全文获取类型
收费全文 | 5539篇 |
免费 | 191篇 |
国内免费 | 30篇 |
专业分类
化学 | 4376篇 |
晶体学 | 49篇 |
力学 | 76篇 |
数学 | 347篇 |
物理学 | 912篇 |
出版年
2023年 | 23篇 |
2022年 | 38篇 |
2021年 | 56篇 |
2020年 | 65篇 |
2019年 | 94篇 |
2018年 | 54篇 |
2017年 | 47篇 |
2016年 | 110篇 |
2015年 | 97篇 |
2014年 | 133篇 |
2013年 | 284篇 |
2012年 | 314篇 |
2011年 | 383篇 |
2010年 | 207篇 |
2009年 | 238篇 |
2008年 | 381篇 |
2007年 | 374篇 |
2006年 | 415篇 |
2005年 | 362篇 |
2004年 | 335篇 |
2003年 | 271篇 |
2002年 | 271篇 |
2001年 | 82篇 |
2000年 | 66篇 |
1999年 | 58篇 |
1998年 | 70篇 |
1997年 | 68篇 |
1996年 | 67篇 |
1995年 | 54篇 |
1994年 | 36篇 |
1993年 | 42篇 |
1992年 | 29篇 |
1991年 | 36篇 |
1990年 | 18篇 |
1989年 | 19篇 |
1988年 | 26篇 |
1987年 | 30篇 |
1986年 | 45篇 |
1985年 | 58篇 |
1984年 | 47篇 |
1983年 | 23篇 |
1982年 | 52篇 |
1981年 | 53篇 |
1980年 | 44篇 |
1979年 | 38篇 |
1978年 | 29篇 |
1977年 | 26篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1973年 | 18篇 |
排序方式: 共有5760条查询结果,搜索用时 218 毫秒
941.
The chelating agent 2,2'-dihydroxyazobenzene (DHAB), as shown in Fig. 1, was superior to the determination of trace metal ions by HPLC with ion-pair partition mode. Among the DHAB-metal chelates, only the cationic DHAB-aluminium 1:lchelate,[AIL]+, is fluorescent. Thus this chelate is expected to be applicable for selective and sensitive determination of aluminium ion by HPLC. However, the retention behavior of[AlL]+ on octadecylsilanized silica stationary phase was not well understood. The interaction between[A1L]+ and octadecylsilanized silica stationary phase has been investigated. 相似文献
942.
Ultra trace amounts of heavy metals, such as Cu, Pb, were determined by graphite furnace-atomic absorption spectrophotometry (GF-AAS) after miniature membrane filer (MF) concentration/dissolution. Heavy metals were concentrated as pyrrolidine-dithiocarbamate (APDC) chelates on a miniature MF of which diameter was 5 mm, effec-tive filtering diameter was 2 mm and pore size was 2 μm. 相似文献
943.
The traffic states are investigated for the noisy traffic flow in the presence of a bottleneck under the open boundary condition. The phase diagrams of the different kinds of congested traffic are presented for different values of sensitivity (the inverse of delay time). It is shown that the five different types of traffic states appear below the critical point: the free traffic with a pinned localized cluster, the weak standing shock, the moving localized cluster, the oscillatory congested traffic, and the strong standing shock. Above the critical point, the moving localized cluster and oscillatory congested traffic do not occur. Also, in the traffic flow without noise, the moving localized cluster and oscillatory congested traffic do not appear. 相似文献
944.
Guohao Yuan Yuko Kimura Takayuki Kobayashi Takashi Takeda Norihisa Hoshino Tomoyuki Akutagawa 《Chemical science》2021,12(40):13520
An alkylamide-substituted (−NHCOC10H21) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Colh) liquid crystal. The introduction of simple M+X− salts such as Na+PF6− and K+I− into the ionic channel of 1 enhanced the ionic conductivity of the Colh phase of the M+·(1)·X− salts, with the highest ionic conductivity reaching ∼10−6 S cm−1 for K+·(1)·I− and Na+·(1)·PF6− at 460 K, which was approximately 5 orders of magnitude higher than that of 1. The introduction of non-ferroelectric 1 into the ferroelectric N,N′,N′′-tri(tetradecyl)-1,3,5-benzenetricarboxamide (3BC) elicited a ferroelectric response from the mixed Colh phase of (3BC)x(1)1−x with x = 0.9 and 0.8. The further doping of M+X− into the ferroelectric Colh phase of (3BC)0.9(1)0.1 enhanced the ferroelectric polarisation assisted by ion displacement in the half-filled ionic channel for the vacant dibenzo[18]crown-6 of (3BC)0.9[(M+)0.5·(1)·(X−)0.5]0.1.An alkylamide-substituted (−NHCOC10H21) hydrogen-bonded dibenzo[18]crown-6 derivative (1) was prepared to stabilise the ionic channel structure in a discotic hexagonal columnar (Colh) liquid crystal. 相似文献
945.
Takashi Kashiwagi Eric Grulke Jenny Hilding Richard Harris Walid Awad Jack Douglas 《Macromolecular rapid communications》2002,23(13):761-765
Nanocomposites based on poly(propylene) and multi‐wall carbon nanotubes (up to 2 vol.‐%) were melt blended, yielding a good dispersion of nanotubes without using any organic treatment or additional additives. Carbon nanotubes are found to significantly enhance the thermal stability of poly(propylene) in nitrogen at high temperatures. Specifically, the nanotube additive greatly reduced the heat release rate of poly(propylene). They are found to be at least as effective a flame‐retardant as clay/poly(propylene) nanocomposites. 相似文献
946.
947.
948.
949.
950.
Tsuneyuki Sato Takashi Miyoshi Makiko Seno 《Journal of polymer science. Part A, Polymer chemistry》2000,38(3):509-515
Polymerization of 2‐methacryloyloxyethyl phosphorylcholine (MPC) was kinetically investigated in ethanol using dimethyl 2,2′‐azobisisobutyrate (MAIB) as initiator. The overall activation energy of the homogeneous polymerization was calculated to be 71 kJ/mol. The polymerization rate (Rp) was expressed by Rp = k[MAIB]0.54±0.05 [MPC]1.8±0.1. The higher dependence of Rp on the monomer concentration comes from acceleration of propagation due to monomer aggregation and also from retardation of termination due to viscosity effect of the MPC monomer. Rate constants of propagation (kp) and termination (kt) of MPC were estimated by means of ESR to be kp = 180 L/mol · s and kt = 2.8 × 104 L/mol · s at 60 °C, respectively. Because of much slower termination, Rp of MPC in ethanol was found at 60 °C to be 8 times that of methyl methacrylate (MMA) in benzene, though the different solvents were used for MPC and MMA. Polymerization of MPC with MAIB in ethanol was accelerated by the presence of water and retarded by the presence of benzene or acetonitrile. Poly(MPC) showed a peculiar solubility behavior; although poly(MPC) was highly soluble in ethanol and in water, it was insoluble in aqueous ethanol of water content of 7.4–39.8 vol %. The radical copolymerization of MPC (M1) and styrene (St) (M2) in ethanol at 50 °C gave the following copolymerization parameters similar to those of the copolymerization of MMA and St; r1 = 0.39, r2 = 0.46, Q1 = 0.76, and e1 = +0.51. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 509–515, 2000 相似文献