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   21497篇
  免费   364篇
  国内免费   390篇
安全科学   801篇
废物处理   951篇
环保管理   3705篇
综合类   3267篇
基础理论   5400篇
环境理论   11篇
污染及防治   5508篇
评价与监测   1272篇
社会与环境   1164篇
灾害及防治   172篇
  2023年   101篇
  2022年   177篇
  2021年   205篇
  2020年   204篇
  2019年   193篇
  2018年   342篇
  2017年   334篇
  2016年   498篇
  2015年   413篇
  2014年   537篇
  2013年   1881篇
  2012年   747篇
  2011年   1087篇
  2010年   829篇
  2009年   927篇
  2008年   1035篇
  2007年   1090篇
  2006年   913篇
  2005年   739篇
  2004年   779篇
  2003年   725篇
  2002年   679篇
  2001年   712篇
  2000年   601篇
  1999年   401篇
  1998年   275篇
  1997年   288篇
  1996年   281篇
  1995年   332篇
  1994年   262篇
  1993年   265篇
  1992年   243篇
  1991年   223篇
  1990年   224篇
  1989年   217篇
  1988年   180篇
  1987年   168篇
  1986年   193篇
  1985年   182篇
  1984年   229篇
  1983年   193篇
  1982年   206篇
  1981年   202篇
  1980年   166篇
  1979年   165篇
  1978年   115篇
  1977年   108篇
  1975年   102篇
  1974年   97篇
  1972年   102篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
351.
Parental decisions concerning the continuation of pregnancy following prenatal detection of abnormal chromosomes were evaluated for 80 patients whose diagnosis and prenatal counselling were performed in our centre. Twenty-two anomalies were diagnosed by chorionic villus sampling (CVS) and 58 by amniocentesis. The severity of the chromosome anomaly and associated ultrasound findings in the first vs. second trimester were correlated with patients' decisions. No difference was found in the likelihood of parental decisions to interrupt or continue a pregnancy between CVS and amniocentesis for either the‘severe’ or the‘questionable’ group of chromosome anomalies. Ninety-three per cent of patients with severe prognosis and 27 per cent with questionable prognosis opted for pregnancy termination (p <0·0001). The association of ultrasound anomalies and termination was highly significant (p< 0·001). The severity of the chromosome anomaly, and, to a lesser extent, the visualization of anomalies on ultrasound were the major determinants of parental decisions to terminate the pregnancy. The diagnosis of an anomaly in the first trimester was no more likely ito lead to a termination of pregnancy than in the second trimester.  相似文献   
352.
In a case of fetal heart failure caused by endocardial fibroelastosis, prenatal echocardiography clearly demonstrated; a thickened endocardium. We therefore suggest that an abnormal endocardium may be detected in utero by ultrasound, thus representing an important clue in the differential diagnosis of fetal nonimmune hydrops and in the evaluation of pregnancies at risk for endocardial fibroelastosis.  相似文献   
353.
IntroductionSincethefirstenvironmentalinputoutputmodel(EIOM)(Cumberland,1966)wasestablishedbyincorporatingenvironmentalfactorsint?..  相似文献   
354.
Fetal urinary concentrations of insulin-like growth factor I (UIGF-I) and binding protein 3 (UIGFBP-3) were determined in patients with prenatal diagnosis of bilateral obstructive uropathy. Patients were retrospectively assigned to three groups, on the basis of outcome: group 1, termination of pregnancies (n = 11) with sonographic evidence of severe oligohydramnios or renal dysplasia, confirmed at histological examination; group 2, patients (n = 10) with postnatal plasma creatinine > 50 μmol/1 at the age of 1 year (1 yr-pCreat); and group 3, patients (n = 16) with 1 yr-pCreat ≤ μmol/1. The results show a significant increase in UIGF-I and UIGFBP-3 in groups 1 (18 159 ± 9083 pg/ml; 2657 ± 669 ng/ml) and 2 (1574 ± 847 pg/ml; 176 ± 50 ng/ml) in comparison with group 3 (35 ± 6 pg/ml; 21 ± 2 ng/ml). UIGF-I and UIGFBP-3 were significantly correlated with postnatal plasma creatinine, and were both sensitive (90 per cent; 80 per cent) and specific (88 per cent; 88 per cent) for prediction of elevated 1 yr-pCreat (>50 μmol/1). Fetal urinary IGF-I and IGFBP-3 are increased in severe fetal bilateral obstructive uropathy, possibly reflecting tubular dysfunction or/and increased synthesis consequent upon fetal kidney injury. Their predictive value for postnatal renal function needs further assessment.  相似文献   
355.
海水和海洋沉积物中总磷的测定   总被引:12,自引:0,他引:12  
系统介绍了海水和海洋沉积物中总磷的测定方法,选用K2S2O8为氧化剂将有关形式的P转化成PO^3-4,连同样品中原有的PO^3-4-起用以抗坏到为还原剂的磷钼蓝法测定。方法的精密度6%,回收率为91%-107%。  相似文献   
356.
Prenatal diagnosis in a pregnancy at risk for a juvenile B1 variant of GM2-gangliosidosis was carried out. The biochemical study of the cultured amniocytes and the affected fetal brain is reported. The results obtained show that the sulphated artificial substrate can be used in the diagnosis of B1 variant, but not the neutral one. The accumulation of GM2-ganglioside in the fetal brain of the B1 juvenile form and an infantile form of GM2-gangliosidosis (0 variant) was compared.  相似文献   
357.
358.
359.
360.
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