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81.
重复累积(RA)码是一种特殊结构的低密度奇偶校验(LDPC)码,不仅具有LDPC码的优点,还能实现差分编码。针对LDPC编码协作系统编码复杂度高、时延长的问题,该文引入准循环RA(QC-RA)码,推导出信源节点和中继节点采用的QC-RA码对应的联合校验矩阵,基于公差构造方法设计该联合校验矩阵,并证明该方法设计的联合校验矩阵不存在围长为girth-4, girth-6的短环。理论分析和仿真结果表明,同等条件下该系统比相应点对点系统具有更优异的误码率性能。仿真结果同时表明,与采用一般构造QC-RA码或基于Z型构造QC-RA码相比,采用基于公差构造的联合设计QC-RA码的多信源多中继协作均可获得更高的编码增益。 相似文献
82.
Ron M. Roth 《Designs, Codes and Cryptography》1996,9(2):177-191
Codes
of length 2
m
over {1, -1} are defined as null spaces of certain submatrices of Hadamard matrices. It is shown that the codewords of
all have an rth order spectral null at zero frequency. Establishing the connection between
and the parity-check matrix of Reed-Muller codes, the minimum distance of
is obtained along with upper bounds on the redundancy of
. An efficient algorithm is presented for encoding unconstrained binary sequences into
. 相似文献
83.
The heat capacities of potassium, rubidium, cesium, and thallium azides were determined from 5 to 350 K by adiabatic calorimetry. Although the alkali-metal azides studied in this work exhibited no thermal anomalies over the temperature range studied, thallium azide has a bifurcated anomaly with two maxima at (233.0±0.1) K and (242.04±0.02) K. The associated excess entropy was 0.90 calth K?1 mol?1. The thermal properties of the azides and the corresponding structurally similar hydrogen difluorides are nearly identical. Both have linear symmetrical anions. However, thallium azide shows a solid-solid phase transition not exhibited by thallium hydrogen difluoride. At 298.15 K the values of Cpo, So, and , respectively, are 18.38, 24.86, and 12.676 calth K?1 mol?1 for potassium azide; 19.09, 28.78, and 15.58 calth K?1 mol?1 for rubidium azide; 19.89, 32.11, and 18.17 calth K?1 mol?1 for cesium azide; and 19.26, 32.09, and 18.69 calth K?1 mol?1 for thallium azide. Heat capacities at constant volume for KN3 were deduced from infrared and Raman data. 相似文献
84.
85.
The High Pressure Asher (HPA-S) was adapted with a Teflon liner for pressurized wet digestion in open vessels. The autoclave was partly filled with water containing 5% (vol/vol) hydrogen peroxide. The digestion vessels dipped partly into the water or were arranged on top of the water by means of a special rack made of titanium or PTFE-coated stainless steel. The HPA-S was closed and pressurized with nitrogen up to 100 bars. The maximum digestion temperature was 250 °C for PFA vessels and 270 °C for quartz vessels. Digestion vessels made of quartz or PFA-Teflon with volumes between 1.5 mL (auto sampler cups) and 50 mL were tested. The maximum sample amount for quartz vessels was 0.5–1.5 g and for PFA vessels 0.2–0.5 g, depending on the material. Higher sample intake may lead to fast reactions with losses of digestion solution. The samples were digested with 5 mL HNO3 or with 2 mL HNO3+6 mL H2O+2 mL H2O2. The total digestion time was 90–120 min and 30 min for cooling down to room temperature. Auto sampler cups made of PFA were used as digestion vessels for GFAAS. Sample material (50 mg) was digested with 0.2 mL HNO3+0.5 mL H2O+0.2 mL H2O2. The analytical data of nine certified reference materials are also within the confidential intervals for volatile elements like mercury, selenium and arsenic. No cross contamination between the digestion vessels could be observed. Due to the high gas pressure, the diffusion rate of volatile species is low and losses of elements by volatilisation could be observed only with diluted nitric acid and vessels with large cross section. In addition, cocoa, walnuts, nicotinic acid, pumpkin seeds, lubrication oil, straw, polyethylene and coal were digested and the TOC values measured. The residual carbon content came to 0.2–10% depending on the sample matrix and amount. 相似文献
86.
