全文获取类型
收费全文 | 104039篇 |
免费 | 16624篇 |
国内免费 | 11841篇 |
专业分类
化学 | 72603篇 |
晶体学 | 1135篇 |
力学 | 5877篇 |
综合类 | 666篇 |
数学 | 12627篇 |
物理学 | 39596篇 |
出版年
2024年 | 351篇 |
2023年 | 2067篇 |
2022年 | 3667篇 |
2021年 | 3949篇 |
2020年 | 4176篇 |
2019年 | 3960篇 |
2018年 | 3714篇 |
2017年 | 3336篇 |
2016年 | 5013篇 |
2015年 | 4925篇 |
2014年 | 6050篇 |
2013年 | 7779篇 |
2012年 | 9277篇 |
2011年 | 9477篇 |
2010年 | 6623篇 |
2009年 | 6352篇 |
2008年 | 6680篇 |
2007年 | 5969篇 |
2006年 | 5579篇 |
2005年 | 4659篇 |
2004年 | 3646篇 |
2003年 | 2928篇 |
2002年 | 2662篇 |
2001年 | 2229篇 |
2000年 | 1947篇 |
1999年 | 2053篇 |
1998年 | 1735篇 |
1997年 | 1559篇 |
1996年 | 1558篇 |
1995年 | 1367篇 |
1994年 | 1240篇 |
1993年 | 1003篇 |
1992年 | 902篇 |
1991年 | 776篇 |
1990年 | 653篇 |
1989年 | 503篇 |
1988年 | 379篇 |
1987年 | 338篇 |
1986年 | 336篇 |
1985年 | 262篇 |
1984年 | 188篇 |
1983年 | 153篇 |
1982年 | 125篇 |
1981年 | 78篇 |
1980年 | 59篇 |
1979年 | 26篇 |
1978年 | 22篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1957年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Zhang Yingzhu Chen Jiehuan Lian Xiaomei Yang Weitao Li Jun Tian Shuoxun Wu Gang Chen Hongzheng 《中国科学:化学(英文版)》2019,62(7):859-865
Layered two-dimensional(2D)perovskite solar cells(PVSCs)with a chemical formula of C(NH_2)_3(CH_3NH_3)_3Pb_3I_(10)(n=3)have been fabricated through additive engineering,wherein stoichiometrically equivalent guanidinium(GA~+)and methylammonium(MA~+)serve as spacer cations.The crystallinity of the perovskite films is dramatically enhanced with proper amount of methylammonium thiocyanate(MASCN)added into the precursor solution.In addition,we substitute a small amount of MA~+with hydrophobic phenylethylammonium(PEA~+),which can passivate trap states of the perovskite films.As a result,the open circuit voltage increases to 1.1 V and the best power conversion efficiency(PCE)of 10.12%is yielded.Furthermore,superior thermal stability and balanced moisture stability of the PEA-substituted GA-based PVSCs are demonstrated,compared to the popular 3D MAPbI_3and 2D PEA-based PVSCs.They retain approximately 80%of the original PCE after 30 d at 20%relative humidity(RH),and 50%of the original PCE after 3200 min at 85°C without any encapsulation.This work suggests a new route to achieve both heat and humidity stable PVSCs by simply mixing different spacer cations. 相似文献
992.
Li Jinfeng Li Chenguang Sun Lingjie Zhang Xiaotao Cheng Shanshan Hu Wenping 《中国科学:化学(英文版)》2019,62(7):916-920
Science China Chemistry - As bifunctional materials, phenanthrene derivatives 2,7-diphenylphenanthrene and 2,7-di(styryl)phenanthrene (DPPa and DSPa) were designed and studied. Both materials show... 相似文献
993.
Herein, we report two novel derivatives of hexabenzoperylene (HBP) that are functionalized with ester groups. Methyl acetate functionalized HBP ( 1 ) in single crystals self‐assembles into a supramolecular nanosheet, which has a two‐dimensional π‐stack of HBP sandwiched between two layers of ester groups. With the same self‐assembly motif, active ester‐functionalized HBP ( 2 ) in field effect transistors has enabled differentiation of tertiary amines from primary and secondary amines, in agreement with the fact that active ester reacts with primary and secondary amines but not with tertiary amines to form amides. 相似文献
994.
