全文获取类型
收费全文 | 170770篇 |
免费 | 13524篇 |
国内免费 | 6798篇 |
专业分类
电工技术 | 9828篇 |
技术理论 | 11篇 |
综合类 | 10242篇 |
化学工业 | 28127篇 |
金属工艺 | 9122篇 |
机械仪表 | 10245篇 |
建筑科学 | 13440篇 |
矿业工程 | 3730篇 |
能源动力 | 4971篇 |
轻工业 | 11504篇 |
水利工程 | 3190篇 |
石油天然气 | 8112篇 |
武器工业 | 1152篇 |
无线电 | 21576篇 |
一般工业技术 | 21857篇 |
冶金工业 | 8895篇 |
原子能技术 | 1804篇 |
自动化技术 | 23286篇 |
出版年
2024年 | 530篇 |
2023年 | 2411篇 |
2022年 | 4272篇 |
2021年 | 6303篇 |
2020年 | 4580篇 |
2019年 | 3880篇 |
2018年 | 4362篇 |
2017年 | 4974篇 |
2016年 | 4533篇 |
2015年 | 6102篇 |
2014年 | 8160篇 |
2013年 | 10361篇 |
2012年 | 10964篇 |
2011年 | 11942篇 |
2010年 | 10473篇 |
2009年 | 10125篇 |
2008年 | 9804篇 |
2007年 | 9494篇 |
2006年 | 9552篇 |
2005年 | 8169篇 |
2004年 | 5507篇 |
2003年 | 4747篇 |
2002年 | 4467篇 |
2001年 | 3967篇 |
2000年 | 4106篇 |
1999年 | 4401篇 |
1998年 | 4102篇 |
1997年 | 3365篇 |
1996年 | 3074篇 |
1995年 | 2576篇 |
1994年 | 2081篇 |
1993年 | 1609篇 |
1992年 | 1227篇 |
1991年 | 981篇 |
1990年 | 773篇 |
1989年 | 647篇 |
1988年 | 549篇 |
1987年 | 340篇 |
1986年 | 293篇 |
1985年 | 233篇 |
1984年 | 181篇 |
1983年 | 124篇 |
1982年 | 119篇 |
1981年 | 107篇 |
1980年 | 86篇 |
1979年 | 66篇 |
1978年 | 45篇 |
1977年 | 64篇 |
1976年 | 69篇 |
1973年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 371 毫秒
31.
Katja F. Hellendahl Felix Kaspar Dr. Xinrui Zhou Zhaoyi Yang Prof. Dr. Zhen Huang Prof. Dr. Peter Neubauer Dr. Anke Kurreck 《Chembiochem : a European journal of chemical biology》2021,22(11):2002-2009
Selenium-modified nucleosides are powerful tools to study the structure and function of nucleic acids and their protein interactions. The widespread application of 2-selenopyrimidine nucleosides is currently limited by low yields in established synthetic routes. Herein, we describe the optimization of the synthesis of 2-Se-uridine and 2-Se-thymidine derivatives by thermostable nucleoside phosphorylases in transglycosylation reactions using natural uridine or thymidine as sugar donors. Reactions were performed at 60 or 80 °C and at pH 9 under hypoxic conditions to improve the solubility and stability of the 2-Se-nucleobases in aqueous media. To optimize the conversion, the reaction equilibria in analytical transglycosylation reactions were studied. The equilibrium constants of phosphorolysis of the 2-Se-pyrimidines were between 5 and 10, and therefore differ by an order of magnitude from the equilibrium constants of any other known case. Hence, the thermodynamic properties of the target nucleosides are inherently unfavorable, and this complicates their synthesis significantly. A tenfold excess of sugar donor was needed to achieve 40−48 % conversion to the target nucleoside. Scale-up of the optimized conditions provided four Se-containing nucleosides in 6–40 % isolated yield, which compares favorably to established chemical routes. 相似文献
32.
33.
