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   195篇
  免费   14篇
  国内免费   9篇
测绘学   10篇
大气科学   19篇
地球物理   36篇
地质学   89篇
海洋学   17篇
天文学   30篇
综合类   8篇
自然地理   9篇
  2023年   1篇
  2022年   4篇
  2021年   7篇
  2020年   5篇
  2019年   1篇
  2018年   21篇
  2017年   17篇
  2016年   24篇
  2015年   10篇
  2014年   12篇
  2013年   16篇
  2012年   4篇
  2011年   8篇
  2010年   9篇
  2009年   8篇
  2008年   3篇
  2007年   4篇
  2006年   3篇
  2005年   8篇
  2004年   7篇
  2003年   3篇
  2002年   1篇
  2001年   1篇
  2000年   2篇
  1999年   1篇
  1998年   3篇
  1996年   1篇
  1995年   5篇
  1992年   1篇
  1991年   2篇
  1990年   2篇
  1989年   2篇
  1987年   2篇
  1986年   2篇
  1982年   2篇
  1980年   4篇
  1979年   1篇
  1978年   2篇
  1977年   1篇
  1976年   3篇
  1975年   1篇
  1974年   1篇
  1973年   3篇
排序方式: 共有218条查询结果,搜索用时 31 毫秒
101.
102.
A critical review on waste paper sorting techniques   总被引:1,自引:1,他引:0  
Efficient waste paper recycling has a significant role in the sustainable environment. Recyclable waste paper as a fundamental ingredient of municipal solid wastes (MSWs) is indeed an “urban ore”. Waste papers are considered as the solid recovered fuel which is recovered from MSW. Recyclable waste papers are segregated into various grades to produce high-quality products. Moreover, sorted paper streams save energy, chemicals, and water, as well as reduce sludge and rejects. Information technology is widely integrated with the waste management industry into its operations such as recycling, reuse, segregating based on categories and so on. This review article focuses on the life cycle of waste paper and existing waste paper sorting techniques. In the paper industry, many types of sensors are used in different mechanical and optical waste paper sorting systems. Such sensors include lignin, gloss, stiffness, mid-infrared, infrared, and color sensors. In this review, also described the effectiveness of different waste paper sorting systems, and finally, recommended appropriate waste paper sorting techniques based on effectiveness and low-cost implementation.  相似文献   
103.
The purpose of the present study was to investigate the effects of brick kiln exhaust on the quantity of polycyclic aromatic hydrocarbons in surrounding soils and plants. In Pakistan, a big problem is the rapid conglomeration of the brick kilns in out skirt of nearly all urban centers to cope with the rapid construction work in big cities. A huge amount of low-grade coal, rubber, tires is used in non-scientific manner. The study was conducted in the City of Peshawar the capital of Kyber Pakhtunkhwa where many brick kilns are located in the periurban areas. Soil and medicinal plants samples were collected from different locations around the bricks kiln and were analyzed for selected polycyclic aromatic hydrocarbons (PAHs), i.e., benzo(a)pyrene, anthracene, chrysene, flourene, flouranthene, phenanthrene, naphthalene, and acenapthylene. Quantitative and qualitative analysis was carried out by UV spectrophotometer and high-performance liquid chromatography. Benzo[a]pyren and Chrysene were found to be the most abundant compounds. The total load of PAHs in the central location was found to be 0.4014 mg/kg. General trend of PAHs distribution was such that the concentration of individual PAHs was found to increase with depth clearly indicating their absorption in the soil. PAHs concentration increased with the distance up to 300 m and then gradual decreased which showed their movement with the water and air. The PAHs load was found high in the leaves as compared to stem and roots. This high load in the aerial parts indicated their excretion route as well as air deposition.  相似文献   
104.
A rigorous theoretical investigation is carried out in analyzing the excitation of electrostatic ion acoustic (IA) solitary wave (SW) structures in two dimensional negative ion magneto-plasmas with superthermal electrons (following κ type distribution). The Zakharov-Kuznetsov (ZK) equation is derived by employing the well known reductive perturbation method, and the analytical solution of ZK equation assists to find out the SW profiles along with their properties. The consequences of different plasma parameters (regarding our considered plasma system) variation on SW structures has been studied. It is found that magnetic field intensity, superthermal parameter κ and temperature of positive and negative ions as well as their densities significantly modify the basic characteristics (amplitude, width, etc.) of the SW waves. A comparison of the SW structures is also presented when the electrons are Maxwellian to when they are superthermal. The relevance of the findings of this work with astrophysical plasmas is briefly pointed out.  相似文献   
105.
106.
The variation of the specific intensity across the stellar disc is an essential input parameter in surface brightness reconstruction techniques such as Doppler imaging, where the relative intensity contributions of different surface elements are important in detecting star-spots. We use phoenix and atlas model atmospheres to model light curves derived from high precision (signal-to-noise ratio ≃ 5000) Hubble Space Telescope ( HST ) data of the eclipsing binary SV Cam (F9V+K4V), where the variation of specific intensity across the stellar disc will determine the contact points of the binary system light curve. For the first time, we use χ2 comparison fits to the first derivative profiles to determine the best-fitting model atmosphere. We show the wavelength dependence of the limb darkening and that the first derivative profile is sensitive to the limb-darkening profile very close to the limb of the primary star. It is concluded that there is only a marginal difference (<1σ) between the χ2 comparison fits of the two model atmospheres to the HST light curve at all wavelengths. The usefulness of the second derivative of the light curve for measuring the sharpness of the primary's limb is investigated, but we find that the data are too noisy to permit a quantitative analysis.  相似文献   
107.
108.
Nonlinear cylindrical and spherical ion acoustic shocks have been studied in unmagnetized dissipative non-Maxwellian electron-positron-ion (e-p-i) plasmas. Modified Korteweg-de Vries Burgers (mKdVB) has been derived by using reductive perturbation method. Two level finite difference scheme is used with the help of Runge Kutta method to simulate the mKdVB. It is noticed that positron concentration, spectral indices of electrons and positrons, kinematic viscosity of ions significantly modifies the strength of shocks in cylindrical and spherical geometries.  相似文献   
109.
110.
We discuss the f(R) gravity model in which the origin of dark energy is identified as a modification of gravity. The Noether symmetry with gauge term is investigated for the f(R) cosmological model. By utilization of the Noether Gauge Symmetry (NGS) approach, we obtain two exact forms f(R) for which such symmetries exist. Further it is shown that these forms of f(R) are stable.  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