全文获取类型
收费全文 | 4278篇 |
免费 | 198篇 |
国内免费 | 82篇 |
专业分类
4558篇 |
出版年
2023年 | 62篇 |
2022年 | 81篇 |
2021年 | 94篇 |
2020年 | 87篇 |
2019年 | 183篇 |
2018年 | 193篇 |
2017年 | 130篇 |
2016年 | 103篇 |
2015年 | 72篇 |
2014年 | 174篇 |
2013年 | 183篇 |
2012年 | 111篇 |
2011年 | 131篇 |
2010年 | 79篇 |
2009年 | 76篇 |
2008年 | 98篇 |
2007年 | 111篇 |
2006年 | 106篇 |
2005年 | 133篇 |
2004年 | 161篇 |
2003年 | 165篇 |
2002年 | 128篇 |
2001年 | 86篇 |
2000年 | 66篇 |
1999年 | 90篇 |
1998年 | 69篇 |
1997年 | 71篇 |
1996年 | 76篇 |
1995年 | 88篇 |
1994年 | 90篇 |
1993年 | 83篇 |
1992年 | 71篇 |
1991年 | 74篇 |
1990年 | 52篇 |
1989年 | 53篇 |
1988年 | 53篇 |
1987年 | 49篇 |
1986年 | 40篇 |
1985年 | 86篇 |
1984年 | 119篇 |
1983年 | 60篇 |
1982年 | 115篇 |
1981年 | 73篇 |
1980年 | 82篇 |
1979年 | 33篇 |
1978年 | 46篇 |
1977年 | 38篇 |
1976年 | 46篇 |
1974年 | 32篇 |
1973年 | 23篇 |
排序方式: 共有4558条查询结果,搜索用时 15 毫秒
91.
Hassanin A Ropiquet A Cornette R Tranier M Pfeffer P Candegabe P Lemaire M 《Comptes rendus biologies》2006,329(2):124-135
The kouprey (Bos sauveli Urbain, 1937) is a very rare bovid species of Cambodia, which may be extinct in the wild, as no living specimen has been observed for a long time. Here, we describe a complete taxidermy mount, which presents astonishing morphological similarities with the kouprey. The animal was mounted in 1871 at the National Museum of Natural History in Paris, where it was referenced as No. 1871-576. It was deposited at the Natural History Museum of Bourges, France, in 1931, where it is still conserved today. To clarify the taxonomic status of the specimen of Bourges, DNA was extracted from a piece of bone taken on the mandible, and two different fragments of the mitochondrial cytochrome b gene were independently amplified and sequenced. The phylogenetic analyses show that the specimen of Bourges is robustly associated with the holotype of the kouprey, and that both are related to other wild species of Bos found in Indochina, i.e., banteng (B. javanicus) and gaur (B. frontalis). Because of doubts for sexing the animal, we applied a molecular test based on the PCR amplification of a DNA fragment specific to the Y chromosome. The results indicate that the specimen of Bourges is a male. The comparisons with male kouprey previously described in the literature reveal important differences concerning the body size, general coloration and horns. As these differences involve phenotypic traits that are strongly selected in case of domestication, we suggest that the specimen of Bourges was a domestic ox. This implies therefore that the kouprey may have been domesticated in Cambodia, and that several extant local races may be directly related to the kouprey. 相似文献
92.
Improving coiled-coil stability by optimizing ionic interactions 总被引:5,自引:0,他引:5
Alpha-helical coiled coils are a common protein oligomerization motif stabilized mainly by hydrophobic interactions occurring along the coiled-coil interface. We have recently designed and solved the structure of a two-heptad repeat coiled-coil peptide that is stabilized further by a complex network of inter- and intrahelical salt-bridges in addition to the hydrophobic interactions. Here, we extend and improve the de novo design of this two heptad-repeat peptide by four newly designed peptides characterized by different types of ionic interactions. The contribution of these different types of ionic interactions to coiled-coil stability are analyzed by CD spectroscopy and analytical ultracentrifugation. We show that all peptides are highly alpha-helical and two of them are 100% dimeric under physiological conditions. Furthermore, we have solved the X-ray structure of the most stable of these peptides and the rational design principles are verified by comparing this structure to the structure of the parent peptide. We show that by combining the most favorable inter- and intrahelical salt-bridge arrangements it is possible to design coiled-coil oligomerization domains with improved stability properties. 相似文献
93.