Koser's reagent is found to be effective in the oxidative double dehydrogenation of various carbocyclic β-dicarbonyl compounds,which constitutes the first example on dehydrogenation reactivity of hypervalent iodine(Ⅲ) reagents for carbocyclic carbonyl compounds. DFT calculations reveal that the rate-determining step is the electrophilic addition of PhI+OH onto enolate of monodehydrogenated product. 相似文献
995.
Experimental Mechanics - Identification of impact force is essential for various engineering applications, such as performance evaluation, design optimisation, noise suppression, and vibration... 相似文献
996.
Meccanica - In this paper the effect of grain fragmentation of a cohesionless granular material on the change of microstructure quantities is investigated using a micropolar continuum model. To... 相似文献
997.
Haolin Lin Shenhe Fu Zhigui Deng Haiqiong Zhou Hao Yin Zhen Li Zhenqiang Chen 《Annalen der Physik》2019,531(11)
Superoscillation is an intriguing wave phenomenon which enables subwavelength features propagating into far field and hence has potential applications in super‐resolution microscopy as well as particle trapping and manipulation. While previous demonstrations mostly concentrate on designing complicated nanostructures for generating uncontrollable superoscillatory functions, here a new technique which allows for creating polynomially shaped superoscillatory functions that contain phase singularity arrays is demonstrated both theoretically and experimentally. Such a technique is implemented in optical experiments for the first time and controllable superoscillatory lobes with feature much below the diffraction limit is achieved. More importantly, a general theoretical framework, which, to our knowledge, has not been reported before, is developed to show how the created superoscillations propagate to a distance of many Rayleigh ranges and eventually disappear when the distance is sufficiently larger. The validity of the model is confirmed by the experiments. The results may trigger further studies in light field shaping and manipulations in subwavelength scale. 相似文献
998.
Yingfen Li Xian Wei Song Bai Zhi‐Gang Xu Menglan Lv 《Journal of heterocyclic chemistry》2019,56(12):3429-3434
The skeleton of fused benzimidazole‐pyrazine was constructed via an Ugi/deprotection/cyclization (UDC) and hydroamination cascade reaction. This four‐step reaction was carried out in a one‐pot procedure with only one‐time column chromatography purification. The representative compound 7b exhibited 67% cell growth inhibitory activity against human breast cancer cell line MDA‐MB‐453 at the concentration of 10μM. 相似文献
999.
The first addition-elimination of nitroalkanes to 3-phenacylideneoxindoles was developed, affording the corresponding 3-alkenylphenacylidene-oxindoles with high yields.The addition-elimination mechanism of 3-phenacylideneoxindoles with nitroalkanes and removable NO2 group in concert guarantees the high regioselectivity. 相似文献
1000.
ABSTRACTA striking feature of lyotropic chromonic liquid crystals confined in cylinder model exhibit double-twist director configurations. Evidence suggests that saddle-splay deformation is among the most important factors for the distortions of director. Previous researches limit the director to distort at a fixed plane (r-? plane) by using specific boundary conditions such as degenerate planar anchoring condition. In this work, we consider lyotropic chromonic liquid crystals confined between two coaxial cylinders with free-surface boundary conditions and Rapini-Papoular-type anchoring conditions. By using finite-difference iterative method to solve the numerical solution of Euler equation, we find that saddle-splay deformation leads to double-twist director configurations under free-surface boundary conditions, which consist of the result under degenerate planar anchoring conditions. Furthermore, at Rapini-Papoular-type anchoring conditions, saddle-splay deformation has a great influence on the director in the radial direction (r direction) and the director distorts in three-dimensional space. Remarkably, our method provides a more accurate theory basis for the measured values of saddle-splay elastic constant K24。 相似文献