全文获取类型
收费全文 | 4015篇 |
免费 | 95篇 |
国内免费 | 23篇 |
专业分类
化学 | 3352篇 |
晶体学 | 42篇 |
力学 | 44篇 |
数学 | 171篇 |
物理学 | 524篇 |
出版年
2023年 | 24篇 |
2022年 | 32篇 |
2021年 | 42篇 |
2020年 | 55篇 |
2019年 | 52篇 |
2018年 | 33篇 |
2017年 | 31篇 |
2016年 | 72篇 |
2015年 | 79篇 |
2014年 | 91篇 |
2013年 | 191篇 |
2012年 | 221篇 |
2011年 | 280篇 |
2010年 | 148篇 |
2009年 | 148篇 |
2008年 | 306篇 |
2007年 | 245篇 |
2006年 | 307篇 |
2005年 | 275篇 |
2004年 | 234篇 |
2003年 | 214篇 |
2002年 | 192篇 |
2001年 | 57篇 |
2000年 | 66篇 |
1999年 | 49篇 |
1998年 | 33篇 |
1997年 | 40篇 |
1996年 | 42篇 |
1995年 | 35篇 |
1994年 | 33篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 23篇 |
1989年 | 14篇 |
1988年 | 21篇 |
1987年 | 26篇 |
1986年 | 15篇 |
1985年 | 35篇 |
1984年 | 41篇 |
1983年 | 15篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 28篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 18篇 |
1974年 | 13篇 |
排序方式: 共有4133条查询结果,搜索用时 15 毫秒
131.
Miyatake K Zhou H Uchida H Watanabe M 《Chemical communications (Cambridge, England)》2003,(3):368-369
Novel sulfonated polyimides containing fluorenyl groups show good thermal and oxidative stability as well as a high proton conductivity of 1.67 S cm(-1) at 120 degrees C and 100% RH. 相似文献
132.
Takeda N Kajiwara T Suzuki H Okazaki R Tokitoh N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(15):3530-3543
The first stable silylene-isocyanide complexes, [Tbt(Mes)SiCNAr] (5 c: Ar=Tip, 5 d: Ar=Tbt, 5 e: Ar=Mes*; Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes=mesityl, Tip=2,4,6-triisopropylphenyl, Mes*=2,4,6-tri-tert-butylphenyl) were successfully synthesized by the reaction of a kinetically stabilized disilene, [Tbt(Mes)Si=Si(Mes)Tbt] (1), with bulky isocyanides, ArNC (3c-e). The spectroscopic data of 5 c-e and theoretical calculations for a model molecule indicated that 5 c-e are not classical cumulative compounds but the first stable silylene-Lewis base complexes. The reactions of 5 c-e with triethylsilane and 1,3-dienes gave the corresponding silylene adducts, and they underwent isocyanide-exchange reactions in the presence of another isocyanide at room temperature. These results indicate dissociation of complexes 5 c-e to the corresponding silylene 2 and isocyanides 3 c-e under very mild conditions. The reaction of 5 c with methanol gave the MeOH adduct 16, [Tbt(Mes)SiHC(OMe)NTip], which has a hydrogen atom on the silicon atom. This regioselectivity can be explained in terms of the contribution of zwitterionic resonance structures D and E, which have an anion on the silicon atom. This result indicates that 5 c is not a classical cumulene having Si=C double bonds that should react with methanol to give adducts bearing a methoxyl group on the silicon atom. Although the reactions of 5 c-e with electrophilic reagents such as methanol, hydrogen chloride, and methyl iodide gave the formal silylene adducts, the studies on the reaction mechanism by trapping experiments and the observation of the intermediate suggested that the reaction mainly or partially proceeds by initial nucleophilic attack of the silicon atom, as is the case in the formation of 16 in the reaction of 5 c with methanol. It was revealed that 5 c-e show the nucleophilicity of the silicon atom, most likely resulting from the contribution of the zwitterionic resonance structures D and E. 相似文献
133.
134.
Ikuo Kawashima Hiroaki Imoto Masatoshi Ishida Hiroyuki Furuta Shunsuke Yamamoto Masaya Mitsuishi Susumu Tanaka Toshiki Fujii Kensuke Naka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):11812-11816
Dibenzo[b,f]arsepins possessing severely distorted cores compared to those of other heteropins were synthesized. These derivatives exhibited dual photoluminescence in the green‐to‐red region (500–700 nm) and the near‐ultraviolet region (<380 nm), which could be attributed to the planarization of the arsepin core in the lowest singlet excited (S1) state. The computational approach for the assessment of the aromatic indices revealed that the dibenzoarsepins studied show aromaticity (8π system) in the S1 states in line with Baird's rule. The lone pair electrons of the arsenic atoms play a crucial role in the aromaticity in the S1 states. 相似文献
135.
