全文获取类型
收费全文 | 27322篇 |
免费 | 355篇 |
国内免费 | 370篇 |
专业分类
安全科学 | 829篇 |
废物处理 | 1151篇 |
环保管理 | 3388篇 |
综合类 | 4427篇 |
基础理论 | 6761篇 |
环境理论 | 15篇 |
污染及防治 | 7313篇 |
评价与监测 | 1808篇 |
社会与环境 | 2191篇 |
灾害及防治 | 164篇 |
出版年
2023年 | 147篇 |
2022年 | 328篇 |
2021年 | 357篇 |
2020年 | 271篇 |
2019年 | 261篇 |
2018年 | 538篇 |
2017年 | 548篇 |
2016年 | 757篇 |
2015年 | 567篇 |
2014年 | 858篇 |
2013年 | 2190篇 |
2012年 | 1064篇 |
2011年 | 1404篇 |
2010年 | 1041篇 |
2009年 | 1138篇 |
2008年 | 1347篇 |
2007年 | 1400篇 |
2006年 | 1146篇 |
2005年 | 970篇 |
2004年 | 962篇 |
2003年 | 884篇 |
2002年 | 818篇 |
2001年 | 915篇 |
2000年 | 713篇 |
1999年 | 428篇 |
1998年 | 289篇 |
1997年 | 309篇 |
1996年 | 288篇 |
1995年 | 363篇 |
1994年 | 293篇 |
1993年 | 263篇 |
1992年 | 239篇 |
1991年 | 249篇 |
1990年 | 251篇 |
1989年 | 241篇 |
1988年 | 204篇 |
1987年 | 174篇 |
1986年 | 217篇 |
1985年 | 197篇 |
1984年 | 243篇 |
1983年 | 183篇 |
1982年 | 224篇 |
1981年 | 193篇 |
1980年 | 185篇 |
1979年 | 195篇 |
1978年 | 124篇 |
1977年 | 129篇 |
1975年 | 123篇 |
1974年 | 122篇 |
1972年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
231.
Dr Marianne Johansen Marian Knight Edward J. Maher Kim Smith Ian L. Sargent 《黑龙江环境通报》1995,15(10):921-931
Trophoblast deportation is known to occur in normal human pregnancy, but it is not yet clear whether these cells routinely enter the maternal peripheral circulation and are available as a source of fetal DNA for non-invasive prenatal diagnosis of genetic disorders. To resolve this issue requires an efficient method of enriching trophoblast from maternal blood combined with a means to confirm its identity. Five different techniques were tested on ten retroplacental blood samples to determine the most sensitive and operator-efficient method. Lysis of red cells alone gave the best recovery of trophoblast but had to be discounted, together with Ficoll density gradient centrifugation, due to the very low purity and the excessive time required. Fluorescence-activated cell sorting (FACS) of pre-enriched trophoblast resulted in the lowest recovery rate (8 per cent) despite a 3250-fold enrichment and a very high purity. Immunomagnetic beads (Dynabeads) coated with anti-CD 16 antibody proved to be the best method for the subsequent immunocytochemical characterization of deported trophoblast. However, IO beads coated with anti-CD45 antibody may be more useful for isolating trophoblast for prenatal diagnosis due to the high purity, enrichment (32-fold), and recovery rate (78 per cent) obtained with this method. 相似文献
232.
As screening for Down syndrome becomes increasingly sophisticated, it is important to evaluate the newer technologies in terms of their cost-effectiveness. One recent addition to Down syndrome screening programmes is maternal serum unconjugated oestriol (uE3), especially when used in conjunction with maternal serum α-fetoprotein and human chorionic gonadotropin. Using assumptions used in a California proposal to justify an expanded screening programme for Down syndrome, we calculated both the average and the incremental cost-effectiveness of adding uE3. Using the base case assumptions, including an $8 fee for the uE3, the incremental cost-effectiveness of adding uE3 to the proposed California programme is $119 100 per case detected, a value that compares favourably with other Down syndrome screening programmes. The sensitivity analysis supports this conclusion over a wide range of assumptions. However, because of the uncertainty with some key data, it is still too early to fully support the inclusion of uE3 in Down syndrome screening programmes. 相似文献
233.
