全文获取类型
收费全文 | 9329篇 |
免费 | 367篇 |
国内免费 | 61篇 |
专业分类
化学 | 6389篇 |
晶体学 | 93篇 |
力学 | 279篇 |
数学 | 808篇 |
物理学 | 2188篇 |
出版年
2023年 | 54篇 |
2022年 | 190篇 |
2021年 | 226篇 |
2020年 | 178篇 |
2019年 | 172篇 |
2018年 | 172篇 |
2017年 | 144篇 |
2016年 | 296篇 |
2015年 | 269篇 |
2014年 | 353篇 |
2013年 | 596篇 |
2012年 | 742篇 |
2011年 | 823篇 |
2010年 | 469篇 |
2009年 | 385篇 |
2008年 | 616篇 |
2007年 | 580篇 |
2006年 | 512篇 |
2005年 | 473篇 |
2004年 | 408篇 |
2003年 | 325篇 |
2002年 | 326篇 |
2001年 | 216篇 |
2000年 | 177篇 |
1999年 | 129篇 |
1998年 | 69篇 |
1997年 | 79篇 |
1996年 | 95篇 |
1995年 | 80篇 |
1994年 | 75篇 |
1993年 | 57篇 |
1992年 | 60篇 |
1991年 | 47篇 |
1990年 | 51篇 |
1989年 | 34篇 |
1988年 | 26篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 26篇 |
1984年 | 18篇 |
1983年 | 17篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1972年 | 9篇 |
排序方式: 共有9757条查询结果,搜索用时 0 毫秒
951.
In Jin Ha Young Wan Ha Minseok Kang Jongsung Lee Deokhoon Park Yeong Shik Kim 《Journal of separation science》2010,33(13):1916-1922
Platycosides, the saponins found in the roots of Platycodon grandiflorum (Platycodi Radix), are typically composed of oleanane triterpenes with two side chains. In platycosides, platycodin D, a glucose unit at C‐3, is a major component, which has several pharmacological activities. Because of the high demand for this compound, we attempted to enzymatically convert platycodin D3 and platycoside E, having two and three glucose units at C‐3, respectively, into platycodin D. In this study, we tested the ability of several glycosidases to transform platycosides, or more specifically, the ability to transform platycoside E and platycodin D3 into platycodin D. To obtain pure platycodin D on a preparative scale, high‐speed countercurrent chromatography with a solvent system of ethyl acetate/n‐butanol/water (1.2:1:2, v/v/v) was used for the separation of the enzymatically transformed product. Approximately 39.4 mg of platycodin D (99.8% purity) was obtained from 200 mg of the product in a one‐step separation. The results strongly support the advantage of enzymatic transformation of the platycosides for the efficient enrichment of platycodin D in the complicated extract of the medicinal plant. 相似文献
952.
An analytical method of CE-MS and CE with an online preconcentration technique induced by a dynamic pH junction, addition of organic solvent and large volume injection was developed for sensitive determination of peptides in biological samples. Leucine enkephalin, methionine enkephalin, dynorphin A, β-endorphin and angiotensin II were used as model peptides. The optimal online preconcentration conditions were obtained at a sample matrix consisting of 100?mM borate buffer (pH 10.0) with 50% v/v acetonitrile and a BGE containing 1?M formic acid at pH 2.0, along with a 25-cm injection length. Under the optimized conditions, a 4.0×10(3)-1.1×10(4)-fold increase in peak intensity was achieved without degrading the peak shape. This online preconcentration method was applied to analyze the intracellular angiotensin II within the peptides extracted from HL1 cells and approximately increase of 1×10(4)-fold sensitivity was achieved compared to normal condition. Thus, the developed method could be applied to the analysis of various peptides for peptidomics study in biological samples. 相似文献
953.
Mi-Young Song Gil-Saeng Jeong Kang-Beom Kwon Sun-O Ka Hyun-Young Jang Jin-Woo Park Youn-Chul Kim Byung-Hyun Park 《Experimental & molecular medicine》2010,42(9):628-638
NF-κB activation has been implicated as a key signaling mechanism for pancreatic β-cell damage. Sulfuretin is one of the main flavonoids produced by Rhus verniciflua, which is reported to inhibit the inflammatory response by suppressing the NF-κB pathway. Therefore, we isolated sulfuretin from Rhus verniciflua and evaluated if sulfuretin could inhibit cytokine- or streptozotocin-induced β-cell damage. Rat insulinoma RINm5F cells and isolated rat islets were treated with IL-1β and IFN-γ to induce cytotoxicity. Incubation of cells and islets with sulfuretin resulted in a significant reduction of cytokine-induced NF-κB activation and its downstream events, iNOS expression, and nitric oxide production. The cytotoxic effects of cytokines were completely abolished when cells or islets were pretreated with sulfuretin. The protective effect of sulfuretin was further demonstrated by normal insulin secretion of cytokine-treated islets in response to glucose. Treatment of mice with streptozotocin resulted in hyperglycemia and hypoinsulinemia, which was further evidenced by immunohistochemical staining of islets. However, the diabetogenic effects of streptozotocin were completely prevented when mice were pretreated with sulfuretin. The anti-diabetogenic effects of sulfuretin were also mediated by suppression of NF-κB activation. Collectively, these results indicate that sulfuretin may have therapeutic value in preventing β-cell damage. 相似文献
954.
