全文获取类型
收费全文 | 23207篇 |
免费 | 641篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 306篇 |
综合类 | 16篇 |
化学工业 | 4524篇 |
金属工艺 | 398篇 |
机械仪表 | 478篇 |
建筑科学 | 1231篇 |
矿业工程 | 115篇 |
能源动力 | 707篇 |
轻工业 | 1664篇 |
水利工程 | 168篇 |
石油天然气 | 210篇 |
武器工业 | 1篇 |
无线电 | 1977篇 |
一般工业技术 | 3799篇 |
冶金工业 | 4695篇 |
原子能技术 | 188篇 |
自动化技术 | 3400篇 |
出版年
2022年 | 233篇 |
2021年 | 345篇 |
2020年 | 209篇 |
2019年 | 285篇 |
2018年 | 342篇 |
2017年 | 338篇 |
2016年 | 420篇 |
2015年 | 343篇 |
2014年 | 528篇 |
2013年 | 1527篇 |
2012年 | 927篇 |
2011年 | 1218篇 |
2010年 | 968篇 |
2009年 | 1008篇 |
2008年 | 1143篇 |
2007年 | 1123篇 |
2006年 | 894篇 |
2005年 | 886篇 |
2004年 | 707篇 |
2003年 | 709篇 |
2002年 | 619篇 |
2001年 | 437篇 |
2000年 | 377篇 |
1999年 | 398篇 |
1998年 | 528篇 |
1997年 | 448篇 |
1996年 | 429篇 |
1995年 | 418篇 |
1994年 | 363篇 |
1993年 | 390篇 |
1992年 | 327篇 |
1991年 | 201篇 |
1990年 | 275篇 |
1989年 | 319篇 |
1988年 | 240篇 |
1987年 | 234篇 |
1986年 | 229篇 |
1985年 | 280篇 |
1984年 | 274篇 |
1983年 | 237篇 |
1982年 | 234篇 |
1981年 | 218篇 |
1980年 | 181篇 |
1979年 | 207篇 |
1978年 | 188篇 |
1977年 | 188篇 |
1976年 | 156篇 |
1975年 | 187篇 |
1974年 | 173篇 |
1973年 | 142篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
This paper considers the axisymmetric steady flow driven by exact counter rotation of two co-axial disks of finite radius.
At the edges of the rotating disks one of three conditions is (typically) imposed: (i) zero velocity, corresponding to a stationary,
impermeable, cylindrical shroud (ii) zero normal velocity and zero tangential fluid traction, corresponding to a (confined)
free surface and (iii) an edge constraint that is consistent with a similarity solution of von Kármán form. The similarity
solution is valid in an infinite geometry and possesses a pitchfork bifurcation that breaks the midplane symmetry at a critical
Reynolds number. In this paper, similar bifurcations of the global (finite-domain) flow are sought and comparisons are made
between the resulting bifurcation structure and that found for the similarity solution. The aim is to assess the validity
of the nonlinear similarity solutions in finite domains and to explore the sensitivity of the solution structure to edge conditions
that are implicitly neglected when assuming a self-similar flow. It is found that, whilst the symmetric similarity solution
can be quantitatively useful for a range of boundary conditions, the bifurcated structure of the finite-domain flow is rather
different for each boundary condition and bears little resemblance to the self-similar flow. 相似文献
43.
Ready-to-drinks (RTDs) are composed of an alcoholic component and a soft-drink base and are primarily consumed by a youth market. The authors explored whether liking and experience with an RTD soft-drink base predicts liking for the RTD. Participants (N=350) from ages 12 to 30 years sampled 3 RTDs and their respective soft-drink and alcoholic components. For milk- and fruit-based RTDs, liking for and familiarity with their soft-drink base was the best predictor of liking for and familiarity with the RTD itself. For the Coke-based RTD, familiarity with and liking for bourbon best predicted familiarity with and liking for the RTD. All of these effects were consistent across blind and nonblind testing. The authors' results suggest that where there is perceptual similarity between the RTD and its soft-drink base, these beverages may provide an easy transition into alcohol consumption for novice drinkers. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
44.
45.
