全文获取类型
收费全文 | 30493篇 |
免费 | 413篇 |
国内免费 | 499篇 |
专业分类
安全科学 | 941篇 |
废物处理 | 1288篇 |
环保管理 | 4107篇 |
综合类 | 5234篇 |
基础理论 | 8133篇 |
环境理论 | 11篇 |
污染及防治 | 7824篇 |
评价与监测 | 1869篇 |
社会与环境 | 1787篇 |
灾害及防治 | 211篇 |
出版年
2022年 | 269篇 |
2021年 | 249篇 |
2020年 | 271篇 |
2019年 | 240篇 |
2018年 | 440篇 |
2017年 | 472篇 |
2016年 | 680篇 |
2015年 | 557篇 |
2014年 | 809篇 |
2013年 | 2413篇 |
2012年 | 1031篇 |
2011年 | 1446篇 |
2010年 | 1175篇 |
2009年 | 1227篇 |
2008年 | 1374篇 |
2007年 | 1457篇 |
2006年 | 1206篇 |
2005年 | 1021篇 |
2004年 | 1030篇 |
2003年 | 986篇 |
2002年 | 931篇 |
2001年 | 1165篇 |
2000年 | 887篇 |
1999年 | 517篇 |
1998年 | 349篇 |
1997年 | 396篇 |
1996年 | 400篇 |
1995年 | 503篇 |
1994年 | 433篇 |
1993年 | 388篇 |
1992年 | 379篇 |
1991年 | 356篇 |
1990年 | 361篇 |
1989年 | 341篇 |
1988年 | 284篇 |
1987年 | 269篇 |
1986年 | 285篇 |
1985年 | 276篇 |
1984年 | 309篇 |
1983年 | 274篇 |
1982年 | 271篇 |
1981年 | 256篇 |
1980年 | 224篇 |
1979年 | 253篇 |
1978年 | 184篇 |
1977年 | 192篇 |
1975年 | 156篇 |
1974年 | 167篇 |
1973年 | 169篇 |
1972年 | 166篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
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
103.
104.
M. Blunck W. -D. Busse G. Meister E. Möller A. Mullen L. A. A. van Rooijen 《Die Naturwissenschaften》1989,76(3):96-98
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur. 相似文献
105.
106.
Climate change and temperature-dependent biogeography: oxygen limitation of thermal tolerance in animals 总被引:2,自引:0,他引:2
Pörtner HO 《Die Naturwissenschaften》2001,88(4):137-146
Recent years have shown a rise in mean global temperatures and a shift in the geographical distribution of ectothermic animals. For a cause and effect analysis the present paper discusses those physiological processes limiting thermal tolerance. The lower heat tolerance in metazoa compared with unicellular eukaryotes and bacteria suggests that a complex systemic rather than molecular process is limiting in metazoa. Whole-animal aerobic scope appears as the first process limited at low and high temperatures, linked to the progressively insufficient capacity of circulation and ventilation. Oxygen levels in body fluids may decrease, reflecting excessive oxygen demand at high temperatures or insufficient aerobic capacity of mitochondria at low temperatures. Aerobic scope falls at temperatures beyond the thermal optimum and vanishes at low or high critical temperatures when transition to an anaerobic mitochondrial metabolism occurs. The adjustment of mitochondrial densities on top of parallel molecular or membrane adjustments appears crucial for maintaining aerobic scope and for shifting thermal tolerance. In conclusion, the capacity of oxygen delivery matches full aerobic scope only within the thermal optimum. At temperatures outside this range, only time-limited survival is supported by residual aerobic scope, then anaerobic metabolism and finally molecular protection by heat shock proteins and antioxidative defence. In a cause and effect hierarchy, the progressive increase in oxygen limitation at extreme temperatures may even enhance oxidative and denaturation stress. As a corollary, capacity limitations at a complex level of organisation, the oxygen delivery system, define thermal tolerance limits before molecular functions become disturbed. 相似文献
107.
The abundance patterns of ant communities were monitored with pitfall traps during 14 weeks in four northern California, dry farmed, apple orchards: an abandoned orchard undisturbed for 25 years, two ‘organically’ managed orchards, one with a cover crop of bell beans (Vicia faba) and grasses and the other kept clean of cover by discing, and a ‘commercial’ clean cultivated orchard sprayed with organophosphate insecticides. Six species of ants coexisted in the abandoned orchard, whereas only two species were found in the managed orchards. In both the organic and sprayed, clean cultivated systems, ants were more abundant in the orchard edges than in the vegetation-free centers. This trend was not apparent in the abandoned or organic cover orchards, where plant diversity in the center was similar to that of the edges. Ant predation on potato tuberworm larvae, Phthorimaea operculella, artificially placed on the orchard floor, declined with the intensity of management and vegetational simplication. A higher incidence of larval removal occurred in the edges than in the centers of the clean cultivated orchards. No noticeable populations of ants were detected on the trees in any of the orchards. Increased vegetational diversity and lack of disturbance appeared to affect ant locomotory activity and foraging efficiency by creating preferred sheltering and feeding sites. 相似文献
108.
P. K. Kuroda 《Die Naturwissenschaften》1983,70(11):536-539
Until recently, scientists believed that the chemical elements were synthesized only in stars. The discovery of the Oklo phenomenon in the Republic of Gabon in 1972 has revealed, however, that a nuclear “fire” had existed on the earth and largescale transmutations of the elements were occurring on our planet 1.7·109 years ago. The formation of natural (or Pre-Fermi) reactors is closely related to the appearance of life on our planet earth. The Pre-Fermi reactors were probably never formed until about 2·109 years ago, when oxygen was injected into the earth's atmosphere by a new generation of living organisms carrying out photosynthesis. 相似文献
109.
110.