全文获取类型
收费全文 | 21267篇 |
免费 | 4113篇 |
国内免费 | 6914篇 |
专业分类
化学 | 15259篇 |
晶体学 | 804篇 |
力学 | 1556篇 |
综合类 | 927篇 |
数学 | 3324篇 |
物理学 | 10424篇 |
出版年
2024年 | 69篇 |
2023年 | 257篇 |
2022年 | 748篇 |
2021年 | 733篇 |
2020年 | 784篇 |
2019年 | 729篇 |
2018年 | 704篇 |
2017年 | 1061篇 |
2016年 | 818篇 |
2015年 | 1003篇 |
2014年 | 1232篇 |
2013年 | 1610篇 |
2012年 | 1668篇 |
2011年 | 1795篇 |
2010年 | 1755篇 |
2009年 | 1762篇 |
2008年 | 2032篇 |
2007年 | 1769篇 |
2006年 | 1794篇 |
2005年 | 1571篇 |
2004年 | 1162篇 |
2003年 | 876篇 |
2002年 | 911篇 |
2001年 | 972篇 |
2000年 | 918篇 |
1999年 | 574篇 |
1998年 | 334篇 |
1997年 | 252篇 |
1996年 | 282篇 |
1995年 | 211篇 |
1994年 | 221篇 |
1993年 | 192篇 |
1992年 | 212篇 |
1991年 | 146篇 |
1990年 | 156篇 |
1989年 | 118篇 |
1988年 | 120篇 |
1987年 | 138篇 |
1986年 | 95篇 |
1985年 | 69篇 |
1984年 | 82篇 |
1983年 | 71篇 |
1982年 | 57篇 |
1981年 | 48篇 |
1980年 | 34篇 |
1979年 | 36篇 |
1978年 | 18篇 |
1977年 | 15篇 |
1965年 | 13篇 |
1964年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
本文通过异氰酸酰化反应合成了含有脲基的苯乙炔新型配体及以它作为辅助配体的4′-(对甲基苯基)-6-苯基-2,2′-二联吡啶铂(II)络合物,初步研究了铂(II)络合物的光物理性质,发现由于脲基的存在,当浓度大于3.32×10-5mol/L时铂(II)络合物能够发生分子间簇集. 相似文献
102.
103.
TCDD的密度泛函理论研究 总被引:3,自引:0,他引:3
用B3LYP/6-311G~(**)方法全优经计算22个四氯二苯并对二(左口右恶)英( 简称TCDD)分子,得到几何构型、总能量、标准熵、标准焓和标准自由能。将2, 3,7,8-TCDD的计算构型与X射线衍射实验测定值进行了比较。计算结果表明,总 能量、标准焓和标准自由能与氯原子量换位置的相关性很高(r > 0.997).1,3,6, 8-TCDD的总能量处自由能最低,即最稳定,以此参照,得到异构体的总能量的相对 稳定性顺序和自由能的相对稳定性顺序。1,3,7,9-TCDD的稳定性次之,1,3,7,8- TCDD居第三,将这二个顺序与焚烧炉产生的TCDD异构体和合成的异构体对的生成面 分比进行了比较,说明焚烧炉中产生的TCDD和合成的TCDD对的分布主要受热力学控 制。 相似文献
104.
105.
106.
HUANG Xi-He SHENG Tian-Lu XIANG Sheng-Chang FU Rui-Biao HU Sheng-Min LI Ya-Min WU Xin-Tao ② 《结构化学》2007,26(2):161-164
The hydrothermal reaction of 1,2-dicyanobenzene with NaN3 in the presence of CuCl2, 2,2′-bipyridine and H2O affords a novel dinuclear copper(II)-ditetrazolate, [Cu(bpy)- (pdtz)]2 (Hpdtz = 5,5′-1,2-phenylene-ditetrazole, bpy = 2,2′-bipyridine). The pdtz ligand is generated in situ through Sharpless 2 3 cycloaddition reaction. Its crystal structure was deter- mined by single-crystal X-ray diffraction method. The crystal crystallizes in the monoclinic system, space group P21/n with a = 8.2096(16), b = 18.580(4), c = 11.838(2) , β = 103.12(3)o, V = 1758.5(6) 3, Z = 2, Mr = 863.83, Dc = 1.631 g/cm3, F(000) = 876 and μ = 1.272 mm-1. In this novel dinuclear structure, the pdtz ligand adopts a peculiar μ2-η1,η2 coordination mode. 相似文献
107.
烷基季铵盐插层剂的合成及应用 总被引:1,自引:0,他引:1
Three novel intercalation agents were synthesized for the first time, which arose from oleic acid diethylenetriamine or triethylenetetramine 3 - chloro - 2 - hydroxypropy trimethylammonium choride (CHPTA) and chloroethanol. Organophilic vermicullites were synthesized from sodium type vermiculite by cation exchange with new intercalation agents. The results of X - ray diffraction study showed that the gallery distance of the organophilic vermiculite was enlarged from 1 nm to 5 nm or more. A new idea of making design for intercalation agent was provided. 相似文献
108.
109.
In order to contribute to the Apparent Polar Wander Path (APWP) of the North China Block (NCB) , we collected paleomagnetic samples of Late Paleozoic rocks from the northern and southern margins of the Alashan (Alxa) terrane (the western part of Inner Mongolia and northern parts of Gansu and Ningxia Provinces) and adjacent regions. Laboratory work revealed different types of demagnetization behavior and isolated a higher temperature characteristic component in most of the samples. Results of IRM experiments show high thermal stability and high coercivities for the magnetic carriers in these rocks. The characteristic component passed the fold and/or reversal tests, suggesting that the characteristic components were probably primary. On the basis of comparing the paleomagnetic results with the geologic evidence, we discuss the tectonic implications. In the Late Paleozoic, the Alashan region had been part of the NCB and was not connected with the northern and southern blocks. During the Carboniferous Alash 相似文献
110.
Expression of foreign genes transferred into mammalian cells by electroporation has been studied. The pX1TK gene, pSV2Neo gene and pUCEJ oncogene have been introduced into MLTK-cells and NIH/3T3 cells, respectively. Stable transformation transient expression of TK gene by MLTK-cells as well as stable and malignant transformation of NIH/3T3 cells have been obtained. Transient expression frequency is about 80% and stable transformation frequency is about 10~(-4). Integration of foreign genes into the cellular genome was verified with molecular hybridization. Tumor development was observed after inoculation of transformed celts into nude mice. 相似文献