全文获取类型
收费全文 | 5706篇 |
免费 | 242篇 |
国内免费 | 466篇 |
专业分类
化学 | 2927篇 |
晶体学 | 246篇 |
力学 | 86篇 |
综合类 | 59篇 |
数学 | 2060篇 |
物理学 | 1036篇 |
出版年
2024年 | 15篇 |
2023年 | 60篇 |
2022年 | 113篇 |
2021年 | 105篇 |
2020年 | 101篇 |
2019年 | 117篇 |
2018年 | 95篇 |
2017年 | 105篇 |
2016年 | 120篇 |
2015年 | 121篇 |
2014年 | 154篇 |
2013年 | 366篇 |
2012年 | 206篇 |
2011年 | 393篇 |
2010年 | 374篇 |
2009年 | 402篇 |
2008年 | 392篇 |
2007年 | 393篇 |
2006年 | 310篇 |
2005年 | 269篇 |
2004年 | 253篇 |
2003年 | 212篇 |
2002年 | 351篇 |
2001年 | 142篇 |
2000年 | 140篇 |
1999年 | 130篇 |
1998年 | 108篇 |
1997年 | 76篇 |
1996年 | 96篇 |
1995年 | 79篇 |
1994年 | 68篇 |
1993年 | 44篇 |
1992年 | 49篇 |
1991年 | 29篇 |
1990年 | 17篇 |
1988年 | 12篇 |
1985年 | 38篇 |
1984年 | 19篇 |
1983年 | 23篇 |
1982年 | 23篇 |
1981年 | 44篇 |
1980年 | 29篇 |
1979年 | 13篇 |
1978年 | 24篇 |
1977年 | 30篇 |
1976年 | 26篇 |
1975年 | 22篇 |
1974年 | 28篇 |
1973年 | 21篇 |
1971年 | 16篇 |
排序方式: 共有6414条查询结果,搜索用时 0 毫秒
71.
72.
Isolation of lipase producer and its performance in enantioselective hydrolysis of glycidyl butyrate
A racemic glycidyl butyrate resolving strain, preliminarily identified as a Rhizopus sp., had been isolated from soil. Its extracellular lipase was found to enantioselectively hydrolyze the (S)-enantiomer of
the chiral ester, with optimal activities at pH 5.3 and 42°C. Higher en antioselectivity of theenzyme was observed at lower
temperatures, while the best anantioselectivity was obtained at pH 5.5–6.0, with an, E value (enantiomeric ratio) of 57. 相似文献
73.
Sousa Pedrares A Teng W Ruhlandt-Senge K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(9):2019-2024
Novel magnesium pyridine-2-thiolates were prepared by using alkane elimination chemistry. The resulting complexes display a metal coordination environment composed of sulfur/nitrogen bonding from the intramolecularly stabilized mercaptopyridine ligand, in addition to coordination by the oxygen centers from two THF donors. The compounds are well-suited model compounds for the magnesium centers in Photosystem I, in which magnesium, situated in the central chlorophyll ligand, is bound to sulfur from a nearby methionine residue. All compounds were characterized by (1)H, (13)C NMR, and IR spectroscopy, in addition to Xray crystallography. 相似文献
74.
F. Sauter J. Fröhlich A. Z. M. S. Chowdhury C. Hametner 《Monatshefte für Chemie / Chemical Monthly》1997,128(5):503-508
Summary A variety of partly novel tri- and tetracyclic hetero systems were obtained by reaction of heteroaromatic 2-aminoesters with 2-(methylthio)-2-thiazoline, yielding double-annelation of a thiazolo[2,3-b]pyrimido moiety in a one-pot process.On leave from University of Chittagong, Bangladesh 相似文献
75.
Summary Free boundary value problems, too complicated for formulation as a variational inequality, are broken up into two problems on overlapping regions. On one region the problem is treated as an ordinary boundary value problem; on the second region, the free boundary part of the problem is reduced to a variational inequality. By solving the two problems successively it is shown that under certain conditions the successive solutions converge to a single function that gives a solution of the original problem. Application to a filtration problem is given. 相似文献
76.
Anna B. DenisovaVyacheslav Ya. Sosnovskikh Wim Dehaen Suzanne ToppetLuc Van Meervelt Vasiliy A. Bakulev 《Journal of fluorine chemistry》2002,115(2):183-192
Reaction of 2-hydrazinothiazoles 1 with 1-thienyl- and 1-furyl-1,3-butanediones 2a,b in methanol in the presence of hydrochloric acid mainly leads to a mixture of pyrazoles 3 and pyrazolines 4 or pyrazoles 3 and 5 in strong acidic conditions. Isomeric hydrazones 6 and pyrazolines 4 were formed and isolated in these reactions in the absence of hydrochloric acid. It has been shown that the regioselectivity in the reaction of diketones 2 with hydrazine 1 is governed by both the concentration of acid and the nature of substituents in the 1,3-diketones 2. Cyclization of hydrazones 6 is shown to occur under milder conditions than dehydration for pyrazolines 4. The new heterocyclic compounds were prepared and fully characterized by NMR spectra and by X-ray analysis for 3c. 相似文献
77.
合成了联苯甲酰双缩氨基脲硫氰酸根、硝酸根混合配位的钕(Ⅲ)配合物。在此配合物中只有1个链状配体,另有2个硫氰酸根、1个硝酸根和1个水分子参与配位。总配位数是9。晶体结构分析表明,该配合物晶体属三斜晶系,P空间群。晶胞参数a=10。866(2),b=13.687(3),c=15.433(3),α=98.75(4)°,β=107.64(5)°,γ=112.14(5)°。最终偏差因子R=0.075。用INDO方法计算结果表明:NCS对Nd(Ⅲ)的配位比=C基对Nd(Ⅲ)的配位强。 相似文献
78.
聚环硫氯丙烷或环硫氯丙烷与环氧氯丙烷共聚物,在少量二乙烯三胺存在下制得交联预聚物,将交联预聚物与4-氨基安替吡啉(4AAP)或乙基原磺酸钾(PEA)反应,制得四种侧链带氨基安替吡啉,乙基原碘酸基的新型螯合树脂。它们对贵金属具有优良的吸附性能和高的吸附选择性。并通过X-射线光电子能谱初步探讨了树脂对金属离子的螯合作用。 相似文献
79.
Joachim Angelkort Sander van Smaalen Prof. Dr. Sven Oliver Hauber Mark Niemeyer 《无机化学与普通化学杂志》2007,633(7):1031-1035
Single crystal X‐ray diffraction of Eu(SC36H49)2 has revealed a first order phase transition at a temperature of 119 K, that involves a reduction of the specific volume by 1 %. The transition corresponds to a doubling of the unit cell, as it is the result from reorientations of isopropyl groups that appear at peripheral sites of the organic ligands. It is argued that a denser packing is achieved at the expense of a less favourable conformation of one of the two crystallographically‐independent complexes in the low‐temperature phase. The Bond‐Valence method is used to show that interactions of equal strengths are present between europium and both sulphur atoms and both coordinating phenyl rings. 相似文献
80.