全文获取类型
收费全文 | 61566篇 |
免费 | 3926篇 |
国内免费 | 6篇 |
出版年
2023年 | 451篇 |
2022年 | 384篇 |
2021年 | 824篇 |
2020年 | 758篇 |
2019年 | 742篇 |
2018年 | 1940篇 |
2017年 | 1806篇 |
2016年 | 2357篇 |
2015年 | 3098篇 |
2014年 | 3049篇 |
2013年 | 4113篇 |
2012年 | 4943篇 |
2011年 | 4410篇 |
2010年 | 2738篇 |
2009年 | 2081篇 |
2008年 | 3414篇 |
2007年 | 3215篇 |
2006年 | 3022篇 |
2005年 | 2576篇 |
2004年 | 2503篇 |
2003年 | 2237篇 |
2002年 | 2056篇 |
2001年 | 1389篇 |
2000年 | 1376篇 |
1999年 | 1052篇 |
1998年 | 438篇 |
1997年 | 315篇 |
1996年 | 322篇 |
1995年 | 304篇 |
1994年 | 238篇 |
1993年 | 221篇 |
1992年 | 525篇 |
1991年 | 446篇 |
1990年 | 402篇 |
1989年 | 397篇 |
1988年 | 392篇 |
1987年 | 349篇 |
1986年 | 334篇 |
1985年 | 334篇 |
1984年 | 337篇 |
1983年 | 231篇 |
1982年 | 212篇 |
1980年 | 171篇 |
1979年 | 208篇 |
1978年 | 202篇 |
1975年 | 194篇 |
1974年 | 212篇 |
1973年 | 219篇 |
1972年 | 181篇 |
1969年 | 170篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used. 相似文献
112.
113.
G. N. Reiner L. Delgado-Marín N. Olguín S. Sánchez-Redondo M. Sánchez-Borzone E. Rodríguez-Farré C. Suñol D. A. García 《Cell biochemistry and biophysics》2013,67(2):515-525
Phenol compounds, such as propofol and thymol, have been shown to act on the GABAA receptor through interaction with specific sites of this receptor. In addition, considering the high lipophilicity of phenols, it is possible that their pharmacological activity may also be the result of the interaction of phenol molecules with the surrounding lipid molecules, modulating the supramolecular organization of the receptor environment. Thus, in the present study, we study the pharmacological activity of some propofol- and thymol-related phenols on the native GABAA receptor using primary cultures of cortical neurons and investigate the effects of these compounds on the micro viscosity of artificial membranes by means of fluorescence anisotropy. The phenol compounds analyzed in this article are carvacrol, chlorothymol, and eugenol. All compounds were able to enhance the binding of [3H]flunitrazepam with EC50 values in the micromolar range and to increase the GABA-evoked Cl? influx in a concentration-dependent manner, both effects being inhibited by the competitive GABAA antagonist bicuculline. These results strongly suggest that the phenols studied are positive allosteric modulators of this receptor. Chlorothymol showed a bell-type effect, reducing its positive effect at concentrations >100 μM. The concentrations necessary to induce positive allosteric modulation of GABAA receptor were not cytotoxic. Although all compounds were able to decrease the micro viscosity of artificial membranes, chlorothymol displayed a larger effect which could explain its effects on [3H]flunitrazepam binding and on cell viability at high concentrations. Finally, it is suggested that these compounds may exert depressant activity on the central nervous system and potentiate the effects of general anesthetics. 相似文献
114.
Carlos Inocencio Cortés-Martínez Norberto Chavarría-Hernández 《Biotechnology and bioengineering》2020,117(12):3968-3985
Monoxenic liquid culture is the most suitable technology for scaling up to industrial production of entomopathogenic nematodes (EPNs); however, the variability of the yield production remains a current problem in the process. The aim of this study was to analyze the parameters and criteria for EPN production in liquid culture based on scientific and technological knowledge from the last two decades. While experimental research has permitted the yield production of Heterorhabditis bacteriophora (362 × 103 infective juveniles [IJs]/ml) and Steinernema carpocapsae (252 × 103 IJs/ml), simultaneously, theoretical approaches have contributed to the understanding of the culture process, based on biological parameters of the bacterium–nematode complex and hydrodynamic and rheological parameters of the complex gas–liquid–solid system. Under this interdisciplinary research approach, bioprocess and biosystem engineering can contribute to design the various control strategies of the process variables, increase the productivity, and reduce the variability that until now distinguishes the in vitro production of EPNs by the liquid culture. 相似文献
115.
116.
117.
118.
Laura Miralles Santiago Lens Antonio Rodríguez-Folgar Manuel Carrillo Vidal Martín Bjarni Mikkelsen Eva Garcia-Vazquez 《PloS one》2013,8(8)
Visual species identification of cetacean strandings is difficult, especially when dead specimens are degraded and/or species are morphologically similar. The two recognised pilot whale species (Globicephala melas and Globicephala macrorhynchus) are sympatric in the North Atlantic Ocean. These species are very similar in external appearance and their morphometric characteristics partially overlap; thus visual identification is not always reliable. Genetic species identification ensures correct identification of specimens. Here we have employed one mitochondrial (D-Loop region) and eight nuclear loci (microsatellites) as genetic markers to identify six stranded pilot whales found in Galicia (Northwest Spain), one of them of ambiguous phenotype. DNA analyses yielded positive amplification of all loci and enabled species identification. Nuclear microsatellite DNA genotypes revealed mixed ancestry for one individual, identified as a post-F1 interspecific hybrid employing two different Bayesian methods. From the mitochondrial sequence the maternal species was Globicephala melas. This is the first hybrid documented between Globicephala melas and G. macrorhynchus, and the first post-F1 hybrid genetically identified between cetaceans, revealing interspecific genetic introgression in marine mammals. We propose to add nuclear loci to genetic databases for cetacean species identification in order to detect hybrid individuals. 相似文献
119.
120.
María Prados-Privado Juan Carlos Prados-Frutos José Luis Calvo-Guirado José Antonio Bea 《Computer methods in biomechanics and biomedical engineering》2016,19(15):1583-1591
To measure fatigue in dental implants and in its components, it is necessary to use a probabilistic analysis since the randomness in the output depends on a number of parameters (such as fatigue properties of titanium and applied loads, unknown beforehand as they depend on mastication habits). The purpose is to apply a probabilistic approximation in order to predict fatigue life, taking into account the randomness of variables. More accuracy on the results has been obtained by taking into account different load blocks with different amplitudes, as happens with bite forces during the day and allowing us to know how effects have different type of bruxism on the piece analysed. 相似文献