全文获取类型
收费全文 | 13840篇 |
免费 | 2439篇 |
国内免费 | 2017篇 |
专业分类
化学 | 10768篇 |
晶体学 | 178篇 |
力学 | 700篇 |
综合类 | 134篇 |
数学 | 1890篇 |
物理学 | 4626篇 |
出版年
2024年 | 37篇 |
2023年 | 258篇 |
2022年 | 330篇 |
2021年 | 399篇 |
2020年 | 524篇 |
2019年 | 553篇 |
2018年 | 462篇 |
2017年 | 430篇 |
2016年 | 690篇 |
2015年 | 710篇 |
2014年 | 870篇 |
2013年 | 1058篇 |
2012年 | 1254篇 |
2011年 | 1263篇 |
2010年 | 911篇 |
2009年 | 854篇 |
2008年 | 932篇 |
2007年 | 788篇 |
2006年 | 763篇 |
2005年 | 701篇 |
2004年 | 632篇 |
2003年 | 536篇 |
2002年 | 572篇 |
2001年 | 410篇 |
2000年 | 316篇 |
1999年 | 373篇 |
1998年 | 242篇 |
1997年 | 198篇 |
1996年 | 183篇 |
1995年 | 171篇 |
1994年 | 152篇 |
1993年 | 89篇 |
1992年 | 93篇 |
1991年 | 100篇 |
1990年 | 98篇 |
1989年 | 67篇 |
1988年 | 46篇 |
1987年 | 33篇 |
1986年 | 47篇 |
1985年 | 34篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1975年 | 4篇 |
1974年 | 4篇 |
1968年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Yin Jingxue 《数学年刊B辑(英文版)》1991,12(4):500-519
This paper applies the compensated compactnessmethod to the study of a class of quasilinear parbolic equations of higher order with doubly strong degeneration. Some existence and uniqueness results are proved under certain conditions. 相似文献
122.
叠层连续开口圆柱壳的精确解 总被引:2,自引:0,他引:2
抛弃任何有关位移和应力模式的假设,引入δ-函数,对正变异性连续开口圆柱壳建立状态方程.给出薄的、中厚的和强厚的叠层连续开口圆柱壳静力问题的统一的精确解.数值结果和SAPS解进行了对比. 相似文献
123.
Wei‐Lie Xiao Jian‐Xin Pu Rui‐Rui Wang Liu‐Meng Yang Xiao‐Li Li Sheng‐Hong Li Rong‐Tao Li Sheng‐Xiong Huang Yong‐Tang Zheng Han‐Dong Sun 《Helvetica chimica acta》2007,90(8):1505-1513
Seven new highly oxygenated nortriterpenoids, rubriflorins D–J ( 1 – 7 ), were isolated from the leaves and stems of Schisandra rubriflora, and their structures were elucidated on the basis of extensive analysis of spectroscopic data. These new compounds feature the opening of ring A compared with related known nortriterpenoids isolated from the genus Schisandra and showed weak activity against HIV‐1. 相似文献
124.
Cellulose carbamate, an environmentally friendly material presents an interesting alternative to petroleum-based polymers because of its renewable, biodegradable, biocompatible nature and its solubility in conventional solvents. In synthesis process of cellulose carbamate, urea was firstly impregnated into the cellulose pulp by supercritical CO2(scCO2), followed by the esterification of cellulose. The structure of cellulose carbamate was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The rheological properties of these cellulose carbamates in 9% sodium hydroxide solution were investigated, using a range of the nitrogen content, concentrations and shear rates. 相似文献
125.
126.
Cu nanotube arrays were fabricated by electroless deposition using porous anodic aluminium oxide membranes as templates. This was accomplished by a four-step procedure, i.e. pore-wall modification, polishing treatment, sensitization-activation and electroless deposition. The as-synthesized Cu nanotubes possess controllable inner diameter and open ends. 相似文献
127.
