全文获取类型
收费全文 | 146146篇 |
免费 | 31549篇 |
国内免费 | 23414篇 |
专业分类
化学 | 95180篇 |
晶体学 | 1695篇 |
力学 | 9818篇 |
综合类 | 616篇 |
数学 | 18280篇 |
物理学 | 75520篇 |
出版年
2024年 | 658篇 |
2023年 | 2156篇 |
2022年 | 3136篇 |
2021年 | 3207篇 |
2020年 | 3550篇 |
2019年 | 3908篇 |
2018年 | 3622篇 |
2017年 | 4000篇 |
2016年 | 5177篇 |
2015年 | 5545篇 |
2014年 | 6023篇 |
2013年 | 8966篇 |
2012年 | 10162篇 |
2011年 | 11765篇 |
2010年 | 13175篇 |
2009年 | 13268篇 |
2008年 | 7405篇 |
2007年 | 6589篇 |
2006年 | 6054篇 |
2005年 | 5871篇 |
2004年 | 6071篇 |
2003年 | 4745篇 |
2002年 | 4422篇 |
2001年 | 4562篇 |
2000年 | 3654篇 |
1999年 | 3993篇 |
1998年 | 3368篇 |
1997年 | 3017篇 |
1996年 | 3396篇 |
1995年 | 3666篇 |
1994年 | 3697篇 |
1993年 | 3572篇 |
1992年 | 3085篇 |
1991年 | 2686篇 |
1990年 | 2242篇 |
1989年 | 2268篇 |
1988年 | 2148篇 |
1987年 | 1443篇 |
1986年 | 1434篇 |
1985年 | 1130篇 |
1984年 | 1158篇 |
1983年 | 519篇 |
1982年 | 1020篇 |
1981年 | 840篇 |
1980年 | 848篇 |
1979年 | 575篇 |
1978年 | 587篇 |
1977年 | 688篇 |
1976年 | 1092篇 |
1972年 | 559篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Fibers and 3D mesh scaffolds from biodegradable starch-based blends: production and characterization
The aim of this work is the production of fibers from biodegradable polymers to obtain 3D scaffolds for tissue engineering of hard tissues. The scaffolds required for this highly demanding application need to have, as well as the biological and mechanical characteristics, a high degree of porosity with suitable dimensions for cell seeding and proliferation. Furthermore, the open cell porosity should have adequate interconnectivity for a continuous flow of nutrients and outflow of cell metabolic residues as well as to allow cell growth into confluent layers. Blends of corn starch, a natural biodegradable polymer, with other synthetic polymers (poly(ethylene vinyl alcohol), poly(epsilon-caprolactone), poly(lactic acid)) were selected for this work because of their good balance of properties, namely biocompatibility, processability and mechanical properties. Melt spinning was used to produce fibers from all the blends and 3D meshes from one of the starch-poly(lactic acid) blends. The experimental characterization included the evaluation of the tensile mechanical properties and thermal properties of the fibers and the compression stiffness, porosity and degradation behavior of the 3D meshes. Light microscopy picture of 3D meshes. 相似文献
972.
本文采用电导、pH滴定法研究了乙醇-水溶液中希土与1′-苯基-3′-甲基-5′-氧代吡唑-4′-基乙醛酸(简称H2A)的配位反应.合成了15种新的希土固态配合物.通过元素分析、化学分析、水份分析确定了配合物的化学组成为RE(HA)3·nH2O(RE=Ce、Pr、Sm、Tm、Lu、n=1;RE=La、Nd、Eu、Gd、Tb、Dy、Ho、Er、Yb、Y,n=1-2).并对配合物的红外光谱、核磁共振谱、热稳定性、紫外光谱、溶解性及摩尔电导进行了测定. 相似文献
973.
Summary For monitoring the ammonium content in environmental waters an optical sensor was developed. The sensor is based on a glass rod coated with a caoutchouc layer in which bromophenolblue was immobilized as indicator. A detection limit of 3 mol/l ammonium is obtained. 相似文献
974.
ICP激发光源以其独特的功能使ICP/AES技术在稀土分析中的应用日益广泛,在一定程度上取代了经典的直流电弧光谱法,但应指出,由于常规雾化器的低雾化效率(≤5%)和试样的高倍稀释,ICP/AES技术的实际检测能力的改善并不明显,本文用ICP光谱法测定了 相似文献
975.
Loomis S. Chen Grace J. Chen Chirst Tamborski 《Journal of organometallic chemistry》1980,193(3):283-292
Experimental conditions have now been developed whereby o-bromophenyllithium(II) may be prepared in excellent yields and used as an organometallic intermediate for the synthesis of a variety of ortho bromo substituted phenyl compounds (o-BrC6H4X). THe thermal stability, decomposition products and reactions of II wre studied. REactions between II and a variety of substrates, e.g., CO2, dimethylformamide, fluorinated esters, hexafluorobenzene, and organosilicon chlorides were examined. 相似文献
976.
A. V. Bobylev N. E. Buyanova A. P. Karnaukhov V. L. Khudyakov N. P. Manyakin 《Reaction Kinetics and Catalysis Letters》1976,5(4):389-394
The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.
.相似文献
977.
V. N. Romannikov N. V. Klueva N. N. Bobrov K. G. Ione 《Reaction Kinetics and Catalysis Letters》1976,5(2):217-222
The dependence of palladium distribution in zeolites on the temperature of thermal treatment has been established from the data on oxygen chemisorption and the statistical processing of electron micrographs. The influence of palladium distribution in zeolites on their catalytic activity towards the complete oxidation of benzene has been shown.
- . .相似文献
978.
模拟透射电镜双倾台进行样品位向调整过程,推导出反映样品倾转前后其合成倾转轴(即共有菊池线对的法线)方向变化规律的计算公式,称为附加旋转角计算公式。指出,实现样品位向调整的双倾操作,等效于样品绕其合成倾转轴的倾转及该倾转轴绕Z轴(平行入射束方向)的旋转之和。利用双倾台对薄膜样品进行的系列倾转实验表明,由附加旋转角公式计算的附加旋转角和实测值相一致。还根据双倾操作过程导出了合成倾转角的计算公式,它可用于判断样品位向调整的准确度。 相似文献
979.
Wolfgang Will Gerhard Hoffmann Andreas Zober 《Fresenius' Journal of Analytical Chemistry》1992,342(9):744-745
Summary A simple method is described which allows the quantification of 1-vinyl-2-pyrrolidone (NVP) in human serum. NVP is extracted from serum with diethylether and determined with HPLC/UV-detection. 1-Cyclohexyl-2-pyrrolidone serves as an internal standard. The detection limit is 0.1 mg/l. The method has shown that NVP can enter the organisms of workers occupationally exposed to this substance. 相似文献
980.