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   596篇
  免费   7篇
  国内免费   4篇
安全科学   6篇
废物处理   17篇
环保管理   29篇
综合类   267篇
基础理论   59篇
环境理论   1篇
污染及防治   152篇
评价与监测   46篇
社会与环境   27篇
灾害及防治   3篇
  2023年   5篇
  2022年   16篇
  2021年   26篇
  2020年   12篇
  2019年   7篇
  2018年   20篇
  2017年   14篇
  2016年   18篇
  2015年   14篇
  2014年   16篇
  2013年   43篇
  2012年   24篇
  2011年   31篇
  2010年   24篇
  2009年   27篇
  2008年   17篇
  2007年   19篇
  2006年   13篇
  2005年   16篇
  2004年   4篇
  2003年   3篇
  2002年   7篇
  2001年   1篇
  2000年   4篇
  1998年   2篇
  1995年   49篇
  1994年   27篇
  1993年   40篇
  1992年   43篇
  1991年   29篇
  1990年   16篇
  1989年   10篇
  1987年   2篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1981年   5篇
排序方式: 共有607条查询结果,搜索用时 31 毫秒
561.
The aim was to assess the role that fetal bladder size has in the determination of fetal hydronephrosis. Forty-three fetuses were evaluated for fetal hydronephrosis in the second trimester of pregnancy. Anteroposterior measurements of the renal pelvis were obtained with a full bladder and again when the bladder emptied in each fetus. Statistical analysis was performed using the Spearman rank order correlation coefficient to assess the relationship between bladder status and renal dilation. The anteroposterior size of the fetal renal pelvis diminished from 6.8 ± 1.8 mm on a full bladder scan to 4.5 ± 1.6 mm when the bladder was emptied (P<0.001). Fifty-three per cent of the fetuses whose renal pelvic measurements were 5 mm or more on a full bladder scan had normal-appearing renal pelvises when their bladders emptied. The status of the fetal bladder should be considered when evaluating fetal hydronephrosis.  相似文献   
562.
The aim of this study was to assess the value of ultrasonographic evaluation in predicting abnormal karyotypes in fetuses with omphalocele. Forty fetuses with antenatally diagnosed omphalocele and available karyotype results were reviewed. Ultrasound evaluation included herniation contents and size, and the detection of other anomalies. Nine of 40 consecutive fetuses had abnormal karyotypes: trisomy 18 (n = 5), trisomy 13 (n = 3), 47,XXX (n = 1). Only 1/25 with an extracorporeal liver versus 8/15 with an intracorporeal liver had abnormal chromosomes [P = 0·0006, RR = 0·14 (0·02 < RR <0·9)]. Small defects (<3 cm) were associated with abnormal karyotypes [P = 0·01, RR = 4·7 (1·4<RR <15·6)]. Finding concurrent malformations was highly associated with chromosomal anomalies [P = 0·00004, RR = 4·4 (2·3 < RR < 8·5)]. The presence of associated malformations, an intracorporeal liver, and a small herniation size are highly suggestive of an associated abnormal karyotype.  相似文献   
563.
We describe here 17 cases of fetal gall bladder anomalies, detected as early as the 14th week of gestation, out of 10 016 fetal systemic examinations performed by us in the last 6 years (015 per cent). In seven cases, agenesis of the fetal gall bladder was detected. The diagnosis was confirmed by post-abortal examination in five cases and in two post-partum. In six other cases, a left-sided gall bladder and in one case, a ‘floating’ gall bladder were detected at 15 weeks' gestation. In two cases, a septated or bilobed gall bladder was visualized. None of these 15 cases was dyskaryotic, but in five cases, two with agenesis and three left-sided gall bladders were associated with other fetal malformations. In two other cases, the gall bladder appeared dysmorphic on sonographic examination and in both of them intrauterine growth retardation and other anomalies were detected. Trisomy 18 was diagnosed by amniocentesis in one of them. According to our experience, failure to visualize the fetal gall bladder by the 15th gestational week is diagnostic of its absence and should raise the differential diagnosis between gall bladder atresia, which has a good prognosis, and external biliary atresia, which has a poor prognosis. Further experience is needed to characterize the various gall bladder malformations and their prognosis.  相似文献   
564.
For the last 6 years, sonographic signs for excessive fluid accumulation in the backs of 10- to 12-week-old fetuses have been looked for prior to transabdominal chorionic biopsy. In 1400 pregnancies, subsequent karyotype analyses revealed 28 cases of Down syndrome. In 15 ( = 54 per cent), a large fluid cushion over most of the back had been documented at the time of biopsy. Only a few chromosomally normal fetuses with the same peculiarity were observed. The cushion was also present in fetuses with trisomies 18 and 13 , and in Turner syndrome. Systematic first-trimester screening for nuchal fluid accumulation seems to be a recommended method for the detection of Down syndrome and other chromosome anomalies in young pregnant women at low risk. It compares favourably with current methods of maternal serum screening performed at 16–18 weeks which require a higher number of invasive procedures.  相似文献   
565.
