本文研究在13SiMnNiCrMoV 结构钢中用尖裂纹的应力强度因子来反映三点弯曲缺口试样的疲劳裂纹萌生规律。当 R=0.1,f=100Hz,试样尺寸 B×W×L=12.5×25×117mm 时,缺口名义应力幅的门槛值为Δσ_(th)=3315ρ~(0.352) MPa,0.5mm≤ρ≤5mmΔK_(th)=250ρ~(0.352) MPam~(1/2)门槛值与ρ有关。同时得到缺口裂纹萌生的循环次数 N_i 与名义应力幅Δσ、缺口曲率半径ρ的定量关系是N_i=3.98×10~(22)ρ~(1.62)/Δσ~(4.85),N_i≤10~(5.5)并讨论了(ΔK_1/ρ~(1/2))_(th)与ρ无关的结论。 相似文献
33.
运用Excel软件,高效解决了混凝土结构计算中较复杂的圆形截面偏压构件的承载力计算问题。该编程计算方法同样适用于土力学、水力学、钢结构等领域。对于解决工程中的各种学科计算问题有着广阔的应用前景。 相似文献
34.
Shou-ren Wang Hao-ran Geng Lin-hai Hui Ying-zi Wang 《Journal of Materials Engineering and Performance》2007,16(1):113-118
A multiphase reticulated porous ceramic (RPC) as Si3N4–Al2O3–SiO2 was fabricated by replication techniques. Proper volumes of additives and twice sinter- twice immerse process endow the RPC
an excellent crack healing and submerging property. The compressive strength and fracture toughness improved owing to the
crack bridging behavior. The existence of pores in struts in RPC blunt the crack tip and increased the external force needed
to propagate the crack. The mechanisms play a beneficial role in enhancing the compressive strength and fracture strength.
Si3N4 RPC with additives of 5%Al and 5% Al2O3 yielded the compressive strength of 9.8 MPa and fracture toughness of 0.3 MPa m1/2. 相似文献
35.
The main subject of this paper is to demonstrate the response of structural concrete to different imposed strain rates. Attention is focused on the strain rate about 10-2 s -1>, where some technical difficulties are experienced when an exact determination of mechanical properties for quasi-brittle materials is attempted. The design of a measurement system, which realizes computer acquisition, analysis, and graphic representation of data, is also presented. 相似文献
36.
37.
Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm2 giving an exposed area of 1500 × 1200 mm2. A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm2. The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
38.
An incremental iterative process based on direct energy minimization is presented for a limit analysis of nonlinear elastic lateral displacements and twists of reinforced and prestressed beams. Problems encountered with the constitutive relations are discussed and two possible material models are presented. 相似文献
39.
本文分析了锌基合金模具制造及使用过程中容易出现热裂、翘曲、收缩的问题,并提出了解决这些问题的措施。 相似文献
40.
The main purpose of this paper is to find the mixed-mode stress intensity factors of composite materials using the crack opening displacement (COD). First, a series solution of the composite material with a crack was used to evaluate COD values. Then, the least-squares method was used to calculate mixed-mode stress intensity factors. This algorithm can be applied to any method that generates or measures COD values. The major advantage of this method is that COD values very near the crack tip are not necessary. Both finite element simulations and laboratory experiments were applied to validate this least-squares method with acceptable accuracy if the even terms of the series solution are removed. 相似文献