全文获取类型
收费全文 | 1191篇 |
免费 | 23篇 |
国内免费 | 5篇 |
专业分类
化学 | 607篇 |
晶体学 | 5篇 |
力学 | 19篇 |
数学 | 132篇 |
物理学 | 456篇 |
出版年
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2016年 | 31篇 |
2015年 | 16篇 |
2014年 | 20篇 |
2013年 | 51篇 |
2012年 | 44篇 |
2011年 | 57篇 |
2010年 | 24篇 |
2009年 | 33篇 |
2008年 | 68篇 |
2007年 | 54篇 |
2006年 | 35篇 |
2005年 | 32篇 |
2004年 | 38篇 |
2003年 | 31篇 |
2002年 | 33篇 |
2001年 | 29篇 |
2000年 | 30篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 10篇 |
1996年 | 17篇 |
1995年 | 24篇 |
1994年 | 10篇 |
1993年 | 21篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 21篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1985年 | 19篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 19篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 24篇 |
1978年 | 19篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1975年 | 18篇 |
1974年 | 20篇 |
1973年 | 14篇 |
1972年 | 12篇 |
1971年 | 12篇 |
1970年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有1219条查询结果,搜索用时 110 毫秒
21.
We have demonstrated that the readily available amido-keto compounds 5, with prearranged carbonyl and glycine moieties, under strongly basic conditions easily undergo complete and highly diastereoselective cyclization, affording a generalized and practical access to the conformationally constrained phenylserine derivatives 4. High chemical yields, virtually complete diastereoselectivity combined with the operational convenience of the experimental procedures render this method useful for preparation of these diastereomerically pure derivatives. 相似文献
22.
The reaction of the phosphate with the expoxyaldehyde is reported as the key step in a novel stereospecific synthesis of (±)-LTA4, methyl ester . 相似文献
23.
A simple and rapid procedure is proposed for the determination of chloride and free fluoride in tin electroplating fluid. Suppressor-column ion-chromatography is used after oxidation of hexafluorostannate(II) to hexafluorostannate(IV) with hydrogen peroxide. Concurrent determination of tin(II) and total tin then allows calculation of the concentrations of fluoride, hexafluorostannate(II) and hexafluorostannate(IV). 相似文献
24.
Misbahul Ain Khan Alina Guerra Cosenza Gwynn Pennant Ellis 《Journal of heterocyclic chemistry》1982,19(5):1077-1085
Various 1H,6H-pyrano[2,3-c]pyrazol-6-ones (III-XXIII) were obtained from β-keto esters and 1H-pyrazol-5-ones or hydrazines. Nitrations, chlorinations and brominations of these pyranopyrazoles were also carried out giving the corresponding derivatives (XXIV-LXIV). The pyrone ring is the more reactive one in these reactions and the preferred position of attack is the 5-position. The substitution products are formed by the addition-elimination route. 相似文献
25.
Herein we report a surprisingly facile and clean synthesis of base-stabilised phosphorus(I) and arsenic(I) iodide salts, which are reagents that provide convenient access to new low oxidation state main group compounds. 相似文献
26.
K. J. Ellis S. Kelleher A. Raciti J. Savory M. Wills 《Journal of Radioanalytical and Nuclear Chemistry》1988,124(1):85-95
In vivo neutron activation analysis was used to examine the total body and partial body (hand) aluminum levels in patients with end-stage renal failure. Patients maintained on chronic hemodialysis had higher mean body burdens of aluminum than, did those clinically managed without dialysis. Approximately 70% of the patients examined indicated elevated levels of body or skeletal aluminum. A significant correlation was observed between the in vivo aluminum/calcium ratio obtained for the hand measurement and the increase in serum aluminum levels following a disferroxamine infusion test. The direct in vivo monitoring of hand Al/Ca values in patients may provide an alternate choice to bone biopsy for the detection of aluminum intoxication. 相似文献
27.
Ulrike Troitzsch Andrew G. Christy David J. Ellis 《Journal of solid state chemistry》2007,180(10):2885-2895
We report a new zirconium titanate compound (Zr,Ti)O2 with 27.5-35 mol% titania (TiO2) formed from the oxides at 35-38 kbar, 1400-1500 °C. Crystal structure investigations at atmospheric conditions with powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed a monoclinic structure related to that of M-fergusonite (beta). Unit-cell dimensions (from 27.5 to 35 mol% TiO2): a=7.267(20)-7.340(2) Å, b=10.435(3)-10.429(1) Å, c=5.023(11)-5.040(1) Å, β=136.45(12)-137.55(1)°, V=262.44(92)-260.40(12) Å3, Z=4. Rietveld refinement (RF=1.55) of a sample with 32.8 mol% TiO2 indicates that site A is 8-fold coordinated, mostly occupied by Zr, while site B has 6-fold average coordination, occupied by Ti and Zr. Site B is at least partly ordered, as indicated by superstructure reflections 0 0 1 and −2 0 1 detected with TEM, reducing the space group from C2/c to C2. Pronounced streaking of selected diffraction spots is linked to the boundaries of lamellar domains in twin orientation, with twin planes either (200) or (20−2). Adjacent lamellae differ slightly in composition, causing subtle asymmetry of the twin diffraction patterns. 相似文献
28.
29.
30.