全文获取类型
收费全文 | 53243篇 |
免费 | 8501篇 |
国内免费 | 5660篇 |
专业分类
化学 | 37368篇 |
晶体学 | 641篇 |
力学 | 3075篇 |
综合类 | 328篇 |
数学 | 5955篇 |
物理学 | 20037篇 |
出版年
2024年 | 182篇 |
2023年 | 1120篇 |
2022年 | 2076篇 |
2021年 | 2214篇 |
2020年 | 2272篇 |
2019年 | 2141篇 |
2018年 | 1829篇 |
2017年 | 1776篇 |
2016年 | 2606篇 |
2015年 | 2638篇 |
2014年 | 3099篇 |
2013年 | 3953篇 |
2012年 | 4849篇 |
2011年 | 4785篇 |
2010年 | 3322篇 |
2009年 | 3112篇 |
2008年 | 3337篇 |
2007年 | 2955篇 |
2006年 | 2651篇 |
2005年 | 2276篇 |
2004年 | 1739篇 |
2003年 | 1388篇 |
2002年 | 1275篇 |
2001年 | 1018篇 |
2000年 | 895篇 |
1999年 | 1046篇 |
1998年 | 856篇 |
1997年 | 806篇 |
1996年 | 794篇 |
1995年 | 727篇 |
1994年 | 612篇 |
1993年 | 519篇 |
1992年 | 430篇 |
1991年 | 392篇 |
1990年 | 331篇 |
1989年 | 240篇 |
1988年 | 178篇 |
1987年 | 163篇 |
1986年 | 159篇 |
1985年 | 139篇 |
1984年 | 87篇 |
1983年 | 93篇 |
1982年 | 55篇 |
1981年 | 39篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 18篇 |
1976年 | 20篇 |
1975年 | 21篇 |
1972年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Yuedi Ding Jun Fan Wenxin Li Runlin Yang Ying Peng Lili Deng Yu Wu Qiang Fu 《Applied biochemistry and biotechnology》2013,170(7):1637-1648
Somatostatin is a natural inhibitor of growth hormone, and its analogues are clinically used for the therapy of acromegaly, gigantism, thyrotropinoma, and other carcinoid syndrome. However, natural somatostatin is limited for clinical usage because of its short half-life in vivo. Albumin fusion technology was used to construct long-acting fusion proteins, and Pichia pastoris was used as an expression system. Three fusion proteins, (somatostatin (SS)14)2-human serum albumin (HSA), (SS14)3-HSA, and HSA-(SS14)3, were constructed with different fusion copies of somatostatin-14 and fusion orientations. The expression level of (SS14)3-HSA and HSA-(SS14)3 was much lower than (SS14)2-HSA due to the additional fusion of the somatostatin-14 molecule. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry revealed that severe degradation occurred in the fermentation process. Similar to the standard of somatostatin-14, all three fusion proteins were able to inhibit growth hormone secretion in the blood, with (SS14)2-HSA being the most effective one. On the whole, (SS14)2-HSA was the most effective protein in both production level and bioactivity, and increasing the number of small protein copies fused to HSA may not be a suitable method to improve the protein bioactivity. 相似文献
942.
Hai Y Chen JJ Zhao P Lv H Yu Y Xu P Zhang JL 《Chemical communications (Cambridge, England)》2011,47(8):2435-2437
A novel class of ZnSalens (ZnL(1-10)) with lipophilic and cationic conjugates as optical probes in single and two-photon fluorescence microscopy images of living cells were prepared, which exhibited chemo- and photostability, low cytotoxicity and high subcellular selectivity. 相似文献
943.
He C Qian X Xu Y Yang C Yin L Zhu W 《Dalton transactions (Cambridge, England : 2003)》2011,40(5):1034-1037
A novel ratiometric fluorescent probe for oxalic acid was designed and synthesized, based on the zinc-containing [DAQZ@2Zn(2+)] complex. It shows highly selective "on-off" fluorescence changes with a more than 20 nm blue shift in wavelength for oxalic acids in aqueous solution. Moreover, it can fluorescently respond to oxalic acid in living cells. 相似文献
944.
A facile one-pot method to high-quality Ag-graphene composite nanosheets for efficient surface-enhanced Raman scattering 总被引:2,自引:0,他引:2
Zhang Z Xu F Yang W Guo M Wang X Zhang B Tang J 《Chemical communications (Cambridge, England)》2011,47(22):6440-6442
Ag-graphene composite nanosheets (AGCN) with adjustable size and well-controlled densities of Ag nanoparticles (Ag NPs) using Poly(N-vinyl-2-pyrrolidone) (PVP) as a reductant and stabilizer are reported. The obtained AGCN substrate is extremely suitable for surface-enhanced Raman spectroscopy (SERS). 相似文献
945.
An efficient synthetic method has been developed for the synthesis of 2-arylacrylic esters from the corresponding aryl methyl ketones via Wittig reaction and singlet oxygen ene reaction. Wittig reaction to aryl methyl ketones with (methoxymethyl)triphenylphosphonium chloride in basic condition afforded the methyl enol ethers, and then 2-arylacrylic esters were obtained by singlet oxygen ene reaction, followed by tosylation and elimination in one-pot to the methyl enol ethers in good yields. 相似文献
946.
