全文获取类型
收费全文 | 7587篇 |
免费 | 399篇 |
国内免费 | 14篇 |
学科分类
工业技术 | 8000篇 |
出版年
2023年 | 58篇 |
2022年 | 28篇 |
2021年 | 114篇 |
2020年 | 110篇 |
2019年 | 128篇 |
2018年 | 166篇 |
2017年 | 146篇 |
2016年 | 214篇 |
2015年 | 187篇 |
2014年 | 311篇 |
2013年 | 544篇 |
2012年 | 443篇 |
2011年 | 481篇 |
2010年 | 351篇 |
2009年 | 426篇 |
2008年 | 364篇 |
2007年 | 332篇 |
2006年 | 335篇 |
2005年 | 288篇 |
2004年 | 274篇 |
2003年 | 250篇 |
2002年 | 269篇 |
2001年 | 198篇 |
2000年 | 164篇 |
1999年 | 154篇 |
1998年 | 355篇 |
1997年 | 212篇 |
1996年 | 155篇 |
1995年 | 131篇 |
1994年 | 114篇 |
1993年 | 111篇 |
1992年 | 58篇 |
1991年 | 70篇 |
1990年 | 55篇 |
1989年 | 57篇 |
1988年 | 40篇 |
1987年 | 42篇 |
1986年 | 39篇 |
1985年 | 30篇 |
1984年 | 29篇 |
1983年 | 20篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1974年 | 6篇 |
1973年 | 8篇 |
排序方式: 共有8000条查询结果,搜索用时 15 毫秒
41.
Production and isolation of chitosan from Aspergillus terreus and application in tin(II) adsorption 下载免费PDF全文
Li‐Chun Cheng Tzung‐Shian Wu Jian‐Wen Wang Szu‐Han Wu Mei‐Hui Chung Yi‐Ming Kuo Cheng‐Hsien Tsai 《应用聚合物科学杂志》2014,131(12)
Fed‐batch fermentation was used for biomass and fungal chitosan production by Aspergillus terreus (BCRC 32068) grown in a potato dextrose agar medium. The polysaccharides were extracted by an alkali–acid treatment, and structural investigations by X‐ray diffraction, Fourier transform infrared analysis, and viscosity and thermal analysis were done. A high level of chitosan was extracted from A. terreus; this implied that it was feasible to produce chitosan from industrial waste mycelia. Fungal chitosan derived from A. terreus showed the highest adsorption capacity for Sn(II). The order of Sn(II) adsorption capacity for these chitosanaceous materials was Fungal chitosan > Chitin > Biomass. Fungal chitosan derived from A. terreus was well correlated with Langmuir's isotherm model. The maximum capacity for Sn(II) sorption deduced from the use of the Langmuir isotherm equation was 303 mg/g; this was significantly higher than that of A. terreus. Fungal chitosan is an easy and cost‐effective material for the abatement of pollution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40436. 相似文献
42.
Joost Duvigneau Edit Kutnyanszky In Yee Phang Hong-Jing Chung Hairong Wu Lionel Dos Ramos Torben Gädt Siti Fairus M. Yusoff Mark A. Hempenius Ian Manners G. Julius Vancso 《Polymer》2014
We report on the morphology evolution during heating and melting of lamellar poly(isoprene)-block-poly(ferrocenyldimethylsilane) (PI76-b-PFDMS76) raft crystals deposited at the native oxide surface of silicon (SiO2) or at a highly ordered pyrolytic graphite (HOPG) surface, studied by in situ temperature controlled atomic force microscopy. Crystals deposited on hydrophilic SiO2 surfaces revealed an irreversible decrease in length at temperatures of up to tens of degrees above their expected melting temperature, while maintaining their platelet-like structure. Crystals deposited on hydrophobic HOPG surfaces initially decreased in length below their expected melting temperature, while at 120 °C and above a typical molten morphology was observed. In addition, the irreversible formation of a PI76-b-PFDMS76 wetting layer around the crystals was observed upon increasing the temperature. These observations in the morphological behavior upon heating emphasize the role of interfacial energy between a surface deposited block copolymer based macromolecular nanostructure and its supporting substrate. 相似文献
43.
