全文获取类型
收费全文 | 51426篇 |
免费 | 4841篇 |
国内免费 | 3598篇 |
专业分类
化学 | 37356篇 |
晶体学 | 586篇 |
力学 | 1909篇 |
综合类 | 238篇 |
数学 | 6832篇 |
物理学 | 12944篇 |
出版年
2023年 | 580篇 |
2022年 | 1040篇 |
2021年 | 1126篇 |
2020年 | 1326篇 |
2019年 | 1330篇 |
2018年 | 1079篇 |
2017年 | 1028篇 |
2016年 | 1670篇 |
2015年 | 1654篇 |
2014年 | 1981篇 |
2013年 | 3076篇 |
2012年 | 3566篇 |
2011年 | 4085篇 |
2010年 | 2559篇 |
2009年 | 2474篇 |
2008年 | 3118篇 |
2007年 | 3039篇 |
2006年 | 2817篇 |
2005年 | 2542篇 |
2004年 | 2102篇 |
2003年 | 1722篇 |
2002年 | 1681篇 |
2001年 | 1033篇 |
2000年 | 928篇 |
1999年 | 875篇 |
1998年 | 769篇 |
1997年 | 736篇 |
1996年 | 814篇 |
1995年 | 635篇 |
1994年 | 607篇 |
1993年 | 614篇 |
1992年 | 551篇 |
1991年 | 479篇 |
1990年 | 415篇 |
1989年 | 354篇 |
1988年 | 320篇 |
1987年 | 306篇 |
1986年 | 284篇 |
1985年 | 363篇 |
1984年 | 363篇 |
1983年 | 247篇 |
1982年 | 296篇 |
1981年 | 296篇 |
1980年 | 232篇 |
1979年 | 239篇 |
1978年 | 255篇 |
1977年 | 191篇 |
1976年 | 194篇 |
1974年 | 206篇 |
1973年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
含羧酸配体的鼓形有机锡氧簇合物:六聚苯基锡氧3-吲哚丁酸酯的合成及晶体结构 总被引:7,自引:0,他引:7
利用Ph3SnOH和3-吲哚丁酸以1:1摩尔比反应,合成了新型含羧酸配体的鼓形 有机锡氧簇合物:六聚苯基锡氧3-吲哚西酸酯。通过元素分析、红外光谱和X射线 单晶衍射对其结构进行了表征。测试结果表明:该化合物为三斜晶系,空间群P1, a=1.1722(6),b=1.5694(8)nm,c=1.7227(9)nm,α=116.251(8)°,β=100. 854(10)°,γ=95.606(9)°,Z=1,V=2.732(3)nm^3,Dc=1.554g·cm^-3,μ =1.420mm^-1,F(000)=1276,R=0.0630,ωR=0.0762。晶体结构中,六配位的锡原 子呈畸变的八面体构型。 相似文献
992.
A series of carbon-covered titania (CCT) were prepared via pyrolysis of sucrose highly dispersed on titania surface in flowing
N2. The samples were characterized by XRD, BET, DTA-TG, UV—Vis, and their photocatalytic properties were evaluated with two
model pollutants, methylene blue (MB) and rhodamine B (RB), at room temperature. The effect of carbon content on photocatalytic
activity of the C/TiO2 composite was investigated. It was found that the effect of carbon content is different for different pollutants or different
light sources. For three tested samples, under UV illumination CCT01 has the highest activity for MB photocatalytic degradation,
while in the case of RB, CCT02 is the most active photocatalyst. Under visible light illumination, CCT005 has the highest
activity for both MB and RB photocatalytic degradation.
Translated from Chinese Journal of Catalysis, 2006, 27(1): (in Chinese) 相似文献
993.
994.
995.
The amount of chemiluminescence (CL) or light that is emitted from human polymorphonuclear leukocytes (PMN) during phagocytosis or activation by soluble stimuli is dependent on the emission of photons from the oxidation of particulate or bystander molecules. Because the compounds luminol and lucigenin yield photons with high quantum efficiency these agents have been introduced to sensitively assess PMN-CL. Since there is limited information about the pathways involved in the chemiluminescence of these compounds, we investigated the role of both myeloperoxidase (MPO) and superoxide anion (· O2?) in luminol-and lucigenin-PMN-CL. We compared the CL between normal and MPO- deficient PMN using zymosan for phagocytosis and N-formylmethionyleucylphenylalanine (FMLP) as a soluble stimulus. Our data demonstrated that luminol-CL was dependent on the presence of MPO and independent of · O2? generation during phagocytosis but independent of MPO during FMLP activation. In contrast lucigenin-CL was independent of MPO during both phagocytosis and FMLP activation and appeared to reflect · O2? production. Consequently, dependent on the type of activation, it appears that luminol- and lucigenin-CL are generated via different oxidative pathways and may serve as potentially useful tools to differentiate the redox activity of phagocytic cells. 相似文献
996.
