全文获取类型
收费全文 | 20775篇 |
免费 | 241篇 |
国内免费 | 121篇 |
专业分类
安全科学 | 555篇 |
废物处理 | 897篇 |
环保管理 | 2803篇 |
综合类 | 3392篇 |
基础理论 | 5844篇 |
环境理论 | 10篇 |
污染及防治 | 5343篇 |
评价与监测 | 1295篇 |
社会与环境 | 865篇 |
灾害及防治 | 133篇 |
出版年
2021年 | 138篇 |
2019年 | 130篇 |
2018年 | 235篇 |
2017年 | 253篇 |
2016年 | 408篇 |
2015年 | 313篇 |
2014年 | 478篇 |
2013年 | 1609篇 |
2012年 | 589篇 |
2011年 | 826篇 |
2010年 | 672篇 |
2009年 | 670篇 |
2008年 | 840篇 |
2007年 | 879篇 |
2006年 | 769篇 |
2005年 | 666篇 |
2004年 | 653篇 |
2003年 | 633篇 |
2002年 | 616篇 |
2001年 | 771篇 |
2000年 | 579篇 |
1999年 | 327篇 |
1998年 | 265篇 |
1997年 | 278篇 |
1996年 | 284篇 |
1995年 | 332篇 |
1994年 | 305篇 |
1993年 | 286篇 |
1992年 | 278篇 |
1991年 | 278篇 |
1990年 | 294篇 |
1989年 | 278篇 |
1988年 | 250篇 |
1987年 | 242篇 |
1986年 | 223篇 |
1985年 | 201篇 |
1984年 | 256篇 |
1983年 | 210篇 |
1982年 | 273篇 |
1981年 | 220篇 |
1980年 | 184篇 |
1979年 | 202篇 |
1978年 | 185篇 |
1977年 | 153篇 |
1976年 | 138篇 |
1975年 | 143篇 |
1974年 | 161篇 |
1973年 | 162篇 |
1972年 | 148篇 |
1971年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
Defense Mechanisms of Arthropods, no. 96; no. 95: Eisner et al.: Chemoecology (in press) 相似文献
54.
55.
Five cases of mosaicism for an isochromosome of 20q have been detected from a total of 50 000 cases analysed for prenatal diagnosis by amniocentesis. Karyotypes were designated mos 46,X_/46,X_,i(20q). In all cases, the abnormal cell line was detected in more than one primary culture, thus fulfilling the criterion for true (level III) mosaicism. Indications for prenatal diagnosis were parental anxiety (two cases), low maternal serum alpha-fetoprotein (AFP) (two cases), and high maternal serum AFP (one case). Level II ultrasounds on all five fetuses were normal, and the abnormal cell line was never detected in fetal blood and/or cord blood. All five pregnancies were continued and had normal outcomes, with birth weights ranging from 2.4 to 3.8 kg. The development of all five children has been normal, with the oldest child in the study now 4 years of age. We suggest that the abnormal cell line in each case was of extrafetal origin, and that this may be one of the more common examples of this phenomenon, occurring in approximately 1/10000 prenatal diagnoses. Mosaicism i(20q) may have been missed in the past because of the higher resolution necessary to detect this subtle change. 相似文献
56.
Dr Alan E. Donnenfeld Larry R. Glazerman Denise M. Cutillo Ronald J. Librizzi Stuart Weiner 《黑龙江环境通报》1989,9(5):301-308
Selective termination by intracardiac potassium chloride injection was performed in twins discordant for hydrocephaly at 20 weeks' gestation. Because of the potential for vascular anastomoses to exist between the twins, fetal angiography was performed prior to the selective termination procedure. Determination of vascular connections between the fetuses was hindered by fetal bradycardia following intracardiac administration of contrast material. Selective termination was performed without difficulty using intracardiac potassium chloride (KCl) to produce asystole in the twin with hydrocephaly. The unaffected fetus appeared active and had a normal heart rate during and immediately after the procedure. However, both twins were found to have died the following day. Pathologic examination documented several vascular anastomoses between the monochorionic, diamniotic fetuses. A likely cause of death was exsanguination of the normal twin into the abnormal one. This case illustrates the difficulties encountered in selective termination of monozygotic twins and, to our knowledge, represents the first reported use of intrauterine fetal angiography. 相似文献
57.
58.
Cynthia J. Sims MD Don T. Fujito Dennis R. Burholt Josef Dadok Harlan R. Giles D. Allan Wilkinson 《黑龙江环境通报》1993,13(6):473-480
We have investigated the ability of high-resolution proton NMR spectroscopy to provide a biochemical constituent screening of human amniotic fluid (AF). Proton NMR spectra were obtained at 300 MHz on AF from patients undergoing amniocentesis in the mid-trimester. Only AF from normal pregnancies (normal fetal karyotype, normal a-fetoprotein levels, normal birth outcome) was used in this study. The AF supernatant was lyophilized and resuspended in deuterated water containing 0.1 mm phosphate buffer and 6.02 mm disodium maleate. Identification of low molecular weight compounds was confirmed by two-dimensional NMR spectra (primarily correlated spectroscopy, or COSY) and standard addition techniques. A broad profile of compounds were ‘NMR visible’ in a single proton spectrum, including creatinine, glucose, organic acids (acetate, citrate, and lactate) and several amino acids (alanine, histidine, leucine, phenylalanine, tyrosine and valine). The proton spectrum was unaffected by prior freezing/thawing of AF samples. We were able to quantify compounds by comparison with an added concentration standard (maleate) at concentrations as low as 30 μm. Good agreement with literature values based on other analytical techniques was obtained. 相似文献
59.
60.