全文获取类型
收费全文 | 568096篇 |
免费 | 43802篇 |
国内免费 | 24886篇 |
专业分类
电工技术 | 34441篇 |
技术理论 | 55篇 |
综合类 | 38754篇 |
化学工业 | 92723篇 |
金属工艺 | 31389篇 |
机械仪表 | 35219篇 |
建筑科学 | 45422篇 |
矿业工程 | 17071篇 |
能源动力 | 15737篇 |
轻工业 | 36951篇 |
水利工程 | 10556篇 |
石油天然气 | 33836篇 |
武器工业 | 4661篇 |
无线电 | 64634篇 |
一般工业技术 | 64130篇 |
冶金工业 | 29459篇 |
原子能技术 | 5901篇 |
自动化技术 | 75845篇 |
出版年
2024年 | 2263篇 |
2023年 | 8172篇 |
2022年 | 15135篇 |
2021年 | 21308篇 |
2020年 | 15869篇 |
2019年 | 13028篇 |
2018年 | 14778篇 |
2017年 | 16881篇 |
2016年 | 15553篇 |
2015年 | 21226篇 |
2014年 | 27197篇 |
2013年 | 33617篇 |
2012年 | 35515篇 |
2011年 | 39662篇 |
2010年 | 35125篇 |
2009年 | 33687篇 |
2008年 | 32781篇 |
2007年 | 31452篇 |
2006年 | 31871篇 |
2005年 | 28018篇 |
2004年 | 19217篇 |
2003年 | 17218篇 |
2002年 | 16040篇 |
2001年 | 14365篇 |
2000年 | 13890篇 |
1999年 | 14918篇 |
1998年 | 12283篇 |
1997年 | 10285篇 |
1996年 | 9587篇 |
1995年 | 7949篇 |
1994年 | 6492篇 |
1993年 | 4725篇 |
1992年 | 3727篇 |
1991年 | 2783篇 |
1990年 | 2225篇 |
1989年 | 1841篇 |
1988年 | 1502篇 |
1987年 | 999篇 |
1986年 | 801篇 |
1985年 | 576篇 |
1984年 | 406篇 |
1983年 | 356篇 |
1982年 | 286篇 |
1981年 | 222篇 |
1980年 | 222篇 |
1979年 | 140篇 |
1978年 | 80篇 |
1977年 | 87篇 |
1976年 | 107篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
An inventory analysis of rural pollution loads in China. 总被引:1,自引:0,他引:1
Rural pollution has attracted increasing attention over the past decade for its important consequences on surface and groundwater quality. This is particularly so in China due to the wide and effective control of industrial and municipal wastewater discharges over the past decade. Based on the discussion of rural activities in China, this paper develops a new method of inventory analysis through the definition of elementary unit (EU). This inventory analysis approach is then applied to estimate the total rural pollution loads of COD, TN and TP, as well as their spatial distributions in China. Further analysis is also conducted to investigate the correlations between rural pollution loads and agricultural production outputs, as well as population. It is found that China's agriculture is developing largely at the cost of environment quality, and a high population, as well as the increasing demand for agricultural products, is one of the dominant driving forces. The constructed EKC, which describes the relationship between rural pollution loads and agricultural income, also reveals that current agricultural development in China is mostly far from de-locked from the environmental problem. 相似文献
12.
本文通过径流还原计算和绘制降水径流深相关图的方法,对天然年径流系列的一致性进行了分析,并通过实例验证了该方法可使水文资料系列更具代表性。 相似文献
13.
The toughness of 31Mn2SiRE wear-resistance cast steel were increased by means of RE compound modification and high temperature austenitizing. The results show that the microstructures can be refined, needle and network ferrite are eliminated, the dislocation density and the quantity of dislocated martensite are increased remarkably, and the shape and distribution of inclusions are improved by the addition of RE. Therefore, the mechanical properties of the modified steel can be greatly increased, especially the toughness (αK) by 44%, yield strength (σs) by 10%, and elongation (δ5) by 42%. 相似文献
14.
