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   248篇
  免费   1篇
  国内免费   10篇
安全科学   11篇
废物处理   45篇
环保管理   11篇
综合类   40篇
基础理论   34篇
污染及防治   93篇
评价与监测   8篇
社会与环境   16篇
灾害及防治   1篇
  2023年   2篇
  2022年   5篇
  2021年   5篇
  2020年   1篇
  2019年   3篇
  2018年   6篇
  2017年   5篇
  2016年   8篇
  2015年   5篇
  2014年   3篇
  2013年   19篇
  2012年   10篇
  2011年   15篇
  2010年   17篇
  2009年   19篇
  2008年   21篇
  2007年   23篇
  2006年   13篇
  2005年   9篇
  2004年   19篇
  2003年   6篇
  2002年   14篇
  2001年   4篇
  2000年   5篇
  1999年   3篇
  1997年   3篇
  1996年   1篇
  1994年   2篇
  1992年   3篇
  1989年   1篇
  1984年   1篇
  1982年   1篇
  1979年   2篇
  1977年   2篇
  1969年   1篇
  1957年   1篇
  1956年   1篇
排序方式: 共有259条查询结果,搜索用时 31 毫秒
151.
How to acquire sufficient quantity of nitrogen is a pivotal issue for herbivores, particularly for lepidopterans (butterflies and moths) of which diet quality greatly differs among their life stages. Male Lepidoptera often feed from mud puddles, dung, and carrion, a behavior known as puddling, which is thought to be supplementary feeding targeted chiefly at sodium. During copulation, males transfer a spermatophore to females that contains, besides sperm, nutrients (nuptial gifts) rich in sodium, proteins, and amino acids. However, it is still poorly understood how adults, mostly nectarivores, extract nitrogen from the environment. We examined the availability of two ubiquitous inorganic nitrogenous ions in nature, viz. ammonium (or ammonia) and nitrate ions, as nutrients in a butterfly, and show that exogenous ammonia ingested by adult males of the swallowtail, Papilio polytes, can serve as a resource for protein biosynthesis. Feeding experiments with 15N-labeled ammonium chloride revealed that nitrogen was incorporated into eupyrene spermatozoa, seminal protein, and thoracic muscle. Ammonia uptake by males significantly increased the number of eupyrene sperms in the reproductive tract tissues. The females also had the capacity to assimilate ammonia into egg protein. Consequently, it is evident that acquired ammonia is utilized for the replenishment of proteins allocable for reproduction and somatic maintenance. The active exploitation of exogenous ammonia as a nutrient by a butterfly would foster better understanding of the foraging and reproductive strategies in insects.  相似文献   
152.
153.
The decomposition of vertebrate carcasses is an important ecosystem function. Soft tissues of dead vertebrates are rapidly decomposed by diverse animals. However, decomposition of hard tissues such as hairs and feathers is much slower because only a few animals can digest keratin, a protein that is concentrated in hairs and feathers. Although beetles of the family Trogidae are considered keratin feeders, their ecological function has rarely been explored. Here, we investigated the keratin-decomposition function of trogid beetles in heron-breeding colonies where keratin was frequently supplied as feathers. Three trogid species were collected from the colonies and observed feeding on heron feathers under laboratory conditions. We also measured the nitrogen (δ15N) and carbon (δ13C) stable isotope ratios of two trogid species that were maintained on a constant diet (feathers from one heron individual) during 70 days under laboratory conditions. We compared the isotopic signatures of the trogids with the feathers to investigate isotopic shifts from the feathers to the consumers for δ15N and δ13C. We used mixing models (MixSIR and SIAR) to estimate the main diets of individual field-collected trogid beetles. The analysis indicated that heron feathers were more important as food for trogid beetles than were soft tissues under field conditions. Together, the feeding experiment and stable isotope analysis provided strong evidence of keratin decomposition by trogid beetles.  相似文献   
154.
The trend of tropospheric ozone from 1998 to 2006 was examined based on continuous measurements made at a site on Mt. Happo, Japan. We focused our study on springtime ozone, to coincide with the East Asian continental outflow that dominates the lower tropospheric ozone over Japan during this season. The observed increase of ~1 ppbv yr?1 in the mean ozone level was statistically significant. We also found that the probability distribution of the springtime ozone mixing ratios was substantially modified, with the ozone mixing ratios greatly increasing at the upper end of the probability distribution. This increase has been particularly large since 2003, with larger increases occurring at the higher percentiles. The number of high-ozone days doubled during 2003–2006 compared to 1999–2002. One of the very likely explanations is the enhancement of regional ozone pollution due to rapidly increasing anthropogenic emissions from East Asia.  相似文献   
155.