Christov A Korol RM Dai E Liu L Guan H Bernards MA Cavers PB Susko D Lucas A 《Photochemistry and photobiology》2005,81(2):457-466
Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P<0.05) after treatment with anti-inflammatory agents, and plaque area decreased on comparison with saline-treated rabbits after stent implant or angioplasty (Por=0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2>or=0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites. 相似文献
997.
Design, synthesis, and binding affinities of pyrrolinone-based somatostatin mimetics 总被引:1,自引:0,他引:1
Smith AB Charnley AK Mesaros EF Kikuchi O Wang W Benowitz A Chu CL Feng JJ Chen KH Lin A Cheng FC Taylor L Hirschmann R 《Organic letters》2005,7(3):399-402
[structure: see text] Tetrapyrrolinone somatostatin (SRIF) mimetics (cf. 1), based on a heterochiral (D,L-mixed) pyrrolinone scaffold, were designed, synthesized, and evaluated for biological activity. The iterative synthetic sequence, incorporating the requisite functionalized coded and noncoded amino acid side chains, comprised a longest linear synthetic sequence of 23 steps. Binding affinities at two somatostatin receptor subtypes (hsst 4 and 5) reveal micromolar activity, demonstrating that the d,l-mixed pyrrolinone scaffold can be employed to generate functional mimetics of peptide beta-turns. 相似文献
998.
With the advent of the big data era, information storage and security are becoming increasingly important. However, high capacity information storage and multilevel anti-counterfeiting are typically difficult to achieve simultaneously. To address this challenge, herein, two electrochromic and electrofluorochromic dual-functional polymers with aggregation-induced emission (AIE) characteristics were rationally designed and facilely prepared. Upon applying voltages, the absorption and fluorescence spectra of the AIE polymers can undergo reversible changes, accompanied by variation of their color and emission. By utilizing the controllable characteristics of the polymers, dual-mode display devices were fabricated via a simple spraying technique. More interestingly, a four-dimensional color code device was constructed by adding color change multiplexing to the two-dimensional space, thereby achieving high capacity information storage. Moreover, the color code device can also be applied in the multilevel anti-counterfeiting area. The encrypted information can be dynamically converted under different voltages. Thus, the AIE polymers show great promise for applications in multidimensional information storage and dynamic anti-counterfeiting, and the design strategy may provide a new avenue for advanced information storage and high security technology.By using electrical stimuli-responsive AIE polymers, dual-mode display devices, multidimensional information storage and anti-counterfeiting devices were constructed. 相似文献
999.
Nonlinear optical (NLO) crystals assembled with conventional non-π-conjugated tetrahedral functional building units (FBUs), generally referring to [PO4] and [BO4], usually exhibit weak nonlinearity and poor birefringence. It is currently proposed that partially substituting oxygen atoms with fluoride atoms in these FBUs could enhance these crucial properties. Hence, we investigated for the first time the NLO-related properties of NH4BAsO4F (ABAF), which was constructed from tetrahedral [BO3F] and [AsO4] FBUs, and enhancements of these properties were observed in this material, that is large second-harmonic generation (SHG) response (2 × KDP) and improved birefringence (0.03 at 1064 nm). Notably, both SHG coefficient and birefringence of ABAF exceeded those of a great majority of phosphates, sulfates, or boron phosphates and achieved a preferable balance. It is interesting that ABAF shows vast structural similarities to the typical NLO crystals Sr2Be2B2O7 (SBBO) and KBe2BO3F2 (KBBF), which might be the partial reason why it showed improvement in these vital properties. This work may afford some inspiration for enhancing the key performances of NLO crystals assembled with non-π-conjugated tetrahedra.We report a new nonlinear optical crystal assembled exclusively with tetrahedral functional building units in which enhanced birefringence (Δn) and second-harmonic generation (deff) were observed. 相似文献
1000.
Cheng-Ting Zi Liu Yang Fa-Wu Dong Qing-Hua Kong Zhong-Tao Ding Jun Zhou 《Natural product research》2020,34(16):2301-2309
Abstract Two new compounds (9 and 10) having a camptothecin (CPT) analog conjugated to the 4β-azido-4-deoxypodophyllotixin analog by untilizing the copper-catalyzed azide-alkyne cycloadditon (CuAAC) reaction, and were evaluated for their cytotoxicity against a panel of five human cancer cell lines (HL-60, SMMC-7721, A-549, MCF-7 and SW480) using the MTT (3-(4,5-dimethyl-thiahiazo-2-yl)-2,5-diphenyltetrazolium bromide) assay. Two novel conjugates shown weak cytotoxicity, compound 10 showed highly potent against HL-60 cell line tested, with IC50 value 17.69?±?0.19?μM. This compound suggested its potential as anticancer agents for further development. 相似文献