Bo?AndreassonEmail author Jennie?Forsstr?m Lars?W?gberg 《Cellulose (London, England)》2005,12(3):253-265
It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached
chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average
pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity
of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results
when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with
both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However,
the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid
structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon
protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius
decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet
strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also
shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength,
measured as zero span-strength of the sheets. 相似文献
87.
一种新的滤纸基质固体表面低温荧光(燐光)测定装置 总被引:1,自引:0,他引:1
对自行研制的铜制滤纸基质低温荧光(燐光)测定的样品支架,进行了滤纸基质固体表面低温荧光测定的可行性研究。与同类冷冻装置和室温装置比较,本装置用于滤纸基质固体表面低温荧光(燐光)测定具有以下优点;样品的分析周期大大地缩短,由45min缩短为5-6min;装置简单、便宜耐用;操作简便,简化了室温测定时的滤纸干燥程序,应用范围广,方法的重现性好,检样分析结果的相对标准偏差RSD%小于10%,荧光(燐光)分析灵敏度高,检出限低,线性范围宽。 相似文献
88.
The proton NMR spectra of N-[2-pyridyl-N-oxide]-derivatives of primary and secondary ethylamines, containing a substituent R on the C atom bearing the amino function, have been completely analysed in terms of the fundamental NMR parameters. The preferred conformations of the compounds investigated were established by the indications from NOE experiments as well as: (1) the long range coupling across the five bond between the aminic hydrogen and the proton in 4-position of the pyridine-N-oxide ring (5JmH,NH ~ 0·5 c/s), (2) the value of the vicinal coupling constant in the fragment CHNH (3JNHCH ~ 7–9 c/s), (3) the large deshielding (Δτ ~ 1–1·5 ppm) observed for the resonance position of the proton on the asymmetric C atom in secondary amine derivatives with respect to the corresponding primary ones, and (4) the diamagnetic shielding produced on protons in position 3 and 4 of the pyridine-N-oxide ring by different aromatic groups introduced in the R substituent.The NMR data confirmed the preferred rotamers previously suggested on the basis of ORD and CD measurements. 相似文献
89.
9-Methylideneflourene (IIa) reacts rapidly with HCo(CO)4 at -67° C to give a quantitative yield of 9-methylfluorene (IIIa); k2 (13.4 ± 0.5) × 10-2 l mol-1S-1. Although the internal olefin, 9-ethylidenefluorene (IIb) reacts more slowly than IIa, it is hydrogenated about 2.5 times as fast as the terminal olefin, 1,1-diphenylethylene (I). Measurement of the rate of the reaction of IIb with DCo(CO)4 and comparison with HCo(CO)4 shows a very large inverse isotope effect kH/kD of 0.43. 相似文献
90.
Continuous chemiluminescence determination of formaldehyde in air based on Trautz-Schorigin reaction 总被引:1,自引:0,他引:1
A new continuous method for the determination of formaldehyde in air is described. A cylindrical wet effluent diffusion denuder is used for the collection of formaldehyde from air into a thin film of absorption liquid (distilled-deionized water). Formaldehyde in the denuder concentrate is on-line detected employing a chemiluminescence flow method based on a reaction of formaldehyde and gallic acid with hydrogen peroxide in an alkaline solution. The collection efficiency of formaldehyde is quantitative at the air flow rate of 0.5 L min−1 (absorption liquid flow rate of 336 μL min−1). The limit of detection (S/N = 3) is 0.60 μg m−3 HCHO (0.49 ppb). The calibration graph is linear up to 300 μg m−3 HCHO (244 ppb). The relative standard deviations of chemiluminescence method for 1 × 10−6 and 5 × 10−6 M HCHO are 2.87% and 1.49%, respectively. Acetaldehyde interferes negligible, other compounds do not interfere. The method was employed for formaldehyde measurement in ambient air. The comparison measurement illustrates the good agreement of results obtained by proposed method with those obtained by reference fluorimetric method. 相似文献