全文获取类型
收费全文 | 40361篇 |
免费 | 1476篇 |
国内免费 | 1447篇 |
专业分类
化学 | 28819篇 |
晶体学 | 318篇 |
力学 | 780篇 |
综合类 | 10篇 |
数学 | 5605篇 |
物理学 | 7752篇 |
出版年
2023年 | 294篇 |
2022年 | 507篇 |
2021年 | 680篇 |
2020年 | 662篇 |
2019年 | 670篇 |
2018年 | 779篇 |
2017年 | 761篇 |
2016年 | 1477篇 |
2015年 | 1189篇 |
2014年 | 1264篇 |
2013年 | 2711篇 |
2012年 | 2959篇 |
2011年 | 3200篇 |
2010年 | 1840篇 |
2009年 | 1884篇 |
2008年 | 2476篇 |
2007年 | 2414篇 |
2006年 | 2114篇 |
2005年 | 2004篇 |
2004年 | 2078篇 |
2003年 | 1508篇 |
2002年 | 1384篇 |
2001年 | 876篇 |
2000年 | 736篇 |
1999年 | 563篇 |
1998年 | 466篇 |
1997年 | 367篇 |
1996年 | 450篇 |
1995年 | 331篇 |
1994年 | 289篇 |
1993年 | 347篇 |
1992年 | 295篇 |
1991年 | 202篇 |
1990年 | 197篇 |
1989年 | 163篇 |
1988年 | 162篇 |
1987年 | 152篇 |
1986年 | 151篇 |
1985年 | 242篇 |
1984年 | 214篇 |
1983年 | 162篇 |
1982年 | 144篇 |
1981年 | 147篇 |
1980年 | 116篇 |
1979年 | 120篇 |
1978年 | 100篇 |
1977年 | 99篇 |
1976年 | 95篇 |
1975年 | 91篇 |
1973年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
A new, highly sensitive, fast responding and stable potentiometric biosensor for creatinine determination is developed. The biosensor is based on an ammonium ion-selective electrode. Creatinine deiminase (EC 3.5.4.21) is chemically immobilized on the surface of the polymeric ion-sensitive membrane in the form of monomolecular layer using a simple, one-step carbodiimide covalent attachment method. The resulting enzyme electrodes are useful for measurement under flow injection analysis (FIA) conditions. The biosensors exhibit excellent operational and storage stability. The enzyme electrodes retain over 70% of initial sensitivity after ten weeks of work under FIA conditions. The storage stability at 4 °C is longer than half a year without loss of sensitivity. Under optimized conditions near 30 samples per hour can be analyzed and the determination range (0.02-20.0 mmol l−1) fully covers creatinine concentrations important from clinical and biomedical point of view. The simple biosensor/FIA system has been successfully used for determination of creatinine in urine, serum and posthemodialysate samples. 相似文献
112.
Herein, we present results from MD simulations of the Michaelis complex formed between the B. cereus zinc-beta-lactamase enzyme and benzylpenicillin. The structural and dynamical effects induced by substrate-binding, the specific role of the conserved residues, and the near attack conformers of the Michaelis complex are discussed. Quantum chemical methods (HF/6-31G* and B3LYP/6-31G*) are also applied to study the hydrolysis reaction of N-methylazetidinone catalyzed by a monozinc system consisting of the side chains of the histidine residues (His86, His88, and His149) complexed with Zn-OH and the side chains of Asp90 and His210. From this model system, we built molecular-mechanics representations of the prereactive complex and transition state configurations docked into the active site. Linear-scaling semiempirical calculations coupled with a continuum solvent model were then performed on these static models. We propose that the experimental rate data for the B. cereus enzyme is compatible with a one-step mechanism for the hydrolysis of beta-lactam substrates in which His210 acts as a proton donor. 相似文献
113.
The ability of enzymes to work in non-aqueous media offers new and almost unexploited possibilities for the development of new optical biosensors. The advantages of performing biocatalytic reactions in non-aqueous media are discussed in relation to their possible application in optical biosensor design. Attention is focused on the factors that influence enzymatic catalysis in organic solvents, including the role of enzyme-associated water, criteria for solvent selection and the alteration of enzyme specificity. Recent examples of relevant applications and future prospects of organic-phase optical biosensing are discussed. 相似文献
114.
When excesses of ammonium thiocyanate and tetrabutylammonium chloride are added to a cobalt(II) solution, a water-insoluble ion-pair is formed; this compound is soluble in chloroform, isoamyl alcohol, and other solvents. The variables which affect the extractions by these two solvents are studied in order to obtain the optimal conditions and two alternative extraction procedures are proposed. Thus, the separation of cobalt as a previous step for its spectrophotometric determination is studied. 相似文献
115.
Gonzlez-Garca I. Jernimo-Castro J. Morales-Amaya E. Verdusco-Hernndez D. J. 《Aequationes Mathematicae》2022,96(4):885-900
Aequationes mathematicae - One of the most important problems in Geometric Tomography is to establish properties of a given convex body if we know some properties over its sections or its... 相似文献
116.
Graciela Díaz de Delgado Ramírez V. Belkis Miguel Delgado José Rosquete P. Carmelo 《Journal of chemical crystallography》1995,25(7):371-374
The title compound, formula C15H20O2, is orthorhombic, P212121 witha=8.747(2),b=12.025(3),c=12.554(3)Å,Z=4, andD
m
=1.32(2)g/ml. The structural analysis shows that the compound corresponds to eudesma-4(15),7(11)-dien-8,12-olide, a sesquiterpene lactone previously isolated fromAster umbellatus but whose crystal structure was unknown. 相似文献
117.
Vladimír Olejček 《International Journal of Theoretical Physics》1995,34(8):1643-1646
The q--algebra, i.e., the system of sets closed under complementation, countable disjoint unions, and containing the empty set, generated by the system of open balls coincides with the -field of Borel sets inR
sun forn=1,2, and 3. A first step to extend the proof forn=4, 5, 6, and 7 is indicated. 相似文献
118.
I. Muzyčenková V. Kellnerová M. Koneracká P. Kopčanský M. Antalík J. Ďurišin 《Czechoslovak Journal of Physics》1995,45(9):727-734
The encapsulation of fine magnetite particles of 10 nm size and marker ANS within asolectin vesicles has been made by sonication of the mixture in water. For the proof of encapsulation of magnetite in vesicles the electron microscope and spectrofluoriphotometer technique were used. The theory for the calculation of the magnetic force acting on the system consisted of non-capsulated magnetic particles dispersed in water and magnetic vesicles was developed.This work was supported by the Slovak Academy of Sciences within the framework of Project GAV No. 1361. 相似文献
119.
In this paper large-scale properties of developed magnetohydrodynamic turbulence have been investigated by using double expansion method in the frame of quantum field renormalization group. It has been shown that universal kinetic scaling regime exists, but the double expansion in general leads to qualitatively different results than those provided by the usual -expansion treatment.This work was supported by Slovak Grant Agency for Science. 相似文献
120.
In the framework of the Nilsson model the calculations of the so called shape factor for the first forbidden
– transitions 5/2+
241Pu 5/2–
241Am and 7/2+
177Lu 7/2–
177Hf are carried out. The dependence on the Nilsson potential parameters is studied. It turns out that for the transitions considered the calculated shape factor depends linearly on the electron energy and its slope is 10–3 per 20 keV. This can affect the analysis of electron spectra if the endpoint energy is sufficiently large. 相似文献