全文获取类型
收费全文 | 4830篇 |
免费 | 99篇 |
国内免费 | 76篇 |
专业分类
安全科学 | 229篇 |
废物处理 | 235篇 |
环保管理 | 1290篇 |
综合类 | 416篇 |
基础理论 | 1104篇 |
环境理论 | 5篇 |
污染及防治 | 1168篇 |
评价与监测 | 333篇 |
社会与环境 | 176篇 |
灾害及防治 | 49篇 |
出版年
2023年 | 23篇 |
2022年 | 22篇 |
2021年 | 48篇 |
2020年 | 32篇 |
2019年 | 63篇 |
2018年 | 73篇 |
2017年 | 90篇 |
2016年 | 116篇 |
2015年 | 112篇 |
2014年 | 109篇 |
2013年 | 551篇 |
2012年 | 176篇 |
2011年 | 247篇 |
2010年 | 201篇 |
2009年 | 195篇 |
2008年 | 264篇 |
2007年 | 260篇 |
2006年 | 237篇 |
2005年 | 167篇 |
2004年 | 185篇 |
2003年 | 194篇 |
2002年 | 166篇 |
2001年 | 81篇 |
2000年 | 109篇 |
1999年 | 97篇 |
1998年 | 75篇 |
1997年 | 66篇 |
1996年 | 75篇 |
1995年 | 74篇 |
1994年 | 62篇 |
1993年 | 66篇 |
1992年 | 73篇 |
1991年 | 46篇 |
1990年 | 51篇 |
1989年 | 44篇 |
1988年 | 34篇 |
1987年 | 39篇 |
1986年 | 44篇 |
1985年 | 42篇 |
1984年 | 45篇 |
1983年 | 52篇 |
1982年 | 40篇 |
1981年 | 57篇 |
1980年 | 45篇 |
1979年 | 22篇 |
1978年 | 27篇 |
1977年 | 18篇 |
1976年 | 13篇 |
1975年 | 14篇 |
1971年 | 13篇 |
排序方式: 共有5005条查询结果,搜索用时 852 毫秒
581.
582.
John P Dwyer Douglas Wallace David R. Larsen 《Journal of the American Water Resources Association》1997,33(2):481-489
ABSTRACT: Following the Midwest flood of 1993, a study was initiated along a 39-mile segment of the Missouri River to determine if there was an association between woody corridors and levee stability. A systematic sample of levee failures revealed that primary levees which did not fail had a significantly wider woody corridor than failed levees. Analysis of the total inventory of failed levees revealed that as the width of the woody corridor decreased, the length of the levee failure increased. Number of levee failures and their severity of damage could be reduced if woody corridors were at least 300 feet wide. 相似文献
583.
In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of prenatal diagnosis. Each bibliography is divided into 17 sections: 1 Books, Reviews & Symposia; 2 General Interest; 3 Normal Fetal Development; 4 Gametogenesis and Pre-implantation Diagnosis; 5 First Trimester Diagnosis; 6 Second Trimester Diagnosis; 7 Fetal Diagnosis by Ultrasound and Other Imaging; 8 Maternal Screening; 9 Screening for Carriers of Genetic Abnormality; 10 Technological Developments; 11 Confined Placental Mosaicism and Uniparental Disomy; 12 Molecular Cytogenetics; 13 Fetal Cells in Maternal Circulation; 14 Fetal Therapy; 15 Psychosocial Aspects; 16 Epidemiology and Environmental Factors; 17 Developmental Pathology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted 相似文献
584.
585.
586.
