全文获取类型
收费全文 | 42098篇 |
免费 | 3411篇 |
国内免费 | 4563篇 |
专业分类
化学 | 32483篇 |
晶体学 | 183篇 |
力学 | 513篇 |
综合类 | 683篇 |
数学 | 6741篇 |
物理学 | 9469篇 |
出版年
2023年 | 387篇 |
2022年 | 573篇 |
2021年 | 1551篇 |
2020年 | 1291篇 |
2019年 | 1252篇 |
2018年 | 958篇 |
2017年 | 985篇 |
2016年 | 1352篇 |
2015年 | 1397篇 |
2014年 | 1726篇 |
2013年 | 3221篇 |
2012年 | 2052篇 |
2011年 | 2272篇 |
2010年 | 2122篇 |
2009年 | 2539篇 |
2008年 | 2800篇 |
2007年 | 2965篇 |
2006年 | 2369篇 |
2005年 | 1716篇 |
2004年 | 1603篇 |
2003年 | 1574篇 |
2002年 | 1320篇 |
2001年 | 1238篇 |
2000年 | 888篇 |
1999年 | 708篇 |
1998年 | 666篇 |
1997年 | 533篇 |
1996年 | 604篇 |
1995年 | 539篇 |
1994年 | 543篇 |
1993年 | 567篇 |
1992年 | 540篇 |
1991年 | 351篇 |
1990年 | 299篇 |
1989年 | 236篇 |
1988年 | 252篇 |
1987年 | 201篇 |
1986年 | 213篇 |
1985年 | 324篇 |
1984年 | 236篇 |
1983年 | 145篇 |
1982年 | 290篇 |
1981年 | 468篇 |
1980年 | 425篇 |
1979年 | 466篇 |
1978年 | 370篇 |
1977年 | 283篇 |
1976年 | 237篇 |
1974年 | 76篇 |
1973年 | 150篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
K. S. Bruzik G. M. Salamończyk B. Soboń 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):39-42
Abstract The structure and the dynamics of D-erythrostearoyl sphingomyelin has been studied by the variable temperature wide-line 31P and high-resolution 1C CP MAS NMR apectroscopy. The results indicate the formation of the highly ordered, relaxed gelphase, and are interpreted based on the conformation of D-erytgrosphingomylin in the unaggregated state. 相似文献
992.
Purnima Dixit J. P. Tandon 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):389-395
Abstract Some organolead(IV) complexes derived from biologically active sulfur and nitrogen donor ligands have been synthesized and characterized by elemental analyses, molecular weight determinations and conductivity measurements. The trigonal bipyramidal and octahedral geometries for these complexes have been proposed on the basis of electronic, infrared and NMR (1H and 13C) spectral evidences. The antifungal activity of some of the ligands and their complexes have also been evaluated against Fursarium oxysporum SCW. ex Frics f. sp. Ciceri (Pedwick) subram. 相似文献
993.
Mohammad Ali Zolfigol Ardeshir Khazaei Arash Ghorbani-Choghamarani Amin Rostami 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2453-2458
The regeneration of carbonyl compounds from oximes were performed by using silica chromate and wet SiO 2 (w/w 50%) under microwave irradiation and solvent-free conditions with excellent yields. 相似文献
994.
Issa Yavari Ali A. Rounaqi Loghman Moradi 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2659-2662
Hexamethylenetetramine-bromine complex, a yellow-orange, very stable homogeneous solid, affects a mild and fairly general conversion of thiols to disulfides. 相似文献
995.
通过溶剂热法成功制备了一种基于金属有机骨架(MOF)的复合材料Cu-Cu2O/UiO-66-NH2,采用傅里叶变换红外光谱(FTIR)、X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)对材料进行全面表征。在空气作氧化剂条件下,以苯甲醇氧化为苯甲醛作为模型反应,系统地考察了溶剂、温度、催化剂各组分用量等因素对催化效果的影响。研究结果表明,该复合催化剂在醇选择性氧化反应中表现出优异的催化性能,60℃下反应5 h便可将苯甲醇定量转化为苯甲醛,并对其他苄基醇、烯丙基醇和杂芳基醇等底物也展现出良好活性。此外,循环利用3次后,该催化剂活性几乎不变,表明其具有良好的稳定性和重复使用性。 相似文献
996.
M. Aminul Haque 《合成通讯》2013,43(4):608-619
Abstract 3-Alkyl-substituted 2,4-pyrrolidinediones were directly oxidized under very mild manganese(III)-catalyzed aerobic oxidation conditions to give the corresponding 3-hydroperoxy-2,4-pyrrolidinediones in quantitative yields. The scope and limitations for the synthesis of the hydroperoxyprrolidinediones are described. 相似文献
997.
A protocol for the direct cross coupling of trialkylsilyl‐alkynes bearing electron‐withdrawing groups and aryl halides using a Pd/Ag catalytic system is described. The procedure allows the straightforward synthesis of a variety of alkynylphosphonates and aryl propiolates derivatives in good yields. 相似文献
998.
A facile, efficient oxidative deblocking of aldoximes and ketoximes to their corresponding aldehydes and ketones have been achieved by using silica gel supported chromium trioxide. 相似文献
999.
D. Missbach 《Isotopes in environmental and health studies》2013,49(5):195-202
An verschiedenen Systemen chemischer Verbindungen wurden Versuche zur Anreicherung des stabilen Isotopes 34S unter Verwendung der Ionenaustauscher Wofatit L 150, SBW und SBK nach den Methoden der Frontalchromatographie und der Bandenverdrāngungschromatographie ausgeführt. Beim Isotopenaustauschsystem Hydrogensulfit (am Ionenaustauscher)/Schwefeldioxid (in wäβriger Lösung) wurden Verfahrensweise und Betriebsparameter hinsichtlich des Anreicherungsgrades optimiert. Mit Hilfe einer einfachen Methode gelang es, aus den Versuchsergebnissen Werle für den elementaren Trennfaktor und die Trennstufenhöhe zu berechnen. 相似文献
1000.
Amitabh Jain 《辐射效应与固体损伤》2013,168(1-4):39-46
The potential advantages of ion implantation have been exploited in virtually every kind of semiconductor device. Several commercially important devices owe their existence to this technique. Ion implantation provides precise control over the amount of dopant, concentration profile and lateral dimensions in device fabrication. The high degree of uniformity and reproducibility have made it possible to produce sophisticated devices and integrated circuits with high yield and tight tolerances. This is a truly planar process. It is possible to achieve high doping concentrations with relatively lower processing temperatures thereby avoiding lifetime degradation. The process is carried out in an inherently clean environment. A wide range of dopants is available and one is not limited by the particular properties of the substrate. There is great flexibility in choice of masking materials and self-alignment of doped regions in MOS devices is facilitated. The increasing impact of ion implantation on device technology is discussed with reference to some recent developments. Specific commercially manufactured devices are mentioned. Ion implantation machines continue to undergo development aimed at higher throughputs and cleaner vacuum. There is the need for greater reliability of machines. Effort is also directed at the development of low cost machines for dedicated applications. Design of implanted devices continues to be an empirical process in some respects. The ability to accurately predict profile shapes in samples implanted (perhaps through a screen oxide) and subject to complicated post-implantation process steps, would cut down development time and costs. 相似文献