全文获取类型
收费全文 | 21801篇 |
免费 | 584篇 |
国内免费 | 175篇 |
专业分类
化学 | 15315篇 |
晶体学 | 168篇 |
力学 | 660篇 |
数学 | 3136篇 |
物理学 | 3281篇 |
出版年
2022年 | 143篇 |
2021年 | 220篇 |
2020年 | 300篇 |
2019年 | 270篇 |
2018年 | 234篇 |
2017年 | 197篇 |
2016年 | 417篇 |
2015年 | 359篇 |
2014年 | 409篇 |
2013年 | 1001篇 |
2012年 | 1096篇 |
2011年 | 1454篇 |
2010年 | 676篇 |
2009年 | 595篇 |
2008年 | 1189篇 |
2007年 | 1211篇 |
2006年 | 1291篇 |
2005年 | 1233篇 |
2004年 | 1055篇 |
2003年 | 944篇 |
2002年 | 933篇 |
2001年 | 314篇 |
2000年 | 291篇 |
1999年 | 220篇 |
1998年 | 250篇 |
1997年 | 249篇 |
1996年 | 320篇 |
1995年 | 246篇 |
1994年 | 237篇 |
1993年 | 189篇 |
1992年 | 194篇 |
1991年 | 202篇 |
1990年 | 159篇 |
1989年 | 142篇 |
1988年 | 174篇 |
1987年 | 171篇 |
1986年 | 129篇 |
1985年 | 252篇 |
1984年 | 278篇 |
1983年 | 208篇 |
1982年 | 277篇 |
1981年 | 264篇 |
1980年 | 266篇 |
1979年 | 229篇 |
1978年 | 242篇 |
1977年 | 210篇 |
1976年 | 215篇 |
1975年 | 194篇 |
1974年 | 193篇 |
1973年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
951.
Previous work has demonstrated that alkylated benzene sulfonanilides undergo sulfuric acid (98%)–catalyzed rearrangement to alkylamino diaryl sulfones. Similar treatment of their unalkylated analogs typically leads only to hydrolysis. Surprisingly, when the unalkylated benzene sulfonanilides react with triflic acid, rearrangement to sulfones does occur. 相似文献
952.
Pei Gan Myles W. Smith Nathaniel R. Braffman Scott A. Snyder 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(11):3689-3694
Although the Diels–Alder reaction has long been utilized for the preparation of numerous heterocycles, opportunities to extend its power remain. Herein, we detail a simple, modular, and robust approach that combines various amines regioselectively with 4,6‐dichloropyrone to create substrates which, under appropriate conditions, can directly deliver varied indolines and hydroindolines through [4+2] cycloadditions with substitution patterns difficult to access otherwise. As an initial demonstration of the power of the strategy, several different natural products have been obtained either formally or by direct total synthesis, with efforts toward one of these—the complex amaryllidaceae alkaloid gracilamine—affording the shortest route to date in terms of linear step count. 相似文献
953.
Thibaut Van Acker Stijn J.M. Van Malderen Marjolein Van Heerden James Eric McDuffie Filip Cuyckens Frank Vanhaecke 《Analytica chimica acta》2016
Two-dimensional elemental mapping (bioimaging) via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was performed on 5 μm thick formalin-fixed, paraffin-embedded kidney tissue sections from Cynomolgus monkeys administered with increasing pharmacological doses of cisplatin. Laterally resolved pixels of 1 μm were achieved, enabling elemental analysis on a (sub-)cellular level. Zones of high Pt response were observed in the renal cortex, where proximal tubules are present, the epithelium of which is responsible for partial reabsorption of cisplatin. Histopathological evaluation, of hematoxylin and eosin-stained serial sections, adjacent to the sections probed via LA-ICP-MS, revealed minimal to mild cisplatin-related lesions (<100 μm) in the renal cortex. Necrotic proximal tubules with sloughed epithelial cells in their lumen could be linked directly to the areas with the highest accumulation of cisplatin, indicating a direct link between cellular concentration and toxicity, thereby providing more insight into the mechanisms through which renal damage occurs. 相似文献
954.
Relatively few constructions are known of negative Latin square type Partial Difference Sets (PDSs), and most of the known constructions are in elementary abelian groups. We present a product construction that produces negative Latin square type PDSs, and we apply this product construction to generate examples in p-groups of exponent bigger than p. 相似文献
955.
956.
957.
John T. Gupton James G. Tarrant Richard H. Yu Traci L. Solarz Hak-Fun Chow 《合成通讯》2013,43(22):3205-3214
An efficient and convenient synthesis of chain lengthened homologs of the important fungicide Metalaxyl is described. The starting material utilized is 2,6-dimethylaniline and the sequence is accomplished utilizing Grignard reactions and ruthenium based oxidations to obtain the proper analogs. 相似文献
958.
This investigation describes the reduction of an aryl thiocyanate with samarium(II) iodide, followed by reaction with various epoxides, to produce β-hydroxy sulfides. This method of ring opening of epoxides provides a substantial improvement in reaction time and convenience over existing methods while maintaining good regioselectivity and excellent yield. 相似文献
959.
960.