全文获取类型
收费全文 | 17668篇 |
免费 | 842篇 |
国内免费 | 1735篇 |
专业分类
化学 | 15974篇 |
晶体学 | 122篇 |
力学 | 103篇 |
综合类 | 211篇 |
数学 | 905篇 |
物理学 | 2930篇 |
出版年
2024年 | 15篇 |
2023年 | 142篇 |
2022年 | 290篇 |
2021年 | 343篇 |
2020年 | 468篇 |
2019年 | 502篇 |
2018年 | 431篇 |
2017年 | 499篇 |
2016年 | 532篇 |
2015年 | 545篇 |
2014年 | 601篇 |
2013年 | 1289篇 |
2012年 | 1113篇 |
2011年 | 1065篇 |
2010年 | 891篇 |
2009年 | 1027篇 |
2008年 | 914篇 |
2007年 | 1061篇 |
2006年 | 877篇 |
2005年 | 841篇 |
2004年 | 733篇 |
2003年 | 514篇 |
2002年 | 398篇 |
2001年 | 368篇 |
2000年 | 1175篇 |
1999年 | 826篇 |
1998年 | 794篇 |
1997年 | 254篇 |
1996年 | 251篇 |
1995年 | 218篇 |
1994年 | 210篇 |
1993年 | 179篇 |
1992年 | 168篇 |
1991年 | 112篇 |
1990年 | 79篇 |
1989年 | 66篇 |
1988年 | 63篇 |
1987年 | 51篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 30篇 |
1983年 | 23篇 |
1982年 | 43篇 |
1981年 | 43篇 |
1980年 | 24篇 |
1979年 | 28篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
71.
研究了充有不同温度退火Fe基纳米晶粉芯LC回路的磁致频移特性(MFS),发现充有不同温度退火Fe基纳米晶粉芯LC回路的磁致频移不同,充有经600℃退火Fe基纳米晶粉芯LC回路的磁致频移最灵敏。 相似文献
72.
利用莫尔条纹的准正弦特性的三维轮廓术 总被引:5,自引:0,他引:5
分析了两个矩形光栅迭合产生的莫尔条纹的光强分布特性,通过选择适当的光栅参数,可得到一个近似的正弦分划板,并把它用于三维面形测量中,实验结果表明,这种方法简单,易于自动处理,有广泛的实用价值。 相似文献
73.
74.
75.
W.T. Ingram 《Topology and its Applications》2006,153(10):1530-1539
76.
Guido Momerency Karel Van Cauwenberghe Ernst A. De Bruijn Allan T. Van Oosterom Martin S. Highley Peter G. Harper 《Journal of separation science》1994,17(9):655-661
A method is described for the determination of the antitumor agent iphosphamide and seven of its metabolites in the plasma of cancer patients by multiple ion monitoring (MIM) GC-MS, mainly using the electron capture chemical ionization mode, of stable methyl and/or trifluoroacetyl derivatives. The metabolites determined were 2- and 3-dechloroethyliphosphamide, 4-ketoiphosphamide, carboxyiphosphamide, iphosphamide mustard, and two previously undetected metabolites, chloroethylamine and 1,3-oxazolidine-2-one. The isolation of the acidic and neutral metabolites was performed by solid phase extraction on to C18 adsorbent at pH 4. The weakly acidic iphosphamide mustard, isolated under these conditions with a yield of ca 50%, was measured as a stable methyltrifluoroacetyl derivative, in contrast to the corresponding phosphoramide mustard of the isomer cyclophosphamide which decomposes during derivatization. Chloroethylamine and 1,3-oxazolidine-2-one were isolated with high yield by liquid extraction with ethyl acetate at pH 10. Selective measurement of several metabolite derivatives with similar retention times was performed by multiple ion monitoring MS of specific ion masses, using a methyl phenyl siloxane capillary column previously employed in the study of cyclophosphamide metabolites. Quantitation of metabolites in patient plasma samples could be performed in the concentration range 3 ng to 20 μg per ml of original plasma. 相似文献
77.
Marie‐France Llauro Julien Loiseau Fernande Boisson Frdric Delolme Catherine Ladavire J. Claverie 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5439-5462
Low‐molecular‐weight poly(acrylic acid) (PAA) was synthesized by reversible addition fragmentation chain transfer polymerization with a trithiocarbonate as chain‐transfer agent (CTA). With a combination of NMR spectroscopy and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, the PAA end‐groups of the polymer were analyzed before and after neutralization by sodium hydroxide. The polymer prior to neutralization is made up of the expected trithiocarbonate chain‐ends and of the H‐terminated chains issued from a reaction of transfer to solvent. After neutralization, the trithiocarbonates are transformed into thiols, disulfides, thiolactones, and additional H‐terminated chains. By quantifying the different end‐groups, it was possible to demonstrate that fragmentation is the rate limiting step in the transfer reaction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5439–5462, 2004 相似文献
78.
Peter D. Verhaert Maria C. Prieto Conaway Tonya M. Pekar Ken Miller 《International journal of mass spectrometry》2007,260(2-3):177
Direct tissue imaging was performed on dissected insect tissue using a MALDI ion trap to visualize endogenous neuropeptides. Coupling tissue imaging to tandem MSn allows for the identification of previously known species and the ability to identify new ones by de novo sequencing, as searchable databases for insects are sparse. Direct tissue imaging is an attractive technique for the study of neuropeptides as minimal sample preparation is required prior to mass spectrometry. We successfully identified neuropeptides present in the corpora cardiaca and allata of Acheta domesticus (the house cricket). Diagnostic fragments at low m/z were used to distinguish between lipids and neuropeptides. The distribution of peptides appears to be more differentially localized than that of phospholipids, which seem to be more evenly distributed within the tissue. 相似文献
79.
A. S. Peregudov L. N. Usatova E. I. Smyslova E. I. Fedin D. N. Kravtsov 《Russian Chemical Bulletin》1995,44(8):1513-1519
It has been shown by the19F NMR method that the relative polarities of nitrogenelement bonds in 2-(4-fluorophenyl)benzimidazole and its PhHg and PPh3Au derivatives increase in the order N-H19F NMR. It has been found that these reactions occur by a bimolecular associative mechanism and that the N-H bond is substantially less reactive than the N-Hg and N-Au bonds, which have identical reactivities within the limits of sensitivity of the method used.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1574–1580, August, 1995.This work was carried out with financial support from the Russian Foundation for Basic Research (Project No. 93-03-5528). 相似文献
80.
以1H-NMR谱和13C双自旋回波的APT脉冲序列测定文献中尚未曾发表的化合物HC≡C-CH2-O-CCH3-O-CH2文中计算了峰强度与脉冲间隔时间的关系,讨论了各谱线的相位并区分出-CH3、-CH2、-CH和季碳。 相似文献