全文获取类型
收费全文 | 1212篇 |
免费 | 193篇 |
国内免费 | 109篇 |
专业分类
化学 | 636篇 |
晶体学 | 17篇 |
力学 | 47篇 |
综合类 | 25篇 |
数学 | 190篇 |
物理学 | 599篇 |
出版年
2024年 | 3篇 |
2023年 | 26篇 |
2022年 | 33篇 |
2021年 | 42篇 |
2020年 | 41篇 |
2019年 | 24篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 46篇 |
2015年 | 38篇 |
2014年 | 57篇 |
2013年 | 63篇 |
2012年 | 83篇 |
2011年 | 99篇 |
2010年 | 80篇 |
2009年 | 75篇 |
2008年 | 75篇 |
2007年 | 55篇 |
2006年 | 50篇 |
2005年 | 51篇 |
2004年 | 44篇 |
2003年 | 50篇 |
2002年 | 38篇 |
2001年 | 36篇 |
2000年 | 24篇 |
1999年 | 43篇 |
1998年 | 47篇 |
1997年 | 39篇 |
1996年 | 30篇 |
1995年 | 30篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 12篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1978年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有1514条查询结果,搜索用时 15 毫秒
991.
An experimental and kinetic modeling study of a four-component surrogate fuel for RP-3 kerosene 总被引:1,自引:0,他引:1
Yebing Mao Jin Xia Can Ruan Zhiyong Wu Yuan Feng Jizhen Zhu Sixu Wang Liang Yu Xingcai Lu 《Proceedings of the Combustion Institute》2021,38(1):555-563
Detailed high-fidelity kinetic models of fuels are of great significance by providing guidance for the improvement of the combustion performance in engines and promising the reduction of design cycle of new concept combustors. However, the kinetic modeling works on Chinese RP-3 kerosene, the most widely used civil aviation fuel in China, are meager to date. In this study, a kinetic model, including a surrogate fuel and its combustion kinetic mechanism, were developed to describe the combustion of RP-3. Firstly, a surrogate comprised of components n-dodecane, 2,2,4,6,6-pentamethylheptane (PMH), n-butylcyclohexane and n-butylbenzene (22.82/31.30/19.19/26.69 mol%) was proposed based on the combustion property target matching method. These components are all within the typical molecular size (C10-C14) of jet fuels and thereby can potentially improve the ability of the surrogate in emulating the properties that depend on molecular size. Experiments were then carried out in a heated rapid compression machine and a heated shock tube to evaluate the performance of the surrogate in reproducing the combustion behavior of the target fuel over wide conditions. It is found that the surrogate can reproduce the autoignition characteristics of RP-3 very well. A chemical kinetic mechanism was developed to describe the oxidation of this surrogate. This mechanism was assembled using a published n-butylbenzene sub-mechanism and our previous sub-mechanisms for the other pure components, and was assessed against the present experimental data. The results showed that the simulations agreed well with the experimental data under the investigated conditions, demonstrating that the composition of the surrogate and its mechanism are appropriate to describe the combustion of RP-3. The first-stage ignition negative temperature coefficient behavior and the evolution of key radicals were investigated using the kinetic model. 相似文献
992.
The current-mode-counting method is a new approach to observing transient processes,especially in transient nuclear fusion,based on the non-homogeneous Poisson process(NHPP)model.In this paper,a new measurement process model of the pulsed radiation field produced by transient nuclear fusion is built based on the NHPP.A simulated measurement is performed using the model,and the current signal from the detector is obtained by simulation based on Poisson process thinning.The neutron time spectrum is reconstructed and is in good agreement with the theoretical value,with its maximum error of a characteristic parameter less than 2.3%.Verification experiments were carried out on a CPNG-6 device at the China Institute of Atomic Energy,with a detection system with a nanosecond response time.The experimental charge amplitude spectra are in good agreement with those obtained by the traditional counting mode,and the characteristic parameters of the time spectrum are in good agreement with the theoretical values.This shows that the current-mode-counting method is effective for the observation of transient nuclear fusion processes. 相似文献
993.
994.
三峡升船机船—水—厢耦合系统的非线性有限元时域计算 总被引:1,自引:0,他引:1
根据三峡升船机船厢的受力特点,在船厢的纵剖面上建立了非线性水波方程和船—水—厢的耦合运动方程。对非线性水波方程利用摄动理论进行分解得到一阶方程和二阶方程,然后运用伽辽金法得到耦合的有限元离散方程,结合精细积分法进行时域计算。计算采用平面八节点等参单元,并给出了若干算例。 相似文献
995.
评价炸药安全性能的苏珊试验 总被引:4,自引:0,他引:4
苏珊试验是测量炸药撞击感度的一种射弹试验。将炸药装入壳体中,用空气炮或火炮以30~300m/s,甚至更高的速度发射,弹丸约经3.7m,与钢靶相撞。本文简介了试验的基本方法,用氦氖激光器、接收转换器、测时仪构成的光电系统测量弹丸的飞行速度;用红宝石序列脉冲激光器、纹影仪以及等待型转镜扫描相机构成的高速摄影系统拍摄弹丸的着靶姿态以及撞靶后挤压变形直至点火爆炸的全过程;用传感器、电荷放大器、瞬态波形存贮器构成的数据采集系统测量炸药爆炸后形成的空气冲击波超压。试验得到弹丸撞靶速度与相对释放能关系的苏珊感度曲线。本文给出了JO-9159、JOB-9003以及TNT/RDX 40/60等几种炸药的试验结果,对其安全性能作出了初步评价。 相似文献
996.
