全文获取类型
收费全文 | 1673篇 |
免费 | 131篇 |
出版年
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 38篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 28篇 |
2017年 | 27篇 |
2016年 | 40篇 |
2015年 | 91篇 |
2014年 | 75篇 |
2013年 | 98篇 |
2012年 | 125篇 |
2011年 | 129篇 |
2010年 | 86篇 |
2009年 | 47篇 |
2008年 | 100篇 |
2007年 | 96篇 |
2006年 | 110篇 |
2005年 | 87篇 |
2004年 | 99篇 |
2003年 | 80篇 |
2002年 | 76篇 |
2001年 | 19篇 |
2000年 | 20篇 |
1999年 | 37篇 |
1998年 | 19篇 |
1997年 | 19篇 |
1996年 | 17篇 |
1995年 | 20篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 15篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1981年 | 5篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1965年 | 2篇 |
1962年 | 2篇 |
1920年 | 2篇 |
排序方式: 共有1804条查询结果,搜索用时 15 毫秒
181.
The nerve tissue hemoglobin of Cerebratulus lacteus (CerHb) is the smallest naturally occurring known hemoglobin. Stabilization of the diatomic bound species (e.g., O(2)) is achieved through a network of hydrogen bonds based on three key residues TyrB10, GlnE7, and ThrE11. The first two residues are typically associated in hemoglobins with enhanced O(2) affinity, related to hydrogen bond stabilization of the heme-bound O(2) resulting in a decrease of the ligand dissociation rates. In contrast to the above observations, the affinity of CerHb for O(2) is only moderate, and the rate of O(2) dissociation is unexpectedly high. To gain insight on the diverse molecular mechanisms controlling ligand affinities, we have analyzed w.t. CerHb and its ThrE11-->Val mutant by means of joint molecular dynamics and quantum mechanics simulation techniques, complementing recent site-directed mutagenesis experiments. Our results suggest that the observed O(2) dissociation rates can only be explained through a dynamic equilibrium between high and low affinity states of the w.t. CerHb heme distal site. 相似文献
182.
183.
Casas J Gijón MA Vigo AG Crespo MS Balsinde J Balboa MA 《The Journal of biological chemistry》2006,281(9):6106-6116
The calcium ionophore ionomycin induces apoptosis-like events in the human embryonic kidney cell line at early times. Plasma membrane blebbing, mitochondrial depolarization, externalization of phosphatidylserine, and nuclear permeability changes can all be observed within 15 min of treatment. However, there is no activation of caspases or chromatin condensation. Expression of a fusion protein containing the enhanced green fluorescent protein (EGFP) and human cytosolic Group IVA phospholipase A(2)alpha (EGFP-cPLA(2)alpha) in these cells prevents ionomycin-induced phosphatidylserine externalization and death. Cells expressing the cPLA(2)alpha mutant D43N, which does not bind calcium, retain their susceptibility to ionomycin-induced cell death. Both nonexpressing and EGFP-D43N-cPLA(2)alpha-expressing human embryonic kidney cells can be spared from ionomycin-induced cell death by pretreating them with exogenous arachidonic acid. Moreover, during calcium overload, mitochondrial depolarization is significantly lower in the EGFP-cPLA(2)alpha-expressing cells than in cells expressing normal amounts of cPLA(2)alpha. These results suggest that early cell death events promoted by an overload of calcium can be prevented by the presence of high levels of arachidonic acid. 相似文献
184.
Marti MA Crespo A Capece L Boechi L Bikiel DE Scherlis DA Estrin DA 《Journal of inorganic biochemistry》2006,100(4):761-770
We present an investigation of the molecular basis of the modulation of oxygen affinity in heme proteins using computer simulation. QM-MM calculations are applied to explore distal and proximal effects on O(2) binding to the heme, while classical molecular dynamics simulations are employed to investigate ligand migration across the polypeptide to the active site. Trends in binding energies and in the kinetic constants are illustrated through a number of selected examples highlighting the virtues and the limitations of the applied methodologies. These examples cover a wide range of O(2)-affinities, and include: the truncated-N and truncated-O hemoglobins from Mycobacterium tuberculosis, the mammalian muscular O(2) storage protein: myoglobin, the hemoglobin from the parasitic nematode Ascaris lumbricoides, the oxygen transporter in the root of leguminous plants: leghemoglobin, the Cerebratulus lacteus nerve tissue hemoglobin, and the Alcaligenes xyloxidans cytochrome c'. 相似文献
185.
