全文获取类型
收费全文 | 15709篇 |
免费 | 1939篇 |
国内免费 | 1966篇 |
专业分类
化学 | 12593篇 |
晶体学 | 281篇 |
力学 | 537篇 |
综合类 | 152篇 |
数学 | 1592篇 |
物理学 | 4459篇 |
出版年
2024年 | 40篇 |
2023年 | 196篇 |
2022年 | 485篇 |
2021年 | 486篇 |
2020年 | 507篇 |
2019年 | 555篇 |
2018年 | 422篇 |
2017年 | 468篇 |
2016年 | 685篇 |
2015年 | 715篇 |
2014年 | 909篇 |
2013年 | 1202篇 |
2012年 | 1354篇 |
2011年 | 1435篇 |
2010年 | 1051篇 |
2009年 | 980篇 |
2008年 | 1227篇 |
2007年 | 1034篇 |
2006年 | 978篇 |
2005年 | 850篇 |
2004年 | 695篇 |
2003年 | 582篇 |
2002年 | 653篇 |
2001年 | 407篇 |
2000年 | 312篇 |
1999年 | 237篇 |
1998年 | 194篇 |
1997年 | 127篇 |
1996年 | 125篇 |
1995年 | 91篇 |
1994年 | 76篇 |
1993年 | 97篇 |
1992年 | 67篇 |
1991年 | 70篇 |
1990年 | 47篇 |
1989年 | 51篇 |
1988年 | 19篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 29篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 9篇 |
1981年 | 13篇 |
1980年 | 12篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Sang Kyu Lee Min Ju Cho Jung‐Il Jin Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2007,45(3):531-542
New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007 相似文献
42.
Kwang Seok Oh 《Applied Surface Science》2007,254(3):677-681
Catalytic decomposition of NO over Cu-Os/13X has been carried out in a tubular fixed bed reactor at atmospheric pressure and the results were compared with literature data performed by high-throughput screening (HTS). The activity and durability of Cu-Os/13X prepared by conventional ion-exchange method have been investigated in the presence of H2O and SO2. It was found that Cu-Os/13X prepared by ion-exchange shows a high activity in a wide temperature range in selective catalytic reduction (SCR) of NO with C3H6 compared to Cu/13X, proving the existence of more NO adsorption site on Cu-Os/13X. However, Cu-Os/13X exhibited low activity in the presence of water, and was quite different from the result reported in literature. SO2 resistance is also low and does not recover its original activity when the SO2 was blocked in the feed gas stream. This result suggested that catalytic activity between combinatorial screening and conventional testing should be compared to confirm the validity of high-throughput screening. 相似文献
43.
Man Young Kim Seung Wook Baek 《Journal of Quantitative Spectroscopy & Radiative Transfer》2005,90(3-4):377-388
Radiative heat transfer in an axisymmetric enclosure with absorbing, emitting, and scattering medium is studied here by using the different methods such as MDOM, FVM, and MFVM with emphasis on the treatment of angular derivative term, which appears in curvilinear coordinates due to angular redistribution. After final discretization equation for MFVM is introduced by using the step scheme and directional weights, the present approach is validated by applying it to three different benchmarking problems with absorbing, emitting, and scattering medium. All of the results presented here support its accuracy as well as moderate efficiency. Finally, the present approaches are applied to a truncated cone-shaped enclosure as a body-fitted geometry case. 相似文献
44.
CHEN Yue WANG Xuan-jun CONG Xian-ling ZHANG Pei-yin WU Xiu-li WEI Hong-fei WANG Li WAN Min WANG Li-ying YU Yong-li 《高等学校化学研究》2006,22(6):712-716
IntroductionClassical swine fever(CSF), included in the listA of the Office International des Epizooties(OIE), is ahighly contagious disease of domestic pigs and is con-sidered as the mostharmful disease occurring in pigs allover the world[1]. Outbreaks o… 相似文献
45.
46.
47.
48.
我国医疗费用增长与医疗设备投入的相关性研究 总被引:3,自引:0,他引:3
近年来我国卫生总费用占GDP的比例增长很快,而在卫生费用结构上则发生政府投入下降和个人支出的上升。本文采集了大量的统计数据,采用统计相关性研究的方法,论证了医疗设备规模的不断扩大是导致医疗费用上升的主要因素之一;医疗设备的快速增长与医院维修费用投入的增长直接相关,而引起医疗设备维修大量投入的主要原因则是故障期内医疗设备的非正常闲置。本文通过对个人卫生费用的上升、医疗设备规模的扩大及其医疗设备维修投入费用增加相关性的分析,说明了在这种关系下,十分有必要研究医院医疗设备维修体系,以在卫生投入和患者权益上达到平衡。 相似文献
49.
Improving Construction for Connected Dominating Set with Steiner Tree in Wireless Sensor Networks 总被引:2,自引:0,他引:2
Manki Min Hongwei Du Xiaohua Jia Christina Xiao Huang Scott C.-H. Huang Weili Wu 《Journal of Global Optimization》2006,35(1):111-119
The connected dominating set plays an important role in ad hoc wireless networking. Many constructions for approximating the minimum connected dominating set have been proposed in the
literature. In this paper, we propose a new one with Steiner tree, which produces approximation solution within a factor of
6.8 from optimal. This approximation algorithm can also be implemented distributedly. 相似文献
50.
研制了一台五通道ROSS-FILTER-PIN软X射线能谱仪,能谱范围为0.28—1.56keV.它由5个连续能段组成,每个能段的起止边由罗斯滤片对(ROSS-FILTERS)的L或K吸收边确定.罗斯滤片对的厚度通过优化计算得到,为了使每个通道的灵敏区外响应(即所测能段外响应)与通道总响应之比最小,在滤片对的第二滤片上镀上了一定厚度的第一滤片材料;为了缩减滤片表面积以增强低能滤片的抗冲击能力及方便滤片加工,能谱仪采用了小探测面积的PIN探测器(1mm2).借助此能谱仪,测量得到了喷气式Z箍缩(Z-pinch)等离子体辐射软X射线能谱的分布,并研究了软X射线产额随箍缩状况的变化趋势.
关键词:
Z箍缩等离子体
罗斯滤片
软X射线能谱 相似文献