全文获取类型
收费全文 | 38762篇 |
免费 | 1749篇 |
国内免费 | 29篇 |
专业分类
电工技术 | 240篇 |
综合类 | 17篇 |
化学工业 | 6917篇 |
金属工艺 | 660篇 |
机械仪表 | 698篇 |
建筑科学 | 929篇 |
矿业工程 | 74篇 |
能源动力 | 637篇 |
轻工业 | 5622篇 |
水利工程 | 315篇 |
石油天然气 | 123篇 |
武器工业 | 5篇 |
无线电 | 1259篇 |
一般工业技术 | 5663篇 |
冶金工业 | 12691篇 |
原子能技术 | 131篇 |
自动化技术 | 4559篇 |
出版年
2024年 | 77篇 |
2023年 | 291篇 |
2022年 | 355篇 |
2021年 | 807篇 |
2020年 | 682篇 |
2019年 | 785篇 |
2018年 | 1341篇 |
2017年 | 1299篇 |
2016年 | 1355篇 |
2015年 | 1054篇 |
2014年 | 1250篇 |
2013年 | 2598篇 |
2012年 | 1959篇 |
2011年 | 1808篇 |
2010年 | 1486篇 |
2009年 | 1336篇 |
2008年 | 1287篇 |
2007年 | 1220篇 |
2006年 | 837篇 |
2005年 | 707篇 |
2004年 | 684篇 |
2003年 | 603篇 |
2002年 | 592篇 |
2001年 | 444篇 |
2000年 | 414篇 |
1999年 | 606篇 |
1998年 | 3858篇 |
1997年 | 2487篇 |
1996年 | 1580篇 |
1995年 | 939篇 |
1994年 | 722篇 |
1993年 | 861篇 |
1992年 | 246篇 |
1991年 | 268篇 |
1990年 | 215篇 |
1989年 | 229篇 |
1988年 | 223篇 |
1987年 | 207篇 |
1986年 | 172篇 |
1985年 | 206篇 |
1984年 | 126篇 |
1983年 | 103篇 |
1982年 | 148篇 |
1981年 | 163篇 |
1980年 | 193篇 |
1979年 | 79篇 |
1978年 | 90篇 |
1977年 | 368篇 |
1976年 | 808篇 |
1973年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
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
32.
Nanocrystalline TiO2 photosensitized with natural polymers with enhanced efficiency from 400 to 600 nm 总被引:1,自引:0,他引:1
Rodolfo Espinosa Inti Zumeta Jorge L. Santana Francisco Martínez-Luzardo Bernardo Gonzlez Sergilus Docteur Elena Vigil 《Solar Energy Materials & Solar Cells》2005,85(3):359-369
TiO2 sensitization for solar applications requires not only efficient but also stable and inexpensive sensitizers. Different condensed tannins extracted from bark wastes of tropical wood trees were studied as possible sensitizers of TiO2. These natural polymers adhere strongly to the TiO2 even from aqueous solutions. Absorption spectra are presented for 1 mM aqueous sensitizing solutions prepared with lyophilized condensed tannins which absorb light in the visible range. Spectral photocurrent measurements and I–V characterization show that no bias is required for electron injection to the TiO2 from all studied condensed tannins. Incident photon to current efficiency (IPCE) analysis indicates that surface complexation originates absorption bands with different electron injection efficiencies. These play a dominant role in determining IPCE spectral shape. We propose that surface modification by the sensitizer changes the surface trap density, thereby decreasing recombination losses. 相似文献
33.
Sebastián López Gustavo M. Callicó Félix Tobajas Valentín de Armas José F. López Roberto Sarmiento 《ETRI Journal》2008,30(6):862-864
This letter presents a novel approach for organizing computational resources into groups within H.264/AVC motion estimation architectures, leading to reductions of up to 75% in the equivalent gate count with respect to state‐of‐the‐art designs. 相似文献
34.
