全文获取类型
收费全文 | 5848篇 |
免费 | 124篇 |
国内免费 | 90篇 |
专业分类
安全科学 | 305篇 |
废物处理 | 261篇 |
环保管理 | 1544篇 |
综合类 | 602篇 |
基础理论 | 1369篇 |
环境理论 | 6篇 |
污染及防治 | 1311篇 |
评价与监测 | 387篇 |
社会与环境 | 210篇 |
灾害及防治 | 67篇 |
出版年
2023年 | 37篇 |
2022年 | 32篇 |
2021年 | 82篇 |
2020年 | 57篇 |
2019年 | 87篇 |
2018年 | 104篇 |
2017年 | 127篇 |
2016年 | 160篇 |
2015年 | 139篇 |
2014年 | 142篇 |
2013年 | 627篇 |
2012年 | 223篇 |
2011年 | 317篇 |
2010年 | 237篇 |
2009年 | 235篇 |
2008年 | 319篇 |
2007年 | 307篇 |
2006年 | 286篇 |
2005年 | 208篇 |
2004年 | 221篇 |
2003年 | 224篇 |
2002年 | 211篇 |
2001年 | 104篇 |
2000年 | 129篇 |
1999年 | 109篇 |
1998年 | 83篇 |
1997年 | 72篇 |
1996年 | 82篇 |
1995年 | 88篇 |
1994年 | 74篇 |
1993年 | 76篇 |
1992年 | 83篇 |
1991年 | 54篇 |
1990年 | 56篇 |
1989年 | 44篇 |
1988年 | 41篇 |
1987年 | 47篇 |
1986年 | 49篇 |
1985年 | 47篇 |
1984年 | 48篇 |
1983年 | 59篇 |
1982年 | 49篇 |
1981年 | 68篇 |
1980年 | 51篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 20篇 |
1976年 | 14篇 |
1975年 | 15篇 |
1971年 | 13篇 |
排序方式: 共有6062条查询结果,搜索用时 140 毫秒
51.
Diana W. Bianchi MD Gretchen K. Zickwolf Melissa C. Yih Alan F. Flint Ossie H. Geifman Marlena S. Erikson John M. Williams 《黑龙江环境通报》1993,13(4):293-300
Fetal nucleated erythrocytes (NRBC) in maternal blood are a non-invasive source of fetal DNA for prenatal genetic screening. We compared the effectiveness of three monoclonal antibodies for the separation of fetal cells from maternal blood by flow sorting. Mononuclear blood cells from 49 healthy pregnant women were incubated with antibody to CD 71, CD 36, and/or glycophorin A (GPA), employed singly or in combination with each other. These monoclonal antibodies recognize surface antigens on haematopoietic precursor cells. Successful isolation of fetal cells was defined as detection of Y chromosomal sequences in maternal blood from women carrying male fetuses, with absence of Y sequences when female fetuses were carried. Thus, gender prediction accuracy was used as a measure of fetal cell separation. Using anti-CD 71 to isolate fetal cells, gender prediction was 57 per cent correct; with anti-CD 36, it was 88 per cent correct. Anti-GPA, an erythrocyte-specific antigen, used alone or in combination with anti-CD 71 or 36, improved gender prediction to 100 per cent. We conclude that antibody to GPA improves the retrieval of fetal NRBC from maternal blood, permitting genetic analysis by the polymerase chain reaction. 相似文献
52.
Data from 2907 transcervical CVS cases performed on singleton pregnancies were reviewed retrospectively and villus sample size was correlated with cytogenetic results, placental location, maternal age at the expected date of confinement (EDC), gestational age at the time of sampling, birth weight, gestational age at the time of delivery, and pregnancy outcome. No correlation was noted between villus sample size and maternal age, gestational age at sampling, gestational age at delivery, birth weight, or pregnancy outcome. An inverse correlation between villus sample size and percentage of abnormal cytogenetic findings was statistically significant (X2 = 8·53, p <0·01). The percentage of small samples was greater when the placenta was anterior, lateral, or fundal than when the placenta was posterior. 相似文献
53.
