全文获取类型
收费全文 | 4452篇 |
免费 | 282篇 |
国内免费 | 1篇 |
出版年
2022年 | 9篇 |
2021年 | 50篇 |
2020年 | 29篇 |
2019年 | 36篇 |
2018年 | 72篇 |
2017年 | 47篇 |
2016年 | 87篇 |
2015年 | 139篇 |
2014年 | 177篇 |
2013年 | 314篇 |
2012年 | 283篇 |
2011年 | 284篇 |
2010年 | 184篇 |
2009年 | 157篇 |
2008年 | 267篇 |
2007年 | 295篇 |
2006年 | 246篇 |
2005年 | 216篇 |
2004年 | 261篇 |
2003年 | 227篇 |
2002年 | 198篇 |
2001年 | 113篇 |
2000年 | 111篇 |
1999年 | 99篇 |
1998年 | 39篇 |
1997年 | 34篇 |
1996年 | 30篇 |
1995年 | 27篇 |
1994年 | 30篇 |
1993年 | 35篇 |
1992年 | 75篇 |
1991年 | 58篇 |
1990年 | 54篇 |
1989年 | 44篇 |
1988年 | 40篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 41篇 |
1984年 | 34篇 |
1983年 | 24篇 |
1982年 | 15篇 |
1981年 | 23篇 |
1980年 | 13篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1973年 | 12篇 |
1972年 | 11篇 |
1971年 | 11篇 |
1968年 | 10篇 |
1967年 | 12篇 |
排序方式: 共有4735条查询结果,搜索用时 15 毫秒
1.
2.
Roles of Four Chitinases (ChiA, ChiB, ChiC, and ChiD) in the Chitin Degradation System of Marine Bacterium Alteromonas sp. Strain O-7 总被引:1,自引:0,他引:1
3.
4.
5.
6.
Mizuki Taniguchi Shunichi Kajioka Habibul B. Shozib Kenta Sawamura Shinsuke Nakayama 《PloS one》2013,8(10)
Smooth and elaborate gut motility is based on cellular cooperation, including smooth muscle, enteric neurons and special interstitial cells acting as pacemaker cells. Therefore, spatial characterization of electric activity in tissues containing these electric excitable cells is required for a precise understanding of gut motility. Furthermore, tools to evaluate spatial electric activity in a small area would be useful for the investigation of model animals. We thus employed a microelectrode array (MEA) system to simultaneously measure a set of 8×8 field potentials in a square area of ∼1 mm2. The size of each recording electrode was 50×50 µm2, however the surface area was increased by fixing platinum black particles. The impedance of microelectrode was sufficiently low to apply a high-pass filter of 0.1 Hz. Mapping of spectral power, and auto-correlation and cross-correlation parameters characterized the spatial properties of spontaneous electric activity in the ileum of wild-type (WT) and W/Wv mice, the latter serving as a model of impaired network of pacemaking interstitial cells. Namely, electric activities measured varied in both size and cooperativity in W/Wv mice, despite the small area. In the ileum of WT mice, procedures suppressing the excitability of smooth muscle and neurons altered the propagation of spontaneous electric activity, but had little change in the period of oscillations. In conclusion, MEA with low impedance electrodes enables to measure slowly oscillating electric activity, and is useful to evaluate both histological and functional changes in the spatio-temporal property of gut electric activity. 相似文献
7.
Tomohiro Hamasaki Takahiro Matsumoto Naoya Sakamoto Akiko Shimahara Shiori Kato Ayumi Yoshitake Ayumi Utsunomiya Hisayoshi Yurimoto Esteban C. Gabazza Tadaaki Ohgi 《Nucleic acids research》2013,41(12):e126
Radioisotopes and fluorescent compounds are frequently used for RNA labeling but are unsuitable for clinical studies of RNA drugs because of the risk from radiation exposure or the nonequivalence arising from covalently attached fluorophores. Here, we report a practical phosphoramidite solid-phase synthesis of 18O-labeled RNA that avoids these disadvantages, and we demonstrate its application to quantification and imaging. The synthesis involves the introduction of a nonbridging 18O atom into the phosphate group during the oxidation step of the synthetic cycle by using 18O water as the oxygen donor. The 18O label in the RNA was stable at pH 3–8.5, while the physicochemical and biological properties of labeled and unlabeled short interfering RNA were indistinguishable by circular dichroism, melting temperature and RNA-interference activity. The 18O/16O ratio as measured by isotope ratio mass spectrometry increased linearly with the concentration of 18O-labeled RNA, and this technique was used to determine the blood concentration of 18O-labeled RNA after administration to mice. 18O-labeled RNA transfected into human A549 cells was visualized by isotope microscopy. The RNA was observed in foci in the cytoplasm around the nucleus, presumably corresponding to endosomes. These methodologies may be useful for kinetic and cellular-localization studies of RNA in basic and pharmaceutical studies. 相似文献
8.
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
9.
10.
S Yamada D R Gehlert K N Hawkins K Nakayama W R Roeske H I Yamamura 《Life sciences》1987,41(26):2851-2861
Light microscopic autoradiography was used to visualize the neuroanatomical distribution of nicotinic receptors in rat brain using a novel radioligand, [3H]methylcarbamylcholine (MCC). Specific [3H]MCC binding to slide-mounted tissue sections of rat brain was saturable, reversible and of high affinity. Data analysis revealed a single population of [3H]MCC binding sites with a Kd value of 1.8 nM and Bmax of 20.1 fmol/mg protein. Nicotinic agonists and antagonists competed for [3H]MCC binding sites in slide-mounted brain sections with much greater potency than muscarinic drugs. The rat brain areas containing the highest densities of [3H]MCC binding were in thalamic regions, the medial habenular nucleus and the superior colliculus. Moderate densities of [3H]MCC binding were seen over the anterior cingulate cortex, the nucleus accumbens, the zona compacta of substantia nigra and ventral tegmental area. Low densities of [3H]MCC binding were found in most other brain regions. These data suggest that [3H]MCC selectively labels central nicotinic receptors and that these receptors are concentrated in the thalamus, the medial habenular nucleus and the superior colliculus of the rat brain. 相似文献