全文获取类型
收费全文 | 1317篇 |
免费 | 33篇 |
国内免费 | 3篇 |
专业分类
化学 | 752篇 |
晶体学 | 14篇 |
力学 | 64篇 |
数学 | 82篇 |
物理学 | 441篇 |
出版年
2023年 | 8篇 |
2022年 | 22篇 |
2021年 | 25篇 |
2020年 | 48篇 |
2019年 | 24篇 |
2018年 | 30篇 |
2017年 | 36篇 |
2016年 | 46篇 |
2015年 | 24篇 |
2014年 | 34篇 |
2013年 | 95篇 |
2012年 | 60篇 |
2011年 | 75篇 |
2010年 | 51篇 |
2009年 | 46篇 |
2008年 | 64篇 |
2007年 | 63篇 |
2006年 | 71篇 |
2005年 | 54篇 |
2004年 | 48篇 |
2003年 | 32篇 |
2002年 | 34篇 |
2001年 | 14篇 |
2000年 | 22篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 14篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 8篇 |
1982年 | 16篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 14篇 |
1973年 | 16篇 |
1956年 | 7篇 |
排序方式: 共有1353条查询结果,搜索用时 15 毫秒
171.
In this article we prove that there does not exist a subgroup H of a finite group G such that the number of isomorphism classes of right transversals of H in G is two. 相似文献
172.
Manoj Kumar H.S. Mavi S. Rath A.K. Shukla V.D. Vankar 《Physica E: Low-dimensional Systems and Nanostructures》2008,40(9):2904-2910
Fabrication of the nanopatterned germanium (Ge) surface is done by laser-induced etching. Atomic force microscopy is utilized here to study the surface and sizes of Ge nanoparticles. Raman and photoluminescence (PL) spectroscopy have been used to characterize their vibrational and light emission properties. Wavelength-dependent Raman investigations of these nanopatterned Ge surface reveal spatial distribution of sizes of nanoparticles. Nanopatterned Ge structures (etched for 60 min) emit a broad PL band having two maxima at 2.1 and 2.35 eV. 相似文献
173.
Vijai K. Rai Suhasini Mahata Smita R. Bhardiya Prashant Shukla Ankita Rai Manorama Singh 《Tetrahedron letters》2019,60(7):524-529
Reduced graphene oxide (rGO)–NaBH4 is reported as mild and efficient catalyst-system for chemo-/regioselective reduction of structurally different aliphatic, aromatic as well as α,β-unsaturated aldehydes and ketones in water. The rGO was prepared by reducing graphene oxide using Tulsi leaf extract as bio-reductant. Operational simplicity, ambient reaction condition, high yield of pure products (80–97%), no by-product formation, no use of column chromatography for purification are the salient features of the envisaged protocol. Furthermore, the recovered TRGO was recycled and reused for subsequent reductions up to five times without any loss in activity. 相似文献
174.
An economical approach for the diastereoselective synthesis of highly functionalized carbocyclic spiropyrazolone derivatives having one quaternary and two tertiary stereocenters along with one exocyclic double bond exploiting dual organo-silver sequential catalysis has been developed. The unified method to both cyclohexyl and cyclopentyl spirocompounds involves the reaction of γ- and β-nitroalkynes with alkylidene pyrazolones catalyzed by Hünig’s base followed by carbophilic activation of the triple bond with a Ag(I) salt leading to cyclization via hydroalkylation. 相似文献
175.
Shukla S. Bishnoi A. Devi P. Kumar S. Srivastava A. Srivastava K. Fatma S. 《Russian Journal of Organic Chemistry》2019,55(6):860-865
Russian Journal of Organic Chemistry - A series of 5,5′-(arylmethylene)bis[1,3-dimethyl-6-(methylamino)pyrimidine-2,4(1H,3H)-diones] have been synthesized by 2: 1 condensation of... 相似文献
176.
Maruthibabu Paidikondala Vignesh Kumar Rangasami Ganesh N. Nawale Tommaso Casalini Giuseppe Perale Sandeep Kadekar Gaurav Mohanty Turkka Salminen Oommen P. Oommen Oommen P. Varghese 《Angewandte Chemie (International ed. in English)》2019,58(9):2815-2819
Circulating nucleic acids, such as short interfering RNA (siRNA), regulate many biological processes; however, the mechanism by which these molecules enter the cell is poorly understood. The role of extracellular‐matrix‐derived polymers in binding siRNAs and trafficking them across the plasma membrane is reported. Thermal melting, dynamic light scattering, scanning electron microscopy, and computational analysis indicate that hyaluronic acid can stabilize siRNA via hydrogen bonding and Van der Waals interactions. This stabilization facilitated HA size‐ and concentration‐dependent gene silencing in a CD44‐positive human osteosarcoma cell line (MG‐63) and in human mesenchymal stromal cells (hMSCs). This native HA‐based siRNA transfection represents the first report on an anionic, non‐viral delivery method that resulted in approximately 60 % gene knockdown in both cell types tested, which correlated with a reduction in translation levels. 相似文献
177.
Density profiles are the most common measure of inhomogeneous structure in confined fluids, but their connection to transport coefficients is poorly understood. We explore via simulation how tuning particle-wall interactions to flatten or enhance the particle layering of a model confined fluid impacts its self-diffusivity, viscosity, and entropy. Interestingly, interactions that eliminate particle layering significantly reduce confined fluid mobility, whereas those that enhance layering can have the opposite effect. Excess entropy helps to understand and predict these trends. 相似文献
178.
S. Mollah Z.A. Khan D.K. Shukla M. Arshad Ravi Kumar A. Das 《Journal of Physics and Chemistry of Solids》2008,69(4):1023-1028
Polycrystalline bulk ferromagnetic insulating (FMI) Ln0.85Ca0.15MnO3 (Ln=Nd, Pr and Sm) samples are prepared by standard solid-state reaction route and characterized. Powder X-ray diffraction (XRD) data of the manganites show single-phase character. Existing theoretical models predict that the high temperature (T>θD/2, θD being the Debye temperature) dc conductivity (σdc) of these samples is due to adiabatic small polaron-hopping conduction. Greaves’ and Mott's variable range hopping (VRH) conduction mechanisms are not suitable to explain the σdc data at low temperature (T<θD/2). 相似文献
179.
Ion-acoustic solitary waves in a dense pair-ion plasma containing degenerate electrons and positrons
Fully nonlinear propagation of ion-acoustic solitary waves in a collisionless dense/quantum electron–positron–ion plasma is investigated. The electrons and positrons are assumed to follow the Thomas–Fermi density distribution and the ions are described by the hydrodynamic equations. An energy balance-like equation involving a Sagdeev-type pseudo-potential is derived. Finite amplitude solutions are obtained numerically and their characteristics are discussed. The small-but finite-amplitude limit is also considered and an exact analytical solution is obtained. The present studies might be helpful to understand the excitation of nonlinear ion-acoustic solitary waves in a degenerate plasma such as in superdense white dwarfs. 相似文献
180.