全文获取类型
收费全文 | 6446篇 |
免费 | 590篇 |
国内免费 | 698篇 |
专业分类
安全科学 | 1036篇 |
废物处理 | 168篇 |
环保管理 | 589篇 |
综合类 | 4216篇 |
基础理论 | 392篇 |
环境理论 | 1篇 |
污染及防治 | 336篇 |
评价与监测 | 516篇 |
社会与环境 | 198篇 |
灾害及防治 | 282篇 |
出版年
2024年 | 15篇 |
2023年 | 75篇 |
2022年 | 164篇 |
2021年 | 226篇 |
2020年 | 171篇 |
2019年 | 146篇 |
2018年 | 150篇 |
2017年 | 194篇 |
2016年 | 229篇 |
2015年 | 248篇 |
2014年 | 277篇 |
2013年 | 314篇 |
2012年 | 457篇 |
2011年 | 491篇 |
2010年 | 349篇 |
2009年 | 334篇 |
2008年 | 269篇 |
2007年 | 417篇 |
2006年 | 391篇 |
2005年 | 352篇 |
2004年 | 293篇 |
2003年 | 284篇 |
2002年 | 240篇 |
2001年 | 211篇 |
2000年 | 119篇 |
1999年 | 110篇 |
1998年 | 96篇 |
1997年 | 113篇 |
1996年 | 65篇 |
1995年 | 128篇 |
1994年 | 112篇 |
1993年 | 106篇 |
1992年 | 78篇 |
1991年 | 74篇 |
1990年 | 62篇 |
1989年 | 72篇 |
1988年 | 49篇 |
1987年 | 55篇 |
1986年 | 31篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 22篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 4篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有7734条查询结果,搜索用时 350 毫秒
981.
Maternal serum unconjugated oestriol (uE3) was measured in 15 375 pregnancies during 2 years of second-trimester risk assessment for Down syndrome using biochemical markers. Very low levels of uE3 (<0·1 MOM) were detected in 22 serum samples (0·14 per cent). Very low uE3 was associated with an adverse outcome in 13 pregnancies including fetal death and miscarriage (N=11), anencephaly (N=1), and Meckel—Gruber syndrome (N=1). Dry scales on the skin appeared in the first year of life in four boys. From dermatological diagnosis, prenatal uE3 levels, and pedigree analysis, it is concluded that at least 5 in approximately 7500 male births in the study population are affected by steroid sulphatase deficiency, which is the biochemical defect in X-linked ichthyosis. Very low uE3 levels in the second trimester are indicative of this disease in pregnancies with normal ultrasound findings. 相似文献
982.
E. E. C. Roelofsen L. I. Kamerbeek Tj. Tymstra J. R. Beekhuis A. Mantingh 《黑龙江环境通报》1993,13(8):741-747
We studied the opinions and experiences concerning maternal serum screening of two groups of women: (A) women who were not eligible for prenatal diagnosis; and (B) women for whom prenatal diagnosis was available because of advanced maternal age, and who either underwent chorionic villus sampling or amniocentesis. Many of the women were in favour of the availability of serum screening and would apply for this test in a future pregnancy. This applied also to many respondents who had previously undergone prenatal diagnosis. Most of these women, however, did not intend to decline diagnostic amniocentesis if the screening results did not indicate an increased risk. The majority of the group of respondents of 36 years and over did not consider it acceptable if age indication was dropped altogether. A system based on serum screening will have other implications than a policy based on age indication, since specific individual risk assessment is perceived as being of more significance than a risk statistically derived from age alone. Serum screening is often seen as a means of reassurance and many women are not aware of the possible drawbacks. As technology becomes increasingly complicated, counselling has to be adjusted correspondingly. Further research is needed to establish whether and how distress can be minimized and well-considered individual choice can be achieved. 相似文献
983.
The relative advantages and disadvantages of transabdominal (TA) and transcervical (TC) chorionic villus sampling (CVS) in terms of fetal risks and efficacy were evaluated in a clinical trial conducted on 1194 women randomized at 7–12 weeks' gestation. The results of the study indicate that, if any, the relative risk of fetal loss following either procedure is less than double that of the alternative technique when performed by a skilled operator. Overall, the fetal loss rate (spontaneous abortions following randomization, terminations of pregnancy, and perinatal deaths) is 16.5 and 15.5 per cent, respectively, among women allocated to TA- and TC-CVS. The two procedures are equally effective, although TA-CVS is associated with a significantly lower rate of repeat device insertions; on the other hand, a higher weight of chorionic tissue is obtained, on average, with TC-CVS. Bleeding is more common following TC-CVS, while peritoneal reaction developed only after TA-CVS. No diagnostic problems specifically related to one sampling technique were identified. 相似文献
984.
T. Tønnesen A.-M. Gerdes E. Damsgaard P. Miny W. Holzgreve F. Søndergaard N. Horn 《黑龙江环境通报》1989,9(3):159-165
Chorionic villus samples with copper contents of 1·91, 4·2, 5·6, and 6·3 ng/mg were observed in four cases with male karyotypes. These values were outside the range for unaffected males (0·30–0·85 ng/mg), and three of them were outside the control range (0·20–2·39 ng/mg). But these three values were below the values previously observed for affected Menkes fetuses (12·0–24·8 ng/mg). Follow-up by 64Cu uptake studies on the amniotic fluid cells was performed in three of these cases. A combination of 64Cu uptake and chase experiments on the amniotic fluid cells showed more convincingly than 64Cu uptake per se the direct copper values of 4·2 and 5·6 ng/mg to correspond to affected fetuses. Amniotic fluid cells from the male fetus with the CV copper value of 1·9 ng/mg showed normal results. The CV copper value of 6·3 ng/mg was considered pathognomonic for Menkes disease. The pregnancy was terminated, and the diagnosis was confirmed on fetal fibroblasts. Maternal deciduum prepared from the placentae showed in one of the cases with an affected fetus copper values ranging from 1·5 to 5·7 ng/mg. In six additional diagnostic cases, the copper content was determined in both CV samples and maternal deciduum. In three of these cases with normal CV sample copper, maternal decidua values of 4·85–7·8 ng/mg copper were observed. These results show that maternal deciduum contamination of a CV sample could cause a false-positive diagnosis. 相似文献
985.
