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991.
《Laser \u0026amp; Photonics Reviews》2017,11(6)
The conversion between different polarizations generally requires an optical element or an optical system. We demonstrate, theoretically and experimentally, that the conversion between different states of polarization (SoP) can be flexibly manipulated in a structured optical field by itself. During the structured optical field propagation in free space, any two orthogonal polarizations can be generated and auto‐focus at any desired propagation positions by purposely designing the initial SoP distribution and a caustic phase in the field cross‐section. The experiment arrangement combines a caustic‐based approach and a 4f optical system. This approach provides a way to flexibly manipulate the polarization conversions in free space propagation by the optical field itself (without any physical element along the propagation path), may lead to more complex and flexible vectorial manipulations of an optical field scenarios and potential applications in corresponding areas. 相似文献
992.
993.
Study of Heat Transfer Control with Magnetic Field Using Higher Order Finite Difference Scheme 下载免费PDF全文
R. Sivakumar S. Vimala S. Damodaran & T. V. S. Sekhar 《advances in applied mathematics and mechanics.》2016,8(3):449-463
The control of convective heat transfer from a heated circular cylinder immersed
in an electrically conducting fluid is achieved using an externally imposed
magnetic field. A Higher Order Compact Scheme (HOCS) is used to solve the governing
energy equation in cylindrical polar coordinates. The HOCS gives fourth order
accurate results for the temperature field. The behavior of local Nusselt number, mean
Nusselt number and temperature field due to variation in the aligned magnetic field is
evaluated for the parameters 5≤$Re$≤40, 0≤$N$≤20 and 0.065≤$Pr$≤7. It is found that
the convective heat transfer is suppressed by increasing the strength of the imposed
magnetic field until a critical value of $N$, the interaction parameter, beyond which the
heat transfer increases with further increase in $N$. The results are found to be in good
agreement with recent experimental studies. 相似文献
994.
For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25℃ and vacuum pressure of (2-6)×10-9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6-8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators. 相似文献
995.
The crystal structure of NH4VO3 was refined by the geometry optimization done by total energy minimization in solid state using DFT/plane waves approach. The lattice parameters were derived by the Le Bail technique from the low temperature X‐ray (40‐293 K) and synchrotron (100‐293 K) powder diffraction data. The structure is formed by the infinite chains of irregular VO4 tetrahedra running approximately parallel to the c‐axis, which are interlinked by the ammonium ions placed between them. The ammonium ions link to the [VO4]∞ chains through one linear, one bifurcated and two trifurcated N‐H…O hydrogen bonds. Considering their stability there are six distinct N‐H…O hydrogen bonds: two strong with the N‐H…O bond angles close to the straight, two medium with the bond angles of 123° and 148° and two very bent (105° and 107°) and hence weak hydrogen bonds. There is a reasonable agreement between the energies of the stretching ν(NH) modes estimated using the optimised N…O contact distances and those obtained experimentally. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
996.
Fault diagnosis of wind turbines is of great importance to reduce operating and maintenance costs of wind farms. At present, most wind turbine fault diagnosis methods are focused on single faults, and the methods for combined faults usually depend on inefficient manual analysis. Filling the gap, this paper proposes a low-pass filtering empirical wavelet transform (LPFEWT) machine learning based fault diagnosis method for combined fault of wind turbines, which can identify the fault type of wind turbines simply and efficiently without human experience and with low computation costs. In this method, low-pass filtering empirical wavelet transform is proposed to extract fault features from vibration signals, LPFEWT energies are selected to be the inputs of the fault diagnosis model, a grey wolf optimizer hyperparameter tuned support vector machine (SVM) is employed for fault diagnosis. The method is verified on a wind turbine test rig that can simulate shaft misalignment and broken gear tooth faulty conditions. Compared with other models, the proposed model has superiority for this classification problem. 相似文献
997.
Liang He Yang Hui Guo Ya Ping Wang Xiang Jing Wang Ji Zhang Wen Sheng Xiang 《中国化学快报》2012,23(5):518-520
A novel and practical synthetic route is presented for the preparation of methyl-(E)-2-(3-(3-(2-(7-chloro-2-quinolinyl)ethenyl) phenyl)-3-oxopropyl)benzoate,the key intermediate of Montelukast,a leukotriene antagonist.The main diarylpropane framework was prepared via a polarity conversation reaction resulting in an acyl anion equivalent followed by a nucleophilic substitution reaction.The overall yield of this approach was 61%.This method is simple for operation and suitable for industrial production. 相似文献
998.
The happy medium: A new catalytic pathway for the synthesis of the linear primary C(8) alcohol products 1-octanol and dioctyl ether from furfural and acetone has been developed using retrosynthetic analysis. This opens a general strategy for the synthesis of medium-chain-length alcohols from carbohydrate feedstock. 相似文献
999.
1000.
在烧结温度为1020℃下,采用固相二步合成法制备了Pb(Ni1/3Nb2/3)0.05(Mn1/3Nb2/3)0.04(Mn1/3Sb2/3)0.01(Zr1/2Ti1/2)0.9O3(PMNNS)压电陶瓷,研究了加入不同掺杂量的SiO2对陶瓷的结构与机电性能的影响。结果表明:加入SiO2可以明显地降低烧结温度;而且当SiO2的掺杂量为0.1%时,陶瓷的性能最佳,其性能如下:d33=331 pC/N,tanδ=0.0041,kp=0.62,Qm=1326,εr=917。 相似文献