全文获取类型
收费全文 | 64854篇 |
免费 | 1730篇 |
国内免费 | 344篇 |
专业分类
化学 | 39410篇 |
晶体学 | 441篇 |
力学 | 1228篇 |
综合类 | 31篇 |
数学 | 11260篇 |
物理学 | 14558篇 |
出版年
2023年 | 412篇 |
2022年 | 488篇 |
2021年 | 698篇 |
2020年 | 893篇 |
2019年 | 848篇 |
2018年 | 1197篇 |
2017年 | 1079篇 |
2016年 | 2072篇 |
2015年 | 1770篇 |
2014年 | 1836篇 |
2013年 | 4020篇 |
2012年 | 3646篇 |
2011年 | 3610篇 |
2010年 | 2483篇 |
2009年 | 2148篇 |
2008年 | 3200篇 |
2007年 | 2968篇 |
2006年 | 2634篇 |
2005年 | 2640篇 |
2004年 | 2380篇 |
2003年 | 2058篇 |
2002年 | 1902篇 |
2001年 | 1443篇 |
2000年 | 1400篇 |
1999年 | 1026篇 |
1998年 | 788篇 |
1997年 | 685篇 |
1996年 | 864篇 |
1995年 | 702篇 |
1994年 | 763篇 |
1993年 | 673篇 |
1992年 | 679篇 |
1991年 | 616篇 |
1990年 | 674篇 |
1989年 | 540篇 |
1988年 | 522篇 |
1987年 | 488篇 |
1986年 | 467篇 |
1985年 | 698篇 |
1984年 | 687篇 |
1983年 | 521篇 |
1982年 | 540篇 |
1981年 | 513篇 |
1980年 | 454篇 |
1979年 | 439篇 |
1978年 | 421篇 |
1977年 | 470篇 |
1976年 | 455篇 |
1975年 | 392篇 |
1973年 | 396篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
21.
Absorption and luminiscence measurements were performed on lead-doped KCl:KI mixed single crystals. Strong differences were found between as-grown and quenched samples. New bands were observed in the absorption spectra of unquenched samples in the spectral region between the limit positions of the A bands, corresponding to chloride or iodide lattices. The strong band at 449 nm dominates the luminescence of these samples at low temperatures. Its kinetics have a complicated form and the decay time is in the interval from ns to ms. Quenched samples have a well-known luminescence spectrum caused by octahedral lead impurity centres in KCl single crystals. The kinetics, however, also indicate mixed chlorine and iodine coordination of lead in the investigated crystals. 相似文献
22.
A. Baeza M. Fernández M. Herranz F. Legarda C. Miró A. Salas 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):321-326
We studied the effectiveness of potable water treatment processes that consist of the stages of coagulation-flocculation-decantation,
using iron-based coagulants, in eliminating gamma-emitting man-made radioisotopes of cesium, strontium, and americium from
two natural waters with different degrees of mineralization. The resulting decontamination was found to depend on the chemical
behavior of each of the radionuclides considered, on the pH at which the process of coagulation is carried out, and on the
concentration of the other stable cations present.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
23.
Daniel Hork Nataliya Benedyk 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5827-5837
Fine magnetite nanoparticles, both electrostatically stabilized and nonstabilized, were synthesized in situ by precipitation of Fe(II) and Fe(III) salts in alkaline medium. Magnetic poly(glycidyl methacrylate) (PGMA) microspheres with core‐shell structure, where Fe3O4 is the magnetic core and PGMA is the shell, were obtained by dispersion polymerization initiated with 2,2′‐azobisisobutyronitrile (AIBN), 4,4′‐azobis(4‐cyanovaleric acid) (ACVA), or ammonium persulfate (APS) in ethanol containing poly(vinylpyrrolidone) or ethylcellulose stabilizer in the presence of iron oxide ferrofluid. The average microsphere size ranged from 100 nm to 2 μm. The effects of the nature of ferrofluid, polymerization temperature, monomer, initiator, and stabilizer concentration on the PGMA particle size and polydispersity were studied. The particles contained 2–24 wt % of iron. AIBN produced larger microspheres than APS or ACVA. Polymers encapsulating electrostatically stabilized iron oxide particles contained lower amounts of oxirane groups compared with those obtained with untreated ferrofluid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5827–5837, 2004 相似文献
24.
The basic features of a chemical measurement 总被引:2,自引:0,他引:2
25.
Sándor G?r?g 《Analytical sciences》2004,20(5):767-782
The development during the last 15 years and the state-of-the-art in the analysis of bulk steroid hormone drugs and hormone-like structures and pharmaceutical formulations made thereof are summarized. Other steroids (sterols, bile acids, cardiac glycosides, vitamins D) as well as biological-clinical aspects and pharmacokinetic and metabolic studies are excluded from this review. The state-of-the-art is summarized based on comparisons of monographs in the latest editions of the European Pharmacopoeia, United States Pharmacopoeia and the Japanese Pharmacopoeia. This is followed by sections dealing with new developments in the methodology for the fields of spectroscopic and spectrophotometric, chromatographic, electrophoretic and hyphenated techniques as well electroanalytical methods. The review is terminated by two problem-oriented sections: examples on impurity and degradation profiling as well as enantiomeric analysis. 相似文献
26.
27.
Bed ich Ko ata V clav Kozmik Ji í Svoboda Vladimí ra Novotn P emysl Van k Milada Glogarov 《Liquid crystals》2003,30(5):603-610
Four series of new [1]benzothieno[3,2- b ][1]benzothiophene derivatives have been synthesized. In the non-chiral series a SmA phase occurs, while the chiral series exhibits a rather wide antiferroelectric SmC * A phase just below the SmA phase. The SmA-SmC * A phase transition has been studied using DSC and dielectric spectroscopy. In the SmC * A phase the spontaneous quantities have been measured. The tilt angle shows a typical temperature dependence and the values of spontaneous polarization are rather moderate. The length of the helical pitch increases on increasing the length of the non-chiral alkyl chain. 相似文献
28.
29.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
30.
No analytic solutions of the Schrödinger equation are known for the quartic anharmonic oscillator. We show in this paper that there are closely related modified quartic oscillators with the potential depending on |x| for which analytic solutions for some states exist. These results can be extended to the higher order oscillators 相似文献