全文获取类型
收费全文 | 1426篇 |
免费 | 96篇 |
国内免费 | 1篇 |
出版年
2022年 | 11篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 18篇 |
2018年 | 27篇 |
2017年 | 21篇 |
2016年 | 50篇 |
2015年 | 52篇 |
2014年 | 75篇 |
2013年 | 76篇 |
2012年 | 97篇 |
2011年 | 86篇 |
2010年 | 73篇 |
2009年 | 55篇 |
2008年 | 64篇 |
2007年 | 95篇 |
2006年 | 81篇 |
2005年 | 70篇 |
2004年 | 85篇 |
2003年 | 74篇 |
2002年 | 64篇 |
2001年 | 13篇 |
2000年 | 8篇 |
1999年 | 10篇 |
1998年 | 20篇 |
1997年 | 15篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 8篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 13篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有1523条查询结果,搜索用时 15 毫秒
361.
Helenton C. Barrena Fabiana P. M. Schiavon Marcia A. Cararra Any de Castro R. Marques Christiano R. Schamber Rui Curi Roberto B. Bazotte 《Cell biochemistry and function》2014,32(4):333-340
The effects of linseed oil (LO) and macadamia oil (MO) on the metabolic changes induced by a high‐fat diet (HFD) rich in saturated fatty acid were investigated. For the purpose of this study, the vegetable oil present in the HFD, i.e. soybean oil (SO) was replaced with LO (HFD‐LO) or MO (HFD‐MO). For comparative purposes, a group was included, which received a normal fat diet (NFD). Male Swiss mice (6‐week old) were used. After 14 days under the dietary conditions, the mice were fasted for 18 h, and experiments were then performed. The HFD‐SO, HFD‐LO and HFD‐MO groups showed higher glycaemia (p < 0.05 versus NFD). However, no significant effect was observed on glycaemia, liver gluconeogenesis and liver ketogenesis when SO was replaced by either LO or MO. The body weight and the sum of epididymal, mesenteric, retroperitoneal and inguinal fat weights were higher (p < 0.05) in the HFD‐SO and HFD‐MO groups as compared with the NFD group. However, there was no significant difference in these parameters between the NFD and HFD‐LO groups. Thus, the protective role of LO on lipid accumulation induced by an HFD rich in saturated fatty acid is potentially mediated by the high content of ?‐3 polyunsaturated fatty acid in LO. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
362.
Sisi Qin Vincent Ricotta Marcia Simon Richard A. F. Clark Miriam H. Rafailovich 《PloS one》2015,10(3)
Fibroblast migration is critical to the wound healing process. In vivo, migration occurs on fibrillar substrates, and previous observations have shown that a significant time lag exists before the onset of granulation tissue. We therefore conducted a series of experiments to understand the impact of both fibrillar morphology and migration time. Substrate topography was first shown to have a profound influence. Fibroblasts preferentially attach to fibrillar surfaces, and orient their cytoplasm for maximal contact with the fiber edge. In the case of en-mass cell migration out of an agarose droplet, fibroblasts on flat surfaces emerged with an enhanced velocity, v = 52μm/h, that decreases to the single cell value, v = 28μm/h within 24 hours and remained constant for at least four days. Fibroblasts emerging on fibrillar surfaces emerged with the single cell velocity, which remained constant for the first 24 hours and then increased reaching a plateau with more than twice the initial velocity within the next three days. The focal adhesions were distributed uniformly in cells on flat surfaces, while on the fibrillar surface they were clustered along the cell periphery. Furthermore, the number of focal adhesions for the cells on the flat surfaces remained constant, while it decreased on the fibrillar surface during the next three days. The deformation of the cell nuclei was found to be 50% larger on the fiber surfaces for the first 24 hours. While the mean deformation remained constant on the flat surface, it increased for the next three days by 24% in cells on fibers. On the fourth day, large actin/myosin fibers formed in cells on fibrillar surfaces only and coincided with a change from the standard migration mechanism involving extension of lamellipodia, and retraction of the rear, to one involving strong contractions oriented along the fibers and centered about the nucleus. 相似文献
363.
Marcia O. Fenley Wilma K. Olson Irwin Tobias Gerald S. Manning 《Biophysical chemistry》1994,50(3):255-271
We present Monte Carlo simulations of the equilibrium configurations of short closed circular DNA that obeys a combined elastic, hard-sphere, and electrostatic energy potential. We employ a B-spline representation to model chain configuration and simulate the effects of salt on chain folding by varying the Debye screening parameter. We obtain global equilibrium configurations of closed circular DNA, with several imposed linking number differences, at two salt concentrations (specifically at the extremes of no added salt and the high salt regime), and for different chain lengths. Minimization of the composite elastic/long-range potential energy under the constraints of ring closure and fixed chain length is found to produce structures that are consistent with the configurations of short supercoiled DNA observed experimentally. The structures generated under the constraints of an electrostatic potential are less compact than those subjected only to an elastic term and a hard-sphere constraint. For a fixed linking number difference greater than a critical value, the interwound structures obtained under the condition of high salt are more compact than those obtained under the condition of no added salt. In the case of no added salt, the electrostatic energy plays a dominant role over the elastic energy in dictating the shape of the closed circular DNA. The DNA supercoil opens up with increasing chain length at low salt concentration. A branched three-leaf rose structure with a fixed linking number difference is higher in energy than the interwound form at both salt concentrations employed here. 相似文献
364.
