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991.
In this paper, pressurized CEC was used for the separation and determination of seven fluoroquinolones (FQs). The effect of different experimental conditions, such as the concentration and pH of the buffer, the organic modifier concentration, the surfactant and ion-paring agents added to the electrolyte, and applied voltage were studied. All the seven FQs were baseline separated using mobile phase containing 27% v/v ACN, 5 mmol/L Na2HPO4 buffer (pH 4.0 adjusted using citric acid), 11 mmol/L SDS, and 0.01% TEA v/v at detection wavelength of 287 nm and at an applied voltage of -10 kV. The calibration curves were linear (r>0.9991) over a concentration range of 1.0-50.0 mg/L for norfloxacin (NFLX); 2.5-50.0 mg/L for fleroxacin (FLX), ciprofloxacin (CPFX), and lomefloxacin (LMX); and 5.0-50.0 mg/L for enoxacin (ENX), ofloxacin (OFLX), and gatifloxacin (GFLX). The detection limits (S/N = 3) for ENX, OFLX, FLX, NFLX, CPFX, LMX, and GFLX were 0.5, 0.8, 0.4, 0.2, 0.4, 0.5, and 1.0 mg/L, respectively. The method is simple, rapid, and reproducible. It was successfully applied to the analysis of fish muscle samples spiked with FQs. Mean recoveries ranged from 81.6 to 97.6%. 相似文献
992.
Rate coefficients of the reaction O((3)P) + CH(3)OH in the temperature range of 835-1777 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO(2) with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm; their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O(2) and He. The rate coefficients determined for the temperature range can be represented by the Arrhenius equation, k(T) = (2.29 +/- 0.18) x 10(-10) exp[-(4210 +/- 100)T] cm(3) molecule(-1) s(-1); unless otherwise noted, all the listed errors represent one standard deviation in fitting. Combination of these and previous data at lower temperature shows a non-Arrhenius behavior described as the three-parameter equation, k(T) = (2.74 +/- 0.07) x 10(-18)T(2.25 +/- 0.13) exp[-(1500 +/- 90)T] cm(3)molecule(-1) s(-1). Theoretical calculations at the Becke-3-Lee-Yang-Parr (B3LYP)6-311 + G(3df,2p) level locate three transition states. Based on the energies computed with coupled clusters singles, doubles (triples) [CCSD(T)]/6-311 + G(3df,2p)B3LYP6-311 + G(3df,2p), the rate coefficients predicted with canonical variational transition state theory with small curvature tunneling corrections agree satisfactorily with the experimental observations. The branching ratios of two accessible reaction channels forming OH + CH(2)OH (1a) and OH + CH(3)O (1b) are predicted to vary strongly with temperature. At 300 K, reaction (1a) dominates, whereas reaction (1b) becomes more important than reaction (1a) above 1700 K. 相似文献
993.
The electrochemiluminescence (ECL) of luminol in aqueous alkaline solution was studied.Trace amounts of chloride showed significant effect on the efficiency of light emission of luminol as a posi-tive trigonometrical wave pulse was exerted on the solution. The detection limit for the chloride is5.0 ×10~(-6) mol/L and the linear calibration range extends up to 1.0 ×10~(-2) mol/L; the relative standarddeviation for 1.0 ×10~(-5) mol / L chloride is 5%. The influencing factors for chloride determination arealso discussed. The possible mechanism for the electrochemiluminescence reaction may be due to theoxidation of chloride ion in the solution to ClO~-, and the latter acts on luminol and then gives outluminescence. The method has been applied to determine the total chloride in tap water with satisfactoryresults. 相似文献
994.
Fei Yu Yuhuan Liu Xuejun Pan Xiangyang Lin Chengmei Liu Paul Chen Roger Ruan 《Applied biochemistry and biotechnology》2006,130(1-3):574-585
This research investigated a novel process to prepare polyester from corn stover through liquefaction and crosslinking processes.
