全文获取类型
收费全文 | 50905篇 |
免费 | 560篇 |
国内免费 | 426篇 |
专业分类
安全科学 | 1644篇 |
废物处理 | 2189篇 |
环保管理 | 6944篇 |
综合类 | 7934篇 |
基础理论 | 13950篇 |
环境理论 | 28篇 |
污染及防治 | 12731篇 |
评价与监测 | 3269篇 |
社会与环境 | 2857篇 |
灾害及防治 | 345篇 |
出版年
2022年 | 405篇 |
2021年 | 441篇 |
2020年 | 305篇 |
2019年 | 402篇 |
2018年 | 735篇 |
2017年 | 738篇 |
2016年 | 1101篇 |
2015年 | 877篇 |
2014年 | 1313篇 |
2013年 | 4014篇 |
2012年 | 1601篇 |
2011年 | 2193篇 |
2010年 | 1814篇 |
2009年 | 1876篇 |
2008年 | 2231篇 |
2007年 | 2243篇 |
2006年 | 2044篇 |
2005年 | 1762篇 |
2004年 | 1729篇 |
2003年 | 1616篇 |
2002年 | 1588篇 |
2001年 | 1947篇 |
2000年 | 1374篇 |
1999年 | 869篇 |
1998年 | 685篇 |
1997年 | 680篇 |
1996年 | 726篇 |
1995年 | 798篇 |
1994年 | 691篇 |
1993年 | 635篇 |
1992年 | 654篇 |
1991年 | 627篇 |
1990年 | 592篇 |
1989年 | 633篇 |
1988年 | 542篇 |
1987年 | 467篇 |
1986年 | 450篇 |
1985年 | 464篇 |
1984年 | 484篇 |
1983年 | 503篇 |
1982年 | 526篇 |
1981年 | 432篇 |
1980年 | 368篇 |
1979年 | 406篇 |
1978年 | 343篇 |
1977年 | 288篇 |
1976年 | 285篇 |
1975年 | 292篇 |
1973年 | 301篇 |
1972年 | 300篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
821.
Finn Stener Jørgensen MD 《黑龙江环境通报》1995,15(5):419-429
The aim of the study was to describe the opinion of pregnant women who had accepted or declined an alpha-fetoprotein (AFP) test, not only on AFP screening in general, but also on whether every pregnant woman should be offered amniocentesis (AC)/chorionic villus sampling (CVS) and an ultrasound scan for fetal malformations. An additional aim was to describe pregnant women's attitudes concerning continued research in the prenatal field. The study was performed as a questionnaire study in two regions over a 1-year period from 1 October 1988 to 30 September 1989. Results are based on answers from 3331 women who had taken an AFP test and 336 women who had declined the offer of a test. A total of 79 per cent of the women thought that an AFP test, 70 per cent that an ultrasound scan for fetal malformations, and 26 per cent that AC or CVS should be offered to all pregnant women. Fifty-nine per cent of the women were positive towards continued research in the prenatal field. Women who had had an AFP test were generally much more positive towards screening and research than women who had declined, who were generally against. Women who had left school without a high school degree were on average more positive towards the screening issues than women who had this degree. In conclusion, the results obtained in this study strongly suggest that women's attitudes are very dependent on how the prenatal screening programme is already organized in their local area. 相似文献
822.
Yun-Ling Zheng Maryann Demaria Dongkai Zhen Theresa J. Vadnais Diana W. Bianchi MD 《黑龙江环境通报》1995,15(10):897-905
Monoclonal antibody to fetal haemoglobin (a2γy2) has been proposed as a fetal-specific reagent. We developed an intracellular staining protocol that combines fluorescein isothiocyanate or phycoerythrin conjugated anti-γ with the DNA binding dye Hoechst 33342 to identify and flow sort fetal erythroblasts from maternal blood. Our preliminary observations on anti-γ-positive cells sorted from four different pregnant women are described here, using fluorescence in situ hybridization (FISH) with chromosome-specific probes to identify fetal cells. Our data demonstrate that far fewer candidate fetal cells are sorted with this protocol than by current cell surface staining methods that employ the monoclonal antibody CD71. This results in increased fetal cell sorting purities. With this protocol, standard FISH techniques require modification due to the rigorous fixation with 4 per cent paraformaldehyde. Our initial data indicate the promise of this approach. 相似文献
823.
Vanessa M. Barnabei MD PhD David A. Krantz James N. Macri John W. Larsen Jr 《黑龙江环境通报》1995,15(12):1131-1134
We have applied our multimarker approach of maternal serum alpha-fetoprotein (AFP) and free-beta human chorionic gonadotropin (hCG) for Down syndrome screening to multiple gestations to assess its efficacy for improved detection of twin and triplet pregnancies. This study matched 225 cases of twin pregnancy and 39 cases of triplet pregnancy each with ten singleton pregnancies based on gestational week, race, time to receive sample, time of year of sample, and geographical area. The ratios of the MOM for each group at the tenth, 50th, and 90th percentiles were compared by the Wilcoxon test. Risks for twins were calculated using Bayes' rule, the age-related incidence of twins, and the levels of AFP and free-beta hCG. The tenth, 50th, and 90th percentiles of free-beta hCG MOMs in twin and triplet cases were 0.85, 1.99, and 4.51, and 1.38, 2.78, and 4.07, respectively. For AFP, the MOMs at these percentiles were 1.26, 1.91, and 2.99, and 2.02, 2.68, and 5.30, respectively. The twin and triplet distributions for each marker were statistically significantly different from the singleton distributions (P<0.0001) and from each other (P=0.0012). At a twin risk cut-off of 1 in 50, 77.4 per cent of all twin gestations can be detected in a second-trimester AFP and free-beta hCG screening protocol with 5.1 per cent of singleton pregnancies falsely identified as at risk for twins. Our dual marker protocol for mid-trimester pregnancy screening combining AFP and free-beta hCG can identify over 77 per cent of twin pregnancies in women less than 35 years of age. This benefit may contribute to an improved outcome of pregnancy by early detection of multiple gestation. 相似文献
824.
825.
826.
827.
Maternal serum alpha-fetoprotein (AFP) and beta-human chorionic gonadotropin (βhCG) measurements taken prior to chorionic villus sampling (CVS) in 21 patients who subsequently miscarried were compared with measurements in a control group of 113 patients with uneventful pregnancies. Patients with AFP levels of 10 iu/ml or more prior to the CVS had a 4·3 times greater risk of miscarriage (95 per cent confidence interval 1·3–13·6). AFP levels obtained 1 week after the CVS in the 13 patients with late miscarriages were higher than in the control group (P = 0·06). Patients miscarrying had a greater rise in AFP (P = 0·06) and a greater fall in βhCG levels (P = 0·04) following the CVS procedure, compared with the control subjects. Each 10-unit change in the difference between AFP or βhCG levels prior to and 1 week following the CVS was associated with a significantly increased risk for late miscarriage. Elevated maternal serum AFP levels early in pregnancy and changes in AFP and βhCG levels following CVS may predict an increased risk for subsequent miscarriage. 相似文献
828.
829.
830.