全文获取类型
收费全文 | 5267篇 |
免费 | 163篇 |
国内免费 | 267篇 |
专业分类
化学 | 4753篇 |
晶体学 | 26篇 |
力学 | 228篇 |
综合类 | 61篇 |
数学 | 144篇 |
物理学 | 485篇 |
出版年
2024年 | 2篇 |
2023年 | 20篇 |
2022年 | 62篇 |
2021年 | 64篇 |
2020年 | 82篇 |
2019年 | 82篇 |
2018年 | 64篇 |
2017年 | 112篇 |
2016年 | 118篇 |
2015年 | 136篇 |
2014年 | 116篇 |
2013年 | 268篇 |
2012年 | 514篇 |
2011年 | 232篇 |
2010年 | 178篇 |
2009年 | 229篇 |
2008年 | 207篇 |
2007年 | 337篇 |
2006年 | 263篇 |
2005年 | 250篇 |
2004年 | 262篇 |
2003年 | 248篇 |
2002年 | 192篇 |
2001年 | 118篇 |
2000年 | 139篇 |
1999年 | 134篇 |
1998年 | 118篇 |
1997年 | 116篇 |
1996年 | 119篇 |
1995年 | 141篇 |
1994年 | 123篇 |
1993年 | 132篇 |
1992年 | 159篇 |
1991年 | 76篇 |
1990年 | 42篇 |
1989年 | 63篇 |
1988年 | 39篇 |
1987年 | 24篇 |
1986年 | 27篇 |
1985年 | 14篇 |
1984年 | 21篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有5697条查询结果,搜索用时 359 毫秒
11.
Using spatially modulated illumination (SMI) light microscopy it is possible to measure the sizes of fluorescent structures that have an extension far below the conventional optical resolution limit (“subresolution size”). Presently, the sizes are determined as the object extension along the optical axis of the SMI microscope. For this, however, “a priori” assumptions on the fluorochrome distribution (“shape”) within the examined fluorescent structure have to be made. Usually it is assumed that the fluorochrome follows a Gauss-distribution or a spherical distribution. In this report we overcome the necessity to make an assumption on the shape of the fluorochrome distribution. We introduce two new experimentally obtained parameters which allow the determination of a shape measure to describe the spatial distribution of the fluorescent dye. This becomes possible by independent measurements with different excitation wavelengths. As an example, we present shape parameter measurements on individual fluorescent microspheres with a nominal geometrical diameter (“size”) of 190 nm. In the case investigated, the experimental shape correlated well with a homogeneous fluorochrome distribution (“spherical shape”) but not with a variety of other “shapes”. 相似文献
12.
在过氧化氢溶液及硝酸镍存在下,用石墨炉原子吸收法测定化妆品中砷的含量,砷的浓度在0-1mg/L时与吸光度线相关,线性方程为A=0.838c 0.003,相关系数为0.99994。对液体和固体化妆品中的砷进行测定,砷的加标回收率为98.3%-98.7%,测定结果的相对标准偏差为0.65%-1.50%。 相似文献
13.
开放式微波消解与干灰化法消解测量食品中铅的方法比较 总被引:1,自引:0,他引:1
对开放式微波消解法与干灰化法消解测量食品中铅的方法进行了比较,试验表明,前者操作简易,试验周期短,在测量精度和加标回收率方面两种方法无显著性差别。 相似文献
14.
15.
在前文研究的基础上,经试验,证明Ag(Ⅰ)与巯萘剂(TN)反应生成非电活性物质,导致电活性物质DTN电流降低。在最佳条件下,Ag(Ⅰ)浓度在3.7×10~(-8)~4.5×10(-7)mol/L范围内与DTN电流峰高降低值成线性关系,检出限为2.2×10~(-8)mol/L(相当于2.4ng/ml)Ag(Ⅰ)。方法用于纯镍和氢氧化钾中痕最银的测定,结果满意。 相似文献
16.
17.
K. Jaques W. Buda L. Dumortier J. Van der Eycken Arnold Venema Pat Sandra 《Journal of separation science》1994,17(2):72-73
Capillary GC on permethyl α-, β-, and γ-cyclodextrins has been applied to separate and quantify the enantiomers of some 2,3-iso-propylidene-1,2,3-cyclohexanetriol derivatives. Quantitative CGC data are compared to those obtained with chiral shift 1H NMR. 相似文献
18.
19.
Tohru OishiHiroshi Tsuchikawa Michio Murata Manabu YoshidaMasaaki Morisawa 《Tetrahedron letters》2003,44(34):6387-6389
A chemoattractant candidate named sperm-activating and attracting factor (SAAF) from the eggs of ascidian Ciona intestinalis, was synthesized from chenodeoxycholic acid in 16 steps. The present synthesis led to the unambiguous structure determination of SAAF to be (3R,4R,7R,25S)-3,4,7,26-tetrahydroxycholestane-3,26-disulfate. The synthetic pure specimen was also used to confirm the dual sperm-activating and attracting activity. 相似文献
20.
Robyn Pierce Kaye Stacey 《International Journal of Computers for Mathematical Learning》2004,9(1):59-93
This article suggests a framework to organise a cluster of variables that are associated with students' effective use of computer algebra systems (CAS) in mathematics learning. Based on a review of the literature and from the authors' own teaching experience, the framework identifies the main characteristics of students' interactions with CAS technology and how these may be used to monitor students' developing use of CAS; from this, the framework may be used to plan teaching in order to gain greater benefit from the availability of CAS. Four case studies describing students' development over a semester are reported. These demonstrate a variety of combinations of technical competencies and personal attributes. They indicate the importance of both the technical and personal aspects but suggest that negative attitudes rather than technical difficulties can limit the effective use of CAS. Finally practical suggestions are given for teaching strategies which may promote effective use of CAS.This revised version was published online in September 2005 with corrections to the Cover Date. 相似文献