全文获取类型
收费全文 | 2283篇 |
免费 | 136篇 |
出版年
2023年 | 6篇 |
2022年 | 19篇 |
2021年 | 43篇 |
2020年 | 15篇 |
2019年 | 27篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 43篇 |
2015年 | 73篇 |
2014年 | 74篇 |
2013年 | 161篇 |
2012年 | 156篇 |
2011年 | 168篇 |
2010年 | 96篇 |
2009年 | 98篇 |
2008年 | 171篇 |
2007年 | 180篇 |
2006年 | 147篇 |
2005年 | 129篇 |
2004年 | 179篇 |
2003年 | 134篇 |
2002年 | 127篇 |
2001年 | 25篇 |
2000年 | 24篇 |
1999年 | 21篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1967年 | 3篇 |
排序方式: 共有2419条查询结果,搜索用时 15 毫秒
1.
Takumi Hiyoshi Hisanori Domon Tomoki Maekawa Kosuke Nagai Hikaru Tamura Naoki Takahashi Daisuke Yonezawa Tomohiro Miyoshi Akihiro Yoshida Koichi Tabeta Yutaka Terao 《Microbiology and immunology》2019,63(3-4):100-110
Aggregatibacter actinomycetemcomitans is considered to be associated with periodontitis. Leukotoxin (LtxA), which destroys leukocytes in humans, is one of this bacterium's major virulence factors. Amounts of neutrophil elastase (NE), which is normally localized in the cytoplasm of neutrophils, are reportedly increased in the saliva of patients with periodontitis. However, the mechanism by which NE is released from human neutrophils and the role of NE in periodontitis is unclear. In the present study, it was hypothesized that LtxA induces NE release from human neutrophils, which subsequently causes the breakdown of periodontal tissues. LtxA‐treatment did not induce significant cytotoxicity against human gingival epithelial cells (HGECs) or human gingival fibroblasts (HGFs). However, it did induce significant cytotoxicity against human neutrophils, leading to NE release. Furthermore, NE and the supernatant from LtxA‐treated human neutrophils induced detachment and death of HGECs and HGFs, these effects being inhibited by administration of an NE inhibitor, sivelestat. The present results suggest that LtxA mediates human neutrophil lysis and induces the subsequent release of NE, which eventually results in detachment and death of HGECs and HGFs. Thus, LtxA‐induced release of NE could cause breakdown of periodontal tissue and thereby exacerbate periodontitis. 相似文献
2.
Scale Arrangement Pattern in a Lepidopteran Wing. 1. Periodic Cellular Pattern in the Pupal Wing of Pieris rapae 总被引:1,自引:1,他引:0
In most species of lepidopteran insects, anteroposterior rows formed by scales are arranged at regular intervals in the adult wing; within each row two kinds of scales are alternately arranged. To investigate the cellular basis for the scale arrangement pattern, we examined cell arrangement in the epidermal monolayer of the pupal wing of a small white cabbage butterfly, Pieris rapae , by scanning electron microscopy and light microscopy.
The arrangement of scale precursor cells, closely resembling that of scales in the adult wing, was observed in the wing epidermis of the early pupa. Scale precursor cells are proximodistally elongated and form anteroposterior rows. Within a row two kinds of scale precursor cells are nearly alternately arranged, which is not so precise as the alternation of scales in the adult wing. Individual rows of scale precursor cells are separated by rows of single or double undifferentiated general epidermal cells. Occasionally, arrangement abnormalities occur both in the adult and the pupal wing. The cellular basis for the regular spacing of scale rows is discussed. 相似文献
The arrangement of scale precursor cells, closely resembling that of scales in the adult wing, was observed in the wing epidermis of the early pupa. Scale precursor cells are proximodistally elongated and form anteroposterior rows. Within a row two kinds of scale precursor cells are nearly alternately arranged, which is not so precise as the alternation of scales in the adult wing. Individual rows of scale precursor cells are separated by rows of single or double undifferentiated general epidermal cells. Occasionally, arrangement abnormalities occur both in the adult and the pupal wing. The cellular basis for the regular spacing of scale rows is discussed. 相似文献
3.