Salazard B Bellon L Jean S Maraninchi M El-Yazidi C Orsière T Margotat A Botta A Bergé-Lefranc JL 《Cell biology and toxicology》2004,20(6):375-385
In this study we analyzed gene expression in 3T3-F442A pre-adipocyte cells that differentiate in the presence of micro-molar arsenate concentration. Two concentrations of arsenite (As2O3, 0.25 micromol/L and 0.5 micromol/L) were applied for three days with and without insulin (170 nmol/L) and gene expressions were evaluated by quantitative RT-PCR. The genes included genes of oxidative-stress responses: heme-oxygenase-1 (HO1) and the hypoxia inducible factor 1a (HIF1alpha), genes of cell-cycle: c-jun and Kruppel like factor 5 (KLF5), and genes that play important roles in adipose determination: a peroxisome proliferator-activated receptor (PPARgamma) and a CCAAT/ enhancer binding protein (C/EBPalpha). Arsenite induced the expression of HO1, HIF1alpha, KLF5, PPARgamma and C/EBPalpha. These results suggest that under condition of oxidative stress arsenite induces genes that are required for adipose differentiation. 相似文献
94.
利用cDNA末端快速扩增 (RACE)技术克隆了一条由左侧视网膜剥夺造成左前脑差异表达EST片段的全长cDNA序列 ,同源性比较后认定 ,其为鸽e(r)基因 .该基因与人类及斑马鱼等脊椎动物e(r)基因的同源性非常高 ,但C端有明显差异 .RNA斑点杂交、逆转录聚合酶链反应 (RT PCR)及Northern印迹等方法检测 ,该基因在不同组织中表达量有差异 .结果表明 ,鸽e(r)基因在左眼视网膜剥夺鸽的左前脑及肝、肾中的表达量较高 ,该基因的表达具有一定的组织表达特异性 . 相似文献
95.
This study examined primary cilia on cultured human and rabbit peritoneal mesothelial cells (PMC) and investigated factors that influence ciliary expression. Primary cilia were examined with indirect immunocytochemistry, laser scanning confocal microscopy and scanning electron microscopy. Ciliary expression was evaluated in cultures with or without l-cysteine (0.25 mM) or exposure to Ca(2+)-free Krebs-Ringer solution supplemented with EGTA, 0.5 mM. This treatment disrupted cell monolayer integrity. Cilia were counted and normalized to total cell counts using NIH image. Primary cilia were identified on both human and rabbit PMC. Cells treated with l-cysteine expressed significantly more cilia compared with monolayers deprived of l-cysteine. Exposure to Ca(2+)-free Krebs-Ringer solution significantly reduced cilia (5.9+/-1.0%, n=7). Although ciliary expression could be augmented with l-cysteine, approximately 60% of human PMC and 84% of rabbit PMC did not exhibit cilia. Together, these data show that monolayers of PMC express apical cilia that can be augmented with l-cysteine, independently of increased cell density. 相似文献
96.
The mechanism responsible for the initial steps in the anaerobic degradation of trans-cinnamate and -phenylalkane carboxylates by the purple non-sulphur photosynthetic bacterium Rhodopseudomonas palustris was investigated. Phenylacetate did not support growth and there was a marked CO2 dependence for growth on acids with greater side-chain lengths. Here, CO2 was presumably acting as a redox sink for the disposal of excess reducing equivalents. Growth on benzoate did not require the addition of exogenous CO2. Aromatic acids with an odd number of side-chain carbon atoms (3-phenylpropionate, 5-phenylvalerate, 7-phenylheptanoate) gave greater apparent molar growth yields than those with an even number of side-chain carbon atoms (4-phenylbutyrate, 6-phenylhexanoate, 8-phenyloctanoate). HPLC analysis revealed that phenylacetate accumulated and persisted in the culture medium during growth on these latter compounds. Cinnamate and benzoate transiently accumulated in the culture medium during growth on 3-phenylpropionate, and benzoate alone accumulated transiently during the course of trans-cinnamate degradation. The transient accumulation of 4-phenyl-2-butenoic acid occurred during growth on 4-phenylbutyrate, and phenylacetate accumulated to a 1:1 molar stoichiometry with the initial 4-phenylbutyrate concentration. It is proposed that the initial steps in the anaerobic degradation of trans-cinnamate and the group of acids from 3-phenylpropionate to 8-phenyloctanoate involves -oxidation of the side-chain.Abbreviation 3-PP
3-phenylpropionic acid
- 4-PB
4-phenylbutyric acid
- 5-PV
5-phenylvaleric acid
- 6-PH
6-phenylhexanoic acid
- 7-PH
7-phenylheptanoic acid
- 8-PO
8-phenyloctanoic acid
- 4-P2B
4-phenyl-2-butenoic acid
- GC/MS
Gas chromatography/Mass spectrometry
- HPLC
High-pressure liquid chromatography 相似文献
97.
