全文获取类型
收费全文 | 34796篇 |
免费 | 2497篇 |
国内免费 | 6篇 |
出版年
2023年 | 262篇 |
2022年 | 450篇 |
2021年 | 1053篇 |
2020年 | 786篇 |
2019年 | 901篇 |
2018年 | 1131篇 |
2017年 | 1016篇 |
2016年 | 1416篇 |
2015年 | 1963篇 |
2014年 | 2059篇 |
2013年 | 2400篇 |
2012年 | 2911篇 |
2011年 | 2651篇 |
2010年 | 1667篇 |
2009年 | 1488篇 |
2008年 | 1913篇 |
2007年 | 1849篇 |
2006年 | 1695篇 |
2005年 | 1446篇 |
2004年 | 1369篇 |
2003年 | 1202篇 |
2002年 | 1112篇 |
2001年 | 515篇 |
2000年 | 432篇 |
1999年 | 420篇 |
1998年 | 253篇 |
1997年 | 238篇 |
1996年 | 201篇 |
1995年 | 168篇 |
1994年 | 174篇 |
1993年 | 136篇 |
1992年 | 203篇 |
1991年 | 169篇 |
1990年 | 130篇 |
1989年 | 143篇 |
1988年 | 115篇 |
1987年 | 116篇 |
1986年 | 91篇 |
1985年 | 108篇 |
1984年 | 130篇 |
1983年 | 70篇 |
1982年 | 72篇 |
1981年 | 62篇 |
1980年 | 52篇 |
1979年 | 58篇 |
1978年 | 55篇 |
1977年 | 43篇 |
1976年 | 44篇 |
1975年 | 53篇 |
1973年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
The N-terminus of Ciona intestinalis (Ci-VSP) is a voltage-sensing domain (VSD) controlling the activity of a phosphatase domain on the C terminus. By replacing the phosphatase domain with a tandem of fluorescent proteins, CFP and YFP, a family of fluorescence resonance energy transfer-based, genetically encoded voltage-sensing fluorescent protein (VSFP) was created. VSFP2.3, one of the latest versions of this family, showed large changes in YFP emission upon changes in membrane potential with CFP excitation when expressed in Xenopus laevis oocytes. The time course of the fluorescence has two components: the fast component correlates with the time course of sensing current produced by the charge movement, while the slow component is at least one order-of-magnitude slower than the sensing current. This suggests that the tandem of fluorescent proteins reports a secondary conformational transition of the VSD which resembles the relaxation of the VSD of Ci-VSP described in detail for the Ci-VSP. This observation indicates that the relaxation of the VSD of VSFP2.3 is a global conformational change that encompasses the entire S4 segment. 相似文献
42.
43.
44.
45.
46.
47.
Samples of microphytobenthos from the Tagus estuary were analysed for photosynthetic pigments by spectrophotometry and High
Performance Liquid Chromatography (HPLC). Chlorophyll a values obtained with HPLC and spectrophotometry methods presented a highly significant positive correlation for both spectrophotometric
methods used (with and without the correction for pheopigments), but this relationship depended on the type of sediment. We
concluded that spectrophotometric methods give reliable Chl-a values, being suited for routine analysis, when a vast number of replicates is needed. However, for the correct estimation
of pheopigments, HPLC analysis is indispensable. In the literature, Chl-a estimations are expressed per content (μg g−1) or concentration (mg m−2). We discuss the influence of sediment type on the results depending on the type of unit used, and propose a simple conversion
factor based on sediment water content. 相似文献
48.
49.
David W. Thomas Amabile K. Matida Célio L. Silva Thuioshi Ioneda 《Chemistry and physics of lipids》1979,23(3):267-282
The purification procedure of 6,6′-diesters of trehalose from Corynebacterium diphtheriae was modified and the isolated substance was analysed by mass spectrometry as its permethylated derivative. The fatty acid moiety released from the glycolipid after alkaline hydrolysis was studied by mass spectral analysis of the O-methylated and O-acetylated methyl ester derivatives. By argentation thin-layer chromatography, three species of O-acetylated methyl esters were recognized, corresponding to saturated, mono-unsaturated and di-unsaturated α-branched-β-hydroxylated fatty acids. The double bond was located by ozonolysis of the O-acetylated methyl ester derivatives, by gas chromatography of the reaction product and mass spectrometry of the effluent from the gas chromatograph. The main components of each species of α-branched-β-hydroxylated fatty acids found in the gly colipid fraction of C. diphtheriae were 2-tetradecyl-3-hydroxyoctadecanoic acid (C32H64O3, corynomycolic acid), 2-tetradecyl-3-hydroxy-11-octadecenoic acid (C32H62O3, corynomycolenic acid), 2-tetradec-7′-enyl-3-hydroxy octadecanoic acid (C32H62O3) and 2-tetradec-7′-enyl-3-hydroxy-11-octadecenoic acid (C32H60O3, corynomycoldienic acid). The glycolipid fraction from C. diphtheriae is obviously a complex mixture of 6,6′-diesters of trehalose. 相似文献
50.
Javier J Gonzalez-Rosa Manuel Vazquez-Marrufo Encarnacion Vaquero Pablo Duque Monica Borges Carlos M Gomez-Gonzalez Guillermo Izquierdo 《BMC neurology》2011,11(1):64-19