全文获取类型
收费全文 | 24911篇 |
免费 | 1137篇 |
国内免费 | 4696篇 |
专业分类
化学 | 28395篇 |
晶体学 | 296篇 |
力学 | 53篇 |
综合类 | 231篇 |
数学 | 17篇 |
物理学 | 1752篇 |
出版年
2024年 | 40篇 |
2023年 | 261篇 |
2022年 | 778篇 |
2021年 | 727篇 |
2020年 | 724篇 |
2019年 | 747篇 |
2018年 | 640篇 |
2017年 | 792篇 |
2016年 | 938篇 |
2015年 | 877篇 |
2014年 | 1023篇 |
2013年 | 2247篇 |
2012年 | 1771篇 |
2011年 | 1384篇 |
2010年 | 1207篇 |
2009年 | 1440篇 |
2008年 | 1514篇 |
2007年 | 1667篇 |
2006年 | 1573篇 |
2005年 | 1466篇 |
2004年 | 1333篇 |
2003年 | 1066篇 |
2002年 | 931篇 |
2001年 | 677篇 |
2000年 | 665篇 |
1999年 | 543篇 |
1998年 | 438篇 |
1997年 | 467篇 |
1996年 | 422篇 |
1995年 | 387篇 |
1994年 | 335篇 |
1993年 | 287篇 |
1992年 | 279篇 |
1991年 | 203篇 |
1990年 | 158篇 |
1989年 | 172篇 |
1988年 | 122篇 |
1987年 | 84篇 |
1986年 | 59篇 |
1985年 | 48篇 |
1984年 | 55篇 |
1983年 | 29篇 |
1982年 | 42篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 22篇 |
1977年 | 5篇 |
1973年 | 5篇 |
1968年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Electrolysis of dimethyl malonate or methyl cyanoacetate in methanol in the presence of LiCl in an undivided cell leads to formation of 1,1,2,2-cyclopropanetetracarboxylic derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1836, October, 1994.This work was supported by the International Science Foundation (Grant No MHY 000). 相似文献
82.
Xiao Huang Bishwa Ranjan Nayak Tao Lu Lowe 《Journal of polymer science. Part A, Polymer chemistry》2004,42(20):5054-5066
A series of novel multifunctional hydrogels that combined the merits of both thermoresponsive and biodegradable polymeric materials were designed, synthesized, and characterized. The hydrogels were copolymeric networks composed of N‐isopropylacrylamide (NIPAAM) as a thermoresponsive component, poly(L‐lactic acid) (PLLA) as a hydrolytically degradable and hydrophobic component, and dextran as an enzymatically degradable and hydrophilic component. The chemical structures of the hydrogels were characterized by an attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR) technique. The hydrogels were thermoresponsive, showing a lower critical solution temperature (LCST) at approximately 32 °C, and their swelling properties strongly depended on temperature changes, the balance of the hydrophilic/hydrophobic components, and the degradation of the PLLA component. The degradation of the hydrogels caused by hydrolytic cleavage of ester bonds in the PLLA component was faster at 25 °C below the LCST than at 37 °C above the LCST, determined by the ATR–FTIR technique. Due to their multifunctional properties, the designed hydrogels show great potential for biomedical applications, including drug delivery and tissue engineering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5054–5066, 2004 相似文献
83.
84.
C. Jeyaprabha 《Applied Surface Science》2005,252(4):966-975
The inhibitor performance of chemically synthesized water soluble poly(aminoquinone) (PAQ) on iron corrosion in 0.5 M sulphuric acid was studied in relation to inhibitor concentration using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. On comparing the inhibition performance of PAQ with that of the monomer o-phenylenediamine (OPD), the OPD gave an efficiency of 80% for 1000 ppm while it was 90% for 100 ppm of PAQ. PAQ was found to be a mixed inhibitor. Besides, PAQ was able to improve the passivation tendency of iron in 0.5 M H2SO4 markedly. 相似文献
85.
Synthesis and herbicidal activity of O,O-dialkyl phenoxyacetoxyalkylphosphonates containing fluorine
Ting Chen 《Journal of fluorine chemistry》2006,127(2):291-295
A series of substituted phenoxyacetoxyalkylphosphonates bearing fluorine were designed and synthesized. All the new compounds were identified by elemental analysis, IR, 1H NMR and MS and were tested for herbicidal activity in greenhouse at a rate of 1.5 kg/ha. The results of preliminary bioassay showed that fluorine moiety introduced to the core structure could help to improve the herbicidal activity, and compounds with a 3-trifluoromethyl in benzene ring exhibited higher inhibitory activity. 相似文献
86.