Ellen Sidransky Susan H. Black Dawn M. Soenksen Shirley L. Jones Andrew D. Dorfmann Joseph D. Schulman MD 《黑龙江环境通报》1990,10(9):583-586
Chorionic villus sampling (CVS) with either transcervical catheters or transabdominal needles is a widely-accepted method for prenatal diagnosis. However, there exists a small subset of patients in whom sampling is difficult or impossible with either route because of individual anatomic variations. A new method of chorionic villus biopsy has been developed to circumvent these problems, utilizing transvaginal chorionic needle aspiration guided by an intravaginal ultrasound probe. This technique was performed successfully in 15 patients in whom villi could not be obtained by either of the conventional methods. This method now makes CVS possible in essentially all women regardless of their uterine anatomy or placental placement; it may also prove useful for very early chorionic sampling. 相似文献
234.
Dr. C. Dawn DeLozier-Blanchet Eric Engel Philippe Extermann Béatrice Pastori 《黑龙江环境通报》1988,8(4):281-286
Cytogenetic study of chorionic villi sampled because of advanced maternal age revealed, after overnight culture, an apparently non-mosaic trisomy 7. Amniocentesis showed exclusively normal mitoses, and the pregnancy continued normally. One hundred mitoses from cord blood of the normal newborn revealed a non-mosaic 46,XX complement. No cells with a proven trisomy 7 were found in cultures from either of two biopsies of the morphologically normal placenta, but the peripheral biopsy showed in multiple cultures an abnormal clone: 47,XX, + 20,-2,-21, + t(2;21)(p13;q22). To our knowledge, this is the first case of non-mosaic trisomy 7 detected on CVS which has had follow-up studies of amniotic fluid, cord blood, and term placenta. 相似文献
235.
236.
M. L. Smith O. L. Pellett M. M. J. Cass N. G. Kennaway N. R. M. Buist J. Buckmaster M. Golbus G. S. Spear J. A. Schneider 《黑龙江环境通报》1987,7(1):23-26
The prenatal diagnosis of cystinosis is currently based on the increased amount of free-cystine present in amniotic fluid cells. Amniocyte cultures must be grown for at least 2 weeks to obtain sufficient cells for such measurements. Thus, the diagnosis cannot be made until close to 20 weeks gestational age by this method. We report a case in which chorionic villi were used for direct cystine measurement resulting in the in utero diagnosis of cystinosis at 9 weeks gestational age. The diagnosis was confirmed by the study of cultured chorionic villus cells, and of the 10-week abortus. 相似文献
237.
The prenatal diagnosis of The Turner Syndrome is described at a menstrual age of 12 weeks. Detection of cystic hygroma was followed by vaginal chorionic villous sampling (CVS) which revealed a 45,X karyotype. Early documentation of fetal karyotype in the presence of a cystic hygroma is essential for accurate diagnosis and genetic counselling. 相似文献
238.
Dr Claire Julian-Reynier Genevieve Macquart-Moulin Jean-Paul Moatti Anderson Loundou Yvette Aurran Françoise Chabal Ségolene Aymé 《黑龙江环境通报》1993,13(7):613-627
The objective of this study was to explore women's attitudes towards prenatal diagnosis of trisomy 21 and to examine some of the factors possibly responsible for these attitudes before implementing in real practice serological screening of pregnant women at risk for trisomy 21. We carried out a telephone survey on a representative sample of women who had recently had a normal livebirth delivery in the Marseille district in 1990. The participation rate was 80 per cent and the average age of the mothers was 28-9 years. Among the 514 women interviewed, 78 per cent stated that they would ask for an amniocentesis for a 1 per cent risk of trisomy 21 at their next pregnancy. When adjusting for confounding factors, the decision to have or not to have an amniocentesis was found to depend not only on the women's attitude towards induced abortion, but also on their understanding of the risk involved and on the social context (knowing a handicapped child, discussion with the father). It also depended on the women's age and on what they knew about amniocentesis from the medical point of view. The risk of miscarriage can influence a woman's choice but this objection was not found to affect the women's decisions significantly in our survey. The data showed the existence of a high potential demand for fetal karyotyping. 相似文献
239.
240.