全文获取类型
收费全文 | 2857篇 |
免费 | 77篇 |
国内免费 | 11篇 |
专业分类
化学 | 2200篇 |
晶体学 | 36篇 |
力学 | 48篇 |
数学 | 178篇 |
物理学 | 483篇 |
出版年
2023年 | 16篇 |
2022年 | 23篇 |
2021年 | 34篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 29篇 |
2017年 | 19篇 |
2016年 | 53篇 |
2015年 | 45篇 |
2014年 | 61篇 |
2013年 | 138篇 |
2012年 | 124篇 |
2011年 | 159篇 |
2010年 | 79篇 |
2009年 | 89篇 |
2008年 | 166篇 |
2007年 | 182篇 |
2006年 | 160篇 |
2005年 | 217篇 |
2004年 | 159篇 |
2003年 | 126篇 |
2002年 | 138篇 |
2001年 | 68篇 |
2000年 | 51篇 |
1999年 | 30篇 |
1998年 | 36篇 |
1997年 | 27篇 |
1996年 | 48篇 |
1995年 | 23篇 |
1994年 | 28篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 28篇 |
1990年 | 18篇 |
1989年 | 24篇 |
1988年 | 26篇 |
1987年 | 19篇 |
1986年 | 16篇 |
1985年 | 35篇 |
1984年 | 36篇 |
1983年 | 26篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 28篇 |
1979年 | 20篇 |
1978年 | 27篇 |
1977年 | 29篇 |
1976年 | 19篇 |
1975年 | 17篇 |
1974年 | 22篇 |
排序方式: 共有2945条查询结果,搜索用时 0 毫秒
21.
Semidifferential electroanalysis is described for hexacyanoferrate(III), dichromate, copper(II), p-aminophenol, p-benzoquinone, m-dinitrobenzene, guanine, guanosine, adenine, and adenosine at a stationary solid working electrode. Nearly symmetrical, peaked curves are obtained for the electrode processes of all the samples investigated. The predicted dependence of peak height and peak potential on concentration, electrode area, and potential scan rate are confirmed-experimentally for the glassy carbon disk electrode. It is demonstrated that the technique with the solid working electrode provides higher sensitivity and better resolution than ordinary linear sweep voltammetry. The sensitivity is somewhat worse than in differential pulse voltammetry, but the technique has the advantage of Speed. 相似文献
22.
Hideki Nishimori Masahiro Tatsumisago Tsutomu Minami 《Journal of Sol-Gel Science and Technology》1997,9(1):25-31
Monodispersed silica particles up to ca. 1.2 μm in diameter were prepared by hydrolysis of tetraethoxysilane in the presence
of sodium dodecyl sulfate (SDS). The particle size was increased with an increase of SDS added. The geometrical standard deviation
of the particles was decreased with an increase of SDS. In the earlier reaction stage, double spherical particles by the coalescence
of the particles were frequently observed when large amounts of SDS were added. Particle size was gradually increased after
the coalescence occurred and spherical particles were finally obtained. The results of Nielsen’s chronomal analysis suggest
that the polynuclear layer growth took place after the coalescence of the particles in the presence of larger amount of SDS. 相似文献
23.
The first total synthesis of (+)?3-deoxyaphidicolin, a selective inhibitor of eukaryotic DNA polymerase α, has been completed efficiently and stereoselectively starting from 1-abietic acid. 相似文献
24.
1-Alkoxy-3-trimethylsilylmethyl- and 1-alkoxy-3-trimethylsilyl-l,3-butadienes () were newly prepared. The cycloaddition reactions of with various dienophiles including heterodienophiles were found to proceed very smoothly in a perfectly regiospecific mode. 相似文献
25.
26.
27.
Nagaoka Y Inoue H el-Koussi N Tomioka K 《Chemical communications (Cambridge, England)》2002,(2):122-123
Upon treatment with lithium diisopropylamide achiral and chiral alpha,beta,psi,omega-unsaturated bisphosphine oxides underwent lithiation-conjugate addition tandem cyclization to afford the corresponding endo-alpha,beta-unsaturated cyclic bisphosphine oxides; sequential stereoselective reduction of the cyclized bisphosphine oxide gave the corresponding trans- and cis-bisphosphines that were successfully applicable in a catalytic asymmetric hydrogenation as chiral bisphosphine ligands. 相似文献
28.
E Ohshima T Kumazawa H Takizawa H Harakawa H Sato H Obase Y Oiji A Ishii H Ishii K Ohmori 《Chemical & pharmaceutical bulletin》1991,39(10):2724-2728
A new series of 11-substituted 6,11-dihydrodibenz[b,e]oxepin derivatives was synthesized and evaluated for antiallergic activity. Convenient methods for the preparation of sulfides from alcohols were developed. Structure-activity relationships are described. Compound 7, 11-[2-(dimethylamin)ethyl]thio-6,11-dihydrodibenz[b,e] oxepin-2-carboxylic acid hydrochloride, was the most potent in the rat passive cutaneous anaphylaxis test (ED50 = 0.92 mg/kg p.o.). It had a potent inhibitory effect on anaphylactic bronchoconstriction in guinea pigs (ED50 = 0.029 mg/kg p.o.) and H1 receptor antagonistic effect (Ki = 14 nM) with few central nervous system side effects. Additionally, an antagonistic effect against prostaglandin D2-induced contraction of isolated guinea pig trachea (pA2 = 5.73) was an attractive mechanism of action of the new antiallergic agent. Compound 7 was selected for further evaluation as KW-4994. 相似文献
29.
Yamamoto Y Ishii J Nishiyama H Itoh K 《Journal of the American Chemical Society》2004,126(12):3712-3713
The Ru(II)-catalyzed [2+2+2] cyclotrimerization of alkynylboronates, propargyl alcohol, and terminal alkynes proceeded chemo- and regioselectively to give rise to arylboronates, which were subjected to Suzuki-Miyaura cross-coupling with aryliodides to afford highly substituted biaryls in 53-76% yields. 相似文献
30.
Summary The simultaneous stereospecific assay of four stereoisomers of diltiazem hydrochloride in bulk drug and aqueous solution was
developed using HPLC on a Chiralcel OF column. The four isomers were quantitated with good precision by the internal standard
method. The chiral inversion of (+)-cis-diltiazem hydrochloride in vitro, stability of its (2S, 3S) configuration in the solid
and aqueous states was examined by HPLC. Chiral inversion of (+)-cis-diltiazem hydrochloride was not observed in the solid
state, and its (2S, 3S) configuration was stable to heat, humidity and light. Chiral inversion of (+)-cis-diltiazem hydrochloride
(2S, 3S) was observed in aqueous solution under UV, but not in aqueous solution stored at 80°C for 5h nor under visible light
for 10 h. The (+)-cis-diltiazem hydrochloride (2S, 3S) epimerized to (+)-trans-diltiazem hydrochloride (2R, 3S) with a half-life
of 5h in aqueous solution under UV but the reverse chiral inversion of (+)-trans-diltiazem hydrochloride (2R, 3S) to (+)-cis-diltiazem
hydrochloride (2S, 3S) was not observed. 相似文献