全文获取类型
收费全文 | 8898篇 |
免费 | 1612篇 |
国内免费 | 2490篇 |
专业分类
化学 | 4259篇 |
晶体学 | 42篇 |
力学 | 1358篇 |
综合类 | 69篇 |
数学 | 2456篇 |
物理学 | 4816篇 |
出版年
2023年 | 166篇 |
2022年 | 184篇 |
2021年 | 147篇 |
2020年 | 146篇 |
2019年 | 124篇 |
2018年 | 191篇 |
2017年 | 86篇 |
2016年 | 188篇 |
2015年 | 220篇 |
2014年 | 368篇 |
2013年 | 326篇 |
2012年 | 435篇 |
2011年 | 409篇 |
2010年 | 395篇 |
2009年 | 311篇 |
2008年 | 240篇 |
2007年 | 475篇 |
2006年 | 462篇 |
2005年 | 561篇 |
2004年 | 536篇 |
2003年 | 352篇 |
2002年 | 428篇 |
2001年 | 529篇 |
2000年 | 422篇 |
1999年 | 516篇 |
1998年 | 227篇 |
1997年 | 154篇 |
1996年 | 199篇 |
1995年 | 264篇 |
1994年 | 222篇 |
1993年 | 224篇 |
1992年 | 212篇 |
1991年 | 160篇 |
1990年 | 192篇 |
1989年 | 192篇 |
1988年 | 221篇 |
1987年 | 227篇 |
1986年 | 196篇 |
1985年 | 257篇 |
1984年 | 170篇 |
1983年 | 116篇 |
1982年 | 109篇 |
1981年 | 89篇 |
1975年 | 114篇 |
1959年 | 84篇 |
1958年 | 125篇 |
1957年 | 123篇 |
1956年 | 111篇 |
1955年 | 121篇 |
1954年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The paper presents a computational model for elastic waves in a structured weld adjacent to the free surface of an elastic solid. The main emphasis is on the interaction of waves with the micro-structure of the weld. Effects of localisation and channeling of waves are addressed. A model of a grain structure within the weld is also considered. 相似文献
992.
Madhav S. Mane Ravi S. Balaskar Sandip N. Gavade Pramod N. Pabrekar Murlidhar S. Shingare Dhananjay V. Mane 《中国化学快报》2011,22(9):1039-1042
The regiospecific oxidation of alkyl group of both sterically hindered and unhindered aromatic amine to corresponding carbonyl compound was done in aq. medium by using DDQ. The optimized reaction protocol was found to be most simple, high yielding and novel method for oxidation of alkyl group of aromatic amine in to its carbonyl compound. 相似文献
993.
TiO 2 nanorods have been successfully grown into a track-etched polycarbonate (PC) membrane by a particulate sol-electrophoretic deposition from an aqueous medium.The prepared sols had a narrow particle size distribution around 17 nm and excellent stability against aging,with zeta potentials in the range of 47-50 mV at pH 2.It was found that TiO 2 nanorods were grown from dilute aqueous sol with a low,0.1-M concentration.Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversi... 相似文献
994.
Nickel-alumina catalysts supported on cordierite monoliths of honeycomb structure surpass essentially the conventional granulated ones with respect to the output in carbon dioxide reforming of methane. Adjusting the surface acid-base properties of catalysts by introduction of alkali metal (Na, K) oxides inhibits the carbonization and as a result, improves the operational stability of these catalysts. An effect of promotion of nickel-alumina based composite doped by lanthanum oxide is found. This effect, caused by an additional route for the CO2 activation on Ni-La2O3/Al2O3/cordierite catalyst, is displayed in increase of methane conversion under conditions of an oxidant excess. 相似文献
995.
In this paper, we shall introduce and characterize simultaneous quasi-Chebyshev (and weakly-Chebyshev) subspaces of normed spaces with respect to a bounded set S by using elements of the dual space. 相似文献
996.
Specified ultra-short pulse waveforms could be synthesized with high-resolution zero-dispersion pulse shaping system.The system and parameters are analyzed and discussed.The pulse shaping system with optimized parameters could resolve the frequency components of ultra-broad bandwidth pulse and prevent the spatial shaping of individual frequency components.The specified waveforms,Meyer wavelet and square root raised cosine pulses,are generated with programmable amplitude and phase masks. 相似文献
997.
Hong Ping HE Yue Mao SHEN Xiao Sheng YANG Bin Gui WANG Ling LI Xiao Jiang HAO * Laboratory of Phytochemistry Kunming Institute of Botany the Chinese Academy of Sciences Kunming . The Key Laboratory of Chemistry for Natural Prod 《中国化学快报》2001,(1)
Spiraea japonica L. (Rosaceae) is widely distributed in Yunnan Provence, P. R. China. Previous chemical investigations on S. japonica and its varieties have led to the report of 7 new atisane-type diterpenoids and 38 new diterpene alkaloids of atisine- and hetisine-type1-11. This paper describes the isolation and structure elucidation of two new diterpene alkaloids named spiratines A and B (1-2). Their structures were elucidated on the basis of 1D and 2D NMR experiments (HMQC, HMBC, 1… 相似文献
998.
Deculsnea./al..gesiiFranch.IsatraditionalChinesemedicinalplantwidely'distributedinChina.usedasananti-rheumaticandalltitussivedrugforalongtimeinChinesefolkmedicine'.Itsmethanolextractshowedantitunlouracidityif71)if)oagainstS:sl},HepaandEhrlichcellsanditsphytochemicalstudiesonsaponinshasreported'.Asacontinuationofthestudiesonthisplant,wepresentthespectralandchemicalevidenceofthestructureofanewdecaisosideF.Thedriedstems(2.23kg)werepercolated\vith95%EtOH.Afterremovalofthepercolatesb}evaporat… 相似文献
999.
Xuexi Tie a Junji Cao b a National Center for Atmospheric Research Boulder CO USA b SKLLQG Institute of Earth Environment Chinese Academy of Sciences No. Fenghui South Road High-Tech Zone Xi’an China 《中国颗粒学报》2010,8(1)
PARTICUOLOGY regrets that the above paper was mistakenly classified as a ‘Review’ rather than an ‘Invited paper’ when originally published in volume 7, issue 6, 426–431. 相似文献
1000.
以Vandermonde矩阵的基本性质、矩阵的特征值与迹之间的关系为理论依据,由矩阵的(理论)特征值生成的Vandermonde矩阵.构造出一种特殊的等幂和矩阵.即幂迹矩阵,在此基础上可给出判定任意n阶实矩阵的互异特征值个数的三个充要条件.以及相应的算法和自定义matlab函数. 相似文献