全文获取类型
收费全文 | 14889篇 |
免费 | 408篇 |
国内免费 | 323篇 |
专业分类
化学 | 9293篇 |
晶体学 | 106篇 |
力学 | 408篇 |
综合类 | 30篇 |
数学 | 1931篇 |
物理学 | 3852篇 |
出版年
2022年 | 157篇 |
2021年 | 190篇 |
2020年 | 180篇 |
2019年 | 187篇 |
2018年 | 174篇 |
2017年 | 145篇 |
2016年 | 337篇 |
2015年 | 309篇 |
2014年 | 371篇 |
2013年 | 792篇 |
2012年 | 634篇 |
2011年 | 739篇 |
2010年 | 526篇 |
2009年 | 506篇 |
2008年 | 676篇 |
2007年 | 714篇 |
2006年 | 582篇 |
2005年 | 588篇 |
2004年 | 586篇 |
2003年 | 580篇 |
2002年 | 618篇 |
2001年 | 444篇 |
2000年 | 402篇 |
1999年 | 309篇 |
1998年 | 225篇 |
1997年 | 205篇 |
1996年 | 225篇 |
1995年 | 238篇 |
1994年 | 229篇 |
1993年 | 182篇 |
1992年 | 175篇 |
1991年 | 182篇 |
1990年 | 193篇 |
1989年 | 156篇 |
1988年 | 141篇 |
1987年 | 137篇 |
1986年 | 123篇 |
1985年 | 218篇 |
1984年 | 236篇 |
1983年 | 160篇 |
1982年 | 184篇 |
1981年 | 149篇 |
1980年 | 152篇 |
1979年 | 140篇 |
1978年 | 117篇 |
1977年 | 164篇 |
1976年 | 143篇 |
1975年 | 119篇 |
1974年 | 113篇 |
1973年 | 116篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Francesco De Sarlo Antonio Guarna Andrea Goti Alberto Brandi 《Journal of organometallic chemistry》1984,269(2):115-121
Organomercury fulminates react with acetylene derivatives to give unstable 3-(organomercurio)isoxazoles, which isomerize to 2-cyanoenolates. These are hydrolyzed with hydrochloric acid to the corresponding enols and are cleaved by water at the double bond. With monosubstituted acetylenes, substitution at the free position by the organomercury residue is predominant. 相似文献
103.
J.-T.De Pascual E. Caballero C. Caballero M. Medarde A.F. Barrero M. Grande 《Tetrahedron》1982,38(12):1837-1842
Trixagol 1 and fourteen derivatives with the skeleton of γ-cyclogeranil geraniol were isolated from Bellardia trixago, the structures were determined by spectroscopic methods and confirmed by partial synthesis. Furthermore. 3,4-dihydro-γ-ionone, α-ambrinol, β-sitosterol and three flavonoids 5-O-demethyl tangeretin, 5-hydroxy auranetin and 3′-methoxy calycopterin were also isolated. 相似文献
104.
Jonathan S. Dordick K. C. Backman R. Balakrishnan R. Brent M. S. Ptashne L. P. Casson S. A. Goff A. L. Goldberg P. A. Cornelius R. M. Hochstrasser N. R. Kallenbach H. Rubin G. J. Todaro H. A. De Boer J. C. Delgoffe M. Lobmann N. ZyGraich L. Gehrke T. Kunkel A. Paau S. G. Platt L. Sequeira M. A. Palladino H. G. Roman D. Hultmark T. T. Rasmusan H. Steiner 《Applied biochemistry and biotechnology》1990,26(1):107-113
Protein engineering and site-directed mutagenesis is becoming immensely important in both fundamental studies and commercial applications involving proteins and enzymes in biocatalysis. Protein engineering has become a powerful tool to help biochemists and molecular enzymologists elucidate structure-function relationships in enzymic active sites, to understand the intricacies of protein folding and denaturation, and to alter the selectivity of enzymatic catalysis. Commercial applications of engineered enzymes are being developed to increase protein stability, widen or narrow substrate specificity, and to develop novel approaches for use of enzymes in organic synthesis, drug design, and clinical applications. In addition to protein engineering, novel expression systems have been designed to prepare large quantities of genetically engineered proteins. Recent US patents and scientific literature on protein engineering, site-directed mutagenesis, and protein expression systems related to protein engineering are surveyed. Patent abstracts are summarized individually and a list of literature references are given. 相似文献
105.
106.
J. J. LaBrecque Z. A. De Benzo E. Marcano C. A. Peña 《Journal of Radioanalytical and Nuclear Chemistry》1984,84(2):407-413
The comparison of an ambient temperature mercuric iodide spectrometer (HgI2) with a conventional cooled Si(Li) spectrometer is presented for the determination of niobium in Venezuelan laterites in the laboratory. The energy resolution of the HgI2 spectrometer was only about 590 eV (FWHM) at 5.9 keV compared to about 150 eV for the conventional Si(Li) spectrometer. The efficiency was about 5 times lower in the region of the NbK
peak as compared to the Si(Li) detector. Even though its energy resolution and efficiency is much poorer than the conventional Si(Li), the results it produced for the determination of niobium were acceptable for use in the exploration and exploitation of a niobium-rich deposit such as Cerro Impacto, Estado Bolívar, Venezuela. 相似文献
107.
S. Jovanović F. De Corte A. Simonits L. Moens P. Vukotić J. Hoste 《Journal of Radioanalytical and Nuclear Chemistry》1987,113(1):177-185
In absolute or comparator standardization methods of (n, ) activation analysis with reactor neutrons, the epithermal neutron flux nonideality, if neglected, max lead to significant errors on the analytical result. The concept of the effective resonance energy
, introduced to correct for this effect, is reviewed. 相似文献
108.
V. Nastro D. Vuono M. Guzzo G. Niceforo I. Bruno P. De
Luca 《Journal of Thermal Analysis and Calorimetry》2006,84(1):181-184
The aim of this paper is to characterize some raw
materials used for ceramics material production. Five samples of clay have
been analyzed. It has been carried out a patterned sampling in a quarry in
Rosarno (South Italy).
Chemical-physical
properties on clay samples are determined. Test pieces have been prepared
and physical properties after firing are determined by DSC thermal analysis,
XRD analysis and X-ray fluorescence. It is important to note the high amount
of Fe2O3. The mixture principally
contains quartz, illite and oligoclase. It has been observed the colour and
the shape after firing: predominant colour is red. In this case the clay has
been used in mixtures covered with glazes. The colour of internal clay is
hidden by opaque of glazes. The analysed raw materials can be used in a slip
for single fired red tiles. The A2sp clay produces best ceramics at 1000°C. 相似文献
109.
110.
32P was separated from the irradiated silicon matrix as ammonium phosphomolybdate and the activity was measured with a GM tube
or on a plastic scintillator. The second-order interference was taken into consideration.
Research associate of the N.F.W.O. 相似文献