全文获取类型
收费全文 | 29640篇 |
免费 | 3234篇 |
国内免费 | 1644篇 |
专业分类
电工技术 | 621篇 |
技术理论 | 1篇 |
综合类 | 2043篇 |
化学工业 | 10517篇 |
金属工艺 | 869篇 |
机械仪表 | 2238篇 |
建筑科学 | 920篇 |
矿业工程 | 521篇 |
能源动力 | 1128篇 |
轻工业 | 2473篇 |
水利工程 | 401篇 |
石油天然气 | 1855篇 |
武器工业 | 631篇 |
无线电 | 1550篇 |
一般工业技术 | 4517篇 |
冶金工业 | 672篇 |
原子能技术 | 445篇 |
自动化技术 | 3116篇 |
出版年
2024年 | 190篇 |
2023年 | 699篇 |
2022年 | 1367篇 |
2021年 | 1490篇 |
2020年 | 1204篇 |
2019年 | 1123篇 |
2018年 | 978篇 |
2017年 | 1108篇 |
2016年 | 1234篇 |
2015年 | 1208篇 |
2014年 | 1734篇 |
2013年 | 2019篇 |
2012年 | 1887篇 |
2011年 | 2118篇 |
2010年 | 1374篇 |
2009年 | 1539篇 |
2008年 | 1374篇 |
2007年 | 1674篇 |
2006年 | 1514篇 |
2005年 | 1268篇 |
2004年 | 1087篇 |
2003年 | 921篇 |
2002年 | 752篇 |
2001年 | 725篇 |
2000年 | 612篇 |
1999年 | 551篇 |
1998年 | 456篇 |
1997年 | 375篇 |
1996年 | 332篇 |
1995年 | 280篇 |
1994年 | 212篇 |
1993年 | 195篇 |
1992年 | 163篇 |
1991年 | 150篇 |
1990年 | 103篇 |
1989年 | 102篇 |
1988年 | 73篇 |
1987年 | 49篇 |
1986年 | 33篇 |
1985年 | 47篇 |
1984年 | 51篇 |
1983年 | 36篇 |
1982年 | 40篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1976年 | 4篇 |
1959年 | 8篇 |
1955年 | 5篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Konstantinos Spyrou Matteo Calvaresi Evmorfia K. Diamanti Theodoros Tsoufis Dimitrios Gournis Petra Rudolf Francesco Zerbetto 《Advanced functional materials》2015,25(2):263-269
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”. 相似文献
2.
The paper considers the problem of stabilization of systems possessing a multiple zero eigenvalue at the origin. The controller that we propose, uses multiple delayed measurements instead of derivative terms. Doing so, we increase the performances of the closed loop in presence of system uncertainties and/or noisy measurements. The problem formulation and the analysis is presented through a classical engineering problem which is the stabilization of an inverted pendulum on a cart moving horizontally. On one hand, we perform a nonlinear analysis of the center dynamics described by a three dimensional system of ordinary differential equations with a codimension-three triple zero bifurcation. On the other hand, we present the complementary stability analysis of the corresponding linear time invariant system with two delays describing the behavior around the equilibrium. The aim of this analysis is to characterize the possible local bifurcations. Finally, the proposed control scheme is numerically illustrated and discussed. 相似文献
3.
前期杂交优化后赤芝菌种经液体深层发酵后,提取灵芝菌丝体多糖,并过DEAE-Sepharose Fast Flow柱分离纯化,利用高效体积排阻色谱(HPSEC)检测多糖级分的纯度,采用完全酸水解PMP柱前衍生化RP—HPLC测定多糖级分的单糖组成,多角度光散射仪联用装置(SEC—MALLS)测定其绝对重均分子量(Mw),并且根据分子旋转半径与分子摩尔数的关系曲线斜率初步推断其空间构象。结果显示:分离纯化得到3个多糖级分GLMP1、GLMP2和GLMP3,HPSEC检测其峰面积百分比分别为93.58%,97.64%,99.19%,单糖组成分析结果表明GLMP1、GLMP2和GLMP3均含有甘露糖、鼠李糖、半乳糖醛酸、葡萄糖、半乳糖、木糖、阿拉伯糖和岩藻糖,但单糖摩尔比各异。SEC—MALLS测试GLMP1、GLMP2和GLMP3的Mw分别为4.526×105,4.603×104,3.760×103 g/mol,3个多糖级分构象可能均为高度紧缩且具有分支结构的聚合物。 相似文献
4.
聚α-烯烃是一种性能优良的润滑油基础油,其相对分子质量及分布直接影响宏观性能。本研究建立了一种用于表征1-癸烯齐聚物相对分子质量及分布的方法。采用带示差折光检测器的凝胶渗透色谱系统,综合考虑分离效果和测试可操作性,优化了流动相流速和凝胶色谱柱的组合方式。以四氢呋喃为流动相,流速为0.8 mL/min,色谱柱组合方式为Styragel HR 0.5,Styragel HR 1,PLGEL 3μm MIXED-E三柱串联,以聚苯乙烯作为标准样品,采用普适校正方法处理色谱流出曲线。此方法测得样品的质均相对分子质量与凝胶渗透色谱-光散射法所测定结果相比较,相对误差相对偏差在3%以内。 相似文献
5.
6.
7.
A stochastic model for local disturbances, particularly for a temporal harmonic with random modulations in amplitude and/or phase, is proposed in this paper. Results for the second moment responses of a linear single-degree-of-freedom system to this type of stochastic loading demonstrate a significant change in response characteristics due to a small uncertainty. A local phenomenon may last much longer and resonance may be smeared to a broad range. Integrated with wavelet transform, the proposed approach may be used to model a random process with non-stationary frequency content. Especially, it can be effectively used for Monte Carlo simulation to generate large size of samples that have similar characteristics in time and frequency domains as a pre-selected mother sample has. The technique has a great potential for the case where uncertainty study is warranted but the available samples are limited. 相似文献
8.
9.
10.
Dynamics of liquid-filled spacecraft 总被引:1,自引:0,他引:1
A method is presented for simulating coupled liquid-solid dynamics. An important example of a coupled liquid-solid system is a satellite carrying fuel. The dynamics of the satellite and the onboard fuel influence each other, which may lead to satellite motion that is uncontrollable. For better understanding of the complex dynamics of coupled systems, a numerical model is developed. The model consists of two parts. The first part that solves the liquid motion is only briefly discussed here. The focus in this paper is on the way in which the dynamics of the liquid and the solid body are coupled. For this, the governing equations are presented in which terms appear that represent the force and torque on the solid body due to the sloshing liquid. The governing equations are rewritten such that the discrete approximation of these equations can be integrated in a stable manner for arbitrary liquid/solid mass ratios. Results are presented demonstrating the stability of the present model. A grid-refinement study and a time-step analysis are performed. Finally, the flat-spin motion of a satellite, partially filled with liquid, that flew in 1992 as part of the Wet Satellite Model experiment is studied. Results from the simulation are compared with the actual flight data. 相似文献