全文获取类型
收费全文 | 24003篇 |
免费 | 1466篇 |
国内免费 | 1859篇 |
专业分类
化学 | 9823篇 |
晶体学 | 160篇 |
力学 | 1325篇 |
综合类 | 227篇 |
数学 | 1481篇 |
物理学 | 4323篇 |
综合类 | 9989篇 |
出版年
2025年 | 42篇 |
2024年 | 109篇 |
2023年 | 214篇 |
2022年 | 450篇 |
2021年 | 370篇 |
2020年 | 401篇 |
2019年 | 385篇 |
2018年 | 295篇 |
2017年 | 385篇 |
2016年 | 413篇 |
2015年 | 427篇 |
2014年 | 1077篇 |
2013年 | 1540篇 |
2012年 | 1298篇 |
2011年 | 1034篇 |
2010年 | 884篇 |
2009年 | 1309篇 |
2008年 | 1348篇 |
2007年 | 1595篇 |
2006年 | 1465篇 |
2005年 | 1466篇 |
2004年 | 1085篇 |
2003年 | 1034篇 |
2002年 | 972篇 |
2001年 | 708篇 |
2000年 | 1617篇 |
1999年 | 1280篇 |
1998年 | 1069篇 |
1997年 | 477篇 |
1996年 | 422篇 |
1995年 | 358篇 |
1994年 | 342篇 |
1993年 | 279篇 |
1992年 | 245篇 |
1991年 | 179篇 |
1990年 | 152篇 |
1989年 | 105篇 |
1988年 | 86篇 |
1987年 | 70篇 |
1986年 | 35篇 |
1985年 | 45篇 |
1984年 | 33篇 |
1983年 | 15篇 |
1982年 | 34篇 |
1981年 | 39篇 |
1980年 | 17篇 |
1979年 | 15篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1957年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
2.
H. William Bosch Sre
o D. kapin Egon Matijevi 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):43-50
Controlled precipitation of the diagnostic imaging agent ethyl 3,5-di(acetylamino)-2,4,6-triiodobenzoate has been used to produce fine particles of various sizes, morphologies, and degrees of crystallinity, which depended on experimental conditions. In addition, two distinct polymorphic forms of the drug have been fully characterized by single crystal X-ray diffraction studies, and evidence for a third polymorph was also observed. Some of the so prepared dry particles were coated with a thin layer of silica. 相似文献
3.
The solvent extraction of cobalt(II), nickel(II) and copper(II) using 2,4-pent-dione (Hacac) and 4-phenyl-2, 4-but-dione (Hbzac)
is carried out by varying the reagent concentration and pH of the aqueous phase. Each of these metals is quantitatively separated
(≈ 98%) from their binary mixtures with monovalent (Ag), divalent (Mn, Zn, Cd, Hg, Mg, Sn, Pb) and trivalent (Cr, Fe) metals.
The extraction constants are calculated from the metal distribution data using linear regression analysis. The extracted species
is MA2 in each case. A most significant result is separation of copper(II) from iron(III) which otherwise interferes when extracted
from the acidic medium. 相似文献
4.
I. L. Dalinger T. K. Shkineva S. A. Shevelev V. Kral Z. Arnold 《Russian Chemical Bulletin》1993,42(7):1215-1218
The double Vilsmeier formylation of theC-methyl group in pyrazole derivatives has been shown to occur when a nitro-group is in the adjacent position of the ring. A method for the synthesis ofC-(diformylmethyl)nitropyrazoles based on this reaction has been developed.For the previous communication, see Ref. 1; for Part 2, see Ref.2
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1273–1276, July, 1993. 相似文献
5.
Characteristic features of reactions involving esters of phosphorus-containing acids in highly organized media (micelles, liquid crystals, vesicles, and emulsions) are surveyed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 298–312, February, 1996. 相似文献
6.
S-Alkylation of 2-acetamido-9-(2-acetoxyethoxymethyl)-6-oxo-8-thioxopurine was used to synthesize its novel S- and N(7)-substituted derivatives. We have established the effect of the structure of the alkylating agent on the reaction conditions and its regioselectivity. We have shown that the synthesized guanine derivatives can be modified further. 相似文献
7.
The behavior of hexafluoroacetone ethoxycarbonylimine in cyclocondensation with different binucleophiles of the amidine type, viz., amino derivatives of N- and N,S-heterocycles, was studied. A preparative method for the synthesis of previously unknown annelated 2,2-bis(trifluoromethyl)-1,3,5-triazinones was developed. 相似文献
8.
Sharpless asymmetric dihydroxylation and aminohydroxylation of (E)-dimethyl-2-alkylidene glutarates 2 were shown to afford enantio-enriched or enantiopure highly functionalized γ-butyrolactones 3 and 7. 相似文献
9.
L. N. Yudina E. I. Lazhko A. M. Korolev M. N. Preobrazhenskaya 《Chemistry of Heterocyclic Compounds》2002,38(10):1200-1204
The methylation and allylation of 6-(3-indolyl)indolo[2,3-b]carbazole were studied, and its trimethyl and mono-, di-, and triallyl derivatives were obtained. 相似文献
10.
N. E. Golantsov A. V. Karchava M. A. Yurovskaya 《Chemistry of Heterocyclic Compounds》2006,42(8):1021-1024
Methods of obtaining ketones and enamino esters have been developed on the basis of reactions of 1-(1-phenylethyl)indole-2-carbonitrile
with organomagnesium and organozinc compounds. Removal of a benzyl group from the indole nitrogen atom by the Grignard reagent
has been discovered.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1179–1183, August, 2006. 相似文献