全文获取类型
收费全文 | 3456篇 |
免费 | 74篇 |
国内免费 | 18篇 |
专业分类
化学 | 2474篇 |
晶体学 | 38篇 |
力学 | 33篇 |
数学 | 138篇 |
物理学 | 865篇 |
出版年
2022年 | 22篇 |
2021年 | 18篇 |
2020年 | 29篇 |
2019年 | 44篇 |
2018年 | 22篇 |
2017年 | 25篇 |
2016年 | 49篇 |
2015年 | 53篇 |
2014年 | 64篇 |
2013年 | 146篇 |
2012年 | 152篇 |
2011年 | 167篇 |
2010年 | 104篇 |
2009年 | 102篇 |
2008年 | 171篇 |
2007年 | 159篇 |
2006年 | 181篇 |
2005年 | 140篇 |
2004年 | 154篇 |
2003年 | 135篇 |
2002年 | 113篇 |
2001年 | 89篇 |
2000年 | 73篇 |
1999年 | 47篇 |
1998年 | 31篇 |
1997年 | 33篇 |
1996年 | 59篇 |
1995年 | 54篇 |
1994年 | 34篇 |
1993年 | 51篇 |
1992年 | 61篇 |
1991年 | 47篇 |
1990年 | 37篇 |
1989年 | 45篇 |
1988年 | 47篇 |
1987年 | 38篇 |
1986年 | 24篇 |
1985年 | 82篇 |
1984年 | 70篇 |
1983年 | 51篇 |
1982年 | 54篇 |
1981年 | 48篇 |
1980年 | 48篇 |
1979年 | 45篇 |
1978年 | 43篇 |
1977年 | 44篇 |
1976年 | 38篇 |
1975年 | 36篇 |
1974年 | 25篇 |
1973年 | 30篇 |
排序方式: 共有3548条查询结果,搜索用时 15 毫秒
961.
Shinji Yamada Emiko Ohta 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(4):o230-o232
The title compound, C13H6F5NO, exists in the enol form and adopts the E configuration about the enol double bond. It is the first example of an enol‐type pyridinium ylide. The enol structure was unambiguously determined on the basis of the significantly longer C—O bond and shorter C—C bond. Intramolecular C—H...O and C—H...F hydrogen bonds are responsible for promotion of the enol form and for the stability of this compound. 相似文献
962.
Yamada T Peng CG Matsuda S Addepalli H Jayaprakash KN Alam MR Mills K Maier MA Charisse K Sekine M Manoharan M Rajeev KG 《The Journal of organic chemistry》2011,76(5):1198-1211
We have previously demonstrated that conjugation of small molecule ligands to small interfering RNAs (siRNAs) and anti-microRNAs results in functional siRNAs and antagomirs in vivo. Here we report on the development of an efficient chemical strategy to make oligoribonucleotide-ligand conjugates using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) or click reaction. Three click reaction approaches were evaluated for their feasibility and suitability for high-throughput synthesis: the CuAAC reaction at the monomer level prior to oligonucleotide synthesis, the solution-phase postsynthetic "click conjugation", and the "click conjugation" on an immobilized and completely protected alkyne-oligonucleotide scaffold. Nucleosides bearing 5'-alkyne moieties were used for conjugation to the 5'-end of the oligonucleotide. Previously described 2'- and 3'-O-propargylated nucleosides were prepared to introduce the alkyne moiety to the 3' and 5' termini and to the internal positions of the scaffold. Azido-functionalized ligands bearing lipophilic long chain alkyls, cholesterol, oligoamine, and carbohydrate were utilized to study the effect of physicochemical characteristics of the incoming azide on click conjugation to the alkyne-oligonucleotide scaffold in solution and on immobilized solid support. We found that microwave-assisted click conjugation of azido-functionalized ligands to a fully protected solid-support bound alkyne-oligonucleotide prior to deprotection was the most efficient "click conjugation" strategy for site-specific, high-throughput oligonucleotide conjugate synthesis tested. The siRNA conjugates synthesized using this approach effectively silenced expression of a luciferase gene in a stably transformed HeLa cell line. 相似文献
963.
964.
One of 5-alkenyl-15-alkynyl-porphyrin and 5,15-dialkynyl-porphyrin was prepared selectively by 2+2 acid-catalyzed condensation of bicyclo[2.2.2]octadiene-fused dipyrrylmethane and TMS propynal in the presence of BF3·OEt2 only by the choice of the solvent. The alkenyl group was expected to be obtained by a protonation followed by intramolecular 1,2-hydride transfer from methine position of porphyrinogen. 相似文献
965.
Photochemical and analytical applications of gold nanoparticles and nanorods utilizing surface plasmon resonance 总被引:1,自引:0,他引:1
In recent years, plasmonics has emerged as a promising tool in the fields of analytical chemistry and biochemistry. In particular,
surface plasmon resonance at the surfaces of gold nanostructures has led to the development of widespread interest in gold
nanoparticles. In this review, we describe some of the recent progress in the manufacture and use of gold nanoparticles, with
particular emphasis on gold nanorods. Furthermore, the spectroscopic and photochemical applications of gold nanospheres and
nanorods are described. 相似文献
966.
Yamada K Koyano Y Okamoto T Asada T Koga N Nagaoka M 《Journal of computational chemistry》2011,32(14):3092-3104
We present an alternative approach to determine "density-dependent property"-derived charges for molecules in the condensed phase. In the case of a solution, it is essential to take into consideration the electron polarization of molecules in the active site of this system. The solute and solvent molecules in this site have to be described by a quantum mechanical technique and the others are allowed to be treated by a molecular mechanical method (QM/MM scheme). For calculations based on this scheme, using the forces and interaction energy as density-dependent property our charges from interaction energy and forces (CHIEF) approach can provide the atom-centered charges on the solute atoms. These charges reproduce well the electrostatic potentials around the solvent molecules and present properly the picture of the electron density of the QM subsystem in the solution system. Thus, the CHIEF charges can be considered as the atomic charges under the conditions of the QM/MM simulation, and then enable one to analyze electrostatic interactions between atoms in the QM and MM regions. This approach would give a view of the QM nuclei and electrons different from the conventional methods. 相似文献
967.
Single enantiomers of 1,8-di(1-adamantyl)naphthalenes were synthesized by the [4+2]cycloaddition reaction of 6-adamantylbenzyne and 2-adamantylfuran. The enantiomers were resolved by conversion into diastereomeric ketopinic acid esters. The absolute configuration was determined by X-ray analysis. Kinetic studies by CD revealed an enantiomerization barrier of 29 kcal mol(-1) for 1,8-(1-adamantyl)naphthalenes. 相似文献
968.
Yamada M Wakahara T Tsuchiya T Maeda Y Kako M Akasaka T Yoza K Horn E Mizorogi N Nagase S 《Chemical communications (Cambridge, England)》2008,(5):558-560
Dimetallofullerene Ce(2)@C(78) and its bis-silylated derivative (1) were successfully prepared and fully characterized. 相似文献
969.
Hirao A Akiyama T Okujima T Yamada H Uno H Sakai Y Aramaki S Ono N 《Chemical communications (Cambridge, England)》2008,(39):4714-4716
Soluble precursors of 2,3-naphthalocyanine (Nc) and phthalocyanine (Pc) were prepared and were converted into insoluble semiconducting thin films of Pc and Nc by heating after fabrication via spin-coating. 相似文献
970.
Hattori R Yamada K Hasegawa K Ishikawa Y Ito Y Sakamoto Y Yoshida N 《Rapid communications in mass spectrometry : RCM》2008,22(21):3410-3414
The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages. 相似文献