全文获取类型
收费全文 | 7994篇 |
免费 | 336篇 |
国内免费 | 76篇 |
专业分类
化学 | 5915篇 |
晶体学 | 70篇 |
力学 | 327篇 |
综合类 | 3篇 |
数学 | 1049篇 |
物理学 | 1042篇 |
出版年
2024年 | 16篇 |
2023年 | 57篇 |
2022年 | 285篇 |
2021年 | 406篇 |
2020年 | 266篇 |
2019年 | 308篇 |
2018年 | 297篇 |
2017年 | 239篇 |
2016年 | 393篇 |
2015年 | 272篇 |
2014年 | 294篇 |
2013年 | 729篇 |
2012年 | 509篇 |
2011年 | 554篇 |
2010年 | 335篇 |
2009年 | 292篇 |
2008年 | 340篇 |
2007年 | 350篇 |
2006年 | 282篇 |
2005年 | 242篇 |
2004年 | 218篇 |
2003年 | 196篇 |
2002年 | 212篇 |
2001年 | 94篇 |
2000年 | 113篇 |
1999年 | 67篇 |
1998年 | 61篇 |
1997年 | 74篇 |
1996年 | 73篇 |
1995年 | 53篇 |
1994年 | 58篇 |
1993年 | 43篇 |
1992年 | 45篇 |
1991年 | 47篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 31篇 |
1987年 | 41篇 |
1986年 | 38篇 |
1985年 | 50篇 |
1984年 | 38篇 |
1983年 | 34篇 |
1982年 | 42篇 |
1981年 | 34篇 |
1980年 | 27篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 20篇 |
1976年 | 12篇 |
1975年 | 15篇 |
排序方式: 共有8406条查询结果,搜索用时 78 毫秒
941.
Mohga M. Eid Mohamed A. Badawy Yehia A. Ibrahim 《Journal of heterocyclic chemistry》1983,20(5):1255-1258
Benzo[h]quinoline-5,6-dione condenses with semicarbazide and its derivatives regioselectively at the 6-position and the products cyclize into the corresponding condensed 1,2,4-triazines. Reactions of the obtained triazines with a variety of reagents are described. 相似文献
942.
A method is described for the determination of 10–100 nmole of methanal and 20–150 nmole of ethanal and propanal. The method is based on the oxidation of aldehydes to the corresponding acids by mercuric ion which in turn is reduced to elemental mercury, followed by cold-vapour atomic absorption spectrometry. Calibration plots were constructed between the concentration of each aldehyde and absorbance, while the calibration from the conventional cold vapour procedure was used for total aldehydes determination. The method is selective and can be used for aldehyde determination in the presence of ketones, acetals, alcohols, acids, esters, ethers, organic chlorides and epoxides. This simple method is characterised by 98–102% recoveries and standard deviations of 3%. 相似文献
943.
944.
Nosrat Mustafa Abed Ebtisam Abdel Aziz Hafez Nadia Sobhy Ibrahim Mohamed Elsaid Mustafa 《Monatshefte für Chemie / Chemical Monthly》1985,116(2):223-228
The behaviour of 3,5-diamino-4-phenylazopyrazole toward a variety of reagents is reported. Several new 3,5-diaminopyrazole derivatives as well as amino derivatives of fused pyrazoles have been prepared.
Untersuchungen an 3,5-Diaminopyrazol-Derivaten
Zusammenfassung Es wird über das Verhalten von 3,5-Diamino-4-phenylazopyrazol gegenüber verschiedenen Agentien berichtet. Es wurden sowohl einige neue 3,5-Diaminooyrazol-Derivate als auch einige Aminoderivate von kondensierten Pyrazolen dargestellt.相似文献
945.
946.
Elizabeth M. Briggs Geoffrey W. Brown Peter M. Cairns Josef Jiricny Mohamed F. Meidine 《Magnetic resonance in chemistry : MRC》1980,13(4):306-307
31P chemical shifts in N-aryliminotriphenylphosphoranes and the corresponding N-methylated phosphonium salts are presented. They can be correlated with those theories of the bonding in phosphorus-nitrogen ylides which involve partial double bonding as a result of pπ–dπ overlap. 相似文献
947.
Drop size distributions have been measured for nitrogen–water annular flow in a 9.67 mm hydraulic diameter duct, at system pressures of 3.4 and 17 bar and a temperature of 38 °C. These new data extend the range of conditions represented by existing data in the literature, primarily through an increase in system pressure. Since most existing correlations were developed from data obtained at lower pressures, it should be expected that the higher-pressure data presented in this paper would not necessarily follow those correlations. For two volume median correlations tested, one does not predict the new data very well, while the other only predicts those data taken at the lower pressure of 3.4 atm. An existing maximum drop size correlation predicts the current data to a reasonable approximation. Similarly, a related correlation for the Sauter mean diameter can predict the new data, provided the coefficient in the equation is adjusted. 相似文献
948.
Khan Tahir Ali Hasan Syed Sirajul Varkey Saji P. Rather Manzoor Ahmad Jahan Nafees Shakir Mohammad 《Transition Metal Chemistry》1997,22(1):4-8
A new class of tetraiminetetraamide macrocyclic (Ph4[20]tetraene, N8O4, and Ph6[20]tetraene, N8O4) complexes have been prepared through the metal ion controlled reaction of 1,2-diphenylethane-1,2-dione dihydrazone (DPEDDH) with succinic acid [ML1X2] or phthalic acid [ML2X2] [M=Mn, Co, Ni, Cu or Zn; X=Cl or NO3]. The structures of the complexes have been elucidated on the basis of i.r, 1H-n.m.r, e.p.r. and electronic spectral data and conductance, as well as magnetic, properties. An octahedral geometry is assigned for all the complexes, involving coordination of the all-imine nitrogens. 相似文献
949.
Using a modified form of the computer code MEDUSA we study the effect of radiative diffusion in laser compression simulations of neon filled, thin glass microballoons. Our calculations show that the radiative preheat of the target reduces the final gas density by up to a factor 3 while the final shell density drops from 105kg/m3 to 1.8 × 104/kgm3. 相似文献
950.
Potentiometric pH titrations (I = 0.15 M NaNO3; 37°C) have been employed to study the various complex equlibria in the systems involving pyridoxamine and histidine with Co(II), Ni(II), Cu(II), and Zn(II). The stoichiometry and formation constants of different species have been determined with the aid of MINIQUAD-75. The complexes obtained were mostly protonated and positively charged. The formation of the ternary species is discussed in terms of the binary species. They were also correlated with the quaternary species involving pyridoxamine, glycine, and imidazole. Spectral analysis of the complex solutions of different compositions are also reported. The relevance of these ternary complex equilibria to some biological functions is discussed. 相似文献