Riichi Tawa Tetsuya Ono Akihiro Kurishita Shigefumi Okada Shingo Hirose 《Differentiation; research in biological diversity》1990,45(1):44-48
DNA methylation in an adult mammalian body shows tissue-specificity. But when and how the specificity is established in the process of development has not yet been elucidated. Here we have investigated age-dependent changes in the amount of 5-methyldeoxycytidine (5mdC) that DNA of various mouse tissues contains during the late-fetal and postnatal periods, using high-performance liquid chromatography. The tissue-specificity in the 5mdC level was observed in the late-fetal stage, and the level continued to change during the subsequent periods. The most pronounced alterations were observed in brain and liver, where similar biphasic changes were seen, but at different ages. At maturation, the 5mdC levels were high in thymus, spleen and brain, intermediate in lung, and low in liver and sperm. The data demonstrate the importance of the peri- and postnatal periods in establishment of tissue-specificity in 5mdC content. 相似文献
4.
5.
Akihiro Hara Hiroyuki Hashimoto Hirofumi Morota Hiroshi Harada Hirofumi Uchimiya 《Journal of plant research》1988,101(2):131-140
Tobacco mesophyll protoplasts were treated with plasmids, pCT2 (17.1 kbp) or pCT2T3 (18.3 kbp), which contained a chimeric aminoglycoside phosphotransferase II (APH(3′)II) gene and an intact nopaline synthase gene. Expression of two marker enzymes, APH(3′)II and nopaline synthase, were analyzed in transformed plants. Four out of 16 transformants obtained by pCT2T3 possessed both enzymes. Upon self-pollination, the progeny of one of transformants (T2) segregated to 153∶4 in terms of resistant and susceptible character to kanamycin, suggesting insertion of foreign genes into three independent chromosomes. The kanamycin resistant character in the rest of transformants showed 3∶1 segregation. DNA blot analysis of the T2 transformant and progenies indicated the presence of two marker genes. 相似文献
6.
Yoshiko Kubota Akihiro Shima 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,160(6):621-625
Summary By using inbred strains (HO4C and HB32C) of the medaka,Oryzias latipes, the involvement of genetic factor(s) in the determination of thermoresistance of fish was investigated. The thermoresistance of embryos of the medaka was quantitated by the fraction of the embryos surviving 1 day after heat treatment. At early stages of development (st. 13 and st. 20–21), the HO4C strain was more resistant than the HB32C strain. At st. 20–21, the HO4C strain was more resistant than the HB32C strain at all temperatures used (42, 43, and 44°C). At later stages of development (st. 27 and st. 32), however, the HB32C strain was more resistant than the HO4C strain.The results of genetic cross experiments raised the following possibilities; the thermoresistance of embryos at early developmental stages can be lowered by some factor(s) inherited in the HO4C strain and/or increased by those in the HB32C strain. By contrast, the sensitivity of embryos at later stages of development was not affected by factor(s) of their parents, but by their own genetic constitution. 相似文献
7.
A phosphorylated analogue of DSIP at Ser7 has been shown to exist endogenously by immunochemical studies. An enzyme which could phosphorylate DSIP has not yet been identified. In the present study, we examined DSIP as a substrate for in vitro phosphorylation by casein kinase II. DSIP was phosphorylated by the enzyme with apparent Km and Vmax values of 20 mM and 90.9 nmol/min/mg protein, respectively. Both ATP and GTP were utilized as phosphoryl donors. Phosphorylation of DSIP was inhibited by heparin and enhanced by spermine. These results demonstrate that DSIP can serve as a possible substrate for casein kinase II in vitro. 相似文献
8.
Disassembly from both ends of thick filaments in rabbit skeletal muscle fibers. An optical diffraction study. 总被引:5,自引:3,他引:2
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We show in this paper that the change of the internal structure of a sarcomere in a rabbit glycerinated psoas muscle fiber can be examined by analyzing the intensity change of the first- and the second-order optical diffraction lines. A unit-cell (sarcomere)-structure model has been applied to the estimation of the length of thick filaments in a muscle fiber while they undergo dissociation. The optical factors, except for the unit-cell-structure factor, hardly changed during the dissociation of the filaments. Our results show that thick filaments dissociate from both ends on increasing the KCl concentration in the presence of 10 mM pyrophosphate and 5 mM MgCl2. Micromolar concentrations of Ca2+ suppressed to some extent the dissociation of thick filaments. The disassembly of thick filaments occurred at higher KCl concentrations in the absence of pyrophosphate. There was a correlation between the stability of the thick filament structure and cross-bridge formation, which was induced either by the addition of micromolar concentrations of Ca2+ in the presence of Mg-pyrophosphate or by removal of Mg-pyrophosphate. 相似文献
9.
