全文获取类型
收费全文 | 487篇 |
免费 | 31篇 |
国内免费 | 194篇 |
专业分类
安全科学 | 43篇 |
废物处理 | 20篇 |
环保管理 | 36篇 |
综合类 | 288篇 |
基础理论 | 87篇 |
污染及防治 | 168篇 |
评价与监测 | 21篇 |
社会与环境 | 24篇 |
灾害及防治 | 25篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 29篇 |
2021年 | 19篇 |
2020年 | 21篇 |
2019年 | 22篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 35篇 |
2015年 | 23篇 |
2014年 | 35篇 |
2013年 | 59篇 |
2012年 | 44篇 |
2011年 | 43篇 |
2010年 | 41篇 |
2009年 | 43篇 |
2008年 | 29篇 |
2007年 | 30篇 |
2006年 | 40篇 |
2005年 | 18篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 7篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有712条查询结果,搜索用时 203 毫秒
621.
622.
Zhang Z Zhan X Yan L Li M Hu J Wei F 《Environmental science and pollution research international》2009,16(1):79-84
Background, aim, and scope Foraging patches can be described as a nested hierarchy of aggregated resources, implying that study of foraging by wild animals
should be directed across different spatial scales. However, almost all previous research on habitat selection by the giant
panda has concentrated upon one scale. In this research, we carried out a field study to understand foraging patch selection
by giant pandas in winter at both microhabitat and feeding site scales and, for the first time, attempted to understand how
long it would stay at the feeding sites before moving on.
Materials and methods The field survey was conducted from November 2002 to March 2003 at Fengtongzhai Nature Reserve (102°48′–103°00′ E, 30°19′–30°47′
N), Baoxing County of Sichuan Province, China, to collect data in both microhabitat and control plots. The microhabitat plots
were located by fresh feces or foraging traces left by giant pandas, and the control plots were established to reflect the
environment. Within each microhabitat plot, one 1 × 1 m2 plot was centralized at the center of each feeding site, in which numbers of old bamboos and old shoots, including eaten
and uneaten, were counted, respectively.
Results The results showed that winter microhabitats selected by this species were characteristic of gentle slopes and high old-shoot
proportions and that the latter was even higher at feeding sites. Two selection processes, namely, from the environment to
microhabitats and from the latter to feeding sites, were found during this species’ foraging patch utilization. Giant pandas
preferred to eat old shoots to old bamboo at feeding sites in winter and did not leave unless old-shoot density fell to lower
than the average in the environment.
Discussion Both microhabitats and feeding sites selected by giant pandas were characteristic of high old-shoot density, indicating that
the preferred food item had a significant influence upon its foraging patch selection. The preference for gentle slopes by
giant pandas was presumed to save energy in movement or reflect the need to sit and free its fore-limbs to grasp bamboo culms
when feeding but also seemed to be correlated with an easier access to old shoots. The utilization of old shoots at feeding
sites was assumed to help maximize energy or nutrient intake during their foraging.
Conclusions The difference between microhabitat plots and control plots and between microhabitats and feeding sites uncovered a continuous
selection process from the environment via microhabitats to feeding sites. The utilization of old shoots at feeding sites
was parallel to the marginal value theorem. The selection and abandonment of foraging patches by giant pandas was an optimal
behavioral strategy adapted to their peculiar food with high cellulose and low protein.
Recommendations and perspectives Our results uncovered the importance of multiple scales in habitat selection research. To further understand the process of
habitat selection, future research should pay more attention to resolve the question of how to locate foraging patches under
dense bamboo forests by the giant panda, which was traditionally considered to have poor eyesight, although our research has
answered what type of habitats the giant panda prefers and when to leave. 相似文献
623.
纳米TiO2-Ag改性VACF处理氨气研究 总被引:1,自引:0,他引:1
利用浸渍法将纳米TiO2·Ag负载于粘胶基活性炭纤维上进行改性来处理低浓度氨气,扫描电镜观测和能量色散谱分析表明纳米TiO2和Ag均较成功地负载于VACF表面上,改性VACF对氨气脱除性能良好,最大脱除率为93.3%;当Ag*掺杂量为TiO2含量的0.5wt%时氨气脱除率达到最大值;存在最佳相对湿度为55%;在氨气浓度为13~65 mg/m3范围内,浓度越低,脱除效果越好;处理较高浓度氨气可通过增加改性VACF用量;随着反应连续进行,改性VACF稳定性受到影响,但仍具有脱除氨气能力. 相似文献
624.
负载型混晶相TiO2光催化剂的低温制备及其光催化活性 总被引:1,自引:0,他引:1
以蒙皂石为载体,钛酸四丁酯为前驱物,在较低温度下由溶胶凝胶法制备得到负载型TiO2光催化剂。研究了理论负载量、固定化温度、干燥、焙烧温度对TiO2/蒙皂石复合光催化剂光催化性能的影响。采用XRD分析技术对复合材料进行了表征。结果表明,负载的TiO2以锐钛矿-金红石的混晶相存在。当TiO2理论负载量为15 mmol/g、溶胶反应温度为25℃、干燥温度为70℃时,TiO2/蒙皂石复合光催化剂对偶氮染料光催化反应1 h降解率达93.40%。该制备技术的特点是在省去高温焙烧的条件下,制备出光催化活性高的负载型光催化剂。 相似文献
625.
不同改性方式对竹炭净化气态氮氧化物效果的影响 总被引:1,自引:1,他引:0
为了研究不同表面改性方法对竹炭空气净化效果的影响,测定了化学药剂活化、超声处理、微波处理后的改性竹炭对低浓度氮氧化物的净化效果。结果表明:活化剂浸渍后的竹炭,对氮氧化物净化效率降低,净化速度减慢;微波功率越大、辐照时间越长,改性后竹炭对氮氧化物处理效率越大,但辐照时间达到一定程度后,竹炭对氮氧化物的处理效率增大变得缓慢;超声处理后的竹炭对NO的处理效率比改性前有明显提高。BET测试结果表明,竹炭产品用微波和超声处理后,平均孔径、微孔表面积和比表面积均比活化前增大;而经过活化剂浸渍后,微孔面积和比表面积都显著下降。因此建议采用微波及超声方式对竹炭进行活化。 相似文献
626.
627.
628.
629.
630.
YuFeng Jiang LeiPing Shi ZhongFeng Mu Hang Sun HuiYing Zhan YingQin Wu 《毒物与环境化学》2017,99(5-6):824-836
Dibenzopyrene and its isomers are considered the most potent carcinogens of all polycyclic aromatic hydrocarbons tested to date. However, despite public concerns over their deleterious effects, they have not been extensively studied. The occurrence of four highly carcinogenic isomers of dibenzopyrene – dibenzo[def,p]chrysene, dibenzo[a,e]pyrene, dibenzo[a,i]pyrene, and dibenzo[a,h]pyrene in urban soil samples from Shanghai, China, have been determined in this study, as well as that of benzo[a]pyrene and coronene. A total of 14 peaks with ions at m/z 302 were detected by gas chromatography-mass spectrometry. Although the concentrations of benzo[a]pyrene and the sum of the 16 priority polycyclic aromatic hydrocarbons were greater than that of dibenzopyrene and its isomers, the carcinogenic potency of the latter was higher than that of benzo[a]pyrene. The results also indicate that the relative carcinogenic potency of the four dibenzopyrene isomers in the samples is higher than that of the 16 priority polycyclic aromatic hydrocarbons. 相似文献