全文获取类型
收费全文 | 13244篇 |
免费 | 1516篇 |
国内免费 | 2149篇 |
专业分类
化学 | 10190篇 |
晶体学 | 305篇 |
力学 | 511篇 |
综合类 | 180篇 |
数学 | 2169篇 |
物理学 | 3554篇 |
出版年
2024年 | 14篇 |
2023年 | 138篇 |
2022年 | 307篇 |
2021年 | 397篇 |
2020年 | 437篇 |
2019年 | 418篇 |
2018年 | 366篇 |
2017年 | 402篇 |
2016年 | 575篇 |
2015年 | 602篇 |
2014年 | 671篇 |
2013年 | 971篇 |
2012年 | 1167篇 |
2011年 | 1255篇 |
2010年 | 982篇 |
2009年 | 902篇 |
2008年 | 1074篇 |
2007年 | 1059篇 |
2006年 | 955篇 |
2005年 | 825篇 |
2004年 | 703篇 |
2003年 | 482篇 |
2002年 | 417篇 |
2001年 | 269篇 |
2000年 | 272篇 |
1999年 | 213篇 |
1998年 | 110篇 |
1997年 | 94篇 |
1996年 | 84篇 |
1995年 | 81篇 |
1994年 | 67篇 |
1993年 | 68篇 |
1992年 | 52篇 |
1991年 | 42篇 |
1990年 | 49篇 |
1989年 | 37篇 |
1988年 | 34篇 |
1987年 | 39篇 |
1986年 | 25篇 |
1985年 | 42篇 |
1984年 | 24篇 |
1983年 | 28篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 20篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1965年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
21.
以PCl3为脱水剂,将邻氨基硫酚与水杨酸脱水环化合成出2-(2-羟基苯基)苯并噻唑,并进一步将所得产物与乙酸锌反应合成出2-(2-羟基苯基)苯并噻唑螯合锌(Zn(BTZ)2)材料。以该配合物作为发光层制备出结构为ITO/PVK:TPD/Zn(BTZ)2/Al近白色电致发光器件,其色坐标位于白场之内(x=0.242,y=0.359),在驱动电压为16V时,亮度达3200cdm2,对应的量子效率为0.32%。进一步在Zn(BTZ)2中掺入橙红色染料Rubrene,制成ITO/PVK:TPD/Zn(BTZ)2:Rubrene/Al结构器件,实现了纯白色发光(色坐标值:x=0.324,y=0.343),非常接近于白色等能点,且量子效率达0.47%。最后对上述器件的发光和电学性能进行了深入的研究和探讨。 相似文献
22.
23.
24.
对一种工业用大功率电子加速器(450kW)的加速管中的空间电荷效应作了5点假设,建立了物理模型。对模型的束内外径向电位分布、空间电荷对轴上电位的影响,以及空间电荷力对束流传输的影响等进行了理论分析,得到了束内径向电位分布。结果表明:束流内部径向电位沿径向均呈抛物线变化,并在轴上达到最小值;而空间电荷产生的束内电场与半径呈线性变化;空间电荷不仅会引起轴上电位的跌落,而且对束流有发散作用,特别是在电子速度较低时更为明显。在考虑了空间电荷效应后,强流静电加速管的电场设计关键在加速管的前端,与弱流加速管相比,强流加速管的电场变化要大得多。 相似文献
25.
Cationic polymer as a kind of flocculant is widely applied in purification treatment of waste water. Because it has positive charge group, it is able to connect strongly the suspended matters, short cellulose and other microparticles. The research on synthesis of cationic polymer and application in treatment of waste water is very universal abroad. But domestic research on those is not general. The technology of synthesis of PEM is simple, and the production cost is low. It is easy to apply in treatment of waste water.Synthesis of PEM Emulsion FlocculantSome distilled water, PVA(poly(vinyl alcohol)), EA(ethyl acrylate), and K2S2O8(potassium persulfate) were put into reaction vessel. Kept stirring up under nitrogen. When heated the solution to 40℃, dropped the water solution of MTA[(2-methacryloxylethyl)trimethyl ammonium].Maintained the temperature at 70℃, reacted about 7-8 hours. Then got the PEM emulsion. Changed the ratio of EA and MTA. Obtained a series of PEM emulsions.Stability and Convertibility of PEM EmulsionThe test results showed that when the EA/MTA was 85/15, the PEM emulsion was most stable.When the total monomer quantity was 35%, the convertibility of PEM emulsion was the highest,i.e.98.6%.The MTA Copolymerization Ratio and Morphology of PEM EmulsionWhen the monomers EA/MTA=85/15 and total monomer quantity was 35%, the MTA copolymerization ratio of PEM emulsion was 95.15%(the highest), and the PEM emulsion was some microspheres with 100-180nm of diameter.The Test Results of PEM Emulsion in Treatment of Waste Water The PEM emulsion flocculant was applied in treatment of waste water of paper mill, and measured the precipitation time(t) and transmittancy(T). The test results were showed in table 1. The optimum value of PEM which was able to make the waste water of paper mill into clear water was 0.008%. 相似文献
26.
Two-dimensional 4,4-bipyridyllead halides, PbI2 (4,4'-bpy) (1) and PbBr2 (4,4'-bpy) (2), were synthesized. The structures were determined by means of X-ray single crystal diffraction.The structure shows a distorted octahedral configuration with six-coordinated central lead atoms. In crystals 1 and 2, the molecules are packed in a two-dimensional network structure through bridging halide atoms and 4,4'-bipyridine ligands between the adjacent lead atoms. 相似文献
27.
A theorem of Birkhoff‐Frink asserts that every algebraic closure operator on an ordinary set arises, from some algebraic structure on the set, as the corresponding generated subalgebra operator. However, for many‐sorted sets, i.e., indexed families of sets, such a theorem is not longer true without qualification. We characterize the corresponding many‐sorted closure operators as precisely the uniform algebraic operators. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
28.
The notion of Kuratowski convergence is applied to describe a kind of convergence in the context of holomorphic functions. We associate it to a convenient topology, explore its relation with the compact-open topology, thus providing a new set theoretic point of view of this classic topology, and present it in the framework of set-valued mappings. 相似文献
29.
30.
Since its discovery in 1946, NMR has become a valuable tool in physics, chemistry, biology, and medicine. With the invention of NMR logging tools that take the medical MRI or laboratory NMR equipment and turn it inside-out, the application of sophisticated laboratory techniques to determine formation properties in situ is now available. The capability has opened a new era in formation evaluation just as the introduction of NMR has revolutionized the other scientific areas. 相似文献