全文获取类型
收费全文 | 25310篇 |
免费 | 4588篇 |
国内免费 | 6236篇 |
专业分类
化学 | 19337篇 |
晶体学 | 688篇 |
力学 | 1297篇 |
综合类 | 533篇 |
数学 | 2968篇 |
物理学 | 11311篇 |
出版年
2024年 | 75篇 |
2023年 | 393篇 |
2022年 | 993篇 |
2021年 | 982篇 |
2020年 | 1032篇 |
2019年 | 993篇 |
2018年 | 968篇 |
2017年 | 1129篇 |
2016年 | 1198篇 |
2015年 | 1355篇 |
2014年 | 1727篇 |
2013年 | 2181篇 |
2012年 | 2386篇 |
2011年 | 2523篇 |
2010年 | 2062篇 |
2009年 | 2012篇 |
2008年 | 2186篇 |
2007年 | 1913篇 |
2006年 | 1808篇 |
2005年 | 1377篇 |
2004年 | 1038篇 |
2003年 | 841篇 |
2002年 | 868篇 |
2001年 | 812篇 |
2000年 | 749篇 |
1999年 | 534篇 |
1998年 | 290篇 |
1997年 | 244篇 |
1996年 | 223篇 |
1995年 | 167篇 |
1994年 | 172篇 |
1993年 | 160篇 |
1992年 | 128篇 |
1991年 | 100篇 |
1990年 | 78篇 |
1989年 | 82篇 |
1988年 | 62篇 |
1987年 | 52篇 |
1986年 | 51篇 |
1985年 | 34篇 |
1984年 | 29篇 |
1983年 | 24篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 7篇 |
1964年 | 3篇 |
1959年 | 4篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
5-甲基吡咯-2-羧酸酯在磺酰氢,溴或四乙酸铅作用下,生成相应的在5-甲基上含取代基的产物,后者不经分离不便可自缩合得标题化合物,核磁共振氢谱研究和分子构象木匠,当3,3位的取代基为甲酸(酯)基或乙酸(酯)基时,可形成3,3位酯基与另一吡咯环上的氮氢之间的分子内氢键,而3,3位是其它取代基,如乙酰基,丙酸(酯)基,丁酸(酯)基时不能形成类似的分子内氢键。 相似文献
92.
Yang Jing Wen Xiang Lin Yang 《International Journal of Infrared and Millimeter Waves》1998,19(7):963-975
The modified quantum nonlinear Schrodinger equation of ultra-short pulse propagating in fiber is derived using dispersion relation and the Hamiltonian of the transmission system. The derived equation is solved with linearization approximation, and modulation instability is analyzed. The equation is also solved with Hartree approximation. The results indicate that pulse power, loss and self-steeping effect change the critical frequency, the maximum gain and the gain spectrum range, but the third order dispersion has no effect on modulation instability. The expectation value of optical field is average of a set of modified classical solitons, and higher order terms change the amplitude, pulse position and phase of soliton. 相似文献
93.
94.
95.
96.
聚乙烯单晶的退火效应 总被引:1,自引:1,他引:1
用混合晶红外光谱法和SAXS、DSC和LAM等方法研究了聚乙烯单晶在75℃、90℃和105℃退火前后的结构变化,发现在90℃以下和105℃以上退火,遵循不同的退火机制 相似文献
97.
Jing Ping WANG Qiang WU Jing Yang NIU* School of Chemistry Chemical Engineering Henan University Kaifeng 《中国化学快报》2002,13(9):915-918
It is becoming a focus to synthesize and assemble organic-inorganic materials, especially, to synthesize charge-transfer complexes formed by polyoxometalate and organic donors. They have attracted much attention because such complexes are active in their electric, magnetic and optic properties1-4, many investigations about them have been done and some crystal structures of them were reported5-6. But, the disadvantage of these crystals is instability at room temperature. According to the view… 相似文献
98.
99.
Polyethylene terephthalate(PET)/polycaprolactone(PCL) segmented copolymers with different hard segment contents and a blend of two of them were studied by using DSC, WAXS, TEM and IR techniques and dynamic mechanical, stress-strain and isothermal crystallization measurements. Emphasis was laid on the studies of influence of compositional heterogeneity on the morphology and properties of these segmented copolymers. It was found that the solution cast specimens of the more heterogeneous sample exhibit better segregation of segments, high crystallinity and melting temperature. They have higher thermal stability of mechanical properties at small deformations. However, they are less stable against large deformations and may become softer than the more homogeneous ones. 相似文献
100.
A Cu(Ⅱ) complex [Cu(L)1.5(OSO3)]·3H2O (1) [L=1,4-bis(imidazol-1-yl)benzene] was synthesized by reaction of ligand L with CuSO4·5H2O using solvothermal method and its structure was determined by X-ray crystal structure analysis. The structure indicates that the complex crystallizes in triclinic, space group P1 with a=0.948 8(2), b=1.078 5(2), c=1.108 4(2) nm, α=74.820(2), β=81.331(2), γ=72.638(2)°, V=1.041 5(3) nm3, Z=2, Dcalc=1.687 g·cm-3, F(000)=544, μ=1.205 cm-1, the final R=0.062 3 and wR=0.132 8. The Cu(Ⅱ) atom has distorted square-pyramidal environment with a N3O2 donor set. Each L ligand links two Cu(Ⅱ) atoms using its imidazole groups to form an infinite one-dimensional (1D) ladder-like chain, which further linked by SO42- to form a two-dimensional (2D) network structure. The 2D sheets are further connected by C-H…O hydrogen bonds to give a three-dimensional (3D) structure. CCDC: 650388. 相似文献