全文获取类型
收费全文 | 2920篇 |
免费 | 185篇 |
专业分类
3105篇 |
出版年
2023年 | 22篇 |
2022年 | 40篇 |
2021年 | 75篇 |
2020年 | 47篇 |
2019年 | 63篇 |
2018年 | 79篇 |
2017年 | 61篇 |
2016年 | 96篇 |
2015年 | 150篇 |
2014年 | 178篇 |
2013年 | 174篇 |
2012年 | 235篇 |
2011年 | 192篇 |
2010年 | 134篇 |
2009年 | 103篇 |
2008年 | 147篇 |
2007年 | 153篇 |
2006年 | 125篇 |
2005年 | 115篇 |
2004年 | 115篇 |
2003年 | 108篇 |
2002年 | 103篇 |
2001年 | 25篇 |
2000年 | 15篇 |
1999年 | 11篇 |
1998年 | 33篇 |
1997年 | 14篇 |
1996年 | 15篇 |
1995年 | 25篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 16篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1978年 | 10篇 |
1976年 | 9篇 |
1973年 | 14篇 |
1971年 | 9篇 |
1967年 | 7篇 |
1966年 | 7篇 |
1935年 | 7篇 |
1917年 | 7篇 |
排序方式: 共有3105条查询结果,搜索用时 15 毫秒
31.
32.
Bélanger LF Roy S Tremblay M Brott B Steff AM Mourad W Hugo P Erikson R Charron J 《Molecular and cellular biology》2003,23(14):4778-4787
MEK is a dual-specificity kinase that activates the extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase upon agonist binding to receptors. The ERK/MAP kinase cascade is involved in cell fate determination in many organisms. In mammals, this pathway is proposed to regulate cell growth and differentiation. Genetic studies have shown that although a single Mek gene is present in Caenorhabditis elegans, Drosophila melanogaster, and Xenopus laevis, two Mek homologs, Mek1 and Mek2, are present in the mammalian cascade. The inactivation of the Mek1 gene leads to embryonic lethality and has revealed the unique role played by Mek1 during embryogenesis. To investigate the biological function of the second homolog, we have generated mice deficient in Mek2 function. Mek2 mutant mice are viable and fertile, and they do not present flagrant morphological alteration. Although several components of the ERK/MAP kinase cascade have been implicated in thymocyte development, no such involvement was observed for MEK2, which appears to be nonessential for thymocyte differentiation and T-cell-receptor-induced proliferation and apoptosis. Altogether, our findings demonstrate that MEK2 is not necessary for the normal development of the embryo and T-cell lineages, suggesting that the loss of MEK2 can be compensated for by MEK1. 相似文献
33.
The dunce gene of Drosophila melanogaster codes for a cyclic adenosine-3',5'-monophosphate-specific phosphodiesterase. Mutations of dunce alter or abolish the activity of this enzyme, produce elevated cAMP levels, cause recessive female sterility, and produce learning deficiencies in both sexes. Aberrant male sexual behavior has also been associated with the memory defects of dunce mutants. Here we show that the longevity of dunce mutant females, homozygous for null-enzyme alleles, is reduced by 50% in the presence of males compared to control dunce females kept without males. Mutant dunce females, mate every 22-24 hr. We propose a cause-effect relationship between mating and reduced longevity. Pheromones or peptides transferred during mating may activate adenylate cyclase and create an increase in cAMP levels that cannot be damped in dunce females. This increase may affect basic physiological functions and lead to reduced longevity. 相似文献
34.
Meiring HD Kuipers B van Gaans-van den Brink JA Poelen MC Timmermans H Baart G Brugghe H van Schie J Boog CJ de Jong AP van Els CA 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(9):5636-5643
The meningococcal class I outer membrane protein porin A plays an important role in the development of T cell-dependent protective immunity against meningococcal serogroup B infection and is therefore a major component of candidate meningococcal vaccines. T cell epitopes from porin A are poorly characterized because of weak in vitro memory T cell responses against purified Ag and strain variation. We applied a novel strategy to identify relevant naturally processed and MHC class II-presented porin A epitopes, based on stable isotope labeling of Ag. Human immature HLA-DR1-positive dendritic cells were used for optimal uptake and MHC class II processing of (14)N- and (15)N-labeled isoforms of the neisserial porin A serosubtype P1.5-2,10 in bacterial outer membrane vesicles. HLA-DR1 bound peptides, obtained after 48 h of Ag processing, contained typical spectral doublets in mass spectrometry that could easily be assigned to four porin A regions, expressed at diverging densities ( approximately 30-4000 copies/per cell). Epitopes from two of these regions are recognized by HLA-DR1-restricted CD4(+) T cell lines and are conserved among different serosubtypes of meningococcal porin A. This mass tag-assisted approach provides a useful methodology for rapid identification of MHC class II presented bacterial CD4(+) T cell epitopes relevant for vaccine development. 相似文献
35.
