全文获取类型
收费全文 | 14564篇 |
免费 | 1776篇 |
国内免费 | 5381篇 |
专业分类
电工技术 | 402篇 |
综合类 | 1507篇 |
化学工业 | 1879篇 |
金属工艺 | 316篇 |
机械仪表 | 773篇 |
建筑科学 | 5042篇 |
矿业工程 | 499篇 |
能源动力 | 294篇 |
轻工业 | 248篇 |
水利工程 | 288篇 |
石油天然气 | 436篇 |
武器工业 | 1115篇 |
无线电 | 3337篇 |
一般工业技术 | 3851篇 |
冶金工业 | 256篇 |
原子能技术 | 78篇 |
自动化技术 | 1400篇 |
出版年
2024年 | 35篇 |
2023年 | 231篇 |
2022年 | 285篇 |
2021年 | 448篇 |
2020年 | 493篇 |
2019年 | 502篇 |
2018年 | 465篇 |
2017年 | 766篇 |
2016年 | 746篇 |
2015年 | 816篇 |
2014年 | 959篇 |
2013年 | 1315篇 |
2012年 | 1177篇 |
2011年 | 1384篇 |
2010年 | 1053篇 |
2009年 | 1226篇 |
2008年 | 1164篇 |
2007年 | 1214篇 |
2006年 | 1308篇 |
2005年 | 1351篇 |
2004年 | 1174篇 |
2003年 | 769篇 |
2002年 | 472篇 |
2001年 | 341篇 |
2000年 | 346篇 |
1999年 | 289篇 |
1998年 | 243篇 |
1997年 | 214篇 |
1996年 | 156篇 |
1995年 | 156篇 |
1994年 | 116篇 |
1993年 | 111篇 |
1992年 | 78篇 |
1991年 | 56篇 |
1990年 | 62篇 |
1989年 | 61篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 5篇 |
1976年 | 3篇 |
1955年 | 5篇 |
1954年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
82.
The optical emission characteristics of biaxially compressed InAs
x
P1−
x
/InP strained single quantum well (QW) structures, with nominal compositionx=0.67, have been investigated using photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies. The highly
strained QWs exhibit intense and narrow PL in the 0.9–1.5 μm wavelength range, similar to the lattice-matched InGaAs(P)/InP
system. The 20 K PLE spectra exhibit well-resolved features attributed ton=1 heavy hole (E1H1) and light hole (E1L1) transitions in the 1.0–1.5 μm wavelength range. In addition, features attributed
to transitions betweenn=2 electrons and heavy holes (E2H2), and betweenn=1 electrons and unconfined holes (E1Hf), were observed. The energy splitting between the heavy-hole and light-hole bands
was found to be a sensitive measure of the band offsets in the system. The best prediction of this splitting was obtained
for a valence band offset of δE
V
∼0.25δE
G
. This value of band offset was in agreement with the energy position of the E1Hf transition. The observed transition energies
were also compared with the results of a finite square well model, taking into account the effects of strain, and the results
offer further support for the band offset assignment. This study indicates that the InAsP system may be advantageous for application
in strained-layer optoelectronic devices operating in the 1.3–1.6 μm wavelength range. 相似文献
83.
84.
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
85.
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
86.
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
87.
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
88.
铰链式井下动力钻具组合是当前短半径水平钻井中最先进的一种新型工具。本文首先建立了铰接式井下动力钻具组合在二维井身条件下的力学模型并介绍了该模型的求解方法和过程,详细分析了若干结构学数、井身几何参数和钻井工艺参数对钻头侧向力的定量影响,为铰接式井下动力钻具组合的结构设计和短半径水平井轨道控制提供了力学分析基础。 相似文献
89.
90.
钢纤维聚合物混凝土抗压本构关系 总被引:2,自引:0,他引:2
钢纤维聚合物混凝土是由聚合物混凝土基体和钢纤维共同组成的纤维增强复合材料,它的力学行为不仅依赖于聚合物混凝土基体的行为,而且与钢纤维的掺量、分散特征以及钢纤维的几何尺寸有关,本文将基于损伤力学原理研究在不同纤维掺量下的钢纤维聚合物混凝土的全程压力-应变曲线及其本构模型。 相似文献