全文获取类型
收费全文 | 30143篇 |
免费 | 764篇 |
国内免费 | 4777篇 |
专业分类
安全科学 | 1439篇 |
废物处理 | 1559篇 |
环保管理 | 3555篇 |
综合类 | 9795篇 |
基础理论 | 6604篇 |
环境理论 | 13篇 |
污染及防治 | 9086篇 |
评价与监测 | 1475篇 |
社会与环境 | 1467篇 |
灾害及防治 | 691篇 |
出版年
2023年 | 278篇 |
2022年 | 740篇 |
2021年 | 640篇 |
2020年 | 536篇 |
2019年 | 503篇 |
2018年 | 772篇 |
2017年 | 818篇 |
2016年 | 938篇 |
2015年 | 1035篇 |
2014年 | 1422篇 |
2013年 | 2694篇 |
2012年 | 1630篇 |
2011年 | 2092篇 |
2010年 | 1520篇 |
2009年 | 1617篇 |
2008年 | 1726篇 |
2007年 | 1586篇 |
2006年 | 1391篇 |
2005年 | 1096篇 |
2004年 | 1004篇 |
2003年 | 1010篇 |
2002年 | 931篇 |
2001年 | 1006篇 |
2000年 | 879篇 |
1999年 | 723篇 |
1998年 | 540篇 |
1997年 | 545篇 |
1996年 | 522篇 |
1995年 | 530篇 |
1994年 | 390篇 |
1993年 | 365篇 |
1992年 | 288篇 |
1991年 | 276篇 |
1990年 | 243篇 |
1989年 | 236篇 |
1988年 | 200篇 |
1987年 | 153篇 |
1986年 | 178篇 |
1985年 | 154篇 |
1984年 | 199篇 |
1983年 | 157篇 |
1982年 | 181篇 |
1981年 | 160篇 |
1980年 | 131篇 |
1979年 | 149篇 |
1978年 | 94篇 |
1977年 | 99篇 |
1975年 | 88篇 |
1974年 | 93篇 |
1972年 | 96篇 |
排序方式: 共有10000条查询结果,搜索用时 648 毫秒
251.
采用温压技术制备铁基粉末冶金材料,研究了干混和湿混两种聚合物添加剂加入方式及压制温度对生坯和烧结体性能的影响,并对其作用机理进行了探讨.试验结果表明,干混混合粉生坯及烧结体的性能略高于湿混混合粉生坯及烧结体的性能,但前者的最佳压制温度范围略高. 相似文献
252.
253.
区域水环境生物学评价浅析 总被引:1,自引:0,他引:1
本文论述了辽河三角洲区域地面水系浮游植物的种类分布,根据调查获得的生态学资料,探讨了其群落结构特征及其与水体环境质量的关系,运用“Shannon—Weaver多样性指数法”对区域水体质量进行了分类评价,并研究了浮游植物的多样性指数与水质理化污染指标之间的关系. 相似文献
254.
地铁环境振动预测方法浅析 总被引:15,自引:0,他引:15
简要介绍了国内外关于地铁环境振动预测方法的研究概况,在作者研究分析地铁振动传播途径和主要影响参数基础上,给出了简单定量预测地铁环境振动程度之方法,应用该方法所得到的预测值,与现场实测值误差在±2dB范围内. 相似文献
255.
在市场经济条件下,对符合法定条件的排污许可证应当允许其有偿转让。可转让的排污许可证必须以污染物申报登记为基础,以污染物总量控制为前提,以环境标准为依据,转让活动应当在政府严格监督下进行。可转让排污许可证制度通过市场机制和价值规律必将有效地促进污染防治。 相似文献
256.
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
257.
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
258.
259.
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
260.