全文获取类型
收费全文 | 1619篇 |
免费 | 69篇 |
国内免费 | 11篇 |
专业分类
化学 | 1126篇 |
晶体学 | 14篇 |
力学 | 54篇 |
数学 | 152篇 |
物理学 | 353篇 |
出版年
2023年 | 8篇 |
2022年 | 7篇 |
2021年 | 33篇 |
2020年 | 36篇 |
2019年 | 37篇 |
2018年 | 28篇 |
2017年 | 25篇 |
2016年 | 53篇 |
2015年 | 49篇 |
2014年 | 51篇 |
2013年 | 77篇 |
2012年 | 120篇 |
2011年 | 132篇 |
2010年 | 93篇 |
2009年 | 93篇 |
2008年 | 138篇 |
2007年 | 104篇 |
2006年 | 83篇 |
2005年 | 85篇 |
2004年 | 73篇 |
2003年 | 57篇 |
2002年 | 66篇 |
2001年 | 21篇 |
2000年 | 33篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 7篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1970年 | 4篇 |
1966年 | 2篇 |
1965年 | 3篇 |
排序方式: 共有1699条查询结果,搜索用时 31 毫秒
991.
Garam Choi Young-Jun Park Minkyoung Cho Heesu Moon Daehong Kim Chang-Yuil Kang Yeonseok Chung Byung-Seok Kim 《Experimental & molecular medicine》2021,53(5):993
Pathogenic conversion of Th17 cells into multifunctional helper T cells or Th1 cells contributes to the pathogenesis of autoimmune diseases; however, the mechanism regulating the plasticity of Th17 cells remains unclear. Here, we found that Th17 cells expressed latent TGF-β1 in a manner dependent on autocrine TGF-β1. By employing IL-17-producing cell-specific Tgfb1 conditional knockout and fate-mapping systems, we demonstrated that TGF-β1-deficient Th17 cells are relatively susceptible to becoming IFN-γ producers through IL-12Rβ2 and IL-27Rα upregulation. TGF-β1-deficient Th17 cells exacerbated tissue inflammation compared to TGF-β1-sufficient Th17 cells in adoptive transfer models of experimental autoimmune encephalomyelitis and colitis. Thus, TGF-β1 production by Th17 cells provides an essential autocrine signal for maintaining the stability and regulating the pathogenicity of Th17 cells in vivo.Subject terms: Autoimmunity, Neuroimmunology 相似文献
992.
Park YB Kim YY Oh SK Chung SG Ku SY Kim SH Choi YM Moon SY 《Experimental & molecular medicine》2008,40(1):98-108
Human embryonic stem cells (hESCs) are considered to be able to stably maintain their characteristics in vitro for prolonged periods, but we had previously encountered changes in proliferative ability and differentiation potential during extended culture of hESCs. Therefore, we investigated the proliferative ability and differentiation potential of hESCs during long-term culture. The hESCs, SNUhES3, were used to analyze population-doubling time, proliferation rate and differentiation potential. We classified hESCs into three groups according to culture period. Ten colonies of hESCs for each group were daily measured colony area and population-doubling time was assessed by the changes of colony area. Proliferation rate of hESCs was measured by 5-bromo-2'-deoxyuridine (BrdU) assay and telomerase activity. To evaluate differentiation potentials for hESCs, expression levels of undifferentiated and/or differentiated hESCs markers were examined by FACS, RT-PCR and immunostaining. Population-doubling time of early passage hESCs was longer than those of middle or late passage. Proliferative ability of hESCs was accelerated depending on culture periods. Cellular morphologies and the expression level of each three germ layer markers were obviously different from each passage of reattached embryoid bodies (EBs) after spontaneous differentiation. Differentiated cells of late passage expressed higher levels of undifferentiated markers such as Oct4 and SSEA4 than those of early and middle passage. But differentiated cells of early and middle passage expressed higher level of differentiated state markers, Nestin (ectoderm), Brachyury (mesoderm), HNF3beta (endoderm). From these results, it can be inferred that hESCs show higher proliferative abilities and reduced differentiation potentials as the passage number increased. Therefore, we conclude that early passage hESCs could be more suitable than middle and late passage hESCs in differentiation studies. 相似文献
993.
