全文获取类型
收费全文 | 48703篇 |
免费 | 6770篇 |
国内免费 | 4292篇 |
专业分类
化学 | 27578篇 |
晶体学 | 1064篇 |
力学 | 1715篇 |
综合类 | 267篇 |
数学 | 1383篇 |
物理学 | 18683篇 |
无线电 | 9075篇 |
出版年
2024年 | 152篇 |
2023年 | 496篇 |
2022年 | 1012篇 |
2021年 | 1087篇 |
2020年 | 1458篇 |
2019年 | 1344篇 |
2018年 | 1368篇 |
2017年 | 1746篇 |
2016年 | 2223篇 |
2015年 | 2236篇 |
2014年 | 2543篇 |
2013年 | 4562篇 |
2012年 | 3187篇 |
2011年 | 3438篇 |
2010年 | 2640篇 |
2009年 | 2971篇 |
2008年 | 2968篇 |
2007年 | 3083篇 |
2006年 | 2717篇 |
2005年 | 2344篇 |
2004年 | 2191篇 |
2003年 | 1941篇 |
2002年 | 2045篇 |
2001年 | 1367篇 |
2000年 | 1315篇 |
1999年 | 1090篇 |
1998年 | 964篇 |
1997年 | 746篇 |
1996年 | 656篇 |
1995年 | 661篇 |
1994年 | 534篇 |
1993年 | 419篇 |
1992年 | 390篇 |
1991年 | 271篇 |
1990年 | 220篇 |
1989年 | 163篇 |
1988年 | 189篇 |
1987年 | 153篇 |
1986年 | 142篇 |
1985年 | 123篇 |
1984年 | 126篇 |
1983年 | 59篇 |
1982年 | 86篇 |
1981年 | 68篇 |
1980年 | 55篇 |
1979年 | 66篇 |
1978年 | 32篇 |
1977年 | 23篇 |
1975年 | 19篇 |
1973年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
R. Kohli 《Journal of Thermal Analysis and Calorimetry》1994,41(6):1571-1576
A research program has been in progress to obtain reliable thermodynamic data on various binary and ternary alkali metal compounds in the temperature range of 300 to 1500 K. To date, heat capacity measurements have been made on cesium and rubidium chromates, dichromates, zirconates, molybdates, dimolybdates, and halides in the temperature range of 300 to 800K. In addition, measurements are planned or are currently in progress on cesium and rubidium chalcogenides, aluminates, uranates, silicates, and several other lithium, sodium, and potassium compounds. The status of the research program is discussed. 相似文献
992.
医用聚丙烯酰胺水凝胶理化性能测试 总被引:2,自引:0,他引:2
测试了医用聚丙烯酰胺水凝胶产品的pH值、折射率、重金属含量、红外光谱、化学热稳定性和丙烯酰胺单体残留量等主要理化性能,重点研究了样品中残留单体丙烯酰胺的高效液相色谱分析法。 相似文献
993.
Elisângela Corradini Luís C. de Morais Nicole R. Demarquette José A. M. Agnelli Luiz H. C. Mattoso 《先进技术聚合物》2007,18(10):861-867
This work involved a study of the effect of processing variables (temperature, water content, rotor speed, and time) on the mechanical properties of starch:gluten:glycerol mixtures in the weight ratio of 40:40:20. The properties of the materials were affected by the processing variables. The torque decreased with water content, indicating that water facilitates the plasticization of mixtures, whereas the increase in temperature accelerated the evaporation of water, thus increasing the torque. Ultimate tensile strength was achieved at the lowest temperature (110°C) and the highest water content (20%), whereas maximum elongation was achieved for the material processed at the highest temperature, 150°C, and the fastest rotor speed, 70 rpm. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
994.
