全文获取类型
收费全文 | 19582篇 |
免费 | 984篇 |
国内免费 | 27篇 |
专业分类
20593篇 |
出版年
2023年 | 171篇 |
2022年 | 389篇 |
2021年 | 732篇 |
2020年 | 426篇 |
2019年 | 457篇 |
2018年 | 660篇 |
2017年 | 620篇 |
2016年 | 802篇 |
2015年 | 926篇 |
2014年 | 1172篇 |
2013年 | 1613篇 |
2012年 | 1711篇 |
2011年 | 1508篇 |
2010年 | 869篇 |
2009年 | 773篇 |
2008年 | 902篇 |
2007年 | 867篇 |
2006年 | 736篇 |
2005年 | 663篇 |
2004年 | 548篇 |
2003年 | 449篇 |
2002年 | 414篇 |
2001年 | 325篇 |
2000年 | 307篇 |
1999年 | 272篇 |
1998年 | 113篇 |
1997年 | 83篇 |
1996年 | 95篇 |
1995年 | 86篇 |
1994年 | 64篇 |
1993年 | 60篇 |
1992年 | 169篇 |
1991年 | 158篇 |
1990年 | 122篇 |
1989年 | 95篇 |
1988年 | 136篇 |
1987年 | 109篇 |
1986年 | 90篇 |
1985年 | 98篇 |
1984年 | 92篇 |
1983年 | 56篇 |
1982年 | 46篇 |
1981年 | 50篇 |
1980年 | 56篇 |
1979年 | 65篇 |
1978年 | 40篇 |
1977年 | 46篇 |
1976年 | 38篇 |
1975年 | 32篇 |
1974年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
ZnO nanostructures of different morphology (nanorods, nano‐leaf, nanotubes) were favourably grown using a chemical precipitation process. The prepared ZnO nanostructures were characterized systematically using absorption spectroscopy, emission spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared studies. XRD results showed the hexagonal wurtzite phase of the synthesized ZnO nanostructures. Structural properties such as average crystallite size, lattice constants, volume of the unit cell, atomic fraction, and structural bonds were also studied. The optical band gap of the synthesized ZnO nanocrystals varied from 3.52 eV to 3.69 eV with high quantum yield of the blue emission (~420 nm). Urbach energy for ZnO nanocrystals was calculated to be 0.702 eV, 0.901 eV, and 0.993 eV for nanorods, nano‐leaf, and tube like ZnO crystals, respectively. Morphology of the fabricated nanostructures was investigated using SEM. Photocatalytic degradation of rhodamine B (Rh B) in solution under UV irradiation was explored with different ZnO morphology. Photocatalytic experiments showed that ZnO nano‐leaf had a higher degradation rate of photocatalytic activity of photodegrading Rh B compared with the other tube shape and rods shape nanostructures. The Rh B dye degraded considerably by ~79.05%, 74.41%, and 69.8% within 120 min in the presence of the as‐fabricated fern nano‐leaf, nanotubes, and nanorods of the ZnO nanocrystals at room temperature. 相似文献
102.
RAGE mediates amyloid-beta peptide transport across the blood-brain barrier and accumulation in brain 总被引:21,自引:0,他引:21
Deane R Du Yan S Submamaryan RK LaRue B Jovanovic S Hogg E Welch D Manness L Lin C Yu J Zhu H Ghiso J Frangione B Stern A Schmidt AM Armstrong DL Arnold B Liliensiek B Nawroth P Hofman F Kindy M Stern D Zlokovic B 《Nature medicine》2003,9(7):907-913
Amyloid-beta peptide (Abeta) interacts with the vasculature to influence Abeta levels in the brain and cerebral blood flow, providing a means of amplifying the Abeta-induced cellular stress underlying neuronal dysfunction and dementia. Systemic Abeta infusion and studies in genetically manipulated mice show that Abeta interaction with receptor for advanced glycation end products (RAGE)-bearing cells in the vessel wall results in transport of Abeta across the blood-brain barrier (BBB) and expression of proinflammatory cytokines and endothelin-1 (ET-1), the latter mediating Abeta-induced vasoconstriction. Inhibition of RAGE-ligand interaction suppresses accumulation of Abeta in brain parenchyma in a mouse transgenic model. These findings suggest that vascular RAGE is a target for inhibiting pathogenic consequences of Abeta-vascular interactions, including development of cerebral amyloidosis. 相似文献
103.
Sivakoti Ramana Ashis Kumar Biswas Amar Bahadur Singh Ajay Narendar Kumar Ahirwar Annangi Subba Rao 《International journal of phytoremediation》2015,17(4):363-368
The potential of an ornamental shrub Crown of thorns (Euphorbia milli) was evaluated for remediation of soil contaminated with Cr. The plant is one of the rare succulent ornamental shrubs with a slow to moderate growth rate and is capable of blooming almost year-round. The plant could tolerate well up to 75 mg of applied Cr and beyond that there was mortality of plants. Though the plant could not be classified as a hyperaccumulator, the plant was still very efficient in translocating Cr from roots to shoots as evident from the data on uptake and translocation efficiency values. The translocation efficiency of over 80% in our study demonstrates that a large proportion of Cr has been translocated to the harvestable biomass of the plant and therefore, this plant could be effectively recommended for the remediation of soils contaminated with low to medium level of contamination i.e., up to 50 mg/kg soil. 相似文献
104.
105.