Y.X. Yin 《Applied Surface Science》2006,253(3):1584-1589
Wear resistant Cu-based solid solution (Cuss) toughened Cr5Si3 metal silicide composite coatings were fabricated on austenitic stainless steel AISI321 by laser cladding process. Due to the rapidly solidified microstructural characteristics and the excellent toughening effect of Cuss on Cr5Si3, the Cuss/Cr5Si3 coatings have outstanding wear resistance and low coefficient of friction under room temperature dry sliding wear test conditions coupling with hardened 0.45% C steel. 相似文献
128.
Li‐Ming Tang Yan‐Guo Li Wei‐Ping Ye Yue‐Sheng Li 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5846-5854
Ethylene–propylene copolymerization, using [(Ph)NC(R2)CHC(R1)O]2TiCl2 (R1 = CF3, Ph, or t‐Bu; R2 = CH3 or CF3) titanium complexes activated with modified methylaluminoxane as a cocatalyst, was investigated. High‐molecular‐weight ethylene–propylene copolymers with relatively narrow molecular weight distributions and a broad range of chemical compositions were obtained. Substituents R1 and R2 influenced the copolymerization behavior, including the copolymerization activity, methylene sequence distribution, molecular weight, and polydispersity. With small steric hindrance at R1 and R2, one complex (R1 = CF3; R2 = CH3) displayed high catalytic activity and produced copolymers with high propylene incorporation but low molecular weight. The microstructures of the copolymers were analyzed with 13C NMR to determine the methylene sequence distribution and number‐average sequence lengths of uninterrupted methylene carbons. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5846–5854, 2006 相似文献
129.
Chun‐Hao Huang Sheng‐Hsiung Yang Kuei‐Bai Chen Chain‐Shu Hsu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):519-531
Five novel fluorene‐containing polymers, poly[(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA1 ), poly[(1‐pentyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene) ( PFA2 ), poly[1‐decyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA3 ), poly[1‐phenyl‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA4 ), and poly[1‐(3,4‐difluorophenyl)‐2‐(9,9‐dimethylfluoren‐2‐yl)acetylene] ( PFA5 ) were synthesized by the polymerization of the corresponding fluorene‐substituted acetylenic monomers ( M1–M5), using WCl6, MoCl5, and TaCl5 as catalysts and n‐Bu4Sn as a cocatalyst. The synthesized polymers were thermally stable and readily soluble in common organic solvents. The degradation temperatures for a 5% weight loss of the polymers were ∼352–503 °C under nitrogen. PFA1–PFA5 show emission peaks from 402 to 590 nm. Besides, their electroluminescent properties were studied in heterostructure light‐emitting diodes (LEDs), using PFA2–PFA5 as an emitting layer. The PFA5 device revealed an orange‐red emission peak at 602 nm with a maximum luminescence of 923 cd/m2 at 8 V. A device with the ITO/PEDOT/ a mixture of PFA2 (98 wt %) and PFA5 (2 wt %)/Ca/Al showed near white emission. Its maximum luminance and current efficiency are 450 cd/m2 at 15 V and 1.3 cd/A, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 519–531, 2006 相似文献
130.
Chin‐Ping Yang Yu‐Yang Su Sheng‐Huei Hsiao 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5909-5922
Two series of novel fluorinated poly(ether imide)s (coded IIIA and IIIB ) were prepared from 2,6‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride and 2,7‐bis(3,4‐dicarboxyphenoxy)naphthalene dianhydride, respectively, with various trifluoromethyl‐substituted aromatic bis(ether amine)s by a standard two‐step process with thermal or chemical imidization of the poly(amic acid) precursors. These fluorinated poly(ether imide)s showed good solubility in many organic solvents and could be solution‐cast into transparent, flexible, and tough films. These films were nearly colorless, with an ultraviolet–visible absorption edge of 364–386 nm. They also showed good thermal stability with glass‐transition temperatures of 221–298 °C, 10% weight loss temperatures in excess of 489 °C, and char yields at 800 °C in nitrogen greater than 50%. The 2,7‐substituted IIIB series also showed better solubility and higher transparency than the isomeric 2,6‐substituted IIIA series. In comparison with nonfluorinated poly (ether imide)s, the fluorinated IIIA and IIIB series showed better solubility, higher transparency, and lower dielectric constants and water absorption. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5909–5922, 2006 相似文献