全文获取类型
收费全文 | 32115篇 |
免费 | 5045篇 |
国内免费 | 5280篇 |
专业分类
化学 | 25398篇 |
晶体学 | 472篇 |
力学 | 1401篇 |
综合类 | 511篇 |
数学 | 3504篇 |
物理学 | 11154篇 |
出版年
2024年 | 75篇 |
2023年 | 438篇 |
2022年 | 880篇 |
2021年 | 919篇 |
2020年 | 1054篇 |
2019年 | 1143篇 |
2018年 | 964篇 |
2017年 | 903篇 |
2016年 | 1466篇 |
2015年 | 1567篇 |
2014年 | 1776篇 |
2013年 | 2439篇 |
2012年 | 2728篇 |
2011年 | 2850篇 |
2010年 | 2099篇 |
2009年 | 2092篇 |
2008年 | 2400篇 |
2007年 | 2172篇 |
2006年 | 2057篇 |
2005年 | 1771篇 |
2004年 | 1544篇 |
2003年 | 1375篇 |
2002年 | 1512篇 |
2001年 | 1154篇 |
2000年 | 966篇 |
1999年 | 746篇 |
1998年 | 467篇 |
1997年 | 458篇 |
1996年 | 396篇 |
1995年 | 342篇 |
1994年 | 296篇 |
1993年 | 270篇 |
1992年 | 226篇 |
1991年 | 163篇 |
1990年 | 146篇 |
1989年 | 123篇 |
1988年 | 73篇 |
1987年 | 77篇 |
1986年 | 64篇 |
1985年 | 55篇 |
1984年 | 34篇 |
1983年 | 27篇 |
1982年 | 17篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1978年 | 11篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1975年 | 8篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
The structures of several sulfones, including dimethyl sulfone, methyl ethyl sulfone, methyl vinyl sulfone, and diphenyl sulfone, have been fit with the MM3 force field to existing experimental data from electron diffraction and microwave spectroscopy. The vibrational spectra have also been fit for six of these compounds. The torsional parameters for the aliphatic sulfones were fit to ab initio 6-31G data. Heats of formation were also fit. © 1993 John Wiley & Sons, Inc. 相似文献
932.
S. M. Jeong S.-B. Park S.-S. Hong C.-S. Seo S.-W. Park 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):349-356
Summary The
electrolytic reduction of U3O8 powder was carried out
using LiCl-Li2O molten salt in a 20-kg U3O8
batch cell to verify the feasibility of the process. As the current passes the
cell, the decomposition of Li2O and the reduction of U3O8
occur simultaneously in a cathode assembly and oxygen gas evolvs at the anode.
The results from a 20-kg U3O8 scale cell were compared
with data obtained from a bench scale cell. The results suggest a successful
demonstration of this process, exhibiting a reduction conversion of U3O8
of more than 99% in a batch.</p>
</p> 相似文献
933.
ICP-AES determination of trace elements after preconcentrated with p-dimethylaminobenzaldehyde-modified nanometer SiO2 from sample solution 总被引:1,自引:0,他引:1
A new method that utilizes p-dimethylaminobenzaldehyde-modified nanometer SiO2 (SiO2-p-DMABD) as a solid phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). The preconcentration conditions of analytes were investigated, including the pH value, the shaking time, the mass of sorbent, the sample flow rate and volume, the elution condition and the interfering ions. The adsorption capacity of nanometer SiO2-p-DMABD was found to be (mg g− 1) Cr(III): 6.2, Cu(II): 18.6, Fe(III): 4.7 and Pb(II): 6.0 at pH 4. The adsorbed metals were quantitatively eluted with 4 mL of 1.0 mol L− 1 HCl. According to the definition of IUPAC, the detection limits (3σ) of this method for Cr(III), Cu(II), Fe(III) and Pb(II) were 0.79, 1.27, 0.40 and 1.79 ng mL− 1, respectively. The proposed method achieved satisfied results when it was applied to the determination of trace Cr(III), Cu(II), Fe(III) and Pb(II) in biological and water samples. 相似文献
934.
在水介质中,研究了新型的过氧化氢/N-甲基苯胺盐酸盐引发体系对 AM 与 PVA 的接枝共聚。产物经紫外光谱、红外光谱和 ~1H-核磁共振进行表征,并提出了引发机理。 相似文献
935.
无光敏剂光引发亲水性单体在嵌段聚醚氨酯膜上接枝聚合的研究 总被引:3,自引:0,他引:3
<正> 嵌段聚醚氨酯(SPEU)是一类应用广泛的医用高分子材料。用亲水性单体进行表面接枝改性,已有不少研究,接枝聚合方法有铈盐引发、辐射引发以及光敏引发等。 本文研究一种新的接枝方法,不加光敏剂,用紫外光照射,直接引发亲水性单体接枝于SPEU膜上、接枝的单体有丙烯酰胺(AAM)与N,N-二甲基丙烯酰胺(DMAA),从接枝前后膜的性能变化可以证实接枝反应的发生。文中研究了反应条件与单体结构对接枝率的影响,并通过模型化合物,对接枝部位进行了研究。 相似文献
936.
