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排序方式: 共有433条查询结果,搜索用时 21 毫秒
71.
由Internet构成的复杂网络的动力学特性主要受到用户需求行为的影响,具备时域的统计规律性. 通过对区域群体用户需求行为的时域实验统计分析,发现用户对Web网站的访问频度及其生成的二分网络的入度分布也呈现幂律分布和集聚现象,其幂指数介于1.7到1.8之间. 建立了虚拟资源网络VRN和物理拓扑网络PTN双层模型,分析了双层模型映射机理,并对网络用户需求行为进行建模. 虚拟资源网络VRN对物理拓扑网络PTN映射过程的不同机理,模拟了Internet资源网络到物理网络的不同影响模式. 幂律分布的用户需求特性会
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复杂网络
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相变 相似文献
72.
This paper reports the theoretical study of combining Z-scan technique with Gauss-Bessel (GB) beams beside a phase object (PO) to measure the third-order nonlinear susceptibility components.By using this method,the sign of refractive index which depends on the shape of the close aperture Z-scan curve can be easily determined.Meanwhile,the magnitude of nonlinear coefficients can also be deduced by theoretical fit.The proposed method is advantageous for high sensitivity and imposes a lower stress in the cases of fragile materials,since small pulse energy is enough for the measurement of nonlinear coefficients.Predictions of the models are compared with Gaussian Z-scan measurement and GB Z-scan measurement.By using GB beams with a PO,the sensitivity of Z-scan measurements is found to be a factor of over 60 times greater than for Gaussian beams and 2 times greater than for Gaussian-Bessel beams. 相似文献
73.
C/FeOF/FeF3 nanocomposite was synthesized by a facile in situ partial oxidation method. High-resolution transmission electron microscopy (HR-TEM) showed a special texture comprised of interpenetrating nanodomains of FeOF and FeF3. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that the introduction of nanodomain FeOF enhanced both the electronic and ionic conductivity of the composite material. Therefore, the improvement of electron and lithium-ion dynamics resulted in the significant enhancement of the electrochemical performances of the material at ambient temperature. At a current density of 20 mA g?1 within potential range 1.5–4.5 V, the specific capacities of the first ten circles were maintained at about 400 mAh g?1 . This material also exhibited excellent cycling capacity retention capability especially for high C rates. When the current density further increased to 100 and 200 mA g?1, a steady capacity of 80 and 60 mAh g?1 was observed, respectively. Furthermore, nearly no capacity loss was observed for the followed cycles. The discharge platforms based on intercalation and conversion reaction were also heightened by about 0.4 V, which increased the contribution of high voltage capacities. Compared to C/FeF3, C/FeOF/FeF3 is showing more of capacitive behavior, which also contributes to the high specific capacity delivered and is believed to be closely related to the enlarged nanodomain interfaces between two electrochemical active materials. An expansion-cracking-oxidation mechanism was proposed to explain the formation of this interpenetrating nanodomains of FeOF and FeF3. 相似文献
74.
强夯加固机理的非线性动态冲击显式有限元数值分析 总被引:1,自引:0,他引:1
根据强夯的特点,采用同时考虑几何非线性、材料非线性、状态非线性,并且考虑瞬态大变形的非线性动态显式有限元,分析了强夯对地基土的冲击碰撞过程。该方法克服了以往有限元计算强夯动力问题时需再引入其他的简化假定的已知量,能较实际地反映强夯加固的动力特性。通过对工程实例计算研究,取得了令人满意的效果。 相似文献
75.
Xin‐Gang Xie Dr. Xun‐Wei Wu Dr. Hing‐Ken Lee Dr. Xiao‐Shui Peng Prof. Dr. Henry N. C. Wong Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6933-6941
Plakortone B is a naturally occurring bicyclic[3.3.0]furanolactone compound with attractive bioactivities. Although the relative configuration of plakortone B’s central core had been established by NMR spectroscopic methods, the absolute configuration of its four stereocenters remained unknown. In the present paper, all four possible isomers of plakortone B were synthesized and one of these molecules was found to be identical with the natural plakortone B on the basis of 1H, 13C NMR spectra and specific rotation comparisons. Thus, the absolute configuration of the natural plakortone B was determined to be (3S,4S,6R,10R). 相似文献
76.
77.
1,3,4—噻二唑的α—氨基膦酸酯衍生物的合成及其生物活性 总被引:7,自引:4,他引:3
利用2-氨基-5-烷基-1,3,4-噻二唑、芳笛醛和亚磷酸三苯酯泊类Mannich反应,合成了一系列1,3,4-噻二唑的α-氨基膦酸酯生物。它们的结构级元素分析、IR,HNMR和MS这。初步生物活性测试结果表明,目标化合物对5种病人有一定的抑制作用。 相似文献
78.
79.
The Initial Reactions of H3PO4 and NaH2PO4Supported on Silica: A Joint Experimental and Theoretical Study 下载免费PDF全文
利用XRD、TG、DRIFTS、31P MAS NMR和密度泛函理论研究了浸渍法制备的硅胶负载型磷酸和磷酸二氢钠催化剂,阐明了催化剂制备过程中生成的初始缩合产物和其反应机理. 光谱试验结果显示,在二氧化硅负载的磷酸上,除了聚磷酸外,还有硅磷酸盐的存在;在二氧化硅负载的磷酸二氢钠上,仅发现聚磷酸钠存在. 密度泛函模拟结果也证明,磷酸与二氧化硅表面硅羟基之间的反应在缩合反应的初始阶段比其自身的二聚反应更为有利. 但是在硅胶负载的磷酸二氢钠上,磷酸二氢钠的二聚和三聚是缩合反应初始阶段的主要反应. 相似文献
80.
We investigate the phantom dark energy model derived from the scalar field with a negative kinetic term.By assuming a particular relation between the time derivative of the phantom field and the Hubble function,an exact solution of the model is constructed.Absence of the ’big rip’ singularity is shown explicitly.We then derive special features of phantom dark energy model and show that its predictions are consistent with all astrophysical observations. 相似文献