Ribose phosphates are either synthesized through the oxidative branch of the pentose phosphate pathway or stem from the phosphorolytic cleavage of the N-glycosidic bond of ribonucleosides. The two major pentose phosphates, ribose-5-phosphate and ribose-1-phosphate, can be readily interconverted by phosphopentomutase. Ribose-5-phosphate is also the direct precursor of 5-phosphoribosyl-1-pyrophosphate, which is used for both de novo and salvage synthesis of nucleotides. On the other hand, the phosphorolysis of deoxyribonucleosides is the major source of deoxyribose phosphates. While the destiny of the nucleobase stemming from nucleoside phosphorolysis has been extensively investigated, the fate of the sugar moiety has been somehow neglected. However, extensive advances have been made in elucidating the pathways by which the pentose phosphates, arising from nucleoside phosphorolysis, are either recycled, without opening of their furanosidic ring, or catabolized as a carbon and energy source. Nevertheless, many aspects of pentose phosphate metabolism, and the possible involvement of these compounds in a number of cellular processes still remain obscure. The comprehension of the role played by pentose phosphates may be greatly facilitated by the knowledge of their steady-state intracellular levels and of their changes in response to variations of intra- and extracellular signals. 相似文献
186.
Marzorati M Alma A Sacchi L Pajoro M Palermo S Brusetti L Raddadi N Balloi A Tedeschi R Clementi E Corona S Quaglino F Bianco PA Beninati T Bandi C Daffonchio D 《Applied and environmental microbiology》2006,72(2):1467-1475
Flavescence dorée (FD) is a grapevine disease that afflicts several wine production areas in Europe, from Portugal to Serbia. FD is caused by a bacterium, "Candidatus Phytoplasma vitis," which is spread throughout the vineyards by a leafhopper, Scaphoideus titanus (Cicadellidae). After collection of S. titanus specimens from FD-contaminated vineyards in three different areas in the Piedmont region of Italy, we performed a survey to characterize the bacterial microflora associated with this insect. Using length heterogeneity PCR with universal primers for bacteria we identified a major peak associated with almost all of the individuals examined (both males and females). Characterization by denaturing gradient gel electrophoresis confirmed the presence of a major band that, after sequencing, showed a 97 to 99% identity with Bacteroidetes symbionts of the "Candidatus Cardinium hertigii" group. In addition, electron microscopy of tissues of S. titanus fed for 3 months on phytoplasma-infected grapevine plants showed bacterial cells with the typical morphology of "Ca. Cardinium hertigii." This endosymbiont, tentatively designated ST1-C, was found in the cytoplasm of previtellogenic and vitellogenic ovarian cells, in the follicle cells, and in the fat body and salivary glands. In addition, cell morphologies resembling those of "Ca. Phytoplasma vitis" were detected in the midgut, and specific PCR assays indicated the presence of the phytoplasma in the gut, fat body and salivary glands. These results indicate that ST1-C and "Ca. Phytoplasma vitis" have a complex life cycle in the body of S. titanus and are colocalized in different organs and tissues. 相似文献
187.
188.
189.
Everett T Hayes Jessica C Wilks Piero Sanfilippo Elizabeth Yohannes Daniel P Tate Brian D Jones Michael D Radmacher Sandra S BonDurant Joan L Slonczewski 《BMC microbiology》2006,6(1):89-18
Background
InEscherichia coli, pH regulates genes for amino-acid and sugar catabolism, electron transport, oxidative stress, periplasmic and envelope proteins. Many pH-dependent genes are co-regulated by anaerobiosis, but the overall intersection of pH stress and oxygen limitation has not been investigated. 相似文献190.