Liu M Gan M Lin S Zhang Y Zi J Song W Fan X Liu Y Yang Y Shi J 《Organic letters》2011,13(11):2856-2859
Two structurally novel homocucurbitane triterpenoid glycosides, machilusides A (1) and B (2), possessing an unprecedented C(36) skeleton with a D-fructose moiety incorporated into a cucurbitane nucleus forming unique cage-like tricyclic ring moieties, were isolated from the stem bark of Machilus yaoshansis. Their structures were determined by spectroscopic methods. Both compounds exhibited nonselective cytotoxic activities against several human cancer cell lines. The biosynthetic pathway of 1 and 2 was postulated. 相似文献
947.
Karunakaran RG Lu CH Zhang Z Yang S 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4594-4602
We report a simple and versatile approach to creating a highly transparent superhydrophobic surface with dual-scale roughness on the nanoscale. 3-Aminopropyltrimethoxysilane (APTS)-functionalized silica nanoparticles of two different sizes (100 and 20 nm) were sequentially dip coated onto different substrates, followed by thermal annealing. After hydrophobilization of the nanoparticle film with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane for 30 min or longer, the surface became superhydrophobic with an advancing water contact angle of greater than 160° and a water droplet (10 μL) roll-off angle of less than 5°. The order of nanoparticles dip coated onto the silicon wafer (i.e., 100 nm first and 20 nm second or vice versa) did not seem to have a significant effect on the resulting apparent water contact angle. In contrast, when the substrate was dip coated with monoscale nanoparticles (20, 50, and 100 nm), a highly hydrophobic surface (with an advancing water contact angle of up to 143°) was obtained, and the degree of hydrophobicity was found to be dependent on the particle size and concentration of the dip-coating solution. UV-vis spectra showed nearly 100% transmission in the visible region from the glass coated with dual-scale nanoparticles, similar to the bare one. The coating strategy was versatile, and superhydrophobicity was obtained on various substrates, including Si, glass, epoxy resin, and fabrics. Thermal annealing enhanced the stability of the nanoparticle coating, and superhydrophobicity was maintained against prolonged exposure to UV light under ambient conditions. 相似文献
948.
Hua Li Siwang Wang Qian Yang Yanhua Xie Wei Cao Bangle Zhang Jianbo Wang Jiepin Wang Meng Wang 《Chromatographia》2011,73(5-6):495-500
Paeonol, an important constituent of the traditional Chinese medicine Cortex Moutan, has a variety of bioactivity. A simple and sensitive HPLC?CUV method has been developed for analysis of paeonol in different rat tissue (heart, liver, spleen, lung, kidney, and brain). Bio-samples were prepared by simple protein precipitation, and separation of paeonol was achieved on a C18 column with methanol?C2% glacial acetic acid solution 70:30 (v/v) as mobile phase at a flow rate of 1.0 mL min?1. UV detection was at 274 nm and the column temperature was 30 °C. Linearity was good between 0.025 and 5.0 ??g mL?1 (r 2 ?? 0.9990) for tissue samples. Inter-day and intra-day accuracy (as relative error, RE) and precision (as relative standard deviation, RSD) were <5.94 and 6.05%, respectively. The limit of detection was 0.025 ??g mL?1 and extraction recovery for all samples was ??85.86%. The method was successfully applied to a tissue-distribution study after oral administration of 40 mg kg?1 paeonol to healthy Sprague?CDawley rats. The study showed that paeonol was quickly distributed and eliminated after oral administration; liver and kidney were the major distribution tissues of paeonol in rats, and paeonol quickly passed through the blood?Cbrain barrier. It was also found there was no long-term accumulation of paeonol in rat tissues. 相似文献
949.
Ma J Yang J Jiao L Wang T Lian J Duan X Zheng W 《Dalton transactions (Cambridge, England : 2003)》2011,40(39):10100-10108
The Bi(2)S(3) nanomaterials with various morphologies such as nanorods, nanowires, nanowire bundles, urchin-like microspheres and urchin-like microspheres with cavities have been successfully synthesized through a simple hydrothermal method. Experimental results indicate that sulfur sources play crucial roles in determining the morphologies of Bi(2)S(3) products. Moreover, formation mechanisms of different Bi(2)S(3) nanostructures are discussed based on understanding of the growth habit of Bi(2)S(3) crystal. Finally, we also studied the morphologies-dependent electrochemical and optical properties of the as-synthesized Bi(2)S(3) nanomaterials. 相似文献
950.
Sha Zhao Guoquan Zhang Lei Fu Lifen Liu Xiaohong Fang Fenglin Yang 《Electroanalysis》2011,23(2):355-363
To analyze the specific roles of anthraquinone‐2‐sulfonate (AQS) and polypyrrole (PPy) layer on oxygen reduction reaction (ORR), the electrocatalytic reduction of oxygen was investigated on the AQS/PPy composite modified graphite electrode. Results show that the enhanced electrocatalytic performance is attributed to the excellent electrocatalytic activity of the immobilized AQS functional groups to mediate two‐electron reduction of O2 to H2O2. The PPy layer may not participate in ORR, but it can further catalyze the two‐electron reduction of H2O2 to produce H2O in the potential range more negative than that the two‐electron reduction of oxygen proceeds efficiently on the AQS sites. 相似文献