全文获取类型
收费全文 | 11664篇 |
免费 | 1181篇 |
国内免费 | 1895篇 |
出版年
2024年 | 57篇 |
2023年 | 237篇 |
2022年 | 290篇 |
2021年 | 365篇 |
2020年 | 453篇 |
2019年 | 533篇 |
2018年 | 439篇 |
2017年 | 496篇 |
2016年 | 512篇 |
2015年 | 441篇 |
2014年 | 523篇 |
2013年 | 777篇 |
2012年 | 529篇 |
2011年 | 507篇 |
2010年 | 394篇 |
2009年 | 529篇 |
2008年 | 535篇 |
2007年 | 594篇 |
2006年 | 544篇 |
2005年 | 490篇 |
2004年 | 417篇 |
2003年 | 437篇 |
2002年 | 391篇 |
2001年 | 319篇 |
2000年 | 298篇 |
1999年 | 298篇 |
1998年 | 235篇 |
1997年 | 203篇 |
1996年 | 258篇 |
1995年 | 222篇 |
1994年 | 216篇 |
1993年 | 206篇 |
1992年 | 160篇 |
1991年 | 182篇 |
1990年 | 140篇 |
1989年 | 135篇 |
1988年 | 120篇 |
1987年 | 124篇 |
1986年 | 120篇 |
1985年 | 127篇 |
1984年 | 141篇 |
1983年 | 87篇 |
1982年 | 120篇 |
1981年 | 74篇 |
1980年 | 97篇 |
1979年 | 79篇 |
1978年 | 56篇 |
1977年 | 54篇 |
1976年 | 43篇 |
1974年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
MARK S. LENARZ JOHN FIEBERG MICHAEL W. SCHRAGE ANDREW J. EDWARDS 《The Journal of wildlife management》2010,74(5):1013-1023
ABSTRACT North temperate species on the southern edge of their distribution are especially at risk to climate-induced changes. One such species is the moose (Alces alces), whose continental United States distribution is restricted to northern states or northern portions of the Rocky Mountain cordillera. We used a series of matrix models to evaluate the demographic implications of estimated survival and reproduction schedules for a moose population in northeastern Minnesota, USA, between 2002 and 2008. We used data from a telemetry study to calculate adult survival rates and estimated calf survival and fertility of adult females by using results of helicopter surveys. Estimated age- and year-specific survival rates showed a sinusoidal temporal pattern during our study and were lower for younger and old-aged animals. Estimates of annual adult survival (when assumed to be constant for ages >1.7 yr old) ranged from 0.74 to 0.85. Annual calf survival averaged 0.40, and the annual ratio of calves born to radiocollared females averaged 0.78. Point estimates for the finite rate of increase (λ) from yearly matrices ranged from 0.67 to 0.98 during our 6-year study, indicative of a long-term declining population. Assuming each matrix to be equally likely to occur in the future, we estimated a long-term stochastic growth rate of 0.85. Even if heat stress is not responsible for current levels of survival, continuation of this growth rate will ultimately result in a northward shift of the southern edge of moose distribution. Population growth rate, and its uncertainty, was most sensitive to changes in estimated adult survival rates. The relative importance of adult survival to population viability has important implications for harvest of large herbivores and the collection of information on wildlife fertility. 相似文献
952.
JERRY W. HUPP JOHN I. HODGES JR. BRUCE P. CONANT BRANDT W. MEIXELL DEBBIE J. GROVES 《The Journal of wildlife management》2010,74(2):274-284
ABSTRACT Management of Pacific Flyway Canada geese (Branta canadensis) requires information on winter distribution of different populations. Recoveries of tarsus bands from Vancouver Canada geese (B. canadensis fulva) marked in southeast Alaska, USA, ≥4 decades ago suggested that ≥83% of the population was non-migratory and that annual adult survival was high (Ŝ = 0.836). However, recovery distribution of tarsus bands was potentially biased due to geographic differences in harvest intensity in the Pacific Flyway. Also, winter distribution of Vancouver Canada geese could have shifted since the 1960s, as has occurred for some other populations of Canada geese. Because winter distribution and annual survival of this population had not recently been evaluated, we surgically implanted very high frequency radiotransmitters in 166 adult female Canada geese in southeast Alaska. We captured Vancouver Canada geese during molt at 2 sites where adults with goslings were present (breeding areas) and 2 sites where we observed nonbreeding birds only. During winter radiotracking flights in southeast Alaska, we detected 98% of 85 females marked at breeding areas and 83% of 70 females marked at nonbreeding sites, excluding 11 females that died prior to the onset of winter radiotracking. We detected no radiomarked females in coastal British Columbia, or western Washington and Oregon, USA. Most (70%) females moved ≤30 km between November and March. Our model-averaged estimate of annual survival (Ŝ = 0.844, SE = 0.050) was similar to the estimate of annual survival of geese marked from 1956 to 1960. Likely <2% of Vancouver Canada geese that nest in southeast Alaska migrate to winter areas in Oregon or Washington where they could intermix with Canada geese from other populations in the Pacific Flyway. Because annual survival of adult Vancouver Canada geese was high and showed evidence of long-term consistency, managers should examine how reproductive success and recruitment may affect the population. 相似文献
953.
