全文获取类型
收费全文 | 9250篇 |
免费 | 1219篇 |
国内免费 | 1600篇 |
专业分类
化学 | 8032篇 |
晶体学 | 96篇 |
力学 | 378篇 |
综合类 | 54篇 |
数学 | 184篇 |
物理学 | 1080篇 |
无线电 | 2245篇 |
出版年
2024年 | 22篇 |
2023年 | 211篇 |
2022年 | 169篇 |
2021年 | 367篇 |
2020年 | 373篇 |
2019年 | 379篇 |
2018年 | 282篇 |
2017年 | 347篇 |
2016年 | 417篇 |
2015年 | 409篇 |
2014年 | 468篇 |
2013年 | 511篇 |
2012年 | 889篇 |
2011年 | 527篇 |
2010年 | 447篇 |
2009年 | 533篇 |
2008年 | 584篇 |
2007年 | 629篇 |
2006年 | 624篇 |
2005年 | 538篇 |
2004年 | 531篇 |
2003年 | 420篇 |
2002年 | 309篇 |
2001年 | 251篇 |
2000年 | 243篇 |
1999年 | 217篇 |
1998年 | 206篇 |
1997年 | 181篇 |
1996年 | 126篇 |
1995年 | 135篇 |
1994年 | 131篇 |
1993年 | 127篇 |
1992年 | 101篇 |
1991年 | 97篇 |
1990年 | 90篇 |
1989年 | 54篇 |
1988年 | 38篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1957年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
1.
Dr. Zaifa Shi Dr. Yihuang Jiang Dr. Jingxiong Yu Prof. Shanjun Chen Prof. Jun Chen Prof. Zichao Tang Prof. Lansun Zheng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(8):e202103546
At present, the reactivity of cyclic alkanes is estimated by comparison with acyclic hydrocarbons. Due to the difference in the structure of cycloalkanes and acycloalkanes, the thermodynamic data obtained by analogy are not applicable. In this study, a molecular beam sampling vacuum ultraviolet photoionization time-of-flight mass spectrometer (MB-VUV-PI-TOFMS) was applied to study the low-temperature oxidation of cyclopentane (CPT) at a total pressure range from 1–3 atm and low-temperature range between 500 and 800 K. Low-temperature reaction products including cyclic olefins, cyclic ethers, and highly oxygenated intermediates (e. g., ketohydroperoxide KHP, keto-dihydroperoxide KDHP, olefinic hydroperoxides OHP and ketone structure products) were observed. Further investigation of the oxidation of CPT – electronic structure calculations – were carried out at the UCCSD(T)-F12a/aug-cc-pVDZ//B3LYP/6-31+ G(d,p) level to explore the reactivity of O2 molecules adding sequentially to cyclopentyl radicals. Experimental and theoretical observations showed that the dominant product channel in the reaction of CPT radicals with O2 is HO2 elimination yielding cyclopentene. The pathways of second and third O2 addition – the dissociation of hydroperoxide – were further confirmed. The results of this study will develop the low-temperature oxidation mechanism of CPT, which can be used for future research on accurately simulating the combustion process of CPT. 相似文献
2.
We propose all printed and highly stable organic resistive switching device (ORSD) based on graphene quantum dots (G-QDs) and polyvinylpyrrolidone (PVP) composite for non-volatile memory applications. It is fabricated by sandwiching G-QDs/PVP composite between top and bottom silver (Ag) electrodes on a flexible substrate polyethylene terephthalate (PET) at ambient conditions through a cost effective and eco-friendly electro-hydrodynamic (EHD) technique. Thickness of the active layer is measured around 97 nm. The proposed ORSD is fabricated in a 3 × 3 crossbar array. It operates switching between high resistance state (HRS) and low resistance state (LRS) with OFF/ON ratio ∼14 for more than 500 endurance cycles, and retention time for more than 30 days. The switching voltage for set/reset of the devices is ±1.8 V and the bendability down to 8 mm diameter for 1000 cycles are tested. The elemental composition and surface morphology are characterized by XPS, FE-SEM, and microscope. 相似文献
3.
《Comptes Rendus Chimie》2015,18(9):993-1000
The electrochemical oxidation of N-acetyl-p-aminophenol (PAR) was investigated at a Pt electrode with the application of cyclic (CV) and differential pulse (DPV) voltammetry methods. An effect of scan rate, substrate concentration and pH on electrode reactions was determined. The parameters of substrate electro-oxidation, i.e. heterogeneous rate constant, charge transfer coefficient, and diffusion coefficient, were calculated. Our investigation's results prove the exchange of two electrons and one proton in the first step, followed by a chemical reaction. PAR electro-oxidation occurs according to an EC mechanism. 相似文献
4.
James E. Tyrrell Martyn G. Boutelle Alasdair J. Campbell 《Advanced functional materials》2021,31(1):2007086
Biological environments use ions in charge transport for information transmission. The properties of mixed electronic and ionic conductivity in organic materials make them ideal candidates to transduce physiological information into electronically processable signals. A device proven to be highly successful in measuring such information is the organic electrochemical transistor (OECT). Previous electrophysiological measurements performed using OECTs show superior signal-to-noise ratios than electrodes at low frequencies. Subsequent development has significantly improved critical performance parameters such as transconductance and response time. Here, interdigitated-electrode OECTs are fabricated on flexible substrates, with one such state-of-the-art device achieving a peak transconductance of 139 mS with a 138 µs response time. The devices are implemented into an array with interconnects suitable for micro-electrocorticographic application and eight architecture variations are compared. The two best-performing arrays are subject to the full electrophysiological spectrum using prerecorded signals. With frequency filtering, kHz-scale frequencies with 10 µV-scale voltages are resolved. This is supported by a novel quantification of the noise, which compares the gate voltage input and drain current output. These results demonstrate that high-performance OECTs can resolve the full electrophysiological spectrum and suggest that superior signal-to-noise ratios could be achieved in high frequency measurements of multiunit activity. 相似文献
5.
采用DIS数字信息化系统,对不同浓度的蓝墨水溶液在激光光源照射下的透射平均照度及照度分布图像进行实验研究,得到了平均照度值随溶液浓度变化的规律。对不同颜色塑料膜片对白炽灯光源透过照度值及照度分布图像进行实验研究得到及其相关之规律。 相似文献
6.
7.
8.
9.
Transparent conducting ZnO:AI thin films with good adhesion and Iow resistivity have been prepared on organic substrates and Coming 7059 glass substrates by r.f. magnetron-sputtering technique at Iow substrate temperature (25-210℃). Structural and photoelectric properties of the deposited films are investigated. The deposited films are polycrystalline with hexagonal structure and a preferred orientation with the c-axis perpendicular to the substrate. Only the (002) peak is observed.High quality films with resistivity as Iow as 1.0 x 10- 3Ω@ cm and 8.4 x 10- 4Ω@ cm, the average transmittance over 74% and 85% in the wavelength range of the visible spectrum have been obtained on different substrates. 相似文献
10.