全文获取类型
收费全文 | 171314篇 |
免费 | 1552篇 |
国内免费 | 507篇 |
专业分类
化学 | 88249篇 |
晶体学 | 3039篇 |
力学 | 7154篇 |
综合类 | 3篇 |
数学 | 19514篇 |
物理学 | 55414篇 |
出版年
2020年 | 1398篇 |
2019年 | 1552篇 |
2018年 | 1980篇 |
2017年 | 2065篇 |
2016年 | 3184篇 |
2015年 | 1889篇 |
2014年 | 3112篇 |
2013年 | 7659篇 |
2012年 | 5747篇 |
2011年 | 6877篇 |
2010年 | 5021篇 |
2009年 | 5002篇 |
2008年 | 6533篇 |
2007年 | 6428篇 |
2006年 | 6076篇 |
2005年 | 5502篇 |
2004年 | 5091篇 |
2003年 | 4592篇 |
2002年 | 4450篇 |
2001年 | 5218篇 |
2000年 | 3861篇 |
1999年 | 2967篇 |
1998年 | 2481篇 |
1997年 | 2385篇 |
1996年 | 2237篇 |
1995年 | 2113篇 |
1994年 | 2091篇 |
1993年 | 2000篇 |
1992年 | 2304篇 |
1991年 | 2244篇 |
1990年 | 2193篇 |
1989年 | 2121篇 |
1988年 | 2119篇 |
1987年 | 2122篇 |
1986年 | 2019篇 |
1985年 | 2629篇 |
1984年 | 2683篇 |
1983年 | 2381篇 |
1982年 | 2492篇 |
1981年 | 2307篇 |
1980年 | 2284篇 |
1979年 | 2426篇 |
1978年 | 2462篇 |
1977年 | 2388篇 |
1976年 | 2436篇 |
1975年 | 2360篇 |
1974年 | 2327篇 |
1973年 | 2504篇 |
1972年 | 1623篇 |
1971年 | 1337篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The arc discharge was studied in a transparent channel at an intense flow rate of nitrogen, hydrogen, air, carbon dioxide in the current range 100–1500 A. The internal diameter of the porous channel varied from 10 to 34 mm, the length - from 50 to 150 mm, the air and nitrogen flow rates - from 0.05 to 1.5 kg/s, hydrogen - from 0.005 to 0.05 kg/s. The electric field strength in the arc channel reached a value of 300 V/cm for N2 and 500 V/cm for H2. The effect of plasma thermochemical non-equilibrium was discovered. 相似文献
142.
143.
Joseph B. Schlenoff W. Jack Rink Lawrence Seger 《Physica C: Superconductivity and its Applications》1991,180(5-6):387-393
Single crystals and polycrystalline pellets of the high-temperature cuprate superconductor Bi2Sr2Ca1Cu2O8 were doped at room temperature by electrochemical reduction at > 95% Coulombic efficiency using lithium dopant ions in propylene carbonate electrolyte. Cyclic voltammetry and potential step measurements on single crystals suggest an unusual reduction mechanism, with a diffusion coefficient for Li+ in the c-axis direction of bulk superconductor of ca. 3 × 10−11 cm2s−1. Sintered pellets of polycrystalline powder could be doped more rapidly, with an apparent diffusion coefficient of 7 × 10−8 cm2s−1. X-ray susceptibility analysis show extensive disordering occurs on heavy Li doping, with a first-order transition from a crystalline/superconducting to an amorphous/non-superconducting phase. Single, crystals of Bi2Sr2Ca1Cu2O8 exhibited a color change on reduction from metallic gray to golden bronze. The reduced material was highly air-sensitive, forming a hydroxide surface film on exposure to ambient atmosphere. 相似文献
144.
T Christensen E B Jensen F Junker H Dalb?ge F Abildgaard J J Led 《Acta chemica Scandinavica (Copenhagen, Denmark : 1989)》1992,46(1):97-99
Biosynthetic human growth hormone specifically 13C-labelled in the carbonyl positions of all 26 leucine residues has been obtained by recombinant DNA techniques using 13C-labelled leucine and an E. coli strain that requires leucine. It is shown that, on the whole, the labelling is specific with no significant mislabelling as would have been the case had the 13C-labelled leucine been metabolized. 相似文献
145.
The reduction of chromate by glutathione, its mono- and diethyl esters,
-cysteine, 2-mercapto-propionic acid and mercapto-succinic acid has been studied. The empirical rate law kobs = ab[Thiol]2/(1 + b[Thiol]) is obeyed by all of these thiols, at neutral pH. No evidence could be obtained for a first-order pathway in glutathione under these conditions. These observations are used to comment on the stability of intermediates potentially important in explaining chromate toxicity. 相似文献
146.
The dynamic behavior of the continuous biological reactor subject to product inhibition is analysed and classified in terms of multiplicity and stability of steady states and existence and stability character of limit cycles. Various boundary conditions are derived which delineate the parameter space into regions of dynamically different behavior. The predicted types of behavior are then illustrated by numerical computation of cells and product concentration trajectories. 相似文献
147.
To assess the historical and sociological significance of the cold fusion saga, researchers need accurate information about the dates of various events associated with the saga. Based on materials in the Cornell Cold Fusion Archive, this article provides both a chronology and citations to documentary evidence for cold fusion events from 1926 to the end of 1990. 相似文献
148.
M. J. Soupioni B. D. Symeopoulos H. V. Papaefthymiou 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(3):441-444
Summary Four different bottled water brands sold in Greece in the winter of 2001-2002 were analyzed for a wide range of chemical elements,
using neutron activation analysis (NAA). The elements Na and Br were determined instrumentally (INAA), whereas the other metals
and trace elements radiochemically (RNAA). The results indicated that the mean level of all the elements determined in the
samples were well within the European Union (EU) directive on drinking water and accomplish the drinking water standards of
the World Health Organisation (WHO) as well as of the Food and Drug Administration (FDA). 相似文献
149.
150.
We exactly calculate the fourth virial coefficient for hard spheres in even dimensions for D = 4, 6, 8, 10, and 12. 相似文献