全文获取类型
收费全文 | 2811篇 |
免费 | 366篇 |
国内免费 | 460篇 |
专业分类
化学 | 2769篇 |
晶体学 | 74篇 |
力学 | 221篇 |
综合类 | 36篇 |
数学 | 23篇 |
物理学 | 514篇 |
出版年
2024年 | 6篇 |
2023年 | 24篇 |
2022年 | 71篇 |
2021年 | 91篇 |
2020年 | 122篇 |
2019年 | 93篇 |
2018年 | 93篇 |
2017年 | 94篇 |
2016年 | 123篇 |
2015年 | 124篇 |
2014年 | 139篇 |
2013年 | 216篇 |
2012年 | 156篇 |
2011年 | 150篇 |
2010年 | 154篇 |
2009年 | 148篇 |
2008年 | 166篇 |
2007年 | 177篇 |
2006年 | 150篇 |
2005年 | 157篇 |
2004年 | 173篇 |
2003年 | 137篇 |
2002年 | 151篇 |
2001年 | 96篇 |
2000年 | 92篇 |
1999年 | 62篇 |
1998年 | 71篇 |
1997年 | 70篇 |
1996年 | 65篇 |
1995年 | 40篇 |
1994年 | 48篇 |
1993年 | 45篇 |
1992年 | 39篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有3637条查询结果,搜索用时 15 毫秒
51.
建立了一种人工神经网络-X射线荧光光谱法测定钢中酸溶铝的方法,用X射线荧光光谱法测定低合金钢中总铝值,应用所建立的ANN-BP网络模型,输入总铝含量直接预测出酸溶铝含量。同时使用改进的BP算法,避免了神经网络学习中可能产生的麻痹现象。该方法用于钢中酸溶铝的测定,结果满意。 相似文献
52.
《Mendeleev Communications》2020,30(1):49-51
- Download : Download high-res image (140KB)
- Download : Download full-size image
53.
贫水电解质体系制备多孔阳极氧化铝模板的研究 总被引:3,自引:0,他引:3
在有机溶剂为主的含草酸电解质中,研究了大孔径有序度高的阳极氧化铝(AAO)的一步法电化学制备.实验证实,电解质中水含量的降低能够有效抑制铝的电氧化速率和溶解速率,使得其氧化膜孔道的生长能够稳定进行,所得到的六方孔道排列有序度明显高于纯水溶剂制备的电解质体系下的产物.考察了水含量、有机溶剂种类以及电解质浓度对AAO模板孔道形貌的影响.结果表明,有机溶剂贫水电解质体系使得电氧化电压的选取范围比水溶液电解质体系更宽,孔径连续可调,反应条件温和.该方法适合于制备均匀大孔径的AAO模板. 相似文献
54.
Highly hydrophobically modified (with n-dodecylamide chain) linear poly(acrylic acid)s (HHMPAAH) and poly(sodium acrylate)s (HHMPAANa) with various degrees of grafting
(τ) were synthesized and used as emulsifiers of the n-dodecane/water system. The type of emulsion, oil in water (O/W) or water in oil (W/O), was investigated as a function of
the polymer chemical structure (τ, salt or acid form of the copolymer) and aqueous phase electrolyte concentration (NaNO3). Increasing τ and/or salt concentration was found to favor the formation of inverse emulsions. Direct liquid–liquid dispersions
are more likely to form with poly(sodium acrylate)s than with poly(acrylic acid)s. Hence, field variables such as τ, pH and
ionic strength are relevant parameters to control emulsion type. Moreover, a balanced polyelectrolyte neither soluble in oil
nor in water was synthesized for the first time. With this original emulsifier, the dispersion type was found to change from
O/W to W/O with polymer salting out. The work provides convenient model system for fundamental studies of polymer conformation
at liquid–liquid interfaces.
Received: 31 March 1998 Accepted: 30 April 1998 相似文献
55.
