全文获取类型
收费全文 | 9897篇 |
免费 | 725篇 |
国内免费 | 4594篇 |
专业分类
电工技术 | 136篇 |
综合类 | 1106篇 |
化学工业 | 1297篇 |
金属工艺 | 231篇 |
机械仪表 | 632篇 |
建筑科学 | 5510篇 |
矿业工程 | 973篇 |
能源动力 | 170篇 |
轻工业 | 131篇 |
水利工程 | 339篇 |
石油天然气 | 559篇 |
武器工业 | 1067篇 |
无线电 | 99篇 |
一般工业技术 | 2316篇 |
冶金工业 | 252篇 |
原子能技术 | 59篇 |
自动化技术 | 339篇 |
出版年
2024年 | 16篇 |
2023年 | 71篇 |
2022年 | 218篇 |
2021年 | 246篇 |
2020年 | 241篇 |
2019年 | 241篇 |
2018年 | 238篇 |
2017年 | 430篇 |
2016年 | 461篇 |
2015年 | 478篇 |
2014年 | 592篇 |
2013年 | 811篇 |
2012年 | 718篇 |
2011年 | 957篇 |
2010年 | 802篇 |
2009年 | 879篇 |
2008年 | 868篇 |
2007年 | 961篇 |
2006年 | 1020篇 |
2005年 | 1091篇 |
2004年 | 972篇 |
2003年 | 642篇 |
2002年 | 345篇 |
2001年 | 230篇 |
2000年 | 241篇 |
1999年 | 218篇 |
1998年 | 228篇 |
1997年 | 202篇 |
1996年 | 146篇 |
1995年 | 145篇 |
1994年 | 90篇 |
1993年 | 90篇 |
1992年 | 71篇 |
1991年 | 44篇 |
1990年 | 47篇 |
1989年 | 32篇 |
1988年 | 36篇 |
1987年 | 26篇 |
1986年 | 18篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1958年 | 1篇 |
1955年 | 4篇 |
1954年 | 1篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
41.
A novel approach to the derivation of Bažant’s size effect law is presented. Contrarily to the original Lagrangian derivation
which hinged on energetic consideration, a Newtonian approach based on local stress intensity factors is presented. Through
this approach, it is shown that Bažant’s size effect law is the first (and dominant) term in a series expansion for the nominal
stress. Furthermore, analytical expressions forB are derived for selected specimen geometries. 相似文献
42.
A framework is presented for examining the effectiveness of limiting and modelling arguments used in the analysis of fluid
flows. It consists of examining the consequences of the arguments on the flow problem as a whole and breaking down the limiting/modelling
process into a sequence of steps and associated sequence of flow problems, termed here as ‘lidels’. The notion of validity
of lidels is given. Several examples are given to explain the present approach.
Invited general lecture at 3rd ACFM, Tokyo, September 1986 相似文献
43.
44.
Shu-Chu Ren Nelson N. Hsu Donald G. Eitzen 《Journal of research of the National Institute of Standards and Technology》2002,107(5):445-473
Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration. 相似文献
45.
This paper presents observations regarding the cracking behavior of tensile-loaded structural adhesive joints. Experiments showed that fracture occurred by the development and propagation of a damage zone, rather than a single, sharp crack, and that the presence of the adhesive spew fillet did not affect the fracture load of the adhesive joints studied. For joints bonded with the mineral-filled epoxy Cybond 4523GB (American Cyanamid), there was approximately 5 mm of subcritical crack propagation prior to final fracture. Fracture-load predictions based on the initial uncracked geometry made in previous papers were unaffected by this small change in geometry. For joints bonded with the rubber-toughened epoxy Permabond ESP 310, approximately 50 mm of subcritical crack propagation was observed. It was again found that predictions made in previous papers on the basis of the initial geometry gave a good estimate of the final fracture load even though this subcritical crack propagation significantly altered the geometry, and thus the applied energy release rates. The effect of shear deformations of the adherends was also investigated, and it was found that shear deformations could be neglected in engineering calculations for joints subject to remote tensile loading. 相似文献
46.