Ning GUO Guang Fu ZENG Shi Quan XI Changchun Institute of Applied Chemistry Academia Sinica.Changchun 《中国化学快报》1993,(3)
The perovskite type of compound [n-C_(11)H_(23)N_3]_2ZnCl_4(abr.C_(11)Zn)exhibits two solid-solid phasetransitions at T_(c1)=298.7 K and T_(c2)=360.1 K.A temperature dependence study of Raman spectra of C_(11)Znprovides the evidence of occurence of the structural phase transition related to the dynamics of thealkylammonium ions.The room temperature phase is ordered and contains the all-trans alkyl chains.Theintermediate temperature phase presents a partial conformational disorder and liquidlike state of allconformational disorder occurs at high-temperature phase. 相似文献
995.
反相键合相高效液相色谱法分离测定萘普生 总被引:1,自引:0,他引:1
建立了分离测定萘普生和溴代萘普生的反相键合相高效液相色谱法。采用ODS柱,以添加50mmol/L乳酸并用高氯酸调节pH为2.5的80%甲醇-水溶液作为流动相,以苯甲酸为内标物,测定了不对称合成工艺产物中萘普生和溴代萘普生的含量。方法的准确度分别为99.83%~102.07%(萘普生)和99.0%~100.83%(溴代萘普生),相对标准偏差分别小于2.58%(萘普生)和3.64%(溴代萘普生)。方法可用于工艺条件的选择和质量检测。 相似文献
996.
This paper reported the research results concerning the surface characterization ofpolystyrene-graft-w-stearyl poly(ethylene oxide) (PS-g-SPEO) by means of XPS,contactangle measurement and TEM, and its in vitro blood compatibility assessment by measuringthe plasma recalcification time (RT) and partial thromboplastin time (PTT). The XPSresults demonstrated that the surface and bulk composition of the PS-g-SPEO graftcopolymers differ remarkably from each other,and that SPEO component was constantlyenriched at the copolymer/air interface. Contact angle studies indicated that the surfacewater wettability can be adjusted effectively by changing the composition of the copolymer.PS-g-SPEO graft copolymers can undergo microphase separation as clearly illustrated byTEM photographs. The relationship between the surface properties of PS-g-SPEO graftcopolymer and its blood compatibility was also discussed. 相似文献
997.
Guang-Ming Yang Peng Cheng Dai-Zheng Liao Zong-Hui Jiang Shi-Ping Yan Geng-Lin Wang Xin-Kan Yao Hong-Gen Wang 《Journal of Cluster Science》1998,9(4):465-471
The preparation, magnetic properties, and crystal structure of [(salen)Cu]4[(salen)Fe(H2O)2]2(ClO4)2 via hydrogen bonding are described [salen=N,N-ethylenebis (salicylideneiminate)]. Crystals are triclinic, of space group
, with cell constants a=12.853(3), b=13.921(3), c=14.251(3) Å, =68.68(3)°, =87.86(3)°, =86.82(3)°, and Z=1. The structure was solved and refined to R=0.064 and R=0.068. The structure comprises the hexanuclear units which result from the linking of four mononuclear fragments [(salen)Cu] and two mononuclear fragment [(salen)Fe(H2O)]+, through Cu -O H -O -Fe -O -H O -Cu hydrogen bonds of coordinating H2O. In this complex, FeIII ions are in almost square-planar surroundings. The temperature dependences of the magnetic susceptibilities of the complex have been studied in the 4.2–300 K range, indicating the presence of an antiferromagnetic interactions between metal ions. 相似文献
998.
在一个石英反应室内,让激光解离的Ni^+与连续喷入的酯类化合物分子束流反应,生成的产物离子经飞行时间质谱仪检测,研究了Ni^+与乙酸乙酯、乙酸丙烯酯、乙酸乙烯酯、乙酸丁酯的气相反应。根据如下机理满意的解释了发生的反应:(1)Ni^+与酯形成激发态络合物;(2)β-H迁移至烃氧基的氧上形成Ni^+的双配体化合物离子;(3)失去一中性配体分子得Ni^+的单配体化合物离子。由酯的ΔH离和D(Ni^+-A 相似文献
999.
1000.