全文获取类型
收费全文 | 11405篇 |
免费 | 910篇 |
国内免费 | 769篇 |
专业分类
13084篇 |
出版年
2024年 | 20篇 |
2023年 | 212篇 |
2022年 | 400篇 |
2021年 | 631篇 |
2020年 | 400篇 |
2019年 | 515篇 |
2018年 | 538篇 |
2017年 | 343篇 |
2016年 | 509篇 |
2015年 | 711篇 |
2014年 | 793篇 |
2013年 | 921篇 |
2012年 | 1070篇 |
2011年 | 931篇 |
2010年 | 577篇 |
2009年 | 498篇 |
2008年 | 534篇 |
2007年 | 492篇 |
2006年 | 430篇 |
2005年 | 366篇 |
2004年 | 305篇 |
2003年 | 234篇 |
2002年 | 190篇 |
2001年 | 203篇 |
2000年 | 170篇 |
1999年 | 178篇 |
1998年 | 102篇 |
1997年 | 123篇 |
1996年 | 105篇 |
1995年 | 87篇 |
1994年 | 92篇 |
1993年 | 49篇 |
1992年 | 74篇 |
1991年 | 55篇 |
1990年 | 44篇 |
1989年 | 47篇 |
1988年 | 39篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Jiheng Zhan Xing Li Dan Luo Yu Hou Yonghui Hou Shudong Chen Zhifeng Xiao Jiyao Luan Dingkun Lin 《Journal of cellular and molecular medicine》2020,24(9):5317-5329
Bone marrow mesenchymal stem cell (BMSC) transplantation represents a promising repair strategy following spinal cord injury (SCI), although the therapeutic effects are minimal due to their limited neural differentiation potential. Polydatin (PD), a key component of the Chinese herb Polygonum cuspidatum, exerts significant neuroprotective effects in various central nervous system disorders and protects BMSCs against oxidative injury. However, the effect of PD on the neuronal differentiation of BMSCs, and the underlying mechanisms remain inadequately understood. In this study, we induced neuronal differentiation of BMSCs in the presence of PD, and analysed the Nrf2 signalling and neuronal differentiation markers using routine molecular assays. We also established an in vivo model of SCI and assessed the locomotor function of the mice through hindlimb movements and electrophysiological measurements. Finally, tissue regeneration was evaluated by H&E staining, Nissl staining and transmission electron microscopy. PD (30 μmol/L) markedly facilitated BMSC differentiation into neuron‐like cells by activating the Nrf2 pathway and increased the expression of neuronal markers in the transplanted BMSCs at the injured spinal cord sites. Furthermore, compared with either monotherapy, the combination of PD and BMSC transplantation promoted axonal rehabilitation, attenuated glial scar formation and promoted axonal generation across the glial scar, thereby enhancing recovery of hindlimb locomotor function. Taken together, PD augments the neuronal differentiation of BMSCs via Nrf2 activation and improves functional recovery, indicating a promising new therapeutic approach against SCI. 相似文献
92.
93.
Alkaline phosphatase(AKP),from the succus entericus of silkworm,was purified using 10%-50% ammonium sulfate fractions,ion exchange chromatography Of DEAE-Sepharose,and size exclusion chromatography of Sephacryl S-200.The purification fold was 464 times and specified activity was 3936 U/mg.Optimum pH value of the phosphatase was 10.5,and was stable between pH 7.5 and 11.The optimum temperature of the phosphatase was 40℃ and it was unstable over 50℃.Km value of the phosphatase was 1.25 mmol/L.In a given condition,the phosphatase was selectively modified by PCMB,NBS,PMSE TNBS,SUAN,DTT,BrAc,and IAc,the results indicate that PMSF,SUA,BrAc,IAc,and TNBS could Obviously inhibit the activity of the phosphatase,and the degree of inhibition depended on the concentration of these reagents.There was little effect on the activity of phosphatase after treatment by PMSF,DTT,and NBT.We primarily conclude that mercapto and imidazole are essential for AKP from silkworm.Also,Lys residue and disulfide bands are necessary to protect the catalysis of the AKP. 相似文献
94.
