全文获取类型
收费全文 | 118812篇 |
免费 | 8172篇 |
国内免费 | 6225篇 |
专业分类
化学 | 58954篇 |
晶体学 | 1373篇 |
力学 | 5718篇 |
综合类 | 391篇 |
数学 | 12246篇 |
物理学 | 35520篇 |
无线电 | 19007篇 |
出版年
2023年 | 1322篇 |
2022年 | 1924篇 |
2021年 | 2768篇 |
2020年 | 2954篇 |
2019年 | 3117篇 |
2018年 | 3485篇 |
2017年 | 3407篇 |
2016年 | 4244篇 |
2015年 | 3179篇 |
2014年 | 4512篇 |
2013年 | 6088篇 |
2012年 | 6490篇 |
2011年 | 6823篇 |
2010年 | 5380篇 |
2009年 | 5550篇 |
2008年 | 5809篇 |
2007年 | 5381篇 |
2006年 | 4967篇 |
2005年 | 4441篇 |
2004年 | 3794篇 |
2003年 | 3476篇 |
2002年 | 3526篇 |
2001年 | 3139篇 |
2000年 | 2530篇 |
1999年 | 2118篇 |
1998年 | 1956篇 |
1997年 | 1725篇 |
1996年 | 1600篇 |
1995年 | 1325篇 |
1994年 | 1343篇 |
1993年 | 1278篇 |
1992年 | 1213篇 |
1991年 | 1272篇 |
1990年 | 1224篇 |
1989年 | 1110篇 |
1988年 | 947篇 |
1987年 | 952篇 |
1986年 | 910篇 |
1985年 | 943篇 |
1984年 | 934篇 |
1983年 | 844篇 |
1982年 | 817篇 |
1979年 | 808篇 |
1978年 | 815篇 |
1977年 | 814篇 |
1976年 | 922篇 |
1975年 | 814篇 |
1974年 | 846篇 |
1973年 | 848篇 |
1972年 | 755篇 |
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
991.
Fengping Yu Junpo He Xiaojun Wang Guangzheng Gao Yuliang Yang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(17):4013-4025
A combination of nitroxide‐mediated radical polymerization and living anionic polymerization was used to synthesize a series of well‐defined graft (co)polymers with “V‐shaped” and “Y‐shaped” branches. The polymer main chain is a copolymer of styrene and p‐chloromethylstyrene (PS‐co‐PCMS) prepared via nitroxide‐mediated radical polymerization. The V‐shaped branches were prepared through coupling reaction of polystyrene macromonomer, carrying 1,1‐diphenylethylene terminus, with polystyryllithium or polyisoprenyllithium. The Y‐shaped branches were prepared throughfurther polymerization initiated by the V‐shaped anions. The obtained branches, carrying a living anion at the middle (V‐shaped) or at the end of the third segment (Y‐shaped), were coupled in situ with pendent benzyl chloride of PS‐co‐PCMS to form the target graft (co)polymers. The purified graft (co)polymers were analyzed by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. The result shows that the viscosities and radii of gyration of the branched polymers are remarkably smaller than those of linear polystyrene. In addition, V‐shaped product adopts a more compact conformation in dilute solution than the Y‐shaped analogy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4013–4025, 2007 相似文献
992.
993.
Yu Lin Shiduan Cheng Wendong Wang Yuehui Jin 《Wireless Communications, IEEE Transactions on》2006,5(8):1971-1975
As a well-known multimedia stream transport protocol, TFRC provides smooth transfer rate under stable network conditions, and achieves good fairness to TCP. However, it is not flexible in heterogeneous mobile networks because the available bandwidth varies rapidly. This paper proposes a measurement based TFRC (MBTFRC) protocol, which uses passive bandwidth measurements at the receiver to improve the flexibility of TFRC. In addition, a window-based EWMA filter with two weights is used to achieve stability and fairness simultaneously. Simulation results verify the flexibility, stability and fairness of MBTFRC. 相似文献
994.