The Fe/C/SiCN composite ceramics were synthesized by polymer-derived method to obtain the integration of structure and functions. The electromagnetic waves (EMW) absorption properties at X and Ku bands were investigated. The addition of nano-sized Fe particles improved the magnetic loss and impedance matching, and the carbon nanotubes generated by the iron in-situ catalysis increased the internal relaxation polarization and interfacial polarization, which together improved the EMW absorption properties significantly. In particular, the Fe/C/SiCN-9 showed the optimum reflection loss (RL) of ?31.06 dB at 10.03 GHz with an effective absorption bandwidth (EAB, RL < ?10 dB) of 3.03 GHz at 2.51 mm, indicating the excellent EMW absorption properties of Fe/C/SiCN composite ceramics. 相似文献
34.
World Wide Web - Rule mechanism has been widely used in many areas, such as databases, artificial intelligent and pervasive computing. In a rule mechanism, rule activation decides which rules are... 相似文献
35.
36.
Fluorescence‐Activated Cell Sorters: Standing Surface Acoustic Wave (SSAW)‐Based Fluorescence‐Activated Cell Sorter (Small 40/2018)
下载免费PDF全文
![点击此处可从《Small (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
37.
38.
39.
Xian Suo Xili Cui Lifeng Yang Nan Xu Yuqi Huang Yi He Sheng Dai Huabin Xing 《Advanced materials (Deerfield Beach, Fla.)》2020,32(29):1907601
The design of highly stable and efficient porous materials is essential for developing breakthrough hydrocarbon separation methods based on physisorption to replace currently used energy-intensive distillation/absorption technologies. Efforts to develop advanced porous materials such as zeolites, coordination frameworks, and organic polymers have met with limited success. Here, a new class of ionic ultramicroporous polymers (IUPs) with high-density inorganic anions and narrowly distributed ultramicroporosity is reported, which are synthesized by a facile free-radical polymerization using branched and amphiphilic ionic compounds as reactive monomers. A covalent and ionic dual-crosslinking strategy is proposed to manipulate the pore structure of amorphous polymers at the ultramicroporous scale. The IUPs exhibit exceptional selectivity (286.1–474.4) for separating acetylene from ethylene along with high thermal and water stability, collaboratively demonstrated by gas adsorption isotherms and experimental breakthrough curves. Modeling studies unveil the specific binding sites for acetylene capture as well as the interconnected ultramicroporosity for size sieving. The porosity-engineering protocol used in this work can also be extended to the design of other ultramicroporous materials for the challenging separation of other key gas constituents. 相似文献
40.
Chuntao Lan Haiyang Zou Longfei Wang Meng Zhang Shuang Pan Ying Ma Yiping Qiu Zhong Lin Wang Zhiqun Lin 《Advanced materials (Deerfield Beach, Fla.)》2020,32(47):2005481
Despite recent rapid advances in metal halide perovskites for use in optoelectronics, the fundamental understanding of the electrical-poling-induced ion migration, accounting for many unusual attributes and thus performance in perovskite-based devices, remain comparatively elusive. Herein, the electrical-poling-promoted polarization potential is reported for rendering hybrid organic–inorganic perovskite photodetectors with high photocurrent and fast response time, displaying a tenfold enhancement in the photocurrent and a twofold decrease in the response time after an external electric field poling. First, a robust meniscus-assisted solution-printing strategy is employed to facilitate the oriented perovskite crystals over a large area. Subsequently, the electrical poling invokes the ion migration within perovskite crystals, thus inducing a polarization potential, as substantiated by the surface potential change assessed by Kelvin probe force microscopy. Such electrical-poling-induced polarization potential is responsible for the markedly enhanced photocurrent and largely shortened response time. This work presents new insights into the electrical-poling-triggered ion migration and, in turn, polarization potential as well as into the implication of the latter for optoelectronic devices with greater performance. As such, the utilization of ion-migration-produced polarization potential may represent an important endeavor toward a wide range of high-performance perovskite-based photodetectors, solar cells, transistors, scintillators, etc. 相似文献