An existing extensive database on the isothermal and thermomechanical fatigue behaviour of high-temperature titanium alloy
EVII 834 and dispersoid-strengthened aluminum alloy X8019 in SiC particle-reinforced as well as unreinv conditions was used
to evaluate both the adaptability of fracture mechanics approaches to TMF and the resulting predictive capabilities of determining
material life by crack propagation consideration. Selection of the correct microstructural concepts was emphasised and these
concepts were, then adjusted by using data from independent experiments in order to avoid any sort of fitting. It is shown
that the cyclic /-integral (δJeff concept) is suitable to predict the cyclic lifetime for conditions where the total crack propagation rate is approximately
identical to pure fatigue crack growth velocity. In the case that crack propagation is strongly affected by creep, the creep-fatigue
damage parameter δCF introduced by Riedel can be successfully applied. If environmental effects are very pronounced, the accelerating influence
of corrosion on fatigue crack propagation can no longer implicitly be taken into account in the fatigue crack growth law.
Instead, a linear combination of the crack growth rate contributions from plain fatigue (determined in vacuum) and from environmental
attack is assumed and found to yield a satisfactory prediction, if the relevant corrosion process is taken into account. 相似文献
47.
A new interaction integral formulation is developed for evaluating the elastic T-stress for mixed-mode crack problems with
arbitrarily oriented straight or curved cracks in orthotropic nonhomogeneous materials. The development includes both the
Lekhnitskii and Stroh formalisms. The former is physical and relatively simple, and the latter is mathematically elegant.
The gradation of orthotropic material properties is integrated into the element stiffness matrix using a “generalized isoparametric
formulation” and (special) graded elements. The specific types of material gradation considered include exponential and hyperbolic-tangent
functions, but micromechanics models can also be considered within the scope of the present formulation. This paper investigates
several fracture problems to validate the proposed method and also provides numerical solutions, which can be used as benchmark
results (e.g. investigation of fracture specimens). The accuracy of results is verified by comparison with analytical solutions. 相似文献
48.
Mohammad Hossein Keshavarz 《含能材料》2006,14(6):449-452
A new method for prediction of Gurney velocity of explosives is introduced in which energy output is correlated with the heat of detonation, the number of moles of gaseous products of detonation per gram of explosive and the average molecular weight of gaseous products. It is assumed that the CHNO explosive reacts to form products composed of N2 , CO, H2O, CO2, H2,O2 and C(s) as determined by the oxygen balance of the unreacted compound. Good agreement is obtained between measured and calculated values of Gurney velocity as compared to previous correlations which assumed the reaction products to consist of N2 , H2O, CO2 and either C(s) or O2. 相似文献
49.
A. Samuelsson O. C. Zienkiewicz 《International journal for numerical methods in engineering》2006,67(2):149-157
This paper presents a brief history of the development of the stiffness method. We start by tracing the evolution of the method to solve discrete‐type problems such as trusses and frames composed of two node members. We then describe the method as it is applied to solve continuum problems modelled by finite‐difference and finite‐element methods. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
50.
It is generally appreciated that the mechanical behavior of granular media depends fundamentally on the interaction of the
constituent particles, and that the validity of numerical models of granular media would be greatly improved with knowledge
of the grain-scale mechanics. However, most supporting experimental work has been conducted on highly idealized materials,
and a limited amount of information exists on grain-scale force–displacement relationships for naturally occurring materials.
To address this shortcoming, we are conducting a program that integrates laboratory experiments on grains of naturally occurring
aggregate with the discrete element modeling method, with the goal of relating the grain-scale physical and mechanical properties
of granular media to bulk behavior. The paper describes the equipment and methods that have been developed to conduct close-loop
controlled, grain-scale experiments under monotonic and cyclic loading conditions, and presents results from an initial set
of experiments on unbonded grains. The implications of the grain-scale results to the discrete element model are discussed.
Discussions center on the applicability of a physically based approach to the mechanics of granular media in general. In light
of future exploration missions and the resulting need to predict the mechanical properties of lunar and planetary regoliths,
the paper examines the potential usefulness of our physically based approach to the problem of predicting the behavior of
the types of materials found in those environments. 相似文献