Ho-Sung Yoon Chul-Joo Kim Kyeong Woo Chung Su-Jeong Lee A-Ram Joe Yang-Ho Shin Se-Il Lee Seung-Joon Yoo Jin-Geol Kim 《Korean Journal of Chemical Engineering》2014,31(4):706-711
The leaching kinetics of neodymium in NdFeB permanent magnet powder was analyzed for the purpose of recovery of neodymium in sulfuric acid (H2SO4) from E-scrap (electric scrap) of NdFeB permanent magnet powder treated by oxidation roasting to form a reactant. The reaction was conducted with H2SO4 concentrations ranging from 2.5 to 3.5M, a pulp density of 110.8 g/L, an agitation speed of 750 rpm, and a temperature range of 30 to 70 °C. After 4 h of leaching, the neodymium content in the E-scrap powders was completely converted into a neodymium sulfate (Nd2(SO4)3) solution phase in H2SO4 in the condition of 70 °C and 3.0M H2SO4. Based on a shrinking core model with sphere shape, the leaching mechanism of neodymium was determined by the rate-determining step of the ash layer diffusion. Generally, the solubility of pure rare earth elements in H2SO4 is decreased with an increase in leaching temperatures. However, the leaching rate of the neodymium in E-scrap powders increased with the leaching temperatures in this study because the ash layer included in the E-scrap powder provided resistance against the leaching. Using the Arrhenius expression, the apparent activation energy values were determined to be 2.26 kJmol?1 in 2.5M H2SO4 and 2.77 kJmol?1 in 3.0 M H2SO4. 相似文献
44.
Robust and high performance pressure retarded osmosis hollow fiber membranes for osmotic power generation 下载免费PDF全文
Novel fabrication perspectives have been demonstrated to molecularly construct robust hollow fiber membrane supports for high performance thin‐film composite (TFC) pressure retarded osmosis (PRO) membranes. For the first time, we found that the desirable hollow fiber supports should possess high stretch resistance and acceptable ductility. The microstructure strength of the hollow fiber support may have more weights on overall robustness of the TFC PRO membranes than the apparent cross‐section morphology. Effectively manipulating the kinetics of phase inversion during spinning by maneuvering bore fluid chemistry, and polymer solution composition is a promising method to tailor the strength of hollow fiber supports. Prestabilization of the TFC membranes at elevated lumen pressures can significantly improve their PRO performance. The newly developed TFC PRO hollow fiber membranes exhibit a power density as high as 16.5 W/m2 and a very low specific reverse salt flux (Js/Jw) of 0.015 mol/L at a hydraulic pressure of 15 bar using synthetic seawater brine (1.0 M NaCl) as the draw solution. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1107–1119, 2014 相似文献
45.
Ground cave-ins caused by damaged sewer pipes have been frequently reported in metropolitan areas and have caused severe socioeconomic losses. In this study, model experiments were conducted to determine how damaged sewer pipes generate ground cave-ins or cavities, with a focus on the influence of the soil type and density. Digital images of the model ground were captured to evaluate the internal deformation of the model grounds. Additionally, the vertical displacement at the surface, the size of the cavity, and the weight of the discharged soil were measured in each test. The results indicate that uniform soil with no fines content was more vulnerable to ground cavities than well-graded soil with fines content. Loose soil led to a ground cave-in with significant deformation over the entire model ground, whereas deformation was concentrated only on the ground cavities in the dense soil ground. 相似文献
46.
Hee‐Chang Eun Young‐Ho Lee Heon‐Soo Chung Keun‐Hyeok Yang 《The Structural Design of Tall and Special Buildings》2006,15(4):445-466
An objective of this study is to establish the shear strength of reinforced concrete deep beam with web opening. Eighteen beams were tested with the variables of the steel ratio and strength of longitudinal bars, concrete strength, and shear span‐to‐depth ratio. It was observed that the opening is strengthened by longitudinal bars but the load‐carrying capacity of deep beams with openings can be largely improved by the increase in concrete strength. Modifying the softened truss model derived by Mau and Hsu and utilizing the results of this experiment carried out with the variables of concrete strength, cross‐section size, shear‐span‐to‐depth ratio, and the strength and steel ratio of longitudinal bars, this study proposes an improved model to predict the shear strength. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
47.