This paper reports on the relationships between creative mental sets and rule-violating actions using questionnaires answered by 218 nursing workers. An exploratory factor analysis was conducted. The results revealed five factors of creative mental sets: curiosity, minutiae, inquiry, sensitivity, and courage. In addition, rule-violating actions were found to consist of three factors: violation of regulations, violation of local rules, and self-style. The results of multiple regression analyses showed a negative relation between curiosity and regular rule violation. Negative correlations were observed among minutiae, inquiry, and local rule violation. Furthermore, the mean score of local rule violation of a person who thinks that it is important for the work environment to offer high and excellent care is significantly higher than that of those who think that other environmental considerations are more important. The result elucidated the necessity of using workers’ heuristics in the process of improving safety rules as well as improving their acceptability to workers. This point is important and applicable not only in the field of patient safety management systems, but also in other fields.  相似文献   
156.
Estrogenic compounds such as 17beta-estradiol (E2) and its analogs are present in the aquatic environment and can adversely affect the reproductive systems of aquatic organisms. Although E2 has been detected at a maximum concentration of 64 ng/l in effluents of sewage treatment works (STWs), few reports address the associated effects on reproduction in fish. Therefore, we exposed adult medaka (Oryzias latipes) to mean measured E2 concentrations of 29.3, 55.7, 116, 227, and 463 ng/l for 21 d and assessed the effects on the egg number and fertility of paired medaka during the exposure period. In addition, we determined the hepatic vitellogenin (Vtg) concentration and histologically assessed the gonads of these fish. The number of egg produced and fertility of the paired medaka exposed to 463 ng/l E2 were significantly less compared with those of the control fish. Males in all treatment groups had developed testis-ova. Males treated with E2 concentrations = 55.7 ng/l contained relating great concentrations of hepatic Vtg. Therefore, although only the greatest E2 concentration tested in our study affected fecundity and fertility, effects of E2 were observed on induction of Vtg and testis-ova in male medaka exposed to environmentally relevant concentrations of E2.  相似文献   
157.
It is generally recognized that the sonographic findings of infantile polycystic kidney disease (IPKD) are bilaterally enlarged kidneys, oligohydramnios, an absent fetal bladder, and the typical kidney texture. Since there is a broad spectrum of renal compromise with IPKD, in utero diagnosis is thought to be limited to the severe forms. This paper reports a mild case of IPKD, where the in utero diagnosis was established by measuring fetal urine production and amniotic fluid volume serially during pregnancy, and by ultrasonographic examination of fetal kidneys.  相似文献   
158.
An electron microscopic DOPA reaction test of fetal skin was used for the prenatal diagnosis of tyrosinase-negative oculocutaneous albinism (OCA). The subject was a 34-year-old Japanese woman in her second pregnancy. Her first child, born in 1982, had been previously examined and confirmed to have tyrosinase-negative OCA. The parents requested a prenatal diagnosis and we sampled skin from the upper trunk of the fetus. On conventional electron microscopy, the development of melanosomes in interfollicular melanocytes had progressed no further than stage II. Fetal skin samples incubated with L-DOPA solution indicated a lack of tyrosinase activity and showed that the melanosomes had not progressed beyond stage II. In skin samples from the trunks of three Japanese fetuses aborted for other reasons at 19–20 weeks of gestation, most premature melanosomes were further melanized to stage IV after incubation with L-DOPA solution. A prenatal diagnosis of tyrosinase-negative OCA was made. The parents requested a termination and skin biopsies of the abortus confirmed the diagnosis. This study shows that tyrosinase is normally present in melanocytes of the fetal epidermis at 20 weeks' gestation, and that the electron microscopic DOPA reaction test of a fetal skin biopsy specimen is safe and practical, and provides reliable information for making a prenatal diagnosis of tyrosinase-negative OCA in the second trimester.  相似文献   
159.
IntroductionTheclimatechangeissignificantlyaffectinghumanlivingenvironmentsinglobal,regional,andlocalscales.Intermsoftheregionalscale ,oneofthemostpromisingapproachesforsimulationofregionalclimatechangeisthedevelopmentofregionalclimatemodel (RCM) .Itiswel…  相似文献   
160.
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