全文获取类型
收费全文 | 23355篇 |
免费 | 1624篇 |
国内免费 | 681篇 |
专业分类
电工技术 | 519篇 |
技术理论 | 5篇 |
综合类 | 1775篇 |
化学工业 | 3769篇 |
金属工艺 | 470篇 |
机械仪表 | 755篇 |
建筑科学 | 1691篇 |
矿业工程 | 179篇 |
能源动力 | 379篇 |
轻工业 | 3644篇 |
水利工程 | 168篇 |
石油天然气 | 275篇 |
武器工业 | 159篇 |
无线电 | 1642篇 |
一般工业技术 | 6494篇 |
冶金工业 | 1224篇 |
原子能技术 | 174篇 |
自动化技术 | 2338篇 |
出版年
2024年 | 166篇 |
2023年 | 497篇 |
2022年 | 720篇 |
2021年 | 1058篇 |
2020年 | 791篇 |
2019年 | 732篇 |
2018年 | 687篇 |
2017年 | 841篇 |
2016年 | 789篇 |
2015年 | 767篇 |
2014年 | 1368篇 |
2013年 | 1717篇 |
2012年 | 1830篇 |
2011年 | 1523篇 |
2010年 | 1195篇 |
2009年 | 1406篇 |
2008年 | 1039篇 |
2007年 | 1054篇 |
2006年 | 969篇 |
2005年 | 763篇 |
2004年 | 707篇 |
2003年 | 553篇 |
2002年 | 490篇 |
2001年 | 378篇 |
2000年 | 254篇 |
1999年 | 239篇 |
1998年 | 194篇 |
1997年 | 121篇 |
1996年 | 1120篇 |
1995年 | 529篇 |
1994年 | 394篇 |
1993年 | 82篇 |
1992年 | 90篇 |
1991年 | 71篇 |
1990年 | 61篇 |
1989年 | 62篇 |
1988年 | 39篇 |
1987年 | 26篇 |
1986年 | 21篇 |
1985年 | 34篇 |
1984年 | 51篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 11篇 |
1964年 | 21篇 |
1961年 | 14篇 |
1955年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
We have assessed the antimicrobial, vapor-phase activity of the following natural essential oils (EOs) when used in paraffin-based “active coatings” for paper packaging materials intended to come into contact with foods: clove (Sygzium aromaticum), cinnamon (Cinnamomum zeylanicum), and oregano (Origanum vulgare) EOs, and cinnamaldehyde-enriched cinnamon EO. To our knowledge, this is the first time that such an approach has been presented for consideration by the scientific community. 相似文献
122.
Influence of Storage Time and Temperature on Absorption of Flavor Compounds from Solutions by Plastic Packaging Materials 总被引:1,自引:0,他引:1
R. Van Willige D. Schoolmeester A. Van Ooij J. Linssen A. Voragen 《Journal of food science》2002,67(6):2023-2031
ABSTRACT: Linear low-density polyethylene (LLDPE), oriented polypropylene (OPP), polycarbonate (PC), polyethylene terephthalate (PET film and PET bottle), and polyethylene naphthalate (PEN) were stored in a model solution containing 10 flavor compounds at 4, 20, and 40 °C and flavor absorption by the plastic materials was followed in time. The absorption rate and/or total amount absorbed increased considerably with temperature from 4 to 40 °C. Depending on storage temperature, total flavor absorption by the polyolefins (LLDPE and OPP) was 3 to 2400 times higher than by the polyesters (PC, PET, and PEN). Therefore, in the factor of flavor absorption, polyesters are preferred over polyolefins as packaging material. 相似文献
123.
