全文获取类型
收费全文 | 35165篇 |
免费 | 5708篇 |
国内免费 | 4828篇 |
专业分类
化学 | 26467篇 |
晶体学 | 527篇 |
力学 | 1816篇 |
综合类 | 352篇 |
数学 | 4042篇 |
物理学 | 12497篇 |
出版年
2024年 | 75篇 |
2023年 | 632篇 |
2022年 | 1048篇 |
2021年 | 1201篇 |
2020年 | 1425篇 |
2019年 | 1427篇 |
2018年 | 1192篇 |
2017年 | 1240篇 |
2016年 | 1687篇 |
2015年 | 1684篇 |
2014年 | 2086篇 |
2013年 | 2647篇 |
2012年 | 3261篇 |
2011年 | 3303篇 |
2010年 | 2496篇 |
2009年 | 2341篇 |
2008年 | 2533篇 |
2007年 | 2249篇 |
2006年 | 2184篇 |
2005年 | 1683篇 |
2004年 | 1282篇 |
2003年 | 1026篇 |
2002年 | 934篇 |
2001年 | 801篇 |
2000年 | 747篇 |
1999年 | 682篇 |
1998年 | 530篇 |
1997年 | 461篇 |
1996年 | 414篇 |
1995年 | 383篇 |
1994年 | 340篇 |
1993年 | 261篇 |
1992年 | 246篇 |
1991年 | 227篇 |
1990年 | 177篇 |
1989年 | 136篇 |
1988年 | 119篇 |
1987年 | 95篇 |
1986年 | 94篇 |
1985年 | 73篇 |
1984年 | 45篇 |
1983年 | 40篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 17篇 |
1979年 | 12篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 671 毫秒
101.
Wang Dunhui Huang Songling Han Zhida Su Zhenghua Wang Yi Du Youwei 《Solid State Communications》2004,131(2):97-99
A series of Gd(1−x)Bx alloys have been prepared by arc melting method. After introducing small quantity of B atom in Gd, the Curie temperature of these alloys increase while the magnetic entropy changes are almost same as that of Gd. The refrigerant capacities of these alloys are also greater than that of Gd. These results suggest that Gd(1−x)Bx alloys may be utilized as refrigerant in household magnetic refrigeration. 相似文献
102.
Imaging mass spectrometry requires the acquisition and interpretation of hundreds to thousands of individual spectra in order to map the mineral phases within heterogeneous geomatrices. A fuzzy logic inference engine (FLIE) was developed to automate data interpretation. To evaluate the strengths and limitations of FLIE, the chemical images obtained using FLIE were compared with those developed using two chemometric methods: principle component analysis (PCA) and cluster analysis (K-Means). Two heterogeneous geomatrices, a low-grade chalcopyrite ore and basalt, were imaged using a laser-desorption Fourier transform mass spectrometer. Similar mineral distribution patterns in the chalcopyrite ore sample were obtained by the three data analysis methods with most of the differences occurring at the interfaces between mineral phases. PCA missed one minor mineral phase in the chalcopyrite ore sample and did not clearly differentiate among the mineral classes of the basalt. K-Means cluster analysis differentiated among the various mineral phases in both samples, but improperly grouped some spectra in the chalcopyrite sample that only contained unanticipated high mass peaks. Unlike the chemometric methods, FLIE was able to classify spectra as unknowns for those spectra that fell below the confidence level threshold. A nearest neighbor approach, included in FLIE, was used to classify the unknowns to form a visually complete image; however, the unknowns identified by FLIE can be informative because they highlight potential problems or overlooked results. In conclusion, this study validated the fuzzy logic-based approach used in our laboratory and reveald some limitations in the three techniques that were evaluated. 相似文献
103.
采用固相反应合成了四羟基苯基卟啉与与Fe^2+,Co^2+金属离子的配合物,在室温下,将其与分子O2作用,提纯后得到两种固态氧合配合物.通过元素分析、红外光谱(IR)、核磁共振氢谱(^1HNMR)、电导、热分析(TG/DTA)、紫外光谱(UV)等测试手段确定了氧合配合物的组成为[Co·THPP·O2](NO3)2·2H2O、[Fe·THPP·O2]Cl2·2H2O],可知1mol配合物吸收了1molO2,采用失重法测定了氧合配合物中的配位氧,确定1mol金属配合物吸收1molO2形成超氧配合物. 相似文献
104.
Dingzhu Du 《应用数学学报(英文版)》1989,5(4):355-360
Lower bounds for Byzantine agreement obtained by Dolev and Strong are shown, by a simpler method, also to be true for weak Byzantine agreement.This work was done while the author was studying at University of California, Santa Barbara, in 1984. 相似文献
105.
106.
107.
108.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献
109.
对Sn-C60薄膜进行紫外可见光吸收,X-射线衍射和扫描电镜的测定结果显示,薄膜样品紫外可见光吸收的两个短波段吸收峰比纯C60薄膜的吸收峰显著下降,说明Sn-C60薄膜的电子光吸收跃迁为间接跃迁,能带中有杂质能级的存在;样品的X射线衍射峰则对应于面心立方结构;扫描电镜结果显示薄膜为纳米级颗粒组成。 相似文献
110.
利用离子速度成像方法,研究CH2I2分子在277—305nm范围内若干波长处的光解离动力学.通过同一束激光经(2+1)共振多光子电离(REMPI)过程探测光解碎片I(2P32)和I(2P12),得到了不同激发波长处的离子速度分布图像,从而获得CH2I2光解产物的能量分配和角分布.实验发现,碎片CH2I自由基有很高的内能激发,约占总可资用能的80%,该能量分配可以较好地用冲击模型来解释.实验还发现,产物I(2P32)和I(2P12)具有很不相同的平动能分布,结合所得到的碎片能量分配和角分布,我们对碎片I(2P32)和I(2P12)生成机理进行了分析,指出CH2I2分子电子激发态的绝热和非绝热解离决定了碎片的平动能分布.
关键词:
CH2I2
离子速度成像
绝热和非绝热解离 相似文献