全文获取类型
收费全文 | 8723篇 |
免费 | 1631篇 |
国内免费 | 2445篇 |
专业分类
化学 | 4200篇 |
晶体学 | 37篇 |
力学 | 1338篇 |
综合类 | 42篇 |
数学 | 2382篇 |
物理学 | 4800篇 |
出版年
2023年 | 165篇 |
2022年 | 180篇 |
2021年 | 147篇 |
2020年 | 147篇 |
2019年 | 118篇 |
2018年 | 186篇 |
2017年 | 85篇 |
2016年 | 186篇 |
2015年 | 214篇 |
2014年 | 367篇 |
2013年 | 325篇 |
2012年 | 436篇 |
2011年 | 413篇 |
2010年 | 391篇 |
2009年 | 318篇 |
2008年 | 231篇 |
2007年 | 474篇 |
2006年 | 453篇 |
2005年 | 554篇 |
2004年 | 515篇 |
2003年 | 342篇 |
2002年 | 425篇 |
2001年 | 525篇 |
2000年 | 418篇 |
1999年 | 507篇 |
1998年 | 226篇 |
1997年 | 145篇 |
1996年 | 190篇 |
1995年 | 256篇 |
1994年 | 208篇 |
1993年 | 212篇 |
1992年 | 204篇 |
1991年 | 154篇 |
1990年 | 191篇 |
1989年 | 184篇 |
1988年 | 219篇 |
1987年 | 226篇 |
1986年 | 193篇 |
1985年 | 255篇 |
1984年 | 169篇 |
1983年 | 114篇 |
1982年 | 108篇 |
1981年 | 89篇 |
1975年 | 114篇 |
1959年 | 83篇 |
1958年 | 125篇 |
1957年 | 123篇 |
1956年 | 109篇 |
1955年 | 118篇 |
1954年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Nylon I I is a high-performance semicrystalline polymer which was used widely in manyfields. In recent years, the curious ferroelectric and piezoelectric propel'ties of nylon I Iwere foundl'2. It is well known that piezoelectricity is related to the crystal form ofNylon I 1.The sample was mounteds in a capillary (diameter was Zmm) within a small ovenwith mica windows. The scattered intensity was recorded from Q = 0.2 to 6.5 A-] (Q =ursine/~) using steps of AQ=o.o5A-'. The values of the p… 相似文献
992.
993.
It has long been known that homologous blood transfusion will result in a lot ofserious problems such as viral infections,for example AIDS,hepatitis,antigenicsensitization and GVHD;therefore aggressive testing of donor blood has beenadopted[1 ,2 ] .Even after this introduction,which is time-consuming and expensive,wecould not eliminate all the risks. In the wake of these kinds of pitfalls,production andclinical use of the blood substitutes have emerged.The essential aim of blood substitutei… 相似文献
994.
Jian Gong SHI Han Qing Wang Min WANG Guang Xiong ZHOU. Yong Chun YANG Wen Yan HU 《中国化学快报》2000,11(3):225-228
In a previous paper' we reported two optically active pyridine-2, 6 (l H. 3H)-dionealkatoids speranskalines A and B from SPeranskia luberculala (Bge.) (Euphorbiaceae)We report here the isolation and structural elucidation of two novel poly-oxygenbipyridine alkaloids named speranculatines A (l) and B (2) from this plant.The acetone (or methanol) extract of the air-dried whole plants of .q. IllhelT.lllaluwas subjected to column chromatography on St gel to afford a fraction. whichdemonstrate… 相似文献
995.
近年来,用光声量热法(photoacoustic calorimetry,缩写PAC)测量液相体系中的光物理或光化学过程有了较快发展.这对于观测无辐射的瞬态粒子有重要意义。Peters及其同事曾分析过这种光声技术的原理.简言之,脉冲激光被体系吸收后将 相似文献
996.
Significant progress has been made in understanding the nature of the transition state andthe paths for electron transfer, especially the influences of environmental factors and themolecular properties on the electron transfer rate. These classical and semi-classical, aswell as quantum-mechanical theory, have been very successful in rationalizing severalstructure-reactivity relationships and in predicting novel features of reactivity. Thesemodels established some links between the electron tra… 相似文献
997.
During the past decade, dense-type oxygen-permeable ceramic membranes have received considerable attention both in the fields of scientific research and industrial application1, 2. Such membranes have mixed oxygen-ionic and electronic conductivity, and they can permeate oxygen at high temperature under an oxygen gradient without the need of outside connecting line and electrodes. Envisioned applications range from small scale oxygen pumps for medical use to large scale integrated gasification … 相似文献
998.
Xiu Hua LIU* Dong Bao ZHAO Chong Ren YANG Han Qing WANG Chemistry Chemical Engineering College of Henan University Kaifeng Phytochemistry Laboratory Kunming Instute of Botany C.A.S.Kunming Lanzhou Institute of Chemical Physi 《中国化学快报》2000,11(11)
Hedychium yunnannense Gagnep is the unique species of Zingiberaceae occurring only in Yunnan province of China and its wild resource is very abundant. Several sesquiterpenoids and diterpenoids from the petroleum ether fraction of the ethanol extract of the plant have been reported1, 2 by Zhao Qing et al. Some of them show antioxidant and cytotoxic activities. In order to use the wild plant resources efficiently, we made further systematic investigations on the chemical constituents of the rh… 相似文献
999.
酰胺和酰亚胺改性聚乙烯的热分解行为 总被引:1,自引:0,他引:1
聚乙烯 (PE)的化学改性已得到广泛应用 ,它能使PE获得新的物理化学或功能特性 ,如改进其表面粘合、亲水及吸湿、染色和印刷性质等 ,尤其在增加它与其它聚合物的相容性 ,制备共混材料时常常是必不可少的[1 ,2 ] .目前最方便和有效的方法是通过马来化聚乙烯用不同基团接枝来实现化学改性 ,由于改性后的PE需经熔融加工成制品 ,化学改性基团必须在加工温度 ( 1 70~2 0 0℃ )和时间内具有足够的热稳定性 ,因此观察它们在热加工条件下的热稳定性和热分解行为显得十分重要 .通常这种化学改性的程度 (改性基团含量 )很小 ,并且在加工温度下所… 相似文献
1000.
Spartloxacin (SPFX) is the fourth generation of the antibacterial quinolones. Due to itsintensive and efficient antibacterial activity compared to the common quinolones '. it hasbeen widely used in clinical practice. Nevertheless. because of the structural dit'ferencesbetween SPFX and other quinolones. the fluorescence of SPFX is so weak that it can notbe determined by means of fluorescence spectra. Hence, it will be of great interest tomake a detailed study on its fluorescence enhancemen… 相似文献