全文获取类型
收费全文 | 43138篇 |
免费 | 5724篇 |
国内免费 | 3215篇 |
专业分类
电工技术 | 9943篇 |
综合类 | 4672篇 |
化学工业 | 1963篇 |
金属工艺 | 1922篇 |
机械仪表 | 3524篇 |
建筑科学 | 8747篇 |
矿业工程 | 2092篇 |
能源动力 | 1905篇 |
轻工业 | 450篇 |
水利工程 | 1913篇 |
石油天然气 | 1460篇 |
武器工业 | 495篇 |
无线电 | 2137篇 |
一般工业技术 | 4568篇 |
冶金工业 | 1392篇 |
原子能技术 | 339篇 |
自动化技术 | 4555篇 |
出版年
2024年 | 253篇 |
2023年 | 639篇 |
2022年 | 1301篇 |
2021年 | 1508篇 |
2020年 | 1609篇 |
2019年 | 1373篇 |
2018年 | 1247篇 |
2017年 | 1631篇 |
2016年 | 1716篇 |
2015年 | 1929篇 |
2014年 | 3005篇 |
2013年 | 2641篇 |
2012年 | 3340篇 |
2011年 | 3640篇 |
2010年 | 2703篇 |
2009年 | 2791篇 |
2008年 | 2583篇 |
2007年 | 2942篇 |
2006年 | 2722篇 |
2005年 | 2190篇 |
2004年 | 1781篇 |
2003年 | 1580篇 |
2002年 | 1288篇 |
2001年 | 1053篇 |
2000年 | 848篇 |
1999年 | 756篇 |
1998年 | 503篇 |
1997年 | 483篇 |
1996年 | 407篇 |
1995年 | 328篇 |
1994年 | 267篇 |
1993年 | 182篇 |
1992年 | 147篇 |
1991年 | 109篇 |
1990年 | 107篇 |
1989年 | 99篇 |
1988年 | 99篇 |
1987年 | 43篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 26篇 |
1983年 | 28篇 |
1982年 | 19篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 18篇 |
1961年 | 6篇 |
1960年 | 6篇 |
1959年 | 7篇 |
1955年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
We study the stressed state of an inhomogeneous welded joint containing an interlayer of a more high-strength material under the action of tensile loads. It is assumed that the contact boundary has a cracklike defect. We deduce analytic dependences of the fracture load on the mechanical inhomogeneity of the joint, thickness of the interlayer, and depth of the defect. The maximum depth of the defect to which the joint is insensitive is established. The proposed theoretical results are innovative and agree with the experimental data obtained for specimens cut out from a pipe of 14KhGS steel. 相似文献
62.
就我公司动力厂给水车间155kW水泵电机无功就地补偿的可行性及经济效益进行了分析和研究,对工厂用电如何节能降耗有一定的参考价值。 相似文献
63.
An increasing amount of laser beam welded T‐joints (e.g. skin‐stringer) of aluminium alloys are now in use in advanced fuselage applications designed as ‘integral structures’ for weight and cost savings. It is known that weld joints generally show lower strength (undermatching) than base metal in both laser beam and friction stir welded joints of 6xxx series Al‐alloys. Damage tolerance considerations in terms of the residual strength of such joints require limit load solutions to be used in engineering fitness‐for‐service (FFS) analysis. The paper, therefore, provides an upper bound limit load solution in closed form for welded T‐joints (idealized) with strength undermatching and subject to a bending moment. In addition to the necessary requirements of the upper bound theorem, the kinematically admissible velocity field chosen leads to a stress field, which satisfies the equilibrium equations and some stress boundary conditions in the plastic zone. This is an advantage of the solution and, therefore, it is expected that the upper bound obtained is close to the exact limit load of such joints. 相似文献
64.
L. T. MO M. HUURMAN S. P. WU A. A. A. MOLENAAR 《Fatigue & Fracture of Engineering Materials & Structures》2007,30(9):823-831
Tensile fatigue behaviours of bitumen–stone adhesion were investigated using a dynamic mechanics analyser under stress‐controlled mode at two temperatures of 5 and 25°C and various controlled‐stress levels. Failure characteristics including interfacial failure and cohesive failure were examined using image analysis of fracture surfaces. Finite‐element analysis on stress distributions was conducted under different temperatures, film thickness and interfacial bonding conditions. A Coulomb–Mohr like criterion in combination with shear and normal stresses is proposed to deal with the extreme thin adhesive layer, which can be further simplified into an adhesive zone without significant loss of accuracy for stress analysis. 相似文献
65.
A method for constructing an approximation of the critical excitation that drives an elastoplastic system from rest to a target threshold at a specified time instant, referred to as the “suboptimal excitation,” is presented in this paper. It is based on the observations gained from study of the critical excitations in the companion paper. Essentially, for the usual case of interest where the failure time is not small compared to the natural period, the duration of the positive and negative pulses of the critical excitation are roughly equal to half of the natural period. This consideration allows for a simple intuitive approximation of the critical excitation. The amplitudes of the positive and negative pulses are obtained in closed forms using energy balance. Numerical investigations show that the critical excitations are well approximated by the suboptimal excitations. 相似文献
66.
Prevention and Mitigation Strategies to Address Recent Brittle Fractures in Steel Bridges 总被引:1,自引:0,他引:1
Robert J. Connor Eric J. Kaufmann John W. Fisher William J. Wright 《Canadian Metallurgical Quarterly》2007,12(2):164-173
Brittle fracture results in unplanned loss of service, very costly repairs, concern regarding the future safety of the structure, and potential loss of life. These types of failures are most critical when there is no evidence of fatigue cracking leading up to the fracture and the fracture origin is concealed from view. Hence, the failure occurs without warning and the details are, essentially, noninspectable. In these cases, it appears desirable to take a proactive approach and introduce preventative retrofits to reduce the potential for future crack development. These efforts will help ensure that the likelihood of unexpected fractures is minimized. This paper examines the behavior of two bridge structures in which brittle fractures have developed in recent times, discusses the causes of the failures, and offers suggested design strategies for prevention and retrofit mitigation techniques. In situations where considerable uncertainty exists in the prediction of accumulated damage or in the ability to reliably inspect critical details, preemptive retrofit strategies appear to be highly desirable. 相似文献
67.
Hitsman Brian; Borrelli Belinda; McChargue Dennis E.; Spring Bonnie; Niaura Raymond 《Canadian Metallurgical Quarterly》2003,71(4):657
The authors conducted a meta-analysis of published studies to (a) evaluate the premise that a history of major depression is associated with failure to quit smoking and (b) identify factors that moderate the relationship between history of depression and cessation outcome. Fifteen studies met the selection requirements and were coded for various study methodology and treatment characteristics. DSTAT was used to calculate individual study effect sizes, determine the mean effect size across studies. and test for moderator effects. No differences in either short-term (≤ 3 months) or long-term abstinence rates (≥ 6 months) were observed between smokers positive versus negative for history of depression. Lifetime history of major depression does not appear to be an independent risk factor for cessation failure in smoking cessation treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
68.
V. P. Efimov 《Journal of Mining Science》2003,39(4):384-386
The procedure is proposed for estimating the crack resistance and tensile strength of rocks by the results of experiments on disk samples with holes. The gradient approach to the strength problem is employed in processing the experimental data. 相似文献
69.
70.
介绍了500W宽频带功率负载的设计及实验结果,并将研究成果扩展到10~1000W范围。负载主要技术指标:输入阻抗50Ω,频带宽度0~1000MHz,电压驻波比≤1.1.表面最高温升△t≤100℃。 相似文献