P. Ravirajan S.A. Haque J.R. Durrant D.D.C. Bradley J. Nelson 《Advanced functional materials》2005,15(4):609-618
We report a study of the effects of polymer optoelectronic properties on the performance of photovoltaic devices consisting of nanocrystalline TiO2 and a conjugated polymer. Three different poly(2‐methoxy‐5‐(2′‐ethylhexoxy)‐1,4‐phenylenevinylene) (MEH‐PPV)‐based polymers and a fluorene–bithiophene copolymer are compared. We use photoluminescence quenching, time‐of‐flight mobility measurements, and optical spectroscopy to characterize the exciton‐transport, charge‐transport, and light‐harvesting properties, respectively, of the polymers, and correlate these material properties with photovoltaic‐device performance. We find that photocurrent is primarily limited by the photogeneration rate and by the quality of the interfaces, rather than by hole transport in the polymer. We have also studied the photovoltaic performance of these TiO2/polymer devices as a function of the fabrication route and device design. Including a dip‐coating step before spin‐coating the polymer leads to excellent polymer penetration into highly structured TiO2 networks, as was confirmed through transient optical measurements of the photoinduced charge‐transfer yield and recombination kinetics. Device performance is further improved for all material combinations studied, by introducing a layer of poly(ethylene dioxythiophene) (PEDOT) doped with poly(styrene sulfonic acid) (PSS) under the top contact. Optimized devices incorporating the additional dip‐coated and PEDOT:PSS layers produced a short‐circuit current density of about 1 mA cm–2, a fill factor of 0.50, and an open‐circuit voltage of 0.86 V under simulated AM 1.5 illumination (100 mW cm–2, 1 sun). The corresponding power conversion efficiency under 1 sun was ≥ 0.4 %. 相似文献
124.
速度密度 10m/s住宅 总被引:4,自引:2,他引:2
本文通过一次参加日本《新建筑》国际住宅竞赛的经历,就未来高密度城市环境中住宅的生存状态进行了探讨。并试图用以速度来定义密度的方式探索当私密性与公共交往之间出现不可调和的矛盾时一种新的解决之道。 相似文献
125.
126.
127.
128.
Shu-Chu Ren Nelson N. Hsu Donald G. Eitzen 《Journal of research of the National Institute of Standards and Technology》2002,107(5):445-473
Pulsed ultrasonic techniques can be and have been used to examine the interface conditions of a bonded structure. To provide a theoretical basis for such testing techniques we model the structure as a layer on top of a half-space, both of different elastic properties, with various interface bonding conditions. The exact dynamic Green’s tensor for such a structure is explicitly derived from the three-dimensional equations of motion. The final solution is a series. Each term of the series corresponds to a successive arrival of a “generalized ray” and each is a definite line integral along a fixed path which can be easily computed numerically. Willis’ method is used in the derivation. A new scheme of automatic generation of the arrivals and ray paths using combinatorial analysis, along with the summation of the corresponding products of reflection coefficients is presented. A FORTRAN code is developed for computation of the Green’s tensor when both the source and the detector are located on the top surface. The Green’s tensor is then used to simulate displacements due to pulsed ultrasonic point sources of known time waveform. Results show that the interface bonding conditions have a great influence on the transient displacements. For example, when the interface bonding conditions vary, some of the first few head waves and regular reflected rays change polarities and amplitudes. This phenomenon can be used to infer the quality of the interface bond of materials in ultrasonic nondestructive evaluation. In addition the results are useful in the study of acoustic microscopy probes, coatings, and geo-exploration. 相似文献
129.
Rubina H. Shreiner 《Journal of research of the National Institute of Standards and Technology》2002,107(5):393-399
The stability of solutions having an electrolytic conductivity, κ, of 5 μS/cm to 100 000 μS/cm packaged in glass screw-cap bottles, glass serum bottles, and glass ampoules was monitored for 1 year to 2 years. The conductivity was determined by measuring the ac resistance of the solution. Mass loss was also monitored for solutions packaged in bottles. The solutions were prepared using KCl in water (κ ≥100 μS/cm) or KCl in 30 % (by mass) n-propanol 70 % (by mass) water (κ ≤ 15 μS/cm). The conductivity changes were compared by packaging type and by nominal κ. The main causes of the κ changes are evaporation (screw-cap bottles) and leaching (screw-cap bottles, serum bottles, and ampoules). Evaporation is determined from mass loss data; leaching occurs from the glass container with no change in mass. The choice of optimal packaging, which depends on the conductivity level, is the packaging in which κ changes the least with time. Ampoules are the most suitable packaging for standards having nominal κ values of 500 μS/cm to 100 000 μS/cm. Screw-cap bottles are most suitable for standards having a nominal κ of 5 μS/cm to 100 μS/cm. 相似文献
130.
tific Experiment Center of Guangxi Medical University,Nanning 530021,China)Objective:To investigate the mutation pattern of adenomatous polyposis coli(APC),Kirsten-ras(K-ras) and p53 genes in sporadic colorectal cancer tissues.Meth 相似文献