全文获取类型
收费全文 | 778篇 |
免费 | 92篇 |
国内免费 | 1篇 |
出版年
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 22篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 36篇 |
2012年 | 55篇 |
2011年 | 33篇 |
2010年 | 33篇 |
2009年 | 30篇 |
2008年 | 40篇 |
2007年 | 32篇 |
2006年 | 39篇 |
2005年 | 25篇 |
2004年 | 42篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 38篇 |
2000年 | 22篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 7篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 6篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1979年 | 9篇 |
1978年 | 4篇 |
1977年 | 10篇 |
1976年 | 6篇 |
1974年 | 6篇 |
1970年 | 6篇 |
1969年 | 4篇 |
1968年 | 4篇 |
1967年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有871条查询结果,搜索用时 15 毫秒
1.
S Ravichandran J Dasgupta C Chakrabarti S Ghosh M Singh J K Dattagupta 《Protein engineering》2001,14(5):349-357
A double-headed chymotrypsin inhibitor, WCI, from winged bean seeds was cloned for structural and biochemical studies. The inhibitor was subjected to two point mutations at a conserved position, Asn14. This residue, known to have a pivotal role in stabilizing the first reactive-site loop (Gln63-Phe68) of the inhibitor, is highly conserved in the sequences of the other members of Kunitz (STI) family as well as in the sequences of Kazal family of serine protease inhibitors. The mutants, N14K and N14D, were subjected to biochemical assay and their characteristics were compared with those of the recombinant inhibitor (rWCI). Crystallographic studies of the recombinant and the mutant proteins are discussed. These studies were primarily aimed at understanding the importance of the protein scaffolding towards the conformational rigidity of the reactive-site loop. Our analysis reveals that, as the Lys14 side chain takes an unusual fold in N14K and the Asp14 side chain in N14D interacts with the loop residues by water-mediated hydrogen bonds, the canonical conformation of the loop has remained effectively intact in both the mutant structures. However, minor alterations such as a 2-fold increase in the inhibitory affinity towards the cognate enzyme were observed. 相似文献
2.
Background
Meiotic prophase is a critical stage in sexual reproduction. Aberrant chromosome recombination during this stage is a leading cause of human miscarriages and birth defects. However, due to the experimental intractability of mammalian gonads, only a very limited number of meiotic genes have been characterized. Here we aim to identify novel meiotic genes important in human reproduction through computational mining of cross-species and cross-sex time-series expression data from budding yeast, mouse postnatal testis, mouse embryonic ovary, and human fetal ovary. 相似文献3.
Primer-dependent synthesis of covalently linked dimeric RNA molecules by poliovirus replicase. 总被引:12,自引:10,他引:2
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Poliovirus-specific RNA-dependent RNA polymerase (replicase, 3Dpol) was purified from HeLa cells infected with poliovirus. The purified enzyme preparation contained two proteins of apparent molecular weights 63,000 and 35,000. The 63,000-Mr polypeptide was virus-specific RNA-dependent RNA polymerase, and the 35,000-Mr polypeptide was of host origin. Both polypeptides copurified through five column chromatographic steps. The purified enzyme preparation catalyzed synthesis of covalently linked dimeric RNA products from a poliovirion RNA template. This reaction was absolutely dependent on added oligo(U) primer, and the dimeric product appeared to be made of both plus- and minus-strand RNA molecules. Experiments with 5' [32P]oligo(U) primer and all four unlabeled nucleotides suggest that the viral replicase elongates the primer, copying the poliovirion RNA template (plus strand), and the newly synthesized minus strand snaps back on itself to generate a template-primer structure which is elongated by the replicase to form covalently linked dimeric RNA molecules. Kinetic studies showed that a partially purified preparation of poliovirus replicase contains a nuclease which can cleave the covalently linked dimeric RNA molecules, generating template-length RNA products. 相似文献
4.
Indirect evidence suggests that legumes can adjust rapidly theresistance of their root nodules to O2 diffusion. Here we describeexperiments using O2 specific micro-electrodes and dark fieldmicroscopy to study directly the operation of this diffusionbarrier. The O2 concentration sensed by the electrode decreasedsharply in the region of the inner cortex and was less than1.0 mmol m3 throughout the infected tissue in nodulesof both pea (Pisum sativum) and french bean (Phaseolus vulgaris).In a number of experiments the ambient O2 concentration wasincreased to 40% while the electrode tip was just inside theinner cortex. In 13 out of 21 cases the O2 concentration atthis position either remained low and unchanged or increasedirreversibly to near ambient values. In the remaining casesthe O2 concentration increased after 1 to 2.5 min and then decreasedto its former value. These results are ascribed to an increasein resistance of the barrier in response to increased O2 fluxinto the nodule. It was shown microscopically that air spacesboth at the boundary between the infected zone and the innercortex, and within the infected zone started to disappear 3min after nodules were exposed to high ambient O2 concentrationsand had disappeared completely after 8 min. These spaces werenot changed by exposure of the nodule for 10 min to either N2or air. Key words: Oxygen, root nodules, air spaces 相似文献
5.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
6.