The red tide dinoflagellate Karenia brevis (Davis) G. Hansen and Moestrup is noted for causing mass mortalities of marine organisms in the Gulf of Mexico. Most research has focused on culture isolates from the eastern Gulf of Mexico. In this investigation, we examine the effects of light, temperature and salinity on the growth rate of K. brevis from the western Gulf of Mexico. Growth rates of K. brevis were determined under various combinations of irradiance (19, 31, 52, 67, and 123 μmol m−2 s−1), salinity (25, 30, 35, 40 and 45), and temperature (15, 20, 25, and 30 °C). Maximum growth rates varied from 0.17 to 0.36 div day−1 with exponential growth rates increasing with increasing irradiance. Little or no growth was supported at 19 μmol photons m−2 s−1 for any experiment. Maximum growth rates at 15 °C were much lower than at other temperatures. Maximum growth rates of the Texas clone (SP3) fell within the range of Florida clones reported in the literature (0.17–0.36 div day−1 versus 0.2–1.0 div day−1). The Texas clone SP3 had a very similar light saturation point compared to that of a Florida isolate (Wilson's clone) (67 μmol m−2 s−1 versus 65 μmol m−2 s−1), and light compensation (20–30 μmol m−2 s−11). The upper and lower salinity tolerance of the Texas clone was similar than that of some Florida clones (45 versus 46 and 25 versus 22.5, respectively). In our study, the Texas clone had the same temperature tolerance reported for Florida clones (15–30 °C). While individual clones can vary considerably in maximum growth rates, our results indicate only minor differences exist between the Texas and Florida strains of K. brevis in their temperature and salinity tolerance for growth. While the literature notes lower salinity occurrences of K. brevis in nearby Louisiana, our isolate from the southern Texas coast has the higher salinity requirements typical of K. brevis in the eastern Gulf of Mexico. 相似文献
36.
Xiaoyu Luo Hugo Mouquet Olivier Schwartz Warner C. Greene 《The Journal of biological chemistry》2021,297(4)
The progressive loss of CD4+ T cells during HIV infection of lymphoid tissues involves both the apoptotic death of activated and productively infected CD4 T cells and the pyroptotic death of large numbers of resting and abortively infected bystander CD4 T cells. HIV spreads both through cellular release of virions and cell-to-cell transmission involving the formation of virological synapses. Cell-to-cell transmission results in high-level transfer of large quantities of virions to the target cell exceeding that achieved with cell-free virions. Broadly neutralizing anti-HIV antibodies (bNAbs) binding to HIV envelope protein capably block cell-free virus spread, and when added at higher concentrations can also interdict cell-to-cell transmission. Exploiting these distinct dose–response differences, we now show that four different bNAbs block the pyroptotic death of bystander cells, but only when added at concentrations sufficient to block cell-to-cell transmission. These findings further support the conclusion that HIV killing of abortively infected bystander CD4 T cells requires cell-to-cell transfer of virions. As bNAbs attract more interest as potential therapeutics, it will be important to consider the higher concentrations of these antibodies required to block the inflammatory death of bystander CD4 T cells. 相似文献
37.