THERMODYNAMIC STUDY OF ADSORPTION OF PHENOLIC COMPOUNDS FROM AQUEOUS SOLUTION BY A WATER-COMPATIBLE HYPERCROSSLINKED POLYMERIC ADSORBENT 总被引:2,自引:0,他引:2
Ai-minLi Hai-suoWu Quan-xingZhang Gen-chengZhang ChaoLong Zheng-haoFei Fu-qiangLiu Jin-longChen 《高分子科学》2004,(3):259-267
Equilibrium data for the adsorption of phenolic compounds, i.e., phenol, p-cresol, p-chlorophenol and p-nitrophenol from aqueous solutions by a water-compatible hypercrosslinked polymeric adsorbent (NJ-8) within temperature range of 283-323 K were obtained and correlated with a Freundlich-type of isotherm equation, so that equilibrium constants KF and n were obtained. The capacities of equilibrium adsorption for all the four phenolic compounds on the NJ-8 from aqueous solutions are around 2 times as high as those of Amberlite XAD-4, which may be attributed to the unusual micropore structure and the partial polarity on the network. The values of the enthalpy (always negative) are indicative of an exothermic process, which manifests the adsorption of all the four phenolic compounds on the two polymeric adsorbents to be a process of physical adsorption. The negative values of free energy change show that the solute is more concentrated on the adsorbent than in the bulk solution. The absolute free energy values of adsorption for NJ-8 are always higher than those for Amberlite XAD-4, which indicates that phenolic compounds are preferentially adsorbed on NJ-8. The negative values of the adsorption entropy are consistent with the restricted mobilities of adsorbed molecules of phenolic compounds as compared with the molecules in solution. The adsorption entropy values of phenolic compounds for NJ-8 are lower than those for Amberlite XAD-4, which means the micropores of NJ-8 require more orderly arranged adsorbate. 相似文献
56.
57.
比较两种超高交联聚苯乙烯吸附树脂NJ-8、AM-1与Amberlite XAD-4(以下简称XAD-4)对对硝基苯乙酮的静态吸附行为,根据吸附等温线研究了吸附热力学性质.在298~318K和研究的浓度范围内,NJ-8,AM-1、XAD-4对对硝基苯乙酮的吸附平衡数据符合Freundlich吸附等温方程.结果表明:吸附为放热过程,适当降低温度有利于吸附.计算了对硝基苯乙酮在NJ-8,AM-1、XAD-4树脂上的吸附焓变、自由能变,吸附熵变.对吸附行为作了合理的解释。 相似文献
58.
Xiao Yan Wu Sanna JÄÄskelÄinen Wu-Yen Linko 《Applied biochemistry and biotechnology》1996,59(2):145-158
A commercialRhizomucor miehei lipase was purified by ammonium sulfate precipitation. Phenyl Sepharose 6 Fast Row hydrophobic interaction chromatography,
and DEAE Sepharose Fast Flow anion-exchange chromatography. The recovery of lipase activity was 32% with a 42-fold purification.
The molecular size of the purified enzyme was 31,600 Dalton and the pI 3.8. The enzyme was stable for at least 24 h within
a pH range of 7.0-10.0, and 96.8% of the enzyme activity remained when kept at 30‡C for 24 h. Further, about 10–30% of the
lipase activity was inhibited by K+, Li+, Ni+, Co2+, Zn2+, Mg2+, Sn2+, Cu2+, Ba2+, Ca2+, and Fe2+ ions and by SDS, but EDTA had no effect. Under the experimental conditions, the optimum temperature for the hydrolysis of
olive oil was 50‡C (pH 8.0), and for the synthesis of 1-butyl oleate, 37‡C. It was concluded that hydrolytic activity of lipase
alone is not a sufficient criterion for its synthetic potential. The optimal molar ratio of oleic acid and 1-butanol was 2:1
for 1-butyl oleate synthesis. The 1-butyl oleate yield was unaffected by purification of the enzyme after 12 h. 相似文献
59.
E. D. Matveeva T. A. Podrugina M. V. Prisyazhnoi I. N. Rusetskaya N. S. Zefirov 《Russian Chemical Bulletin》2007,56(4):798-805
Interaction of aliphatic and aromatic aldehydes and ketones with optically active L-α-amino acids or their esters in the three-component catalytic one-pot synthesis of α-aminophosphonates was studied. The
corresponding α-amino phosphonates are formed in high yields as mixtures of diastereomers.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 768–774, April, 2007. 相似文献
60.
Synthesis and Crystal Structure of a Novel Hexagonal Modification of Al2S3 with Five-coordinated Aluminum A new hexagonal high temperature modification of Al2S3 could be prepared by chemical vapour transport with iodine (860 → 750°C) or by annealing of α -Al2S3 at 550°C. According to the single crystal X-ray structure determination the novel form of Al2S3 crystallizes in space group P 61 (No. 169) with a = 6.491(1), c = 17.169(4) Å, V = 626.5 Å3, Z = 6; R = 0.0253. In this modification one half of the aluminum atoms are tetrahedrally coordinated [d(Al? S): 2.226–2.267 Å], whereas the other half are in trigonal bipyramidal coordination of five S atoms with bond lengths of 2.272–2.315 Å (equatorial) and 2.495–2.521 Å (axial). Aluminum in AlS5 coordination is observed for the first time in this compound. The crystal structure is isotypic to In2Se3 and AlInS3. In addition, results of a refinement of the α -Al2S3 crystal structure are reported which were obtained on crystals prepared also by chemical vapour transport with iodine. 相似文献