全文获取类型
收费全文 | 116030篇 |
免费 | 9956篇 |
国内免费 | 5192篇 |
专业分类
电工技术 | 6744篇 |
技术理论 | 9篇 |
综合类 | 7548篇 |
化学工业 | 19066篇 |
金属工艺 | 7082篇 |
机械仪表 | 8072篇 |
建筑科学 | 9557篇 |
矿业工程 | 3856篇 |
能源动力 | 3363篇 |
轻工业 | 7419篇 |
水利工程 | 1961篇 |
石油天然气 | 8160篇 |
武器工业 | 971篇 |
无线电 | 12719篇 |
一般工业技术 | 13460篇 |
冶金工业 | 5775篇 |
原子能技术 | 1178篇 |
自动化技术 | 14238篇 |
出版年
2024年 | 578篇 |
2023年 | 2087篇 |
2022年 | 3728篇 |
2021年 | 5095篇 |
2020年 | 3925篇 |
2019年 | 3175篇 |
2018年 | 3394篇 |
2017年 | 3802篇 |
2016年 | 3547篇 |
2015年 | 4825篇 |
2014年 | 5762篇 |
2013年 | 6752篇 |
2012年 | 7317篇 |
2011年 | 7770篇 |
2010年 | 6739篇 |
2009年 | 6400篇 |
2008年 | 6319篇 |
2007年 | 5952篇 |
2006年 | 6254篇 |
2005年 | 5514篇 |
2004年 | 3631篇 |
2003年 | 3313篇 |
2002年 | 3163篇 |
2001年 | 2850篇 |
2000年 | 2747篇 |
1999年 | 3040篇 |
1998年 | 2420篇 |
1997年 | 2041篇 |
1996年 | 1992篇 |
1995年 | 1645篇 |
1994年 | 1352篇 |
1993年 | 914篇 |
1992年 | 765篇 |
1991年 | 522篇 |
1990年 | 435篇 |
1989年 | 379篇 |
1988年 | 274篇 |
1987年 | 182篇 |
1986年 | 152篇 |
1985年 | 84篇 |
1984年 | 70篇 |
1983年 | 61篇 |
1982年 | 59篇 |
1981年 | 36篇 |
1980年 | 45篇 |
1979年 | 22篇 |
1978年 | 6篇 |
1977年 | 13篇 |
1973年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A novel series of temperature‐sensitive poly[(N‐isopropylacrylamide)‐co‐(ethyl methacrylate)] (p(NIPAM‐co‐EMA)) microgels was prepared by the surfactant‐free radical polymerization of N‐isopropylacrylamide (NIPAM) with ethyl methacrylate (EMA). The shape, size dispersity and volume‐phase transition behavior of the microgels were investigated by transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy, dynamic light scattering (DLS) and differential scanning calorimetry (DSC). The transmission electron micrographs and DLS results showed that microgels with narrow distributions were prepared. It was shown from UV–Vis, DLS and DSC measurements that the volume‐phase transition temperature (VPTT) of the p(NIPAM‐co‐EMA) microgels decreased with increasing incorporation of EMA, but the temperature‐sensitivity was impaired when more EMA was incorporated, causing the volume‐phase transition of the microgels to become more continuous. It is noteworthy that incorporation of moderate amounts of EMA could not only lower the VPTT but also enhance the temperature‐sensitivity of the microgels. The reason for this phenomenon could be attributed to changes in the complicated interactions between the various molecules. Copyright © 2004 Society of Chemical Industry 相似文献
92.
Shaofeng Wang Jianwei Xu Yuejin Tong Lin Wang Chaobin He 《Polymer International》2005,54(9):1268-1274
A novel cholesterol‐imprinted polymer (CMIP‐H) was prepared by a hybrid method of covalent imprinting and non‐covalent imprinting. This approach involves the copolymerization of a template‐containing monomer, cholesteryl 2‐hydroxyethyl methacrylate carbonate, and a cross‐linker, followed by hydrolysis to afford a flexible guest‐binding site accompanied with the easy and efficient removal of a ‘sacrificial spacer’. The effect of solvent on the binding capacity of CMIP‐H towards cholesterol was studied, indicating that a good binding capacity towards cholesterol could be achieved in a less‐polar solvent. The binding experiments of CMIP‐H towards a series of structural analogues of cholesterol, including cholesterol acetate, progesterone and stigmasterol, were carried out in hexane. The results showed that CMIP‐H almost did not bind cholesterol acetate at all because the hydrogen‐bonding site is blocked. It exhibited a similar binding towards both cholesterol and stigmasterol, but much higher binding towards progesterone. Copyright © 2005 Society of Chemical Industry 相似文献
93.
94.
95.
Dongchang Sun Liyong Tong 《International journal for numerical methods in engineering》2004,60(11):1911-1932
A novel finite element model is presented for static and dynamic analysis of composite plates integrated with a laminated piezoelectric layer, a host laminated composite plate and an adhesive layer between them. A new adhesive element is developed which includes both peel and shear effects in the adhesive layer based on first‐order shear deformation plate theory. The thin adhesive layer between the piezoelectric layer and the host plate is modelled by assuming that it carries constant shear and peel strains throughout its thickness. In addition, a weighted static shape control scheme for finding the optimal voltage distribution for static shape control is given. By selecting different weighting matrices, a variety of items such as displacements, slopes, curvatures, strains and even generalized forces, can be included in finding the optimal actuating voltage for static shape control. The present model is validated by comparing with those results available in the literature. The numerical results show that the weighted linear least method can give a satisfactory voltage distribution to best match the desired shape. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
97.
Xue‐Bing Zhao Lei Wang De‐Hua Liu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(6):950-956
Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry 相似文献
98.
Shi Wei Zhao Xuefeng Ma Conghui Management of the National Development Reform Commission 《中国通信》2008,(3)
After the new round of restructuring of Chinese telecom sector,it's pressing to formulate and implement asymmetric regulation policies so as to shape an effectively competitive market structure in a relatively short term.This paper reviewed the asymmetric regulation policies and practices carried out in foreign telecom market,and then according to the specific situations of Chinese telecom market,proposed the principles and corresponding policies for establishing an asymmetric regulation system fit for Chin... 相似文献
99.
100.
Hui Chen D.T.K. Tong 《Photonics Technology Letters, IEEE》2005,17(4):801-803
Symmetric interference in two-dimensional multimode silicon waveguides is experimentally investigated. For a 100/spl times/100 /spl mu/m/sup 2/ cross section, 2700-/spl mu/m-long waveguide fabricated on silicon-on-insulator substrate, an 8/spl times/8 matrix of replicated images with high contrast ratio is demonstrated for 1530-1570 nm wavelength range. Symmetric interference results in reduced device length, and the actual device length is consistent with the theoretical expectation. The device also exhibits stable imaging in terms of good loss uniformity, and low wavelength and polarization dependencies among the replicated images. 相似文献