全文获取类型
收费全文 | 95801篇 |
免费 | 1246篇 |
国内免费 | 1130篇 |
专业分类
安全科学 | 3950篇 |
废物处理 | 3567篇 |
环保管理 | 14825篇 |
综合类 | 21297篇 |
基础理论 | 27176篇 |
环境理论 | 76篇 |
污染及防治 | 16616篇 |
评价与监测 | 5803篇 |
社会与环境 | 4246篇 |
灾害及防治 | 621篇 |
出版年
2022年 | 837篇 |
2021年 | 853篇 |
2020年 | 675篇 |
2019年 | 882篇 |
2018年 | 1285篇 |
2017年 | 1309篇 |
2016年 | 2262篇 |
2015年 | 1874篇 |
2014年 | 2617篇 |
2013年 | 9276篇 |
2012年 | 2473篇 |
2011年 | 2989篇 |
2010年 | 3429篇 |
2009年 | 3581篇 |
2008年 | 2578篇 |
2007年 | 2390篇 |
2006年 | 2662篇 |
2005年 | 2585篇 |
2004年 | 2865篇 |
2003年 | 2682篇 |
2002年 | 2228篇 |
2001年 | 2476篇 |
2000年 | 2066篇 |
1999年 | 1572篇 |
1998年 | 1393篇 |
1997年 | 1378篇 |
1996年 | 1519篇 |
1995年 | 1620篇 |
1994年 | 1501篇 |
1993年 | 1348篇 |
1992年 | 1340篇 |
1991年 | 1320篇 |
1990年 | 1260篇 |
1989年 | 1231篇 |
1988年 | 1071篇 |
1987年 | 1009篇 |
1986年 | 1007篇 |
1985年 | 1073篇 |
1984年 | 1173篇 |
1983年 | 1183篇 |
1982年 | 1189篇 |
1981年 | 1111篇 |
1980年 | 945篇 |
1979年 | 939篇 |
1978年 | 837篇 |
1977年 | 725篇 |
1976年 | 645篇 |
1975年 | 612篇 |
1973年 | 653篇 |
1972年 | 649篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
51.
F. Pricope Ştefănescu G. Tiţescu I. Cărăuş D. Ureche 《Environmental Chemistry Letters》2003,1(2):149-151
During the artificial reproduction of salmonides, the fecundity can be increased either by improving the viability of spermatozoa,
or by extending the time period during which a roe micropile remains open, thus allowing its fecundation. Practically, this
can be achieved by the use of some fertilising techniques suitable for fish species. Here, we show that the reproduction of
rainbow trout in a 1:1 solution of deuterium-depleted water and distilled water led to a significant increase in survival
of roes during their embryonic development. Moreover, the addition of glucose and fructose into the deuterium-depleted fertilising
solutions led to a further increase in roe survival during embryonic development. The increase in survival is mainly explained
by an increase in the motility of spermatozoa. 相似文献
52.
Large Estimates of Minimum Viable Population Sizes 总被引:2,自引:0,他引:2
53.
54.
55.
56.
57.
58.
A transition zone in the otoliths of orange roughy (Hoplostethus atlanticus) is described where annulus width decreases markedly. For fish sampled at spawning time, the relationship between gonad stage
and the presence or absence of a transition zone is consistent with the hypothesis that this zone marks the onset of maturity,
if allowance is made for some error in gonad staging and identification of the zone. Another data set from a non-spawning
area after the spawning season is not consistent with the hypothesis. However, these latter data are considered less reliable
because of the small size of the fish in the sample and difficulties in determining, outside the spawning season, whether
a fish has been reproductively active. This hypothesis was used to provide estimates of the median age (30 yr) and length
(31 cm) at the onset of maturity for the Chatham Rise, New Zealand population. These estimates are unaffected by the biases
associated with the usual ogive method of estimation.
Received: 27 June 1997 / Accepted: 1 July 1997 相似文献
59.
Jürgen Tomiuk Lutz Bachmann Michael Leipoldt Jörg U. Ganzhorn Reiner Ries Michaela Weis & Volker Loeschcke 《Conservation biology》1997,11(2):491-497
The genetic polymorphism of natural populations of Lepilemur mustelinus ruficaudatus was studied by protein electrophoresis. We sampled blood from 72 individuals from four populations separated by geographic or anthropogenic barriers from southwestern Madagascar. Six out of 22 enzyme loci showed genetic variation with a degree of polymorphism of 0.273. The expected and observed degree of genetic heterozygosity over all loci is similar to that of other primates (He = 0.058, Ho = 0.036). The F-statistics revealed that the four subpopulations were similar with respect to gene structure (FST = 0.065, p = 0.016), but the genotypic structures within subpopulations were inconsistent with random mating. For the total of the four subpopulations the proportion of heterozygous individuals was significantly smaller than expected under random mating (FIS = 0.373, FIT = 0.414, p < 0.01). These results correspond closely to what is expected considering the low migration ability of individuals of L. m ruficaudatus leading to small and rather isolated inbred populations. 相似文献
60.