全文获取类型
收费全文 | 22198篇 |
免费 | 2174篇 |
国内免费 | 930篇 |
学科分类
工业技术 | 25302篇 |
出版年
2024年 | 59篇 |
2023年 | 309篇 |
2022年 | 623篇 |
2021年 | 1006篇 |
2020年 | 812篇 |
2019年 | 651篇 |
2018年 | 722篇 |
2017年 | 780篇 |
2016年 | 714篇 |
2015年 | 1061篇 |
2014年 | 1405篇 |
2013年 | 1725篇 |
2012年 | 2006篇 |
2011年 | 2130篇 |
2010年 | 1819篇 |
2009年 | 1732篇 |
2008年 | 1603篇 |
2007年 | 1501篇 |
2006年 | 1182篇 |
2005年 | 876篇 |
2004年 | 585篇 |
2003年 | 419篇 |
2002年 | 342篇 |
2001年 | 239篇 |
2000年 | 184篇 |
1999年 | 143篇 |
1998年 | 118篇 |
1997年 | 97篇 |
1996年 | 76篇 |
1995年 | 59篇 |
1994年 | 42篇 |
1993年 | 36篇 |
1992年 | 33篇 |
1991年 | 24篇 |
1990年 | 25篇 |
1989年 | 18篇 |
1988年 | 15篇 |
1987年 | 21篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 11篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 12篇 |
1966年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
F Javier Benítez Ana I Leal Francisco J Real Juan L Acero Gloria Roldán 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):309-316
BACKGROUND: The first stage of the cork industrial process generates great volumes of wastewater with moderate to high organic pollutant content that must be purified using different procedures, such as filtration by membranes. RESULTS: The tangential filtration of these wastewaters was studied using two different laboratory equipments. In the first one, three ultrafiltration (UF) membranes were tested, with molecular weight cut‐off (MWCO) 100 kDa and 30 kDa, and two operating modes were used: total recycling of permeate and retentate streams, and in continuous mode, without recycling both streams. In the total recycling UF experiments, the influence of the operating variables on the permeate flux was first established. The effectiveness of the different membranes was determined by evaluating the rejection coefficients for several parameters that measure the global pollutant content of the effluent. The values found for these rejection coefficients were in the following order: ellagic acid and color > absorbance at 254 nm > tannic content > COD (chemical oxygen demand). In the continuous mode experiments, the fouling mechanism for each membrane was established by fitting the experimental data to various filtration fouling models given in the literature. The operating mode in the second equipment was batch concentration, and additional experiments were carried out with an UF membrane (2 kDa), and with a NF membrane (with MWCO in the range 150–300 Da). CONCLUSIONS: The three operating modes tested provided different rejection levels of organic matter; among them, the most effective procedure tested was batch concentration mode using a NF membrane. Copyright © 2007 Society of Chemical Industry 相似文献
42.
Vanesa Rodríguez-Amor Juan P. Fernández-Blázquez Antonio Bello Ernesto Pérez María L. Cerrada 《Polymer Bulletin》2008,60(1):89-96
Summary The effect of molecular weight on the uniaxial orientation process has been analyzed in two samples of thermotropic poly(diethylene
glycol p,p′-bibenzoate), evaluating the influence of that parameter on the type of orientation obtained. Several strain rates and deformation
temperatures have been tested in order to map out the conditions for obtaining the two different kinds of orientation. The
results show that in the lower molecular weight PDEB sample (Mw=31200) it is rather easy to get exclusively perpendicular “anomalous” orientation, with the molecular axes aligned transversely
to the stretching direction. However, it is extremely difficult to obtain 100% parallel “normal” orientation. On the contrary,
either type of orientation or a mixture of them can be easily developed for the higher molecular weight PDEB sample (Mw=102900). 相似文献
43.
44.
LIJuan HUAYu-lin WANGChang-sheng XIONGShao-zhen 《半导体光子学与技术》2004,10(1):41-43,47
The white organic light emitting device (OLED) with single-structure using a polymer blend as the light emitting layer is fabricated. Heat treatment is used to control the ratio between the intensities of main electroluminescent spectral peaks. The electroluminescent spectrum of our device is quite similar to that of white inorganic LED produced by Nichia Corporation after being annealed, and its turn-on voltage can be decreased by 1V. 相似文献
45.
46.
47.
Juan D. Manrique Mohamed Al-Hussein Avi Telyas Geoff Funston 《Canadian Metallurgical Quarterly》2007,133(3):208-216
This paper focuses on the procedure utilized in the construction of tilt-up irregular concrete panels that are constructed on-site using concrete slabs and wooden formwork. The case study required high-quality concrete finishing. The erection and installation procedure called for a maximum panel-to-panel joint tolerance of 1.27?cm (0.5?in.), often 90° joints between panels. To meet precision requirements, the casting slabs were leveled and flattened with laser screed technology and smoothed with chemical solutions. To ensure that the final result met expectations, a mock-up model was built using different types of materials and to simulate site constraints. The architectural design is a composition of precast concrete panels like “Lego” pieces assembled similarly to a jigsaw puzzle. The unique construction process required a state-of-the-art analysis to produce the set quality. Quality conditions as set by the owner included creating a smooth concrete surface on all panels while avoiding damages and reducing equipment and material costs. The proposed methodology is described through its implementation on the case study, which is also described in this paper. 相似文献
48.
Ana Cuesta Amelia Martí nez-Alonso Juan M. D. Tasc n 《Fullerenes, Nanotubes and Carbon Nanostructures》1997,5(5):1075-1081
Fullerene reactivity in an oxygen plasma was measured and compared with those determined under the same conditions for a comprehensive set of 50 carbon materials. The possible reasons for the high plasma reactivity of the fullerene sample in an oxygen plasma are discussed. 相似文献
49.
Abstract: Maintainability problems associated with traditional software systems are exacerbated in rule-based systems. The very nature of that approach — separation of control knowledge and data-driven execution — hampers maintenance. While there are widely accepted techniques for maintaining conventional software, the same is not true for rule-based systems. In most situations, both a knowledge engineer and a domain expert are necessary to update the rules of a rule-based system. This paper presents, first, an overview of the software engineering techniques and object-oriented methods used in maintaining rule-based systems. It then discusses alternate paradigms for expert system development. The benefits of using case-based reasoning (from the maintenance point of view) are illustrated through the implementation of a case-based scheduler. The main value of the scheduler is that its knowledge base can be modified by the expert without the assistance of a knowledge engineer. Since changes in application requirements can be given directly to the system by the expert, the effort of maintaining the knowledge base is greatly reduced. 相似文献
50.