全文获取类型
收费全文 | 233359篇 |
免费 | 21883篇 |
国内免费 | 13330篇 |
专业分类
电工技术 | 23832篇 |
技术理论 | 9篇 |
综合类 | 15767篇 |
化学工业 | 37774篇 |
金属工艺 | 19412篇 |
机械仪表 | 16422篇 |
建筑科学 | 12924篇 |
矿业工程 | 7453篇 |
能源动力 | 7378篇 |
轻工业 | 15053篇 |
水利工程 | 3510篇 |
石油天然气 | 10203篇 |
武器工业 | 2129篇 |
无线电 | 25344篇 |
一般工业技术 | 28065篇 |
冶金工业 | 10936篇 |
原子能技术 | 2576篇 |
自动化技术 | 29785篇 |
出版年
2024年 | 634篇 |
2023年 | 3346篇 |
2022年 | 5183篇 |
2021年 | 7343篇 |
2020年 | 7121篇 |
2019年 | 6458篇 |
2018年 | 6033篇 |
2017年 | 7547篇 |
2016年 | 8492篇 |
2015年 | 9231篇 |
2014年 | 13411篇 |
2013年 | 13127篇 |
2012年 | 15403篇 |
2011年 | 18168篇 |
2010年 | 13982篇 |
2009年 | 14842篇 |
2008年 | 13673篇 |
2007年 | 15668篇 |
2006年 | 14157篇 |
2005年 | 12190篇 |
2004年 | 10364篇 |
2003年 | 9898篇 |
2002年 | 8388篇 |
2001年 | 6466篇 |
2000年 | 5573篇 |
1999年 | 4494篇 |
1998年 | 3198篇 |
1997年 | 2557篇 |
1996年 | 2260篇 |
1995年 | 1957篇 |
1994年 | 1650篇 |
1993年 | 1262篇 |
1992年 | 1035篇 |
1991年 | 674篇 |
1990年 | 487篇 |
1989年 | 449篇 |
1988年 | 327篇 |
1987年 | 232篇 |
1986年 | 198篇 |
1985年 | 168篇 |
1984年 | 140篇 |
1983年 | 88篇 |
1982年 | 100篇 |
1981年 | 117篇 |
1980年 | 129篇 |
1979年 | 41篇 |
1978年 | 38篇 |
1977年 | 32篇 |
1976年 | 33篇 |
1975年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
This paper presents the Kriging model approach for stochastic free vibration analysis of composite shallow doubly curved shells. The finite element formulation is carried out considering rotary inertia and transverse shear deformation based on Mindlin’s theory. The stochastic natural frequencies are expressed in terms of Kriging surrogate models. The influence of random variation of different input parameters on the output natural frequencies is addressed. The sampling size and computational cost is reduced by employing the present method compared to direct Monte Carlo simulation. The convergence studies and error analysis are carried out to ensure the accuracy of present approach. The stochastic mode shapes and frequency response function are also depicted for a typical laminate configuration. Statistical analysis is presented to illustrate the results using Kriging model and its performance. 相似文献
72.
Various methods have been developed to monitor the health and strain state of carbon fiber reinforced polymers, each with a unique set of pros and cons. This research assesses the use of piezoresistive sensors for in situ strain measurement of carbon fiber and other composite structures in multidirectional laminates. The piezoresistive sensor material and the embedded circuitry are both evaluated. For the piezoresistive sensor, a conductive nickel nanocomposite sensor is compared with the piezoresistivity of the carbon fiber itself. For the circuit, the use of carbon fibers already present in the structure is compared with the use of nickel coated carbon fiber. Successful localized strain sensing is demonstrated for several sensor and circuitry configurations. Numerous engineering applications are possible in the ever-growing field of carbon-composites. 相似文献
73.
This short communication presents a generic mathematical programming formulation for computer-aided molecular design (CAMD). A given CAMD problem, based on target properties, is formulated as a mixed integer linear/non-linear program (MILP/MINLP). The mathematical programming model presented here, which is formulated as an MILP/MINLP problem, considers first-order and second-order molecular groups for molecular structure representation and property estimation. It is shown that various CAMD problems can be formulated and solved through this model. 相似文献
74.