芳香二磺酸的配位化学研究化合物[Ni(cyclam)(1,5nds)]·1/3H_2O(1)和[Co(cyclam)(H_2O)_2](1,5nds)·2H_2O(2)的合成与结构(英文)
下载免费PDF全文
![点击此处可从《无机化学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
合成了两个二价的过渡金属磺酸化合物,并通过X-射线衍射单晶结构分析进行结构表征。化合物犤Ni(cyclam)(1,5nds)犦·1/3H2O(1)以P2(1)/c空间群结晶,晶胞参数为a=8.583(5),b=10.533(6),c=12.946(7)?,β=92.433(9)°。犤Ni(cyclam)犦2+与两个磺酸基团形成弱配位,从而构筑了一维的配聚物。犤Ni(cyclam)犦2+与磺酸基团之间的作用还通过O2S-O…H-N型氢键进一步被加强。化合物犤Co(cyclam)(H2O)2犦(1,5nds)·2H2O(2)以P1珔空间群结晶,晶胞参数为a=8.738(5),b=9.324(5),c=10.118(5)?,α=81.382(8),β=64.868(8),γ=62.999(8)°。在该化合物中,磺酸基团没有与Co2+形成配位键,而是以平衡离子的形式存在并与配离子形成氢键,构筑了有序的三维结构。 相似文献
937.
Qi FANG* Hong LEI Wen XU State Key Laboratory of Crystal Materials Shandong University Jinan School of Information Science Engineering Shandong University Jinan 《中国化学快报》2003,(11)
It was commonly thought that a molecular conductor or semiconductor should be composed of at least two components to make the conducting component in partially charged state. However, this idea became questionable by the recent report of the single-component molecular conductor [Ni(tmdt)2]1 as well as several reports about single-component molecular semiconductors such as [Ni(ptdt)2]2 and [Ni(C10H10S8)2]3. In fact, as early as 1985, [Ni(dmit)2] as a by-product in synthesizing TTF[Ni(dmit… 相似文献
938.
The development of broadly applicable and practical catalytic approaches for the enantioselective creation of quaternary stereocenters remains a highly desirable yet challenging goal. In this Communication, we describe a highly enantioselective cyanosilylation of acetal ketones (alpha,alpha-dialkoxy ketones) catalyzed by modified cinchona alkaloids. This reaction is the first highly enantioselective cyanosilylation of ketones catalyzed by an organic chiral Lewis base and is found to be highly efficient with acetal ketones bearing a broad range of alkyl, aryl, alkenyl, and alkynyl substituents. This new catalytic asymmetric reaction, coupled with the versatility of the acetal functionality, provides a broadly useful synthetic method for chiral building blocks bearing quaternary stereocenters. Acetal ketones, readily accessible but previously unexplored in asymmetric synthesis, demonstrate unusual reactivity and selectivity toward the nucleophilic cyanosilylation, thereby suggesting that they may be interesting substrates for other catalytic enantioselective reactions. 相似文献
939.
CoCl_2·6H_2O or LaCl_3·7H_2O Catalyzed Biginelli Reaction. One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1 H)-ones 总被引:1,自引:0,他引:1
Introduction1,4 Dihydropyridinesofthenifedipinetype (e .g .I—III)arethemoststudiedclassoforganiccalciumchannelmedicine ,whichhavebecomealmostindispens ableforthetreatmentofcardiovasculardiseasessuchashypertension ,cardiacarrhythmias ,orangina .1Inthepastdecade… 相似文献
940.
Jun Yue Bai Liang Wang Hong Jing Wang Peng Fei Huang Yu Qing Zhao Sheng Di Fan 《Mikrochimica acta》2006,156(3-4):321-326
The electrochemical behavior of epinephrine (EP) at a mercaptoacetic acid (MAA) self-assembled monolayer modified gold electrode
was studied. The MAA/Au electrode is demonstrated to promote the electrochemical response of epinephrine by cyclic voltammetry.
The possible reaction mechanism is also discussed. The diffusion coefficient D of EP is 6.85 × 10−6 cm2 s−1. In 0.1 mol L−1 phosphate buffer (pH 7.20), a sensitive oxidation peak was observed at 0.177 V, and the peak current is proportional to the
concentration of EP in the range of 1.0 × 10−5–2.0 × 10−4 mol L−1 and 1.0 × 10−7–1.0 × 10−6 mol L−1. The detection limit is 5 × 10−8 mol L−1. The modified electrode is highly stable and can be applied to the determination of EP in practical injection samples. The
method is simple, quick, sensitive and accurate. 相似文献