Blockade of L-type voltage-gated Ca channel inhibits ischemia-induced neurogenesis by down-regulating iNOS expression in adult mouse 总被引:3,自引:0,他引:3
Luo CX Zhu XJ Zhang AX Wang W Yang XM Liu SH Han X Sun J Zhang SG Lu Y Zhu DY 《Journal of neurochemistry》2005,94(4):1077-1086
Neurogenesis in the adult mammalian hippocampus may contribute to repairing the brain after injury. The signals that regulate neurogenesis in the dentate gyrus following ischemic stroke insult are not well known. We have previously reported that inducible nitric oxide synthase (iNOS) expression is necessary for ischemia-stimulated neurogenesis in the adult dentate gyrus. Here, we show that mice subjected to 90 min of middle cerebral artery occlusion (MCAO) significantly increased the number of new neurons and up-regulated iNOS expression in the dentate gyrus. Blockade of the L-type voltage-gated Ca(2+) channel (L-VGCC) prevented neurogenesis in the dentate gyrus and subventricular zone (SVZ), and down-regulated iNOS expression in the dentate gyrus after cerebral ischemia. This study suggests that Ca(2+) influx through L-VGCC is involved in ischemia-induced neurogenesis by up-regulating iNOS expression. 相似文献
95.
96.
Hornby JA Luo JK Stevens JM Wallace LA Kaplan W Armstrong RN Dirr HW 《Biochemistry》2000,39(40):12336-12344
The conformational stabilities of two homodimeric class mu glutathione transferases (GSTM1-1 and GSTM2-2) were studied by urea- and guanidinium chloride-induced denaturation. Unfolding is reversible and structural changes were followed with far-ultraviolet circular dichroism, tryptophan fluorescence, enzyme activity, chemical cross-linking, and size-exclusion chromatography. Disruption of secondary structure occurs as a monophasic transition and is independent of protein concentration. Changes in tertiary structure occur as two transitions; the first is protein concentration dependent, while the second is weakly dependent (GSTM1-1) or independent (GSTM2-2). The second transition corresponds with the secondary structure transition. Loss in catalytic activity occurs as two transitions for GSTM1-1 and as one transition for GSTM2-2. These transitions are dependent upon protein concentration. The first deactivation transition coincides with the first tertiary structure transition. Dimer dissociation occurs prior to disruption of secondary structure. The data suggest that the equilibrium unfolding/refolding of the class mu glutathione transferases M1-1 and M2-2 proceed via a three-state process: N(2) <--> 2I <--> 2U. Although GSTM1-1 and GSTM2-2 are homologous (78% identity/94% homology), their N(2) tertiary structures are not identical. Dissociation of the GSTM1-1 dimer to structured monomers (I) occurs at lower denaturant concentrations than for GSTM2-2. The monomeric intermediate for GSTM1-1 is, however, more stable than the intermediate for GSTM2-2. The intermediates are catalytically inactive and display nativelike secondary structure. Guanidinium chloride-induced denaturation yields monomeric intermediates, which have a more loosely packed tertiary structure displaying enhanced solvent exposure of its tryptophans and enhanced ANS binding. The three-state model for the class mu enzymes is in contrast to the equilibrium two-state models previously proposed for representatives of classes alpha/pi/Sj26 GSTs. Class mu subunits appear to be intrinsically more stable than those of the other GST classes. 相似文献
97.
用菠菜甜菜碱醛脱氢酶 ( BADH)免疫巴比西 ( BALB/c)小鼠 ,将其脾细胞与骨髓瘤细胞 SP2 /O-Ag1 4融合 ,在 1 92孔中 ,有约 1 4 %孔生长的杂交瘤细胞 ,用间接酶联免疫方法 ( ELISA)检测表现为阳性。选择其中 2 G3和 2 D10 细胞系 ,用有限稀释法进行克隆化培养 ,约 2 0 %克隆化细胞为强阳性。选择其中 2 G3- H3细胞株注射到 BALB/c小鼠腹腔中诱导腹水 ,腹水的单抗效价为 1∶ 1 0 3。应用 BADH单抗检查了大麦、水稻、高粱、小麦幼苗的叶片和根的粗提物 ,均呈阳性反应 ,表明 BADH除在光合组织中存在外 ,在非光合组织中也可能存在。讨论了非光合组织 BADH的意义 相似文献
98.
