全文获取类型
收费全文 | 57071篇 |
免费 | 3788篇 |
国内免费 | 3469篇 |
专业分类
化学 | 31105篇 |
晶体学 | 623篇 |
力学 | 2791篇 |
综合类 | 247篇 |
数学 | 12455篇 |
物理学 | 17107篇 |
出版年
2023年 | 450篇 |
2022年 | 685篇 |
2021年 | 823篇 |
2020年 | 935篇 |
2019年 | 947篇 |
2018年 | 1968篇 |
2017年 | 2186篇 |
2016年 | 1820篇 |
2015年 | 1690篇 |
2014年 | 1821篇 |
2013年 | 2535篇 |
2012年 | 5376篇 |
2011年 | 4788篇 |
2010年 | 3551篇 |
2009年 | 3261篇 |
2008年 | 2460篇 |
2007年 | 2341篇 |
2006年 | 2169篇 |
2005年 | 5771篇 |
2004年 | 4984篇 |
2003年 | 3171篇 |
2002年 | 1347篇 |
2001年 | 1019篇 |
2000年 | 709篇 |
1999年 | 750篇 |
1998年 | 614篇 |
1997年 | 511篇 |
1996年 | 520篇 |
1995年 | 425篇 |
1994年 | 413篇 |
1993年 | 362篇 |
1992年 | 492篇 |
1991年 | 430篇 |
1990年 | 366篇 |
1989年 | 297篇 |
1988年 | 265篇 |
1987年 | 185篇 |
1986年 | 184篇 |
1985年 | 191篇 |
1984年 | 129篇 |
1983年 | 90篇 |
1982年 | 89篇 |
1981年 | 71篇 |
1980年 | 64篇 |
1979年 | 87篇 |
1978年 | 64篇 |
1976年 | 116篇 |
1975年 | 69篇 |
1974年 | 80篇 |
1973年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
长江中下游的主要防洪工程是长江干堤 ,长江堤防线路长、工程浩大、堤基工程地质水文地质条件复杂 ,涉及大量的已有地质数据和资料。今后在整治加固堤防的工程地质勘察工作中 ,还需随时进行数据的收集、存储、检索、分析、统计和维护 ,随时调用这些数据进行综合处理、编制报告和图件 ;在防汛期间可以针对堤防险工险段的险情 ,随时查询和调用有关的资料、数据或者图件 ,提供采取抢险措施决策的地质依据。这既提高了地质数据的利用价值和利用率 ,又保证了信息的准确性、完整性和共享性。因此 ,建立合理的长江堤防工程地质信息处理模型及其成熟的技术方法具有重要的意义。 相似文献
92.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
93.
A novel field emission pressure sensor has been achieved utilizing carbon nanotubes (CNTs) as the electron source. The sensor consists of the anode sensing film fabricated by wet etching process and multi-wall carbon nanotubes (MWNTs) cathode in the micro-vacuum chamber. MWNTs on the silicon substrate were grown by thermal CVD. The prototype pressure sensor has a measured sensitivity of about 0.17-0.77 nA/Pa (101-550 KPa). The work shows the potential use of CNTs-based field-emitter in microsensors, such as accelerometers and tactile sensors. 相似文献
94.
Daniel Pa?ca 《Journal of Mathematical Analysis and Applications》2007,325(1):90-100
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian. 相似文献
95.
96.
相位差与q变形广义相干叠加态的压缩特性 总被引:1,自引:0,他引:1
对于q变形的非简谐振子广义相干态的叠加态β〉+eiφβeiδ〉,其量子涨落的可能高阶压缩阶数可以表示为k≠2πn/δ,这里n是整数.当δ=π时,压缩阶数不能是偶数即只能是奇数,这正是q变形非简谐振子广义奇偶相干态的结果.由此表明参数相位差δ对决定q变形的非简谐振子广义相干态叠加态的高阶压缩阶数起决定性作用. 相似文献
97.
Goran Pavi? 《Applied Acoustics》2006,67(9):864-881
A method is formulated for the identification of an unknown physical parameter of a fluid-filled pipe using the measurement of sound speed in the pipe. The method uses a simple formula which provides the relationship between the sound speed and a few physical parameters of the pipe: thickness, diameter, wall material constants and fluid constants. Once the sound speed in the pipe is measured, the simple formula can be used to extract one of the unknown parameters providing the remaining ones are known.The sound speed in the pipe is measured using a 3-transducer array. In order to demonstrate the potential of the technique the results of several measurements obtained in a water-filled steel pipe are presented.The required accuracy of the measurement of sound speed and of the specification of known parameters is analysed. The accuracy depends on the unknown parameter which is to be identified. For example, if the pipe thickness is the unknown parameter, the other parameters have to be known within a very narrow margin of error. On the contrary, if the fluid properties have to be identified the needed accuracy of known parameters gets much lower. 相似文献
98.
新疆野生黑加仑与马林果实的营养成分分析 总被引:2,自引:0,他引:2
通过对新疆野生黑加仑和野生马林的脂肪油,8种微量元素,17种氨基酸以及维生素C的含量进行测定得出:黑加仑脂肪油含量为17.9%,马林的脂肪油含量为22.3%,其中,黑加仑脂肪油中,r-亚麻酸的含量为19.02%,而马林中,其含量为9.40%,黑加仑中K,Na,Ca,Cu,Zn,Fe的含量比马林中的含量高,而Mn,Mg元素的含量却比马林含量低;马林的维生素C含量为16.22mg/g,黑加仑的含量为108mg/g,黑加仑的氨基酸的总量为1.63%,马林为1.14%。 相似文献
99.
A tree T is arbitrarily vertex decomposable if for any sequence τ of positive integers adding up to the order of T there is a sequence of vertex-disjoint subtrees of T whose orders are given by τ. An on-line version of the problem of characterizing arbitrarily vertex decomposable trees is completely solved here. 相似文献
100.
Yi-Shiue Lin 《Applied Surface Science》2006,252(16):5892-5899
Dissociative adsorption of CCl4 on TiO2 at 35 °C has been studied by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance. CCl4 decompose to form CO, CO2, and CO3 on the surface, at such a low temperature, in which CO2 formation is not from CO oxidation on TiO2, but CO3 can be produced by CO and CO2 adsorption. The Cl generated from CCl4 decomposition is left on the surface and bonded to titanium ions. Mineralization of CCl4 on TiO2 involves the lattice oxygens. Thermodynamical driving force and possible reaction routes for CO and CO2 formation in the CCl4 decomposition on TiO2 are discussed. 相似文献