全文获取类型
收费全文 | 3099篇 |
免费 | 173篇 |
专业分类
3272篇 |
出版年
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 59篇 |
2020年 | 31篇 |
2019年 | 46篇 |
2018年 | 57篇 |
2017年 | 53篇 |
2016年 | 82篇 |
2015年 | 106篇 |
2014年 | 132篇 |
2013年 | 160篇 |
2012年 | 238篇 |
2011年 | 196篇 |
2010年 | 138篇 |
2009年 | 119篇 |
2008年 | 200篇 |
2007年 | 149篇 |
2006年 | 140篇 |
2005年 | 152篇 |
2004年 | 147篇 |
2003年 | 140篇 |
2002年 | 104篇 |
2001年 | 43篇 |
2000年 | 37篇 |
1999年 | 50篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 13篇 |
1995年 | 23篇 |
1994年 | 17篇 |
1993年 | 23篇 |
1992年 | 38篇 |
1991年 | 31篇 |
1990年 | 46篇 |
1989年 | 52篇 |
1988年 | 33篇 |
1987年 | 38篇 |
1986年 | 32篇 |
1985年 | 39篇 |
1984年 | 23篇 |
1983年 | 23篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 12篇 |
1978年 | 19篇 |
1977年 | 12篇 |
1976年 | 11篇 |
1975年 | 14篇 |
1972年 | 13篇 |
1968年 | 12篇 |
排序方式: 共有3272条查询结果,搜索用时 15 毫秒
911.
Effects of hyperosmotic solutions on the filament lattice of intact frog skeletal muscle. 总被引:1,自引:1,他引:1 下载免费PDF全文
The effect of increasing the osmotic strength of the extracellular solution on the fifament lattice of living frog sartorius and semitendinosus muscle has been studied using low-angle x-ray diffraction to measure the lattice spacing. As the extracellular osmotic strength is increased, the filament lattice shrinks like an osmometer until a minimal spacing between the thick filaments is reached. This minimal spacing varies from 20 to 31 nm, depending on the sarcomere length. Further increase in the osmotic strength produces little further shrinkage. The osmotic shrinkage curve indicates, for both muscles, an osmotically-inactive volume of approximately 30% of the volume in normal Ringer's solution. Shrinkage appears to be independent of temperature and the type of particle used to increase the osmotic strength (glucose, sucrose, small ions). The rate at which osmotic equilibruim is reached depends on muscle size, being slower for greater muscle diameters. Equilibrium spacings are approached exponentially with time constants ranging from 20 to 60 min. Independent of osmotic equilibrium, the lattice tends to shrink slowly by approximately 3% over the first few hours after dissection, probably because of a leakage of K+ ions from inside the muscle cells. This can be partly prevented by using an extracellular solution which contains a higher concentration of K+ ions or which is hypoosmotic. The volume of the muscle filament lattice (1.155d10(2) . S) is constant over a very wide range of sarcomere lengths, and is equal to approximately 3.6 x 10(6) nm3 for a range of amphibian muscle types. 相似文献
912.
Suto K Shimizu Y Watanabe K Ueda T Fukai S Nureki O Tomita K 《The EMBO journal》2006,25(24):5942-5950
Eubacterial leucyl/phenylalanyl-tRNA protein transferase (L/F-transferase), encoded by the aat gene, conjugates leucine or phenylalanine to the N-terminal Arg or Lys residue of proteins, using Leu-tRNA(Leu) or Phe-tRNA(Phe) as a substrate. The resulting N-terminal Leu or Phe acts as a degradation signal for the ClpS-ClpAP-mediated N-end rule protein degradation pathway. Here, we present the crystal structures of Escherichia coli L/F-transferase and its complex with an aminoacyl-tRNA analog, puromycin. The C-terminal domain of L/F-transferase consists of the GCN5-related N-acetyltransferase fold, commonly observed in the acetyltransferase superfamily. The p-methoxybenzyl group of puromycin, corresponding to the side chain of Leu or Phe of Leu-tRNA(Leu) or Phe-tRNA(Phe), is accommodated in a highly hydrophobic pocket, with a shape and size suitable for hydrophobic amino-acid residues lacking a branched beta-carbon, such as leucine and phenylalanine. Structure-based mutagenesis of L/F-transferase revealed its substrate specificity. Furthermore, we present a model of the L/F-transferase complex with tRNA and substrate proteins bearing an N-terminal Arg or Lys. 相似文献
913.
Proteogenomic analysis reveals alternative splicing and translation as part of the abscisic acid response in Arabidopsis seedlings 下载免费PDF全文
Fu‐Yuan Zhu Mo‐Xian Chen Neng‐Hui Ye Lu Shi Kai‐Long Ma Jing‐Fang Yang Yun‐Ying Cao Youjun Zhang Takuya Yoshida Alisdair R. Fernie Guang‐Yi Fan Bo Wen Ruo Zhou Tie‐Yuan Liu Tao Fan Bei Gao Di Zhang Ge‐Fei Hao Shi Xiao Ying‐Gao Liu Jianhua Zhang 《The Plant journal : for cell and molecular biology》2017,91(3):518-533
In eukaryotes, mechanisms such as alternative splicing (AS) and alternative translation initiation (ATI) contribute to organismal protein diversity. Specifically, splicing factors play crucial roles in responses to environment and development cues; however, the underlying mechanisms are not well investigated in plants. Here, we report the parallel employment of short‐read RNA sequencing, single molecule long‐read sequencing and proteomic identification to unravel AS isoforms and previously unannotated proteins in response to abscisic acid (ABA) treatment. Combining the data from the two sequencing methods, approximately 83.4% of intron‐containing genes were alternatively spliced. Two AS types, which are referred to as alternative first exon (AFE) and alternative last exon (ALE), were more abundant than intron retention (IR); however, by contrast to AS events detected under normal conditions, differentially expressed AS isoforms were more likely to be translated. ABA extensively affects the AS pattern, indicated by the increasing number of non‐conventional splicing sites. This work also identified thousands of unannotated peptides and proteins by ATI based on mass spectrometry and a virtual peptide library deduced from both strands of coding regions within the Arabidopsis genome. The results enhance our understanding of AS and alternative translation mechanisms under normal conditions, and in response to ABA treatment. 相似文献
914.
