全文获取类型
收费全文 | 1645篇 |
免费 | 81篇 |
学科分类
生物科学 | 1726篇 |
出版年
2022年 | 8篇 |
2021年 | 12篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 25篇 |
2017年 | 13篇 |
2016年 | 31篇 |
2015年 | 48篇 |
2014年 | 48篇 |
2013年 | 173篇 |
2012年 | 93篇 |
2011年 | 101篇 |
2010年 | 72篇 |
2009年 | 47篇 |
2008年 | 81篇 |
2007年 | 84篇 |
2006年 | 84篇 |
2005年 | 72篇 |
2004年 | 74篇 |
2003年 | 68篇 |
2002年 | 75篇 |
2001年 | 27篇 |
2000年 | 29篇 |
1999年 | 25篇 |
1998年 | 23篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 14篇 |
1992年 | 13篇 |
1991年 | 16篇 |
1990年 | 22篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 10篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 20篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1975年 | 11篇 |
1974年 | 13篇 |
1973年 | 12篇 |
1972年 | 6篇 |
排序方式: 共有1726条查询结果,搜索用时 15 毫秒
991.
Cloning and functional characterization of a new subtype of the amino acid transport system N 总被引:4,自引:0,他引:4
Nakanishi Takeo; Kekuda Ramesh; Fei You-Jun; Hatanaka Takahiro; Sugawara Mitsuru; Martindale Robert G.; Leibach Frederick H.; Prasad Puttur D.; Ganapathy Vadivel 《American journal of physiology. Cell physiology》2001,281(6):C1757
We have cloned a new subtype of theamino acid transport system N2 (SN2 or second subtype of system N) fromrat brain. Rat SN2 consists of 471 amino acids and belongs to therecently identified glutamine transporter gene family that consists ofsystem N and system A. Rat SN2 exhibits 63% identity with rat SN1. Italso shows considerable sequence identity (50-56%) with themembers of the amino acid transporter A subfamily. In the rat, SN2 mRNA is most abundant in the liver but is detectable in the brain, lung,stomach, kidney, testis, and spleen. When expressed in Xenopus laevis oocytes and in mammalian cells, rat SN2 mediatesNa+-dependent transport of several neutral amino acids,including glycine, asparagine, alanine, serine, glutamine, andhistidine. The transport process is electrogenic, Li+tolerant, and pH sensitive. The transport mechanism involves the influxof Na+ and amino acids coupled to the efflux ofH+, resulting in intracellular alkalization. Proline,-(methylamino)isobutyric acid, and anionic and cationic amino acidsare not recognized by rat SN2. 相似文献
992.
Ablimit A Aoki T Matsuzaki T Suzuki T Hagiwara H Takami S Takata K 《Chemical senses》2008,33(5):481-488
The vomeronasal organ comprises a pair of narrow tubes in the mammalian nasal septum, serving as a chemosensory system for pheromones. We examined the expression and localization of water channel aquaporins (AQPs) in the rat vomeronasal organ. AQP1 was localized in blood vessels, being particularly abundant in cavernous tissues of the nonsensory mucosa. AQP5 was found in the apical membrane of the gland acinar cells in the vomeronasal organ. AQP3 was detected in the basal cells of the nonsensory epithelium, whereas it was absent in the sensory epithelium. AQP4 was found in both the sensory and the nonsensory epithelia. Interestingly, AQP4 was highly concentrated in the sensory cells of the sensory epithelium. Immunoelectron microscopic examination clearly showed that AQP4 was localized at the plasma membrane in the cell body and lateral membrane of the dendrite, except for the microvillous apical membrane. Nerve fiber bundles emanating from neuronal sensory cells were positive for AQP4, whereby the plasma membrane of each axon was positive for AQP4. These observations clearly show that neuronal sensory cells in the vomeronasal organ are unique in that they express abundant AQP4 at their plasma membrane. This is in marked contrast to the olfactory and central nervous systems, where AQPs are not detectable in neurons, and instead, AQP4 is abundant in the supporting cells and astrocytes surrounding them. The present findings suggest a unique water-handling feature in neuronal sensory cells in the vomeronasal organ. 相似文献
993.
The seeds of 38 species of 29 genera in 21 tribes of the Leguminosae were screened for stizolamine. It was detected in 19 species of the subfamily Lotoideae. Its occurrence in Lotoideae was wide (82% in tribes, 56% both in genera and species) but sporadic. The content was fairly varied (0·249–9540 nmol/g of seeds), the largest amount occurring in Stizolobium hassjoo. 相似文献
994.
995.
Debutenoyl-aspertetronin A was synthesized from γ-valerolactone-γ-carboxylic acid (4) via 2, 5-dihydro-3-hydroxy-2-methyl-5-oxo-2-furanpropanoic acid. Starting from (?)-(S)-4, (+)-(S)-5-hexyl-4-hydroxy-5-methyl-2(5H)furanone (19) was synthesized, and by comparison of its optical rotation with that of an authentic sample it was proved that aspertetronin A had (R) configuration, and gregatin A had (S) configuration at their respective chiral carbon. 相似文献
996.
