全文获取类型
收费全文 | 854篇 |
免费 | 42篇 |
国内免费 | 26篇 |
专业分类
922篇 |
出版年
2024年 | 2篇 |
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 19篇 |
2020年 | 19篇 |
2019年 | 32篇 |
2018年 | 19篇 |
2017年 | 14篇 |
2016年 | 16篇 |
2015年 | 19篇 |
2014年 | 29篇 |
2013年 | 48篇 |
2012年 | 21篇 |
2011年 | 31篇 |
2010年 | 35篇 |
2009年 | 33篇 |
2008年 | 42篇 |
2007年 | 37篇 |
2006年 | 39篇 |
2005年 | 43篇 |
2004年 | 47篇 |
2003年 | 38篇 |
2002年 | 32篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 18篇 |
1998年 | 16篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 22篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 10篇 |
1983年 | 5篇 |
1982年 | 11篇 |
1981年 | 7篇 |
1980年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有922条查询结果,搜索用时 15 毫秒
111.
Takayoshi Yoshida Hiroshi Watari 《European journal of applied physiology and occupational physiology》1993,67(3):274-278
The rates of change in intracellular pH during repeated exercise sessions with rest periods was determined by 31 phosphorus-nuclear magnetic resonance spectroscopy (31P-MRS). Five long-distance runners and six healthy male subjects as controls performed a 2-min femoral flexion at 20 kg · m · min–1 in a 2.1 T superconducting magnet with a 67-cm bore and repeated this exercise four times with 2-min rest periods intervening. In all cases during exercise the inorganic phosphate (Pi) peak split into two, the earlier increased rapidly (high-pH Pi) and the later (low-pH Pi) increased more slowly. The Pi peaks were separated by a fitting procedure using the least square mean method. The high-pH Pi area during exercise decreased as the number of repeated exercise periods increased, while the low-pH Pi area gradually increased. Although the total Pi area decreased exponentially during the recovery period, the high-pH Pi area decreased first and then the low-pH Pi area reduced gradually. The pH values were estimated from the chemical shift between the phosphocreatine peak and each split peak in the Pi. The high-pH in pooled data ranged from 6.6 to 7.0 during exercise and recovery, while the low pH decreased to 6.2 during exercise. As the number of exercise periods increased, each pH value gradually became less acidic, although there was a tendency to more acidity in the control subjects than in the long-distance runners. In conclusion, it was possible to obtain by non-invasive, continuous31P-MRS, a split pattern of Pi peaks during exercise and there were at least tow different intracellular pH values during exercise, suggesting that each Pi peak might be attributed to the types of muscle fibre recruited. 相似文献
112.
Miroslav Vacek Marie Zarevúcka Zdeněk Wimmer Karel Stránský Kateřina Demnerová Marie-Dominique Legoy 《Biotechnology letters》2000,22(19):1565-1570
Selective enzymic esterification of free fatty acids, obtained from blackcurrant oil by chemical saponification, with n-butanol using four immobilized lipases under microwave irradiation and under classical heating was studied. A positive effect of microwave irradiation on chemical yields of the products of the enzymic reactions and specificity of lipases were observed in comparison with a controlled heating in an incubator equipped with shaking (classical heating) applied during the identical enzyme-mediated processes. The maximum quantity of -linolenic acid (30%) was obtained with Lipozyme used as biocatalyst of the reaction under microwave irradiation. The maximum quantity of butyl -linolenate (20%) was obtained by a Pseudomonas cepacia lipase catalyzed esterification under classical heating. 相似文献
113.
目的 探究长链非编码RNA(lncRNA)ZNF667-AS1通过靶向miR-31-5p对食管癌细胞增殖和迁移的影响及潜在的机制.方法 采用实时荧光定量PCR(qPCR)技术检测ZNF667-AS1在食管癌细胞Eca109、EC1、TE1和正常食管上皮细胞Het-1A的表达水平,并选择表达差异最大的细胞株进行后续实验.... 相似文献
114.
115.
L. T. Boni T. P. Stewart J. L. Alderfer S. W. Hui 《The Journal of membrane biology》1981,62(1-2):71-77
Summary Polyethylene glycol, a known cell fusogen, is found to induce the formation of structural defects in egg phosphatidylcholine multilamellar vesicles, as shown by freeze-fracture microscopy.31P NMR spectra of these vesicles reveal the existence of a nonbilayer (isotropic) phase. The observed disruption in the bilayers is believed to be associated with an intermediate stage of membrane fusion.Abbreviations PEG
Polyethylene glycol
- IMP
Intramembranous particle
- PC
Phosphatidylcholine
- PS
Phosphatidylserine
- SUV
Small unilamellar vesicles
- MLV
Multilamellar vesicles
- DPPC
Dipalmitoyl phosphatidylcholine
- DSC
Differential scanning calorimetry
- DMPC
Dimyristoylphosphatidylcholine
-
T
c
Phase transition temperature 相似文献
116.
Platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) is expressed on the surface of endothelial cells (EC) at high levels with important roles in angiogenesis and inflammation. However, the physiological role PECAM-1 plays during vascular development and angiogenesis remains largely unknown. Here we determined the role of PECAM-1 in the postnatal development of retinal vasculature and retinal neovascularization during oxygen-induced ischemic retinopathy (OIR) using PECAM-1-deficient (PECAM-1−/−) mice. A significant decrease in retinal vascular density was observed in PECAM-1−/− mice compared with PECAM-1+/+ mice. This was attributed to a decreased number of EC in the retinas of PECAM-1−/− mice. An increase in the rate of apoptosis was observed in retinal vessels of PECAM-1−/− mice, which was compensated, in part, by an increase in the rate of proliferation. However, the development and regression of hyaloid vasculature were not affected in the absence of PECAM-1. We did not observe a significant defect in astrocytes, the number of endothelial tip cell filopodias, and the rate of developing retinal vasculature progression in PECAM-1−/− mice. However, we observed aberrant organization of arterioles and venules, decreased secondary branching, and dilated vessels in retinal vasculature of PECAM-1−/− mice. In addition, retinal neovascularization was attenuated in PECAM-1−/− mice during OIR despite an expression of VEGF similar to that of PECAM-1+/+ mice. Mechanistically, these changes were associated with an increase in EphB4 and ephrin B2, and a decrease in eNOS, expression in retinal vasculature of PECAM-1−/− mice. These results suggest that PECAM-1 expression and its potential interactions with EphB4/ephrin B2 and eNOS are important for survival, migration, and functional organization of EC during retinal vascular development and angiogenesis. 相似文献
117.
Marina Ikegaya Toshio Moriya Naruhiko Adachi Masato Kawasaki Enoch Y. Park Takatsugu Miyazaki 《The Journal of biological chemistry》2022,298(5)
Carbohydrate-active enzymes are involved in the degradation, biosynthesis, and modification of carbohydrates and vary with the diversity of carbohydrates. The glycoside hydrolase (GH) family 31 is one of the most diverse families of carbohydrate-active enzymes, containing various enzymes that act on α-glycosides. However, the function of some GH31 groups remains unknown, as their enzymatic activity is difficult to estimate due to the low amino acid sequence similarity between characterized and uncharacterized members. Here, we performed a phylogenetic analysis and discovered a protein cluster (GH31_u1) sharing low sequence similarity with the reported GH31 enzymes. Within this cluster, we showed that a GH31_u1 protein from Lactococcus lactis (LlGH31_u1) and its fungal homolog demonstrated hydrolytic activities against nigerose [α-D-Glcp-(1→3)-D-Glc]. The kcat/Km values of LlGH31_u1 against kojibiose and maltose were 13% and 2.1% of that against nigerose, indicating that LlGH31_u1 has a higher specificity to the α-1,3 linkage of nigerose than other characterized GH31 enzymes, including eukaryotic enzymes. Furthermore, the three-dimensional structures of LlGH31_u1 determined using X-ray crystallography and cryogenic electron microscopy revealed that LlGH31_u1 forms a hexamer and has a C-terminal domain comprising four α-helices, suggesting that it contributes to hexamerization. Finally, crystal structures in complex with nigerooligosaccharides and kojibiose along with mutational analysis revealed the active site residues involved in substrate recognition in this enzyme. This study reports the first structure of a bacterial GH31 α-1,3-glucosidase and provides new insight into the substrate specificity of GH31 enzymes and the physiological functions of bacterial and fungal GH31_u1 members. 相似文献
118.
P34, a storage protein and major soybean allergen, has undergone a functional transition from a cysteine peptidase to a syringolide receptor. An exploration of the evolutionary mechanism of this functional transition is made. To identify homologous genes of P34, syntenic network was constructed using syntenic relationships from the Plant Genome Duplication Database. The collected homologous genes, along with SPE31, a highly homologous protein to P34 from the seeds of Pachyrhizus erosus, were used to construct a phylogenetic tree. The results show that multiple gene duplications, exon shuffling and following granulin domain loss and some critical point mutations are associated with the functional transition. Although some tests suggested the existence of positive selection, the possibility that random fixation under relaxation of purifying selection results in the functional transition is also supported. In addition, the genes Glyma08g12340 and Medtr8g086470 may belong to a new group within the papain family. 相似文献
119.
Sinorhizobium meliloti natural populations show a high level of genetic polymorphism possibly due to the presence of mobile genetic elements such as insertion sequences (IS), transposons, and bacterial mobile introns. The analysis of the DNA sequence polymorphism of the nod region of S. meliloti pSymA megaplasmid in an Italian isolate led to the discovery of a new insertion sequence, ISRm31. ISRm31 is 2,803 bp long and has 22-bp-long terminal inverted repeat sequences, 8-bp direct repeat sequences generated by transposition, and three ORFs (A, B, C) coding for proteins of 124, 115, and 541 amino acids, respectively. ORF A and ORF C are significantly similar to members of the transposase family. Amino acid and nucleotide sequences indicate that ISRm31 is a member of the IS66 family. ISRm31 sequences were found in 30.5% of the Italian strains analyzed, and were also present in several collection strains of the Rhizobiaceae family, including S. meliloti strain 1021. Alignment of targets sites in the genome of strains carrying ISRm31 suggested that ISRm31 inserts randomly into S. meliloti genomes. Moreover, analysis of ISRm31 insertion sites revealed DNA sequences not present in the recently sequenced S. meliloti strain 1021 genome. In fact, ISRm31 was in some cases linked to DNA fragments homologous to sequences found in other rhizobia species. 相似文献
120.
Guillem Prats-Ejarque Jose A. Blanco Vivian A. Salazar Victòria M. Nogués Mohammed Moussaoui Ester Boix 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(1):105-117