Lisman Suryanegara Antonio Norio Nakagaito Hiroyuki Yano 《Cellulose (London, England)》2010,17(4):771-778
Polylactic acid (PLA) in a crystallized state has mechanical properties at high temperatures superior to PLA in an amorphous state. However, a long annealing time is required to fully crystallize PLA. In this study, microfibrillated cellulose (MFC)-reinforced partially crystallized PLA composites were produced, with the goal of reducing the time required to fabricate PLA parts. A series of PLA/MFC composites at a fiber content of 10 wt% from degree of crystallinity (Xc) 0 to 43% was obtained by annealing at 80 °C. Although the annealing time required to obtain a composite (Xc: 17%) was only around one-seventh of the 20 min needed to fully crystallize neat PLA (Xc: 41%), both materials had comparable rigidity above the glass transition temperature (T g) and creep deformation at around T g. These results showed that partially crystallized PLA/MFC composite can replace fully crystallized neat PLA. 相似文献
136.
Nanometer-sized metallic palladium particles can be synthesized by hydrogen reduction of Pd2+ ions dissolved in the water core of a water-in-CO2 microemulsion. The Pd nanoparticles, stabilized by the micromeulsion and uniformly dispersed in the supercritical fluid phase, are effective catalysts for hydrogenation of olefins. Examples of rapid and efficient hydrogenation of water-soluble and CO2-soluble olefins catalyzed by the Pd nanoparticles in supercritical CO2 are given. 相似文献
137.
Koide T Yuguchi M Kawakita M Konno H 《Journal of the American Chemical Society》2002,124(32):9388-9389
Collagen model peptides that contain 2,2'-bipyridyl (bpy) ligands were designed and synthesized. The thermal stability of the collagenous triple helix was increased by forming an Fe(II)(bpy-peptide)(3) complex. The chirality of the metal center was shifted to form right-handed Delta-isomers induced by the supercoiling of the peptide moiety. Moreover, the refolding rate of the triple helix was increased in the presence of Fe(II). This metal-coordinating system possesses potential to be used to stabilize the triple-helical conformation as well as to probe the folding status of collagen model peptides. 相似文献
138.
Tetrakis-acridinyl peptide 1 assuming a right-handed helical stacked conformation of the acridinyl units can bind to DNA duplex with a very high affinity of 10(8) (M-bp)(-1) even at a high salt concentration of 0.2 M NaCl, irrespective of the base composition. Peptide 1 gave rise to 1600-times enhancement of its fluorescence upon binding to an AT polymer due to the collapse of this stacked structure, but the fluorescence is not enhanced with a GC polymer, though the binding constants of 1 for both polymers were the same. 相似文献
139.
Takuji Hirose Kumiko Naito Megumi Nakahara Hiroaki Shitara Yoshio Aoki Hiroyuki Nohira Bruce W. Baldwin 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(1-2):87-93
Two Kemp's acid diamides were synthesized and applied to chiral amine recognition using 1H NMR analysis. One derivative based on 1-(1-naphthyl)ethylamine had good chiral recognition of six amines and was useful to determine the optical purity for three amines, i.e., methylbenzylamine, 1-(1-naphthyl)ethylamine and 1- henylpropylamine,however, the cyclohexylethylamine derivative showed little discrimination for the amines studied. Together with the results for alkylamines, it was shown that aromatic structure was important for aromatic shielding anisotropy and –– interactions between host and guest. The structure of the 1-(1-naphthyl)ethylamine derivative in solution was also considered based on 1H NMR data and computer simulation. 相似文献
140.
Hiromitsu Maeda Atsuhiro Osuka Hiroyuki Furuta 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(1-2):33-36
Ni(II), Pd(II), and Cu(II) complexes of N-confused porphyrin (NCP) exhibit anion binding properties through a hydrogen bonding interaction at the peripheral NH of confused pyrrole ring. The binding constants of the tetrakis(pentafluorophenyl)-NCP metal complexes (1-M, M= Ni, Pd, Cu) for various halide anions in CH2C12 increase in the order of F? > Cl? > Br? > I?, respectively. Zwitterionic resonance form of the NCP complexes as well as interactions between halide anions and a pentafluorophenyl group are suggested to be important for efficient anion binding. 相似文献