全文获取类型
收费全文 | 1282篇 |
免费 | 27篇 |
国内免费 | 5篇 |
专业分类
化学 | 993篇 |
晶体学 | 11篇 |
力学 | 18篇 |
数学 | 124篇 |
物理学 | 168篇 |
出版年
2021年 | 9篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2016年 | 24篇 |
2015年 | 15篇 |
2014年 | 15篇 |
2013年 | 42篇 |
2012年 | 40篇 |
2011年 | 44篇 |
2010年 | 21篇 |
2009年 | 28篇 |
2008年 | 28篇 |
2007年 | 38篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 41篇 |
2003年 | 31篇 |
2002年 | 32篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 14篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 16篇 |
1991年 | 18篇 |
1990年 | 7篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 13篇 |
1986年 | 11篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 10篇 |
1976年 | 10篇 |
1974年 | 6篇 |
1973年 | 9篇 |
1966年 | 38篇 |
1965年 | 85篇 |
1964年 | 117篇 |
1956年 | 85篇 |
1955年 | 91篇 |
1954年 | 16篇 |
排序方式: 共有1314条查询结果,搜索用时 31 毫秒
1.
2.
Jonathan L. Sessler Patricia J. Melfi Anne E.V. Gorden Doris K. Ford C. Drew Tait 《Tetrahedron》2004,60(49):11089-11097
Hexaphyrin(1.0.1.0.0.0) (isoamethyrin) undergoes a significant color change in the presence of UO22+, PuO22+, and NpO22+. The complexation of the first of these dioxo actinide cations was studied in semi-quantitative fashion in 1:1 MeOH-CH2Cl2. Under these conditions, the detection limit for UO22+ was found to be ca. 5.8 ppm by naked eye monitoring and <28 ppb by UV-vis spectroscopy. Isoamethyrin does not undergo a color change in the presence of most transition metals or when exposed to Gd(III). Isoamethyrin thus constitutes an attractive alternative to 2,2′(1,8-dihydroxy-3,6-disulfonaphthylene-2,7-bisazo)-bisbenzenarsonic acid (AzIII) and 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP), systems currently used as actinide cation sensors. 相似文献
3.
4.
In the nineteenth century, field theory brilliantly resolveda number of questions that had taxed mathematicians for centuries;for example, The circle cannot be squared by straightedge and compass, and solving polynomial equations by radicalsis not always possible. These successes have continued to beheld up as superb examples of the power of mathematical thought,and are demonstrated at an undergraduate level. The purposeof this article is to provide another such natural example whichleads to a concrete realisation of the free group on 2 generators. 相似文献
5.
The major goal of this paper is to examine the hypothesis that stock returns and return volatility are asymmetric, threshold nonlinear, functions of change in trading volume. A minor goal is to examine whether return spillover effects also display such asymmetry. Employing a double-threshold GARCH model with trading volume as a threshold variable, we find strong evidence supporting this hypothesis in five international market return series. Asymmetric causality tests lend further support to our trading volume threshold model and conclusions. Specifically, an increase in volume is positively associated, while decreasing volume is negatively associated, with the major price index in four of the five markets. The volatility of each series also displays an asymmetric reaction, four of the markets display higher volatility following increases in trading volume. Using posterior odds ratio, the proposed threshold model is strongly favored in three of the five markets, compared to a US news double threshold GARCH model and a symmetric GARCH model. We also find significant nonlinear asymmetric return spillover effects from the US market. 相似文献
6.
Transition temperatures (TN1) from the nematic lyotropic liquid-crystalline phase to the isotropic phase were measured for the system cetyltrimethylammonium bromide (CTAB) water in the presence of small amounts of 3-stilbene carboxylic acid (3SC), 4-stilbene carboxylic acid (4SC) and Δ2/2'-bi-(2H-l,4-benzothiazine) (BT). TNI, increases as a function of trans-3SC or trans-4SC concentration, ranging from 01 to 08 wt %, by up to 12°C. A further increase in TNI between 2 and 5°C can be achieved by photochemically converting the solubilized trans stilbene derivatives to the cis isomers. Irradiation of a trans-3SC containing sample at a temperature just above TNl leads to a light-induced phase transition to the lyotropic liquid-crystalline phase. Solubilization of trans-BT causes a slight decrease of TNI while photoisomerization to cis-BT increases TNI by 1°C. 相似文献
7.
8.
Elvira Vidović Doris Klee Hartwig Höcker 《Journal of polymer science. Part A, Polymer chemistry》2007,45(19):4536-4544
Poly(D ,L ‐lactide) and poly(D ,L ‐lactide‐co‐glycolide) with various composition and with one methacrylate and one carboxylate end group were synthesized and grafted onto poly(vinyl alcohol) (PVA) via the carboxylate group. The graft copolymers were crosslinked via the methacrylate groups using a free radical initiator. The polymer networks were characterized by means of NMR and studied qualitatively by means of IR spectroscopy. The influence of the glycolide content in the polyester grafts and of the number of ester units in the grafts on thermal properties and swellability were studied as well. The high swellability in water is characteristic of all hydrogels. Differential scanning calorimetry (DSC) showed a single glass transition temperature that occurs in the range between 51 and 69 °C. Thermogravimetric analysis (TGA) of the networks showed the main loss in weight in the temperature range between 290 and 370 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4536–4544, 2007 相似文献
9.
10.