7.
Herpes simplex virus type 1-specific cytotoxic T lymphocytes recognize immediate-early protein ICP27.
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The identity of herpes simplex virus type 1 (HSV-1) antigens that serve as targets for cytotoxic T lymphocytes (CTL) and their ability to induce protective immunity remain uncertain. In this article, we report the identification of the immediate-early protein ICP27 as a CTL antigen in H-2d mice but not in H-2k or H-2b mice. Calculation of the frequencies of H-2d-restricted virus-specific CTL demonstrated that approximately one-fourth of the total HSV-1-specific response was directed against ICP27. To define the location of this CTL epitope, four truncated derivatives of the ICP27 gene which place the epitope in a 217-amino-acid region (amino acids 189 to 406) near the central portion of the protein were constructed. Mice immunized with ICP27 were able both to induce HSV-1-specific CTL and to survive a lethal intraperitoneal challenge with virulent HSV-1. However, neither appreciable antibody nor delayed-type hypersensitivity responses were induced in immunized mice, and they were also unable to clear a local epithelial virus challenge. It appears that ICP27, although capable of inducing several aspects of the immune response, is by itself unable to provide complete immunity. 相似文献
8.
The 7 ns 436 nm pulses of an H2-shifted YAG laser have been used to photolyze the CO adduct of cytochrome-c peroxidase and produce the resonance Raman spectrum of the photoproduct. A 3 cm-1 downshift, relative to the spectrum of reduced enzyme, was observed for the porphyrin C-N breathing mode, v4. The downshift diminishes with decreasing CO /protein ratio, implying, in conjunction with a recent study of CO binding, that the unrelaxed heme is associated with adduct having a tilted, H-bonded FeCO unit. The downshift is eliminated when the phosphate buffer concentration is increased from 0.01 to 0.1 M. It is proposed that the heme relaxation under study involves a transition between two conformations, B and A, differing in the disposition of the distal residues, and having different v4 frequencies for unligated Fe(II) heme. Conformation B allows H-bonding to bound CO, and is favored at high CO and phosphate concentrations, while conformation A, which is unfavorable to CO H-bonding, is favored at low CO and phosphate concentrations. The recently reported absence of unrelaxed frequencies in the 7 ns photo-product of the CO adduct of horseradish peroxidase has been confirmed, and is attributed to lower stability for conformation B and a smaller A - B v4 difference. 相似文献
9.
Mode of reversible binding of neocarzinostatin chromophore to DNA: evidence for binding via the minor groove 总被引:4,自引:0,他引:4
Two general approaches have been taken to understand the mechanism of the reversible binding of the nonprotein chromophore of neocarzinostatin to DNA: (1) measurement of the relative affinity of the chromophore for various DNAs that have one or both grooves blocked by bulky groups and (2) studies on the influence of adenine-thymine residue-specific, minor groove binding agents such as the antibiotics netropsin and distamycin on the chromophore-DNA interaction. Experiments using synthetic DNAs containing halogen group (Br, I) substituents in the major groove or natural DNAs with glucosyl moieties projecting into the major groove show that obstruction of the major groove does not decrease the binding stoichiometry or the binding constant for the DNA-chromophore interaction. Chemical methylation of bases in both grooves of calf thymus DNA, resulting in 13% methylation of N-7 of guanine in the major groove and 7% methylation of N-3 of adenine in the minor groove, decreases the binding affinity and increases the size of the binding site for neocarzinostatin chromophore. Similar results were obtained whether binding parameters were determined directly by spectroscopic measurements or indirectly by measuring the ability of the DNA to protect the chromophore against degradation. On the other hand, netropsin and distamycin compete with neocarzinostatin chromophore for binding to the minor groove of DNA, as shown by their decrease in the ability of poly(dA-dT) to protect the chromophore against degradation and their reduction in chromophore-induced DNA damage as measured by thymine release.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
10.
Shyamali Mukherjee Mihir Nag Tultul Nayyar Indrani Maitra Parul Chakrabarti Pramod R. Dasgupta 《Journal of biosciences》1986,10(3):311-317
The effect of estradiol-17β and progesterone given separately as well as in combination on the rate of hydrogen peroxide formation
and lipid peroxidation in the uteri of ovariectomized rats was studied. Estradiol in 3μg dose per day per animal elicited maximum stimulatory response and progesterone (100μg), on the other hand, was without any such effect. However, progesterone given along with estradiol completely prevented the
effect due to the latter. In the same way, vitamin E, a well known antioxidant was found to be extremelv effective in protecting
the uterus from the highly peroxidative action of estradiol-17β. 相似文献