全文获取类型
收费全文 | 1454篇 |
免费 | 45篇 |
国内免费 | 4篇 |
专业分类
化学 | 929篇 |
晶体学 | 35篇 |
力学 | 66篇 |
数学 | 113篇 |
物理学 | 360篇 |
出版年
2023年 | 8篇 |
2022年 | 51篇 |
2021年 | 51篇 |
2020年 | 35篇 |
2019年 | 48篇 |
2018年 | 38篇 |
2017年 | 41篇 |
2016年 | 46篇 |
2015年 | 53篇 |
2014年 | 69篇 |
2013年 | 85篇 |
2012年 | 88篇 |
2011年 | 89篇 |
2010年 | 77篇 |
2009年 | 67篇 |
2008年 | 53篇 |
2007年 | 51篇 |
2006年 | 49篇 |
2005年 | 40篇 |
2004年 | 34篇 |
2003年 | 27篇 |
2002年 | 23篇 |
2001年 | 17篇 |
2000年 | 19篇 |
1999年 | 17篇 |
1998年 | 16篇 |
1997年 | 13篇 |
1996年 | 13篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 14篇 |
1992年 | 22篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1975年 | 6篇 |
1974年 | 9篇 |
1967年 | 5篇 |
排序方式: 共有1503条查询结果,搜索用时 15 毫秒
1.
2.
Guanidinium nitrate: a novel reagent for aryl nitrations 总被引:1,自引:0,他引:1
Nitration of various aromatic compounds utilising guanidinium nitrate in 85% sulfuric acid as a nitrating agent has been studied. 相似文献
3.
This paper deals with the study of the MHD flow of non-Newtonian fluid on a porous plate. Two exact solutions for non-torsionally generated unsteady hydromagnetic flow of an electrically conducting second order incompressible fluid bounded by an infinite non-conducting porous plate subjected to a uniform suction or blowing have been analyzed. The governing partial differential equation for the flow has been established. The mathematical analysis is presented for the hydromagnetic boundary layer flow neglecting the induced magnetic field. The effect of presence of the material constants of the second order fluid on the velocity field is discussed. 相似文献
4.
This article studies some geometrical aspects of the semidefinite linear complementarity problem (SDLCP), which can be viewed as a generalization of the well-known linear complementarity problem (LCP). SDLCP is a special case of a complementarity problem over a closed convex cone, where the cone considered is the closed convex cone of positive semidefinite matrices. It arises naturally in the unified formulation of a pair of primal-dual semidefinite programming problems. In this article, we introduce the notion of complementary cones in the semidefinite setting using the faces of the cone of positive semidefinite matrices and show that unlike complementary cones induced by an LCP, semidefinite complementary cones need not be closed. However, under R0-property of the linear transformation, closedness of all the semidefinite complementary cones induced by L is ensured. We also introduce the notion of a principal subtransformation with respect to a face of the cone of positive semidefinite matrices and show that for a self-adjoint linear transformation, strict copositivity is equivalent to strict semimonotonicity of each principal subtransformation. Besides the above, various other solution properties of SDLCP will be interpreted and studied geometrically. 相似文献
5.
6.
7.
Nadeem Saeed Basant K Puri Angela Oatridge Joseph V Hajnal Ian R Young 《Magnetic resonance imaging》1998,16(10):1237-1247
Two semi-automated methods for quantification of ventricular volume change from baseline and follow-up magnetic resonance imaging scans have been developed. Technique 1 employs direct segmentation of the ventricles from both the scans using thresholding and contour extraction. Technique 2 operates on difference images produced by voxel based intensity subtraction of the baseline from the registered follow-up images. Here, all voxels with intensities above a noise threshold and in a restricted area are monitored to compute volumetric changes. In phantom measurements the first technique was accurate to 0.0046%, the second to 0.167% of the phantom volume. Results from normal volunteers was that the average ventricular volume changed by 1.52% and 1.54% for images acquired within 9 months using techniques 1 and 2, respectively. With schizophrenic patients mean change of 10.78% and 9.43% were found employing the first and second procedures, respectively. All measurements agreed with a radiologist’s visual grading of the changes. Robust, objective, fast, easy-to-use, and fairly accurate procedures have been developed and validated to quantify volumetric changes. 相似文献
8.
9.
BinaS. Siddiqui M.Nadeem Kardar S.Tariq Ali Shazia Khan 《Helvetica chimica acta》2003,86(6):2164-2169
A new obtusafuran derivative, lawsonicin ( 1 ), and a new naphthaquinone, lawsonadeem ( 2 ), along with a known constituent, vomifoliol ( 3 ), were isolated from the aerial parts of Lawsonia alba and characterized by chemical transformation and spectroscopic experiments, including 2D‐NMR techniques. 相似文献
10.
Polarographic reduction of 4-arylhydrazono-1-guanylnitrate-3-methyl-2-pyrazoline-5-ones takes place in a single 4-electron transfer, giving a diffusion controlled irreversible wave in B.R. buffers of pH range 2.0–10.0. The reduction in these compounds takes place at the ?NH?N=C-bond. Effect of various cations, anions and solvent percentage on the reduction has been discussed. The effect of substituents and its correlation with the Hammett substituent constant (δ) have also been studied. 相似文献