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991.
针对在信道环境恶劣的情况下,数字信号接收端的误码率较高的问题,提出一种基于自适应参数调节双稳随机共振系统降低误码率的新方法,得到了输入信噪比小于0db、相干解调接收二进制相移键控信号(binary phase shift keying,简记为2PSK)条件下,系统误码率与输入信噪比的仿真曲线。研究表明:通过非线性双稳系统的2PSK在输入信噪比达到-7.4db时较传统线性解调系统误码率可降低20.1%,这正是对2PSK信号在信道环境恶劣情况下传输的一个补充,对数字带通信号传输具有一定的参考价值。 相似文献
992.
We studied the exponential stabilization problem of a compounded system composed of a flow equation and an Euler–Bernoulli beam, which is equivalent to a cantilever Euler–Bernoulli beam with a delay controller. We designed a dynamic feedback controller that stabilizes exponentially the system provided that the eigenvalues of the free system are not the zeros of controller. In this paper we described the design detail of the dynamic feedback controller and proved its stabilization property. 相似文献
993.
Ming Shang Shang‐Zheng Sun Hong‐Li Wang Brian N. Laforteza Hui‐Xiong Dai Jin‐Quan Yu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(39):10607-10610
The direct ortho‐trifluoromethylation of arenes, including heteroarenes, with TMSCF3 has been accomplished by a copper(II)‐promoted C H activation reaction which completes within 30 minutes. Mechanistic investigations are consistent with the involvement of C H activation, rather than a simple electrophilic aromatic substitution (SEAr), as the key step. 相似文献
994.
Small molecule‐mediated control of hydroxyapatite growth: Free energy calculations benchmarked to density functional theory 下载免费PDF全文
Zhijun Xu Yang Yang Ziqiu Wang Donald Mkhonto Cheng Shang Zhi‐Pan Liu Qiang Cui Nita Sahai 《Journal of computational chemistry》2014,35(1):70-81
The unique, plate‐like morphology of hydroxyapatite (HAP) nanocrystals in bone lends to the hierarchical structure and functions of bone. Proteins enriched in phosphoserine (Ser‐OPO3) and glutamic acid (Glu) residues have been proposed to regulate crystal morphology; however, the atomic‐level mechanisms remain unclear. Previous molecular dynamics studies addressing biomineralization have used force fields with limited benchmarking, especially at the water/mineral interface, and often limited sampling for the binding free energy profile. Here, we use the umbrella sampling/weighted histogram analysis method to obtain the adsorption free energy of Ser‐OPO3 and Glu on HAP (100) and (001) surfaces to understand organic‐mediated crystal growth. The calculated organic‐water–mineral interfacial energies are carefully benchmarked to density functional theory calculations, with explicit inclusion of solvating water molecules around the adsorbate plus the Poisson–Boltzmann continuum model for long‐range solvation effects. Both amino acids adsorb more strongly on the HAP (100) face than the (001) face. Growth rate along the [100] direction should then be slower than in the [001] direction, resulting in plate‐like crystal morphology with greater surface area for the (100) than the (001) face, consistent with bone HAP crystal morphology. Thus, even small molecules are capable of regulating bone crystal growth by preferential adsorption in specific directions. Furthermore, Ser‐OPO3 is a more effective growth modifier by adsorbing more strongly than Glu on the (100) face, providing one possible explanation for the energetically expensive process of phosphorylation of some proteins involved in bone biomineralization. The current results have broader implications for designing routes for biomimetic crystal synthesis. © 2013 Wiley Periodicals, Inc. 相似文献
995.
Y. Wang T. T. Feng L. L. Shi F. Liu Z. B. Shang W. J. Jin 《Journal of inclusion phenomena and macrocyclic chemistry》2013,76(1-2):151-158
In the presence of small amount of 1-iodo butane (IBu) (0.1 % (v/v)), Naproxen (Nap) displays strong room temperature phosphorescence (RTP) in β-cyclodextrin (β-CD) solution without deoxygenation because of the formation of ternary complex of β-CD, Nap, and IBu. The results indicate that β-CD shows good enantiodiscrimination for (R)-Nap and (S)-Nap. The RTP intensity of (R)-Nap is larger than that of (S)-Nap, the difference being 29.2 %. Both (R)-Nap and (S)-Nap exhibit single exponential phosphorescence decay with different lifetimes of 2.535 ± 0.056 and 1.798 ± 0.076 ms for (R)-Nap and for (S)-Nap, respectively. The corresponding association constants evaluated for (R)-Nap/β-CD/IBu and (S)-Nap/β-CD/IBu ternary complexes are (8.02 ± 0.15) × 103 and (2.50 ± 0.06) × 103 L mol?1, respectively. Thus, the observation of RTP differences between (R)-Nap and (S)-Nap can be attributed to their different ability to form complexes with chiral β-CD. 相似文献
996.