Microwave irradiation has been proven to be an effective heating source in synthetic chemistry, and can accelerate the reaction rate, provide more uniform heating and help in developing better synthetic routes for the fabrication of bone-grafting implant materials. In this study, a new technique, which comprises microwave heating and powder metallurgy for in situ synthesis of Ti/CaP composites by using Ti powders, calcium carbonate (CaCO3) powders and dicalcium phosphate dihydrate (CaHPO4·2H2O) powders, has been developed. Three different compositions of Ti:CaCO3:CaHPO4·2H2O powdered mixture were employed to investigate the effect of the starting atomic ratio of the CaCO3 to CaHPO4·2H2O on the phase, microstructural formation and compressive properties of the microwave synthesized composites. When the starting atomic ratio reaches 1.67, composites containing mainly alpha-titanium (α-Ti), hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP) and calcium titanate (CaTiO3) with porosity of 26%, pore size up to 152 μm, compressive strength of 212 MPa and compressive modulus of 12 GPa were formed. The in vitro apatite-forming capability of the composite was evaluated by immersing the composite into a simulated body fluid (SBF) for up to 14 days. The results showed that biodissolution occurred, followed by apatite precipitation after immersion in the SBF, suggesting that the composites are suitable for bone implant applications as apatite is an essential intermediate layer for bone cells attachment. The quantity and size of the apatite globules increased over the immersion time. After 14 days of immersion, the composite surface was fully covered by an apatite layer with a Ca/P atomic ratio approximately of 1.68, which is similar to the bone-like apatite appearing in human hard tissue. The results suggested that the microwave assisted-in situ synthesis technique can be used as an alternative to traditional powder metallurgy for the fabrication of Ti/CaP biocomposites. 相似文献
75.
76.
As a solid state joining process, ultrasonic spot welding has been proven to be a promising technique for joining copper alloys. However, challenges still remain in employing ultrasonic spot welding to join copper alloys. This article comprehensively reviews the current state of ultrasonic spot welding of copper alloys with a number of critical issues including materials flow, plastic deformation, temperature distribution, vibration, relative motion, vertical displacement, interface friction coefficient, online monitoring technique, coupled with the macrostructure and microstructure, the mechanical properties and electrical conductivity. In addition, the future trends in this field are provided. 相似文献
77.
某出口型号交流电力机车牵引控制系统要求变流器控制逻辑具备接触器控制、牵引系统数据交互、变流器故障保护、变流器启动自检等功能。针对以上功能,基于MATLAB中的Simulink/Stateflow可视化编程工具进行牵引控制模型的搭建,遵循模块化编程理念,采用较少的程序代码编写实现复杂的逻辑控制模型,生成逻辑清晰的控制功能流程图,进行半实物仿真测试,增强控制模型的可靠性。通过该变流器产品型式试验检验,验证变流器控制逻辑的功能可以满足控制系统的需求。 相似文献
78.
Effects of different carbon sources and C/N values on nonvolatile taste components of Pleurotus eryngii
下载免费PDF全文
![点击此处可从《International Journal of Food Science & Technology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wen Li Xiaobei Li Yan Yang Feng Zhou Yanfang Liu Shuai Zhou Hailong Yu 《International Journal of Food Science & Technology》2015,50(11):2360-2366
Pleurotus eryngii, the second largest industrial cultivation mushroom in China, is usually cultivated on substrates mainly consisting of sawdust and corncob. In this study, experiments were performed to determine the effects of different carbon sources and C/N values on nonvolatile taste components of P. eryngii. The effects of different carbon sources on nonvolatile taste components levels revealed that sawdust was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while corncob was beneficial to high contents of carbohydrate, polysaccharides and trehalose. At the similar C/N values, relatively higher sawdust content was beneficial to umami amino acid production, while relatively higher corncob content was beneficial to high contents of carbohydrate, polysaccharides and mannitol. Higher C/N value was beneficial to high levels of crude protein, amino acids, 5′‐nucleotides and equivalent umami concentration, while lower C/N value was beneficial to high contents of carbohydrate, polysaccharides and trehalose. These results provided information for P. eryngii fruit body industrial cultivation to obtain specific nonvolatile taste components with high levels. 相似文献
79.
MC nylon-6-b-polyether amine copolymers were prepared with macro-initiator based on amino-terminated polyether amine functionalized with isocyanate via in-situ polymerization. It was found that the introduction of polyether amine delayed the polymerization process of caprolactam by increasing apparent activation energy and pre-exponential factor, resulting in the decrease of molecular weight of nylon-6. The motion of molecular chain of the copolymers was easy because of the decreased hydrogen bonds and weakened inter-molecular forces. The physical entanglement of molecular chains of the copolymers was significant and strong which increased the entanglement density. Only the nylon-6 phase crystallized in the copolymers and the crystal grain size, spherulite size and crystallinity of the copolymers decreased. A small amount of γ crystal formed at high polyether amine content. The copolymers presented obvious strain hardening behavior in stress-strain curves and the loss factor dramatically increased while the glass transition temperature and storage module decreased. The fracture surface of the copolymers became rough and presented hairy structure, indicating that the toughening mechanism of the copolymers corresponded to the multi-layer crack extension mechanism. 相似文献
80.
Thermoresponsive behavior and rheology of SiO2–hyaluronic acid/poly(N‐isopropylacrylamide) (NaHA/PNIPAm) core–shell structured microparticles
下载免费PDF全文
![点击此处可从《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》网站下载免费的PDF全文](/ch/ext_images/free.gif)