全文获取类型
收费全文 | 3309篇 |
免费 | 97篇 |
国内免费 | 22篇 |
专业分类
化学 | 2047篇 |
晶体学 | 11篇 |
力学 | 147篇 |
数学 | 493篇 |
物理学 | 730篇 |
出版年
2024年 | 3篇 |
2023年 | 33篇 |
2022年 | 57篇 |
2021年 | 113篇 |
2020年 | 100篇 |
2019年 | 80篇 |
2018年 | 58篇 |
2017年 | 45篇 |
2016年 | 129篇 |
2015年 | 91篇 |
2014年 | 134篇 |
2013年 | 168篇 |
2012年 | 223篇 |
2011年 | 252篇 |
2010年 | 142篇 |
2009年 | 123篇 |
2008年 | 199篇 |
2007年 | 194篇 |
2006年 | 210篇 |
2005年 | 194篇 |
2004年 | 149篇 |
2003年 | 129篇 |
2002年 | 126篇 |
2001年 | 51篇 |
2000年 | 24篇 |
1999年 | 30篇 |
1998年 | 33篇 |
1997年 | 41篇 |
1996年 | 38篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 8篇 |
1991年 | 18篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 15篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 9篇 |
排序方式: 共有3428条查询结果,搜索用时 1 毫秒
981.
982.
983.
Emanuela Licandro Stefano Maiorana Antonio Papagni Daniele Tarallo Alexandra M. Z. Slawin David J. Williams 《Journal of heterocyclic chemistry》1990,27(4):1103-1107
This paper reports the first example of Wittig reaction on arylazomethylenetriphenylphosphoranes, producing the new cinnolines 6 and 7 . A new unexpected rearrangement reaction producing quinoline 8 is also reported. The structure of compound 8 was determined by X-ray analysis. 相似文献
984.
Fabio Marchesoni Massimo Sparpaglione Stefano Ruffo Paolo Grigolini 《Physics letters. A》1982,88(3):113-116
New theoretical insights into the generalized Langevin approach to the onset of chaos are given. To make it possible to compare theory with “experiments” a fast computer algorithm is set up. 相似文献
985.
Alessandro De Robertis Concetta De Stefano Carmelo Rigano Silvio Sammartano 《Journal of solution chemistry》1990,19(6):569-587
The protonation constants of 21 carboxylic acids (formic, acetic, propionic, benzoic, phenoxyacetic, salicylic, oxalic, malonic, succinic, itaconic, malic, tartaric, oxydiacetic, thiodiacetic, thiodipropionic, phthalic, maleic, citric, 1,2,3-tricarboxylic, 1,2,4-tricarboxylic and 1,2,4,5-tetracarboxylic), have been determined potentiometrically, by pH-metric measurements, at several temperatures and ionic strengths, 5T55°C, 0<11 mol-dm–3, using tetraethylammonium iodide as background salt. General equations for the dependence on ionic strength of thermodynamic parameters have been found. The statistical significance of results and the possibility of using a simple model for the thermodynamics of carboxylic acids protonation, is discussed. 相似文献
986.
987.
Bertoni-Freddari C Fattoretti P Casoli T Di Stefano G Solazzi M Meier-Ruge W 《Micron (Oxford, England : 1993)》2001,32(4):405-410
Mitochondrial metabolic competence, defined as the organelle's capacity to provide adequate amounts of ATP in due time, appears to constitute an important determinant in several biological processes and pathological conditions. Thus, the assessment of the metabolic efficiency of the mitochondrial population in a given tissue area or cellular compartment may provide clues to identifying alterations of the cellular bioenergetic machinery, which may constitute a predisposing condition leading to impaired organ and system functions.In the cerebellar cortex of adult rats, the activities of the enzymes cytochrome oxidase (COX) and succinic dehydrogenase (SDH) were, respectively, evidenced by means of the diaminobenzidine and copper ferrocyanide preferential cytochemical techniques. At the electron microscope, the activities of these two key molecules of the respiratory chain were clearly visualised as dark precipitates at the inner mitochondrial membrane sites where COX and SDH are located. By means of the disector method, unbiased mitochondrial samplings were carried out to measure: the number of mitochondria/microm(3) of tissue (numeric density: Nv); the mitochondrial volume fraction/microm(3) of tissue (volume density: Vv) and the average mitochondrial volume (V) both on COX- and SDH-positive organelles in the cerebellar glomeruli and Purkinje cells, respectively. The ratio R (total area of the precipitates due either to COX or SDH activity within the single mitochondrion/area of the same organelle) was also evaluated to get information on the enzyme activity related to mitochondrial size.The documented accumulation of mutant mitochondrial DNA particularly in postmitotic cells results in a marked heteroplasmy (mixtures of normal and mutated genomes) at mitochondrial and cellular levels, thus the cellular potential for energy production is demanded to a mosaic of organelles with different functional capabilities. Assessment of the mitochondrial mosaic outline by means of quantitative cytochemistry of key enzymes of the respiratory chain, such as COX and SDH, may allow for the morphofunctional metabolic mapping of mitochondrial efficiency in discrete cellular or tissue compartments. 相似文献
988.
Stefano Vidussi 《Proceedings of the American Mathematical Society》2001,129(8):2489-2496
In this paper we prove that simple type four manifolds with 1$">which are diffeomorphic outside a point or outside a wedge of circles have the same Seiberg-Witten invariants, excluding the use of these invariants to detect eventual inequivalent smooth structures.
989.
High-resolution magic angle spinning (HRMAS) NMR is probably the most apt NMR method to analyze complex materials involving a solid phase, e.g. foodstuffs. We present here an HRMAS analysis of grated cheese (Parmigiano Reggiano). A full NMR characterization of this cheese allows the identification of the presence of fatty acids (saturated and unsaturated), amino acids and other small organic molecules. Since the presence and relative concentration of these molecules have previously been shown to correlate with organoleptic, origin and age characterization, HRMAS NMR of cheese is likely to provide a good complimentary tool for the analysis of this food material. 相似文献
990.
Cristoni S Cuccato D Sciannamblo M Bernardi LR Biunno I Gerthoux P Russo G Weber G Mora S 《Rapid communications in mass spectrometry : RCM》2004,18(1):77-82
Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by 21-hydroxylase deficit (21-OHD). Deletions or mutations of the CYP21 gene induce the impairment of glucocorticoid and mineralcorticoid synthesis. 17-Hydroxyprogesterone (17-OHP) is the hormonal marker in patients, but not in the heterozygous subjects. Excess 17-OHP is hydroxylated into 21-deoxycortisol (21-DF), and therefore 21-DF can be used as a specific marker for diagnosis of heterozygous individuals. We report an analytical method for analysis of 21-DF in blood samples using electrospray (ESI) and atmospheric pressure chemical ionization (APCI), showing that ESI is very sensitive for the analysis of this marker molecule. The multiple reaction monitoring (MRM) approach was used to increase the specificity and the sensitivity of the method. 相似文献