In this study, elemental composition of PM2.5 and the status of indoor/outdoor pollution were investigated in a commercial building near a roadside area in Daejeon, Korea. A total of 60 parallel PM2.5 samples were collected both on the roof (outdoor) and in an indoor office of a building near a highly congested road during the spring and fall of 2008. The concentrations of 23 elements were analysed from these PM2.5 samples using instrumental neutron activation analysis. PM2.5 levels in indoor environment (47.6 ± 16.5 μg/m(3)) were noticeably higher than the outdoor levels (37.7 ± 17.2 μg/m(3)) with the I/O concentration ratio of 1.37 ± 0.33 [correlation coefficient (r) = 0.89, P < 0.001]. Principal component analysis results coincidently showed the predominance of sources such as soil dust, traffic, oil/coal combustion and road dust for both indoor and outdoor microenvironments. An isolated source in the indoor environment was assigned to environmental tobacco smoke (ETS) with high factor loading of Ce, Cl, I, K, La and Zn. The overall results of our study indicate that the sources of indoor constituents were strongly dependent on outdoor processes except for the ones affected by independent sources such as ETS. PRACTICAL IMPLICATIONS: An improved understanding of the factors affecting the indoor PM2.5 concentration levels can lead to the development of an efficient management strategy to control health risks from exposure to indoor PM2.5 and related toxic components. A comparison of our comprehensive data sets indicated that most indoor PM2.5 and associated elemental species were strongly enriched by indoor source activities along with infiltration of ambient outdoor air for a naturally ventilated building. 相似文献
48.
Experiment and numerical modeling of prestressed concrete curved slab with spatial unbonded tendons 总被引:1,自引:0,他引:1
Curved prestressed concrete structures with unbonded tendons are widely used in highway interchanges and industrial cooling towers, etc. In engineering practice, there is a demand to establish calculating methods for analyzing and designing these prestressed concrete curved structures with unbonded tendons. However, there are some difficulties in calculating the ultimate strength of these curved structures. The major difficulty is to calculate the ultimate stress in unbonded tendons. The assumption of a plane cross-section cannot be adopted here because of the slip between unbonded tendon and concrete. Thus, many formulas for calculating the ultimate stress in unbonded tendons were mainly based on experimental data fitting. In order to obtain the ultimate stress in unbonded tendons from mechanical principles, instead of using experimental data fitting formula, an advanced nonlinear analysis method to calculate ultimate stress in unbonded tendons is developed. The analysis model is established by using the Reissner-Mindlin medium thickness plate theory allowing for the influence of the transverse shear deformation. The orthotropic increment constitutive model of concrete is extended to solve the medium thickness plate problem. The tension stiffening of the cracked concrete is considered in the nonlinear analysis model. The numerical formulation of calculating the stress increment in an unbonded tendon is established by using the spatial displacement relationship. Instead of using general-purpose programs such as ANSYS and ABAQUS, a computer program specifically for predicting the nonlinear response of a prestressed concrete curved slab structure with unbonded tendons and calculating the ultimate stress in unbonded tendons is developed by authors. Six test models of prestressed concrete curved slabs with unbonded tendons are reported. The calculated results using this program are compared with test results, where their relative deviation is less than 3.0%, which validates the proposed method. These study results can be used for analysis, especially to design the strength of prestressed concrete curved structures with unbonded tendons. And, this research work also proposes a new approach, which can be customized to fit into general purposed FEM programs, such as APDL (ANSYS Parametric Design Language), for analyzing the nonlinear structural behavior of these curved structures. 相似文献
49.
Polycyclic aromatic hydrocarbons (PAHs) in urban surface dust of Guangzhou, China: Status, sources and human health risk assessment 总被引:7,自引:0,他引:7
Wang W Huang MJ Kang Y Wang HS Leung AO Cheung KC Wong MH 《The Science of the total environment》2011,409(21):4519-4527
Ninety-six urban surface dust samples collected from Guangzhou, a typical urban center in South China, were analyzed for 16 PAHs (2-6 rings). ∑ PAHs concentrations in the urban surface dust ranged from 0.84 to 12.3 μg/g with a mean of 4.80 μg/g. High molecular weight compounds (4-6 rings) contributed to 62 to 94% of ∑ PAHs mass in the surface dust samples. Four hotspots with highest ∑ PAHs were identified via kriging prediction mapping, representing the highly-urbanized regions: central downtown, highway and industrial area. Two major origins of PAHs inputs to urban surface dust were identified as vehicle emissions (51.9%) and coal combustion (26.8%). The 95% UCL of Incremental Lifetime Cancer Risk (ILCR) due to human exposure to urban surface dust PAHs in central South China was 3.03 × 10−6 for children and 2.92 × 10−6 for adults. 相似文献
50.