Kaname SasakiHideyuki Nagai Shuichi MatsumuraKazunobu Toshima 《Tetrahedron letters》2003,44(30):5605-5608
The glycosidations of glucopyranosyl diethyl phosphite and alcohols using an ionic liquid, 1-n-hexyl-3-methylimidazolium trifluoromethanesulfonimidide (C6mim[NTf2]) containing a protic acid, trifluoromethanesulfonimide (HNTf2), as a novel solvent-catalyst system, effectively proceeded under mild conditions to give the corresponding glycosides in good to high yields. Furthermore, this acid-ionic liquid combination could be reused many times for the glycosidations without any loss in efficiency. 相似文献
87.
Brian H. Davison Nhuan P. Nghiem Gerald L. Richardson 《Applied biochemistry and biotechnology》2004,114(1-3):653-669
More than 25 sorbents were tested for uptake of succinic acid from aqueous solutions. The best resins were then tested for
successive loading and regeneration using hotwater. The key desired properties for an ideal sorbent are high capacity, complete
stable regenerability, and specificity for the product. The best resins have a stable capacity of about 0.06 g of succinic
acid/g of resin at moderate concentrations (1–5 g/L) of succinic acid. Several sorbents were tested more exhaustively for
uptake of succinic acid and for successive loading and regeneration using hot water. One resin, XUS 40285, has a good stable
isotherm capacity, prefers succinate over glucose, and has good capacities at both acidic and neutral pH. Succinic acid was
removed from simulated media containing salts, succinic acid, acetic acid, and sugar using a packed column of sorbent resin,
XUS 40285. The fermentation byproduct, acetate, was completely separated from succinate. A simple hot water regeneration successfully
concentrated succinate from 10 g/L (inlet) to 40–110 g/L in the effluent. If successful, this would lower separation costs
by reducing the need for chemicals for the initial purification step. Despie promising initial results of good capacity (0.06
g of succinic/g of sorbent), 70% recovery using hot water, and a recovered concentration of >100 g/L, this regeneration was
not stable over 10 cycles in the column. Alternative regeneration schemes using acid and base were examined. Two (XUS 40285
and XFS-40422) showed both good stable capacities for succinic acid over 10 cycles and >95% recovery in a batch operation
using a modified extraction procedure combining acid and hot water washes. These resins showed comparable results with actual
broth. 相似文献
88.
89.
Huseyin Bekir Yildiz Jaime Castillo Dmitrii A. Guschin Levent Toppare Wolfgang Schuhmann 《Mikrochimica acta》2007,159(1-2):27-34
An amperometric biosensor for the detection of phenolic compounds was developed based on the immobilization of tyrosinase
within an Os-complex functionalized electrodeposition polymer. Integration of tyrosinase within the redox polymer assures
efficient catechol recycling between the enzyme and the polymer bound redox sites. The non-manual immobilization procedure
improves the reproducibility of fabrication process, greatly reduces the desorption of the enzyme from the immobilization
layer, and, most importantly prevents fast inactivation of the enzyme by its substrate due to fast redox cycling.
A two-layer sensor architecture was developed involving ascorbic acid oxidase entrapped within an electrodeposition polymer
in a second layer on top of the redox polymer/tyrosinase layer. Using this sensor architecture it was possible to eliminate
the current interference arising from direct ascorbate oxidation up to a concentration of 630 μM ascorbic acid. The effects
of the polymer thickness, the enzyme/polymer ratio, and the applied potential were evaluated with respect to optimal sensor
properties. The sensitivity of the optimized sensors for catechol was 6.1 nA μM−1 with a detection limit of 10 nM, and for phenol 0.15 nA μM−1 with a detection limit of 100 nM. 相似文献
90.
Efficient synthesis of ferrocenylenones using a Friedel-Crafts acylation reaction is described. Acryloyl, methacryloyl, crotonoyl, cinnamoyl, and β-methylcrotonoyl chlorides react with ferrocene in the presence of a Lewis acid (EtAlCl2 or EtAlCl2-Me3Al) to give the corresponding ferrocenylenones (acryloyl, methacryloyl, crotonoyl, cinnamoyl, and methylcrotonoylferrocenes) in good isolated yields. Besides ferrocenylenones, chloroactylferrocene is also synthesised by this method. 相似文献