全文获取类型
收费全文 | 2626篇 |
免费 | 54篇 |
国内免费 | 7篇 |
专业分类
化学 | 1782篇 |
晶体学 | 44篇 |
力学 | 31篇 |
数学 | 148篇 |
物理学 | 682篇 |
出版年
2023年 | 19篇 |
2022年 | 17篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 32篇 |
2018年 | 26篇 |
2017年 | 26篇 |
2016年 | 41篇 |
2015年 | 41篇 |
2014年 | 41篇 |
2013年 | 105篇 |
2012年 | 105篇 |
2011年 | 128篇 |
2010年 | 76篇 |
2009年 | 76篇 |
2008年 | 150篇 |
2007年 | 134篇 |
2006年 | 137篇 |
2005年 | 132篇 |
2004年 | 140篇 |
2003年 | 110篇 |
2002年 | 107篇 |
2001年 | 77篇 |
2000年 | 54篇 |
1999年 | 33篇 |
1998年 | 27篇 |
1997年 | 25篇 |
1996年 | 36篇 |
1994年 | 33篇 |
1993年 | 22篇 |
1992年 | 31篇 |
1991年 | 30篇 |
1990年 | 29篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 24篇 |
1986年 | 23篇 |
1985年 | 49篇 |
1984年 | 42篇 |
1983年 | 34篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 27篇 |
1979年 | 42篇 |
1978年 | 38篇 |
1977年 | 24篇 |
1976年 | 35篇 |
1975年 | 27篇 |
1974年 | 17篇 |
1973年 | 16篇 |
排序方式: 共有2687条查询结果,搜索用时 15 毫秒
41.
Masahiko Ishikawa Ken-ichi Okamoto Jinsai Hidaka Hisahiko Einaga 《Helvetica chimica acta》1985,68(7):2015-2021
Substitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine)-glycinatocobalt(III) complex has been studied in the presence of photo-excited tris(2,2′-bipyridine)ruthenium(II) complex in alkaline aqueous solution (buffered around pH 12) containing 1.0M chloride ion at 25°C. VIS absorption and CD spectra were used for the racemate and the optically active isomers of the Co(III) complexes, respectively. The reaction was catalyzed by the excited Ru(II) complex to give tris(ethylenediamine)cobalt(III) complex. Mechanism of the ligand-substitution reaction and role of the excited Ru(II) complex were discussed. 相似文献
42.
A family of alkaline earth organosulfonate coordination solids is reported. In contrast to more typical crystal engineering approaches, these solids are sustained by the assembly of building blocks that are coordinatively adaptable rather than rigid in their bonding preferences. The ligand, 4,5-dihydroxybenzene-1,3-disulfonate, L, progressively evolves from a 0D, 1D, 2D, to a 3D microporous network with the Group II cations Mg(2+), Ca(2+), Sr(2+), and Ba(2+), (compounds 1-4), respectively. This trend in dimensionality can be explained by considering factors such as hard-soft acid-base principles and cation radii, a rationalization which follows salient crystal engineering principles. The selective gas sorption properties of the microporous 3D network [Ba(L)(H(2)O)].H(2)O, 4, with different gaseous guests are also presented. 相似文献
43.
Novel synthetic procedure of heterocycles was developed using nickel-mediated alkylative carboxylation, and the total synthesis of erythrocarine was achieved using this method and RCM of dienyne as the key steps. [reaction: see text] 相似文献
44.
Allylation of carbonucleophiles with allylic carbamates under neutral conditions has been studied. The C-allylation of carbonucleophile is competitive with the N-allylation of amines, and the structure of amines is crucial for the selectivity. Bulky secondary amines gave the best results. Also a new method of protection-deprotection of amines as carbamates has been developed. Smooth deprotection is possible by the palladium-catalyzed reaction of allyl carbamates with formic acid. This method is particulary useful for primary amines, including optically active amino acids. 相似文献
45.
M Shimizu S Horie S Terashima H Ueno T Hayashi M Arisawa S Suzuki M Yoshizaki N Morita 《Chemical & pharmaceutical bulletin》1989,37(9):2531-2532
Aldose reductase (AR) inhibitory activity-directed fractionation of the 70% ethanolic extract of Para-parai mí, Phyllanthus niruri, has led to the isolation of three active components, ellagic acid (1), brevifolin carboxylic acid (4) and ethyl brevifolin carboxylate (5). Among them, 1 showed the highest inhibitory activity, being about 6 times more potent than quercitrin, which is a known natural inhibitor of AR. 相似文献
46.
Doi H Sakai T Iguchi M Yamada K Tomioka K 《Journal of the American Chemical Society》2003,125(10):2886-2887
The external chiral ligand-controlled asymmetric conjugate addition reaction of lithium amides with alpha,beta-unsaturated esters provided beta-amino esters in high yields and high enantioselectivities. 相似文献
47.
48.
Hitoshi Shimizu Kazuki Shimizu Atsuko Sugita Tsuyoshi Yamauchi Kazumi Morikawa 《Tetrahedron letters》2004,45(42):7837-7841
Two 21-nor-22-oxa-1α,25-dihydroxyvitamin D3 derivatives have been synthesized in quest of a drug with lower calcemic activity than Maxacalcitol, 22-oxa-1α,25-dihydroxyvitamin D3, being used as antihyperparathyroidism and antipsoriatic drug. Of two 21-nor products obtained, the product carrying one carbon elongated side chain with diethylcarbinol moiety has been found to exhibit comparable differentiation-inducing activity to Maxacalcitol with much lower exhibition of calcemic activity. 相似文献
49.
Hiroshi Mitsui Yuichi Shimizu 《Journal of polymer science. Part A, Polymer chemistry》1980,18(3):1115-1122
The γ radiolysis of polyethylene preirradiated with electron beams to 3 Mrad was carried out at 30–100°C in vacuo with a dose rate of 6.35 × 105 rad/hr. The hydrogen formation in the γ radiolysis was little affected by the preirradiation of electron beams, whereas the formation of trans-vinylene unsaturation and gel was somewhat retarded. The rates of the formation of hydrogen and trans-vinylene unsaturation were described by the zero-order formation kinetics with respect to each concentration combined with the first-order disappearance. The apparent rate constants and activation energies for the formation and disappearance of hydrogen and trans-vinylene unsaturation were almost independent of the preirradiation. The gel fraction was analyzed by using the Charlesby–Pinner equation. The G values of crosslinking and main chain scission were increased by the preirradiation, whereas their activation energies remained unaltered. On the basis of these results the effects of preirradiation on the reactions induced by γ rays in polyethylene were discussed. 相似文献
50.
Zeolite T membranes were synthesized on tubular porous mullite tubes by hydrothermal synthesis. The membranes selectively permeated carbon dioxide from CO2/CH4 and CO2/N2 mixtures with high separation performances, which were due to combined effects of molecular sieving and competitive adsorption. 相似文献