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   1059篇
  免费   195篇
  国内免费   577篇
安全科学   73篇
废物处理   61篇
环保管理   60篇
综合类   996篇
基础理论   332篇
污染及防治   237篇
评价与监测   56篇
社会与环境   12篇
灾害及防治   4篇
  2023年   19篇
  2022年   50篇
  2021年   74篇
  2020年   40篇
  2019年   60篇
  2018年   127篇
  2017年   59篇
  2016年   69篇
  2015年   59篇
  2014年   67篇
  2013年   114篇
  2012年   103篇
  2011年   113篇
  2010年   79篇
  2009年   98篇
  2008年   74篇
  2007年   82篇
  2006年   72篇
  2005年   63篇
  2004年   55篇
  2003年   66篇
  2002年   44篇
  2001年   42篇
  2000年   43篇
  1999年   29篇
  1998年   19篇
  1997年   20篇
  1996年   18篇
  1995年   24篇
  1994年   9篇
  1993年   15篇
  1992年   5篇
  1991年   3篇
  1990年   1篇
  1988年   2篇
  1987年   1篇
  1986年   1篇
  1985年   3篇
  1984年   1篇
  1983年   3篇
  1982年   3篇
  1981年   1篇
  1980年   1篇
排序方式: 共有1831条查询结果,搜索用时 31 毫秒
21.
基于营养液培养,添加外源稀土和ICP-MS分析技术,研究了无机配体PO43-(Pi)及有机配体柠檬酸(Cit)对小麦器官中稀土元素积累和分异的影响.结果表明,不同Pi水平对小麦根中的稀土总含量(∑REE)影响较小,但显著降低叶中∑REE含量;而不同Cit水平对小麦根、叶中∑REE含量都有明显降低作用.对照植物(无Pi、Cit添加)中,稀土元素在小麦根中具有中稀土(MREE)富集及M-型四重效应分布特征,叶中有重稀土(HREE)富集及W-型四重效应分布特征.不同Pi处理对四重效应无明显作用,但进一步加强HREE在小麦叶片中的富集.添加柠檬酸使对照植物根和叶中的分异有逐渐减弱的趋势,在高浓度处理时(Cit≥150μmol.L-1),小麦根和叶中出现轻稀土(LREE)富集.  相似文献   
22.
Bagasse, a biomass fuel, is the waste generated by the sugar-making process from sugar cane. Sugar making is one of the most important agricultural-produce processing industries for developing countries in Southeast Asia, Latin America and Africa. As sugar producing plants need electric power and process steam, co-generation using bagasse as an alternate fuel for petroleum has been in use for some time. Thailand recently became one of the largest sugar exporters by enlarging plant capacities and improving equipment, thus reducing its production cost. In addition, the Thai government promotes power generation using bagasse as a means to combat global warming by raising the purchase price of the surplus power. The industry is in the process of further raising the plant capacity, and improving the power-generating efficiency. This will enable a plant to generate more electric power than its in-plant need so that the surplus power can be sold to the commercial grid. It also plans to become a local power supplier during off-season of sugar making by adding a condensing turbine generator. A typical Thai sugar plant of the latest design generates steam of 4Mpa at the bagasse boiler outlet with the temperature of 400°C at 84% boiler efficiency. With the bagasse LHV of 7,540 kJ/kg and that of fuel oil 41, 840 kJ/kg, and taking 90%as oil-burning boiler efficiency, 5.95 kg of bagasse would replace 1 kg of oil. The Kyoto Mechanism defines CO2 generation by fuel oil as 2.65 kg per liter. Using 0.85for the specific gravity of fuel oil, the amount of CO2 generation will be 3.12 kg-CO2/kg. Therefore, CO2reduction per ton of bagasse in terms of fuel oil will be: 3.12/5.95 =0.524 kg-CO2/kg-bagasse. As 1 kg of bagasse generates 2 kg of steam, the CO2reduction of a 100t/h steam boiler will be112,660 ton/year for an annual operation of4,300 hours, as follows. 0.524 × 100/2 = 26.2 t-CO2/h, 26.2 × 4,300 =112,660 t-CO2/year. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
23.
通过分析柴油加氢装置的腐蚀现象及腐蚀原因,找出了因腐蚀造成的安全隐患。通过化验分析推断出发生腐蚀的重点部位。采用了加注缓蚀剂等有效的防腐措施,使腐蚀得到有效控制,保证了装置的安全运行。  相似文献   
24.
We report herein a de novo unbalanced chromosome translocation in a fetus resulting from in vitro fertilization technology. Prenatal diagnostic analysis of an amniotic fluid revealed a 46,XX,4p+ karyotype. The origin of the extra material on the short arm of chromosome 4 could not be identified by a variety of banding techniques. However, examination of fetal parts did reveal some dysmorphic features.  相似文献   
25.
