全文获取类型
收费全文 | 1933篇 |
免费 | 224篇 |
国内免费 | 182篇 |
出版年
2024年 | 9篇 |
2023年 | 42篇 |
2022年 | 19篇 |
2021年 | 34篇 |
2020年 | 59篇 |
2019年 | 86篇 |
2018年 | 89篇 |
2017年 | 78篇 |
2016年 | 71篇 |
2015年 | 93篇 |
2014年 | 92篇 |
2013年 | 161篇 |
2012年 | 96篇 |
2011年 | 84篇 |
2010年 | 74篇 |
2009年 | 88篇 |
2008年 | 76篇 |
2007年 | 110篇 |
2006年 | 92篇 |
2005年 | 89篇 |
2004年 | 57篇 |
2003年 | 70篇 |
2002年 | 85篇 |
2001年 | 64篇 |
2000年 | 56篇 |
1999年 | 62篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 33篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 20篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 14篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 16篇 |
1977年 | 4篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 3篇 |
排序方式: 共有2339条查询结果,搜索用时 15 毫秒
1.
2.
BackgroundComparative evidence on the burden, trend, and risk factors of cancer is limited. Using data from the Global Burden of Disease (GBD) study, we aimed to assess cancer burden – incidence, prevalence, mortality, disability-adjusted life years (DALYs) – and attributable risk factors for Australia between 1990 and 2015, and to compare them with those of 34 members of the Organisation for Economic Co-operation and Development (OECD).MethodsThe general GBD cancer estimation methods were used with data input from vital registration systems and cancer registries. A comparative risk assessment approach was used to estimate the population-attributable fractions due to risk factors.ResultsIn 2015 there were 198,880 (95% uncertainty interval [UI]: 183,908–217,365) estimated incident cancer cases and 47,562 (95% UI: 46,061–49,004) cancer deaths in Australia. Twenty-nine percent (95% UI: 28.2–29.8) of total deaths and 17.0% (95% UI: 15.0–19.1) of DALYs were caused by cancer in Australia in 2015. Cancers of the trachea, bronchus and lung, colon and rectum, and prostate were the most common causes of cancer deaths. Thirty-six percent (95% UI: 33.1–37.9) of all cancer deaths were attributable to behavioral risks. The age-standardized cancer incidence rate (ASIR) increased between 1990 and 2015, while the age-standardized cancer death rate (ASDR) decreased over the same period. In 2015, compared to 34 other OECD countries Australia ranked first (highest) and 24th based on ASIR and ASDR, respectively.ConclusionThe incidence of cancer has increased over 25 years, and behavioral risks are responsible for a large proportion of cancer deaths. Scaling up of prevention (using strategies targeting cancer risk factors), early detection, and treatment of cancer is required to effectively address this growing health challenge. 相似文献
3.
4.
Daphniopsis australis, a new species of cladoceran in Australian salt lakes, is described, and some brief comments on its distribution are given. 相似文献
5.
Analyses of ITS sequences for 49 species of Olearia, including representatives from all currently recognised intergeneric sections, and 43 species from 23 other genera of Astereae,
rooted on eight sequences from Anthemideae, provide no support for the monophyly of this large and morphologically diverse
Australasian genus. Eighteen separate lineages of Olearia are recognised, including seven robust groups. Three of these groups and another eight species are placed within a primary
clade incorporating representatives of Achnophora, Aster, Brachyscome, Calotis, Camptacra, Erigeron, Felicia, Grangea, Kippistia, Lagenifera, Minuria, Oritrophium,
Peripleura, Podocoma, Remya, Solidago, Tetramolopium and Vittadinia. The remaining four groups and three individual species lie within a sister clade that also includes Celmisia, Chiliotrichum, Damnamenia, Pleurophyllum and Pachystegia. Relationships within each primary clade are poorly resolved. There is some congruence between this molecular estimate of
the phylogeny and the distribution of types of abaxial leaf-hair, which is the basis of the present sectional classification
of Olearia, but all states appear to have arisen more than once within the tribe. It is concluded that those species placed within the
second primary clade should be removed from the genus, but the extent to which species placed within the first primary clade
constitute a monophyletic group can only be resolved with further sequence data.
Received November 12, 2001; accepted April 29, 2002 Published online: November 22, 2002
Addresses of authors: Edward W. Cross, Centre for Plant Biodiversity Research, CSIRO, GPO Box 1600, Canberra, ACT 2601, Australia
(E-mail: ed.cross@csiro.au); Christopher J . Quinn, Royal Botanic Gardens, Mrs Macquaries Rd., Sydney, NSW 2000, Australia;
Steven J. Wagstaff, Landcare Research, PO Box 69, Lincoln 8152, New Zealand. 相似文献
6.
