全文获取类型
收费全文 | 81508篇 |
免费 | 8020篇 |
国内免费 | 3910篇 |
学科分类
工业技术 | 93438篇 |
出版年
2024年 | 219篇 |
2023年 | 1494篇 |
2022年 | 2678篇 |
2021年 | 4117篇 |
2020年 | 2992篇 |
2019年 | 2491篇 |
2018年 | 2714篇 |
2017年 | 2921篇 |
2016年 | 2566篇 |
2015年 | 3667篇 |
2014年 | 4476篇 |
2013年 | 5119篇 |
2012年 | 5643篇 |
2011年 | 6055篇 |
2010年 | 5392篇 |
2009年 | 4940篇 |
2008年 | 4728篇 |
2007年 | 4386篇 |
2006年 | 4298篇 |
2005年 | 3684篇 |
2004年 | 2401篇 |
2003年 | 2037篇 |
2002年 | 2015篇 |
2001年 | 1645篇 |
2000年 | 1547篇 |
1999年 | 1698篇 |
1998年 | 1288篇 |
1997年 | 1086篇 |
1996年 | 1074篇 |
1995年 | 937篇 |
1994年 | 752篇 |
1993年 | 497篇 |
1992年 | 386篇 |
1991年 | 315篇 |
1990年 | 246篇 |
1989年 | 210篇 |
1988年 | 181篇 |
1987年 | 112篇 |
1986年 | 101篇 |
1985年 | 61篇 |
1984年 | 55篇 |
1983年 | 38篇 |
1982年 | 34篇 |
1981年 | 32篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1977年 | 10篇 |
1976年 | 14篇 |
1959年 | 7篇 |
1951年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
Water Resources Management - Urban river not only has the important function in urban hydrological environment, but also is an area for entertainment. Water quality assessment is the core technique... 相似文献
44.
Shanshan Zhuang Wenxiong Zheng Yunong Na Naiyi Chen Fan Gong Bingxuan Huang Stephen Brennan Charles Congyi Liu Jian Cheng Lukai Ma Huifan Liu 《International Journal of Food Science & Technology》2022,57(2):1093-1103
The β-Carotene (BC), an important precursor of vitamin A (VA), possesses antioxidant activity but is fat-soluble and has low bioavailability. In previous in-vitro assays evaluating antioxidant and 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) free radical scavenging, both BC and VA showed a strong ability to scavenge radicals and protected cells from oxidative stress. Here, we used artificially simulated gastrointestinal digestion and Caco-2 cell absorption models to evaluate the bioavailability of the BC during gastrointestinal digestion and absorption using high-performance liquid chromatography (HPLC) analysis. We observed high absorptive and transfer rates of BC and detected retinol metabolites (Vitamin A). Therefore, BC can be detected in the acidic gastrointestinal environment using HPLC. Optimised method provided better separation of BC and VA in the column, improving the accuracy of the test results. 相似文献
45.
46.
Weiyu Bi Panfeng Zhang Xiangrui Du Wei Lü Shitou Wang Tangying Yang Liping Ma Xiaochun Liu Haifeng Zhao Shaoran Ren 《Journal of surfactants and detergents》2022,25(3):387-398
Natural gas foam can be used for mobility control and channel blocking during natural gas injection for enhanced oil recovery, in which stable foams need to be used at high reservoir temperature, high pressure and high water salinity conditions in field applications. In this study, the performance of methane (CH4) foams stabilized by different types of surfactants was tested using a high pressure and high temperature foam meter for surfactant screening and selection, including anionic surfactant (sodium dodecyl sulfate), non-anionic surfactant (alkyl polyglycoside), zwitterionic surfactant (dodecyl dimethyl betaine) and cationic surfactant (dodecyl trimethyl ammonium chloride), and the results show that CH4-SDS foam has much better performance than that of the other three surfactants. The influences of gas types (CH4, N2, and CO2), surfactant concentration, temperature (up to 110°C), pressure (up to 12.0 MPa), and the presence of polymers as foam stabilizer on foam performance was also evaluated using SDS surfactant. The experimental results show that the stability of CH4 foam is better than that of CO2 foam, while N2 foam is the most stable, and CO2 foam has the largest foam volume, which can be attributed to the strong interactions between CO2 molecules with H2O. The foaming ability and foam stability increase with the increase of the SDS concentration up to 1.0 wt% (0.035 mol/L), but a further increase of the surfactant concentration has a negative effect. The high temperature can greatly reduce the stability of CH4-SDS foam, while the foaming ability and foam stability can be significantly enhanced at high pressure. The addition of a small amount of polyacrylamide as a foam stabilizer can significantly increase the viscosity of the bulk solution and improve the foam stability, and the higher the molecular weight of the polymer, the higher viscosity of the foam liquid film, the better foam performance. 相似文献
47.
49.
支承或连接构件对梁结构的动力学性能有至关重要影响,必须保证其在振动过程中不发生破坏或者失效。通过合理设计和布局附加弹性支承可以实现对这些重要连接构件所承受约束反力的控制。应用微分变换法推导含附加支承的梁结构支承约束反力及其对于附加支承位置和刚度的灵敏度表达式,并通过优化设计附加支承位置和刚度实现具有弹性约束端的简支梁结构各支承约束反力的平衡,可提高结构的动力学性能。 相似文献
50.
Yixuan ZHOU Huajie WANG Yi YU Yihang CHEN Rui KE Min XU Chijie XIAO Zhanhui WANG Jiquan LI Xuru DUAN Minyou YE 《等离子体科学和技术》2021,23(7):75105-52
In this article, we present the optical design of a novel diagnostic on the HL-2 A tokamak, i.e. the20-channel edge Lyman-alpha beam emission spectroscopy, which is a promising solution for edge density turbulence research on tokamaks, as it offers the possibility of density fluctuation measurement with a 3.3 mm spatial resolution while maintains a high temporal resolution of1 μs. The optical path, including the reflective collection optics, the high-dispersion spectrometer, and the linear detector array, is carefully optimized to obtain a good image quality and a high throughput. The maximum root mean square radius of the collection optics is 64 μm.The detected photon flux is estimated to be about 10~(11) photons/s/channel. 相似文献