全文获取类型
收费全文 | 9369篇 |
免费 | 1539篇 |
国内免费 | 1262篇 |
专业分类
化学 | 6891篇 |
晶体学 | 147篇 |
力学 | 424篇 |
综合类 | 108篇 |
数学 | 1074篇 |
物理学 | 3526篇 |
出版年
2024年 | 37篇 |
2023年 | 155篇 |
2022年 | 326篇 |
2021年 | 331篇 |
2020年 | 360篇 |
2019年 | 428篇 |
2018年 | 306篇 |
2017年 | 303篇 |
2016年 | 424篇 |
2015年 | 497篇 |
2014年 | 595篇 |
2013年 | 723篇 |
2012年 | 889篇 |
2011年 | 869篇 |
2010年 | 678篇 |
2009年 | 666篇 |
2008年 | 721篇 |
2007年 | 634篇 |
2006年 | 551篇 |
2005年 | 426篇 |
2004年 | 376篇 |
2003年 | 277篇 |
2002年 | 255篇 |
2001年 | 202篇 |
2000年 | 142篇 |
1999年 | 147篇 |
1998年 | 110篇 |
1997年 | 91篇 |
1996年 | 107篇 |
1995年 | 100篇 |
1994年 | 77篇 |
1993年 | 68篇 |
1992年 | 59篇 |
1991年 | 46篇 |
1990年 | 40篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 19篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 9篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1959年 | 1篇 |
1957年 | 2篇 |
1936年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Coating Carbon Nanotubes with Europium Oxide 总被引:4,自引:0,他引:4
HuiQunCAO GuangYanHONG JingHuiYAN JiLinZHANG GuiXiaLIU 《中国化学快报》2003,14(12):1293-1295
Carbon nanotubes (CNTS) coating with europium oxide by a simple method is reported in this letter for the first time. The CNTS were refluxed in a solution of nitric acid containing europium nitrate, and the pH value was subsequently ajusted with ammonia solution. At last, the mixture was filtered and annealed. The TEM micrograph showed that the CNTS were covered with a uniform thin layer with thickness of about 15 nm. The XRD results revealed that the CNTS were coated with europium oxide. 相似文献
62.
Chun‐Xiang Wang Chen‐Xia Du Zhi‐Feng Li 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):m488-m490
In the title compound, [Zn(C17H10N5O)2(H2O)2]·4H2O, cyclic water hexamers forming one‐dimensional metal–water chains are observed. The water clusters are trapped by the co‐operative association of coordination interactions and hydrogen bonds. The ZnII ion resides on a centre of symmetry and is in an octahedral coordination environment comprising two O atoms and two N atoms from two 2′‐(4,5‐diazafluoren‐9‐ylidene)picolinohydrazidate ligands and two water molecules. 相似文献
63.
The goal of this study was to investigate the effect of photothermal laser irradiation on rat breast tumor (DMBA-4) vascular contents. An 805-nm diode laser was used in our experiment with a power density ranging from 0.32 to 1.27 W/cm2. The dynamic changes of oxygenated hemoglobin and total hemoglobin concentrations, delta[HbO2] and delta[Hb]total, in rat tumors during photothermal irradiation were noninvasively monitored by a near-infrared spectroscopy system. A multichannel thermal detection system was also used simultaneously to record temperatures at different locations within the tumors. Our experimental results showed that: (1) photoirradiation did have the ability to induce hyperthermic effects inside the rat breast tumors in a single exponential trend; (2) the significant changes (P < 0.005) of delta[HbO2] and delta[Hb]total in response to a low dosage of laser irradiation (0.32 W/cm2) have a single exponential increasing trend, similar to that seen in the tumor interior temperature; and (3) the increase in magnitude of delta[HbO2] is nearly two times greater than that of delta[Hb]total, suggesting that photoirradiation may enhance tumor vascular oxygenation. The last observation may be important to reveal the hidden mechanism of photoirradiation on tumors, leading to improvement of tumor treatment efficiency. 相似文献
64.
Six new ent‐abietane diterpenoids, rubescensins I–M ( 1 – 5 ) and P ( 6 ), along with two related acetonide derivatives ( 7 and 8 ), were isolated from Isodon rubescens. Their structures were elucidated by detailed spectroscopic analysis. Compound 5 is the first N‐containing diterpenoid from the genus Isodon, exhibiting notable cytotoxicity against human tumor K562 cells. 相似文献
65.
含羧酸配体的鼓形有机锡氧簇合物:六聚苯基锡氧3-吲哚丁酸酯的合成及晶体结构 总被引:7,自引:0,他引:7
利用Ph3SnOH和3-吲哚丁酸以1:1摩尔比反应,合成了新型含羧酸配体的鼓形 有机锡氧簇合物:六聚苯基锡氧3-吲哚西酸酯。通过元素分析、红外光谱和X射线 单晶衍射对其结构进行了表征。测试结果表明:该化合物为三斜晶系,空间群P1, a=1.1722(6),b=1.5694(8)nm,c=1.7227(9)nm,α=116.251(8)°,β=100. 854(10)°,γ=95.606(9)°,Z=1,V=2.732(3)nm^3,Dc=1.554g·cm^-3,μ =1.420mm^-1,F(000)=1276,R=0.0630,ωR=0.0762。晶体结构中,六配位的锡原 子呈畸变的八面体构型。 相似文献
66.
K. W. Cheah L. C. Ho J. B. Xia J. Li W. H. Zheng W. R. Zhuang Q. M. Wang 《Applied Physics A: Materials Science & Processing》1995,60(6):601-606
Photoluminescence studies on porous silicon show that there are luminescence centers present in the surface states. By taking photoluminescence spectra of porous silicon with respect to temperature, a distinct peak can be observed in the temperature range 100–150 K. Both linear and nonlinear relationships were observed between excitation laser power and the photoluminescence intensity within this temperature range. In addition, there was a tendency for the photoluminescence peak to red shift at low temperature as well as at low excitation power. This is interpreted as indicating that the lower energy transition becomes dominant at low temperature and excitation power. The presence of these luminescence centers can be explained in terms of porous silicon as a mixture of silicon clusters and wires in which quantum confinement along with surface passivation would cause a mixing of andX band structure between the surface states and the bulk. This mixing would allow the formation of luminescence centers. 相似文献
67.
Cr1-x
Fe
x
and Mn1-x
Fe
x
films were prepared at room temperature by thermal coevaporation at a deposition rate of about 25 Å/min. It was found that an amorphous phase can be obtained for Cr1-x
Fe
x
(0.25<x<0.60) films, while a metastable-Mn-type phase was observed for Mn1-x
Fe
x
(x<0.70) films. The influence of the structure on the magnetic properties has been studied. The amorphization ability of the two systems was discussed in terms of thermodynamic considerations. 相似文献
68.
69.
Daoxing Xia 《Proceedings of the American Mathematical Society》1996,124(6):1743-1753
The generalized cyclic cohomology is introduced which is associated with -deformed commutators . Some formulas related to the trace of the product of -deformed commutators are established. The Chern character of odd dimension associated with -deformed commutators is studied.
70.