全文获取类型
收费全文 | 52306篇 |
免费 | 5533篇 |
国内免费 | 3165篇 |
专业分类
电工技术 | 1429篇 |
综合类 | 4473篇 |
化学工业 | 12309篇 |
金属工艺 | 7166篇 |
机械仪表 | 2642篇 |
建筑科学 | 5937篇 |
矿业工程 | 1266篇 |
能源动力 | 733篇 |
轻工业 | 5186篇 |
水利工程 | 1084篇 |
石油天然气 | 2944篇 |
武器工业 | 646篇 |
无线电 | 2617篇 |
一般工业技术 | 6898篇 |
冶金工业 | 3129篇 |
原子能技术 | 219篇 |
自动化技术 | 2326篇 |
出版年
2024年 | 194篇 |
2023年 | 681篇 |
2022年 | 1448篇 |
2021年 | 1716篇 |
2020年 | 1607篇 |
2019年 | 1505篇 |
2018年 | 1496篇 |
2017年 | 1966篇 |
2016年 | 2024篇 |
2015年 | 2241篇 |
2014年 | 2852篇 |
2013年 | 2910篇 |
2012年 | 3676篇 |
2011年 | 4008篇 |
2010年 | 3017篇 |
2009年 | 3097篇 |
2008年 | 2523篇 |
2007年 | 3588篇 |
2006年 | 3293篇 |
2005年 | 2889篇 |
2004年 | 2386篇 |
2003年 | 2103篇 |
2002年 | 1763篇 |
2001年 | 1470篇 |
2000年 | 1261篇 |
1999年 | 1127篇 |
1998年 | 927篇 |
1997年 | 693篇 |
1996年 | 607篇 |
1995年 | 477篇 |
1994年 | 420篇 |
1993年 | 268篇 |
1992年 | 244篇 |
1991年 | 161篇 |
1990年 | 97篇 |
1989年 | 79篇 |
1988年 | 53篇 |
1987年 | 32篇 |
1986年 | 24篇 |
1985年 | 11篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 6篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 8篇 |
1973年 | 2篇 |
1959年 | 5篇 |
1955年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The effects of yttrium and cerium on microstructures and properties of Nb-Si system composites were investigated by scanning electron microscopy( SEM), energy dispersive spectrum(EDS), X-ray diffraction(XRD) and high temperature oxidation experiments.It is found that the coarse primary silicide phase became finer and more homogeneous with Y and Ce addition.The results of high temperature oxidation experiments show that the oxidation rates of NbSi system composites with an appropriate amount of Y and Ce decrease compared with those of alloys without Y or Ce addition, and oxidation products mainly distribute along the phase boundaries between the Nb solid solution and silicide. 相似文献
72.
采用人工合成高纯度的羟基磷灰石粉末,喷涂在具有注册证的钛合金和钴铬钼合金人工关节上。通过生物学基础检测、动物实验和临床试用,证明所制作的各种羟基磷灰石涂层人工关节,能诱发骨质生长,起生物固定作用,对治疗丧失功能的骨胳效果甚佳。 相似文献
73.
Stepanov G. V. Kharchenko V. V. Babutskii A. I. Romanov S. V. Feofentov N. A. Kravchenko I. V. 《Strength of Materials》2004,36(3):321-326
The procedure for calculating the life of header – steam generator connector weld joints is proposed. It allows for running out the material plasticity reserve upon static cyclic elastoplastic loading as well as operating conditions, local stress concentrations, and residual stresses after welding. 相似文献
74.
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
75.
76.
通过对国内外大量石油套管螺纹参数的测量和全尺寸的模拟试验,以及对测量和试验数据的理论分析,找出了影响国产套管发生粘扣的原因,并在实际生产中实施验证。采取相应的措施改善了套管的抗粘结性能,同时套管的密封和抗滑脱性能并未下降。 相似文献
77.
芳烃抽提装置技术改造 总被引:3,自引:0,他引:3
由于中国石化锦西石化分公司600kt/a连续重整装置的建设,芳烃抽提装置的原料由原来的脱戊烷油变为Ce组分。为此,对抽余油水洗塔和芳烃分离部分的苯塔塔盘,以及苯塔塔顶和塔底抽出部分进行了改造,更换部分机泵和增加变频泵,并将常规仪表改为DCS控制。改造后装置实现一次开车成功,生产出合格产品。抽余油中总芳烃含量小于0.1%,苯回收率达到99%以上。 相似文献
78.
The purpose of this study is to clarify damage process of “Type IV cracking” in weldment of a 2.25Cr-1Mo steel and to propose a micro damage prediction method. From continuous observation under a creep-fatigue test, it was found that spherical shape voids initiated and grew on grain boundaries in fine grain region and these voids grow continuously by changing their shape to crack-like. Both spherical and crack-like void growth rate equations were derived from the proposed void growth model. It was indicated that measured void growth rate under the creep-fatigue loading was well predicted by the growth rate equations. 相似文献
79.
Discussed in this paper is the Cartesian stiffness matrix, which recently has received special attention within the robotics
research community. Stiffness is a fundamental concept in mechanics; its representation in mechanical systems whose potential
energy is describable by a finite set of generalized coordinates takes the form of a square matrix that is known to be, moreover,
symmetric and positive-definite or, at least, semi-definite. We attempt to elucidate in this paper the notion of “asymmetric
stiffness matrices”. In doing so, we show that to qualify for a stiffness matrix, the matrix should be symmetric and either
positive semi-definite or positive-definite. We derive the conditions under which a matrix mapping small-amplitude displacement
screws into elastic wrenches fails to be symmetric. From the discussion, it should be apparent that the asymmetric matrix
thus derived cannot be, properly speaking, a stiffness matrix. The concept is illustrated with an example. 相似文献
80.
杨加峰 《武汉理工大学学报(材料科学英文版)》2005,20(Z1)
1Introduction HA(hydroxyapatite)wasakindofbioactiveceram ics,whichhadexcellentbiocompatibilityandtissueaffin ityinthatitscomponentsweresimilartothoseofhuman bone[1].Soitwasthebestknownhumanbonesubstitute,andunprecedentedeffecthadbeenharvestedinrecenttwo d… 相似文献