Bo Dong Takeo Horie Elsa Denker Takehiro Kusakabe Motoyuki Tsuda William C. Smith Di Jiang 《Developmental biology》2009,330(2):237-249
In the course of embryogenesis multicellular structures and organs are assembled from constituent cells. One structural component common to many organs is the tube, which consists most simply of a luminal space surrounded by a single layer of epithelial cells. The notochord of ascidian Ciona forms a tube consisting of only 40 cells, and serves as a hydrostatic “skeleton” essential for swimming. While the early processes of convergent extension in ascidian notochord development have been extensively studied, the later phases of development, which include lumen formation, have not been well characterized. Here we used molecular markers and confocal imaging to describe tubulogenesis in the developing Ciona notochord. We found that during tubulogenesis each notochord cell established de novo apical domains, and underwent a mesenchymal–epithelial transition to become an unusual epithelial cell with two opposing apical domains. Concomitantly, extracellular luminal matrix was produced and deposited between notochord cells. Subsequently, each notochord cell simultaneously executed two types of crawling movements bi-directionally along the anterior/posterior axis on the inner surface of notochordal sheath. Lamellipodia-like protrusions resulted in cell lengthening along the anterior/posterior axis, while the retraction of trailing edges of the same cell led to the merging of the two apical domains. As a result, the notochord cells acquired endothelial-like shape and formed the wall of the central lumen. Inhibition of actin polymerization prevented the cell movement and tube formation. Ciona notochord tube formation utilized an assortment of common and fundamental cellular processes including cell shape change, apical membrane biogenesis, cell/cell adhesion remodeling, dynamic cell crawling, and lumen matrix secretion. 相似文献
997.
Joji Kitayama Nelson Tsuno Hiroshi Yasuhara Hirokazu Nagawa Wataru Kimura Akira Kuroda Yoichi Shibata Takeo Juji Tetsuichiro Muto 《Cancer immunology, immunotherapy : CII》1994,38(5):317-322
The mechanisms of lysis of endothelial cells derived from human umbilical vein (HUVEC) by autologous lymphokine-activated killer (LAK) cells, generated from cord blood lymphocytes of the same donor, were investigated. Freshly isolated HUVEC as well as HUVEC cultured for several passages were efficiently lysed by autologous LAK cells, and their susceptibility to the LAK cells was almost the some as that of allogenic HUVEC. Complement-depletion experiments revealed that the lysis was mainly dependent on CD16-natural killer (NK) LAK cells. Pretreatment of HUVEC with recombinant interferon (rIFN) for 24 h made them resistant to lysis by autologous LAK cells, while pretreatment with either rIL-1. rTNF, or acidic or basic fibroblast growth factor did not alter the lytic sensitivity of HUVEC. The resistance of rIFN-treated HUVEC was specific to lysis by CD16+ NK LAK cells, and their lysis by CD3+ T-LAK cells was not significantly altered. Moreover, in comparison with control HUVEC or rIL-1-treated HUVEC, rIFN-treated HUVEC had a significantly less potent inhibitory effect on the lysis of untreated HUVEC, when used as an unlabeled target. This suggests that rIFN treatment may down-regulate the recognition of some molecules on HUVEC by rIL-2-activated NK cells. These data suggest that damage of the endothelium during LAK therapy is mainly dependent on LAK cells with a NK phenotype that can specifically recognize a certain molecule on autologous endothelial cells. 相似文献
998.
Hiroshi Morita Jun Deguchi Yusuke Motegi Seizo Sato Chihiro Aoyama Jiro Takeo Motoo Shiro Yusuke Hirasawa 《Bioorganic & medicinal chemistry letters》2010,20(3):1070-1074
Two cyclic diarylheptanoids, acerogenins A (1) and B (2) have been isolated from the bark of Acer nikoense as inhibitors of Na+-glucose cotransporter (SGLT). Acerogenins A (1) and B (2) inhibited both isoforms, SGLT1 and SGLT2. Structure–activity relationship of acerogenin derivatives on inhibitory activity of SGLT as well as conformational analysis of 1 and 2 on the basis of J-resolved HMBC spectra and X-ray analysis were discussed. 相似文献
999.
Incomplete flagellar structures in nonflagellate mutants of Salmonella typhimurium. 总被引:9,自引:39,他引:9 下载免费PDF全文
Incomplete flagellar structures were detected in osmotically shocked cells or membrane-associated fraction of many nonflagellate mutants of Salmonella typhimurium by electron microscopy. The predominant types of these structures in the mutants were cistron specific. The incomplete basal bodies were detected in flaFI, flaFIV, flaFVIII, and flaFIX mutants, the structure homologous to a basal body in flaFV mutants, the polyhook-basal body complex in flaR mutants, and the hook-basal body complex in flaL and flaU mutants. No structures homologous to flagellar bases or their parts were detected in the early-fla group nonflagellate mutants of flaAI, flaAII, flaAIII, flaB, flaC, flaD, flaE, flaFII, flaFIII, flaFVI, flaFVII, flaFX, flaK, and flaM. From these observations, a process of flagellar morphogenesis was postulated. The functions of the early-fla group are essential to the formation of S ring-M ring-rod complexes bound to the membrane. The completion of basal bodies requires succeeding functions of flaFI, flaFIV, flaFVIII, and flaFIX. Next, the formation of hooks attached to basal bodies proceeds by the function of flaFV and by flaR, which controls the hook length. Flagellar filaments appear at the tips of hooks because of the functions of flaL, flaU, and flagellin genes. 相似文献
1000.