全文获取类型
收费全文 | 5299篇 |
免费 | 355篇 |
专业分类
5654篇 |
出版年
2024年 | 4篇 |
2023年 | 20篇 |
2022年 | 66篇 |
2021年 | 97篇 |
2020年 | 45篇 |
2019年 | 80篇 |
2018年 | 116篇 |
2017年 | 94篇 |
2016年 | 152篇 |
2015年 | 218篇 |
2014年 | 273篇 |
2013年 | 408篇 |
2012年 | 453篇 |
2011年 | 436篇 |
2010年 | 274篇 |
2009年 | 206篇 |
2008年 | 342篇 |
2007年 | 341篇 |
2006年 | 320篇 |
2005年 | 319篇 |
2004年 | 283篇 |
2003年 | 231篇 |
2002年 | 244篇 |
2001年 | 52篇 |
2000年 | 46篇 |
1999年 | 54篇 |
1998年 | 50篇 |
1997年 | 37篇 |
1996年 | 44篇 |
1995年 | 39篇 |
1994年 | 30篇 |
1993年 | 41篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 22篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 7篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1973年 | 3篇 |
1965年 | 3篇 |
排序方式: 共有5654条查询结果,搜索用时 15 毫秒
991.
Martínez-Ibarra JA Grant-Guillén Y Ventura-Rodríguez LV Osorio-Pelayo PD Macías-Amezcua MD Meillón-Isáis K Alejandre-Aguilar R Rodríguez-Bataz E Nogueda-Torres B 《Memórias do Instituto Oswaldo Cruz》2011,106(3):293-300
The degree of reproductive isolation between Meccus phyllosomus and the remaining five species of the genus Meccus, as well as between Meccus bassolsae and Meccus pallidipennis, Meccus longipennis and Meccus picturatus, was examined. Fertility and the segregation of morphological characteristics were examined in two generations of hybrids from crosses between these species. The percentage of couples with offspring (fertile) was high in the vast majority of sets of crosses, with the exception of that between ♀M. phyllosomus and ♂Meccus mazzottii. In sets of crosses involving M. bassolsae specimens, no first-generation (F1) individuals were morphologically similar to M. bassolsae, but instead shared the morphology of the other parental species. A similar phenomenon was observed in most sets of crosses involving M. phyllosomus. These results indicated that different degrees of reproductive isolation exist among the species of Meccus involved in this study. The biological evidence obtained in this study does not support the proposal that M. bassolsae is a full species. It could indicate that, on the contrary, it should be considered a subspecies of a single polytypic species. The biological evidence does support the proposal that M. phyllosomus is a full species. 相似文献
992.
993.
Background and Aims
Gluten proteins are the major storage protein fraction in the mature wheat grain. They are restricted to the starchy endosperm, which forms white flour on milling, and interact during grain development to form large polymers which form a continuous proteinaceous network when flour is mixed with water to give dough. This network confers viscosity and elasticity to the dough, enabling the production of leavened products. The starchy endosperm is not a homogeneous tissue and quantitative and qualitative gradients exist for the major components: protein, starch and cell wall polysaccharides. Gradients in protein content and composition are the most evident and are of particular interest because of the major role played by the gluten proteins in determining grain processing quality.Methods
Protein gradients in the starchy endosperm were investigated using antibodies for specific gluten protein types for immunolocalization in developing grains and for western blot analysis of protein extracts from flour fractions obtained by sequential abrasion (pearling) to prepare tissue layers.Key Results
Differential patterns of distribution were found for the high-molecular-weight subunits of glutenin (HMW-GS) and γ-gliadins when compared with the low-molecular-weight subunits of glutenin (LMW-GS), ω- and α-gliadins. The first two types of gluten protein are more abundant in the inner endosperm layers and the latter more abundant in the subaleurone. Immunolocalization also showed that segregation of gluten proteins occurs both between and within protein bodies during protein deposition and may still be retained in the mature grain.Conclusions
Quantitative and qualitative gradients in gluten protein composition are established during grain development. These gradients may be due to the origin of subaleurone cells, which unlike other starchy endosperm cells derive from the re-differentiation of aleurone cells, but could also result from the action of specific regulatory signals produced by the maternal tissue on specific domains of the gluten protein gene promoters. 相似文献994.