V. I. Burkov E. P. Peredereĭ E. V. Fedotov B. V. Mill’ Yu. V. Pisarevskiĭ 《Crystallography Reports》2008,53(5):843-846
The absorption and circular dichroism spectra of langasite family crystals are studied. Wide bands in the range of 285–500 nm that are related to the structure lattice defects are found. For all the crystals, these bands are in approximately the same spectral region, have identical structures, and can be attributed to one type of defects formed by cation vacancies and excess oxygen atoms in the optically active positions. 相似文献
995.
996.
997.
A new co‐ordinate invariant streamwise upwind formulation for convection dominated flows is developed. The eddy diffusivity/viscosity is added directly to the equations in order to remove the oscillations in the solution. The equations then can be solved by any high‐order scheme and the solution retains the accuracy of the high‐order scheme. The accuracy and reduced lateral thickness growth rate are demonstrated with several numerical examples, including pure convective flows and lid‐driven cavity flow. The lateral spreading due to the numerical diffusion is controlled by the anisotropic tensor. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
998.
S. Burachas S. Beloglovsky D. Elizarov I. Makov Yu. Saveliev N. Vassilieva M. Ippolitov V. Manko S. Nikulin A. Nyanin A. Vasiliev A. Apanasenko G. Tamulaitis 《Radiation measurements》2004,38(4-6):367-370
Technological conditions ensuring growth of optically homogeneous lead tungstate (PWO) crystals are reported. It is shown that the basic scintillator characteristics of PWO grown from highly purified raw material and properly doped with lanthanides are mainly determined by inclusions of oxides W1−yLyO3−x (L=Y, La, Gd; 0<x<0.3). Moreover, surface-located inclusions with structure close to tungstenite may also be of importance. It is demonstrated that the scintillation properties can be intentionally designed by varying the oxygen content in the inclusions x and the surface structure. The optimal value for x and the most favorable surface structure are achieved by proper thermal regimes and environment content during the crystal annealing. The results enabled low-cost fabrication of PWO scintillators with steady and reproducible characteristics acceptable for the CERN project ALICE and ensured production of PWO on an industrial scale by “North Crystals” company at a rate of 125–135 crystals per year from every growth apparatus. 相似文献
999.
N. A. Demekhina G. S. Karapetyan S. M. Lukyanov Yu. E. Penionzhkevich N. K. Skobelev A. B. Yakushev 《Physics of Atomic Nuclei》2004,67(8):1417-1423
The absolute values of the cross sections for the production of target fragments in the interaction of copper with 7Li ions at an energy of 35 MeV per nucleon were measured. The measurements were performed by recording the yields of radioactive nuclear residues with the aid of a semiconductor detector from ultrapure germanium. The charge and isobaric distributions in the mass-number range 22–69 amu were used to deduce the mass yield of reaction products and to calculate the total interaction cross section. The results are presented that were derived from a comparison with data obtained for 12C + Cu reactions and with estimates based on theoretical models. 相似文献
1000.
A. N. Vasiliev V. N. Grishin A. M. Davidenko A. A. Derevschikov Yu. A. Matulenko Yu. M. Melnik A. P. Meschanin V. V. Mochalov L. V. Nogach S. B. Nurushev A. F. Prudkoglyad P. A. Semenov L. F. Soloviev V. L. Solovianov V. Yu. Khodyrev K. E. Shestermanov A. E. Yakutin N. S. Borisov V. N. Matafonov A. B. Neganov Yu. A. Plis Yu. A. Usov A. N. Fedorov A. A. Lukhanin 《Physics of Atomic Nuclei》2004,67(8):1487-1494
Results are presented that were obtained by measuring single-spin asymmetry in the inclusive production of neutral pions in the reaction p+p ↑→ π 0+X at x F≈0. A beam of 70-GeV protons was extracted directly from the vacuum chamber of the accelerator by means of a bent single crystal. For transverse momenta in the range 1.0<p T<3.0 GeV/c, the single-spin asymmetry independently measured by two detectors is zero within the errors. This result is in agreement with Fermilab data obtained at 200 GeV, but it is at odds with CERN data measured at 24 GeV. 相似文献