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981.
982.
<正>In this article,an efficient,simple and environmentally friendly approach to the synthesis of diacetals(diketals) pentaerythritol using SO_3H-functionalized ionic liquids(ILs) as catalysts was reported.The ILs show high catalytic activity and reusability with good to excellent yields of the desired products.Hammett method has been used to determine the acidity order of these ionic liquids and the results are consistent with the catalytic activities observed in acetalization reaction.Maximum product yield of 93%was observed on using[PSPy][OTf]as catalyst and it can be reused at least 8 times without obvious activity loss. 相似文献
983.
<正>A new derivative of triterpene named Erigeronol 1 was isolated from the EtOH extract of the aerial part of Conyza canadensis together with 15 known compounds for the first time from this plant.The structure of Erigeronol 1 was elucidated as 3-O-(hydroxyacetyl) -23,28-dihydroxy-β-amyrin by hydrolysis and spectroscopic analysis.Erigeronol 1 showed potent cytotoxic activity with IC_(50) value of 7.77±0.47μg/mL against melanoma B16 determined by the 3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyltetrazolium bromide(MTT) method. 相似文献
984.
银在光催化分解NO反应中的光催化行为研究 总被引:1,自引:0,他引:1
以光催化分解NO反应为探针,研究了负载银催化剂在紫外光激发作用下光催化分解NO反应的催化行为.对银物种的调变会对银的光催化活性产生显著影响,结合XRD(X射线粉末衍射),UV-vis(紫外可见漫反射)等表征手段对反应中起重要作用的活性银物种的表征结果表明,高度分散于分子筛内的银离子及银簇是光催化分解NO的活性中心. 相似文献
985.
本文考虑的是允许采用比例再保险策略和投资策略的两个保险公司如何寻找最优合并时刻的问题.两个保险公司的风险过程由漂移布朗运动刻画,目标为最大化它们的生存概率.各个公司的安全负荷系数和波动系数在决定两公司是否要合并时起到了关键作用.决定合并后,公司合并费用,合并前后公司的生存概率状况在决定最优合并时刻时起到了关键作用.我们分两种情况讨论了这个问题并分别给出相应情况下的最优策略和值函数. 相似文献
986.
The streamwise fluctuating velocity in the turbulent boundary layer is measured under approximately medium Reynolds Number
by hot wire in order to investigate the scaling properties of the overlapped turbulent spectrum among energy-containing area,
inertial subrange and dissipation range based on FFT analysis. The experiment indicates that the high Reynolds flow reported
before is not indispensable to produce −1 scaling. So far as the measured position is provided with much higher spatial resolution
and enough closing to the wall, −1 scaling is determinate to exist when approaching medium Reynolds. The scaling ranges are
supposed to begin at inner scale and end in outer scale, which reveals the local similarity of the energy spectrum over the
energy-containing eddies near the wall. In the logarithmic area (y
+ > 130), −5/3 scaling occurs in the energy spectrum, while moving away from the wall with Reynolds numbers increasing, the
inertial subrange extends to the lower wavenumbers. On the condition k
1
η ≫ 0.1, the curves of the turbulence spectrum in the logarithmic layer are superposed, which expresses the similarity of turbulence
energy distributed in Komogorov scaling area and exhibits local isotropy characteristics by virtue of the viscous dissipation.
Supported by the National Natural Science Foundation of China (Grant Nos. 10832001 and 10872145), the Program for New Century
Excellent Talents in Universities of Education Ministry of China, and the Plan of Tianjin Science and Technology Development
(Grant No. 06TXTJJC13800) 相似文献
987.
Microcalorimetric Study of the Screening Specific Promoter Bacteria of Nutrient Drug 总被引:3,自引:0,他引:3
H. Zhang X. Yu H. Sun Y. Liu Z. Nan C. Lu M. Ru G. Mai Y. Wang Z. Li 《Journal of Thermal Analysis and Calorimetry》1999,58(2):435-440
The power vs. time curves of the promoter bacteria of a nutrient drug were determined by using a 2277 Thermal Activity Monitor (Sweden). A new experimental model of bacterial growth were established. The growth rate constant, heat output and optimum concentration of specific promoter bacterial of nutrient drug were calculated.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
988.
989.
Zheng‐Ren Xu Xing‐Yun Chai Chang‐Cai Bai Hong‐Yan Ren Ya‐Nan Lu Hai‐Ming Shi Peng‐Fei Tu 《Helvetica chimica acta》2008,91(7):1346-1354
Seven new phenolic glucosides, xylocosides A–G ( 1 – 7 ), together with 18 known compounds were isolated from the stems of Xylosma controversum Clos . In compounds 3 – 6 , the glucose residue is esterified at C(6) by 2‐hydroxycyclopentanecarboxylic acid. These new structures were established by spectroscopic‐data interpretation and chemical methods. 相似文献
990.