Dorn Watthanakulpanich Jitra Waikagul Wanna Maipanich Supaporn Nuamtanong Surapol Sanguankiat Somchit Pubampen Rangson Praevanit Srisuchat Mongkhonmu Yukifumi Nawa 《The Korean journal of parasitology》2010,48(3):225-229
The aim of this study is to clarify the clinical features of Haplorchis taichui infection in humans in Nan Province, Thailand, and to correlate the clinical features with irritable bowel syndrome (IBS)-like symptoms. In this study area, only H. taichui, but neither other minute intestinal flukes nor small liver flukes were endemic. The degree of infection was determined by fecal egg counts and also by collecting adult worms after deworming. The signs and symptoms of individual patients together with their hematological and biochemical laboratory data were gathered to evaluate the relationship between the clinical features and the severity of infection. Special emphasis was made to elucidate the possible similarities of the clinical features of H. taichui infection and IBS-like symptoms. The results showed useful clinical information and the significant (> 50%) proportion of haplorchiasis patients complained of abdominal pain, lassitude, and flatulence, which were the important diagnostic symptoms of IBS. This study has reported a possible link between H. taichui and IBS, and H. taichui might probably play a role in the etiology of these IBS-like symptoms. 相似文献
954.
JAN CHRISTIAN HABEL DENNIS RÖDDER SCALERCIO STEFANO MARC MEYER THOMAS SCHMITT 《Biological journal of the Linnean Society. Linnean Society of London》2010,99(4):818-830
The sea acts as an effective dispersal barrier for most terrestrial animal species. Narrow sea straits, therefore, often represent areas where species are able to disperse from one land mass to another. In the Mediterranean Sea, the narrowest connecting points between North Africa and Europe are the Strait of Gibraltar and the Strait of Sicily. In the past, climatic oscillations caused changing sea levels and thus influenced the permeability of these sea straits. We analysed the genetic structure of four butterfly species that all occur on both sides of the Strait of Sicily. In all four species, we observed a lack of genetic differentiation between the populations of North Africa and those of Italy. Species distribution models support the strong cohesiveness in that they show a largely continuous glacial distribution over Italy and North Africa. The data obtained reveal that there was a large exchange of individuals between Italy and the eastern Maghreb during the last ice age. This might not only be the case for the species under investigation in the present study, but also might represent a more general pattern for mobile thermophilic western Palearctic species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 818–830. 相似文献
955.
JEONG EUN HAN KOOK‐HYUN CHUNG TOMOYUKI NEMOTO BYOUNG‐HEE CHOI 《Botanical journal of the Linnean Society. Linnean Society of London》2010,164(3):221-235
Lespedeza (tribe Desmodieae, Fabaceae) follows a disjunct distribution in eastern Asia and eastern North America. Phylogenetic relationships among its species and related taxa were inferred from nuclear ribosomal internal transcribed spacer (ITS) and plastid sequences (trnH‐psbA, psbK‐psbI, trnK‐matK and rpoC1). We examined 35 species of Lespedeza, two of Kummerowia and one of Campylotropis, the sole constituents of the Lespedeza group. An analysis of these data revealed that the genus Campylotropis is sister to the other two genera. However, we were unable to resolve the relationships between Kummerowia and Lespedeza in the strict consensus trees of parsimony analyses based on plastid and combined DNA data. In the genus Lespedeza, the Old World subgenus Macrolespedeza is monophyletic, whereas the transcontinental subgenus Lespedeza is paraphyletic. Monophyly of eastern Asian species and of North American species is strongly supported. Although inconsistent with the traditional classification, this phylogenetic finding is consistent with seedling morphology. Three subgroups recognized in subgenus Macrolespedeza were unresolved in our phylogenetic trees. An incongruence length difference (ILD) test indicated that the two partitions (nuclear ITS and plastid sequences) were significantly incongruent, perhaps because of hybridization between species in Lespedeza. Most of the primary clades of tribe Desmodieae are Asian, implying that the relatively few New World ones, such as those in Lespedeza, are more recently derived from Asia. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 221–235. 相似文献
956.
This paper presents the concentration distribution around a growing nitrogen gas bubble in the blood and other tissues of divers who surface too quickly, when the ambient pressure through the decompression process is variable and constant. This effort is a modification of Sirinivasan et al. model (1999) [9]. The mathematical model is solved analytically to find the growth rate of a gas bubble in a tissue after decompression in the ambient pressure. Moreover, the concentration distribution around the growing bubble is introduced. The growth process is affected by ascent rate , tissue diffusivity DT, initial concentration difference ΔC0, surface tension σ and void fraction ?0. 相似文献
957.