Occupancy is an important metric to understand current and future trends in populations that have declined globally. In addition, occupancy can be an efficient tool for conducting landscape-scale and long-term monitoring. A challenge for occupancy monitoring programs is to determine the appropriate spatial scale of analysis and to obtain precise occupancy estimates for elusive species. We used a multi-scale occupancy model to assess occupancy of Columbia spotted frogs in the Great Basin, USA, based on environmental DNA (eDNA) detections. We collected three replicate eDNA samples at 220 sites across the Great Basin. We estimated and modeled ecological factors that described watershed and site occupancy at multiple spatial scales simultaneously while accounting for imperfect detection. Additionally, we conducted visual and dipnet surveys at all sites and used our paired detections to estimate the probability of a false positive detection for our eDNA sampling. We applied the estimated false positive rate to our multi-scale occupancy dataset and assessed changes in model selection. We had higher naïve occupancy estimates for eDNA (0.37) than for traditional survey methods (0.20). We estimated our false positive detection rate per qPCR replicate at 0.023 (95% CI: 0.016–0.033). When the false positive rate was applied to the multi-scale dataset, we did not observe substantial changes in model selection or parameter estimates. Conservation and resource managers have an increasing need to understand species occupancy in highly variable landscapes where the spatial distribution of habitat changes significantly over time due to climate change and human impact. A multi-scale occupancy approach can be used to obtain regional occupancy estimates that can account for spatially dynamic differences in availability over time, especially when assessing potential declines. Additionally, this study demonstrates how eDNA can be used as an effective tool for improved occupancy estimates across broad geographic scales for long-term monitoring. 相似文献
7.
Michael L. Roderick Ian R. Noble Shane W. Cridland 《Global Ecology and Biogeography》1999,8(6):501-508
In this paper we test a method to estimate the tree and grass vegetation cover over Australia from satellite-derived normalized difference vegetation index (NDVI) time series (monthly 1981–91, ≈5 km pixels) observations. The evergreen cover is assumed to track along the base of the NDVI time series, which is assumed to be equivalent to the woody vegetation cover. The base of the NDVI time series is estimated using modifications to a classical econometric model (i.e. time series is the sum of trend, seasonal and random components). Estimates of the average evergreen component during 1982–85 and 1986–89 were generally consistent with known vegetation distributions. Changes in evergreen cover were largely restricted to the south-west and south-east of Australia. Those changes were largely the result of differences in rainfall between the two periods. The proposed method for estimating woody vegetation cover is found to be generally robust. However, there are some regions where the grass (or pasture) is mostly evergreen. Some possible refinements are proposed to handle such cases. 相似文献
8.
John A. H. Benzie 《Hydrobiologia》1987,145(1):51-65
The AustralianDaphnia (D. occidentalis, D. jollyi, D. lumholtzi, D. carinata, D. nivalis, andD. cephalata) include representatives from three distinct groups within the genus. The worldwide distribution of species within these three
groups is consistent with a Gondwanan or pre-Gondwanan origin for each group. These data suggest an even more ancient origin
for the genusDaphnia.
The finding thatD. cephalata must have been separated fromD. carinata since Gondwanan times is consistent with recent biochemical data on the phylogenetic relations of AustralianDaphnia, but contrasts with electrophoretic evidence of continuing hybridization between these two taxa. It is suggested that continued
gene exchange between otherwise discrete species, or clonal complexes, ofDaphnia may be maintained for millions of years, partly as a result of the varying degrees of cyclical parthenogenesis, and partly
as a result of the highly fragmented population structures, found in these taxa. 相似文献
9.
The macro-invertebrate communities of temporary pools in an intermittent stream in tropical Queensland 总被引:2,自引:1,他引:1
Nine pools were studied in an intermittent stream. They were close to each other but differed in size, substratum, amount of shade and duration of water presence. Initial conditions were set by wet season flooding, following which each pool developed its own character. Cluster analysis showed that communities changed substantially with time in both species composition and abundance, and that some initially similar communities diverged while some initially dissimilar ones converged.Principal Components Analysis showed that these community changes were due largely to the drying of the pools, and to seasonal effects. Specialised drying communities developed in the pools of longer duration (up to 8 months), but not in the short-lived pools (3–4 months). Apparently similar numerical responses in different pools were often caused by different suites of predominant species.The diversity of the fauna (total of 78 species) was high in comparison with similar habitats in non-tropical regions.The pattern of development of the pools' communities was much as expected from island biogeography theory, except that there was no relationship between species richness and duration and size of pools. The species complements were largely opportunistic, being governed by extreme environmental disturbance. 相似文献
10.
A comparison of karyotypes ofBrachyscome breviscapis (2n = 8),B. lineariloba cytodemes E (2n = 10), B (2n = 12) and C (2n = 16) suggests that these species have a homoelogous basic set of four chromosome pairs, two large pairs and two small, and that theB. lineariloba cytodemes E, B and C are related toB. breviscapis by successive additions of small chromosomes. A pronounced asynchrony of chromosome condensation between these large and small chromosomes has been observed. In the artificial hybrids betweenB. dichromosomatica (2n = 4) ×B. breviscapis, and theB. lineariloba cytodemes, theB. dichromosomatica chromosomes are similar in size and condensation behaviour to the small chromosomes ofB. breviscapis and ofB. lineariloba cytodemes E, B and C. Meiotic pairing in these hybrids also demonstrates the strong affinities between these chromosomes. It is suggested thatB. breviscapis may be of amphidiploid origin between a species with two large early condensing chromosome pairs and another,B. dichromosomatica-like species with two small late condensing pairs. It seems most likely that the additional small and late condensing chromosomes inB. lineariloba cytodemes E, B and C are derived from theB. dichromosomatica-like parent, and that each addition increases vigour, fecundity and drought tolerance, allowing these cytodemes to colonize more open and arid environments. Transmission of the univalents in the quasidiploidB. lineariloba cytodeme E was verified as being via the pollen, and not via the embryo sacs.The cytology ofBrachyscome lineariloba (Compositae, Asteroidae), 10. 相似文献