We report the prenatal diagnosis of a male fetus with X-linked recessive chondrodysplasia punctata (CDPX), steroid sulphatase (STS) deficiency, X-linked Kallmann syndrome (KAL), and a chromosome deletion at Xp22.31. Biochemical analysis of bone from this case indicates that CDPX is not a defect of vitamin K metabolism. Immunocytochemical study of the brain suggests that KAL is a defect in neuronal migration.  相似文献   
566.
Familial congenital pyloric atresia is a rare malformation of the fetal gastrointestinal tract. It usually manifests as maternal polyhydramnios and enlarged fetal stomach on ultrasound scan. Sonographic prenatal diagnosis and management of a pregnancy complicated by familial congenital pyloric atresia are presented.  相似文献   
567.
With proximal and distal obstruction to the lacrimal drainage system, mucus accumulates forming a cyst. In order to diagnose a nasolacrimal duct cyst antenatally, the sonographer must image the region adjacent to the orbits.  相似文献   
568.
Our aim was to evaluate the potential value of the ratio of the maternal urinary beta-core fragment of human chorionic gonadotropin (βC-hCG) to creatinine (Cr) in discriminating between normal pregnancies and pregnancies associated with fetal chromosomal abnormalities. We hypothesized that pregnancies with fetal chromosomal abnormalities had abnormal quantities of βC-hCG in the urine. The aims of the present study were to investigate retrospectively whether maternal urinary ratios of βC-hCG/Cr are abnormal in women carrying fetuses with chromosome aberrations and to determine normative median values and a reference range for βC-hCG/Cr between 14 and 19 weeks' gestation. Maternal urinary βC-hCG and Cr concentrations were measured in 150 healthy women from 14 to 19 weeks and compared with ten cases of fetal chromosomal abnormalities matched for gestational age. The preliminary cut-off points corresponded to 0·29 multiple of the normal median (MOM) and 2·83 MOM, which were equivalent to the tenth and 90th centiles of the normal range. Of ten cases of fetal chromosomal abnormalities, one out of one (100 per cent) case with trisomy 18 and three of four (75 per cent) cases of variant 9 chromosome had low βC-hCG/Cr (≤0·29 MOM). One of five (20 per cent) cases with Down syndrome had elevated βC-hCG/Cr (≤2·83 MOM). Urinary βC-hCG/Cr ratios obtained in the second trimester may be useful for improved detection efficiency of Down syndrome, trisomy 18, and inversion of chromosome 9. Second-trimester maternal urinary βC-hCG/Cr should be investigated further as a potential marker for fetal chromosome anomalies.  相似文献   
569.
The photodegradation of the herbicides atrazine and ametryn with visible light in aerated neutral aqueous solutions and 5, 10, 15, 20-tetrakis (2,6-dichloro-3-sulfophenyl) porphyrin or 5, 10, 15, 20-tetrakis (4-sulfophenyl) porphyrin as sensitizers are reported for the first time. Our findings show that the degradation percentage reached 30% for atrazine and 63% for ametryn. The final photoproducts were characterized as dealkylated s-triazines. Photolysis of the pesticides in the presence of a singlet oxygen quencher showed only a minor contribution of this type of mechanism, while a bimolecular quenching reaction between the triplet state of the sensitizer and the pesticides is excluded by flash photolysis studies. It is proposed that the mechanism may involve the formation of a superoxide radical anion from the triplet state of the sensitizer and molecular oxygen, followed by a radical decomposition pathway. Selected article from 1st International Meeting on Photochemistry, Photocatalysis and Environmental Applications, Agadir, 2006, organised by Prof. Dr. Ait Ichou, University Ibn Zohr, Agadir, Morocco  相似文献   
570.
Here, we show a fast and sensitive method for the determination of inorganic arsenic in natural waters using differential pulse cathodic stripping voltammetry. All the arsenite determinations were done in 2.0 mol L−1 HCl + 3.15 × 10−4 mol L−1 Cu(II) supporting electrolyte. 1 × 10−3 mol L−1 sodium thiosulphate was used as As(V) reducing agent. The detection limit was 0.5 μg L−1 for both species. The method has been applied to water samples collected in an arsenic-contaminated region of Brazil, in particular, to verify the efficiency of the solar oxidation and removal of arsenic process applied to these waters.  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