全文获取类型
收费全文 | 7963篇 |
免费 | 492篇 |
国内免费 | 290篇 |
专业分类
8745篇 |
出版年
2023年 | 151篇 |
2022年 | 256篇 |
2021年 | 239篇 |
2020年 | 235篇 |
2019年 | 319篇 |
2018年 | 310篇 |
2017年 | 213篇 |
2016年 | 214篇 |
2015年 | 260篇 |
2014年 | 464篇 |
2013年 | 607篇 |
2012年 | 364篇 |
2011年 | 461篇 |
2010年 | 342篇 |
2009年 | 367篇 |
2008年 | 371篇 |
2007年 | 375篇 |
2006年 | 336篇 |
2005年 | 320篇 |
2004年 | 307篇 |
2003年 | 247篇 |
2002年 | 226篇 |
2001年 | 138篇 |
2000年 | 107篇 |
1999年 | 109篇 |
1998年 | 97篇 |
1997年 | 92篇 |
1996年 | 92篇 |
1995年 | 73篇 |
1994年 | 68篇 |
1993年 | 62篇 |
1992年 | 53篇 |
1991年 | 60篇 |
1990年 | 48篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 23篇 |
1985年 | 56篇 |
1984年 | 85篇 |
1983年 | 55篇 |
1982年 | 87篇 |
1981年 | 64篇 |
1980年 | 46篇 |
1979年 | 48篇 |
1978年 | 39篇 |
1977年 | 39篇 |
1976年 | 30篇 |
1975年 | 28篇 |
1974年 | 21篇 |
1973年 | 27篇 |
排序方式: 共有8745条查询结果,搜索用时 15 毫秒
81.
Early events of apoptosis following HSV-1 infection were investigated at the single-cell level using intensified fluorescence digital-imaging microscopy. The results provide evidence that infection of differentiated ND7 neuronlike cells by HSV-1 triggers detectable alterations indicative of physiological changes associated with the early stages of apoptosis. Less than 1 h after infection with HSV-1 (KOS strain) or K26GFP (GFP being fused to HSV-1 capsid protein VP26) we observed (i) moderate decrease in mitochondrial membrane potential (about 20%), (ii) exposure of phosphatidyl serine, (iii) morphological change in the mitochondria that became spherical instead of filamentous, and (iv) activation of caspase-8. Within 3 h changes reverted to normal, which indicated that apoptosis was counteracted very early following HSV-1 infection. Similar results were obtained with KOS-TK27GFP, lacking TK and UL24 proteins, suggesting that TK and UL24 play no role in apoptosis. In Vero cells mitochondrial changes characteristic of the apoptotic process were not observed following HSV-1 infection. The UV-inactivated K26GFP had the capacity to induce apoptosis in neuronlike cells. This real-time multiparametric analysis, in combination with relevant viral mutants, could be a useful approach for dissecting the roles of various viral genes in modulating apoptotic pathways during infection. 相似文献
82.
Shigeru Kitayama Takashi Karasawa Akira Matsuyama 《Bioscience, biotechnology, and biochemistry》2013,77(4):628-630
The conversion of prochaetoglobosins as plausible precursors into mycotoxin chaetoglobosin A (1) in a cell-free system of Chaetomium subaffine was unsuccessful. However, reductase activity of the 20-keto-analogues (1), and prochaetoglobosins II (5) and III (6) were found in a microsomal fraction of this fungi. Two new metabolites of chaetoglobosins, named chaetoglobosin Fex (2) and 20-dihydro-chaetoglobosin A (3), were also isolated from the same micro-organisms. Their structures were elucidated by spectroscopic data and chemical transformation. 相似文献
83.
84.
85.
86.
87.