M Isabel Sánchez de Rojas Julián Rivera Moisés Frías Félix Marín 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(3):209-217
Copper slag is a by‐product generated during smelting to extract copper metal from the ore. The copper slag obtained may exhibit pozzolanic activity and may therefore be used in the manufacture of addition‐containing cements. In this paper the effect of the incorporation of the copper slag in cement is measured. Blends of copper slag with Portland cement generally possess properties equivalent to Portland cement containing fly ash, but very different to the silica fume incorporation. Copper slag and fly ash reduce the heat of hydration more effectively than silica fume in mortars. The replacement of 30% cement by copper slag reduces the flexural and compressive strength in a similar way to fly ash; however, after 28 days, the reduction is less than the percentage of substitution. Hydrated calcium aluminate phases were analysed using scanning electron microscopy (SEM) and X‐ray diffraction (XRD) techniques. The pozzolanic activity of copper slag is similar to that of fly ash and higher than silica fume. In the presence of low water/cement ratios, certain pozzolanic materials produce a very compact cement paste that limits the space available for hydration products, a determining factor in the formation of hydrated calcium aluminates. SEM was found to be a useful analytical technique when aluminates are formed and can be clearly detected by XRD. Copyright © 2008 Society of Chemical Industry 相似文献
35.
36.
This paper presents an analysis of the data collected in the ambient vibration test of the International Guadiana cable-stayed Bridge, which links Portugal and Spain, based on different output-only identification techniques: peak-picking, frequency domain decomposition, covariance-driven stochastic subspace identification, and data-driven stochastic subspace identification. The purpose of the analysis is to compare the performance of the four techniques and evaluate their efficiency in dealing with specific challenges involved in the modal identification of the tested cable-stayed bridge, namely the existence of closely spaced modes, the perturbation produced by the local vibration of stay-cables, and the variation of modal damping coefficients with wind velocity. The identified natural frequencies and mode shapes are compared with the corresponding modal parameters provided by a previously developed numerical model. Additionally, the variability of some modal damping coefficients is related with the variation of the wind characteristics and associated with a component of aerodynamic damping. 相似文献
37.
M. Mar López-González 《Polymer》2005,46(12):4322-4329
This work reports the experimental isotherms describing the concentration of oxygen and nitrogen in poly(bisphenol A carbonate-co-4,4′-(3,3,5-trimethylcyclohexylidene) diphenol carbonate) vs pressure, at 30 °C. The solubility coefficients are interpreted in terms of the Flory-Huggins theory, obtaining reasonable values for the enthalpic polymer-gas parameter. A new method is outlined to simulate the probabilities of inserting/removing a gas molecule in a host matrix already containing n molecules of gas. The simulated isotherms representing the pressure dependence of the concentration exhibit the same pattern as those experimentally obtained. 相似文献
38.
Here we are presenting the case of a 70-years-old woman who has hepatic cirrhosis anti-HCV and insulin-dependent diabetes mellitus, without relevant epidemiologic ascendants or previous transfusions and HBV, HIV negatives. On admission to our hospital she showed signs of autoimmune hemolytic anaemia (AHA) which was confirmed by positive direct Coombs test and an improvement in blood test after corticoid treatment. Having discarded other possible causes such as drugs infectious diseases or essential mixed cryoglobulinemia (CME), we put forward the possible association between AHA and infection by HCV, where AHA was an extrahepatic immunological manifestation of HCV. This fact has never been brought to light in previous medical literature. 相似文献
39.
40.
Although accepted surgical techniques for peripheral nerve repair remain largely unchanged over the past three decades, much progress has been made toward understanding the mechanisms involved in nerve regeneration, and consequently toward providing adjunctive measures to enhance this regenerative process. We present a comprehensive review of the significant advances made in several aspects of nerve repair over the past decade, and particularly the past few years, and provide a few examples of facial nerve repair using the standard neurorrhaphy techniques recommended today. Several conclusions were drawn after thorough review of the literature. Early repair of injured nerves is preferred, and there appears to be no benefit to waiting for 3 weeks. Severed nerves should be repaired with monofilament 9-0 nylon suture placed in epineurial fashion. Fibrin glue confers no benefit in reattaching injured nerves. Likewise, theoretical advantages of laser neurorrhaphy have not resulted in improved nerve regeneration. Finally, trophic factors, such as apolipoproteins and nerve growth factor, and tubulization both appear to offer promise for future experimental and clinical progress in nerve repair. However, further work must be done to prove their efficacy. 相似文献