全文获取类型
收费全文 | 1909篇 |
免费 | 281篇 |
国内免费 | 192篇 |
专业分类
化学 | 1382篇 |
晶体学 | 23篇 |
力学 | 122篇 |
综合类 | 15篇 |
数学 | 202篇 |
物理学 | 638篇 |
出版年
2024年 | 3篇 |
2023年 | 49篇 |
2022年 | 30篇 |
2021年 | 61篇 |
2020年 | 116篇 |
2019年 | 93篇 |
2018年 | 69篇 |
2017年 | 62篇 |
2016年 | 114篇 |
2015年 | 91篇 |
2014年 | 104篇 |
2013年 | 152篇 |
2012年 | 168篇 |
2011年 | 194篇 |
2010年 | 104篇 |
2009年 | 102篇 |
2008年 | 129篇 |
2007年 | 111篇 |
2006年 | 70篇 |
2005年 | 64篇 |
2004年 | 53篇 |
2003年 | 56篇 |
2002年 | 60篇 |
2001年 | 62篇 |
2000年 | 45篇 |
1999年 | 44篇 |
1998年 | 23篇 |
1997年 | 25篇 |
1996年 | 18篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1988年 | 7篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2382条查询结果,搜索用时 15 毫秒
11.
取代硫脲化合物对作物的生长调节作用 总被引:2,自引:0,他引:2
取代脲类化合物已广泛用作除草剂、杀虫剂、杀鼠剂。根据结构活性关系,亦对烯丙基、甲基、二芳基取代硫脲衍生物的植物生长调节活性进行了研究。本文合成了3类取代硫脲化合物:R_1NHCSNHR_2,其中:R_1=苯基,α-萘基,叔丁基,R_2=α-苯基乙 相似文献
12.
13.
14.
15.
Wu J Huang J Xiao Q Zhang S Xiao Z Li Q Long L Huang L 《Magnetic resonance in chemistry : MRC》2004,42(7):659-662
Ten phenylethanoid glycosides, including two new ones, isolated from the aerial parts of the mangrove plant Acanthus ilicifolius were identified. The first complete assignments of the 1H and 13C NMR chemical shifts for these glycosides were achieved by means of 2D NMR techniques, including 1H-1H COSY, TOCSY, HSQC and HMBC spectra. 相似文献
16.
17.
Single-crystalline and monodisperse LaF3 triangular nanoplates from a single-source precursor 总被引:3,自引:0,他引:3
Single-crystalline and monodisperse LaF3 triangular nanoplates (2.0 x 16.0 nm) in trigonal tysonite structure were synthesized by the thermolysis of a single-source precursor (SSP), La(CF3COO)3, in a hot oleic acid/octadecene solution. The combined use of SSP and coordinating and noncoordinating solvents was demonstrated to have played key roles in the formation of such high-quality nanoplates, which could spontaneously organize into two types of superlattices (edge-to-edge and face-to-face) on a large area. This SSP approach has advantages of one-step, mass production, and easy operation, and may represent a rather general route toward metal fluoride nanocrystals. 相似文献
18.
硫脲化合物的合成及其生物活性 总被引:13,自引:0,他引:13
硫脲化合物的合成及其生物活性董燕红,司宗兴(北京农业大学应用化学系北京100094)关键词噻二陛-甲酰基,硫脲,胺类,合成,生物活性酰基硫脲在抗真菌、抗结核、抗病毒、除草以及调节植物生长方面具有广泛应用[1,2]。1,2,3-噻二唑杂环作为有效前体正... 相似文献
19.
Biosynthesis of polyhydroxyalkanoates (PHAs) consisting of 3-hydroxyalkanoates (3HAs) of 4 to 10 carbon atoms was examined
in metabolically engineered Escherichia coli strains. When the fadA and/or fadB mutant E. coli strains harboring the plasmid containing the Pseudomonas sp. 61-3 phaC2 gene and the Ralstonia eutropha phaAB genes were cultured in Luria-Bertani (LB) medium supplemented with 2 g/L of sodium decanoate, all the recombinant E. coli strains synthesized PHAs consisting of C4, C6, C8, and C10 monomer units. The monomer composition of PHA was dependent on
the E. coli strain used. When the fadA mutant E. coli was employed, PHA containing up to 63 mol% of 3-hydroyhexanoate was produced. In fadB and fadAB mutant E. coli strains, 3-hydroxybutyrate (3HB) was efficiently incorporated into PHA up to 86 mol%. Cultivation of recombinant fadA and/or fadB mutant E. coli strains in LB medium containing 10 g/L of sodium gluconate and 2 g/L of sodium decanoate resulted in the production of PHA
copolymer containing a very high fraction of 3HB up to 95 mol%. Since the material properties of PHA copolymer consisting
of a large fraction of 3HB and a small fraction of medium-chain-length 3HA are similar to those of low-density polyethylene,
recombinant E. coli strains constructed in this study should be useful for the production of PHAs suitable for various commercial applications. 相似文献
20.
[reaction: see text] Addition of amines to the triple bond in alpha,alpha,alpha-trichloromethylpropargyl mesylate to give alpha,alpha-dichloromethylenaminones and its use in the preparation of 2-phenyl-4-dichloromethylquinolines in good yields are reported. 相似文献