Plasmacytoid dendritic cells (pDCs) represent a unique and crucial immune cell population capable of producing large amounts
of type I interferons (IFNs) in response to viral infection. The function of pDCs as the professional type I IFN-producing
cells is linked to their selective expression of Toll-like receptor 7 (TLR7) and TLR9, which sense viral nucleic acids within
the endosomal compartments. Type I IFNs produced by pDCs not only directly inhibit viral replication but also play an essential
role in linking the innate and adaptive immune system. The aberrant activation of pDCs by self nucleic acids through TLR signaling
and the ongoing production of type I IFNs do occur in some autoimmune diseases. Therefore, pDC may serve as an attractive
target for therapeutic manipulations of the immune system to treat viral infectious diseases and autoimmune diseases. 相似文献
88.
Luminescence properties of green‐emitting Ca2MgSi2O7:Eu2+ phosphor by a solid‐state reaction method 下载免费PDF全文
A europium (Eu)‐doped di‐calcium magnesium di‐silicate phosphor, Ca2MgSi2O7:Eu2+, was prepared using a solid‐state reaction method. The phase structure, particle size, surface morphology, elemental analysis, different stretching mode and luminescence properties were analyzed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) with energy dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and mechanoluminescence (ML). The phase structure of Ca2MgSi2O7:Eu2+ was an akermanite‐type structure, which belongs to the tetragonal crystallography with space group P4?21m; this structure is a member of the melilite group and forms a layered compound. The surface of the prepared phosphor was not found to be uniform and particle distribution was in the nanometer range. EDX and FTIR confirm the components of Eu2+‐doped Ca2MgSi2O7 phosphor. Under UV excitation, the main emission peak appeared at 530 nm, belonging to the broad emission ascribed to the 4f65d1→4f7 transition of Eu2+. The ML intensity of the prepared phosphor increased linearly with increasing impact velocity. A CIE color chromaticity diagram and ML spectrum confirmed that the prepared Ca2MgSi2O7:Eu2+ phosphor would emit green color and the ML spectrum was similar to that of PL, which indicated that ML is emitted from the same center of Eu2+ ions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
89.
Kinetic screening of antibody-Im7 conjugates by capture on a colicin E7 DNase domain using optical biosensors 总被引:1,自引:0,他引:1
Antibody generation by phage display and related in vitro display technologies routinely yields large panels of clones detected in primary end-point screenings such as enzyme-linked immunosorbent assay (ELISA). However, for the development of clinical lead candidates, rapid determination of secondary characteristics such as kinetics and thermodynamics is of nearly equal importance. Surface plasmon resonance-based biosensors are ideal tools for carrying out such high-throughput secondary screenings, allowing preliminary but confident ranking and identification of lead clones. A key feature of these assays is the stable and reversible capture of antibody fragments from crude samples leading to high-resolution kinetic analysis of library outputs. Here we exploit the high-affinity interaction between the naturally occurring nuclease domain of E. coli colicin E7 (DNaseE7) and its cognate partner, the immunity protein 7 (Im7), to develop a ligand capture system suitable for accurate kinetic ranking of library clones. We demonstrate generic applicability for a range of antibody formats: scFv antibodies, diabodies, antigen binding fragments (Fabs), and shark VNAR single domain antibodies. The system is adaptable and reproducible, with comparable results achieved for both the Biacore T100 and ProteOn XPR36 array biosensors. 相似文献
90.
Boutz DR Cascio D Whitelegge J Perry LJ Yeates TO 《Journal of molecular biology》2007,368(5):1332-1344
A growing number of organisms have been discovered inhabiting extreme environments, including temperatures in excess of 100 degrees C. How cellular proteins from such organisms retain their native folds under extreme conditions is still not fully understood. Recent computational and structural studies have identified disulfide bonding as an important mechanism for stabilizing intracellular proteins in certain thermophilic microbes. Here, we present the first proteomic analysis of intracellular disulfide bonding in the hyperthermophilic archaeon Pyrobaculum aerophilum. Our study reveals that the utilization of disulfide bonds extends beyond individual proteins to include many protein-protein complexes. We report the 1.6 A crystal structure of one such complex, a citrate synthase homodimer. The structure contains two intramolecular disulfide bonds, one per subunit, which result in the cyclization of each protein chain in such a way that the two chains are topologically interlinked, rendering them inseparable. This unusual feature emphasizes the variety and sophistication of the molecular mechanisms that can be achieved by evolution. 相似文献