全文获取类型
收费全文 | 61697篇 |
免费 | 4062篇 |
国内免费 | 4005篇 |
专业分类
化学 | 36822篇 |
晶体学 | 947篇 |
力学 | 4187篇 |
综合类 | 779篇 |
数学 | 9572篇 |
物理学 | 17457篇 |
出版年
2024年 | 76篇 |
2023年 | 536篇 |
2022年 | 1369篇 |
2021年 | 1303篇 |
2020年 | 1370篇 |
2019年 | 1371篇 |
2018年 | 1248篇 |
2017年 | 1533篇 |
2016年 | 2073篇 |
2015年 | 1749篇 |
2014年 | 2395篇 |
2013年 | 4492篇 |
2012年 | 3472篇 |
2011年 | 3359篇 |
2010年 | 2951篇 |
2009年 | 3672篇 |
2008年 | 3615篇 |
2007年 | 4010篇 |
2006年 | 3449篇 |
2005年 | 3002篇 |
2004年 | 2951篇 |
2003年 | 2413篇 |
2002年 | 1904篇 |
2001年 | 1573篇 |
2000年 | 2293篇 |
1999年 | 1874篇 |
1998年 | 1749篇 |
1997年 | 1074篇 |
1996年 | 999篇 |
1995年 | 924篇 |
1994年 | 839篇 |
1993年 | 692篇 |
1992年 | 607篇 |
1991年 | 492篇 |
1990年 | 422篇 |
1989年 | 303篇 |
1988年 | 284篇 |
1987年 | 182篇 |
1986年 | 152篇 |
1985年 | 184篇 |
1984年 | 142篇 |
1983年 | 77篇 |
1982年 | 129篇 |
1981年 | 96篇 |
1980年 | 63篇 |
1979年 | 91篇 |
1978年 | 53篇 |
1977年 | 33篇 |
1976年 | 33篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
R.?Mitchell C.?M.?CarrEmail author M.?Parfitt J.?C.?Vickerman C.?Jones 《Cellulose (London, England)》2005,12(6):629-639
The surface chemical composition of raw unscoured cotton was successfully investigated by the surface analytical techniques
X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The presence of non-cellulosic
material at the fibre surface was established and determined to be a complex mixture of fatty acids, alcohols, alkanes, esters
and glycerides. The effect of scouring and bleaching was to reduce the surface concentration of these materials but even after
aqueous processing some non-cellulosic material residue was still detected at the fibre surface. 相似文献
82.
《Surface and interface analysis : SIA》2006,38(5):931-940
The initial oxidation of magnesium at oxygen partial pressures between 1.3 × 10?8 and 1.3 × 10?5 Pa and at temperatures ranging from 273 to 550 K has been investigated in situ with X‐ray photoelectron spectroscopy (XPS), ellipsometry and high resolution elastic recoil detection analysis (HERDA). Quantitative analysis of the XPS spectra showed a clear oxygen deficiency with respect to MgO for the initial oxide. HERDA measurements confirmed this relatively low oxygen content in the thin oxide layers formed. Ellipsometry measurements showed that the electronic structure of the initially formed oxide differs significantly from that of bulk MgO. The band gap values at room temperature for the oxide layers investigated are clearly smaller than the value for bulk MgO. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
83.
Christoph Kratky Heinz Falk Ulrich Zrunek 《Monatshefte für Chemie / Chemical Monthly》1985,116(5):607-623
The molecular and crystal structures of the two racemic diastereomeric 3,4-dihydropyrromethenone derivatives1 and2 of configurations (Z) and (E) were determined at 93 K (1, 2) and at room temperature (1). From an analysis of the crystallographically observed temperature coefficients a pseudorotation flexibility of the pyrrolidinone ring in the crystal is deduced. In both compounds a nearly orthogonal arrangement between the two heterocyclic ring systems is observed, which is ascribed to the steric bulk of the substituents in positions 1 and 3 of the pyrrolidinone ring.Herrn Prof.Josef Schurz zum 60. Geburtstag gewidmet. 相似文献
84.
Hanns Malissa 《Angewandte Chemie (International ed. in English)》1976,15(3):141-149
Environmental analyses show that the air which we breathe, and which is so essential to life, is in general a mixture of gaseous, liquid, and solid components. The solid airborne particles, whose concentration, homogeneity, chemical composition, size, and shape can vary over wide ranges, and whose origin may be “natural” or “artificial” are referred to as “dust”. Dust particles can act, inter alia, as condensation nuclei, catalysts, and directly as hazardous materials. Unfortunately, we still know far too little about dust. Dust analysis is extremely difficult and challenging, even for modern analytical chemistry; it is still far from being fully automated. The simultaneous determination of as many “dust parameters” as possible, and particularly the synoptic consideration of all available data against a background of physicochemical and technological knowledge on the development, transformation, and effects of dust, are summarized as “integrated dust analysis”. 相似文献
85.
根据Fe(Ⅲ)、Mo(Ⅵ)对H2O2氧化邻氨基酚的催化反应速率不同,结合流动注射停留技术,建立了同时测定Fe(Ⅲ)、Mo(Ⅵ)的速差动力学分光光度法.测定铁和钼的线性范围分别为0.1~2.5μg/mL和0.5~15μg/mL.除W(Ⅵ)的允许量较小外,其它离子不干扰测定.用本法测定了合成样液中铁和钼含量,结果满意. 相似文献
86.
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
87.
The molecular structure of samarium dibromide has been studied by electron diffraction at T
exp = 1250(50) K. The molecule has C2v symmetry; the internuclear distance Rg(Sm–Br) = 274.5(5) pm; g =131(6)°. The vibration frequencies were estimated from the experimental values of the mean square vibration amplitudes. 相似文献
88.
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
89.
I. V. Ukrainets N. L. Bereznyakova O. V. Gorokhova A. V. Turov 《Chemistry of Heterocyclic Compounds》2007,43(11):1426-1433
The bromination of 3-allyl-4-hydroxy-2-oxo-1,2-dihydroquinoline by molecular bromine is accompanied by the closure of a five
membered furan ring and gives the corresponding 2-bromomethyl-3,9-dihydro-2H-furo[2,3-b]quinolin-4-one.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1677–1686, November, 2007. 相似文献
90.
M. Z. Krimer F. Z. Makaev Yu. B. Kal'yan V. P. Tashchi Yu. G. Putsykin 《Russian Chemical Bulletin》1993,42(12):1995-2000
O-Methyloximes and nitrones of a series of substituted 4-[2-hydroxy-2-(1H-1,2,4-triazol-1-ylmethyl)cyclohexylidenemethyl]benzaldehydes have been synthesized, and their fungicidal activity has been assayed. All of them exhibit low fungicidal activity in thein vitro assays and high activity in thein vivo assays; theO-methyl oximes are more active than the corresponding nitrones.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2082–2087, December, 1993. 相似文献