全文获取类型
收费全文 | 83017篇 |
免费 | 5955篇 |
国内免费 | 19篇 |
出版年
2023年 | 424篇 |
2022年 | 675篇 |
2021年 | 1303篇 |
2020年 | 1004篇 |
2019年 | 1226篇 |
2018年 | 1924篇 |
2017年 | 1715篇 |
2016年 | 2521篇 |
2015年 | 3491篇 |
2014年 | 3735篇 |
2013年 | 4793篇 |
2012年 | 5784篇 |
2011年 | 5527篇 |
2010年 | 3622篇 |
2009年 | 3188篇 |
2008年 | 4342篇 |
2007年 | 4359篇 |
2006年 | 4088篇 |
2005年 | 3594篇 |
2004年 | 3626篇 |
2003年 | 3273篇 |
2002年 | 3094篇 |
2001年 | 1900篇 |
2000年 | 1758篇 |
1999年 | 1550篇 |
1998年 | 936篇 |
1997年 | 673篇 |
1996年 | 662篇 |
1995年 | 644篇 |
1994年 | 549篇 |
1993年 | 517篇 |
1992年 | 913篇 |
1991年 | 817篇 |
1990年 | 764篇 |
1989年 | 746篇 |
1988年 | 684篇 |
1987年 | 676篇 |
1986年 | 608篇 |
1985年 | 590篇 |
1984年 | 536篇 |
1983年 | 465篇 |
1982年 | 410篇 |
1981年 | 353篇 |
1980年 | 330篇 |
1979年 | 449篇 |
1978年 | 328篇 |
1977年 | 304篇 |
1974年 | 363篇 |
1973年 | 346篇 |
1972年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Ratul Saha Robert S. Donofrio Susan T. Bagley 《Journal of industrial microbiology & biotechnology》2010,37(8):843-848
A TaqMan quantitative real-time polymerase chain reaction (qPCR) assay was developed for the detection and enumeration of
three Pseudomonas species belonging to the mendocina sublineage (P. oleovorans, P. pseudoalcaligenes, and P. oleovorans subsp. lubricantis) found in contaminated metalworking fluids (MWFs). These microbes are the primary colonizers and serve as indicator organisms
of biodegradation of used MWFs. Molecular techniques such as qPCR are preferred for the detection of these microbes since
they grow poorly on typical growth media such as R2A agar and Pseudomonas isolation agar (PIA). Traditional culturing techniques not only underestimate the actual distribution of these bacteria but
are also time-consuming. The primer–probe pair developed from gyrase B (gyrB) sequences of the targeted bacteria was highly sensitive and specific for the three species. qPCR was performed with both
whole cell and genomic DNA to confirm the specificity and sensitivity of the assay. The sensitivity of the assay was 101 colony forming units (CFU)/ml for whole cell and 13.7 fg with genomic DNA. The primer–probe pair was successful in determining
concentrations from used MWF samples, indicating levels between 2.9 × 103 and 3.9 × 106 CFU/ml. In contrast, the total count of Pseudomonas sp. recovered on PIA was in the range of <1.0 × 101 to 1.4 × 105 CFU/ml for the same samples. Based on these results from the qPCR assay, the designed TaqMan primer–probe pair can be efficiently
used for rapid (within 2 h) determination of the distribution of these species of Pseudomonas in contaminated MWFs. 相似文献
92.
Restriction mapping of the rRNA genes from Artemia larvae 总被引:4,自引:0,他引:4
J Cruces J Sebastián J Renart 《Biochemical and biophysical research communications》1981,98(2):404-409
A restriction endonuclease analysis of the genes coding for the ribosomal RNA from Artemia larvae has shown that these genes consist of a repeat unit of 16.2 kilobase pairs (10.7 Mdaltons) and that the repeat unit seems to be homogeneous in size. 相似文献
93.
94.
95.
96.
The antigen-antibody interaction occurring previous to the triggering of the immunological response is analyzed as a relational process in terms of lattices. Accordingly, this process is expressed as a lattice belonging to a pseudo-Boolean algebraic variety. The Heyting arrow operation, which appears in this kind of algebra, is used to analyze behaviors between non-comparable biological states expressed by the lattice. The resulting states coming from the arrows are connected with the influence of increasing and decreasing energies involved in the linking process. 相似文献
97.
Background
While traditional models of Alzheimer's disease focused on large fibrillar deposits of the Aβ42 amyloid peptide in the brain, recent work suggests that the major pathogenic effects may be attributed to SDS-stable oligomers of Aβ42. These Aβ42 oligomers represent a rational target for therapeutic intervention, yet factors governing their assembly are poorly understood. 相似文献98.
99.
David Dávila Silvia Fernández Ignacio Torres-Alemán 《The Journal of biological chemistry》2016,291(5):2510-2523
Disruption of insulin-like growth factor I (IGF-I) signaling is a key step in the development of cancer or neurodegeneration. For example, interference of the prosurvival IGF-I/AKT/FOXO3 pathway by redox activation of the stress kinases p38 and JNK is instrumental in neuronal death by oxidative stress. However, in astrocytes, IGF-I retains its protective action against oxidative stress. The molecular mechanisms underlying this cell-specific protection remain obscure but may be relevant to unveil new ways to combat IGF-I/insulin resistance. Here, we describe that, in astrocytes exposed to oxidative stress by hydrogen peroxide (H2O2), p38 activation did not inhibit AKT (protein kinase B) activation by IGF-I, which is in contrast to our previous observations in neurons. Rather, stimulation of AKT by IGF-I was significantly higher and more sustained in astrocytes than in neurons either under normal or oxidative conditions. This may be explained by phosphorylation of the phosphatase PTEN at the plasma membrane in response to IGF-I, inducing its cytosolic translocation and preserving in this way AKT activity. Stimulation of AKT by IGF-I, mimicked also by a constitutively active AKT mutant, reduced oxidative stress levels and cell death in H2O2-exposed astrocytes, boosting their neuroprotective action in co-cultured neurons. These results indicate that armoring of AKT activation by IGF-I is crucial to preserve its cytoprotective effect in astrocytes and may form part of the brain defense mechanism against oxidative stress injury. 相似文献
100.
De novo-synthesized ceramide signals apoptosis in astrocytes via extracellular signal-regulated kinase. 总被引:10,自引:0,他引:10
Recent observations support the importance of ceramide synthesis de novo in the induction of apoptosis. However, the downstream targets of de novo-synthesized ceramide are unknown. Here we show that palmitate incorporated into ceramide and induced apoptotic DNA fragmentation in astrocytes. These effects of palmitate were exacerbated when fatty acid breakdown was uncoupled and were not evident in neurons, which show a very low capacity to take up and metabolize palmitate. Palmitate-induced apoptosis of astrocytes was prevented by L-cycloserine and fumonisin B1, two inhibitors of ceramide synthesis de novo, and by PD098059, an inhibitor of the extracellular signal-regulated kinase (ERK) cascade. Accordingly, palmitate activated ERK by a process that was dependent on ceramide synthesis de novo and Raf-1, but independent of kinase suppressor of Ras. Other potential targets of ceramide in the control of cell fate, namely, c-Jun amino-terminal kinase, p38 mitogen-activated protein kinase, and protein kinase B, were not significantly affected in astrocytes exposed to palmitate. Results show that the Raf-1/ERK cascade is the selective downstream target of de novo-synthesized ceramide in the induction of apoptosis in astrocytes and also highlight the importance of ceramide synthesis de novo in apoptosis of astrocytes, which might have pathophysiological relevance. 相似文献