全文获取类型
收费全文 | 9661篇 |
免费 | 2002篇 |
国内免费 | 3872篇 |
专业分类
化学 | 7256篇 |
晶体学 | 430篇 |
力学 | 919篇 |
综合类 | 639篇 |
数学 | 1653篇 |
物理学 | 4638篇 |
出版年
2024年 | 18篇 |
2023年 | 103篇 |
2022年 | 391篇 |
2021年 | 350篇 |
2020年 | 337篇 |
2019年 | 349篇 |
2018年 | 261篇 |
2017年 | 471篇 |
2016年 | 308篇 |
2015年 | 524篇 |
2014年 | 604篇 |
2013年 | 774篇 |
2012年 | 721篇 |
2011年 | 773篇 |
2010年 | 856篇 |
2009年 | 878篇 |
2008年 | 1033篇 |
2007年 | 888篇 |
2006年 | 897篇 |
2005年 | 813篇 |
2004年 | 596篇 |
2003年 | 473篇 |
2002年 | 468篇 |
2001年 | 467篇 |
2000年 | 489篇 |
1999年 | 266篇 |
1998年 | 160篇 |
1997年 | 115篇 |
1996年 | 119篇 |
1995年 | 108篇 |
1994年 | 101篇 |
1993年 | 103篇 |
1992年 | 103篇 |
1991年 | 57篇 |
1990年 | 66篇 |
1989年 | 76篇 |
1988年 | 71篇 |
1987年 | 64篇 |
1986年 | 46篇 |
1985年 | 36篇 |
1984年 | 31篇 |
1983年 | 31篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 16篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 7篇 |
1965年 | 7篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
1INTRoDUrnoNSomecomplexessynthesizedaccordingtotheideaof"combiningtheinorganicdistOrtedpoyhedronwithasymmetricconjugateorganicmo1ecules"areacategoryof,..promisingnonlinearopticalmaterialtl3.Thecomplexcrystalsareundoubtedlyanewimportantfieldfortheexplorationoffrequencydoublingandotherfunctionalmateri-alswhichwillbecomethefocusoftheworld'sattentiont2i.Inordertostudytherela-tionshipbetweenthestructure,synthesis,propertiesandapplicationsfurthermore,wereportthesynthesisandcrystalstructureofanewt… 相似文献
82.
A highly efficient Pd/C-catalyzed ligandless, heterogeneous Suzuki reaction of p-(un)substituted phenyl halide with (p-substituted phenyl)boronic acid in DMF/H2O solvent in a short reaction time (0.5 h) at 75 ℃ was developed. The key for such a catalytic system was the addition of 1 equivalent of tetrabutylammonium bromide. A wide variety of substituents can be tolerated and high yields of cross coupling products were achieved. The palladium catalyst can be easily recovered and reused without significantly decreasing its efficiency. 相似文献
83.
In this work, Ba(NO3)2 crystals with single crystal face were induced by using the the method of bio-mimetic mineralization and double LB films of behenic acid (BA) as the template. The crystals were characterized by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The crystals were observed in regular square shape with uniform size about 5~8 μm by SEM, and they were found by XRD to grow along the (111) plane. From these experiments, we can conclude that the good selection of the (111) crystal face of Ba(NO3)2 is due to the electrostatic interactions , the match between this crystal face and the definite lattice structure of the LB films. 相似文献
84.
N-Acyl-β-hydroxy-4-phenyl-oxazolidinethiones could be rapidly converted into their ethyl thiol esters in high yields by treatment with EtSH at 0 ℃ in CH3CN or 9 : 1 (V : V) THF-H2O in the presence of a catalytic amount of K2CO3. 相似文献
85.
86.
87.
水合醋酸铈直接热分解制备超细氧化铈及其抛光性能 总被引:3,自引:0,他引:3
Ultra fine ceria was prepared by calcining hydrate cerium acetate. The effects of pyrolysis temperature on the particle size, morphology, specific surface area and loose packing density of ceria were investigated, and the removal rate of optical glasses polishing by ceria was determined. The results show that with the increase of pyrolysis temperature, the loose deposit density and crystallinity increases and the specific surface area decreases, however, the particle size decreases firstly and then increases, the minimum medium particle size D50 is 0.47 μm at pyrolysis temperature of 1 000 ℃. The SEM images of ceria prepared by the decomposition at 800 ℃ or at 1 100 ℃ show porous powders or quasi-sphere small particles with loosely agglomeration, respectively. It was found that the removal rate varied with pyrolysis temperature in preparation of ceria and the property of glass polished. The removal rate for three kinds of glasses was in the order of ZF7> F1> K9, and the maximum value appeared at around 1 000 ℃ for ZF7 and F1, and at around 1 100 ℃ for K9. 相似文献
88.
89.
90.
基于精确的晶体结构数据并设定B=0.037nm以拟合经验参数R0是通常采用的键价参数推导方法.与此相反,作者提出从分子气相电子衍射的键长设定经验参数如然后从晶体结构数据拟合经验参数B.以Pb(II)-卤素键为例,PbX2气相电子衍射Pb—x(X=F,Cl,Br,I)键长分别为0.2036,0.2447,0.2598和0.2804nm,经拟合到最佳B值分别为0.0382,0.040,0.040,0.0386nm,与普适参数B值0.037nm有一定的差距.所提出的键价参数不仅得到比较理想的键价值和计算结果,而且保留了键价参数风作为单价键长明确的物理意义. 相似文献