全文获取类型
收费全文 | 936篇 |
免费 | 9篇 |
国内免费 | 8篇 |
专业分类
化学 | 532篇 |
晶体学 | 1篇 |
力学 | 24篇 |
数学 | 184篇 |
物理学 | 212篇 |
出版年
2020年 | 12篇 |
2019年 | 15篇 |
2017年 | 8篇 |
2016年 | 7篇 |
2014年 | 10篇 |
2013年 | 45篇 |
2012年 | 21篇 |
2011年 | 34篇 |
2010年 | 23篇 |
2009年 | 16篇 |
2008年 | 32篇 |
2007年 | 44篇 |
2006年 | 30篇 |
2005年 | 38篇 |
2004年 | 43篇 |
2003年 | 33篇 |
2002年 | 30篇 |
2001年 | 28篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 10篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 17篇 |
1993年 | 20篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 18篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 15篇 |
1981年 | 21篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 6篇 |
1977年 | 9篇 |
1976年 | 9篇 |
1975年 | 15篇 |
1974年 | 9篇 |
1973年 | 17篇 |
1972年 | 7篇 |
1970年 | 7篇 |
1969年 | 6篇 |
1968年 | 6篇 |
1967年 | 9篇 |
排序方式: 共有953条查询结果,搜索用时 0 毫秒
11.
We have synthesized novel heterocyclic compounds from resin-bound guanidines. For this purpose, an amine immobilized on a solid support was acylated with protected amino acids. Following the deprotection, the liberated amines were guanidinylated utilizing a new member of the family of diurethane-protected triflyl guanidine reagents, N,N'-bis(allyloxycarbonyl)-N' '-triflylguanidine. The deprotected guanidines were subsequently regioselectively cyclized with beta-keto esters yielding novel compounds containing heterocyclic structures in high purities. 相似文献
12.
13.
We prove the existence of uncountably many nonisomorphic topological projective planes, each universal in the sense that it contains an isomorphic copy of every pseudoline arrangement. 相似文献
14.
15.
16.
17.
18.
Human tooth enamel provides a nearly permanent and chronological record of an individuals nutritional status and anthropogenic trace metal exposure during development; it might thus provide an excellent bio archive. We investigated the micro-spatial distribution of trace metals (Cu, Fe, Mg, Sr, Pb, and Zn) in 196×339 m2 raster pattern areas (6.6×104 m2) in a deciduous tooth using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Ablated areas include prenatal and postnatal enamel, the neonatal line, the dentine–enamel junction (DEJ), dentine, and the dentine–pulp junction. Topographic variations in the surface elemental distribution of lead, zinc, strontium, and iron intensities in a deciduous tooth revealed heterogeneous distribution within and among regions. 43Ca normalized elemental intensities showed the following order: Sr>Mg>>Zn>Pb>Fe>Cu. Elevated zinc and lead levels were present in the dental pulp region and at the neonatal line. This study demonstrates the ability of LA–ICP–MS to provide unique elemental distribution information in micro spatial areas of dental hard tissues. Elemental distribution plots could be useful in decoding nutrition and pollution information embedded in their bio apatite structure.Presented in part at the 2002 Winter Conference on Plasma Spectrochemistry, Scottsdale, AZ, January 6–12, 2002. The poster was selected as an outstanding poster presentation. 相似文献
19.
R. A. English S. G. Davidson Z. L. Miskovic F. O. Goodman A. T. Amos B. L. Burrows 《Progress in Surface Science》1996,53(2-4):323-330
A recursive Green-function (RGF) technique is used to study the surface states of an electrified solid. The concatenating nature of the method leads to a continued-fraction form of the RGF, which can be expressed as a ratio of Bessel functions. The surface density of states (SDOS), derived from the RGF, reveals a quasi-Stark-ladder distribution of the energy levels at the surface atom. The dependence of the SDOS on the applied field and surface perturbation parameters is discussed. 相似文献
20.
Zhang L Mattern RH Malaney TI Pierschbacher MD Goodman M 《Journal of the American Chemical Society》2002,124(12):2862-2863
We report the results of (15)N-edited 2D transferred NOE experiments of the partially (15)N-labeled alpha(5)beta(1) antagonist c[Mpa(15)N-Arg-(15)N-Gly-(15)N-Asp-(15)N-Asp-(15)N-Val-Cys]-NH(2) (Mpa denotes mercaptopropionic acid) in the presence of the native alpha(5)beta(1) receptor. The alpha(5)beta(1) integrin receptor is believed to be involved in tumor metastasis and the rational design of alpha(5)beta(1) integrin antagonist is therefore of considerable interest. Our experiments provide insight into the alpha(5)beta(1) receptor-bound conformation of the antagonist c[MpaRGDDVC]-NH2 and will be important for the design of novel antagonists. 相似文献