First, corn stover was liquefied in organic solvents (90 wt% ethylene glycol and 10 wt% ethylene carbonate) with catalysts
at moderate temperature under atmospheric pressure. The effect of liquefaction temperature, biomass content, and type of catalyst,
such H2SO4, HCl, H3PO4, and ZnCl2, was evaluated. Higher liquefaction yield was achieved in 2 wt% sulfuric acid, 1/4 (w/w) stover to liquefying reagent ratio;
160°C temperature, in 2h. The liquefied corn stover was rich in polyols, which can be directly used as feedstock for making
polymers without further separation or purification. Second, polyester was made from the liquefied corn stover by crosslinking
with multifunctional carboxylic acids and/or cyclic acid anhydrides. The tensile strength of polyester is about 5 MPa and
the elongation is around 35%. The polyester is stable in cold water and organic solvents and readily biodegradable as indicated
by 82% weight loss when buried in damp soil for 10 mo. The results indicate that this novel polyester could be used for the
biodegradable garden mulch film production. 相似文献
995.
Ming‐Lin Guo Hong‐Xia Cao 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):m431-m433
The title complex, [Ba2Ni(C3H2O4)2(NO3)2(H2O)10]n, has a two‐dimensional layer structure. The Ni atom lies on a crystallographic centre of symmetry in an octahedral NiO6 environment, and is coordinated by four malonate O atoms in a planar arrangement and by two water molecules in axial positions. The coordination of the unique Ba atom involves two nitrate O atoms, five water molecules and three malonate O atoms. 相似文献
996.
以脉冲激光在高真空中溅射钒粉和硫粉的混合物,产生了一系列钒硫原子簇正负离子。根据对其实验记录的激光等离子体质谱进行分析,发现钒硫原子簇的化学键基本上是共价型的,对应于相同钒原子数目的正负离子的相对丰度分别符合于不同形式的对数正态分布。正离子的相对丰度随硫原子数的增加呈对数衰减,由此可以确定各种大小簇合物的簇骼与几何构型;负离子的相对丰度则基本上呈正常的正态分布,说明在簇骼上结合了不同数量硫原子的负离子之结构稳定性大致相近。在实验中还观察到一类硫原子含量较高的簇离子,其中的部分硫原子可能在本身成键形成环状的硫集团后,又与原来的簇骼结合,因而在硫原子数较多时它们的相对丰度符合另一条对数正态分布曲线。 相似文献
997.
7-deaza-2,8-diaza-2'-deoxyadenosine (4) was synthesized from 8-aza-7-deaza-2'-deoxyadenosine (1) via the 1,N(6)-etheno derivative 5. Ring opening with sodium hydroxide followed by ring closure in the presence of sodium nitrite formed the tricyclic intermediate 5 from which the transiently introduced "etheno" moiety was removed with NBS. Compound 4 was converted to the phosphoramidite 11, which was employed in solid-phase oligonucleotide synthesis. Base pairing studies on 4, incorporated in a 12-mer duplex, showed that this adenine nucleoside analogue forms a strong base pair with dG but not with dT. This novel base pair is as stable as that of the canonical dA-dT pair. As a result of the absence of nitrogen-7 compound 4 is expected to form a face to face base pair with dG. 相似文献
998.
999.
Anodic deposition of iodide ion on silver at 25° in aqueous (0.5 M KNO3) and in 90% (w/w) ethanol-water (0.05 M KClO4) solutions was studied galvanostatically. The exchange current density, transfer coefficient and the rate constants for the electrode reaction were evaluated. The experimental results revealed that the overall electrode reaction and the charge-transfer step was the same one, i.e., , which might be assumed highly reversible as reflected by the exchange current density (i) and transfer coefficient (α). The numerical values of the rate constants, and at 25° were, in aqueous solution, 1.02×10?5 and 2.88×10?6, and in ethanol solution, 2.88×10?5 and 6.3×10?6 cm sec?1, respectively. 相似文献
1000.
The apparent molar volumes, V
φ
, of glycine, L-alanine and L-serine were obtained in aqueous 0 to ∼4 mol⋅kg−1 N,N-dimethylacetamide (DMA) solutions from density measurements at 298.15 and 308.15 K. The standard partial molar volume,
V
φ
o, and standard partial molar volumes of transfer, Δtr
V
φ
o, were determined for these amino acids. It has been shown that hydrophilic-hydrophilic interactions between charged groups
of the amino acids and the —CON= group of DMA are predominant in the case of glycine and L-serine, but for L-alanine the interactions
between its side group (—CH3) and DMA are predominant. An increase in temperature increases the standard partial molar volumes but decreases the transfer
volumes of the amino acids. The results have been interpreted in terms of cosphere overlap model. 相似文献