全文获取类型
收费全文 | 10863篇 |
免费 | 1254篇 |
国内免费 | 1081篇 |
专业分类
化学 | 8710篇 |
晶体学 | 48篇 |
力学 | 1059篇 |
综合类 | 161篇 |
数学 | 987篇 |
物理学 | 2233篇 |
出版年
2024年 | 28篇 |
2023年 | 145篇 |
2022年 | 353篇 |
2021年 | 389篇 |
2020年 | 499篇 |
2019年 | 412篇 |
2018年 | 409篇 |
2017年 | 418篇 |
2016年 | 558篇 |
2015年 | 481篇 |
2014年 | 562篇 |
2013年 | 1154篇 |
2012年 | 668篇 |
2011年 | 614篇 |
2010年 | 441篇 |
2009年 | 518篇 |
2008年 | 504篇 |
2007年 | 592篇 |
2006年 | 533篇 |
2005年 | 478篇 |
2004年 | 441篇 |
2003年 | 354篇 |
2002年 | 362篇 |
2001年 | 278篇 |
2000年 | 251篇 |
1999年 | 230篇 |
1998年 | 222篇 |
1997年 | 195篇 |
1996年 | 165篇 |
1995年 | 145篇 |
1994年 | 88篇 |
1993年 | 119篇 |
1992年 | 108篇 |
1991年 | 69篇 |
1990年 | 62篇 |
1989年 | 50篇 |
1988年 | 36篇 |
1987年 | 35篇 |
1986年 | 32篇 |
1985年 | 29篇 |
1984年 | 27篇 |
1983年 | 14篇 |
1982年 | 20篇 |
1981年 | 16篇 |
1980年 | 19篇 |
1979年 | 18篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 687 毫秒
51.
We prove that directly reducible lattices and selfdual subdirectly irreducible lattices of locally finite length are determined by their sublattice-lattices. As a corollary we obtain that splitting varieties are closed under the isomorphism of sublattice-lattices iff they are selfdual. A class of selfdual non-closed varieties is given too. 相似文献
52.
本文研究并比较了分别以8-羟基喹啉和巯基苯骈噻唑为萃取剂,以活性硅胶为载体的柱式萃取色谱法对环境水中Zn、Cu、Pb、Cd、Fe、Co、Ni和Mn的最佳富集和洗脱条件。实验证明,后者明显优于前者。以巯基苯骈噻唑为萃取剂的色谱柱对金属元素的吸附具有快速、完全、寿命长和重现性好等特点。在pH=7~8之间回收率可达98%以上,富集倍数为200倍。 相似文献
53.
54.
三角帆蚌(Hyriopsis cumingii Lea)对水体Cr,Pb,Cd污染有明显的净化能力,持续处理12d,能使水体Cr,Pb,Cd含量分别下降83%,77.6%和72%。蚌体的斧足、鳃、外磁膜、体表粘液、肝脏、肠道和生殖腺等组织对3种污染物的吸收和富集作用不尽相同,其中分别以体表粘液、鳃和肝脏最为显著。3种污染物进入蚌体的速度很快,其组织吸收量一般在第3天即可达到较高水平。进入蚌体的污染物,可在组织转移和重新分布。研究结果为生物治理Cr,Pb,Cd等重金属污染积累了资料。 相似文献
55.
56.
利用球磨法制备石墨-六角氮化硼微晶混合物,并在6.1 GPa、800~1 500 ℃条件下与水进行高压反应,以便研究用水作触媒合成B-C-N三元化合物的可能性。通过对反应产物的XRD、XPS谱分析发现:高压下随着温度的升高,反应产物中出现再结晶石墨,其晶化程度逐渐提高;但没有出现再结晶六角氮化硼,也未出现立方氮化硼。在球磨不充分条件下,石墨-六角氮化硼混合物的XRD谱没有完全弥散,它们与水高压反应时,能观察到石墨与立方氮化硼分别结晶的现象,但都没有形成B-C-N晶化结构。 相似文献
57.
几种旱生植物水分生理特性的比较研究 总被引:3,自引:0,他引:3
魏良民 《新疆大学学报(理工版)》1991,8(2):75-79
本文对梭梭(Halorylon ammodendron)等几种典型荒漠旱生植物在干旱环境下体内含水量、相对合水量、水分饱和亏缺、自由水、束缚水、水势、离体枝叶吸水速率等的变化及其与植物抗旱的关系进行了比较研究。 相似文献
58.
59.
An analytical method is presented to investigate the bending-torsion vibration characteristics of a cylinder with an arbitrary cross-section and partially submerged in water. The compressibility and the free surface waves of the water are considered simultaneously in the analysis. The exact solution of structure–water interaction is obtained mathematically. Firstly, the analytical expression of the velocity potential of the water is derived by using the method of separation of variables. The unknown coefficients in the velocity potential are determined by the longitudinal and circumferential Fourier expansions along the outer surface of the cylinder and are expressed in the form of integral equations including the unknown dynamic bending deflection and torsional angle of the cylinder. Secondly, the force and torque acting on the cylinder per unit length, provided by the water, are obtained by integrating the water dynamic pressure along the circumference of the cylinder. The general solution of bending-torsion vibration of the cylinder under the water dynamic pressure is derived analytically. The integral equations included in the velocity potential of the water can be solved exactly. Finally, the eigenfrequency equation of cylinder–water interaction is obtained by means of the boundary conditions of the cylinder. Some numerical examples for elliptical columns partially submerged in water are provided to show the application of the present method. 相似文献
60.
B. V. Pal’tsev I. I. Chechel’ 《Computational Mathematics and Mathematical Physics》2006,46(5):820-847
The convergence rate of a fast-converging second-order accurate iterative method with splitting of boundary conditions constructed by the authors for solving an axisymmetric Dirichlet boundary value problem for the Stokes system in a spherical gap is studied numerically. For R/r exceeding about 30, where r and R are the radii of the inner and outer boundary spheres, it is established that the convergence rate of the method is lower (and considerably lower for large R/r) than the convergence rate of its differential version. For this reason, a really simpler, more slowly converging modification of the original method is constructed on the differential level and a finite-element implementation of this modification is built. Numerical experiments have revealed that this modification has the same convergence rate as its differential counterpart for R/r of up to 5 × 103. When the multigrid method is used to solve the split and auxiliary boundary value problems arising at iterations, the modification is more efficient than the original method starting from R/r ~ 30 and is considerably more efficient for large values of R/r. It is also established that the convergence rates of both methods depend little on the stretching coefficient η of circularly rectangular mesh cells in a range of η that is well sufficient for effective use of the multigrid method for arbitrary values of R/r smaller than ~ 5 × 103. 相似文献