首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   125006篇
  免费   1338篇
  国内免费   461篇
化学   68467篇
晶体学   2035篇
力学   4955篇
综合类   5篇
数学   12103篇
物理学   39240篇
  2016年   1272篇
  2015年   982篇
  2014年   1319篇
  2013年   4776篇
  2012年   3376篇
  2011年   4383篇
  2010年   2733篇
  2009年   2513篇
  2008年   3923篇
  2007年   3978篇
  2006年   4036篇
  2005年   3965篇
  2004年   3453篇
  2003年   3150篇
  2002年   3053篇
  2001年   3570篇
  2000年   2674篇
  1999年   2195篇
  1998年   1884篇
  1997年   1872篇
  1996年   1802篇
  1995年   1772篇
  1994年   1545篇
  1993年   1533篇
  1992年   1753篇
  1991年   1745篇
  1990年   1677篇
  1989年   1683篇
  1988年   1684篇
  1987年   1674篇
  1986年   1587篇
  1985年   2135篇
  1984年   2262篇
  1983年   1887篇
  1982年   2212篇
  1981年   2027篇
  1980年   2073篇
  1979年   2058篇
  1978年   2186篇
  1977年   2090篇
  1976年   2115篇
  1975年   2053篇
  1974年   1895篇
  1973年   2102篇
  1972年   1282篇
  1971年   975篇
  1970年   912篇
  1969年   923篇
  1968年   1050篇
  1967年   1101篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
This note discusses the need to use various data-compaction schemes in the implementation of sophisticated large-scale linear programming codes on modest personal computers. It demonstrates a method whereby the overhead of using these schemes is significantly reduced on Intel 80 x 86 processors.  相似文献   
112.
Measurements from depolarized lidars provide a promising method to retrieve both cloud and aerosol properties and a versatile complement to passive satellite-based sensors. For lidar observations of clouds and aerosols, multiple scattering plays an important role in the scattering process. Monte Carlo simulations are carried out to investigate the sensitivity of lidar backscattering depolarization to cloud and aerosol properties. Lidar parameters are chosen to be similar to those of the upcoming space-based CALIPSO lidar. Cases are considered that consist of a single cloud or aerosol layer, as well as a case in which cirrus clouds overlay different types of aerosols. It is demonstrated that besides thermodynamic cloud phase, the depolarized lidar signal may provide additional information on ice or aerosol particle shapes. However, our results show little sensitivity to ice or aerosol particle sizes. Additionally, for the case of multiple but overlapping layers involving both clouds and aerosols, the depolarized lidar contains information that can help identify the particle properties of each layer.  相似文献   
113.
The basic damage and failure models of multiaxially reinforced composites with a thermoplastic matrix are presented and verified. Within the framework of continuum damage mechanics, a phenomenological model is introduced, where the damage is defined as a change in the elasticity tensor. For damage identification, a specific ultrasonic device was developed. A combination of an immersion set-up and a contact coupling device formed a system for an efficient determination of stiffness-tensor components from convenient sets of velocity measurements. Linked to a tensile machine, it allowed us to measure the anisotropic damage of the new materials group caused by tensile loading. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 221–234, March–April, 2006.  相似文献   
114.
Hyperfine Interactions - Rotational J=1→J=0 transitions in muonic molecule, (3Heμd) J ++, in [(3Heμd)++,2e]–D and [(3Heμd)++,e]+–D collisions are considered. The...  相似文献   
115.
This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism.  相似文献   
116.
Manning's method of calculating the ratio of mobility and diffusion coefficient in ionic conductors, sensitive to the type of particle jumps, is analytic. This paper presents a computer orientated treatment in terms of an averaging procedure recently proposed.  相似文献   
117.
We discuss some variant superfield representations which can arise by the replacement of some of the usual fields in a multiplet with p-form gauge fields.  相似文献   
118.
In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO2) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO2 thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO2 absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO2 are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO2 films prepared for undoped sol-gels and by sputtering is performed.  相似文献   
119.
Information is presented on structure, composition, and response to enzymes of corn stover related to barriers for bioconversion to ethanol. Aromatic compounds occurred in most tissue cell walls. Ferulic acid esterase treatment before cellulase treatment significantly improved dry weight loss and release of phenolic acids and sugars in most fractions over cellulase alone. Leaf fractions were considerably higher in dry weight loss and released sugars with esterase treatment, but stem pith cells gave up the most phenolic acids. Results help identify plant fractions more appropriate for coproducts and bioconversion and those more suitable as residues for soil erosion control.  相似文献   
120.
The purpose of this note is to describe a procedure for transferring familiar estimates for transition probabilities on RN to transition probabilities on compact manifolds.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号