This paper describes the elastic response of a block sample of compressible Chicago glacial clay under a variety of stresses and its relationship with the deformation characteristics at relatively large strains. The elastic shear stiffness was obtained from bender element tests during consolidation and shearing in drained triaxial stress probe tests. An empirical correlation was established based on the elastic shear stiffness in a preyield condition. By comparing the empirical correlation with the measured elastic shear stiffness in the stress region during probing, the changes of elastic shear stiffness were investigated. The departure of elastic shear stiffness from values computed by the empirical relation based on K0 loading directly relates to the yielding characteristics of the clay. The large-scale change of soil structure at yielding alters the well-established relationship between the elastic shear stiffness and stresses in the preyield condition. The mechanical yielding response of clays can be detected based on the systematic analysis of the elastic shear wave velocities. 相似文献
46.
Two-Dimensional Physical and Numerical Modeling of a Pile-Supported Earth Platform over Soft Soil 总被引:1,自引:0,他引:1
This paper focuses on the mechanisms occurring in a granular earth platform over soft ground improved by rigid piles. Two-dimensional physical model experiments were performed using the Schneebeli’s analogical soil to investigate the load transfer mechanisms by arching and the settlement reduction and homogenization. Experimental outputs are compared to results obtained on a numerical model using a plane strain continuum approach. The impact of the constitutive model complexity to simulate the platform material behavior was first assessed, but no large difference was recorded. As far as the proposed model, which takes the main features of the observed behavior satisfactorily into account, the numerical procedure could be validated and the parametric studies extended numerically. Both approaches of this study underlined the main geometrical and geotechnical parameters which should inevitably be taken into account in a simplified design method, namely the capping ratio, the platform height, and the platform material shear strength. 相似文献
47.
An efficient, convenient and quantitative method for characterising polyester end-groups is described. We have found that trichloroacetyl isocyanate (TAI) reacts rapidly and quantitatively with both carboxyl [C(O)OH] and hydroxyl (OH) chain ends to form derivatives that can be readily determined by 1H NMR spectroscopy. The TAI capped end-groups give rise to characteristic imidic NH resonances in a normally clear region of the 1H NMR spectrum [δ∼10-11.5 for C(O)-O-C(O)-NH-C(O)CCl3 from C(O)OH, δ∼8-9 for O-C(O)-NH-C(O)CCl3 from OH]. The method has been successfully applied to quantitative determination of the end-groups of a wide variety of oligomeric polyesters. It has also been applied to higher molecular weight polyesters including commercial, bottle grade, poly(ethylene terephthalate) (PET) and PET based copolyesters (e.g. PETG). 相似文献
48.
49.
The results of study of the effects of yttria stabilization (0–6 mol.%) on the room-temperature fracture behavior and toughening mechanisms in zirconia-reinforced MoSi2 are presented in this paper. Transformation toughening is shown to occur only in composites reinforced with zirconia particles stabilized with 2 mol.% yttria. However, the fracture toughness levels are comparable in the other composites with yttria levels between 0 and 6 mol.%. Toughening in the other composites is attributed to the combined effects of residual stress, microcrack shielding/anti-shielding and/or crack deflection. A rigorous micromechanics-based model is presented for the estimation of residual stress levels in brittle materials reinforced with phases that can transform during cooling or under stress. The model is applied successfully to the rationalization of the observed fracture and toughening phenomena. 相似文献
50.
Intracellular tyrosine kinases link the G protein-coupled m1 muscarinic acetylcholine receptor (mAChR) to multiple cellular responses. However, the mechanisms by which m1 mAChRs stimulate tyrosine kinase activity and the identity of the kinases within particular signaling pathways remain largely unknown. We show that the epidermal growth factor receptor (EGFR), a single transmembrane receptor tyrosine kinase, becomes catalytically active and dimerized through an m1 mAChR-regulated pathway that requires protein kinase C, but is independent of EGF. Finally, we demonstrate that transactivation of the EGFR plays a major role in a pathway linking m1 mAChRs to modulation of the Kv1.2 potassium channel. These results demonstrate a ligand-independent mechanism of EGFR transactivation by m1 mAChRs and reveal a novel role for these growth factor receptors in the regulation of ion channels by G protein-coupled receptors. 相似文献