Mutants of Anabaena sp. PCC 7120 with O2-sensitive acetylene-reducing activity were studied to identify envelope components that contribute to the barrier limiting diffusion of oxygen into the heterocyst. Mutant strain EF114, deficient in a heterocyst-specific glycolipid, reduced acetylene only under strictly anaerobic conditions. Analysis of in vivo O2 uptake as a function of dissolved pO2 showed that EF114 has lost the low affinity, diffusion-limited respiratory component associated with heterocysts in wild-type filaments. The low affinity respiratory activity was also lost in EF116, a mutant in which the cohesiveness of the outer polysaccharide layer was reduced. Restoration of aerobic nitrogen fixation in a spontaneous revertant of EF116 and in a strain complemented with cosmid 41E11 was associated with restoration of the low affinity component of respiratory activity. The results provide evidence that the barrier to diffusion of gas into heterocysts depends upon both the glycolipid layer and the polysaccharide layer of the heterocyst envelope.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea 相似文献
365.
366.
Morphometric analytical procedures were employed to study the pineal gland of the Mongolian gerbil following superior cervical ganglionectomy (SCGX). The purpose of this study was to define the effects of sympathetic denervation on the morphology of the gland at two time periods, 0500 and 1900 h (one hour before lights-on and lights-off, respectively). Fluorescence histochemistry was employed to determine catecholamine and indoleamine content in intact and denervated pineal glands. After SCGX, the pinealocytes decrease in size, concretions are prevented from forming, and the yellow fluorescence in the gland is lost. Following denervation a depression in the volume of most of the pinealocyte organelles, i.e., SER, RER/ribosomes, free cytoplasm, mitochondria and presumptive secretory vesicles, was also observed. However, synaptic ribbons increased in volume in the gerbils that had been killed at 1900 h. It appears that the sympathetic innervation to the pineal gland is a requirement for the presumptive secretory activity of the pinealocytes. 相似文献
367.
Verónica Nava Marcia Morales Sergio Revah 《Reviews in Environmental Science and Biotechnology》2007,6(4):339-352
The release of methyl tert-butyl ether (MTBE) to the environment, mainly from damaged gasoline underground storage tanks or
distribution systems spills, has provoked extended groundwater pollution. Biological treatments are, in general, a good alternative
for bioremediation of polluted sites; however, MTBE elimination from environment has constituted a challenge because of its
chemical structure and physicochemical properties. The combination of a stable ether link and the branched moiety hinder biodegradation.
Initial studies found MTBE to be highly recalcitrant but, in the last decade, reports of its biodegradation have been published
first under aerobic conditions and just recently under anaerobic conditions. Microbial MTBE degradation is characterized by
bacteria having low growth rates (0.35 day−1) and biomass yields (average value 0.24 g biomass/g MTBE). Alternatively, cometabolism (defined as the transformation of
a non-growth substrate in the obligate presence of a growth substrate), has been considered since it uncouples biodegradation
of the contaminant from growth, reducing the long adaptation and propagation period. This period has been reported to be of
several months in systems where it is degraded as sole carbon source. Cometabolic degradation rates are between 0.3 and 61 nmol/min/mg
protein (in the same range of direct aerobic metabolism). However, a major concern in MTBE cometabolism is that the accumulation
of tert-butyl alcohol (TBA) may, under certain cases, result in an incomplete site cleanup. This paper reviews in detail the
implicated enzymes and field treatments for the cometabolism of MTBE degradation with alkanes as growth substrates. 相似文献
368.
Coulibaly MB Lobo NF Fitzpatrick MC Kern M Grushko O Thaner DV Traoré SF Collins FH Besansky NJ 《PloS one》2007,2(9):e849
The malaria vector Anopheles gambiae maintains high levels of inversion polymorphism that facilitate its exploitation of diverse ecological settings across tropical Africa. Molecular characterization of inversion breakpoints is a first step toward understanding the processes that generate and maintain inversions. Here we focused on inversion 2Rj because of its association with the assortatively mating Bamako chromosomal form of An. gambiae, whose distinctive breeding sites are rock pools beside the Niger River in Mali and Guinea. Sequence and computational analysis of 2Rj revealed the same 14.6 kb insertion between both breakpoints, which occurred near but not within predicted genes. Each insertion consists of 5.3 kb terminal inverted repeat arms separated by a 4 kb spacer. The insertions lack coding capacity, and are comprised of degraded remnants of repetitive sequences including class I and II transposable elements. Because of their large size and patchwork composition, and as no other instances of these insertions were identified in the An. gambiae genome, they do not appear to be transposable elements. The 14.6 kb modules inserted at both 2Rj breakpoint junctions represent low copy repeats (LCRs, also called segmental duplications) that are strongly implicated in the recent (approximately 0.4N(e) generations) origin of 2Rj. The LCRs contribute to further genome instability, as demonstrated by an imprecise excision event at the proximal breakpoint of 2Rj in field isolates. 相似文献
369.
The genus Brachygasterina Macquart is Neotropical, with six species recorded from Argentina, Chile, Ecuador and Colombia. A new species was found among an extensive unidentified muscid material from South America in the collection of the California Academy of Sciences collection (San Francisco, California, U.S.A.). Brachygasterina maculata, new species, from Santiago, Chile, is here described and illustrated, and its position in the genus Brachygasterina is discussed. 相似文献
370.
Charles E. Birse Robert J. Lagier William FitzHugh Harvey I. Pass William N. Rom Eric S. Edell Aaron O. Bungum Fabien Maldonado James R. Jett Mehdi Mesri Erin Sult Elizabeth Joseloff Aiqun Li Jenny Heidbrink Gulshan Dhariwal Chad Danis Jennifer L. Tomic Robert J. Bruce Paul A. Moore Tao He Marcia E. Lewis Steve M. Ruben 《Clinical proteomics》2015,12(1)