Yang Kyoo Han Moon Young Jin Sam Kwon Choi 《Journal of polymer science. Part A, Polymer chemistry》1983,21(1):73-81
Polymerization of acrylonitrile initiated by a potassium superoxide (KO2)-nitrobenzene system was carried out in anhydrous dimethylsulfoxide (DMSO) at 25°C. The initial rate of polymerization was rapid and a high-molecular-weight polymer was obtained. The molecular weight was proportional to monomer concentration and inversely to concentration of initiator within 5 min. The overall activation energy was estimated as ?2.6kcal/mol deg in the temperature range of 20–50°C. In addition to nitrobenzene anion radical, other anion radicals generated by one-electron transfer from KO2 to charge transfer agents such as m-dinitrobenzene benzoquinone, benzophenone, and naphthalene were effective in the polymerization of acrylonitrile. It is proposed that polymerization proceeds via an anionic mechanism that involves one-electron transfer from anion radicals to monomer. 相似文献
994.
995.
Lee KJ Kim SJ Kim SW Choi SH Shin YC Park SH Moon BH Cho E Lee MS Choi SH Chun BG Shin KH 《Experimental & molecular medicine》2006,38(1):44-54
New-born cells continue to proliferate and survive to become mature granule cells in adult rat hippocampus. Although this process, known as neurogenesis, is inhibited by acute stress, it is not clear whether chronic stress affects neurogenesis. To determine whether chronic mild stress (CMS) influences neurogenesis in the adult rat hippocampus, male Sprague-Dawley rats were exposed to CMS and administered bromodeoxyuridine (BrdU) before or after CMS to observe the survival/differentiation or proliferation of new-born cells, respectively. In addition, we measured brain-derived neurotrophic factor (BDNF) mRNA in the granule cell layer (GCL) of the hippocampus, because BDNF is known to play an important role in the survival of new-born cells. CMS significantly decreased the survival of new-born cells in the GCL, but did not influence the proliferation or differentiation of new-born cells. CMS did not affect the proliferation and survival of new-born cells in the hilus. In addition, CMS did not change BDNF mRNA levels in the GCL. These results demonstrate that CMS reduces the survival of new-born cells but not of their proliferation, suggesting that repeated mild stress could influence a part of neurogenesis, but not the whole part of neurogenesis. These results raise the possibility that the survival of new-born cells may be suppressed in the presence of normal BDNF mRNA levels in GCL. 相似文献
996.
Bong‐Hwan Han Moon‐Gun Choi 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(8):1001-1003
The structure of tetrakis(3,4‐ethylenedioxy‐2‐thienyl)silane carbon tetrachloride solvate, Si(C6H5O2S)4·CCl4, has been determined in the noncentrosymmetric space group I. The Si and C atoms of the CCl4 are located on the fourfold inversion axes. The Si atom has a tetrahedral geometry. The thiophene ring in the 3,4‐ethylenedioxythiophene group is nearly planar to within 0.005 Å, and the ethylenedioxy moiety is in a half‐chair conformation. 相似文献
997.
Weak signal intensity and poor precursor ion selection are the major difficulties in tandem time-of-flight (TOF) mass spectrometry of ions generated by matrix-assisted laser desorption/ionization (MALDI). Even though the latter can be overcome in photodissociation (PD) tandem TOF mass spectrometry via ion pulse-PD laser pulse synchronization, clean monoisotopic selection of precursor ions of high m/z can often be difficult for various reasons. A considerable enhancement of post-source decay (PSD) and PD tandem mass spectra has been achieved in this work via single-ion detection and post-acquisition reduction of the spectra. Also, an algorithm has been developed to clean up isotopomeric contamination when the resolution for precursor ion selection is less than adequate. A high-quality tandem TOF mass spectrum which results from PD of virtually monoisotopic precursor ions has been obtained. 相似文献
998.
