全文获取类型
收费全文 | 1634篇 |
免费 | 123篇 |
国内免费 | 63篇 |
出版年
2023年 | 7篇 |
2022年 | 31篇 |
2021年 | 69篇 |
2020年 | 37篇 |
2019年 | 58篇 |
2018年 | 54篇 |
2017年 | 41篇 |
2016年 | 71篇 |
2015年 | 108篇 |
2014年 | 115篇 |
2013年 | 117篇 |
2012年 | 150篇 |
2011年 | 122篇 |
2010年 | 83篇 |
2009年 | 67篇 |
2008年 | 70篇 |
2007年 | 83篇 |
2006年 | 66篇 |
2005年 | 72篇 |
2004年 | 56篇 |
2003年 | 57篇 |
2002年 | 48篇 |
2001年 | 38篇 |
2000年 | 21篇 |
1999年 | 32篇 |
1998年 | 16篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 13篇 |
1994年 | 15篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 13篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1976年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 2篇 |
排序方式: 共有1820条查询结果,搜索用时 15 毫秒
21.
D Manor G Z Weng H Deng S Cosloy C X Chen V Balogh-Nair K Delaria F Jurnak R Callender 《Biochemistry》1991,30(45):10914-10920
We have measured the Raman spectrum of GDP bound to the elongation factor protein, EF-Tu, and the c-Harvey-ras protein, p21, two proteins of the guanine nucleotide binding family. In order to separate the Raman spectrum of the nucleotide from the much more intense protein spectrum, we investigate the feasibility of "tagging" the normal modes of the nucleotide by isotopic substitution, here by incoporating deuterium-labeled guanine at the C8 position into the active site. A difference spectrum between the labeled and unlabeled protein-nucleotide complex shows the changes in the Raman spectrum of the bound nucleotide that arise from the isotopic exchange. We find that surprisingly good Raman spectra of bound ligands can be obtained with this method and that the method can be easily generalized to other systems. The data show that the guanine amino group of the nucleotide interacts differently with both EF-Tu and p21 than it does with water, showing a change in hydrogen-bonding properties upon binding. On the other hand, no change in hydrogen bonding is observed at guanine's N7. The data strongly suggest that the conformation of the nucleotide when bound to EF-Tu and that p21 is the C2' endo pucker of the ribose ring and anti about the glycosidic bond. These results are compared to previous structural and chemical studies. 相似文献
22.
Summary Cellulose acetate phthalate was used to prepare the Mycoplasma hyopneumoniae vaccine (MHV) microspheres using a solvent evaporation method. Swine serum was used as an additive in the antigen to form the core materials. The addition of serum had a significant effect on surface topography of the MHV microspheres. By using this modified solvent evaporation method, the recoveries of antigens in the MHV microspheres were generally over 90% of the weight and antigenicity of antigens originally added in the formulation. 相似文献
23.
Pulmonary gas exchange was measured in seven resting supine subjects breathing air or a dense gas mixture containing 21% O2 in sulfur hexafluoride (SF6). The mean value of the alveolar-arterial oxygen difference (AaDO2) decreased from 12.4 on air to 7.0 on SF6 (P less than 0.01), and increased again to 13.4 when air breathing resumed (P less than 0.01). No differences occurred between gas mixtures for O2 consumption, respiratory quotient, minute ventilation, breathing frequency, heart rate, or blood pressure, and the improved oxygen transfer could not be attributed to changes in cardiac output or mixed venous oxygen content in the one subject in which they were measured. These results are best explained by an altered distribution of ventilation during dense gas breathing, so that the ventilation-perfusion ratio (VA/Q) variance was reduced. Of several considered mechanisms, we favor one in which SF6 promotes cardiogenic gas mixing between peripheral parallel units having different alveolar gas concentrations. This mechanism allows for observed increases in arterial carbon dioxide tension and dead space-to-tidal volume ratio during dense gas breathing, and suggests that intraregional VA/Q variance accounts for at least one-half of the resting AaDO2 in healthy supine young men. 相似文献
24.
Early and late replicating chromosomal banding patterns of Gallus domesticus were investigated by cell synchronization and incorporation of 5'-bromodeoxyuridine during early and late DNA synthesis. The early replicating chromosomal banding patterns observed, as revealed by either acridine orange or Hoechst 33258/propidium iodide staining, were similar to the structural G-banding patterns obtained by trypsin digestion and Giemsa staining. Late replicating chromosomal banding showed extensive reverse band complementarity to the G-banding pattern. Cell synchronization increased the number of prometaphase and metaphase plates available for analysis. G-banding obtained by Hoechst 33258/propidium iodide staining was investigated due to the fact that it is compatible with chromosomal in situ hybridization procedures that use nonisotopically-labeled DNA probes. Standard replicative G-banded and R-banded idiograms, as obtained after cell synchronization, are proposed. 相似文献
25.