Based on the current spin density functional theory, a theoretical model of three vertically aligned semiconductor quantum dots is proposed and numerically studied. This quantum dot molecule (QDM) model is treated with realistic hard-wall confinement potential and external magnetic field in three-dimensional setting. Using the effective-mass approximation with band nonparabolicity, the many-body Hamiltonian results in a cubic eigenvalue problem from a finite difference discretization. A self-consistent algorithm for solving the Schrödinger-Poisson system by using the Jacobi-Davidson method and GMRES is given to illustrate the Kohn-Sham orbitals and energies of six electrons in the molecule with some magnetic fields. It is shown that the six electrons residing in the central dot at zero magnetic field can be changed to such that each dot contains two electrons with some feasible magnetic field. The Förster-Dexter resonant energy transfer may therefore be generated by two individual QDMs. This may motivate a new paradigm of Fermionic qubits for quantum computing in solid-state systems. 相似文献
15.
This study was undertaken to develop a modified atmosphere package to control microbial growth in ready‐to‐eat (RTE) products stored at ambient temperature. Ethanol and/or limonene associated with modified atmosphere (CO2 : O2 : N2 = 30% : 5% : 65%) was used to inhibit the growth of total air‐borne microorganisms and Escherichia coli in RTE products stored at 25°C. The results indicated that 0.05% ethanol vapour in the headspace was effective to inhibit the growth of air‐borne microorganisms and E. coli at 25°C for 72 h in a model study, and the effectiveness was related to ethanol content. Both 73 ppm limonene and 0.05% ethanol vapour enhanced the bacteriostatic effect of modified atmosphere in RTE sushi roll products, and no off‐flavour was detected using this formulated gas; however, no significant inhibitory effect was observed for RTE cold noodle products. This study concludes that combinations of carbon dioxide, ethanol or limonene vapours are effective to inhibit microbial growth in RTE food at ambient temperature, and the outcome may be due to the hurdle effect. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
16.
Rheological properties of MR fluids under large step strain shear are presented in this paper. The experiments were carried out using a rheometer with parallel-plate geometry. Under the large step strain shear, MR fluids behave as nonlinear viscoelastic properties, where the stress relaxation modulus, G(t, γ), shows a decreasing trend with step strain. The experimental results indicate that G(t, γ) obeys time-strain separability. Thus, a mathematical form based on finite exponential serials is proposed to predict MR behavior. In this model, G(t, γ) is represented as the product of a linear stress relaxation, G(t), and the damping function, h(γ), i.e. G(t, γ)=G(t) h(γ). G(t) is simply represented as a three-parameter exponential serial and h(γ) has a sigmoidal form with two parameters. The parameters are identified by adopting an efficient optimization method proposed by Stango et al. The comparison between the experimental results and the model-predicted values indicates that this mathematical model can accurately predict MR behavior. 相似文献
17.
城域网的建设是今后光纤网络建设的一个热点,根据城域网的特点和系统技术要求选择光纤光缆是网络设计的重要组成部分。本根据城域网的特点和需求,对市场上现有的光纤光缆做了详细的分析和探讨,提出了城域网规划中光纤光缆选择的原则和具体的建议。 相似文献
18.
大牛地气田为低渗-致密气田,因存在启动压力梯度等因素,修正等时试井曲线按常规方法处理出现异常,无法准确获取气井的产能方程.采用LIT法和异常曲线校正法对气田异常试井资料进行了重新处理,最终获得气井产能方程,为同类气藏产能试井可能出现的异常资料处理解释探索了新的途径. 相似文献
19.
VE432可控震源控制系统常见故障分析 总被引:1,自引:0,他引:1
VE432系统为新一代可控震源控制系统,文中简要地介绍了该系统的功能,根据实际生产中出现的常见故障进行分析并给出解决方法. 相似文献
20.