915.
916.
Kanemitsu Takuya Kawabata Shinji Fukumura Masao Futamura Gen Hiramatsu Ryo Nonoguchi Naosuke Nakagawa Fumiko Takata Takushi Tanaka Hiroki Suzuki Minoru Masunaga Shin-Ichiro Ono Koji Miyatake Shin-Ichi Nakamura Hiroyuki Kuroiwa Toshihiko 《Radiation and environmental biophysics》2019,58(1):59-67
Radiation and Environmental Biophysics - Folic acid (FA) has high affinity for the folate receptor (FR), which is limited expressed in normal human tissues, but over-expressed in several tumor... 相似文献
917.
918.
Nobutake Tamai Takuya Izumikawa Suguru Fukui Maiko Uemura Masaki Goto Hitoshi Matsuki Shoji Kaneshina 《生物化学与生物物理学报:生物膜》2013
Thermotropic phase behavior of diacylphosphatidylcholine (CnPC)–cholesterol binary bilayers (n = 14–16) was examined by fluorescence spectroscopy using 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and differential scanning calorimetry. The former technique can detect structural changes of the bilayer in response to the changes in polarity around Prodan molecules partitioned in a relatively hydrophilic region of the bilayer, while the latter is sensitive to the conformational changes of the acyl chains. On the basis of the data from both techniques, we propose possible temperature T–cholesterol composition Xch phase diagrams for these binary bilayers. A notable feature of our phase diagrams, including our previous results for diheptadecanoylphosphatidylcholine (C17PC) and distearoylphosphatidylcholine (C18PC), is that there is a peritectic-like point around Xch = 0.15, which can be interpreted as indicating the formation of a 1:6-complex of cholesterol and CnPCs within the binary bilayer irrespective of the acyl chain length. We could give a reasonable explanation for such complex formation using the modified superlattice view. Our results also showed that the Xch value of the abolition of the main transition is almost constant for n = 14–17 (ca. 0.33), while it increases to ca. 0.50 for n = 18. By contrast, a biphasic n-dependence of Xch was observed for the abolition of the pretransition, suggesting that there are at least two antagonistic n-dependent factors. We speculate that this could be explained by the enhancement of the van der Waals interaction with increases in n and the weakening of the repulsion between the neighboring headgroups with decreases in n. 相似文献
919.
Tebayashi S Kawahara T Kim CS Nishi A Takahashi K Miyanoshita A Horiike M 《Zeitschrift für Naturforschung. C, Journal of biosciences》2003,58(3-4):295-299
Four fatty acid methyl esters identified in the solvent extract of Tribolium confusum (Jacquelin du Val) larvae as kairomones were individually and collectively tested for probing behavior of Peregrinator biannulipes Montrouzier et Signoret. All identified fatty acid methyl eaters, methyl palmitate, methyl linolate, methyl oleate and methyl stearate, exhibited characterisitic kairomonal probing behavior of P. biannulipe toward the lure. These fatty acid methyl ester were active at 0.2 microg/lure but a synergistic effect was not observed among them. Commercially available C8-C14 even-numbered fatty acid methyl esters that were not detected in the extract of T. confusum larvae also elicited a probing behavior but their activities were weaker than those of four fatty acid methyl ester (C16:0, C18:0, C18:1 and C18:2) identified in the extract. On the other hand, C17 and C19 odd-numbered fatty acid methyl esters did not show any activity at all. 相似文献
920.
Kinuyo Yamashita Yoshitaka Nakajima Hayato Matsushita Ryuji Yamazawa Futoshi Matsubara Kiyoshi Ito Tadashi Yoshimoto 《Journal of molecular biology》2010,396(4):1081-1096
Creatininase is a binuclear zinc enzyme and catalyzes the reversible conversion of creatinine to creatine. It exhibits an open-closed conformational change upon substrate binding, and the differences in the conformations of Tyr121, Trp154, and the loop region containing Trp174 were evident in the enzyme-creatine complex when compared to those in the ligand-free enzyme. We have determined the crystal structure of the enzyme complexed with a 1-methylguanidine. All subunits in the complex existed as the closed form, and the binding mode of creatinine was estimated. Site-directed mutagenesis revealed that the hydrophobic residues that show conformational change upon substrate binding are important for the enzyme activity.We propose a catalytic mechanism of creatininase in which two water molecules have significant roles. The first molecule is a hydroxide ion (Wat1) that is bound as a bridge between the two metal ions and attacks the carbonyl carbon of the substrate. The second molecule is a water molecule (Wat2) that is bound to the carboxyl group of Glu122 and functions as a proton donor in catalysis. The activity of the E122Q mutant was very low and it was only partially restored by the addition of ZnCl2 or MnCl2. In the E122Q mutant, kcat is drastically decreased, indicating that Glu122 is important for catalysis. X-ray crystallographic study and the atomic absorption spectrometry analysis of the E122Q mutant-substrate complex revealed that the drastic decrease of the activity of the E122Q was caused by not only the loss of one Zn ion at the Metal1 site but also a critical function of Glu122, which most likely exists for a proton transfer step through Wat2. 相似文献