全文获取类型
收费全文 | 2289篇 |
免费 | 61篇 |
国内免费 | 7篇 |
专业分类
化学 | 1618篇 |
晶体学 | 39篇 |
力学 | 19篇 |
数学 | 55篇 |
物理学 | 626篇 |
出版年
2022年 | 16篇 |
2021年 | 14篇 |
2020年 | 24篇 |
2019年 | 26篇 |
2018年 | 22篇 |
2017年 | 12篇 |
2016年 | 45篇 |
2015年 | 36篇 |
2014年 | 50篇 |
2013年 | 93篇 |
2012年 | 84篇 |
2011年 | 86篇 |
2010年 | 49篇 |
2009年 | 61篇 |
2008年 | 126篇 |
2007年 | 103篇 |
2006年 | 125篇 |
2005年 | 124篇 |
2004年 | 144篇 |
2003年 | 110篇 |
2002年 | 82篇 |
2001年 | 58篇 |
2000年 | 41篇 |
1999年 | 50篇 |
1998年 | 21篇 |
1997年 | 22篇 |
1996年 | 37篇 |
1995年 | 40篇 |
1994年 | 30篇 |
1993年 | 23篇 |
1992年 | 53篇 |
1991年 | 44篇 |
1990年 | 27篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 37篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 22篇 |
1980年 | 30篇 |
1979年 | 21篇 |
1978年 | 18篇 |
1977年 | 17篇 |
1976年 | 13篇 |
1975年 | 22篇 |
1974年 | 21篇 |
1973年 | 27篇 |
排序方式: 共有2357条查询结果,搜索用时 31 毫秒
121.
A highly sensitive method for the quantitative determination of 2,6-dimethy-4-(3-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylic acid 3-[2-(N-benzyl-N-methyl-amino)]-ethyl ester 5-methyl ester hydrochloride (YC-93) in plasma is described. After extraction, YC-93 was oxidized to pyridine analogue with nitrous acid and detected by electron capture gas chromatography. The sensitivity was 2–3 ng/ml, which is suficient to determine plasma concentrations of YC-93 after oral administration of clinical doses to humans. 相似文献
122.
Tomohisa Nagamatsu Yoshiji Hantani Minoru Yamada Kenji Sasaki Hiromi Ohtomo Taiji Nakayama Takashi Hirota 《Journal of heterocyclic chemistry》1993,30(1):193-202
As a series of polyheterocyclic compounds for exploitation as anti-platelet agents, tricyclic heterocyclic compounds, 4-substituted 6,7-dihydro-5H-pyrimido[5,4-d][1]benzazepines 3–6, 9, 12–14 , and 16–26 , having nitrogen, oxygen, or sulfur containing functional groups at the 4-position, were prepared. In addition, tetra-cyclic heterocyclic compounds, 3-methyl-1,2,5,6-tetrahydro-4H-imidazo[1′,2′:1,6]pyrimido[5,4-d][1]benzaze-pinium chloride ( 7 ), 1,2,5,6-tetrahydro-4H-imidazo[1′,2′:1,6]pyrimido[5,4-d][1]benzazepines 10a-e , 2,3,6,7-tetrahydro-1H 5H-pyrimido[1′,2′:1,6]pyrimido[5,4-d][1]benzazepine ( 11 ), and 1,2,5,6-tetrahydro-4H-thiazolo-[3′,2′:1,6]pyrimido[5,4-d][1]benzazepinium chloride ( 15 ) via ring closure of 4-(hydroxyalkylamino)- 6, 9a-e , and 3c , and 4-(2-hydroxyethylthio)-6,7-dihydro-5H-pyrimido[5,4-d][1]benzazepine ( 14 ) with phosphoryl chloride or thionyl chloride, respectively, were also prepared. Their inhibitory activities against collagen-induced aggregation of rabbit blood platelets in vitro were investigated. Among them, compound 5 having a morpholino group at the 4-position on the tricyclic nucleus, which enhanced the activity more than 14-fold as compared with aspirin, was found to have the most satisfactory in inhibitory activity. 相似文献
123.
Tadahiro Yamamoto Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1968,6(1):49-55
In order to study the effects of substituents on the chain transfer reaction to cumenes, the polymerization of methyl methacrylate in a series of nuclear-substituted cumenes with α,α′-azobisisobutyronitrile as initiator was carried out at 60°C. and the chain transfer constants C were determined. The C values obtained for all substituted cumenes were greater than that (C0) for unsubstituted cumene, regardless of the electronattracting or -repelling nature of the substituents. Hence the plot of log (C/C0) against the Hammett σ constants gave no linear relationship. When the plots were made by the modified Hammett equation including resonance effect of the substituents: log (C/C) = ρσ + γER, however, a straight line with ρ = 0.03 and γ = 0.9 was obtained. From these results, it may be concluded that the effect of the substitutents on the chain transfer reactivities of cumenes toward attack of a poly(methyl methacrylate) radical is attributable mainly to the resonance contribution in the transition state. These results are also compared with those for polystyryl radical reported previously and discussed. 相似文献
124.
Y Ikeya H Mitsuhashi H Sasaki Y Matsuzaki T Matsuzaki E Hosoya 《Chemical & pharmaceutical bulletin》1990,38(1):136-141
After oral administration of gomisin A (1) to rats, the bile and urine were collected and treated with beta-glucuronidase and arylsulfatase. Seven metabolites, met B (2), met A-III (3), met E (4), met D (5), met F (6), met G (7), and met H (8) were isolated from the bile treated with the enzymes. Eight metabolites 2-8, and met A-II (9) were isolated from the urine treated with the enzymes. A major metabolite 2, and two minor metabolites 3 and 9 were identified as met B, met A-III, and met A-II, respectively, which are oxidative products of 1 formed by rat liver S9 mix. The structures of five new metabolites 4-7, and 8 were determined on the basis of chemical and spectral studies. 相似文献
125.
Yorihiko Sasaki Shigehiro Konaka Takao Iijima Masao Kimura 《International journal of quantum chemistry》1982,21(2):475-485
The total (elastic and inelastic) intensity of electrons scattered by CO2 was measured in the s range of 1 to 12 Å?1 and compared with the theoretical intensity calculated from the Hartree-Fock molecular wave function and those calculated for the independent-atom-model (IAM ) molecule. In the range of s ? 4 Å?1 the electron correlation effect on the total scattered intensity was found to be represented by that for the IAM molecule. 相似文献
126.
When tert-alcohols were treated with (COOH)2 and NaSCN in the presence of iodine, tertiary alkyl isothiocyanates were obtained in good yield, whereas the corresponding thiocyanates were obtained in low yield in the absence of iodine. 相似文献
127.
Kevin E. Bassler Kazuo Sasaki Robert B. Griffiths 《Journal of statistical physics》1991,62(1-2):45-88
Certain features in Frenkel-Kontorova and other models of phases with a one-dimensional modulation can be analyzed by assuming parallel interfaces separating sets of lattice planes belonging to two different phases, and treating the free energy to create interfaces, as well as the interaction of two, three, or more interfaces, as phenomenological parameters. A strategy employed by Fisher and Szpilka for interacting defects can be extended to the case of interfaces, allowing a systematic study of the phase diagram by ignoring all interface interactions, and then successively taking into account pair, triple, and higher-order terms. The possible phase diagrams which can occur near the point where =0 include: various sorts of endpoints analogous to critical endpoints, an accumulation point of first-order transitions and triple points, and a self-similar structure which we call an upsilon point, which turns out to be an accumulation point of an infinite number of segments of first-order transition lines, each of which terminates in two upsilon points. 相似文献
128.
129.
130.