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971.
Colon-specific drug delivery systems (CDDS) can improve the bioavailability of drug through the oral route. A novel formulation for oral administration using pH-enzyme Di-dependent chitosan mcirospheres (MS) and 5-Fu as a model drug has been investigated for colon-specific drug delivery by the emulsification/chemical cross-linking and coating technique, respectively. The influence of polymer concentration, ratio of drug to polymer, the amount of crosslinking agent and the stirring speed on the encapsulation efficiency, particle size in microspheres were evaluated. The best formulation was optimized by an orthogonal design. Drug release studies under conditions mimicking stomach to colon transit have shown that the drug was protected from being released in the physiological environment of the stomach and small intestine. The plasma concentrations of 5-Fu after oral administration of coated chitosan MS to rats were determined and compared with that of 5-Fu solution. The in vivo pharmacokinetics study of 5-Fu loaded pH-enzyme Di-dependent chitosan MS showed sustained plasma 5-Fu concentration-time profile. The in vitro release correlated well with the pharmacokinetics profile. The results clearly demonstrated that the pH-enzyme Di-dependent chitosan MS is potential system for colon-specific drug delivery of 5-Fu. 相似文献
972.
Using Stuttgart/Dresden effective core potentials MWB28, MWB60, and GTO valence basis sets (8s7p6d)/[6s5p3d], (8s7p6d)/[6s5p3d]
for Zr and Hf atoms and 6-311++G(3df,3pd) basis set for C, H, O, and Ti atoms, tight convergence criteria geometry optimizations
and harmonic frequency calculations are performed at B3LYP and B3LYP/IEF-PCM levels of theory so as to model the gas phase
and argon matrix infrared spectra of the tetrahedral molecules R2MH2 (R = D(H), CH3, OH; M = Ti, Zr, Hf). Influence of the transition metal and/or substituent group on the symmetric and asymmetric stretching
frequencies of the MH2 fragment of the R2MH2 molecules is investigated at both the levels of theory. The modelling of the argon matrix effect improves the agreement between
the calculated frequencies and the experimental ones. The calculated argon matrix to gas phase frequency shifts is compared
reasonably to the experimental argon to neon matrix shifts. 相似文献
973.
Xiu-Li Wang Hong-Yan Lin Guo-Cheng Liu Hai-Yan Zhao Bao-Kuan Chen 《Journal of organometallic chemistry》2008,693(16):2767-2774
Two novel coordination polymers [Cu3(1,3-BDC)4(Dpq)2] (1) and [Cu2(BTC)(OH)(Dpq)2] · H2O (2), have been hydrothermally synthesized by self-assembly of aromatic polycarboxylate ligands 1,3-H2BDC (1,3-H2BDC = 1,3-benzenedicarboxylate) or H3BTC (H3BTC = 1,3,5-benzenetricarboxylate), chelating ligand Dpq (Dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline), and copper chloride. X-ray diffraction analysis reveals that each trinuclear CuII cluster is bridged by two coordination modes of 1,3-BDC ligands to form one-dimensional (1-D) chain structure in complex 1. Complex 2 possesses a two-dimensional (2-D) layer network composed of dinuclear [Cu2(OH)(Dpq)2] unit and bridging ligand BTC. The adjacent chains for 1 or the adjacent layers for 2 are further linked by π-π stacking interactions to form the three-dimensional (3-D) supramolecular frameworks. Moreover, the electrochemical properties of the two copper(II) complexes bulk-modified carbon paste electrodes (Cu-CPEs: 1-CPE and 2-CPE) have been studied, and the results indicate that both Cu-CPEs give one-electron quasi-reversible redox waves in potential range of 600 to −400 mV due to the metal copper ion Cu(II)/Cu(I). The Cu-CPEs have good electrocatalytic activities toward the reduction of nitrite and bromate in 0.1 M pH 2 phosphates buffer solution, and have remarkable long term stability and especially good surface renewability by simple mechanical polishing in the event of surface fouling, which is important for practical application. 相似文献
974.
975.
PeiDe Zhao Ping Chen GuoQing Tang JinWei Liu Lie Lin Peng Guo Qing Yu JianZhong Yao DongMing Ma GuiLan Zhang WenJu Chen 《中国科学B辑(英文版)》2008,51(6):529-538
The spectroscopic properties of a new chlorophyll derivate photosensitizer(CDP) are studied under the excitation wavelengths at 800 and 400 nm using femtosecond pulses from a Ti:sapphire laser.The damaging effect of CDP on the BEL-7402 cancer cells is also investigated upon two-photon illumination at 800 nm.The normalized fluorescence spectra of CDP in tetrahydrofuran(THF) show that two-photon and one-photon spectra have the same distributions and the same emission bands(675 nm).The life-times of two-and one-photon induced fluorescence of this molecule are of the order of 5.0 ns.By comparing the data it is shown that there is some difference between the two lifetimes,but the differ-ence is less than one nanosecond.The two-photon absorption cross section of the molecule is also measured at 800 nm and estimated as about σ′2 ≈ 31.5×10-50 cm4·s·photon-1.The results of two-photon photodynamic therapy(TPPDT) tests show that CDP can kill all of the tested cancer cells according to the usual Eosine assessment.Our results indicate that the two-photon-induced photophysical,photo-chemical and photosensitizing processes of CDP may be basically similar to those of one-photon ex-citation.These behaviors of the sample suggest that one may find other possible methods to estimate some photosensitizers' effects in details such as their distribution in cells and the reactive targets of the sub-cellular parts of some tumor cells via two-photon excitation techniques. 相似文献
976.
