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   12587篇
  免费   111篇
  国内免费   93篇
安全科学   357篇
废物处理   458篇
环保管理   1855篇
综合类   2163篇
基础理论   3262篇
环境理论   7篇
污染及防治   3173篇
评价与监测   788篇
社会与环境   639篇
灾害及防治   89篇
  2022年   106篇
  2021年   102篇
  2020年   83篇
  2019年   95篇
  2018年   166篇
  2017年   146篇
  2016年   234篇
  2015年   198篇
  2014年   272篇
  2013年   978篇
  2012年   369篇
  2011年   520篇
  2010年   434篇
  2009年   502篇
  2008年   554篇
  2007年   553篇
  2006年   493篇
  2005年   439篇
  2004年   382篇
  2003年   392篇
  2002年   380篇
  2001年   483篇
  2000年   361篇
  1999年   216篇
  1998年   145篇
  1997年   171篇
  1996年   174篇
  1995年   202篇
  1994年   203篇
  1993年   165篇
  1992年   142篇
  1991年   180篇
  1990年   168篇
  1989年   168篇
  1988年   124篇
  1987年   122篇
  1986年   126篇
  1985年   100篇
  1984年   123篇
  1983年   121篇
  1982年   127篇
  1981年   121篇
  1980年   99篇
  1979年   123篇
  1978年   81篇
  1977年   78篇
  1976年   70篇
  1975年   80篇
  1973年   74篇
  1972年   70篇
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
191.
A fetus with multiple structural defects was seen at prenatal ultrasound examination. After termination of the pregnancy a bilateral cleft lip, alveolus, and palate; micrognathia; and webbed joints were seen. Fetal tissues showed indications of infection, intranuclear inclusion bodies, chronic stress, haemolysis, arterial wall damage, and profuse haemorrhage. Parvovirus B19 DNA was detected in fetal tissues by dot hybridization after polymerase chain reaction. The possibility of parvovirus B19 infection leading to congenital malformations is discussed.  相似文献   
192.
We present a remarkable chain of events in which percutaneous umbilical cord sampling was performed in an attempt to clarify a situation of possible fetal sex chromosome mosaicism in an amniotic fluid culture and led to the discovery that the mother herself had a 45,X/46,XX/ 47.XXX chromosome constitution. This may have simply represented the chance concurrence of pseudo-mosaicism in the amniotic fluid culture of a woman with an abnormal sex chromosome constitution, but it is also possible that the 45,X colony was maternal in origin. Although clearly a most unusual circumstance, the possibility should be kept in mind when termination of a pregnancy is being considered because of apparent mosaicism in a prenatal diagnostic study.  相似文献   
193.
194.
195.
The sinusoidal fetal heart rate pattern has been described in association with severe fetal anaemia, with fetal hypoxaemia, and with the administration of parenteral narcotics. Here, we report a case of decreased fetal movement in which a sinusoidal tracing was recorded. The sonographic diagnosis of a massive fetal intracranial haemorrhage was made. A non-interventive approach was taken and the fetus died soon after in utero. We review 28 previous cases in which the prenatal sonographic diagnosis of fetal intracranial haemorrhage was made, including the underlying maternal and fetal factors and neonatal outcomes. We propose that the sinusoidal tracing in this case was due to the intracranial bleed and suggest that fetal intracranial haemorrhage be considered in the sonographic evaluation of the fetus with a sinusoidal pattern.  相似文献   
196.
We report two cases of apparently balanced complex de novo chromosomal rearrangements (BCCR) detected prenatally at 17 weeks and 10 weeks of gestation, respectively. Chromosomes were studied using GTG-banding and fluorescent in situ hybridization (FISH). In one case four chromosomes and in the other case three chromosomes were involved in the rearrangements. One of the pregnancies was terminated and no external or internal abnormalities were detected at autopsy. The other pregnancy continued to term. Level III ultrasound examination showed no abnormalities. The child is now 3 years old and has neither congenital anomalies nor evidence of delayed psychomotor development.  相似文献   
197.
198.
199.
In a retrospective survey, the incidence of neural tube defects in liveborn trimsomy 18 was found to be 6·2 per cent. Based on these data one would expect to find trisomy 18 in 1 of the 117 patients with myeloidysplasia; the incidence of trisomy 18 in dysraphic fetuses would be anticipated to be higher. These observations underscore the need for amniocentesis karyotyping of fetuses with neural tube defects, and the importance of careful examination of infants born with neural tube defects.  相似文献   
200.
Long-term copper smelting in the Anaconda and Deer Lodge Valley area of Montana has resulted in an extensive area of trace element contamination. Aerial extent of contamination is generally established, but total analysis of soils does not correlate to relative degree of impact on vegetation growth. Three pedons (Beaverell, Cetrack and Judco) were analyzed by routine soil characterization methods, aqua regia microwave digestion, sequential chemical extraction, and X-ray diffraction analysis with the objective of providing a better understanding of chemical forms and potential reactivity of selected trace elements (Cd, Co, Cr, Cu, Hg, Mn, Ni, P, Pb). Surface horizons of soils are more acidic than subsoils, with pH for all horizons ranging from 4.0 to 8.7. Beaverell is the most contaminated in the upper 20 cm with the sum of total extractable (SUMTE) trace elements by microwave digestion ranging from 1836 to 3605 mg kg−1, largest H2O-soluble (WS) and exchangeable (EX) fractions (e.g. 1.6 and 9.3%, respectively), and smallest residual (RES) fraction (e.g. 14.3%). Cetrack has greater SUMTE elements than Judco, though a lower WS+EX fraction due to the effects of alkaline pH, carbonates and high P. Oxide (OX), organic matter/sulfide (OM/S), and RES fractions predominate over WS, EX, and specially-sorbed/carbonate-bound fractions (SS/CAR) for all horizons. Copper, Zn, Pb and Cd are elevated in surface over subsurface horizons in these latter fractions, indicating these elements were anthropogenic additions. X-ray data indicate that Pb, Cu, Cr and Cd partially exists as both OX and sulfide mineral forms.  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