全文获取类型
收费全文 | 46641篇 |
免费 | 9686篇 |
国内免费 | 17759篇 |
专业分类
化学 | 33783篇 |
晶体学 | 2281篇 |
力学 | 3660篇 |
综合类 | 2025篇 |
数学 | 7848篇 |
物理学 | 24489篇 |
出版年
2024年 | 85篇 |
2023年 | 422篇 |
2022年 | 1752篇 |
2021年 | 1658篇 |
2020年 | 1545篇 |
2019年 | 1540篇 |
2018年 | 1449篇 |
2017年 | 2357篇 |
2016年 | 1558篇 |
2015年 | 2459篇 |
2014年 | 2952篇 |
2013年 | 3961篇 |
2012年 | 3814篇 |
2011年 | 4051篇 |
2010年 | 4253篇 |
2009年 | 4407篇 |
2008年 | 5016篇 |
2007年 | 4386篇 |
2006年 | 4358篇 |
2005年 | 3802篇 |
2004年 | 2886篇 |
2003年 | 2066篇 |
2002年 | 2049篇 |
2001年 | 2109篇 |
2000年 | 2205篇 |
1999年 | 1242篇 |
1998年 | 650篇 |
1997年 | 520篇 |
1996年 | 480篇 |
1995年 | 426篇 |
1994年 | 504篇 |
1993年 | 465篇 |
1992年 | 399篇 |
1991年 | 272篇 |
1990年 | 270篇 |
1989年 | 309篇 |
1988年 | 247篇 |
1987年 | 202篇 |
1986年 | 157篇 |
1985年 | 121篇 |
1984年 | 113篇 |
1983年 | 129篇 |
1982年 | 107篇 |
1981年 | 83篇 |
1980年 | 65篇 |
1979年 | 60篇 |
1978年 | 24篇 |
1977年 | 16篇 |
1971年 | 16篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
991.
Regenerated cellulose films with water-resistance were obtained by an improved method ofpreparing cellulose cuoxam solution from pulps of agricultural wastes (linters, wheat straw, reedand Bamao). Experimental results showed that the mechanical properties of both the dry. and wetfilms were excellent. Data from IR, SEM and tensile strength measurements implied that thesignificant improvement of water-resistance of the films was due to the cohesion between the thinTung oil covers with hydrophobicity and the regenerated cellulose films. The films werecompletely biodegraded after being buried in soil for 100 days. The transmittance of the filmsderived from linter and reed in visible band range were 80-90%. 相似文献
992.
SynthesesandStudiesofPEG┐b┐PNIPABlockPolymersCAOWei-xiao**andZHANGTao(ColegeofChemistryandMolecularEnginering,PekingUniversit... 相似文献
993.
994.
根据活性亚结构拼接原理,以ε-己内酯和硫代对称二氨基脲为基体,制得中间体3-(5-羟戊基)-4-氨基-5-巯基-1,2,4-三唑,再与ω-卤代芳基乙酮反应合成了8个新的3-(5-羟戊基)-6-芳香基-7H-1,2,4-三唑并[3,4-b][1,3,4]噻二嗪类化合物,其结构经1H NMR、 13C NMR、 IR和元素表征。采用室内培养皿法考察了化合物的植物生长调节活性。结果表明: 3a~3h对双子叶萝卜茎和单子叶小麦茎的生长均有显著的抑制作用,浓度为10 mg·L-1时,抑制率为50%~69%,浓度为50 mg·L-1时,抑制率达到88%以上,3c对两种植物茎生长的抑制率均达到100%。 相似文献
995.
996.
Schiff碱双核Mn配合物的合成、结构和性能研究 总被引:3,自引:0,他引:3
Five manganese complexes of Schiff base were synthesized: [MnⅣ,Ⅳ(μ-O)(Salen)]2·DMF·H2O (1), [MnⅣ,Ⅳ(μ-O)(5-BrSalen)]2·DMF·0.5H2O (2), {MnⅣ,Ⅳ(μ-O)[Sal(1,2-pn)]}2·H2O (3), {MnⅣ,Ⅳ(μ-O)[5-Br-Sal(1,2-pn)]}2·H2O (4), {MnⅣ,Ⅳ(μ-O)[5-CH3-Sal(1,2-pn)]}2·2H2O (5), and were characterized by element analysis, IR and UV-Vis spectra. The results of cyclic voltammogram show that Schiff base ligands can drop the potential of manganese and steady high oxide state of manganese. The magnetic properties of 1 and 3 have also been studied. The results show that there is a weak ferromagnetically coupling of MnⅣ2 pair at room and low temperature, and the interactions of complex 3 are weaker than complex 1. 相似文献
997.
998.
999.
1000.
A star network polymer with a pentaerythritol core linking four PEG-block polymeric arms was synthesized, and its corresponding gel polymer electrolyte based on lithium perchlorate and plasticizers EC/PC with the character being colorless and highly transparent has been also prepared. The polymer host was characterized and confirmed to be of a star network and an amorphous structure by FTIR, ^1H NMR and XRD studies. The polymer host hold good mechanical properties for pentaerythritol cross-linking. Maximum ionic conductivity of the prepared polymer electrolyte has reached 8.83 × 10 ^-4 S·cm^-1 at room temperature. Thermogravimetry (TG) of the polymer electrolyte showed that the thermal stability was up to at least 150 ℃. The gel polymer electrolyte was further evaluated in electrochromic devices fabricated by transparent PET-ITO and electrochromically active viologen derivative films, and its excellent performance promised the usage of the gel polymer electrolyte as ionic conductor material in electrochrornic devices. 相似文献