Imbrici P D'Adamo MC Grottesi A Biscarini A Pessia M 《American journal of physiology. Cell physiology》2011,300(6):C1314-C1322
Episodic ataxia type 1 (EA1) is an autosomal dominant disorder characterized by continuous myokymia and episodic attacks of ataxia. Mutations in the gene KCNA1 that encodes the voltage-gated potassium channel Kv1.1 are responsible for EA1. In several brain areas, Kv1.1 coassembles with Kv1.4, which confers N-type inactivating properties to heteromeric channels. It is therefore likely that the rate of inactivation will be determined by the number of Kv1.4 inactivation particles, as set by the precise subunit stoichiometry. We propose that EA1 mutations affect the rate of N-type inactivation either by reduced subunit surface expression, giving rise to a reduced number of Kv1.1 subunits in heterotetramer Kv1.1-Kv1.4 channels, or by reduced affinity for the Kv1.4 inactivation domain. To test this hypothesis, quantified amounts of mRNA for Kv1.4 or Kv1.1 containing selected EA1 mutations either in the inner vestibule of Kv1.1 on S6 or in the transmembrane regions were injected into Xenopus laevis oocytes and the relative rates of inactivation and stoichiometry were determined. The S6 mutations, V404I and V408A, which had normal surface expression, reduced the rate of inactivation by a decreased affinity for the inactivation domain while the mutations I177N in S1 and E325D in S5, which had reduced subunit surface expression, increased the rate of N-type inactivation due to a stoichiometric increase in the number of Kv1.4 subunits. 相似文献
995.
Villanueva-Peñacarrillo ML Martín-Duce A Ramos-Álvarez I Gutiérrez-Rojas I Moreno P Nuche-Berenguer B Acitores A Sancho V Valverde I González N 《Regulatory peptides》2011,168(1-3):39-44
Direct effects of GLP-1, kinase-mediated, on glucose and lipid metabolism in rat and human extrapancreatic tissues, are amply documented and also changes in type-2 diabetic (T2D) patients. Here, we explored the characteristics of the GLP-1 action and those of its analogs Ex-4 and Ex-9, on muscle glucose transport (GT) and metabolism in human morbid obesity (OB), as compared with normal and T2D subjects. In primary cultured myocytes from OB, GT and glycogen synthase a (GSa) activity values were lower than normal, and comparable to those reported in T2D patients; GT was increased by either GLP-1 or Ex-9 in a more efficient manner than in normal or T2D, up to normal levels; the Ex-4 increasing effect on GSa activity was two times that in normal cells, while Ex-9 failed to modify the enzyme activity. In OB, the control value of all kinases analyzed - PI3K, PKB, MAPKs, and p70s6K - although lower than that in normal or T2D subjects, the cells maintained their response capability to GLP-1, Ex-4, Ex-9 and insulin, with some exceptions. GLP-1 and exendins showed a direct normalizing action in the altered glucose uptake and metabolism in the muscle of obese subjects, which in the case of GLP-1 could account, at least in part, for the reported restoration of the metabolic conditions of these patients after restrictive surgery. 相似文献
996.
Paola BendinelliPaola Maroni Emanuela Matteucci Maria Alfonsina Desiderio 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2011,1813(10):1767-1776
Metastatic cells switch between different modes of migration through supramolecular plasticity mechanism(s) still largely unknown. The aim of the present paper was to clarify some molecular aspects of the epigenetic control of migration of 1833-bone metastatic cells compared to MDA-MB231-parental mammary carcinoma cells. Active c-Src overexpression enhanced 1833-cell spontaneous migration and CXCR4-mediated chemoinvasion toward CXCL12 ligand. Only in metastatic cells, in fact, c-Src seemed to stabilize nuclear CXCR4-protein receptor possibly due to tyrosine phosphorylation, by impairing protein-degradative smear and causing instead an electrophoretic-mobility shift; the cytosolic steady-state level of CXCR4 was enhanced, and the protein appeared also phosphorylated. These findings suggested the triggering of unique signaling pathways in metastasis for homing of breast-cancer cells to congenial environment of specific organs. Microenvironmental stimuli activating c-Src might influence Ets1 binding to CXCR4 promoter and consequent transactivation, as well as CXCR4 post-translational regulatory mechanisms such as phosphorylation. Enhancement of Ets1 activity and CXCR4 induction by c-Src overexpression were prevented by histone deacetylase (HDAC) blockade. In contrast, HDAC inhibition with trichostatin A increased cytosolic phosphorylated CXCR4 expression in MDA-MB231 cells, but Ets1 involvement was practically unneeded. c-Src might be suggested as a bio-marker predicting metastasis sensitivity patterns to HDAC inhibitors. Rationally designed and individualized therapy may become possible as more is learned about the target molecules of HDAC's inhibitory agents and their roles, as undertaken for CXCR4 that is likely to be crucial for homing, angiogenesis and survival in a c-Src-dependent manner in bone-metastatic mammary cells. 相似文献
997.
