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排序方式: 共有9170条查询结果,搜索用时 15 毫秒
231.
Xu X Zhao J Jiang D Kong J Liu B Deng J 《Analytical and bioanalytical chemistry》2002,374(7-8):1261-1266
A novel hydrogen peroxide biosensor was developed based on the immobilization of horseradish peroxidase (HRP) in a TiO(2) sol-gel matrix on an electropolymerized phenazine methosulfate (PMS) modified electrode surface. Such membranes are of interest due to their high surface area, biological compatibility, and ease of fabrication. HRP entrapped in the TiO(2) matix was stable and retained its activity to a large extent. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of electron transfer between immobilized HRP and the glassy carbon electrode via electropolymerized PMS. The influence of various experimental parameters such as operating potential, pH, temperature, and stability was investigated for optimum analytical performance. The biosensor provided a wide linear calibration range from 4.0x10(-6) M to 1.0x10(-3) M, with a detection limit of 8.0x10(-7) M at a signal-to-noise ratio of 3. The sensor retained 80% of its original activity after two months of operation. 相似文献
232.
Qiutian Liu Chunxi Zhang Changneng Chen Hongping Zhu Yuheng Deng Jinhua Cai 《中国科学B辑(英文版)》1997,40(6):616-623
In a reaction system consisting of FeCl2, tetrathiometallate and cycloalkylthiolate, two Fe4S4 cubanelike cluster compounds were obtained with the following crystallographic data: (PhCH2NMe3)2 [ Fe4S4 (SC5H9)4] (I), monoclinic space groupP21/c,a = 1.632 7(4),b=1.122 9(3),c = 2. 802 5(10) nm, β= 94.63(2)°, Z=4, andR= 0.074; (Et4N)2[F4S4(SC6HlI)4] (II), tetragod space group
,a = l.167 05(9),b = 1.167 06(2),c = 2.063 26(5) nm,Z = 2, Dobs = 1. 28 g/cm3, andR = 0. 078. The participation of cycloalkylthiolate ligand does not obviously arouse the change of the Fe4S4 core structure. Meanwhile, the influence of the cation on the structural symmetry of the Fe4S4 cluster dianion is also discussed.
Project supported by the National Natural Science Foundation of China and the Climbing Program Foundation of China. 相似文献
233.
Simple interface for capillary electrophoresis-inductively coupled plasma atomic emission spectrometry 总被引:4,自引:0,他引:4
A simple interface has been developed to couple capillary electrophoresis (CE) to inductively coupled plasma atomic emission spectrometry (ICP-AES) for metal speciation. A concentric glass nebulizer with elongated tip is used as the CE-ICP interface. The CE capillary is the central tube of the nebulizer. A platinum wire is wrapped across the exit end of the CE capillary to provide electrical connection to the CE power supply. No sheath flow of buffer solution is needed. A simple cooling system has also been developed. A peristaltic pump circulates water through a plastic tube that encloses the section of the CE capillary between the CE instrument and the ICP spectrometer. Characteristics of the CE-ICP interface, e.g., elution time, nebulization and transport efficiency and peak broadening, versus carrier gas flow-rate have been studied. Comparisons to a previous design with the Pt electrode inserted into the end of the CE capillary are made where appropriate. The reproducibility (RSD) in ICP emission intensity of the system is <4%. Detection limits of Cr and Cu are approximately 5 ng/ml. 相似文献
234.
环状芴基张力半导体由于其特殊的分子结构,发射状排布的p轨道和纳米级空腔等诸多特点,引起了科学家广泛的关注.相对于直链型芴基半导体,环状芴基张力半导体展现出独特的光电性质.然而,迄今为止其振动性质没有被报道.对四元环芴的晶体与直链四聚芴粉末样品进行拉曼光谱表征和归一化处理,并结合理论计算.结果表明,与直链寡聚芴相比,环芴类似于碳纳米管的G峰发生了偏移,并且低频区域拉曼频移峰的峰强增加.其原因是由于张力的引入,改变了芴基主链的骨架和电子结构,加强芴骨架上π电子离域,同时使环芴中每个芴单元都参与到振动中.该研究结果为芴基张力半导体材料拉曼光谱的研究提供了一定的工作基础. 相似文献
235.
多维核磁共振技术的飞速发展议得其在生物大分子结构测定方面的应用已经达到可以与【射线晶体学并驾齐驱的地步.蛋白质结构堆积紧密,较适合于用核磁共振方法给出确定的结构.与蛋白质不同的是多肽的柔性较大,在溶液中可能存在多种构象,核磁共振实验给出的只是平均信息*.利用核磁,(振数据构建分子结构模型常用的方法有距离几何、分子动力学等,在由核磁共振NOESZ得到的距离信息足够多时可以给出较好的结果问.由于多肽本身的特点:柔性较大,由核磁共振得到的距离信息较少等,利用距离几何、分子动力学方法进行构象搜索时容易陷入… 相似文献
236.
237.
Rapid determination of volatile constituents of Michelia alba flowers by gas chromatography-mass spectrometry with solid-phase microextraction 总被引:12,自引:0,他引:12
The volatile constituents of Michelia alba flowers, including fresh flowers, frozen flowers and withered flowers, were investigated by GC-MS. The volatiles in a simulated natural environment were sampled by solid-phase microextraction (SPME), with a 100 microm polydimethylsiloxane fiber at 25+/-5 degrees C for 4 h. The fibers were desorbed in a GC injection liner at 250 degrees C for 3 min. With headspace SPME-GC-MS analysis, 61 peaks were separated. The main compounds in headspace of fresh Michelia alba flowers included alpha-myrcene, (S)-limonene, (R)-fenchone, linalool, camphor, caryophyllene, germacrene D, etc., a greater number of compounds than for frozen flowers and withered flowers. At the same time, the biomarkers of fresh flowers were compared with the frozen flowers and withered flowers. In this study, headspace SPME-GC-MS afforded a simple and more sensitive sampling method for fresh Michelia alba flowers and other fresh flowers. 相似文献
238.
239.
H Deng D Manor G Weng P Rath Y Koutalos T Ebrey R Gebhard J Lugtenburg M Tsuda R H Callender 《Photochemistry and photobiology》1991,54(6):1001-1007
The resonance Raman spectrum of octopus bathorhodopsin in the fingerprint region and in the ethylenic-Schiff base region have been obtained at 80 K using the "pump-probe" technique as have its deuterated chromophore analogues at the C7D; C8D; C8,C7D2; C10D; C11D; C11, C12D2; C14D; C15D; C14, C15D2; and N16D positions. While these data are not sufficient to make definitive band assignments, many tentative assignments can be made. Because of the close spectral similarity between the octopus bathorhodopsin spectrum and that of bovine bathorhodopsin, we conclude that the essential configuration of octopus bathorhodopsin's chromophore is all-trans like. The data suggest that the Schiff base, C = N, configuration is trans (anti). The observed conformationally sensitive fingerprint bands show pronounced isotope shifts upon chromophore deuteration. The size of the shifts differ, in certain cases, from those found for bovine bathorhodopsin. Thus, the internal mode composition of the fingerprint bands differs somewhat from bovine bathorhodopsin, suggesting a somewhat different in situ chromophore conformation. An analysis of the NH bend frequency, the Schiff base C = N stretch frequency, and its shift upon Schiff base deuteration suggests that the hydrogen bonding between the protonated Schiff base with its protein binding pocket is weaker in octopus bathorhodopsin than in bovine bathorhodopsin but stronger than that found in bacteriorhodopsin's bR568 pigment. 相似文献
240.