John C. Eccles 《Die Naturwissenschaften》1979,66(3):147-153
Synaptic plasticity is manifested by long-lasting changes in synaptic potency. Increased potency is of special importance in relation to the neural basis of memory. Even mild repetitive stimulation evokes large and prolonged potentiations of hippocampal synapses, as is revealed by electrical recording either in vivo or in vitro. More importantly there is a matching hypertrophy of the synaptic spines on the dendrites of hippocampal granule cells, as is shown by most convincing electronmicrographs. The increase is to about 40% some 2 h after a mild stimulation (900 impulses) and there was relatively little decline by 23 h. There is brief reference to the metabolic processes that could be involved in this plastic response. 相似文献
54.
Maternal serum CA 125 levels were determined at 9–11 menstrual weeks for 26 cases of trisomy 13 (n = 4), trisomy 18 (n = 7), trisomy 21 (n = 15), and appropriate controls. There were no statistically significant differences between groups. 相似文献
55.
Reverse phase HPLC of radioactive globin chains has been compared to classical carboxy methyl cellulose chromatography for the prenatal diagnosis of β thalassaemia. The two methods correlated highly (r = 0.97 p < 0.0005) and provided an identical diagnosis for 40 fetal blood samples of fetuses homozygous or heterozygous for β thalassaemia. The HPLC procedure was much faster and required fewer biochemical steps (no globin preparation). It was at least as accurate and more sensitive than the classical chromatography. A single column can be used for 150 analyses and is always ready to be used. Last but not least it is much less expensive than CMC chromatography. 相似文献
56.
A Framework for Monitoring and Evaluating Carbon Mitigation by Farm Forestry Projects: Example of a Demonstration Project in Chiapas,Mexico 总被引:1,自引:0,他引:1
De Jong Ben H.J. Tipper Richard Taylor John 《Mitigation and Adaptation Strategies for Global Change》1997,2(2-3):231-246
Mitigation and Adaptation Strategies for Global Change - In Mexico an estimated 4.5 × 106ha are available for farm forestry, while up to 6.1 × 106 ha could be saved from deforestation by... 相似文献
57.
58.
David M. Sherer MD James R. Woods Jr Jacques S. Abramowicz John A. Dipreta Leon A. Metlay Richard Jaffe 《黑龙江环境通报》1993,13(12):1079-1084
Although malignant transformation of fetal cervical teratoma is extremely rare, perinatal morbidity is high and usually related to the size of the tumour, which may compromise fetal swallowing and subsequently lead to upper airway obstruction. We present a case in which mid-trimester serial sonography demonstrated markedly rapid early growth of a lesion of this type between 17 and 19 weeks' gestation indicating the aggressive nature of this tumour, assisting parental decision to terminate the pregnancy. Histopathology confirmed grade 3 immaturity of the lesion. 相似文献
59.
Joe Leigh Simpson James L. Mills George G. Rhoads George C. Cunningham Howard J. Hoffman Mary R. Conley 《黑龙江环境通报》1991,11(8):641-648
No clear answer concerning whether multivitamin/folate supplementation prevents neural tube defects (NTDs) is provided by three studies in the United States. All these studies are occurrence in nature, no recurrence studies having been conducted. The Atlanta Birth Defects Study is subject to pronounced memory and recall biases, the length between event and interview being as long as 16 years. In a second study (Boston University), objections can be raised to certain aspects of the experimental design, and the claim that 22 per cent of women started vitamins sufficiently early after pregnancy diagnosis to influence NTD formation is suspicious. Our NICHD case control study of 541 women in California and Illinois revealed no evidence for multivitamins or folic acid preventing NTDs. U.S. public policy-makers face difficulties in applying results of recurrence or occurrence studies in high-risk areas to low-risk areas in the U.S. 相似文献
60.
Joe C. Rutledge Arthur G. Weinberg Jan M. Friedman Mary Jo Harrod Rigoberto Santos-Ramos 《黑龙江环境通报》1986,6(1):51-61
In utero sonographic diagnoses from forty-five malformed infants were correlated with their autopsy findings. Fifty-two malformations were diagnosed prenatally in 42 of the patients but 90 additional malformations were not. Nine sonographically diagnosed abnormalities were not confirmed at autopsy. Factors compromising sonographic diagnosis included: limited examinations, small fetal size, timing of examination, oligohydramnios, fetal position, nature of the malformation and unfamiliarity of the ultrasonographer with specific malformation syndromes. In vitro ultrasonography is an invaluable tool of diagnosing congenital malformations but has limitations. 相似文献