Sundo Jung Yoon-Kyung Park Hyunji Lee Jung Hoon Shin Gap Ryol Lee Se-Ho Park 《Experimental & molecular medicine》2010,42(3):187-194
Collagen-induced arthritis (CIA) is mediated by self-reactive CD4+ T cells that produce inflammatory cytokines. TGF-β2-treated tolerogenic antigen-presenting cells (Tol-APCs) are known to induce tolerance in various autoimmune diseases. In this study, we investigated whether collagen-specific Tol-APCs could induce suppression of CIA. We observed that Tol-APCs could suppress the development and severity of CIA and delay the onset of CIA. Treatment of Tol-APCs reduced the number of IFN-γ- and IL-17-producing CD4+ T cells and increased IL-4- and IL-5-producing CD4+ T cells upon collagen antigen stimulation in vitro. The suppression of CIA conferred by Tol-APCs correlated with their ability to selectively induce IL-10 production. We also observed that treatment of Tol-APCs inhibited not only cellular immune responses but also humoral immune responses in the process of CIA. Our results suggest that in vitro-generated Tol-APCs have potential therapeutic value for the treatment of rheumatoid arthritis as well as other autoimmune diseases. 相似文献
955.
Min Kyong Moon Min Kim Sung Soo Chung Hyun Joo Lee Sung Hee Koh Peter Svovoda Myung Hee Jung Young Min Cho Young Joo Park Sung Hee Choi Hak Chul Jang Kyong Soo Park Hong Kyu Lee 《Experimental & molecular medicine》2010,42(5):345-352
An association between inflammatory processes and the pathogenesis of insulin resistance has been increasingly suggested. The IκB kinase-β (IKK-β)/ nuclear factor-κB (NF-κB) pathway is a molecular mediator of insulin resistance. S-Adenosyl-L-methionine (SAM) has both antioxidative and anti-inflammatory properties. We investigated the effects of SAM on the glucose transport and insulin signaling impaired by the tumor necrosis factor α (TNFα) in 3T3-L1 adipocytes. SAM partially reversed the basal and insulin stimulated glucose transport, which was impaired by TNFα. The TNFα-induced suppression of the tyrosine phosphorylation of the insulin receptor substrate-1 (IRS-1) and Akt in 3T3-L1 adipocytes was also reversed by SAM. In addition, SAM significantly attenuated the TNFα-induced degradation of IκB-α and NF-κB activation. Interestingly, SAM directly inhibited the kinase activity of IKK-β in vitro. These results suggest that SAM can alleviate TNFα mediated-insulin resistance by inhibiting the IKK-β/NF-κB pathway and thus can have a beneficial role in the treatment of type 2 diabetes mellitus. 相似文献
956.
Chen X Nam SW Kim GH Song N Jeong Y Shin I Kim SK Kim J Park S Yoon J 《Chemical communications (Cambridge, England)》2010,46(47):8953-8955
A new NIR fluorescent sensor based on an amine-substituted heptamethine cyanine dye displayed a highly selective fluorescence enhancement with cyanide in aqueous solutions, and was applied for the imaging of anthropogenic and biogenic cyanide. 相似文献
957.
Hwan-Seo Park In-Tae Kim Yong-Jun Cho Mi-Sook Son Hee-Chul Eun 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(2):267-272
Radioactive molten salt generated from a pyrochemical process to separate reusable U and TRU elements is one of problematic
wastes to manage for a final disposal. For the minimization of final waste, it is desirable to selectively remove radionuclides
from the waste salts. In this paper, structural change of some zeolites in a series of molten salt systems and its removal
behavior of CsCl was investigated. Zeolite-4A(LTA) was transformed into LiAlSiO4 and Li-sodalite with the mol-fraction of LiCl in LiCl–KCl system at 650 °C while it was not changed in NaCl–KCl at 750 °C,
regardless of mol-fraction of metal chloride. Other commercial zeolite with specific structure (FAU) had the same trends on
the structural stability in molten salt system. From the Cs removal experiments, the decomposed zeolitic materials in molten
salt lost their removal ability of Cs. In conclusion, a new selective material or method should be investigated or developed
for obtaining the validity on the separation of group I and II radionuclides from a molten waste salt because the zeolite
4A is unstable in the LiCl system and it also showed a low capacity in the LiCl–KCl phase. This paper gives basic information
on the removal of radionuclides from molten systems by using zeolitic materials. 相似文献
958.