Alexandro Bonifaz Berenice Córdoba-García Tania Simancas-Llanos Marco A. Hernández Erick Martínez-Herrera Andrés Tirado-Sánchez 《Revista iberoamericana de micología》2019,36(1):30-33
Background
Nannizzia nana is a zoophilic dermatophyte that affects animals like pigs, boars and, exceptionally, humans, in whom it causes tinea capitis, as well as tinea corporis and onychomycosis.Case report
Case 1. A previously healthy 8 year-old boy presented to our clinic with a 1-month evolution dermatosis that affected scalp, developing a pseudoalopecic tumor lesion with abundant seropurulent material. The patient had worked in a pig farm. Case 2. A previously healthy 6 year-old girl, sister of the aforementioned child, presented to our clinic with a dermatosis characterized by multiple erythematous-scaly plaques that affected her face, trunk and arms. N. nana was the fungus isolated on culture in both cases. The children were treated with oral griseofulvin and topical ketoconazole that led to clinical and mycological cures.Conclusions
N. nana dermatophytosis, although being rare in humans, can be treated as other cases of dermatophytosis. 相似文献98.
Nariko Kawamura 《Neurochemical research》1989,14(1):9-15
The interrelation of palmitate oxidation with amino acid formation in rat brain mitochondria has been investigated in purified mitochondria of nonsynaptic origin by measuring the formation of aspartate, -ketoglutarate, and glutamate during palmitate oxidation, and also by assaying14C-products of [1-14C]palmitate oxidation. Oxidation of palmitate (or [1-14C]palmitate) resulted in the formation of aspartate (or14C-aspartate), and the oxidation was inhibited by aminooxyacetate (an inhibitor of transaminase), Palmitate oxidation also resulted in -ketoglutarate formation, which was sensitive to the effect of aminooxyacetate. Addition of NH4Cl was found to increase14C-products and formation of -ketoglutarate, whereas glutamate formation was not increased unless the rate of palmitate oxidation was reduced by 50% by aminooxyacetate or -ketoglutarate was added exogenously. Exogenous -ketoglutarate was found to decrease14C-products, but not aspartate formation. These results indicated that palmitate oxidation was closely related to aspartate formation via aspartate aminotransferase. During palmitate oxidation without aminooxyacetate or added -ketoglutarate, however, -ketoglutarate was not available for glutamate formation via glutamate dehydrogenase. We discuss the possibility that this was because (a) oxidative decarboxylation of -ketoglutarate to form succinyl-CoA was favored over glutamate formation for the competition for -ketoglutarate in the same pool, and (b) the pool of -ketoglutarate produced in the aspartate aminotransferase reaction did not serve as substrate for glutamate formation. 相似文献
99.
Summary M1 is a virulent bacteriophage of Methanobacterium thermoautotrophicum strain Marburg. Restriction enzyme analysis of the linear, 30.4 kb phage DNA led to a circular map of the 27.1 kb M1 genome. M1 is thus circularly permuted and exhibits terminal redundancy of approximately 3 kb. Packaging of M1 DNA from a concatemeric precursor initiates at the pac site which was identified at coordinate 4.6 kb on the circular genome map. It proceeds clockwise for at least five packaging rounds. Headful packaging was also shown for M2, a phage variant with a 0.7 kb deletion at coordinate 23.25 on the map. 相似文献
100.