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   6966篇
  免费   62篇
  国内免费   35篇
安全科学   148篇
废物处理   280篇
环保管理   653篇
综合类   1020篇
基础理论   1490篇
环境理论   6篇
污染及防治   1690篇
评价与监测   558篇
社会与环境   1178篇
灾害及防治   40篇
  2022年   73篇
  2021年   92篇
  2020年   50篇
  2019年   60篇
  2018年   130篇
  2017年   159篇
  2016年   188篇
  2015年   121篇
  2014年   232篇
  2013年   574篇
  2012年   255篇
  2011年   314篇
  2010年   247篇
  2009年   274篇
  2008年   338篇
  2007年   373篇
  2006年   291篇
  2005年   285篇
  2004年   253篇
  2003年   234篇
  2002年   221篇
  2001年   252篇
  2000年   205篇
  1999年   94篇
  1998年   74篇
  1997年   78篇
  1996年   68篇
  1995年   83篇
  1994年   67篇
  1993年   60篇
  1992年   59篇
  1991年   62篇
  1990年   73篇
  1989年   56篇
  1988年   46篇
  1987年   44篇
  1986年   52篇
  1985年   50篇
  1984年   51篇
  1983年   40篇
  1982年   47篇
  1981年   38篇
  1980年   47篇
  1979年   45篇
  1975年   32篇
  1974年   34篇
  1973年   34篇
  1972年   40篇
  1971年   32篇
  1969年   31篇
排序方式: 共有7063条查询结果,搜索用时 15 毫秒
851.
We report a case of prenatal diagnosis of trisomy 20p resulting from a maternal pericentric inversion. The diagnosis was confirmed on both chorionic villi and amniotic cells. This case underlines the fact that prenatal ultrasound diagnosis of this structural anomaly is difficult. The only early sonographic feature was increased nuchal translucency. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
852.
The aim of the present study was to examine the distribution of pollutants in two coastal systems in Georgia: (1) Kubitskali river which flows into the Black sea through the city of Batumi and is polluted mainly from the effluents of an oil refinery; (2) Paliastomi lake, which is a shallow water body at the south-east of the city of Poti. During 2000-2001, two samplings took place in each system, one in the low-flow period and one in the high-flow period. During these samplings, pH, temperature, dissolved oxygen, and salinity were measured in situ, whereas water samples were collected for the analysis of trace metals, nutrients, and organic pollutants with standard methods. The results of the measurements indicate the significant pollution of both systems by ammonia and in the case of Kubitskali River also by oil products. The need for a sustainable management plan of the activities taking place in the river basin is urgent.  相似文献   
853.
854.
The spatial structure of populations has been studied in two rodent species inhabiting the subzone of meadow steppes of the steppe zone of Omsk oblast: the narrow-sculled vole (Microtus gregalis Pall.) and steppe lemming (Lagurus lagurus Pall.). Their populations are represented by combinations of territorial family groups whose structure and spatial distribution vary by season depending on population density, the phase of the population cycle, and the status of their members in the population. In the areas cohabited by M. gregalis and L. lagurus, the pattern of territory use and the rhythm of animal activity during the day depend primarily on their total density: under conditions of low density, the population groups of both species are spatially separated; at increased density, they are distributed with respect to the pattern of daily activity. Both species jointly use part of the territory but at different times of day: M. gregalis, mainly at night and in the morning; L. lagurus, in the daytime.  相似文献   
855.
856.
Reproductive output, as the percentage of the mother weight devoted to egg production, was estimated for the burrowing shrimp Callianassa tyrrhena in wet, dry and ash-free dry weight. Three biometrical approaches were used. First, the relationship between the egg mass and the mother weight was determined. A second approach was to estimate the weight loss of the female caused by oviposition. Similar results were obtained from these methods for dry and ash-free dry weight (about 20 and 35%, respectively), but not for the wet weight estimation. The third approach, based on the weight loss of the ovary, did not reveal a constant value for reproductive output throughout the female size range, although it was found that the ovary loses a constant percentage of its weight during oviposition. This discrepancy is due to the fact that the ovary weight shows positive allometry to the weight of the female body. The comparison of the three methods offers insight into the biological events that are related to ovary maturation and oviposition. It is suggested that molting just before oviposition and its inhibition during the yolk accumulation in the ovary play dominant roles in the expression of the reproductive output in the different approaches used. Received: 17 July 1996 / Accepted: 11 September 1996  相似文献   
857.
A 40-year-old woman underwent amniocentesis at 15.3 weeks of gestation. Chromosome analysis performed using QFQ, DA-DAPI and CBG banding revealed two de novo extra-chromosomal markers (ESACs) in 11 of the 16 colonies analysed. Fluorescence in situ hybridization (FISH) showed that both chromosomes came from the Yq11.22.1 region of the Y chromosome. PCR analysis of genes and STS localized on the Y chromosome excluded the Yp presence specifically of the SRY gene, and most of the euchromatic region of Yq. After extensive genetic counselling and considering both laboratory and second-level ultrasound data, the couple decided to continue the pregnancy. At 37.4 weeks of gestational age, a girl weighing 2750 g was born with an Apgar score of 9/10. A blood sample taken from the umbilical cord showed three cellular lines:mos47,XX, +mar1 ish.der (Y)(wcpY+) [21%]/48,XX, +mar1 ish.der (Y)(wcpY+), +mar2 ish.der (Y)(wcpY+) [41%]/46,XX [38%]. One year after birth, the baby was developing normally and had normal psychomotorial activity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
858.
859.
This study uses the process simulator ASPEN Plus® and Life Cycle Assessment (LCA) to compare three process design alternatives for biodiesel production from waste vegetable oils that are: the conventional alkali-catalyzed process including a free fatty acids (FFAs) pre-treatment, the acid-catalyzed process, and the supercritical methanol process using propane as co-solvent. Results show that the supercritical methanol process using propane as co-solvent is the most environmentally favorable alternative. Its smaller steam consumption in comparison with the other process design alternatives leads to a lower contribution to the potential environmental impacts (PEI’s). The acid-catalyzed process generally shows the highest PEI’s, in particular due to the high energy requirements associated with methanol recovery operations.  相似文献   
860.
The life of a product begins with the initial product design concepts; the costs and potential impacts of a product are heavily influenced by the final design, the production processes, the economic and environmental costs of all raw materials. Additionally, both of these factors are very much affected by how the products are managed during and after consumer usage. Thus, there is an urgent need for a tool to facilitate the integration and assessment of environmental and economic demands into the product planning and development processes. The introduction of environmental accounting based on emergy as a tool to assist in product design is proposed. This complementary tool may be inserted into the conventional design methodology to facilitate in the selection of materials and processes as well as in the actual design of the products. To illustrate the application of the proposed method for material selection, PET (polyethylene terephthalate) bottles and aluminum cans for beverage packaging are compared. Despite the exceptional condition of aluminum recycling in Brazil, results show that the best option for beverage packages is the PET bottles.  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