Neeraj J Agrawal Bernhard Helk Sandeep Kumar Neil Mody Hasige A. Sathish Hardeep S. Samra 《MABS-AUSTIN》2016,8(1):43-48
Highly concentrated antibody solutions often exhibit high viscosities, which present a number of challenges for antibody-drug development, manufacturing and administration. The antibody sequence is a key determinant for high viscosity of highly concentrated solutions; therefore, a sequence- or structure-based tool that can identify highly viscous antibodies from their sequence would be effective in ensuring that only antibodies with low viscosity progress to the development phase. Here, we present a spatial charge map (SCM) tool that can accurately identify highly viscous antibodies from their sequence alone (using homology modeling to determine the 3-dimensional structures). The SCM tool has been extensively validated at 3 different organizations, and has proved successful in correctly identifying highly viscous antibodies. As a quantitative tool, SCM is amenable to high-throughput automated analysis, and can be effectively implemented during the antibody screening or engineering phase for the selection of low-viscosity antibodies. 相似文献
106.
107.
K. Ghosh N. L. Selokar S. K. Gahlawat Dharmendra Kumar Pawan Kumar 《Animal biotechnology》2016,27(1):38-43
Aim of the present study was the isolation, culture, and characterization of amniotic membrane-derived epithelial cells (AE) from term placenta collected postpartum in buffalo. We found that cultured cells were of polygonal in shape, resistance to trypsin digestion and expressed cytokeratin-18 indicating that they were of epithelial origin. These cells have negative expression of mesenchymal stem cell markers (CD29, CD44, and CD105) and positive for pluripotency marker (OCT4) genes indicated that cultured cells were not contaminated with mesenchymal stem cells. Immunofluorescence staining with pluripotent stem cell surface markers, SSEA-1, SSEA-4, TRA-1-60, and TRA-1-81 indicated that these cells may retain pluripotent stem cell characteristics even after long period of differentiation. Differentiation potential of these cells was determined by their potential to differentiate into cells of neurogenic lineages using retinoic acid. In conclusion, we demonstrate that AE cells expressed pluripotent stem cell markers and have propensity to differentiate into cells of neurogenic lineage upon directed differentiation in vitro. 相似文献
108.
Manoj Kumar Vladimir León Angela De Sisto Materano Olaf A. Ilzins 《World journal of microbiology & biotechnology》2007,23(2):211-220
A Bacillus sp. strain DHT, isolated from oil-contaminated soil, grew and produced biosurfactant when cultured in variety of substrate
at salinities of up to 100 g l−1 and temperatures up to 45°C. It was capable of utilizing crude oil, fuels, various pure alkanes and PAHs as a sole carbon
and energy source across a wide range of temperature and salinity. Over the range evaluated, the degradation of hydrocarbon
and biosurfactant production was not influenced by salinity (0–10% wv−1) and temperature (30–45°C). The biosurfactant produced by the organism emulsified a range of hydrocarbons with hexadecane
as the best substrate and toluene as the poorest. From 16S rDNA analysis, strain DHT was related to Bacillus licheniformis. 相似文献
109.
Products of inflammation and the activation of nitric oxide synthase have been proposed as a mechanism of oligodendrocyte injury in CNS inflammation. There are currently three well described and known isoforms of NOS. Of these, neuronal NOS (nNOS) was initially discovered in neurons, endothelial NOS (eNOS) in vascular endothelium, while the inducible form of NOS (iNOS) is known to be activated in oligodendrocytes, astrocytes and microglia. We examined the activation of nNOS and the down stream effects of NO production in oligodendrocyte precursor cells (OPC) and MO3.13 cell line following culture with LPS. Our studies show that both MO3.13 cells and OPC are susceptible to the cellular injury resulting from LPS mediated activation and NO production. Activation of the TLR4 receptor with LPS led to decrease in cell viability that was associated with loss of mitochondrial membrane potential and impaired enzymatic activity of complex I and complex IV protein of the respiratory chain. 7-NI, a known inhibitor of nNOS was able to rescue of cells from LPS mediated mitochondrial damage. Loss of mitochondrial function was associated with translocation of cytochrome C and apoptosis inducing factor to the cytosol, setting the stage for apoptosis. Phosphorylation of PI3K and Akt was required for optimal activation of NOS. These studies provide a biochemical basis for nNOS mediated oligodendrocyte injury and suggest similar mechanisms may play a role in diseases characterized by oligodendrocyte loss and demyelination. 相似文献
110.
Zhuang Jin Hua Lin Sathish Srinivasan Jerome C. Nwachukwu Nelson Bruno Patrick R. Griffin Kendall W. Nettles Theodore M. Kamenecka 《Bioorganic & medicinal chemistry letters》2017,27(2):347-353
Adverse effects of glucocorticoids could be limited by developing new compounds that selectively modulate anti-inflammatory activity of the glucocorticoid receptor (GR). We have synthesized a novel series of steroidal GR ligands, including potent agonists, partial agonists and antagonists with a wide range of effects on inhibiting secretion of interleukin-6. Some of these new ligands were designed to directly impact conformational stability of helix-12, in the GR ligand-binding domain (LBD). These compounds modulated GR activity and glucocorticoid-induced gene expression in a manner that was inversely correlated to the degree of inflammatory response. In contrast, compounds designed to directly modulate LBD epitopes outside helix-12, led to dissociated levels of GR-mediated gene expression and inflammatory response. Therefore, these new series of compounds and their derivatives will be useful to dissect the ligand-dependent features of GR signaling specificity. 相似文献