Porro D Gasser B Fossati T Maurer M Branduardi P Sauer M Mattanovich D 《Applied microbiology and biotechnology》2011,89(4):939-948
Recombinant DNA (rDNA) technologies allow the production of a wide range of peptides, proteins and metabolites from naturally
non-producing cells. Since human insulin was the first heterologous compound produced in a laboratory in 1977, rDNA technology
has become one of the most important technologies developed in the 20th century. Recombinant protein and metabolites production
is a multi-billion dollar market. The development of a new product begins with the choice of the cell factory. The final application
of the compound dictates the main criteria that should be taken into consideration: (1) quality, (2) quantity, (3) yield and
(4) space time yield of the desired product. Quantity and quality are the most predominant requirements that must be considered
for the commercial production of a protein. Quantity and yield are the requirements for the production of a metabolite. Finally,
space time yield is crucial for any production process. It therefore becomes clear why the perfect host does not exist yet,
and why—despite important advances in rDNA applications in higher eukaryotic cells—microbial biodiversity continues to represent
a potential source of attractive cell factories. In this review, we compare the advantages and limitations of the principal
yeast and bacterial workhorse systems. 相似文献
998.
In the present study, we developed a rapid and efficient fluorescence in situ hybridization assay (FISH) in non-embedded tissues of the model plant Catharanthus roseus for co-localizing phytoplasmas and endophytic bacteria, opening new perspectives for studying the interaction between these microorganisms. 相似文献
999.
Marco Camardo Leggieri Neus Planas Pont Paola Battilani Naresh Magan 《Mycotoxin Research》2011,27(1):29-35
The aim of this work was to evaluate the potential use of qualitative volatile patterns produced by Penicillium nordicum to discriminate between ochratoxin A (OTA) producers and non-producer strains on a ham-based medium. Experiments were carried
out on a 3% ham medium at two water activities (aw ; 0.995, 0.95) inoculated with P. nordicum spores and incubated at 25°C for up to 14 days. Growing colonies were sampled after 1, 2, 3, 7 and 14 days, placed in 30-ml
vials, sealed and the head space analysed using a hybrid sensor electronic nose device. The effect of environmental conditions
on growth and OTA production was evaluated based on the qualitative response. However, after 7 days, it was possible to discriminate
between strains grown at 0.995 aw, and after 14 days, the OTA producer and non-producer strain and the controls could be discriminated at both aw levels. This study suggests that volatile patterns produced by P. nordicum strains may differ and be used to predict the presence of toxigenic contaminants in ham. This approach could be utilised
in ham production as part of a quality assurance system for preventing OTA contamination. 相似文献
1000.
Scocco P Aralla M Catorci A Belardinelli C Arrighi S 《Folia histochemica et cytobiologica / Polish Academy of Sciences, Polish Histochemical and Cytochemical Society》2011,49(3):458-464
Mammalian aquaporins (AQPs) are a family of at least 13 integral membrane proteins expressed in various epithelia, where they function as channels to permeate water and small solutes. AQP5 is widely expressed in the exocrine gland where it is likely involved in providing an appropriate amount of fluid to be secreted with granular contents. As regards AQP5 expression in the salivary glands, literature is lacking concerning domestic animal species. This study was chiefly aimed at immunohistochemically investigating the presence and localization of AQP5 in sheep mandibular and parotid glands. In addition, AQP5 immunoreactivity was comparatively evaluated in animals fed with forage containing different amounts of water related to the pasture vegetative cycle, in order to shed light on the possible response of the gland to environmental modifications. Moderate AQP5-immunoreactivity was shown at the level of the lateral surface of mandibular serous demilune cells, not affected by the pasture vegetative cycle or water content. On the contrary, the parotid gland arcinar cells showed AQP5-immunoreactivity at the level of apical and lateral plasma membrane, which was slight to very strong, according to the pasture vegetative development and interannual climatic variations. AQP5 expression is likely due to its involvement in providing appropriate saliva fluidity. Indeed, the lowest AQP5 immunoreactivity was noticed when food water content increased. 相似文献