Chang Yeon Lee Dr. Jae Kwon Jang Chul Hoon Kim Dr. Jaehoon Jung Bo Keun Park Dr. Jihee Park Wonyong Choi Prof. Young‐Kyu Han Dr. Taiha Joo Prof. Joon T. Park Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(19):5586-5599
A new artificial photosynthetic triad array, a [60]fullerene–triosmium cluster/zinc–porphyrin/boron–dipyrrin complex ( 1 , Os3C60/ZnP/Bodipy), has been prepared by decarbonylation of Os3(CO)8(CN(CH2)3Si(OEt)3)(μ3‐η2:η2:η2‐C60) ( 6 ) with Me3NO/MeCN and subsequent reaction with the isocyanide ligand CNZnP/Bodipy ( 5 ) containing zinc porphyrin (ZnP) and boron dipyrrin (Bodipy) moieties. Triad 1 has been characterized by various spectroscopic methods (MS, NMR, IR, UV/Vis, photoluminescence, and transient absorption spectroscopy). The electrochemical properties of 1 in chlorobenzene (CB) have been examined by cyclic voltammetry; the general feature of the cyclic voltammogram of 1 is nine reversible one‐electron redox couples, that is, the sum of those of 5 and 6 . DFT has been applied to study the molecular and electronic structures of 1 . On the basis of fluorescence‐lifetime measurements and transient absorption spectroscopic data, 1 undergoes an efficient energy transfer from Bodipy to ZnP and a fast electron transfer from ZnP to C60; the detailed kinetics involved in both events have been elucidated. The SAM of triad 1 ( 1 /ITO; ITO=indium–tin oxide) has been prepared by immersion of an ITO electrode in a CB solution of 1 and diazabicyclo‐octane (2:1 equiv), and characterized by UV/Vis absorption spectroscopy, water contact angle, X‐ray photoelectron spectroscopy, and cyclic voltammetry. The photoelectrochemical properties of 1 /ITO have been investigated by a standard three‐electrode system in the presence of an ascorbic acid sacrificial electron donor. The quantum yield of the photoelectrochemical cell has been estimated to be 29 % based on the number of photons absorbed by the chromophores. Our triad 1 is unique when compared to previously reported photoinduced electron‐transfer arrays, in that C60 is linked by π bonding with little perturbation of the C60 electron delocalization. 相似文献
959.
Jookeun Park Gun Woong Bahng JongOh Choi Jongseon Park 《Accreditation and quality assurance》2010,15(8):445-450
Technical barrier to trade (TBT) has become one of the significant non-tariff measures with the advent of the WTO system in
1995. The key issue in TBT is that technical regulations, standards, and conformity assessment should not be used as barriers
to trade. Regarding conformity assessment, the WTO/TBT Agreement recommends members to enter into negotiations for the mutual
recognition of results of each other’s conformity assessment, as well as to permit participation of conformity assessment
bodies located in other members. In this paper, it will be reviewed why the role of measurement science is important in terms
of international effort to eliminate technical barriers to trade particularly in the area of conformity assessment. 相似文献
960.
Intermittent synchronization in a network of bursting neurons 总被引:1,自引:0,他引:1
Synchronized oscillations in networks of inhibitory and excitatory coupled bursting neurons are common in a variety of neural systems from central pattern generators to human brain circuits. One example of the latter is the subcortical network of the basal ganglia, formed by excitatory and inhibitory bursters of the subthalamic nucleus and globus pallidus, involved in motor control and affected in Parkinson's disease. Recent experiments have demonstrated the intermittent nature of the phase-locking of neural activity in this network. Here, we explore one potential mechanism to explain the intermittent phase-locking in a network. We simplify the network to obtain a model of two inhibitory coupled elements and explore its dynamics. We used geometric analysis and singular perturbation methods for dynamical systems to reduce the full model to a simpler set of equations. Mathematical analysis was completed using three slow variables with two different time scales. Intermittently, synchronous oscillations are generated by overlapped spiking which crucially depends on the geometry of the slow phase plane and the interplay between slow variables as well as the strength of synapses. Two slow variables are responsible for the generation of activity patterns with overlapped spiking, and the other slower variable enhances the robustness of an irregular and intermittent activity pattern. While the analyzed network and the explored mechanism of intermittent synchrony appear to be quite generic, the results of this analysis can be used to trace particular values of biophysical parameters (synaptic strength and parameters of calcium dynamics), which are known to be impacted in Parkinson's disease. 相似文献