全文获取类型
收费全文 | 2314篇 |
免费 | 83篇 |
国内免费 | 18篇 |
专业分类
化学 | 1850篇 |
晶体学 | 14篇 |
力学 | 17篇 |
数学 | 132篇 |
物理学 | 402篇 |
出版年
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 15篇 |
2019年 | 42篇 |
2018年 | 32篇 |
2017年 | 13篇 |
2016年 | 33篇 |
2015年 | 58篇 |
2014年 | 52篇 |
2013年 | 147篇 |
2012年 | 136篇 |
2011年 | 136篇 |
2010年 | 83篇 |
2009年 | 89篇 |
2008年 | 136篇 |
2007年 | 146篇 |
2006年 | 143篇 |
2005年 | 136篇 |
2004年 | 121篇 |
2003年 | 89篇 |
2002年 | 104篇 |
2001年 | 39篇 |
2000年 | 59篇 |
1999年 | 35篇 |
1998年 | 22篇 |
1997年 | 17篇 |
1996年 | 41篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 16篇 |
1985年 | 27篇 |
1984年 | 26篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 15篇 |
1977年 | 26篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 10篇 |
1973年 | 18篇 |
排序方式: 共有2415条查询结果,搜索用时 31 毫秒
61.
62.
Koga T Taguchi K Kinoshita T Higuchi M 《Chemical communications (Cambridge, England)》2002,(3):242-243
A novel artificial protein with simple primary structure, poly(gamma-methyl-L-glutamate)-grafted polyallylamine, has been prepared and the resultant peptide has shown a unique property of pH-regulated conformation and morphology. 相似文献
63.
Tetsuo Suami Hiroaki Sasai Kazuhiro Matsuno Nobuo Suzuki Yoshimasa Fukuda Osamu Sakanaka 《Tetrahedron letters》1984,25(40):4533-4536
Tunicamycins and their eight analogs have been synthesized by condensation of a N-acetyl-D-glucosamine derivative and an anomeric chloride of tunicaminyl uracil, followed by deprotections and N-acylation. 相似文献
64.
A method was developed for determination of total dietary fiber (TDF) in foods containing resistant maltodextrin (RMD) which includes nondigestible carbohydrates that are not fully recovered as dietary fiber by conventional TDF methods such as AOAC 985.29 or 991.43. Because the average molecular weight (MW) of RMD is 2000 daltons, lower MW soluble dietary fiber components do not precipitate in 78% ethanol; therefore, RMD is not completely quantitated as dietary fiber by current AOAC methods. The accuracy and precision of the method was evaluated through an AOAC collaborative study. Ten laboratories participated and assayed 12 test portions (6 blind duplicates) containing RMD. The 6 test pairs ranged from 1.5 to 100% RMD. The method consisted of the following steps: (1) The insoluble dietary fiber (IDF) and high MW soluble dietary fiber (HMWSDF) were determined by AOAC 985.29. (2) Ion exchange resins were used to remove salts and proteins contained in the AOAC 985.29 filtrates (including ethanol and acetone). (3) The amount of low MWRMD (LMWRMD) in the filtrates were determined by liquid chromatography. (4) The TDF was calculated by summation of the IDF, HMWSDF, and LMWRMD fractions having nondigestible carbohydrates with a degree of polymerization of 3 and higher. Repeatability standard deviations (RSDr) were 1.33-7.46%, calculated by including outliers, and 1.33-6.10%, calculated by not including outliers. Reproducibility standard deviations (RSDR) were 2.48-9.39%, calculated by including outliers, and 1.79-9.39%, calculated by not including outliers. This method is recommended for adoption as Official First Action. 相似文献
65.
A rhodium-catalyzed isomerization of alpha-arylpropargyl alcohols to indanones has been developed under mild conditions. Considering the ease of preparation of these propargyl alcohols (terminal alkynes + aromatic aldehydes), this method provides a new way of constructing indanones with high efficiency. By the mechanistic investigations using deuterium-labeled substrates, it has also been demonstrated that the reaction goes through an unexpected cascade, with a 1,4-hydrogen shift being the turnover-limiting step of the catalytic cycle. 相似文献
66.
Five Ci-Se...O...Se-Ci atoms in anthraquinone and 9-(methoxy)anthracene bearing phenylselanyl groups at 1,8-positions align linearly, the origin of which is shown to be a nonbonded 5c-6e interaction of the five atoms. 相似文献
67.
68.
Atsushi Itagaki Kazuki Nakanishi Kazuyuki Hirao 《Journal of Sol-Gel Science and Technology》2003,26(1-3):153-156
The phase separation behavior of gelling systems containing the mixture of 3-functional and 4-functional alkoxysilanes has been investigated. The relation between the starting composition and resultant macroporous morphology was examined using tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as starting alkoxysilanes, formamide (FA) as an additive, under an acidic condition. Up to TMOS:VTMS molar ratio of 0.5:0.5, the phase relation remained almost unchanged from that of pure TMOS system which exhibits morphology with well-defined co-continuous macropores in a very limited concentration region. On the VTMS-rich side typically TMOS:VTMS = 0.2:0.8, however, the co-continuous macroporous morphology was obtained in a broader composition range than those of either pure TMOS or VTMS system. A dome-like pseudo binary region was obtained with the two-phase region extending toward FA-rich direction. The domain size and pore volume of the gels with macroporous morphology could be controlled by alkoxide:water ratio and total solvent fraction, respectively. 相似文献
69.
Yasuko Ishizuka Yoshinobu Nagawa Hiroshi Nakanishi Akira Kuboyama 《Journal of inclusion phenomena and macrocyclic chemistry》1990,9(3):219-225
Two aromatic rings of a phlorizin molecule form inclusion complexes with -CD and -CD. Induced circular dichroism spectra of these complexes have been measured to estimate the orientation of the two aromatic rings in the hydrophobic space of CDs. Apparent complex formation constants have been also estimated for each complex. It is concluded that phlorizin forms a stronger inclusion complex with -CD than with -CD. 相似文献
70.
The reaction of glycine with NBD-F (4-fluoro-7-nitrobenzo-2-oxa-1,3-diazole) is investigated to establish conditions that provide a high formation rate of NBD-glycine and a low hydrolysis rate of the reagent. The reaction rate increases with higher temperature, larger contents of organic solvent and a sodium borate buffer. The use of borate buffer decreases ther ate of hydrolysis of the reagent. For low-molecular-weight amines, condition for a suitable liquid chromatographic postcolumn reactor include a high content of acetonitrile and 0.1 M sodium borate (pH 8.0–8.5). For proteins, separated by molecular-exclusion chromatography, water is needed for sensitive reactions. Suitable postcolumn reactor conditions include borate buffer (pH 7.9) containing 0.1 M potassium chloride, a 0.02% (w/v) NBD-F solution in acetonitrile with reaction at 50°C for about 45 s. The detection limits for human serum albumin, β-lactoglobulin and myoglobin are 6.6 pmol, 8.4 pmol and 11 pmol, respectively. 相似文献