全文获取类型
收费全文 | 16518篇 |
免费 | 682篇 |
国内免费 | 42篇 |
专业分类
化学 | 11017篇 |
晶体学 | 267篇 |
力学 | 532篇 |
综合类 | 1篇 |
数学 | 1231篇 |
物理学 | 4194篇 |
出版年
2024年 | 49篇 |
2023年 | 175篇 |
2022年 | 453篇 |
2021年 | 448篇 |
2020年 | 504篇 |
2019年 | 550篇 |
2018年 | 525篇 |
2017年 | 494篇 |
2016年 | 740篇 |
2015年 | 514篇 |
2014年 | 815篇 |
2013年 | 1376篇 |
2012年 | 1239篇 |
2011年 | 1277篇 |
2010年 | 835篇 |
2009年 | 649篇 |
2008年 | 832篇 |
2007年 | 820篇 |
2006年 | 652篇 |
2005年 | 588篇 |
2004年 | 449篇 |
2003年 | 356篇 |
2002年 | 291篇 |
2001年 | 192篇 |
2000年 | 151篇 |
1999年 | 114篇 |
1998年 | 82篇 |
1997年 | 112篇 |
1996年 | 119篇 |
1995年 | 100篇 |
1994年 | 87篇 |
1993年 | 122篇 |
1992年 | 116篇 |
1991年 | 96篇 |
1990年 | 76篇 |
1989年 | 89篇 |
1988年 | 66篇 |
1987年 | 58篇 |
1986年 | 58篇 |
1985年 | 98篇 |
1984年 | 78篇 |
1983年 | 67篇 |
1982年 | 75篇 |
1981年 | 62篇 |
1980年 | 57篇 |
1979年 | 72篇 |
1978年 | 58篇 |
1977年 | 63篇 |
1976年 | 48篇 |
1975年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
A short and efficient RCM route is reported for the construction of the key nine-membered B ring of eleutherobin starting from the readily available 1,2,5,6-diisopropylidene-d-glucose. 相似文献
52.
Munish Kumar 《Journal of Physics and Chemistry of Solids》2004,65(6):1177-1180
A critical analysis of the Suzuki, Shanker, and Kumar formulations is presented by studying different classes of materials under high pressure. A similar trend for all the materials studied in the present work, demonstrates that Suzuki formulation is not capable to yield compression behaviour of solids. The Shanker formulation improves the results obtained by the Suzuki formulation in small compression range (0.9<V/V0<1). For further compressions Shanker formulation also fails. On the other hand, the Kumar formulation is found to work well for the entire range of pressure. The reasons for the failure of Suzuki and Shanker formulations are discussed. 相似文献
53.
Gel polymer electrolyte (GPE) films comprising of poly(vinylidenefluoride), propylene carbonate, ethylene carbonate and zinc trifluoromethane sulfonate are prepared and characterized. The composition of GPE is optimized to contain minimum liquid components with a maximum specific conductivity of 3.94×10−3 S cm−1 at (25±1) °C. A detailed investigation on the properties such as ionic conductivity, transport number, electrochemical stability window, reversibility of Zn/Zn2+ couple and Zn/gel electrolyte interfacial stability have been carried out. The ionic conductivity follows a VTF behaviour with an activation energy of about 0.0014 eV. Cationic transport number varies from 0.51 at 25 °C to 0.18 at 70 °C. Several cells have been assembled with GPE as the electrolyte, zinc as the anode, γ-MnO2 as the cathode and their charge–discharge behaviour followed. Capacity values of 105, 82, 64 and 37 mAh/g of MnO2 have been achieved at 10, 50, 100 and 200 μA/cm2 discharge current densities, respectively. The discharge capacity values are almost constant for about 55 cycles for all values of current densities. Cyclic voltammetric study of MnO2 electrode in Zn/GPE/MnO2 cell clearly shows intercalation/deintercalation of Zn2+. 相似文献
54.
Anirudh Pradhan Sudhir Kumar Srivastav Kanti R. Jotania 《Czechoslovak Journal of Physics》2004,54(2):255-272
Some cylindrically symmetric inhomogeneous viscous-fluid cosmological models with electromagnetic field are obtained. To get
a solution a supplementary condition between metric potentials is used. The viscosity coefficient of bulk viscous fluid is
assumed to be a power function of mass density. Without assuming anyad hoc law, we obtain a cosmological constant as a decreasing function of time. The behaviour of the electromagnetic field tensor
together with some physical aspects of the model are also discussed. 相似文献
55.
56.
D. Behera T. Mohanty S. K. Dash T. Banerjee D. Kanjilal N. C. Mishra 《Radiation measurements》2003,36(1-6):125-129
Swift heavy ions (SHI) with electronic energy loss exceeding a value of 14.4 keVnm−1 create amorphized latent tracks in YBCO type superconductors. In the low fluence regime of an ion beam where tracks do not overlap, a decrease of the superconducting transition temperature as probed through resistivity studies, is not expected due to availability of percolating current paths. The present study however shows Tc decrease by about 1–3 K in thin films of YBCO when irradiated by 250 MeVAg ions at 79 K at a fluence of 5×1010–1×1012 ionscm−2. The highest fluence used in the present study is three times less than the fluence where track overlapping becomes significant. The Tc tends to increase towards the preirradiation value on annealing the films at room temperature. To explain this unusual result, we consider the effect of ion irradiation in inducing materials modification not only through creation of amorphized latent tracks along the ion path, but also through creation of atomic disorder in the oxygen sublattice in the Cu–O chains of YBCO by the secondary electrons. These electrons are emitted radially from the tracks during the passage of the SHI. Considering the correlation between the charge state of copper and its oxygen coordination, we show in particular that the latter process is a consequence of the inelastic interaction of the SHI induced low-energy secondary electrons with the YBCO lattice, which result in chain oxygen disorder and Tc decrease. 相似文献
57.
M.K. Gupta Vijay Gupta Manoj Kumar 《Journal of Mathematical Analysis and Applications》2007,330(2):799-816
In the present paper we introduce a new family of linear positive operators and study some direct and inverse results in simultaneous approximation. 相似文献
58.
Vattoly J. MajoJaya Prabhakaran J.John MannJ.S. Dileep Kumar 《Tetrahedron letters》2003,44(47):8535-8537
A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease. 相似文献
59.
We demonstrate the phenomenon of Talbot self-image plane shift by tuning the wavelength of the broadband light source. A superluminescent diode (SLD) is used as a broad-band light source and an acousto-optic tunable filter (AOTF) as wavelength-scanning device. A periodic grating is illuminated by the wavelength tuned light of SLD using AOTF and Talbot self-image plane is shifted continuously in the longitudinal direction without mechanically moving the grating. The wavelength-scanning Talbot effect is then implemented for the measurement of arbitrary step-height of discontinuous objects with extended range. The main advantages of the proposed system are non-mechanical scanning, high stability because of it’s common-path geometry and compactness. Since the measurement of the phase is not required the system is free from phase ambiguity problem and therefore, the range of measurement is large as compare to interferometric techniques. 相似文献
60.
We consider the effects of quark masses to the perturbative thrust in e
+
e
− annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably
alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of αs. 相似文献