A synthetic progestin Nestorone® is being developed for female-contraception. This study was conducted to determine the distribution, metabolism, and excretion of tritium-labeled Nestorone (3H Nestorone) in adult female rats. Rats were injected subcutaneously (S.C.) with a single dose of 400 μCi 3H Nestorone/kg BW. Its distribution and concentrations in blood, plasma and other tissues were determined at defined times. The excreta were examined for elimination of 3H Nestorone. Radioactivity in all samples was analyzed by liquid scintillation counter. Metabolite profiling was performed by HPLC and LC/MS analysis of the plasma, urine, and feces samples. Following subcutaneous injection of 3H Nestorone, the mean peak concentrations of radioactivity (Cmax) in the blood and plasma were 58.1 and 95.5 ng equiv. 3H Nestorone/g, respectively, at 2-h postdose (Tmax). Thereafter, the concentration of drug steadily declined through 96-h postdose with a terminal elimination half-life (t1/2) of 15.6 h. 3H Nestorone-derived radioactivity was widely distributed in most tissues by 0.5 h and attained a mean maximal concentration by 2-h postdose. Approximately, 81.4% and 7.62% of the administered dose was excreted via feces and urine, respectively. In vivo metabolism of 3H Nestorone resulted into a total of 19 metabolites. Among them, two metabolites viz., 17α-deacetyl-Nestorone (M9) and 4,5-dihydro-17α-deacetyl-Nestorone (M19) were identified by HPLC and LC/MS analysis. Metabolite profiling of plasma samples showed that most of the circulating radioactivity was associated with unchanged parent drug, and M19. The M19 was a major metabolite in the profiled urine and feces samples. Presence of large proportion of drug/drug-related material in feces suggested that the biliary excretion is a main elimination route of 3H Nestorone. The distribution, metabolism, and excretion profiles of 3H Nestorone obtained in this study provide a fairly good insight about its fate in women. 相似文献
958.
Berit Oestergaard Christoffersen Laust Peter Gade Ove Svendsen Kirsten Raun 《Steroids》2010,75(10):676-684
Low testosterone and estradiol concentrations are predictive for the development of the metabolic syndrome in men and women, respectively. The aim of this study was to investigate the influence of sex hormone deficiency on food intake, body weight, body composition and glucose metabolism in male Göttingen minipigs.Five adult male Göttingen minipigs were studied before castration (pre-cast), 10-18 days (post-cast 1) and 10-11 weeks (post-cast 2) after castration. Parameters of interest were food intake, body weight, body fat percentage and sex hormone concentrations. Furthermore glucose tolerance, glucagon suppression, insulin resistance, beta cell function and disposition index were evaluated by oral and intravenous glucose tolerance tests.Castration led to almost complete disappearance of circulating testosterone and estradiol and secondarily to increased food intake, body weight and body fat percentage. Ten-eighteen days sex hormone deficiency (post-cast 1) did not significantly change any of the investigated metabolic parameters compared to pre-cast levels. Ten weeks after castration (post-cast 2) significant insulin resistance, glucose intolerance and hyperglucagonemia was found, and the beta cell function and the disposition index both were decreased.In conclusion, castration-induced sex hormone deficiency in male Göttingen minipigs results in hyperphagia, obesity and disturbed glucose metabolism, which are some of the features typical for the human metabolic syndrome. 相似文献
959.
A Surowiec 《Journal of biochemical and biophysical methods》1981,4(2):91-100
A method is described for the molecular weight distribution of DNA which is determined from sedimentation-velocity analysis. Knowing the distribution of sedimentation coefficients for a single DNA concentration it is possible to extrapolate such a distribution to infinite dilution of the solute in a simple way. Two versions (using two or three terms of a series) of extrapolating equations are considered and discussed in detail. The sedimentation coefficients distribution calculated from these equations differs only insignificantly with that obtained in a conventional way. 相似文献
960.
为探讨中国腹枝衣属地衣的物种多样性,进一步明确其分布特征与种类组成,该研究通过野外调查及采集地衣标本,结合形态、解剖、化学等方法,对128份采自中国热带及亚热带地区多个省份的腹枝衣属(Herpothallon)地衣标本进行了分类鉴定,共鉴定出腹枝衣属地衣12种,其中南方腹枝衣 [H. australasicum (Elix)Elix & G. Thor]、颗粒腹枝衣(H. granulosum Jagadeesh Ram & G. P. Sinha)、喜马拉雅腹枝衣(H. himalayanum Jagadeesh & G. P. Sinha)、裂芽腹枝衣(H. isidiatum Jagadeesh Ram & G. P. Sinha)和小腹枝衣(H. minutum Jagadeesh)为中国新记录种。并且对该属所有已知(已报道和本次鉴定)种类进行综合分析。结果表明:(1)中国已知腹枝衣属地衣14种,占世界已报道种类的29.17%。(2)地理成分有5种类型,即泛热带分布、热带亚洲至热带澳大利亚分布、热带亚洲和热带美洲间断分布、热带亚洲分布和中国特有分布。(3)中国腹枝衣属地衣主要分布在海拔300~2 500 m的范围内。(4)生长基物多为树皮,叶生、石生和藓生的物种较少。该研究结果表明,中国南方腹枝衣属地衣的物种多样性较高,这对明确中国该属地衣物种组成以及地衣多样性保护具有重要意义。 相似文献