A graphite carbon nitride(g-C_3N_4) modified Bi_4O_5I_2 composite was successfully prepared insitu via the thermal treatment of a g-C_3N_4/Bi OI precursor at 400°C for 3 hr.The as-prepared g-C_3N_4/Bi_4O_5I_2 showed high photocatalytic performance in Methyl Orange(MO) degradation under visible light.The best sample presented a degradation rate of 0.164 min~(-1),which is 3.2 and 82 times as high as that of Bi_4O_5I_2 and g-C_3N_4,respectively.The g-C_3N_4/Bi_4O_5I_2 was characterized by X-ray powder diffractometer(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),Raman,X-ray photoelectron spectroscopy(XPS),ultraviolet-visible diffuse reflectance spectra(DRS),electrochemical impedance spectroscopy(EIS) and transient photocurrent response in order to explain the enhanced photoactivity.Results indicated that the decoration with a small amount of g-C_3N_4 influenced the specific surface area only slightly.Nevertheless,the capability for absorbing visible light was improved measurably,which was beneficial to the MO degradation.On top of that,a strong interaction between g-C_3N_4 and Bi_4O_5I_2 was detected.This interplay promoted the formation of a favorable heterojunction structure and thereby enhanced the charge separation.Thus,the g-C_3N_4/Bi_4O_5I_2 composite presented greater charge separation efficiency and much better photocatalytic performance than Bi_4O_5I_2.Additionally,g-C_3N_4/Bi_4O_5I_2 also presented high stability.·O_2~-and holes were verified to be the main reactive species.  相似文献   
26.
研究了对处理铝材加工含Al3+的酸性废液过程中产生的二次污染物Al(OH)3凝胶废渣的应用。含水分约90%、80%左右的Al(OH)3凝胶200g分别与14~16mL、22~24mL95%的工业浓硫酸酸反应,可制得浓度为20%~23%的Al(SO4)3溶液,经稀释可用作造纸原料。  相似文献   
27.
HLA typing of amniotic fluid cells has been used for the prenatal diagnosis of the HLA linked diseases congenital adrenal hyperplasia (21-OH-deficiency (21-OH-def) type) and complement C4 deficiency and it has also been used for the prenatal de termination of paternity. There are, however, technical difficulties in this test associated with the weak expression of some B locus antigens on amniotic fluid cells, and theoretical difficulties related to associations between particular HLA antigens and the 21-OH-def allele. Since certain HLA-B locus antigens are found in significantly increased frequencies among patients with 21-OH-def, there is a relatively high incidence of HLA-B homozygosity among the patients and over 40 percent of the parents of these patients share one or more HLA-B locus antigens. Results of some prenatal HLA typing tests may thus be difficult to interpret, and supplementary tests should be used whenever possible. HLA typing of amniotic cells is, however, the only available procedure for prenatal diagnosis of C4 deficiency and it is the best available procedure for prenatal determination of paternity. A modification of our original procedure allows HLA typing to be performed with increased numbers of HLA typing sera, and sera with optimum reactivity for amniotic fluid cells have now been selected for the definition of most of the more commonly expressed HLA antigens. Although amniotic fluid cells do not express DR antigens, amniotic fluid cells can be typed for the HLA-linked marker glyoxalase I (GLO) and this may be the informative for prenatal diagnosis in some cases.  相似文献   
28.
假单胞菌的氯儿茶酚1,2-双加氧酶基因的克隆和表达   总被引:2,自引:0,他引:2       下载免费PDF全文
 从土壤中分离得到1株降解2,4-二氯酚(2,4-DCP)能力较强的细菌菌株GT241-1,克隆了该菌株的3,5-二氯儿茶酚1,2-双加氧酶基因(dcpB),采用的克隆策略为:用Southern杂交对dcpB进行定位后,构建重组质粒,再用斑点杂交从重组质粒中筛选目的转化子.经序列测定得知dcpB亚克隆片段全长4303bp,其中dcpB基因编码区765bp.核苷酸和推测的氨基酸序列分析表明,dcpB与已在GenBank登记的相关基因有一定的差异.dcpB基因能够在大肠杆菌转化子中成功地表达有生物活性的酶.  相似文献   
29.
三维叠前时间偏移技术在江苏WZD地区的应用   总被引:1,自引:0,他引:1  
当地下地质构造复杂、断裂发育,横向速度变化不是太剧烈的情况下,提高偏移成像精度,三维叠前时间偏移是一种行之有效的方法。三维叠前时间偏移取得成功的关键:一是高保真、高信噪比的叠前数据;二是建立一个合理的三维偏移速度场。随着计算机性能的不断提高,三维叠前时间偏移逐渐成为常规处理技术,该技术在江苏油田WZD地区得到了广泛的应用,实际资料处理结果及钻探效果证实了三维叠前时间偏移技术是解决WZD地区复杂构造成像精度的一种好方法。  相似文献   
30.
通过红外光谱和核磁共振方法分析生产水杨酸甲酯时所产生的废渣的主要在分,得出主要成分是4-羟基-1,3-苯二甲酸二甲酯的讨论。该化合物在药物合成上一定的用途。  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