Bingxin Wang Daniel G. Rocha Mark I. Abrahams Andr P. Antunes Hugo C. M. Costa Andr Luis Sousa Gonalves Wilson Roberto Spironello Milton Jos de Paula Carlos A. Peres Juarez Pezzuti Emiliano Ramalho Marcelo Lima Reis Elildo Carvalho Jr Fabio Rohe David W. Macdonald Cedric Kai Wei Tan 《Ecology and evolution》2019,9(9):5049-5062
Amazonia forest plays a major role in providing ecosystem services for human and sanctuaries for wildlife. However, ongoing deforestation and habitat fragmentation in the Brazilian Amazon has threatened both. The ocelot is an ecologically important mesopredator and a potential conservation ambassador species, yet there are no previous studies on its habitat preference and spatial patterns in this biome. From 2010 to 2017, twelve sites were surveyed, totaling 899 camera trap stations, the largest known dataset for this species. Using occupancy modeling incorporating spatial autocorrelation, we assessed habitat use for ocelot populations across the Brazilian Amazon. Our results revealed a positive sigmoidal correlation between remote‐sensing derived metrics of forest cover, disjunct core area density, elevation, distance to roads, distance to settlements and habitat use, and that habitat use by ocelots was negatively associated with slope and distance to river/lake. These findings shed light on the regional scale habitat use of ocelots and indicate important species–habitat relationships, thus providing valuable information for conservation management and land‐use planning. 相似文献
38.
Madina Mst Hur Rahman Md Saifur Zheng Huanquan Germain Hugo 《Plant molecular biology》2019,101(4-5):343-354
Plant Molecular Biology - Short review focussing on the role and targeting of vacuolar substructure in plant immunity and pathogenesis. Plants lack specialized immune cells, therefore each plant... 相似文献
39.
Rodrigo Fortes-Silva Fabiola De Oliveira Paes Leme Túlio Pacheco Boaventura Helena Corrêa Pinto De Mendonça Jane Prado Leite Moreira Pedro Hugo Henriques Cunha 《Chronobiology international》2019,36(2):276-287
The aim of this study was to investigate the daily rhythms of hematological, biochemical and enzymatic parameters of the blood of a nocturnal model of fish (Lophiosilurus alexandri) bred in the laboratory (F1). Thirty-six juveniles were stocked in six tanks of a recirculation aquaculture system for 20 days. The fish were exposed to a light:dark cycle of 12:12 h and were fed 1% of biomass twice a day with commercial diet. The daily rhythms of hematological, biochemical and enzymatic parameters were then measured at six sampling times “zeitgeber time = ZT” at four-hour intervals under light:dark 12:12 h (lights on = ZT0, at 8.00 a.m). No differences were observed to alkaline phosphatase, glucose, cortisol, aspartate aminotransferase, superoxide dismutase, total protein and hematocrit (p > 0.05). However, white blood cell count, Lymphocytes (LYN), Neutrophils (NEU), Eosinophil and Neutrophils to Lymphocytes ratio were significant different between sample times (p < 0.05). Also, a significant difference in alanine transaminase was observed, with a peak of production at nighttime. In contrast, glutathione peroxidase peaked at 8:00. Uric acid, magnesium and Calcium (Ca++) showed statistically significant differences (p < 0.05). A significant difference was observed (p < 0.05), with a peak of albumin at 08:00 and triglycerides at 12:00, while cholesterol was low (p < 0.05) at 08:00 and higher from 12:00 to 04:00. Cosinor analysis revealed also rhythmicity to SOD, UA, Mg and Ca++, ALB and CHO (p < 0.05). In conclusion, the time of day must be considered a key factor when using blood parameters as biomarkers for disease, health and welfare in the L. alexandri aquaculture. 相似文献
40.
Ready-to-use DNA extracted with a CTAB method adapted for herbarium specimens and mucilaginous plant tissue 总被引:2,自引:0,他引:2
J. Hugo Cota-Sánchez Kirsten Remarchuk Kumary Ubayasena 《Plant Molecular Biology Reporter》2006,24(2):161-167
This report summarizes major changes in previously published protocols for DNA extraction to improve the quality of DNA extracted
from plants. Here, we highlight the critical modifications in the original protocols. The efficiency of these changes results
in high-quality DNA ready to use in a variety of phytogenetically distant plant families, in particular species with mucopolysaccharides.
The DNA obtained can be used without further purification in various molecular biology assays, including direct sequencing
and AFLP and RAPD (random-amplified polymorphic DNA) analyses. The effectiveness of this method is proven by the amplification
and sequencing of PCR products of up to 1 kb with DNA extracted from herbarium tissue ≥60 years old. This versatility is not
usually found in DNA extraction protocols. In addition, this method is quick, adaptable to standard laboratories, and most
important, safer and more cost-effective. 相似文献