全文获取类型
收费全文 | 68164篇 |
免费 | 5511篇 |
国内免费 | 4610篇 |
专业分类
化学 | 38350篇 |
晶体学 | 755篇 |
力学 | 3496篇 |
综合类 | 365篇 |
数学 | 13997篇 |
物理学 | 21322篇 |
出版年
2023年 | 598篇 |
2022年 | 732篇 |
2021年 | 1120篇 |
2020年 | 1367篇 |
2019年 | 1363篇 |
2018年 | 2320篇 |
2017年 | 2531篇 |
2016年 | 2368篇 |
2015年 | 2293篇 |
2014年 | 2506篇 |
2013年 | 3439篇 |
2012年 | 6301篇 |
2011年 | 5780篇 |
2010年 | 4247篇 |
2009年 | 4049篇 |
2008年 | 3375篇 |
2007年 | 3153篇 |
2006年 | 2935篇 |
2005年 | 6477篇 |
2004年 | 5558篇 |
2003年 | 3666篇 |
2002年 | 1944篇 |
2001年 | 1411篇 |
2000年 | 1051篇 |
1999年 | 953篇 |
1998年 | 652篇 |
1997年 | 491篇 |
1996年 | 534篇 |
1995年 | 413篇 |
1994年 | 396篇 |
1993年 | 319篇 |
1992年 | 434篇 |
1991年 | 379篇 |
1990年 | 360篇 |
1989年 | 291篇 |
1988年 | 280篇 |
1987年 | 182篇 |
1986年 | 161篇 |
1985年 | 187篇 |
1984年 | 141篇 |
1983年 | 115篇 |
1982年 | 85篇 |
1981年 | 84篇 |
1980年 | 78篇 |
1979年 | 76篇 |
1978年 | 73篇 |
1976年 | 129篇 |
1975年 | 82篇 |
1974年 | 92篇 |
1973年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
101.
Fei Chang Dongheng Zhang Haijian Yang Haibin Song 《Journal of organometallic chemistry》2004,689(5):936-946
The synthesized 1-aryliminomethylenylnaphthalen-2-ol derivatives reacted with nickel chloride to form bis(1-aryliminomethylenylnaphthalen-2-oxy)nickel complexes. All resultant compounds were structurally characterized by elemental analyses, IR and H NMR, and the structures of the formed complexes were elucidated by X-ray crystal structure analysis. The complexes show high catalytic activities for the vinyl polymerization of norbornene in the presence of methylaluminoxane. The catalytic activity variations have been followed by gas chromatography through monitoring the conversion of norbornene. 相似文献
102.
Mao‐Chuan Yuan Ping‐I Shih Chen‐Han Chien Ching‐Fong Shu 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2925-2937
We have synthesized a blue‐light‐emitting polyfluorene (PF) derivative ( PF‐CBZ‐OXD ) that presents bulky hole‐transporting carbazole and electron‐transporting oxadiazole pendent groups functionalized at the C‐9 positions of alternating fluorene units. The results from photoluminescence and electrochemical measurements indicate that both the side chains and the PF main chain retain their own electronic characteristics in the copolymer. An electroluminescent device incorporating this polymer as the emitting layer was turned on at 4.5 V; it exhibited a stable blue emission with a maximum external quantum efficiency of 1.1%. Moreover, we doped PF‐CBZ‐OXD and its analogue PF‐TPA‐OXD with a red‐light‐emitting iridium phosphor for use as components of phosphorescent red‐light emitters to investigate the effect of the host's HOMO energy level on the degree of charge trapping and on the electrophosphorescent efficiency. We found that spectral overlap and individual energy level matching between the host and guest were both crucial features affecting the performance of the electroluminescence devices. Atomic force microscopy measurements indicated that the dipolar nature of PF‐CBZ‐OXD , in contrast to the general nonpolarity of polydialkylfluorenes, provided a stabilizing environment that allowed homogeneous dispersion of the polar iridium triplet dopant. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2925–2937, 2007 相似文献
103.
Donghyun Cho Taihyun Chang Apostolos Avgeropoulos Nikos Hadjichristidis 《European Polymer Journal》2003,39(11):2155-2160
Temperature gradient interaction chromatography (TGIC) was applied for the separation of a complex miktoarm star copolymer which has one polystyrene (PS) arm and three polystyrene-b-polyisoprene (PS-b-PI) diblock copolymer arms. Such miktoarm star polymers are much more difficult to characterize than branched homopolymers since the byproduct, typically polymers with missing arm(s) or coupled products, have not only different molecular weights but also different compositions. TGIC was able to fully separate the byproducts, and the composition of the molecular species corresponding to the different separated elution peaks was determined by two methods, fractionation/NMR and multiple detection (UV and RI). A reasonable agreement between the results of the two methods was obtained. By using the composition found, the corresponding molecular weights were determined by multi-angle light scattering detection. Based on the composition and the molecular weight we were able to identify the structure of the different molecular species. 相似文献
104.
105.
106.
GM(1,1)的周期修正模型及其在泉水流量预测中的应用 总被引:6,自引:2,他引:4
本文阐述了 GM( 1 ,1 )的残差周期修正模型 ,并将它应用于山西神头泉的流量预测中 ,建立了神头泉流量的 GM( 1 ,1 )周期修正模型 ,对其流量进行了预测 ,为神头泉域岩溶水资源开发利用和保护提供了科学依据 相似文献
107.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator 下载免费PDF全文
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
108.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献
109.
110.
CONG Fuzhong & LI YongSchool of Mathematics Information Science Shandong Institute of Business Technology Yantai China Office of Mathematics Changchun Flight Academy of the Air Force Changchun China Department of Mathematics Jilin University Changchun China 《中国科学A辑(英文版)》2004,47(5):675-686
An effective stability result for generalized Hamiltonian systems is obtained by applying the simultaneous approximation technique due to Lochak. Among these systems, dimensions of action variables and angle variables might be distinct. 相似文献