This controlled prospective study assesses the relative risks of first trimester chorionic villus sampling (CVS) versus mid-trimester gentic amniocentesis (GA). CVS subjects and amnio-centesis controls were comparable with regard to several confounding variables which might influence the risk of pregnancy loss including maternal age, smoking, alcohol consumption, gestational age at study entry, and history of vaginal bleeding or poor prior reproductive outcome. The most common indication for prenatal diagnosis was advanced maternal age (n = 511). In this subgroup, spontaneous abortion (<24 weeks) occurred in 2·9 per cent of CVS subjects versus 4−3 per cent of amniocentesis controls. The sum of spontaneous and therapeutic abortions (<24 weeks) was identical (5·3 per cent) in both groups. Therefore, intervention in the CVS group (i.e., therapeutic abortion for cytogenetic abnormalities) did not influence the observed risk of pregnancy loss. Overall perinatal mortality rates were also similar in both groups. No significant differences were identified for a number of pregnancy outcome parameters including 5 min Apgar score, birth weight, body length, head circumference, gestational age at delivery, preterm delivery, fetal growth retardation, congenital malformations, and neonatal complications. Preliminary results of this controlled prospective study suggest that chorionic villus sampling carries a low and acceptable risk. 相似文献
986.
A. H. J. T. Bröcker-Vriends M.D. E. Briët H. H. H. Kanhai E. Bakker J. C. F. M. Dreesen N. J. Leschot J. J. P. van de Kamp P. L. Pearson 《黑龙江环境通报》1988,8(6):411-421
We evaluated the feasibility, reliability, and acceptability of prenatal diagnosis of haemophilia A by DNA analysis of chorionic villi. Twenty-two women at risk to transmit the abnormal gene were referred for prenatal diagnosis, two of them twice. Two of the 22 women appeared to be non-carriers by DNA analysis. In one of these women, the results were known only after chorionic villus sampling had been carried out. Thirteen of the twenty carriers were heterozygous for an intragenic (Bell or Xbal) marker; six women were only heterozygous for the extragenic DXS52 (Stl4) locus. One of the women was homozygous for all the presently known DNA markers within or closely linked with the factor VIII locus. Twelve of the 22 fetuses at risk were male, ten were female. Seven of the 12 male fetuses were shown to be affected and were subsequently aborted. Four male fetuses appeared to be not affected. In one case, the diagnosis was made by use of an extragenic marker. The woman rejected fetal blood sampling to confirm the diagnosis. After birth, a normal factor VIII level was found in three of the four cases. The fourth pregnancy is still continuing. In one of the 12 male fetuses, no diagnosis at the gene level was possible. DNA analysis is expected to provide maximum certainty as to the phenotype of the fetus for approximately 60 per cent of the women; for another 37 per cent a rate of misdiagnosis of 4–5 per cent applies. In only 3 per cent of the cases will no diagnosis at the gene level be possible as yet. The new possibility of a prenatal diagnosis in the first trimester of pregnancy enabled some of these women to have a family of their own and was appreciated in particular by the women who underwent fetoscopy in an earlier pregnancy. 相似文献
987.
J. W. Wladimiroff M.D. Ph.D. M. F. Niermeijer J. J. Van Der Harten P. A. Stewart F. G. A. Versteegh W. Blom J. G. M. Huijmans 《黑龙江环境通报》1985,5(1):47-52
Congenital hypophosphatasia is an autosomal recessive disorder, which usually has a fatal outcome during the neonatal period. This report presents the prenatal diagnosis of hypophosphatasia at 16 weeks of gestation. The characteristic ultrasonic findings in this abnormality demonstrate the superiority of ultrasound as compared with radiography. 相似文献
988.
目的 实现炮弹气密性检测及其自动化、智能化设备的开发.方法 提出了一种基于负压法的炮弹气密性检测方法.首先,阐述了负压法气密性检测工作原理和实施流程,并对炮弹检测设备的用例模型和检测设备功能框架进行了讨论.其次,针对工程实际,详细给出了测量腔安装密封性计算、测量腔泄漏的压差泄漏率计算、测量腔的初始测量压力值计算、炮弹气体泄漏量计算等检测算法和判定方法.结果 基于负压法的炮弹气密性检测方法的灵敏度比正压法高.结论 本方法可为实现对全弹的气密性检验提供参考,同时也可促进和指导炮弹气密性检验设备的研制,将有效保障炮弹气密性检验自动化设备开发效率和有效性. 相似文献
989.
990.
离子选择电极法与离子色谱法测量低浓度氟化物比较 总被引:1,自引:0,他引:1
用离子选择电极法、离子色谱法两种方法对氟化物国家标准样品进行测量,通过比较发现两种方法测量国家标样低浓度样品时有显著差异. 相似文献