Studies of the otariids (fur seals and sea lions), a highly sexually dimorphic group, have provided conflicting evidence of
differential maternal expenditure in male and female offspring and, thus, suggestions that they conform to predictions of
investment theory are equivocal. Since the mid-1970s, a diversity of research on Antarctic fur seals (Arctocephalus gazella) including studies of their reproductive ecology, lactation energetics, and foraging behaviour have been conducted at Bird
Island, South Georgia that have resulted in one of the more complete and diverse data sets for any species of otariid. These
long-term data were reviewed to determine whether there was any evidence to support that differential maternal expenditure
occurred in Antarctic fur seals. Most of the data examined were collected during five consecutive austral summers from 1988
through 1992 and included years in which local food resources were abundant and scarce. We were unable to detect differences
in the sex ratios of pups at birth or sex-biased differences in growth rates estimated from serial data, the number of foraging
trips made, the duration of attendance ashore, diving behaviour, suckling behaviour, or milk consumption in any year and in
the duration of foraging trips or age at weaning in 2 of 3 years. In addition, we found no evidence of greater reproductive
costs between mothers with sons or daughters relative to their reproductive performance the following year. In contrast, sex-biased
differences were only found in the duration of foraging trips in 1990, the age at weaning in 1988, and consistently in growth
rates estimated from cross-sectional data. We suggest that differential maternal expenditure does not occur in Antarctic fur
seals because male pups probably do not gain greater benefit from additional maternal expenditure than female pups. After
weaning, males experience a period of rapid juvenile growth over 3–4 years during which time body mass nearly trebles. This
growth will almost certainly be dependent upon available food resources then rather than on any maternal expenditure received
over the first 4 months of life and, thus, the assumptions of the Trivers and Willard hypothesis are probably invalid for
Antarctic fur seals.
Received: 10 July 1996 / Accepted after revision: 3 March 1997 相似文献
587.
John C. Briggs 《Conservation biology》1996,10(3):713-718
The superior diversity of the tropics is well known and, for the largest marine and continental areas, there appears to be a positive relationship between area and species diversity (richness). There are certain portions of the tropics, however, in which species diversity has reached unusually high levels. Such areas apparently function as centers of evolutionary origin. In the ocean the largest of the four tropical shelf regions is the Indo-West Pacific, which stretches almost two thirds of the distance around the globe. Within that expanse by far the greatest diversity is found within the relatively small East Indies Triangle. From the Triangle an evolutionary radiation has reached many other parts of the marine world. On land the Neotropical, Ethiopian, and Oriental biogeographic regions demonstrate very high levels of species diversity. Various major groups of animals and plants have originated in these regions and subsequently spread to other parts of the world. There is no accepted scientific agreement on a conservation strategy for these areas. By focusing our attention on centers of origin, we can save the areas containing species that apparently have the greatest evolutionary potential. 相似文献
588.
589.
Cliff I. Davidson Chris T. Hendrickson H. Scott Matthews Michael W. Bridges David T. Allen Cynthia F. Murphy Braden R. Allenby John C. Crittenden Sharon Austin 《Journal of Cleaner Production》2010,18(7):698-701
The field of engineering is changing rapidly as the growing global population puts added demands on the earth's resources: engineering decisions must now account for limitations in materials and energy as well as the need to reduce discharges of wastes. This means educators must revise courses and curricula so engineering graduates are prepared for the new challenges as practicing engineers. The Center for Sustainable Engineering has been established to help faculty members accommodate such changes through workshops and new educational materials, including a free access website with peer-reviewed materials. 相似文献
590.
Desorption of PCBs from sediment can significantly affect the ultimate fate and effects of PCBs in aquatic systems. Using a gas purging technique to strip soluble and sorbed polychlorinated biphenyls (PCBs) from solutions and sediment suspensions, Henry's law constants, approach to equilibrium, and desorption rate constants for four PCB congeners were measured. Henry's law constants were on the order of 10−4 m3 atm mole−1. Desorption rate constants measured for a predominantly kaolinitic, low-organic carbon sediment were on the order of 0.03–0.1 days−1. In contrast, desorption rate constants measured for a sediment composed of montmorillonite with a 3% organic carbon content were on the order of 0.009–0.04 days−1. Desorption data suggest that equilibration times for PCBs with low chlorine content are on the order of six weeks, and months to years for PCBs with a significantly higher chlorine content. 相似文献