全文获取类型
收费全文 | 3026篇 |
免费 | 57篇 |
国内免费 | 4篇 |
专业分类
化学 | 2316篇 |
晶体学 | 37篇 |
力学 | 57篇 |
数学 | 139篇 |
物理学 | 538篇 |
出版年
2021年 | 20篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 18篇 |
2017年 | 17篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 44篇 |
2013年 | 141篇 |
2012年 | 119篇 |
2011年 | 132篇 |
2010年 | 74篇 |
2009年 | 89篇 |
2008年 | 143篇 |
2007年 | 142篇 |
2006年 | 168篇 |
2005年 | 138篇 |
2004年 | 152篇 |
2003年 | 141篇 |
2002年 | 111篇 |
2001年 | 54篇 |
2000年 | 57篇 |
1999年 | 41篇 |
1998年 | 39篇 |
1997年 | 32篇 |
1996年 | 30篇 |
1995年 | 25篇 |
1994年 | 45篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 45篇 |
1990年 | 34篇 |
1989年 | 27篇 |
1988年 | 45篇 |
1987年 | 33篇 |
1986年 | 34篇 |
1985年 | 51篇 |
1984年 | 61篇 |
1983年 | 26篇 |
1982年 | 56篇 |
1981年 | 57篇 |
1980年 | 48篇 |
1979年 | 52篇 |
1978年 | 37篇 |
1977年 | 52篇 |
1976年 | 36篇 |
1975年 | 43篇 |
1974年 | 37篇 |
1973年 | 37篇 |
1968年 | 24篇 |
排序方式: 共有3087条查询结果,搜索用时 343 毫秒
91.
92.
93.
Takashi Hirota Kenji Sasaki Yohsuke Tashima Taiji Nakayama 《Journal of heterocyclic chemistry》1991,28(2):263-267
Syntheses of 2,3-dihydrobenzofuro[2,3-e]imidazo[1,2-c]pyrimidine and its 5-substituted derivatives, corresponding to B-nor-6-oxa-11,13,15-triazasteroids, are described. These products and their precursors were screened to evaluate the antidepressive activity. 相似文献
94.
95.
Yoshio Okamoto Motoyuki Toki Heimei Yuki 《Journal of polymer science. Part A, Polymer chemistry》1979,17(11):3705-3712
S-Methyl thiomethacrylate (methyl thiolmethacrylate, MTMA) was polymerized with a variety of anionic initiators such as n-BuLi, octylpotassium, PhMgBr, and Et2AlNPh2 in toluene and THF. Stereoregularity of the polymer (PMTMA) was determined from the 1H-NMR spectrum of poly(methyl methacrylate), which had been derived from PMTMA, because the α-methyl resonance in the 1H-NMR spectrum of PMTMA was not satisfactorily solved owing to the overlap of pentad signals. The 13C-NMR spectrum of PMTMA also showed the splitting due to pentad sequences. Stereoregularity of PMTMA was always low compared with that of poly(methyl methacrylate), which was prepared under the same reaction conditions. MTMA was much more reactive than methyl methacrylate and methacrylonitrile in the copolymerization with n-BuLi in toluene and in THF at ?78°C. The lower stereoregulation of the polymerization of MTMA and the higher reactivity of MTMA were mainly ascribed to the higher resonance effect of MTMA. 相似文献
96.
97.
Yoshiyuki Oishi Shoichi Nakata Masa-Aki Kakimoto Yoshio Imai 《Journal of polymer science. Part A, Polymer chemistry》1992,30(10):2217-2221
New segmented aromatic poly(ether sulfone)-amide and poly(ether sulfone)-imide copolymers were synthesized by the chain extension of α,w-diamine-terminated poly(ether sulfone) oligomer with both aromatic dicarboxylic acid chlorides and tetracarboxylic dianhydrides, respectively. Crystallization of the poly(ether sulfone)unit was suppressed by the introduction of amide or imide linkage along the polymer backbone, giving amorphous copolymers that were +eadily soluble in various organic solvents. The copolymers had somewhat higher glass transition temperatures than the parent poly(ether sulfone). They afforded transparent and tough films by solution casting. © 1992 John Wiley & Sons, Inc. 相似文献
98.
Yoshio Imai Hiroshi Koga 《Journal of polymer science. Part A, Polymer chemistry》1973,11(10):2623-2632
New thermally stable poly(imide-oxoisoindolobenzothiadiazine dioxides) (PIOD) have been prepared by the three-step cyclopolycondensation reaction of diaminobenzenesulfonamides with aromatic tetracarboxylic dianhydrides. The polymerization proceeded through the formation of poly(amic acid-sulfonamides) (PAAS), followed by cyclodehydration to yield polyimide-sulfonamides (PIS), which were subsequently converted to PIOD at 300°C. PAAS having inherent viscosities in the range of 0.1–0.5 in N-methyl-2-pyrrolidone (NMP) were obtained in approximately quantitative yield. PIOD were insoluble in most organic solvents, whereas PAAS and PIS were soluble in NMP and dimethyl sulfoxide. Differential thermal analysis and thermogravimetric analysis indicated that PIOD began to decompose at 460°C in air. The cyclodehydration of the model compounds was also investigated. 相似文献
99.
100.
Oseki Y Fujitsuka M Hara M Cai X Ie Y Aso Y Majima T 《The journal of physical chemistry. B》2005,109(21):10695-10698
Photophysical properties of oligo(2,3-thienyleneethynylene)s (nTE, n denotes the number of thiophene rings, n = 2, 3) in benzene were investigated using steady-state, time-resolved fluorescence, and transient absorption spectroscopies. For 2TE, generation of the radiative S2 and nonradiative S1 states was confirmed. Upon excitation, the S2 state was initially generated and deactivated to the S1 state within 10 ps. The S1 state exhibited the transient absorption band at 470 nm, of which the lifetime was estimated to be 5.3 ns. In the case of 3TE, on the other hand, it was revealed that the radiative S1 state with a transient absorption peak at 650 nm was generated upon excitation. The T1 states of nTE were generated from the S1 states. The quantum yields were estimated to be 0.52 and 0.54 for 2TE and 3TE, respectively. Extremely fast reactions in the higher triplet excited state were indicated for both 2TE and 3TE. 相似文献