Mass analysis in islands of stability with linear quadrupoles with added octopole fields 总被引:1,自引:0,他引:1
Konenkov N Zhao X Xiao Z Douglas DJ 《Journal of the American Society for Mass Spectrometry》2007,18(5):826-834
Mass analysis with linear quadrupole mass filters is possible by forming "islands" in the stability diagram with auxiliary quadrupole excitation. In this work, computer simulations are used to calculate stability boundaries, island positions, and peak shapes and ion transmission for mass analysis with linear quadrupole mass filters that have added octopole fields of about 2 to 4%. Rod sets with exact geometries that have quadrupole and octopole fields only in the potential, and round rod sets, with multipoles up to N = 10 (the twenty pole term) included in the calculations, show the same stability boundaries, island positions, and peak shapes. With the DC voltage applied to the rods so that the Mathieu parameter a < 0, conventional mass analysis is possible without the use of an island. With the DC polarity reversed so that a > 0, the resolution and transmission are poor preventing conventional mass analysis. In principle, mass analysis in an island is possible with operation at either of two tips. Provided the correct island tip is chosen for mass analysis, peak shapes comparable to those with a > 0 and no excitation are possible, both with a > 0 and with a < 0. In the latter case, the use of an island of stability allows mass analysis when the added octopole otherwise prevents conventional mass analysis. 相似文献
977.
Liu GuiLin Chen ChunCheng Ji HongWei Ma WanHong Zhao JinCai 《中国科学:化学(英文版)》2012,55(9):1953-1958,2012,2013
A three-layer structure of n-type organic semiconductors(PTCDA/PTCDA:PCBM/PCBM) is successfully identified as photoanode for photoelectrochemical water oxidation during the overall splitting of water into hydrogen/oxygen in a nearly stoichiometric ratio(H2:O2=2:1) under visible irradiation(λ > 420 nm).A possible charge separation mechanism under visible light illumination was also proposed. 相似文献
978.
哺乳类催产素及其衍生物是一系列包含S—S键的多肽分子. 应用原子-键电负性均衡σπ(ABEEMσπ)模型, 我们研究了该系列多肽分子的分子内氢键和整体软度与生物活性关系. 首先利用点电荷模型计算了该系列多肽分子的分子内氢键能, 并与实验值对比, 得到了基本一致的结果. 再根据整体软度与生物活性的关系: 即整体软度越大, 分子生物活性越大, 我们成功解释了催产素及其衍生物的分子生物活性的变化关系. 将ABEEMσπ模型初步应用于研究含 S—S键多肽的相关性质方面, 并取得了和实验以及其它理论计算较为一致的结果. 因此, 以上研究为该模型进一步探讨其它多肽的相关性质提供了一定的理论基础. 相似文献
979.
Xin Zhou Yang Zhao Peihai Lei Zongwei Cai Hai Liu 《Journal of separation science》2010,33(15):2258-2265
The LC–ESI‐MSn method was developed for the analysis and characterization of alkaloids in the extract of E. rutaecarpa (called Wuzhuyu in Chinese). Thirty‐six batches of Wuzhuyu from different locations of China were investigated and the common fingerprinting profile was established with a professional analytical software recommended by the State Food and Drug Administration. Fifteen chemical components of the common peaks were identified by multi‐stage MS. The effects on the chromatographic profile resulting from different collecting locations, harvesting times or storage times were studied. Hierarchical clustering analysis and principal components analysis were also performed to classify and differentiate the 36 batches of the samples. As a result, those which had same chemical properties were sorted into one cluster, which was very useful in evaluating and controlling the quality of Wuzhuyu. 相似文献
980.
A novel temperature controlled ionic liquid dispersive liquid phase microextraction(TCIL-DLPME) coupled with rapid resolution liquid chromatography-electrospray tandem mass spectrometry(RRLC-ESI-MS-MS) has been developed for the enrichment and determination of three hexabromocyclododecane diastereomers(HBCDs) in water samples.Green solvent ionic liquid(IL) was used as extraction solvent instead of toxic organic solvents.This technique also avoided the usage of dispersive solvent.Some important parameters that might affect the extraction efficiency were optimized.Under the optimum conditions,good linear relationship,sensitivity and reproducibility were obtained.All the limits of detection for the three diastereomers were 0.1 ng/ mL.The linear range was obtained in the range of 1-100 ng/mL for the total amount of three HBCD diastereomers.It was satisfactory to analyze real environmental water samples with the recoveries ranging from 77.2%to 99.3%.The main advantage of the method is toxic organic solvent-free. 相似文献