Globular actin (G-actin) polymerizes into a fibrous form (F-actin) under physiological salt conditions. The polymerization process of muscle actin was studied by a dynamic light-scattering method. The intensity correlation functions G2(tau) of scattered light from a G-actin solution containing 2 mM Tris-HCl (pH 8.0) and 0.1 mM ATP were analyzed by a cumulant expansion method, and the translational diffusion coefficient was determined to be D = (8.07 +/- 0.10) X 10(-7) cm2/s at 20 degrees C. This D value gave a diameter of 5.3 nm for spherical G-actin including a hydration layer. Polymerization of 1-3 mg/ml G-actin in a solution containing 10 mM Tris-HCl (pH 8.0), 0.2 mM ATP and 60 mM KCl was followed by successive measurements of G2(tau) for a data accumulation period of 60-300 s/run. The time evolution of G2(tau) was analyzed by a least-squares fitting to the field correlation function of a multiexponential form g1(tau) = sigma iAi exp(-gamma i tau) with gamma 1 greater than gamma 2 greater than 3 greater than ..., and the static scattering intensity I(t) = mean value of I as a function of time t after initiation of polymerization was decomposed as I(t) = mean value of I sigma iAi. At the early stage of polymerization, a two-exponential fit gave results indicating that component 1 came from G-actin and component 2 from F-actin growing linearly with t. At the middle stage of polymerization, a three-exponential fit gave the results that component 1 came from G-actin and possibly its small oligomers, component 2 from polymers with a number-average length Ln of about 900 nm which was independent of t, and component 3 from 'ghosts' in dynamic light scattering in a semidilute regime. Component 3 was concluded to arise from restricted motions of polymers with lengths much longer than Ln in cages formed by polymers giving component 2, and a fragmentation-elongation process of F-actin was suggested to start at the middle stage of polymerization, resulting in the size redistribution of F-actin. 相似文献
10.
Takao Tsuji Akihiro Ogawa Takashi Miyata Tatsuya Iida Takeshi Honda Toshio Miwatani 《FEMS microbiology letters》1986,37(3):345-350
Abstract A mutant (TUH No. 9) of a porcine strain of enterotoxigenic Escherichia coli (ETEC) produces as abnormal B subunit (B') of heat-labile enterotoxin (LT), which has aspartate instead of glycine at residue 33 from the N-terminus and does not bind to the receptor, GM1 ganglioside. The antigenicities of the receptor-binding site of LT were analyzed.
The antibody, which could not bind to the B' subunit in the anti-B subunit of porcine LT(LTp)-serum, could bind to cholera toxin (CT), LTp and LT produced by a human ETEC strain (LTh), suggesting that it recognizes a common epitope of LTp, LTh and CT. Thus glycine at residue 33 from the N-terminus in the B subunit of CT, LTh and LTp may be related to the common epitope of these three toxins. The bindings of CT, LTh and LTp to the antibody were inhibited by the GM1 ganglioside.
These data indicate that the antibody recognizes a common epitope in the receptor (GM1 ganglioside)-binding site of CT, LTh and LTp. 相似文献
The antibody, which could not bind to the B' subunit in the anti-B subunit of porcine LT(LTp)-serum, could bind to cholera toxin (CT), LTp and LT produced by a human ETEC strain (LTh), suggesting that it recognizes a common epitope of LTp, LTh and CT. Thus glycine at residue 33 from the N-terminus in the B subunit of CT, LTh and LTp may be related to the common epitope of these three toxins. The bindings of CT, LTh and LTp to the antibody were inhibited by the GM1 ganglioside.
These data indicate that the antibody recognizes a common epitope in the receptor (GM1 ganglioside)-binding site of CT, LTh and LTp. 相似文献