以2-(2-吡啶基)咪唑(pIM)、Co2+和NaVO3为原料,在水热条件下,制备了新的钒氧簇化合物[Co(pIM)V2O6] (1)。采用X射线单晶衍射、粉末X射线衍射、傅里叶变换红外光谱和元素分析等方法对化合物进行了表征。单晶解析表明,该化合物由VO4四面体和CoO3N2四方锥通过氧原子共边、共角连接成二维结构。基于钒氧簇在催化氧化体系中的高效活性,1作为非均相反应的催化剂,在以H2O2为氧化剂的催化烯烃环氧化反应中表现出优秀的催化性能,催化剂能够多次重复使用且活性基本保持不变。此外,磁化率研究表明1中存在反铁磁相互作用。 相似文献
997.
Yu‐Chien Ku Mei‐I Leong Wan‐Ting Wang Shang‐Da Huang 《Journal of separation science》2013,36(8):1470-1477
Sun protection is an important part of our lives. UV filters are widely used to absorb solar radiation in sunscreens. However, excess UV filters constitute persistent groups of organic micropollutants present in the environment. An environmentally friendly ionic‐liquid‐based up‐and‐down shaker‐assisted dispersive liquid?liquid microextraction device combined with ultra‐performance liquid chromatography coupled with photodiode‐array detection has been developed to preconcentrate three UV filters (benzophenone, 2‐hydroxy‐4‐methoxybenzophenone, 2,2′‐dihydroxy‐4‐methoxybenzophenone) from field water samples. In this method, the optimal conditions for the proposed extraction method were: 40 μL [C8MIM][PF6] as extraction solvent and 200 μL methanol as disperser solvent were used to extract the UV filters. After up‐and‐down shaking for 3 min, the aqueous solution was centrifuged at 5000 rpm speed, then using microtube to collect the settled extraction solvent and using ultra‐performance liquid chromatography for further analysis. Quantification results indicated that the linear range was 2–1000 ng/mL. The LOD of this method was in the range 0.2–1.3 ng/mL with r2 ≥ 0.9993. The relative recovery in studies of different types of field water samples was in the range 92–120%, and the RSD was 2.3–7.1%. The proposed method was also applied to the analysis of field samples. 相似文献
998.
Yubo Chen Hao Feng Liang Li Songmin Shang Marcus Chun-Wah Yuen 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1225-1229
Conducting polymer hydrogels consisting of polypyrrole (PPy) and chitosan (CS) are prepared by static polymerization of pyrrole using methyl orange (MO) as the dopant and Fe2(SO4)3 as the oxidant in the CS aqueous solution. PPy/CS composite hydrogels not only have good electrical conductivities, but also exhibit excellent swelling/deswelling behaviors due to the participation of one-dimensional conducting PPy blocks in the hydrogel network. The effects of the amount of the oxidant and ionic strength on the physical properties of PPy/CS composite hydrogels are studied in detail. The results show that PPy/CS composite hydrogels have improved water absorbencies in saline solutions compared with the conventional polyelectrolyte hydrogel. 相似文献
999.
A surface modification technique was proposed for the modification of silicon surface with glucose oxidase (GOD). The silicon surface was first graft copolymerized with acrylic acid (AAc) via surface-initiated reversible addition-fragmentation chain-transfer (RAFT)-mediated process. With the aid of a water-soluble carbodiimide, GOD was then covalently immobilized on the silicon surface through the amide linkage between the amino group of GOD and the carboxyl group of the grafted AAc polymer. The changes in the surface composition after polymer grafting and enzyme immobilization on the silicon surface were investigated using X-ray photoelectron spectroscopy (XPS). The amount of GOD immobilized could be varied by changing the thickness of the polymer layer and the immobilization time. The GOD-functionalized silicon hybrids are potential useful in the application of the silicon-based biosensors. 相似文献
1000.
The electron temperature (Te) of positive dc corona plasma in Ar/O2 atmosphere was diagnosed, and plasma decomposition of toluene/benzene was studied in a razor–plate reactor. Experimental results revealed that Te would increase with corona current until it reached a peak value, and then decrease; the volume fraction of Ar (φAr) in Ar/O2 mixed gas also influenced Te, the higher φAr, the lower Te. Though the decomposed volume fraction of toluene/benzene was positively related to the input power, the decomposition efficiency did not monotonically increase with the specific energy density. The highest energy yield reached 3.8 g-toluene/kWh and 2.4 g-benzene/kWh, respectively. 相似文献