Two new ent-kaurane diterpenoids, ent-7a,14b-dihydroxykaur-16-en-15-one-20-oic acid(1) and 1,7a,12b,14b-tetrahydroxy-1,10-seco-ent-kaur-10,16-dien-15-one(2), together with six known ones(3–8), were isolated from the EtOAc extract of the aerial parts of Isodon excisoides. Their structures were elucidated on the basis of 1D NMR and 2D NMR analyses as well as HR-ESI-MS experiments. 相似文献
997.
Hai-Bao Zhu Yun-Chang Fan Ya-Ling Qian Hong-Fang Tang Zheng Ruan Dan-Hua Liu Han Wang 《中国化学快报》2014,25(3):465-468
In the present work, a novel method to extract three kinds of spices, namely vanillin, ethyl vanillin and ethyl maltol from food products such as biscuit, chocolate and milk powder was developed. 1-Octyl-3-methylimidazolium chloride([Omim]Cl) aqueous solution was selected as the extracting medium. A 0.5 g powder of food product was extracted by 5.0 mL of [Omim]Cl aqueous solution(0.3 mol/L, pH 6.0) under ultrasonication at 50 8C, and then the extract was centrifuged for 10 min at 4000 rpm. The extract was filtered through a syringe filter and injected into ion chromatography system for analysis. The separation of the three spices was carried out on an anion exchange column. The detection wavelength was set at 280 nm. Compared with traditional extraction solvents, [Omim]Cl aqueous solution displayed particular advantages. The applicability of the proposed method to real sample was confirmed. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation(RSD) values ranging from 1.9% to 6.3%. The recoveries of spiked samples were between 79.8% and 95.8%. The detection limits(LOD, S/N = 3) of vanillin, ethyl vanillin and ethyl maltol were in the range of 20–45 mg/kg. The use of ionic liquid aqueous solution as extraction solvent was operationally easy and environmental-friendly. 相似文献
998.
Swine Manure-Based Pilot-Scale Algal Biomass Production System for Fuel Production and Wastewater Treatment—a Case Study 总被引:1,自引:0,他引:1
Min Min Bing Hu Michael J. Mohr Aimin Shi Jinfeng Ding Yong Sun Yongcheng Jiang Zongqiang Fu Richard Griffith Fida Hussain Dongyan Mu Yong Nie Paul Chen Wenguang Zhou Roger Ruan 《Applied biochemistry and biotechnology》2014,172(3):1390-1406
Integration of wastewater treatment with algae cultivation is one of the promising ways to achieve an economically viable and environmentally sustainable algal biofuel production on a commercial scale. This study focused on pilot-scale algal biomass production system development, cultivation process optimization, and integration with swine manure wastewater treatment. The areal algal biomass productivity for the cultivation system that we developed ranged from 8.08 to 14.59 and 19.15–23.19 g/m2?×?day, based on ash-free dry weight and total suspended solid (TSS), respectively, which were higher than or comparable with those in literature. The harvested algal biomass had lipid content about 1.77–3.55 %, which was relatively low, but could be converted to bio-oil via fast microwave-assisted pyrolysis system developed in our lab. The lipids in the harvested algal biomass had a significantly higher percentage of total unsaturated fatty acids than those grown in lab conditions, which may be attributed to the observed temperature and light fluctuations. The nutrient removal rate was highly correlated to the biomass productivity. The NH3-N, TN, COD, and PO4-P reduction rates for the north-located photo-bioreactor (PBR-N) in July were 2.65, 3.19, 7.21, and 0.067 g/m2?×?day, respectively, which were higher than those in other studies. The cultivation system had advantages of high mixotrophic growth rate, low operating cost, as well as reduced land footprint due to the stacked-tray bioreactor design used in the study. 相似文献
999.
Liang Zhang Xiaoqing Wang Zhenhua Ruan Ying Liu Xiaorui Niu Zhengbo Yue Zhimin Li Wei Liao Yan Liu 《Applied biochemistry and biotechnology》2014,172(2):1045-1054
Three pretreated corn stover (ammonia fiber expansion, dilute acid, and dilute alkali) were used as carbon source to culture Trichoderma reesei Rut C-30 for cellulase and xylanase production. The results indicated that the cultures on ammonia fiber expansion and alkali pretreated corn stover had better enzyme production than the acid pretreated ones. The consequent enzymatic hydrolysis was performed applying fungal enzymes on pretreated corn stover samples. Tukey’s statistical comparisons exhibited that there were significant differences on enzymatic hydrolysis among different combination of fungal enzymes and pretreated corn stover. The higher sugar yields were achieved by the enzymatic hydrolysis of dilute alkali pretreated corn stover. 相似文献
1000.