全文获取类型
收费全文 | 6487篇 |
免费 | 200篇 |
国内免费 | 14篇 |
专业分类
化学 | 4705篇 |
晶体学 | 47篇 |
力学 | 122篇 |
数学 | 658篇 |
物理学 | 1169篇 |
出版年
2023年 | 54篇 |
2022年 | 71篇 |
2021年 | 228篇 |
2020年 | 170篇 |
2019年 | 177篇 |
2018年 | 147篇 |
2017年 | 111篇 |
2016年 | 252篇 |
2015年 | 206篇 |
2014年 | 264篇 |
2013年 | 394篇 |
2012年 | 438篇 |
2011年 | 513篇 |
2010年 | 334篇 |
2009年 | 334篇 |
2008年 | 427篇 |
2007年 | 390篇 |
2006年 | 337篇 |
2005年 | 305篇 |
2004年 | 240篇 |
2003年 | 174篇 |
2002年 | 145篇 |
2001年 | 103篇 |
2000年 | 93篇 |
1999年 | 69篇 |
1998年 | 59篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 45篇 |
1994年 | 47篇 |
1993年 | 49篇 |
1992年 | 52篇 |
1991年 | 31篇 |
1990年 | 34篇 |
1989年 | 20篇 |
1988年 | 24篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 19篇 |
1984年 | 21篇 |
1983年 | 22篇 |
1982年 | 13篇 |
1981年 | 27篇 |
1980年 | 18篇 |
1979年 | 13篇 |
1978年 | 17篇 |
1977年 | 11篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有6701条查询结果,搜索用时 625 毫秒
111.
112.
J. C. Moreno J. Nilsen J. A. Koch B. J. MacGowan J. H. Scofield L. B. Da Silva 《Applied physics. B, Lasers and optics》1994,58(1):3-5
Neon-like niobium X-ray lasers have been studied using both slab and thin-foil target geometries. Niobium foils of various lengths were irradiated from both sides with two beams of the frequency-doubled Nova laser system using a line focus. We looked for gain by measuring spectrally integrated line intensities at different plasma lengths. Gain was observed in four neon-like niobium lines corresponding to 3s–3p transitions. The line profile of theJ = 0–1 line ( = 145.9 ) shows splitting due to the hyperfine effect. Improved contrast in the hyperfine structure is observed as the plasma length is increased. Hyperfine splitting may be relevant to other 3s–3p transitions in neon-like niobium as well as other neon-like X-ray laser systems. 相似文献
113.
T. Missana C. N. Afonso M. F. da Silva 《Applied Physics A: Materials Science & Processing》1994,59(6):653-658
Interdiffusion processes are induced by nanosecond laser pulses from an excimer laser. The Bi-based systems studied are formed by a Bi layer and a Sb or Ge layer. Configurations with Bi at the surface layer or at the innermost layer are both studied. Real-time reflectivity measurements are performed during the irradiation to determine the process kinetics and times and Rutherford backscattering spectrometry is used to obtain the concentration depth profiles. It will be shown that there is an interfacially initiated diffusion process in the Bi-Sb system and that the diffusion coefficients of this system within the liquid phase are in the 10–5–10–6 cm2/s range. The Bi-Ge system shows instead little mixing, the diffusion coefficients of the system within the liquid phase being at least two orders of magnitude lower. The differences observed when Bi is the surface layer or the innermost one are related to the different thermal responses of the system. 相似文献
114.
115.
116.
The present work describes a selective, rapid and economical method for the determination of cobalt using the 2-(2-benzothiazolylazo)-p-cresol (BTAC) as a spectrophotometric reagent associated with a solid extraction on polyurethane foam. The BTAC reacts with Co(II) in the presence of Triton-X100 surfactant forming a green complex with maximum absorption at 615 nm. The reaction is used for cobalt determination within a pH range of 6.50-7.50, with an apparent molar absorptivity of 1.62 x 10(4) L mol(-1) cm(-1). Beer's Law is obeyed for a concentration of at least 1.60 microg ml(-1). A selective procedure is proposed for cobalt determination in the presence of Fe(II), Hg(II), Zn(II) and Cu(II) up to milligram levels using masking agents. Polyurethane foam is used for the preconcentration and separation of cobalt from thiocyanate media and this procedure is applied to its determination in nickel salts and steel alloys. 相似文献
117.
118.
119.
L. Fernandes C. Pagano Gonçalves da Silva 《Journal of Radioanalytical and Nuclear Chemistry》1993,172(2):313-318
The radiopharmaceutical201TlCl(thallium-201 chloride) is used in nuclear medicine for myocardial visualization. The solution of201TlCl was prepared using201Tl obtained by irradiating a natural mercury target with protons from the CV-28 cyclotron installed at IPEN-CNEN/SP. This solution was subjected to different quality control processes required for its use in medicine. Some of these controls concerned the determination of the radionuclidic impurities:200Tl,202Tl and203Hg; the chemical identification of201Tl+; the hydrazine concentration, mercury contamination and the presence of phosphate. Furthermore. the biological distribution in Wistar rats and tests for sterility, pyrogenicity and toxicity were carried out. It was verified that the solution obtained was in the form of thallous chloride. This radiopharmaceutical gave good heart images in animals but due to the high levels of200Tl and202Tl its use in humans is not possible unless enriched202Hg is used as target in the irradiation. 相似文献
120.