Lanthanide(III) Cryptate (2.2.1) chlorides (Ln(2.2.1)Cl(3); Ln = La (1a), Ce(1b), and Eu(1c); (2.2.1) = 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8.8.5]tricosane) are effective for the catalytic hydrolysis of bis(4-nitrophenyl) phosphate. Kinetic studies reveal that the europium(III) complex (1c) catalyzes the hydrolysis to produce 6 equiv of 4-nitrophenol with a significant rate (k(1) = 1.5 x 10(-)(4) s(-)(1) at 0.40 mM) at pH 8.5 and 50 degrees C. The catalytic activity of the complexes is increased with decreasing the ionic size, i.e, La < Ce < Eu. While the use of hydrogen peroxide further increase the activity of 1b (k(1) = 1.6 x 10(-)(3) s(-)(1) at 0.40 mM), the presence of molecular oxygen does not affect the activity at all. Crystal of 1a.CH(3)OH([La(2.2.1)(Cl)(2)](Cl)(CH(3)OH)) belongs to the space group Pnma with a = 17.072(3) ?, b = 19.037(3) ?, c = 14.725(2) ?, V = 4786(1) ?(3), Z = 8, D(x)() = 1.691 g cm(-)(3), &mgr; = 21.7 cm(-)(1). The encryptated metal ion is nine-coordinated, and all the heteroatoms of the cryptate (2.2.1) ligand coordinate the metal center to form a bowl-shaped structure. Two coordinating chloride anions are located on the open face with a cis geometry. The existence of coordinated water to the europium(III) complex 1c in the aqueous solution was confirmed by time-resolved Eu(III) luminescence spectroscopy. From the decay constants in H(2)O and D(2)O, the numbers of coordinated water molecules (q) are found to be 3.02 at pH of 5.0. The above kinetic and spectroscopic observation are supportive of mechanisms in which the metal complexes act as a center for binding and activation as well as a source of nucleophilic metal hydroxides. 相似文献
999.
d-Allose, a rare, naturally occurring monosaccharide, is known to exert anti-proliferative effects on cancer cells. The effects
of d-allose on the cellular membranes of hormone-refractory prostate cancer cell line (DU145), hormone-sensitive prostate cancer
cell line (LNCaP), and normal prostate epithelial cells (PrEC) were studied at the molecular level by phospholipid (PL) profiling
using a shotgun lipidomic method. The molecular structures of 85 PL species including 23 phosphatidylcholines, 12 phosphatidylethanolamines
(PEs), 11 phosphatidylserines (PSs), 16 phosphatidylinositols, 9 phosphatidic acids (PAs), and 14 phosphatidylglycerols (PGs)
were identified by data-dependent collision-induced dissociation of nanoflow liquid chromatography–tandem mass spectrometry,
and the PL amounts were quantified. The addition of d-allose to prostate cancer cell lines during their growth phases had negligible or decreased effects on the relative regulation
of PL species, but several new PS molecules (two for DU145 and three for LNCaP) emerged. In contrast, experiments on the PrEC
cell line revealed that some high abundant species (14:0/14:0-PE, 16:2/16:0-PG, and 20:6/18:1-PA) showed significant increases
in concentration. These findings support a mechanism for the anti-proliferative effect of d-allose on prostate cancer cell lines that involves the induction of programmed cell death since PS molecules are known to
induce apoptosis. Principal component analysis was carried out to examine differences in PL distributions among the three
cell lines promoted by d-allose. 相似文献
1000.
Lee JA Moon HR Kim HO Kim KR Lee KM Kim BT Hwang KJ Chun MW Jacobson KA Jeong LS 《The Journal of organic chemistry》2005,70(13):5006-5013
On the basis of the biological activity of neplanocin A and apio-dideoxyadenosine (apio-ddA), novel apio-neplanocin A analogues 5a-d, combining the properties of two nucleosides, were stereoselectively synthesized. The apio moiety of the target nucleosides 5a-d was stereoselectively introduced by treating lactol 10 with 37% formaldehyde in the presence of potassium carbonate. The carbasugar moiety of neplanocin A was successively built by exposing diene 12 on a Grubbs catalyst in methylene chloride. The final nucleosides 5a-d were synthesized from the condensation of the glycosyl donor 14 with nucleic bases under the standard Mitsunobu conditions. Similarly, apio-aristeromycin 6 and (N)-apio-methanocarbaadenosine 7 were derived from the common intermediate 13 using catalytic hydrogenation and Simmons-Smith cyclopropanation as key steps. All of the final nucleosides 5a-d, 6, and 7 did not show significant inhibitory activity against S-adenosylhomocysteine hydrolase (SAH) up to 100 muM, maybe due to the absence of the secondary hydroxyl group at the C3'-position, which should be oxidized by cofactor-bound NAD(+). However, apio-neplanocin A (5a) showed potent and highly selective binding affinity (K(i) = 628 +/- 69 nM) at the A(3) adenosine receptor without any binding affinity at the A(1) and A(2A) adenosine receptors. In conclusion, we have first developed novel carbocyclic nucleosides with unnatural apio-carbasugars using stereoselective hydroxymethylation and RCM reaction and also discovered a new template of human A(3) adenosine receptor agonist, which play a great role in developing new A(3) adenosine receptor agonist as well as in identifying the binding site of the receptor. 相似文献