全文获取类型
收费全文 | 1462篇 |
免费 | 144篇 |
专业分类
1606篇 |
出版年
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 37篇 |
2020年 | 31篇 |
2019年 | 30篇 |
2018年 | 59篇 |
2017年 | 37篇 |
2016年 | 40篇 |
2015年 | 87篇 |
2014年 | 75篇 |
2013年 | 94篇 |
2012年 | 124篇 |
2011年 | 97篇 |
2010年 | 65篇 |
2009年 | 64篇 |
2008年 | 105篇 |
2007年 | 79篇 |
2006年 | 89篇 |
2005年 | 62篇 |
2004年 | 49篇 |
2003年 | 56篇 |
2002年 | 56篇 |
2001年 | 21篇 |
2000年 | 19篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 12篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 18篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1968年 | 2篇 |
1964年 | 3篇 |
排序方式: 共有1606条查询结果,搜索用时 15 毫秒
1.
The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients. 相似文献
2.
From the roots of Ferula loscosii the coumarins umbelliprenin, coladin and coladonin and the new natural isovaleryl derivative of the latter have been isolated. A study which confirms the structure of coladonin and its difference from farnesiferol A is also given. 相似文献
3.
Mariano Sigman 《PLoS biology》2005,3(2):e37
Parsing a mental operation into components, characterizing the parallel or serial nature of this flow, and understanding what each process ultimately contributes to response time are fundamental questions in cognitive neuroscience. Here we show how a simple theoretical model leads to an extended set of predictions concerning the distribution of response time and its alteration by simultaneous performance of another task. The model provides a synthesis of psychological refractory period and random-walk models of response time. It merely assumes that a task consists of three consecutive stages—perception, decision based on noisy integration of evidence, and response—and that the perceptual and motor stages can operate simultaneously with stages of another task, while the central decision process constitutes a bottleneck. We designed a number-comparison task that provided a thorough test of the model by allowing independent variations in number notation, numerical distance, response complexity, and temporal asynchrony relative to an interfering probe task of tone discrimination. The results revealed a parsing of the comparison task in which each variable affects only one stage. Numerical distance affects the integration process, which is the only step that cannot proceed in parallel and has a major contribution to response time variability. The other stages, mapping the numeral to an internal quantity and executing the motor response, can be carried out in parallel with another task. Changing the duration of these processes has no significant effect on the variance. 相似文献
4.
José Fayos Aurea Perales Mariano Pinar Manuel Rico Benjamín Rodríguez 《Phytochemistry》1983,22(9):1983-1984
The structure and absolute configuration of desangeloylshairidin, a guaianolide isolated from Guillonea scabra, have been established by X-ray diffraction analysis. No conformational change was observed in its seven-membered ring between the crystal and deuterochloroform solution states. 相似文献
5.
6.
Human ETS1 oncoprotein. Purification, isoforms, -SH modification, and DNA sequence-specific binding. 总被引:1,自引:0,他引:1
R J Fisher S Koizumi A Kondoh J M Mariano G Mavrothalassitis N K Bhat T S Papas 《The Journal of biological chemistry》1992,267(25):17957-17965
The human ETS1 proto-oncogene proteins have been isolated from the T-cell leukemia line, CEM, by immunoaffinity chromatography and their identity confirmed by NH2-terminal amino acid sequencing. Incubation of CEM cells with N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) indicates that ETS proteins can be modified in their cellular context and that pretreatment of the cells with N-ethylmaleimide (NEM) protects ETS1 proteins from TLCK modification. These data show that ETS1 proteins can exist in at least two different states, -SH-available and -SH-protected. Renatured human ETS1 has DNA sequence-specific binding to the PEA3 (CAGGAAGT) motif. The ETS1.PEA3 complex can be observed by electrophoretic mobility shift assays (EMSA). Purified ETS1 retards a band which is exactly the same size as a complex that is retarded from nuclear extracts prepared from CEM cells. Reduced ETS1 is required to form the ETS1.PEA3 complex, however; modification of the ETS1 -SH groups by either NEM or by TLCk does not inhibit formation of the complex. The ETS1.PEA3 complex formed with TLCK-modified ETS1 has a slower mobility than the complex formed with unmodified ETS1. Zone sedimentation analysis of purified ETS1 indicates that it is the monomer of ETS1 which binds to the PEA3 oligonucleotide. 相似文献
7.
Mariano A. Garcia-Blanco 《The Yale journal of biology and medicine》1981,54(5):405-Oct;54(5):405
8.
9.
Conformationally restricted 3,5-O-di-tert-butylsilylene-d-galactofuranosyl trichloroacetimidate donors were synthesized from allyl α-d-galactofuranoside for the construction of 1,2-cis α-d-galactofuranosyl linkages. Glycosylation reactions were performed with several acceptors, including d-galactono-1,4-lactone, d-rhamnopyranosyl, and d-mannopyranosyl derivatives. The influence of the temperature and the reaction solvents was evaluated, as well as the 6-O-substitution pattern of the donor. The higher α-selectivities were obtained at −78 °C in diethyl ether as solvent. 6-O-Acetyl substitution on constrained donor increased the α-selectivity compared to the 6-O-benzyl substitution. Almost no selectivities were observed in the non-participating solvent CH2Cl2. In contrast, ethereal solvents enhanced the α-selectivity suggesting a participating effect in the reaction intermediate. 相似文献
10.
Pietro D’Addabbo Moira Scascitelli Vincenzo Giambra Mariano Rocchi Domenico Frezza 《BMC evolutionary biology》2011,11(1):71