全文获取类型
收费全文 | 35017篇 |
免费 | 3831篇 |
国内免费 | 2289篇 |
专业分类
电工技术 | 1728篇 |
综合类 | 3835篇 |
化学工业 | 2004篇 |
金属工艺 | 1043篇 |
机械仪表 | 2634篇 |
建筑科学 | 9108篇 |
矿业工程 | 1437篇 |
能源动力 | 995篇 |
轻工业 | 989篇 |
水利工程 | 1707篇 |
石油天然气 | 867篇 |
武器工业 | 363篇 |
无线电 | 3410篇 |
一般工业技术 | 2880篇 |
冶金工业 | 857篇 |
原子能技术 | 321篇 |
自动化技术 | 6959篇 |
出版年
2024年 | 166篇 |
2023年 | 494篇 |
2022年 | 986篇 |
2021年 | 1053篇 |
2020年 | 1081篇 |
2019年 | 865篇 |
2018年 | 890篇 |
2017年 | 990篇 |
2016年 | 1167篇 |
2015年 | 1380篇 |
2014年 | 2276篇 |
2013年 | 1952篇 |
2012年 | 2687篇 |
2011年 | 2825篇 |
2010年 | 2249篇 |
2009年 | 2254篇 |
2008年 | 2158篇 |
2007年 | 2578篇 |
2006年 | 2193篇 |
2005年 | 1980篇 |
2004年 | 1477篇 |
2003年 | 1284篇 |
2002年 | 1064篇 |
2001年 | 927篇 |
2000年 | 824篇 |
1999年 | 687篇 |
1998年 | 493篇 |
1997年 | 441篇 |
1996年 | 311篇 |
1995年 | 269篇 |
1994年 | 280篇 |
1993年 | 179篇 |
1992年 | 142篇 |
1991年 | 101篇 |
1990年 | 82篇 |
1989年 | 80篇 |
1988年 | 62篇 |
1987年 | 39篇 |
1986年 | 28篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 7篇 |
1980年 | 21篇 |
1979年 | 5篇 |
1975年 | 4篇 |
1959年 | 8篇 |
1954年 | 2篇 |
1951年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Using a comprehensive set of drop weight impact test data (h50) newly compiled from literature for 308 materials, a recent approach to predict impact sensitivities of nitro compounds is generalized to most explosive substances of interest. Compared to previous ones, this procedure is more thoroughly validated and exhibits a good predictive value. Furthermore, it yields new insight into the physical mechanisms involved, explaining for instance the unexpected desensitization of some oxygen-deficient triazoles upon nitration. 相似文献
2.
This paper proposes a novel optimization algorithm inspired by the ions motion in nature. In fact, the proposed algorithm mimics the attraction and repulsion of anions and cations to perform optimization. The proposed algorithm is designed in such a way to have the least tuning parameters, low computational complexity, fast convergence, and high local optima avoidance. The performance of this algorithm is benchmarked on 10 standard test functions and compared to four well-known algorithms in the literature. The results demonstrate that the proposed algorithm is able to show very competitive results and has merits in solving challenging optimization problems. 相似文献
3.
4.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents. 相似文献
5.
提取地震信号高频信息方法的若干问题 总被引:1,自引:0,他引:1
王西文 《石油地球物理勘探》2006,41(1):67-75
岩性油气藏勘探已成为当代油气勘探的重要组成部分,因此提取地震资料高频信息已成为一个重要研究课题。文中对分辨率、分频处理地震信号、波阻抗反演中的一些问题进行了较深入的讨论,并得出以下认识:1要提高垂向和横向分辨率,必须设法提高野外采集地震资料的频率;2地震分频处理是偏移后提高分辨率的常用方法之一,这种方法应该限定在地震波的有效频带内,而超出有效频带,可能会带来很多假像;3低频合成地震记录中高频反射系数存在不确定性。在基于模型波阻抗反演的方法中,反演结果受初始模型的影响非常大,初始模型是依据测井资料建立的,初始模型与实际情况越接近,反演效果就越好;否则,会产生模型化的现象;4在相对波阻抗数据体(相当于地震数据体)作为约束条件下的SP测井参数协克里金插值是正演过程,消除了模型化的问题,使反演结果更接近真实情况,提高了砂层真实的分辨率。 相似文献
6.
The scale along the coordinate axes in the equations of motion hitherto used for an H-maser (in relative units) is shown to depend on Q as the quality factor for an H-maser. This hinders both analysis of the operation of the H-maser and optimization of its parameters. The modified equations of motion proposed here do not have that shortcoming. We determine the atomic flux into the bulb that gives the H-maser the best metrological characteristics. 相似文献
7.
S V Bhat 《Bulletin of Materials Science》1994,17(7):1271-1285
When examined using continuous wave electron paramagnetic resonance and nuclear magnetic resonance spectrometers, the highT
c superconductors give rise to intense, low field, ‘non-resonant’ absorption signals in the superconducting state. This phenomenon
can be used as a highly sensitive, contactless technique for the detection and characterization of superconductivity even
in samples containing only minute amounts of the superconducting phase. Further, it can also be applied to the determination
of material parameters of interest such asJ
c andH
c2 in addition to being a powerful way of distinguishing between weak-link superconductivity and bulk superconductivity. The
details of these aspects are discussed. 相似文献
8.
通过探讨、分析无缝钢管壁厚偏差产生的原因,提出了改善钢管壁厚偏差的一些措施,并结合实际生产,得出了比较满意的结果。 相似文献
9.
10.
G. M. Kulikov S. V. Plotnikova 《International journal for numerical methods in engineering》2002,55(10):1167-1183
The precise representation of rigid body motions in the displacement patterns of curved Timoshenko–Mindlin (TM) shell elements is considered. This consideration requires the development of the strain–displacement relationships of the TM shell theory with regard to their consistency with the rigid body motions. For this purpose a refined TM theory of multilayered anisotropic shells is elaborated. The effects of transverse shear deformation and bending‐extension coupling are included. The fundamental unknowns consist of five displacements and eight strains of the face surfaces of the shell, and eight stress resultants. On the basis of this theory the simple and efficient mixed models are developed. The elemental arrays are derived using the Hu–Washizu mixed variational principle. Numerical results are presented to demonstrate the high accuracy and effectiveness of the developed 4‐node shell elements and to compare their performance with other finite elements reported in the literature. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献