Carbonyl stretching frequencies of acyl groups conjugated with porphyrin rings are useful probes of the effective electronegativities of corrdinated iron atoms in iron porphyrins. Acetyl carbonyl stretching frequencies for 2,4-diacetyldeuteroporphyrin IX dimethyl ester derivatives exhibit both metal oxidation state and axial ligand effects. Infrared spectra of chloroform and pyridine solutions, corrected for solvation, showed the sequences of acetyl carbonyl stretching frequencies: dipyridine iron(II) less than mu-oxo bisiron(III) less than bromo iron(III) approximately equal to chloro iron(III) and dipyridine nickel(II) less than nickel(II). Applications of the probe to the study of hemeproteins are indicated. 相似文献
26.
Huiwen Chen Chao Fang Xin Zhi Shaojun Song Yanqiu Gu Xiaofei Chen Jin Cui Yan Hu Weizong Weng Qirong Zhou Yajun Wang Yao Wang Hao Jiang Xiaoqun Li Liehu Cao Xiao Chen Jiacan Su 《Journal of cellular and molecular medicine》2020,24(16):9067-9084
Psoralea corylifolia (P corylifolia) has been popularly applied in traditional Chinese medicine decoction for treating osteoporosis and promoting fracture healing since centuries ago. However, the bioactive natural components remain unknown. In this study, applying comprehensive two‐dimensional cell membrane chromatographic/C18 column/time‐of‐flight mass spectrometry (2D CMC/C18 column/TOFMS) system, neobavaisoflavone (NBIF), for the first time, was identified for the bioaffinity with RAW 264.7 cells membranes from the extracts of P corylifolia. Here, we revealed that NBIF inhibited RANKL‐mediated osteoclastogenesis in bone marrow monocytes (BMMCs) and RAW264.7 cells dose dependently at the early stage. Moreover, NBIF inhibited osteoclasts function demonstrated by actin ring formation assay and pit‐formation assay. With regard to the underlying molecular mechanism, co‐immunoprecipitation showed that both the interactions of RANK with TRAF6 and with c‐Src were disrupted. In addition, NBIF inhibited the phosphorylation of P50, P65, IκB in NF‐κB pathway, ERK, JNK, P38 in MAPKs pathway, AKT in Akt pathway, accompanied with a blockade of calcium oscillation and inactivation of nuclear translocation of nuclear factor of activated T cells cytoplasmic 1 (NFATc1). In vivo, NBIF inhibited osteoclastogenesis, promoted osteogenesis and ameliorated bone loss in ovariectomized mice. In summary, P corylifolia‐derived NBIF inhibited RANKL‐mediated osteoclastogenesis by suppressing the recruitment of TRAF6 and c‐Src to RANK, inactivating NF‐κB, MAPKs, and Akt signalling pathways and inhibiting calcium oscillation and NFATc1 translocation. NBIF might serve as a promising candidate for the treatment of osteoclast‐associated osteopenic diseases. 相似文献
27.
28.
29.
Xiangcheng Qin Aimei Lu Meilin Ke Weizhi Zhu Xiaolei Ye Gang Wang Guobin Weng 《Cell biology international》2020,44(4):937-946
The regulation of DJ‐1 on AR signaling plays an important role in the pathogenesis of prostate cancer (PCa). DJ‐1 could alter autophagy and regulate Beclin1‐involved autophagy response through JNK‐dependent pathway. JNK is known to mediate autophagy through Bcl2–Beclin1 complex. Therefore, this study aimed to investigate the significance of autophagy in DJ‐1‐modulated PCa cells. The current studies showed that DJ‐1 overexpression in LNCaP decreased LC3 transformation and autophagosome formation. However, DJ‐1 knockdown exerted the opposite effect. Moreover, DJ‐1 silencing inhibited survival and promoted death in LNCaP, which was recovered by autophagy inhibition with 3‐MA. In addition, DJ‐1 overexpression inhibited the phosphorylation of JNK and Bcl2, and the dissociation of Beclin1 and Bcl2; while the effect of silencing DJ‐1 was completely opposite. More important, JNK activated by anisimycin inhibited the proliferation and promoted death of DJ‐1‐overexpressed LNCaP while increasing LC3 transformation and LC3‐puncta formation, but these results were reversed by the decrease of Beclin1 (by spautin‐1). In contrast, when DJ‐1 was silenced, the death of LNCaP, LC3 transformation, and LC3‐puncta formation were inhibited by JNK inhibitor SP600125, which promoted cell proliferation. However, Bcl2 inhibition (by ABT737) reversed all the effects of SP600125. Our results suggested that DJ‐1 in PCa cells could promote the growth of PCa through autophagy inhibition, and JNK–Bcl2–Beclin1 signaling played an important role in it. The study provided new insights into the role of DJ‐1 in the development of PCa. 相似文献
30.
Liu Tengfei Sun Liang Meng Qiucheng Yu Jianghui Weng Lushui Li Jinjiang Deng Lihua Zhu Qihong Gu Xingyou Chen Caiyan Teng Sheng Xiao Guoying 《Plant and Soil》2021,463(1-2):39-53
Plant and Soil - Rice accumulates higher levels of cadmium (Cd) in grain than other cereals, and hybrid rice varieties cover around half of the total rice area in China. Therefore, understanding... 相似文献