全文获取类型
收费全文 | 27428篇 |
免费 | 620篇 |
国内免费 | 3273篇 |
专业分类
安全科学 | 1114篇 |
废物处理 | 1278篇 |
环保管理 | 3069篇 |
综合类 | 8147篇 |
基础理论 | 6144篇 |
环境理论 | 12篇 |
污染及防治 | 8079篇 |
评价与监测 | 1534篇 |
社会与环境 | 1454篇 |
灾害及防治 | 490篇 |
出版年
2023年 | 234篇 |
2022年 | 621篇 |
2021年 | 532篇 |
2020年 | 411篇 |
2019年 | 458篇 |
2018年 | 590篇 |
2017年 | 664篇 |
2016年 | 797篇 |
2015年 | 775篇 |
2014年 | 1085篇 |
2013年 | 2433篇 |
2012年 | 1262篇 |
2011年 | 1510篇 |
2010年 | 1197篇 |
2009年 | 1207篇 |
2008年 | 1386篇 |
2007年 | 1297篇 |
2006年 | 1221篇 |
2005年 | 954篇 |
2004年 | 877篇 |
2003年 | 934篇 |
2002年 | 830篇 |
2001年 | 968篇 |
2000年 | 813篇 |
1999年 | 589篇 |
1998年 | 459篇 |
1997年 | 454篇 |
1996年 | 426篇 |
1995年 | 404篇 |
1994年 | 362篇 |
1993年 | 357篇 |
1992年 | 343篇 |
1991年 | 313篇 |
1990年 | 259篇 |
1989年 | 238篇 |
1988年 | 193篇 |
1987年 | 163篇 |
1986年 | 188篇 |
1985年 | 181篇 |
1984年 | 180篇 |
1983年 | 188篇 |
1982年 | 183篇 |
1981年 | 182篇 |
1980年 | 161篇 |
1979年 | 159篇 |
1978年 | 120篇 |
1977年 | 129篇 |
1974年 | 116篇 |
1973年 | 101篇 |
1972年 | 117篇 |
排序方式: 共有10000条查询结果,搜索用时 739 毫秒
691.
The presence and characteristics of a membrane-bound adenylate cyclase from Mytilus galloprovincialis Lmk posterior adductor muscle have been investigated. The enzyme has a Michaelis constant (K
m) of 0.38 mM at 20°C and requires divalent cations (Mg2+/Mn2+) for its activity. Optimal GTP concentrations are between 10-5 and 10-4
M. The non-hydrolizable GTP-analogues GMPpNHp and GTPS increase the activity of the enzyme four- to ten-fold. Sodium fluoride stimulates the enzymatic activity seven- to eight-fold. Forskolin increases the enzymatic activity two- to three-fold. Serotonin stimulates the adenylate cyclase activity in a dose-dependent manner. These experiments were performed with mussels collected from the estuary of Muros, Spain, in 1990. 相似文献
692.
The accumulation of parasites in a fish host is modelled as a function of the total amount of prey consumed. The accumulated parasite load is then expressed as a function of fish length so that the asymptotic growth, L
, of any population of commonly infected fish can be estimated. Estimates of L
are obtained for orange roughy (Hoplostethus atlanticus), albacore tuna (Thunnus alalunga) and the New Zealand southern arrow squid (Nototodarus sloanii). 相似文献
693.
Prey selection by larval weakfish (Cynoscion regalis): the effects of prey size,speed, and abundance
We examined feeding by larval weakfish, Cynoscion regalis (Bloch and Schneider), in laboratory experiments conducted during the 1991 spawning season. under natural conditions weakfish larval development is ca. 3 wk, and we ran separate experiments with larvae of five different ages (5, 8, 11, 14, and 17 d post-hatching). We used two different size classes of rotifers (Brachionus plicatilis) and brine shrimp nauplii (Artemia sp.) as prey organisms. Contrary to results of previous research, weakfish larvae did not select prey based on size alone. When prey abundance was above 100 itemsl-1 weakfish, larvae always chose large rotifers (length = 216 m) over small rotifers (length = 160 m). At 11 d post-hatching, larvae switched their diet from large rotifers to small brine shrimp nauplii (length = 449 m); however, when fed small rotifers and small brine shrimp nauplii the change in diet occurred at 14 d post-hatching. This pattern of selectivity was maintained in each larval age class. Early-stage larvae (5 and 8 d post-hatching) did not feed selectively when prey abundance was less than 100 itemsl-1. Late-stage larvae (17 d post-hatching) fed selectively at abundances ranging from 10 to 10000 items-1. Lwimming speeds of prey items, which ranged from 1 to 6 mms-1, had no consistent effect on prey selection. These results suggest that weakfish larvae are able to feed selectively, that selectivity changes as larvae age, and that selectivity is also influenced by prey abundance. 相似文献
694.