Shuilian Luo Yuhang Chen Rui He Yujun Shi Li Su 《Biochemical and biophysical research communications》2018,495(1):607-613
Objective
The decreased expression of muscle-specific microRNA-1 (miR-1) has been found in many cardiovascular diseases and is considered to contribute to heart failure (HF). Here we investigated the role of miR-1 in myocardium protection by infusion of miR-1 in a cardiac global miRNA-deficient mouse.Methods
We generated a cardiac-selective miRNA-deficient mouse by crossing Dicerflox/flox mice with mice expressing tamoxifen-inducible Cre recombinase under the control of a mouse αMHC promoter. When Dicer gene was removed following tamoxifen injection, the mice were treated with micrONTM mmu-miR-1a-3p agomir (agomir-1). The mice were subjected to echocardiography measurement, and the heart tissue specimens were stained with hematoxylin and eosin (H&E) and Sirius red. Terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling assay and Ki67 immunofluorescence were used to determine apoptosis and proliferation.Results
Dicer deletion resulted in extensive decrease in cardiac miRNAs in the mice. In echocardiography, the mice developed rapid and dramatic left ventricular enlargement. In histology, apparent cardiomyocyte hypertrophy, myofiber disarray, ventricular fibrosis, inflammatory infiltration, and severe ventricular remodeling were exhibited. When the mice were treated with agomir-1, they did not show any significant abnormalities in heart structure and histology in response to Dicer ablation.Conclusion
The proper expression of miRNAs plays vital roles in the maintenance of heart histology and function. Among these miRNAs, miR-1 is critical to inhibit myocyte hypertrophy and extracellular matrix deposition, thereby preventing cardiac remodeling in cardiac-selective Dicer deficient mice. 相似文献99.
利用枯草杆菌的分泌系统构建分泌型表达载体表达和分泌外源基因产物具有重要的商业价值。我们用鸟枪法克隆了枯草杆菌染色体的启动子和信号肽序列,将克隆的序列连接到能在枯草杆菌中复制的质粒pUB18上,获得分泌型表达载体pUS186。为了测试构建的载体pUS186的功能,将地衣杆菌α-淀粉酶基因的缺失了启动子和信号肽序列的片段重组进该质粒,经过Bal31酶切,T4DNA聚合酶补齐等处理,获得pUSA186Ⅱ及pUSA186Ⅰ系列质粒,将这些重组质粒转化枯草杆菌QB1130(amy-)后都能向胞外分泌淀粉酶,酶活测定结果表明,基因表达水平比用原有的启动子高1-2倍,蛋白质分泌率在84-96%之间。 相似文献
100.
Tianyuan Li Saif Ullah He Liang Izhar Ali Quan Zhao Anas Iqbal Shanqing Wei Tariq Shah Yuqiong Luo Ligeng Jiang 《Phyton》2021,90(1):223-243
Readily available chemical fertilizers have resulted in a decline in the
use of organic manure (e.g., green manures), a traditionally sustainable source
of nutrients. Based on this, we applied urea at the rate of 270 kg ha−1 with and
without green manure in order to assess nitrogen (N) productivity in a double rice
cropping system in 2017. In particular, treatment combinations were as follows:
winter fallow rice-rice (WF-R-R), milk vetch rice-rice (MV-R-R), oil-seed rape
rice-rice (R-R-R) and potato crop rice-rice (P-R-R). Results revealed that green
manure significantly (p ≤ 0.05) improved the soil chemical properties and net soil
organic carbon content increased by an average 117.47%, total nitrogen (N) by
28.41%, available N by 26.64%, total phosphorus (P) by 37.77%, available P
by 20.48% and available potassium (K) by 33.10% than WF-R-R, however pH
was reduced by 3.30% across the seasons. Similarly, net dry matter accumulation
rate enhanced in green manure applied treatments and ranked in order: P-R-R >
R-R-R > MV-R-R > WF-R-R. Furthermore, the total leaf dry matter transport
(t ha−1
) for the P-R-R in both seasons was significantly higher by an average
11.2%, 7.2% and 36 % than MV-R-R, R-R-R, and WF-R-R, respectively. In addition, net total nitrogen accumulation (kg ha−1
) was found higher in green manure
applied plots compared to the control. Yield and yield attributed traits were
observed maximum in green manure applied plots, with treatments ranking as follows: P-R-R > R-R-R > MV-R-R > WF-R-R. Thus, results obtained highlight
ability of green manure to sustainably improve soil quality and rice yield. 相似文献