The perturbant effects of four Triton adjuvants, namely Triton X-15, X-35, X-100, and X-114 (alkyl aryl polyether alcohols), on some of the biochemical determinants of membrane integrity were determined under laboratory conditions. Two of these, Triton X-100 and X-114, are currently being assessed as emulsifiers for use in fenitrothion insecticidal formulations. Lemna minor L. plants were exposed to 40 microM (10-25 microg ml(-1) in 965 microg mg(-1) Dowanol (tripropylene glycol methyl ether) carrier solvent) adjuvant for a treatment time period of two weeks. A decrease in the contents of the total phospholipids and a concomitant increase in the contents of the galactolipids were found. No change was observed in the total lipid content. An unsaturation occurred in the fatty acids of the total lipids, phospholipids, and monogalactosyl diacylglycerides. This accounted for a significant decrease in palmitic and stearic acids and a concomitant increase in oleic, linoleic, and linolenic acids when these are compared with the fatty acids in the nontreated control sets. The fatty-acid profile of the digalactosyl diacylglycerides, however, differed only slightly from controls. Membrane-fatty-acid unsaturation suggests the possibility of a desaturase enzyme's being induced by these adjuvants. 相似文献
695.
Little is known about the concentrations, deposition rates, and effects of nitrogenous and sulfurous compounds in photochemical smog in the San Bernardino National Forest (SBNF) in southern California. Dry deposition of NO(3)(-) and NH(4)(+) to foliage of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) was correlated (R = 0.83-0.88) with historical average hourly O(3) concentations at 10 sites across an O(3) gradient in the SBNF. Mean deposition fluxes of NO(3)(-) to ponderosa and Jeffrey pine branches were 0.82 nmol M(-2)s(-1) at Camp Paivika (CP), a high-pollution site, and 0.19 nmol m(-2) s(-1) at Camp Osceola (CAO), a low-pollution site. Deposition fluxes of NH(4)(+) were 0.32 nmol m(-2) s(-1) at CP and 0.17 nmol m(-2) s(-1) at CAO, while mean values for SO(4)(2-) were 0.03 at CP and 0.02 nmol m(-2) s(-1) at CAO. Deposition fluxes to paper and nylon filters were higher in most cases than fluxes to pine branches at the same site. The results of this study suggest that an atmospheric concentration and deposition gradient of N and S compounds occurs along with the west-east O(3) gradient in the SBNF. Annual stand-level dry deposition rates for S and N at CP and CAO were estimated. Further studies are needed to determine if high N deposition loads in the SBNF significantly affect plant/soil nutrient relations, tree health, and the response of ponderosa pine to ozone. 相似文献
696.
697.
The exploration of offshore areas for hydrocarbons has involved new technical and economic considerations and has posed new problems, not the least of which has been the changing relationship between companies and governments. In this article, the authors present an analysis of the different perspectives and policies which emanate from national governments on the one hand and from transnational oil companies on the other. The issues examined include the considerations involved in establishing exploration legislation, post-discovery problems, the impact on revenues of increased production, the interests of companies in developing fields and the overall economic environment within which decisions have to be agreed. 相似文献
698.
Various suggested definitions of the term “traceability” are discussed from the standpoint of proposed adoption and use of the concept by the International Organization of Legal Metrology. 相似文献
699.
Deposition velocities have been determined for corn and soybeans in the first 4–6 weeks of growth in a full-scale study of canopy flow in a wind tunnel. Particles of 1, 5, 10 and 15 μm aerodynamic diameter made of sodium florescein were injected into the Environmental Wind Tunnel Facility at Colorado State University. Deposition velocities were determined as a function of free stream velocity (183, 305 and 610 cm/s) and approach flow turbulence intensity (~1% and 8%). Plants were arranged in realistic field configurations. Hot-wire anemometer studies confirmed that the fluid velocity profiles developed in the wind tunnel were similar to the flow realized in canopies in natural fields. An increase in velocity and turbulence intensity was found to decrease the deposition velocities. A minimum deposition velocity was observed at a particle diameter of 5 μm. 相似文献
700.